Micromachines doi: 10.3390/mi16040439

Authors: Kai Takeuchi Eiji Higurashi

Effective thermal management is a critical challenge in achieving high-power output for semiconductor laser devices. A key factor in laser device packaging is the bonding between the laser device on a GaAs substrate and a heat spreader, typically composed of high thermal conductivity materials such as SiC. Conventional soldering methods introduce thick bonding layers with relatively low thermal conductivity, resulting in high thermal resistance at the interface. In this study, we demonstrate the room temperature bonding of GaAs and SiC via a 30 nm thick Au layer, eliminating the need for a thermal reaction bonding layer or vacuum process. Using surface-activated bonding (SAB), GaAs and SiC were successfully bonded, with a strength comparable to bulk fracture. A uniform and ultrathin Au bonding interface significantly reduces thermal resistance compared to conventional soldering methods. These results highlight the potential of SAB with thin Au films as a promising approach for improving thermal management in high-power semiconductor laser devices.

Micromachines doi: 10.3390/mi16040438

Authors: Siyuan Chen Caoyuan Wang Cong Xiong Yu Qin Jie Zhu Yichun Shen Limin Xiao

The liquid-core anti-resonant fiber (LCARF) has emerged as a versatile platform for applications in nonlinear photonics, biological sensing, and other domains. In this study, a systematic and comprehensive analysis of LCARF was conducted via the finite element method to evaluate its performance across a wavelength range of 400–1200 nm. This included an assessment of the effects of structural parameters such as capillary wall thickness and the ratio of cladding tube diameter to core diameter on confinement loss and effective refractive index. The results reveal that the proposed core-only-filled approach significantly reduces the confinement loss compared to the conventional fully filled approach, thus facilitating signal transmission. Furthermore, the optimization of geometrical parameters greatly improves the single-mode characteristics of LCARFs. This work establishes a robust theoretical framework and provides valuable support for enhancing the LCARF applications in optofluidics, thereby contributing to the evolution of specialty fiber technologies.

Micromachines doi: 10.3390/mi16040437

Authors: Rodrigo del Prado Santamaría Mahmoud Dhimish Gisele Alves dos Reis Benatto Thøger Kari Peter B. Poulsen Sergiu V. Spataru

This review paper presents a comprehensive analysis of electroluminescence (EL) imaging techniques for photovoltaic (PV) module diagnostics, focusing on advancements from conventional indoor imaging to outdoor and daylight EL imaging. It examines key challenges, including ambient light interference and environmental variability, and highlights innovations such as infrared-sensitive indium gallium arsenide (InGaAs) cameras, optical filtering, and periodic current modulation to enhance defect detection. The review also explores the role of artificial intelligence (AI)-driven methodologies, including deep learning and generative adversarial networks (GANs), in automating defect classification and performance assessment. Additionally, the emergence of drone-based EL imaging has facilitated large-scale PV inspections with improved efficiency. By synthesizing recent advancements, this paper underscores the critical role of EL imaging in ensuring PV module reliability, optimizing performance, and supporting the long-term sustainability of solar energy systems.

Micromachines doi: 10.3390/mi16040436

Authors: Shaqin Wang Yunhao Feng Liangming Duan Yueming Shang Huaihang Fan Ji Liu Jiahao Han Xiaoqi Wang Bin Yang

This study presents a structurally tunable Au-based solid polymer electrolyte (SPE) membrane electrode with significantly enhanced performance in organic hydrogenation reactions. Compared to a Pt-based counterpart, the Au-based electrode achieved a 277% increase in cyclohexane yield and a 4.8% reduction in hydrogen evolution during cyclohexene hydrogenation, demonstrating superior catalytic selectivity and energy efficiency. The improved performance is attributed to synergistic optimization of the electrode’s nanostructure and electronic properties. The Au-based electrode exhibited a 215% increase in specific surface area (SSA) relative to its initial state, along with a markedly enhanced electrochemical active surface area (ECSA). These enhancements stem from its mesoporous architecture, lattice contraction, and high density of zero-dimensional defects. X-ray photoelectron spectroscopy (XPS) revealed a negative shift in Au4f binding energy, a positive shift in Ni0 peaks, and an increased concentration of oxygen vacancies (Ov), indicating favorable modulation of the surface electronic structure. This reconstruction promotes H* adsorption and accelerates the hydrogenation reaction, serving as a key mechanism for catalytic enhancement. The core innovation of this work lies in the coordinated engineering of nanoscale structure and surface electronic states, enabling concurrent improvements in reaction rate, selectivity, and energy efficiency. These findings offer valuable guidance for designing noble metal-based membrane electrodes in advanced hydrogen energy conversion and storage systems.

Micromachines doi: 10.3390/mi16040435

Authors: Lexi L. C. Simpkins Tunglin Tsai Emmanuel Egun Tayloria N. G. Adams

Human mesenchymal stem cells (hMSCs) are widely used in regenerative medicine, but large-scale in vitro expansion alters their function, impacting proliferation and differentiation potential. Currently, a predictive marker to assess these changes is lacking. Here, we used dielectrophoresis (DEP) to characterize the electrical phenotype of hMSCs derived from bone marrow (BM), adipose tissue (AT), and umbilical cord (UC) as they aged in vitro from passage 4 (P4) to passage 9 (P9). The electrical phenotype was defined by the DEP spectra, membrane capacitance, and cytoplasm conductivity. Cell morphology and size, growth characteristics, adipogenic differentiation potential, and osteogenic differentiation potential were assessed alongside label-free biomarker membrane capacitance and cytoplasm conductivity. Differentiation was confirmed by histological staining and RT-qPCR. All hMSCs exhibited typical morphology, though cell size varied, with UC-hMSCs displaying the largest variability across all size metrics. Growth analysis revealed that UC-hMSCs proliferated the fastest. The electrical phenotype varied with cell source and in vitro age, with high passage hMSCs showing noticeable shifts in DEP spectra, membrane capacitance, and cytoplasm conductivity. Correlation analysis revealed that population doubling level (PDL) correlated with membrane capacitance and cytoplasm conductivity, indicating PDL as a more precise marker of in vitro aging than passage number. Additionally, we demonstrate that membrane capacitance correlates with the osteogenic marker COL1A1 and that cytoplasm conductivity correlates with the adipogenic markers ADIPOQ and FABP4, suggesting that DEP-derived electrical properties serve as label-free biomarkers of differentiation potential. While DEP has previously been applied to BM-hMSCs and AT-hMSCs, and more recently to UC-hMSCs, few studies have provided a direct comparison across all three sources or tracked changes across continuous expansion. These findings underscore the utility of DEP as a label-free approach for assessing hMSC aging and function, offering practical applications for optimizing stem cell expansion and stem cell banking in clinical settings.

Micromachines doi: 10.3390/mi16040434

Authors: Yanru Ren Min Zhu Xuehui Dai Longxian Li Minghui Liu

This article reviews the properties and formation process of interface traps in MOS and linear bipolar devices. Transistors are the core components of modern electronic devices, and their performance and reliability directly affect the performance of the entire system. In radiation environments, the emergence and evolution of interface traps severely impacts the functionality of transistors, being a significant factor in device failure. However, our understanding of the properties and formation processes of interface traps is still limited. Therefore, research on interface traps is of great theoretical and practical significance. This paper focuses on studying the radiation response patterns of transistor interface traps. By reviewing relevant literature and research findings from both domestic and international sources, this review provides a detailed overview of the current state of research on the transformation of interface traps and the annealing processes that occur during the irradiation of microelectronic devices. Finally, based on this foundation, this paper discusses the current state of simulation research methods for interface traps. Through an in-depth exploration of the formation mechanisms of interface traps and their role in transistor performance, this study aims to provide guidance for device design, radiation hardening, and reliability assessment, and ensure the reliability and stability of devices in radiation environments.

Micromachines doi: 10.3390/mi16040433

Authors: Haoyi Zhao Jun Liu Tao Rong Shiyue Fan Zhanfei Chen Junchao Wang

This paper focuses on the modeling challenges of a multi-cell heterojunction bipolar transistor (HBT) used in radio frequency (RF) power amplifiers and proposes an innovative linear small-signal modeling method. Based on devices with an emitter size of 3 μm × 40 μm × 2–6 (emitter width × emitter length × emitter index-cell number), an equivalent circuit model including peripheral parasitic parameters is constructed by analyzing device layout characteristics in response to additional parasitic effects introduced by the multi-cell structure. A step-by-step parameter extraction method is used, with particular attention paid to the correction of saturated current parameters, temperature coefficients, thermal resistance correction, and the optimization of junction capacitance parameters based on the capacitance ratio relationship. After the extraction of parasitic parameters, the input and output reflection coefficient errors of the model under zero-bias conditions are below 1.66% in the 0.7–25 GHz frequency band. The accuracy of this model is significantly improved compared to the directly parallel single-cell model. The power simulation results match the measured results very well at frequencies of 2.6 GHz and 3.5 GHz. This modeling method significantly improves the model accuracy of multi-cell HBT devices in RF circuit design and provides an effective tool for high-power amplifier optimization.

Micromachines doi: 10.3390/mi16040431

Authors: Guoliang Chen Guiqi Wang Zhenzhen Wang Lijun Wang

With the growing demand for high-performance computing (HPC), artificial intelligence (AI), and data communication and storage, new chip technologies have emerged, following Moore’s Law, over the past few decades. As we enter the post-Moore era, transistor dimensions are approaching their physical limits. Advanced packaging technologies, such as 3D chiplets hetero-integration and co-packaged optics (CPO), have become crucial for further improving system performance. Currently, most solutions rely on silicon-based technologies, which alleviate some challenges but still face issues such as warpage, bumps’ reliability, through-silicon vias’ (TSVs) and redistribution layers’ (RDLs) reliability, and thermal dissipation, etc. Glass, with its superior mechanical, thermal, electrical, and optical properties, is emerging as a promising material to address these challenges, particularly with the development of femtosecond laser technology. This paper discusses the evolution of both conventional and advanced packaging technologies and outlines future directions for design, fabrication, and packaging using glass substrates and femtosecond laser processing.

Micromachines doi: 10.3390/mi16040432

Authors: Shengsen Yang Zihan Xu Kun Ren

This paper proposes an improved parameter extraction optimization algorithm for radio frequency (RF) devices. The algorithm integrates parameter classification and correction, gradient-based performance handling, bias-aware updates, and group-based optimization strategies, achieving enhanced optimization accuracy, accelerated convergence, and improved stability. It effectively addresses the limitations of deterministic algorithms in RF device parameter extraction optimization, such as low efficiency, sensitivity to initial values, and unstable convergence. To validate the algorithm’s effectiveness, a Ka-band filter performance curve fitting case study was conducted. By comparing simulated curves with optimized fitted curves, the advantages of the algorithm in terms of optimization efficiency, accuracy, and convergence stability were demonstrated. Experimental results show that, compared to traditional optimization algorithms, the proposed method significantly improves curve fitting accuracy, computational efficiency, and stability, highlighting its application value in RF device parameter extraction.

Micromachines doi: 10.3390/mi16040430

Authors: Yue Cao Bin Wang Zhehang Li Jiajia Wang Yinan Xiao Qingyang Zeng Xinfeng Wang Wenwu Zhang Qunli Zhang Liyuan Sheng

SiCf/SiC ceramic matrix composite (CMC), a hard and brittle material, faces significant challenges in efficient and high-quality processing of small-sized shapes. To address these challenges, the nanosecond laser was used to process micro-holes in the SiCf/SiC CMC using a two-step drilling method, including laser pre-drilling in air and laser final-drilling with a water jet. The results of the single-parameter variation and optimized orthogonal experiments reveal that the optimal parameters for laser pre-drilling in air to process micro-holes are as follows: 1000 processing cycles, 0.7 mJ single-pulse energy, −4 mm defocus, 15 kHz pulse-repetition frequency, and 85% overlap rate. With these settings, a micro-hole with an entrance diameter of 343 μm and a taper angle of 1.19° can be processed in 100 s, demonstrating high processing efficiency. However, the entrance region exhibits spattering slags with oxidation, while the sidewall is covered by the recast layer with a wrinkled morphology and attached oxides. These effects are primarily attributed to the presence of oxygen, which enhances processing efficiency but promotes oxidation. For the laser final-drilling with a water jet, the balanced parameters for micro-hole processing are as follows: 2000 processing cycles, 0.6 mJ single-pulse energy, −4 mm defocus, 10 kHz pulse-repetition frequency, 85% overlap rate, and a 4.03 m/s water jet velocity. Using these parameters, the pre-drilled micro-hole can be finally processed in 96 s, yielding an entrance diameter of 423 μm and a taper angle of 0.36°. Due to the effective elimination of spattering slags and oxides by the water jet, the final micro-hole exhibits a clean sidewall with microgrooves, indicating high-quality micro-hole processing. The sidewall morphology could be ascribed to the different physical properties of SiC fiber and matrix, with steam explosion and cavitation erosion. This two-step laser drilling may provide new insights into the high-quality and efficient processing of SiCf/SiC CMC with small-sized holes.

Micromachines doi: 10.3390/mi16040429

Authors: Kuo Yao Kai Guo Heran Wang Xiongfei Zheng

Scaffolds play a crucial role in tissue engineering as regenerative templates. Fabricating scaffolds with good biocompatibility and appropriate mechanical properties remains a major challenge in this field. This study proposes a method for preparing multi-material scaffolds, enabling the 3D printing of collagen and thermoplastic elastomers at room temperature. Addressing the previous challenges such as the poor printability of pure collagen and the difficulty of maintaining structural integrity during multilayer printing, this research improved the printability of collagen by optimizing its concentration and pH value and completed the large-span printing of thermoplastic elastomer using a precise temperature-control system. The developed hybrid scaffold has an interconnected porous structure, which can support the adhesion and proliferation of fibroblasts. The scaffolds were further treated with different post-treatment methods, and it was proven that the neutralized and cross-linked collagen scaffold, which has both nano-fibers and a certain rigidity, can better support the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). The research results show that the collagen thermoplastic elastomer hybrid scaffold has significant clinical application potential in soft tissue and hard tissue regeneration, providing a versatile solution to meet the diverse needs of tissue engineering.

Micromachines doi: 10.3390/mi16040428

Authors: Wei Yu Faxing Che Vance Liu Raymond Chen Sam Ireland Yeow Chon Ong Hong Wan Ng Gokul Kumar

The high input/output demands of memory packages require precise trace width and spacing, posing challenges for contemporary package design. Substrate copper trace cracks are a major reliability issue during temperature cycling tests (TCTs). This study offers a detailed analysis of copper trace crack mechanisms through experimental observations, material characterization, and numerical simulations. Common failure modes of trace cracks are identified from experimental data, pinpointing initiation sites and propagation paths. Young’s modulus of copper foil samples is assessed using four testing methods, revealing consistent trends across samples from different substrate suppliers. Sample A with higher E/H values tested via nanoindentation correlated with lower failure rates in the experiment. Stress–strain testing on copper foil was successfully performed at the lower TCT temperature limit of −65 °C, providing vital input for finite element (FE) models. The simulations show strong alignment with trace crack locations under different failure modes. The impact of copper trace width and material properties is illustrated in numerical models by comparing variations in plastic strain responses, which show differences of up to 40% and 30%, respectively. The simulation design of the experiments (DOE) indicates that high-strength solder resist (SR) can significantly enhance temperature cycling performance by reducing SR and copper trace stress and strain by up to 75%. The accumulation of plastic strain in copper traces is predicted to increase up to four times when SR breaks at the crack location, underscoring the importance of SR in copper trace reliability.

Micromachines doi: 10.3390/mi16040427

Authors: Debottam Datta Ali Eskandari Junaid Syed Himanshu Rai Nitya Nand Gosvami Ting Y. Tsui

Tantalum metal and tantalum oxide thin films are commonly used in semiconductor devices, protective coatings, and biomedical implants. However, there is limited information on their nanotribological behavior and small-scale mechanical properties. This study characterized the chemical, mechanical, and tribological properties of as-deposited and 400 °C annealed β-Ta thin films using nanoindentation and atomic force microscope (AFM)-based nanoscale friction and wear tests. X-ray photoelectron spectroscopy (XPS) results revealed that a thermally grown Ta oxide layer forms on the surface of Ta film after being annealed at 400 °C. The nanoindentation data indicated an increase in both the hardness and elastic modulus in the heat-treated sample compared to the as-deposited Ta film (13.1 ± 1.3 GPa vs. 12.0 ± 1.4 GPa for hardness) and (213.1 ± 12.7 GPa vs. 175.2 ± 12.3 GPa for elastic modulus). Our nanotribological results show that the friction increased and wear resistance decreased on the surface of the annealed sample compared to the as-deposited Ta film. This discrepancy may be caused by the oxidation of Ta on the film surface, which induces residual compressive stresses in the film and degrades its wear resistance. Our results highlight the influence of thermal annealing and oxidation on nanotribological behavior and small-scale mechanical properties of Ta thin films.

Micromachines doi: 10.3390/mi16040426

Authors: Yueqiu Sun Nianzuo Yu Junhu Zhang Bai Yang

The development of micro- and nano-fabrication technologies has greatly advanced single-cell and spatial omics technologies. With the advantages of integration and compartmentalization, microfluidic chips are capable of generating high-throughput parallel reaction systems for single-cell screening and analysis. As omics technologies improve, microfluidic chips can now integrate promising transcriptomics technologies, providing new insights from molecular characterization for tissue gene expression profiles and further revealing the static and even dynamic processes of tissues in homeostasis and disease. Here, we survey the current landscape of microfluidic methods in the field of single-cell and spatial multi-omics, as well as assessing their relative advantages and limitations. We highlight how microfluidics has been adapted and improved to provide new insights into multi-omics over the past decade. Last, we emphasize the contributions of microfluidic-based omics methods in development, neuroscience, and disease mechanisms, as well as further revealing some perspectives for technological advances in translational and clinical medicine.

Micromachines doi: 10.3390/mi16040425

Authors: Oluwaseyi O. Ayeni Holly A. Stretz Ahmad Vasel-Be-Hagh

Fiber extractors, as process-intensified equipment, facilitate many applications, such as the purification of oils. The development of high-fidelity computational models is crucial to optimize the design. However, simulating microscale flows around tens of thousands of microfiber arrays is computationally unfeasible. Thus, it is necessary to identify smaller elements, consisting of only a few fibers, that can represent flow within massively arrayed fiber extractors. This study employed computational fluid dynamics to investigate different configurations of four-fiber elements to achieve this aim. Following previous modeling featuring flow around only one fiber, the goal was to understand how variations in inter-fiber distances affect the phase structures of a corn oil/water mixture, the steady-state interfacial surface area per unit of fluid volume, and the pressure drop along the flow direction. The study explored various total and relative flow rates and contact angles. The research characterized the flow as semi-restricted annular, noting the influence of neighboring fibers on phase complexity. The inter-fiber distance played a crucial role in generating high interfacial areas and reducing pressure. The chaotic nature of the slug interfaces facilitated intermixing between flows along different fibers. Interestingly, the specific interfacial area reached an optimum when the inter-fiber distance was between 10 and 50 μm.

Micromachines doi: 10.3390/mi16040424

Authors: Dominik Kowal Yuntian Chen Muhammad Danang Birowosuto

Recent advancements in metal/perovskite photodetectors have leveraged plasmonic effects to enhance the efficiency of photogenerated carrier separation. In this work, we present an innovative approach to designing heterostructure photodetectors that involved integrating a perovskite film with a plasmonic metasurface. Using finite-difference time-domain (FDTD) simulations, we investigated the formation of hybrid photonic–plasmonic modes and examined their quality factors in relation to loss mechanisms. Our results demonstrate that these hybrid modes facilitated strong light confinement within the perovskite layer, with significant intensity enhancement at the metal–perovskite interface—an ideal condition for efficient charge carrier generation. We also propose the use of low-bandgap perovskites for direct infrared passive detection and explore the potential of highly Stokes-shifted perovskites for active detection applications, including ultraviolet and X-ray radiation.

Micromachines doi: 10.3390/mi16040423

Authors: Joanna Smajdor Katarzyna Fendrych Anna Górska-Ratusznik

This review concentrates on the application of carbon-based materials in the development and fabrication of voltammetric sensors of antidepressant drugs used in the treatment of moderate to severe depression, anxiety disorders, personality disorders, and various phobias. Voltammetric techniques offer outstanding sensitivity and selectivity, accuracy, low detection limit, high reproducibility, instrumental simplicity, cost-effectiveness, and short time of direct determination of antidepressant drugs in pharmaceutical and clinical samples. Moreover, the combination of voltammetric approaches with the unique characteristics of carbon and its derivatives has led to the development of powerful electrochemical sensing tools for detecting antidepressant drugs, which are highly desirable in healthcare, environmental monitoring, and the pharmaceutical industry. In this review, carbon-based materials, such as glassy carbon and boron-doped diamond, and a wide spectrum of carbon nanoparticles, including graphene, graphene oxides, reduced graphene oxides, single-walled carbon nanotubes, and multi-walled carbon nanotubes were described in terms of the sensing performance of agomelatine, alprazolam, amitriptyline, aripiprazole, carbamazepine, citalopram, clomipramine, clozapine, clonazepam, desipramine, desvenlafaxine, doxepin, duloxetine, flunitrazepam, fluoxetine, fluvoxamine, imipramine, nifedipine, olanzapine, opipramol, paroxetine, quetiapine, serotonin, sertraline, sulpiride, thioridazine, trazodone, venlafaxine, and vortioxetine.

Micromachines doi: 10.3390/mi16040422

Authors: Marek Wojnicki Xuegeng Yang Piotr Zabinski Gerd Mutschke

This study presents both numerical and experimental analyses of enhanced mixing in a microflow system under the influence of a magnetic field. The research employed COMSOL Multiphysics for numerical simulations and Particle Image Velocimetry (PIV) for experimental validation. In the experimental microfluidic setup, permanent neodymium magnets were used to influence a laminar flow of water partially enriched with Ho(III) ions using the magnetic field. The findings confirmed that the strong interaction between Ho(III) ions and the magnetic field significantly affected the flow and may have resulted in vortex shedding downstream of the region with the highest magnetic field intensity. The numerical simulations demonstrated good agreement with the PIV experimental results. These findings suggest that it is possible to significantly enhance mixing in microflow systems without mechanical components, solely by exploiting the differences in the magnetic properties between the mixing substances. Traditionally, microreactors have been limited by mixing speeds governed by diffusion. These new results indicate the practical possibility of increasing mixing intensity in a cost-effective and safe manner.

Micromachines doi: 10.3390/mi16040421

Authors: Bowen Hou Dali Xu Fangfa Fu Bing Yang Na Niu

In advanced multicore embedded systems, network-on-chip (NoC) is vital for core communication. With a rise in the number of cores, the incidence of core failures rises, potentially affecting system performance and stability. To address the challenges associated with core failures in network-on-chip (NoC) systems, researchers have proposed numerous topology reconfiguration algorithms. However, these algorithms fail to achieve an optimal balance between topology reconfiguration rate and recovery time. Addressing these issues, we propose an adaptive core distribution optimization topology reconfiguration algorithm, which involves the distribution of faulty cores as the main factor for the reconfiguration procedure. This algorithm is based on a 2D REmesh structure to achieve physical topology reconfiguration, optimized through a bidirectional search algorithm, and features an adaptive algorithm for optimizing core distribution. Experimental results show that a 96.70% successful reconfiguration rate with the proposed algorithm can be guaranteed when faulty cores are less than 68.75% of the max faulty cores. In particular, when the faulty cores reach 8 in the 8 × 9 REmesh, the successful reconfiguration rate is 63.60% with the proposed algorithm, which is 14.80% higher than BTTR and 9.30% higher than BSTR. Additionally, the average recovery time of our algorithm is reduced by 98.60% compared with BTTR and by 15.87% compared with BSTR, significantly improving both the performance and reliability in embedded systems.

Micromachines doi: 10.3390/mi16040420

Authors: Yong Yang Yunyan Xie Jiahu Yuan Yuehua Cui Qiangeng Cheng Lianghui Shi

The BWR (Black–White–Red) electronic paper display has the advantage of low power consumption and offers a paper-like reading experience. However, refreshing images between black and red can easily produce ghosting images. In this article, a new driving waveform is proposed, in which classic black, white, and red particles are modeled as spheres, and the Com state is introduced as a renewal element because the motion of the sphere particles must ensure momentum conservation in the BWR EPD (Electrophoresis Display) during electronic field removal. Additionally, we adopted the concepts of gradual iteration and successive promotion in the new driving waveform based on the principles of electrophoretic particle displays and combined the momentum and inertia theorem with Stokes Law. A large number of experimental data confirmed that not only was the ghosting value optimized appreciably to below 0.5, but the actual ghosting performance has been significantly improved, especially for black and red images.

Micromachines doi: 10.3390/mi16040419

Authors: Nargish Parvin Sang Woo Joo Jae Hak Jung Tapas K. Mandal

The rapid evolution of micro- and nano-architectures is revolutionizing biomedical engineering, particularly in the fields of therapeutic and diagnostic micromechanics. This review explores the recent innovations in micro- and nanostructured materials and their transformative impact on healthcare applications, ranging from drug delivery and tissue engineering to biosensing and diagnostics. Key advances in fabrication techniques, such as lithography, 3D printing, and self-assembly, have enabled unprecedented control over material properties and functionalities at microscopic scales. These engineered architectures offer enhanced precision in targeting and controlled release in drug delivery, foster cellular interactions in tissue engineering, and improve sensitivity and specificity in diagnostic devices. We examine critical design parameters, including biocompatibility, mechanical resilience, and scalability, which influence their clinical efficacy and long-term stability. This review also highlights the translational potential and current limitations in bringing these materials from the laboratory research to practical applications. By providing a comprehensive overview of the current trends, challenges, and future perspectives, this article aims to inform and inspire further development in micro- and nano-architectures that hold promise for advancing personalized and precision medicine.

Micromachines doi: 10.3390/mi16040417

Authors: Mengtian Bao Ying Wang Jianqun Yang Xingji Li

In this work, the single-event burnout (SEB) effect and degradation behaviors induced by heavy-ion irradiation are investigated in a 120 V-rated transverse split-gate trench (TSGT) power metal-oxide-semiconductor field-effect transistor (MOSFET). Bismuth heavy-ions are used to conduct heavy-ion irradiation tests. The experimental results show that the SEB failure threshold voltage (VSEB) of the tested sample is 72 V, which only accounts for 52.6% of the actual breakdown voltage of the device. The VSEB value decreased with the increase in the flux. The simulation results show that the local “hot spot” formed after the incident heavy ion is an important reason for the drain current degradation of TSGT MOSFETs. To improve the single-event effect tolerance of TSGT MOSFETs, an SEB hardening method based on process optimization is proposed in this paper, which does not require additional customized epitaxial wafers. The simulation results show that, after SEB hardening, the VSEB is increased to 115 V, which accounts for 89.1% of the breakdown voltage.

Micromachines doi: 10.3390/mi16040418

Authors: Cunhua Dou Weijia Song Yu Yan Xuan Zhang Zhiyu Tang Xing Zhao Fanyu Liu Shujian Xue Huabin Sun Jing Wan Binhong Li Yun Wang Tianchun Ye Yong Xu Sorin Cristoloveanu

The core–shell junctionless MOSFET (CS-JL FET) meets the process requirements of FD-SOI technology. The transistor body comprises a heavily doped ultrathin layer (core linking the source and the drain), located underneath an undoped layer (shell). Drain current, transconductance, and capacitance characteristics demonstrate striking performance improvement compared with conventional junctionless MOSFETs. The addition of the shell results in one order of magnitude higher mobility (peak value), transconductance, and drive current. The doping and thickness of the core can be engineered to achieve a positive threshold voltage for normally-off operation. The CS-JL FET is compatible with back-biasing and downscaling schemes. The physical mechanisms are revealed by emphasizing the roles of the main device parameters.

Micromachines doi: 10.3390/mi16040416

Authors: Jiang Liu Hairui Bian Guoqiang Yu Jiachao Zhang Yaozheng Wang Dang Ding Ning Sang Fangsheng Huang

Microfluidic granulation technology enables high-quality production of energy-containing microspheres, significantly enhancing both performance and safety. Although microfluidic methods allow control over microsphere particle size, the adjustment range remains limited; low yield and process discontinuity also restrict broader application in the synthesis of energy-containing materials. This paper presents a microfluidic granulation system for energy-containing materials utilizing pulsed pneumatic printing, co-flow, and flow-focusing techniques to achieve wide particle size adjustment, consistent particle formation, high granulation speed, and production efficiency. This system allows microsphere sizes between 110 and 2500 μm, with a coefficient of variation (CV) as low as 1.9%, a frequency exceeding 13,000 Hz, and a suspension consumption rate reaching 100 mL/h. Calcium alginate/potassium perchlorate microspheres, prepared with sodium alginate hydrogel as a binder, exhibit uniform structure, narrow size distribution, and efficient energy material loading. We anticipate further advancements in applying microfluidic technology to energy-containing microsphere production based on this system.

Micromachines doi: 10.3390/mi16040415

Authors: Jaemyung Shin Yoonjung Lee Zhangkang Li Jinguang Hu Simon S. Park Keekyoung Kim

In the original publication [...]

Micromachines doi: 10.3390/mi16040414

Authors: Chenguang Ouyang Wenzheng He Lu Jia Peng Wang Kaichun Zhao Fei Xing Zheng You

This study presents a full-system simulation methodology for MEMS, addressing the critical need for reliable performance prediction in microsystem design. While existing digital tools have been widely adopted in related fields, current approaches often remain fragmented and focused on specific aspects of device behavior. In contrast, our proposed framework conducts comprehensive device physics-level analysis by integrating mechanical, thermal and electrical modeling with process simulation. The methodology features a streamlined workflow that enables direct implementation of simulation results into fabrication processes. We model a MEMS gyroscope as an example to verify our simulation approach. Multiphysics coupling is considered to capture real-world device behavior, followed by quantitative assessment of manufacturing variations through virtual prototyping and experimental validation demonstrating the method’s accuracy and practicality. The proposed approach not only improves design efficiency but also provides a robust framework for MEMS gyroscope development. With its ability to predict device performance, this methodology is expected to become an essential tool in microsensor research and development.

Micromachines doi: 10.3390/mi16040413

Authors: Yan Mi Yiqin Peng Wentao Liu Lei Deng Benxiang Shu

The electric field orientation method effectively promotes the orientation and arrangement of BN nanosheets, forming a thermal conduction network and enhancing the thermal conductivity of the composite material. In this study, microsecond pulsed electric field and direct current electric field were applied to induce the orientation and arrangement of BN nanosheets and improve the thermal conductivity of epoxy resin composites. Under a microsecond pulsed electric field of 50 Hz, 1.5 μs, and 8 kV/mm, the average orientation angle of BN nanosheets increased by 147.7%, and the thermal conductivity of the composite reached 0.352 W/(m·K), which is 1.84 times that of pure epoxy resin. In contrast, under a DC electric field of 70 V/mm, the average orientation angle of BN nanosheets increased by only 57.9%, while the thermal conductivity of the composite reached 0.364 W/(m·K), 1.91 times that of pure epoxy resin. The results indicate that the microsecond pulsed electric field primarily enhances the local orientation of the fillers to improve thermal conductivity, whereas the DC electric field mainly enhances the global arrangement of the fillers to achieve a similar effect. Additionally, thermogravimetric analysis and differential scanning calorimetry were conducted to evaluate the thermal properties of the composites. The results demonstrate that after BN nanosheets orientation and arrangement within the epoxy resin induced by both microsecond pulsed and DC electric fields, the composites exhibited a higher glass transition temperature and improved thermal stability. This study systematically explores the effects of microsecond pulsed and DC electric fields on filler orientation and arrangement, providing valuable insights for the fabrication of electric field-oriented composites.

Micromachines doi: 10.3390/mi16040412

Authors: Jen-Chieh Cheng Min-Chang You Aswin kumar Anbalagan Guang-Yang Su Kai-Wei Chuang Chao-Yao Yang Chih-Hao Lee

The anisotropic magnetoresistance (AMR) effect is widely used in microscale and nanoscale magnetic sensors. In this study, we investigate the correlation between AMR and the crystal structure, epitaxial relationship, and magnetic properties of Co50Fe50 thin films deposited on rigid MgO and flexible mica substrates. The AMR ratio is approximately 1.6% for CoFe films on mica, lower than the 2.5% observed in epitaxially grown films on MgO substrates. The difference is likely due to the well-defined easy axis in the single domain epitaxial thin films on MgO, which enhances the AMR ratio. Microscopic strain induced by lattice mismatch and bending on flexible substrates were determined using grazing incidence X-ray diffraction and extended X-ray absorption fine structure techniques. These results showed that neither microscopic nor macroscopic strain (below 0.5%) affects the AMR ratio on mica, suggesting its suitability for magnetic sensors in flexible and wearable devices. Additionally, investigating M-H loops under various growth temperatures, lattice mismatch conditions, and bending strains could further benefit the fabrication and integration of the micro-scale magnetic sensors in the microelectronic industry.

Micromachines doi: 10.3390/mi16040411

Authors: Yong-Jae Kim Woon-Seop Choi

Solution-processed oxide thin-film transistors (TFTs) can lead to a significant cost-effective process and suitable for large-scale fabrication. However, they often face limitations, such as lower field-effect mobility, the use of indium which is toxic and rare, and degradation compared to vacuum-based technologies. The single-walled carbon nanotubes (SWNTs) were incorporated with zinc–tin oxide (ZTO) precursor solution without dispersants for the device’s active layer. Sol–gel solution-based ZTO/single-wall carbon nanotube (ZTO/SWNT) (TFTs) with various SWNT concentrations were fabricated to improve the performance of ZTO TFTs. ZTO TFTs containing SWNTs exhibited better electrical performance than those without SWNTs. Among the samples, the ZTO TFT with an SWNT concentration of 0.07 wt.% showed a field-effect mobility (μsat) of 13.12 cm2/Vs (increased by a factor of 3) and an Ion/Ioff current ratio of 7.66 × 107 with a lower threshold voltage. SWNTs in the ZTO/SWNTs acted as carrier transfer rods, playing a crucial role in controlling the electrical performance of ZTO TFTs. The proposed fabrication of a sol–gel solution-based process is highly compatible with existing processes because it brings ZTO/SWNT hybrid TFTs closer to practical application, opening up the possibilities for next-generation electronics in flexible devices and low-cost manufacturing.

Micromachines doi: 10.3390/mi16040410

Authors: Sonia Bradai Slim Naifar Piotr Wolszczak Jarosław Bieniaś Patryk Jakubczak Andrzej Rysak Grzegorz Litak Olfa Kanoun

A bistable effect on a laminate structure with a piezoelectric patch was tested to harvest kinetic energy. The composite bistable plate was prepared in the autoclave with two different orientations of the glass fibers. The dynamic tests were performed on the universal testing machine using cyclic vertical compression excitation. During the tests, the bottom edge of the plate was clamped firmly while its upper edge was attached with some clearance to enable sliding. In such a configuration, the friction force between the plate and upper clamp element is responsible for the plate excitation. Simultaneously, the plate has enough space to change the shape between the two equilibria. During the harmonic excitation of the testing machine operating mode, a piezoelectric element was placed on the bistable plate and its voltage and normalized power outputs were evaluated. The experiments were repeated with additional mass distribution, which influenced the natural frequency of the plate.

Micromachines doi: 10.3390/mi16040409

Authors: Zhuorui Liu Yan Li Xiaoyang Zeng

Emerging applications like deep neural networks require high off-chip memory bandwidth and low dynamic loaded Double Data Rate SDRAM (DDR) latency. However, under the stringent physical constraints of chip packages and system boards, it is extremely expensive to further increase the bandwidth and reduce the dynamic loaded latency of off-chip memory in terms of DDR devices. To address the latency issues in DDR subsystems, this paper presents a novel architecture aiming at achieving latency optimization through a use case sensitive controller. We propose a reevaluation of conventional decoupling mechanisms and quasi-static arbitration methods in the DDR scheduling architecture. The adaptive scheduling algorithms offer significant advantages in various real-world scenarios. The research methodology involves implementing a rank-level timing aware read/write turnaround arbiter and setting read/write queue thresholds and read/write turnaround settings based on observed patterns. By implementing the arbiter and dynamically adjusting these parameters, the proposed architecture aims to optimize the performance of the DDR subsystem. To validate the effectiveness of the architecture, we conduct multiple experiments. These experiments evaluate the performance of the DDR subsystem under various workloads and configurations. The results demonstrate that the adaptive scheduling algorithms have advantages in achieving DDR performance attributes for workloads and improving system performance. The experimental results provide evidence of the architecture’s effectiveness in reducing latency by around 10% to 50% in various real-world scenarios.

Micromachines doi: 10.3390/mi16040408

Authors: Weiqing Huang Kaijie Huang Qunyou Zhong Jialun Wu Dawei An

Due to the high hardness and brittleness of sapphire, traditional machining methods are prone to surface scratches and microcracks. As an advanced processing technique, ultrasonic machining can reduce damage to hard–brittle materials and improve surface quality. In this study, an integrated ultrasonic longitudinal–torsional vibration system consisting of both a horn and a tool was designed. The resonant frequency and output amplitude of the horn were simulated and tested. The results indicated that the resonant frequency was 19.857 kHz, the longitudinal amplitude at the tool end was 4.2 µm, and the torsional amplitude was 1.8 µm. Experiments were then carried out to investigate the effects of various machining parameters on the reduction of sapphire surface roughness (Ra) and material removal rate (MRR). A comparative experiment was then conducted to evaluate the effects of ultrasonic longitudinal and longitudinal–torsional vibration on sapphire grinding. The ultrasonic longitudinal–torsional grinding experiments showed that the surface roughness of the sapphire workpiece was reduced from 960.6 nm to 82.6 nm, and the surface flatness was improved to 84.3 nm. Compared with longitudinal ultrasonic vibration, longitudinal torsional grinding reduced the surface roughness of sapphire workpieces by 48% and increased the surface flatness by 88.3%. The results of this study provide specific guidance for the longitudinal–torsional composite ultrasonic machining of hard–brittle materials.

Micromachines doi: 10.3390/mi16040407

Authors: Qingyue Xian Jie Zhang Yu Ching Wong Yibo Gao Qi Song Na Xu Weijia Wen

The technology of digital polymerase chain reaction (dPCR) is rapidly evolving, yet current devices often suffer from bulkiness and cumbersome sample-loading procedures. Moreover, challenges such as droplet merging and partition size limitations impede efficiency. In this study, we present a super-hydrophilic microarray chip specifically designed for dPCR, featuring streamlined loading methods compatible with micro-electro-mechanical systems (MEMS) technology. Utilizing hydrodynamic principles, our platform enables the formation of a uniform array of 120-pL independent reaction units within a closed channel. The setup allows for rapid reactions facilitated by an efficient thermal cycler and real-time imaging. We achieved absolute quantitative detection of hepatitis B virus (HBV) plasmids at varying concentrations, alongside multiple targets, including cancer mutation gene fragments and reference genes. This work highlights the chip’s versatility and potential applications in point-of-care testing (POCT) for cancer diagnostics.

Micromachines doi: 10.3390/mi16040403

Authors: Shujie Yang Victor Klinkov Natalia Grozova Svetlana Shalnova Tatiana Larionova Oleg Tolochko Olga Klimova-Korsmik

The pursuit of eco-friendly and renewable power generation has driven technological breakthroughs in nanoscale engineering, particularly regarding triboelectric nanogenerators (TENGs). These devices have become a focus of interest due to their capacity to effectively transform kinetic energy into electrical power via combined triboelectrification and electrostatic charge separation mechanisms. TENGs now find expanding implementations across multiple fields including in flexible electronics, autonomous sensing systems, and ambient energy conversion technologies. Enhancing TENG performance critically depends on the strategic design and application of nanostructures and nanomaterials. Nonetheless, challenges such as material selection, compatibility, homogeneous dispersion, interfacial stability, and production scalability must be overcome to advance TENG technology. Moreover, the mechanisms by which nanomaterials contribute to the triboelectric effect remain insufficiently understood, underscoring the necessity for systematic theoretical models. This review provides a comprehensive overview of recent advancements in integrating nanostructures and nanomaterials into TENGs, elucidating their roles, advantages, and underlying mechanisms in enhancing energy conversion efficiency, while identifying key challenges and proposing future research directions.

Micromachines doi: 10.3390/mi16040405

Authors: Xinrong Yang Jiamin Rong Enbo Xing Jianglong Li Yujie Zhang Yanru Zhou Wenyao Liu Huanfei Wen Jun Tang Jun Liu

We propose a low-frequency magnetic sensing method using a magnetically modulated microcavity resonant mode. Our magnetically sensitive unit with periodically changing magnetic poles is formed by combining an AC excitation coil with a microcavity. The microcavity vibrates at the frequency of the AC amplitude-modulated signal and changes its resonant mode when the sensing unit interacts with a low-frequency magnetic field. Signal processing is performed on the resonant spectrum to obtain low-frequency magnetic signals. The results of the experiment show that the measured sensitivity to a 0.5 Hz magnetic field is 12.49 V/mT, and a bias instability noise of 16.71 nT is achieved. We have extended the measurable frequency range of the whispering gallery mode microcavity magnetometer and presented a development in microcavity magnetic sensing and optical readout.

Micromachines doi: 10.3390/mi16040406

Authors: Fuling Yang Sicheng Zong Xinghan Li Yating Hu Zelong Wang Yuanyuan Qu Jing Wang Yan Li

In this paper, based on the multimode interference structure fiber and the sensitive advantages of a zeolitic imidazolate framework-8/Polydimethylsiloxane (ZIF-8/PDMS)-sensitive film in methane detection, a methane sensor based on an interferometer induced by multimode interference is designed and built with the aid of modeling. The methane-sensitive single mode fiber (MS-SMF) is obtained by coating a ZIF-8/PDMS-sensitive film around the cladding of a thin-diameter SMF. The change in methane concentration leads to a change in the cladding mode of the MS-SMF, which causes a change in interference spectrum and realizes methane concentration sensing. The factors affecting the sensitivity of the methane sensor are analyzed. Methane sensors with various parameters are fabricated and tested on a methane sensor platform for performance estimation at methane concentrations of 0–4%. The experimental results show that the sensitivity of the sensor to methane reaches 2.364 nm/% when the length of the MS-SMF is 42 mm, the thickness of the sensitive film is 1.8 µm, and the diameter of the MS-SMF is 58 µm. The limit of detection is about 338 ppm. The average response time is 30 s and the recovery time is 45 s. The temperature sensitivity of the methane sensor is approximately 0.026 nm/°C. The experimental results verify the correctness of the methane sensor model. This study provides a new design idea for optical methane sensors, showing great application potential in the field of methane detection.

Micromachines doi: 10.3390/mi16040404

Authors: Wenshen Luo Chaowen Zheng Cuimin Sun Zekun Li Hui You

The precise preparation and application of nanomicrospheres is currently an emerging research hotspot in the cutting-edge cross-disciplines. As an important functional material, nanosized microspheres show a broad application prospect in biomedicine, chemical engineering, materials science, and other fields. However, microspheres with good monodispersity are still facing technical bottlenecks, such as complicated preparation process and high cost. In this study, a multistage cyclic dielectrophoresis (MC-DEP) technique is innovatively proposed to successfully realize the high-resolution sorting of submicron microspheres. A dielectrophoresis chip adopts a unique electrode design, in which the electrodes are arranged at the top and bottom of the microchannel at the same time. This symmetric electrode structure effectively eliminates the difference in the distribution of dielectrophoretic force in the perpendicular direction and ensures the homogeneity of the initial state of particle sorting. Three pairs of focusing electrodes are in the front section of the microchannel for preaggregation of the microspheres, and the deflection electrodes in the back section are to realize particle size sorting. After this, the upper and lower limits of particle size are limited by multiple cycles of sorting. The multistage cyclic sorting increases the stability of particle deflection under dielectrophoretic forces and reduces the error perturbation caused by the fluid environment. The experimental results show that the multistage cycling sorting scheme significantly improves the monodispersity of the microspheres, and the coefficient of variation of the particle size is significantly reduced from the initial 12.3% to 5.4% after three cycles of sorting, which fully verifies the superior performance of this technology.

Micromachines doi: 10.3390/mi16040402

Authors: Xing Liu Pengxin Yu Haiduo Chen Bihui Peng Zhao Wang Fusheng Liang

Real-time parametric interpolation plays a crucial role in achieving high-speed and high-precision multi-axis CNC machining. In the interpolation cycle, the position of the next interpolation point is required to be calculated in real-time to guide the action of the machining process. Due to the existence of the positioning error of the interpolation point, it is extremely difficult to eliminate the feedrate fluctuation, which may lead to dramatic decreases in machining quality and the driving capabilities’ saturation of each axis. A computationally efficient and precise feedrate fluctuation minimization method is proposed for the NURBS tool path interpolation in the CNC milling process. The model for the arc length and curvature, with respect to the parameter of the NURBS tool path, is established to reduce the calculation amount required by interpolation points determination. The deviation between the theoretical and actual interpolation step length is decreased by the proposed arc length compensation method to minimize the feedrate fluctuation. In addition, the interpolation points derived from the arc length compensation process are further corrected by performing the Newton iteration to restrict the feedrate fluctuation within the preset accuracy threshold. The effectiveness and superiorities of the proposed feedrate fluctuation minimization method are verified by simulation and milling experiments.

Micromachines doi: 10.3390/mi16040401

Authors: Siyang Hu Billy Manansala Ulrike Fitzer Dennis Hohlfeld Tamara Bechtold

In this work, we propose a two-phase approach for a fast topology optimization of multi-resonant MEMSs. The approach minimizes the computation effort required to achieve an optimal design. In the first step, we perform a pre-optimization using bi-directional evolutionary structural optimization (BESO). We found in previous research that BESO can achieve optimal MEMS designs in a significantly lower number of iterations when compared to classical density-based methods. However, we encountered convergence issues with BESO towards the end of the optimization. Therefore, we introduced a second, density-based optimization phase to circumvent this issue. Finally, we introduced model order reduction to reduce the optimization time further. The novel approach is benchmarked with the design task of two common multi-resonant MEMS devices: a linear gyroscope and a micromirror. We show that the two-phase approach can achieve an optimal design within 200 iterations. With the addition of MOR, the computation of the goal function can be further reduced by 50% in our examples.

Micromachines doi: 10.3390/mi16040400

Authors: Jialuo Liao Pinghua Li Jiaqi Miao Ruimei Liang Zhongfeng Gao Xuye Zhuang

The feed-through effect of resonant pressure sensors usually introduces interfering noise signals, leading to the degradation of sensitivity, linearity, and other performances of the sensor test system. A low-noise charge amplifier and its feed-through compensation circuit are designed to realize high-precision measurements. The designed improved charge amplifier has a differential common-source structure as the output buffer stage, which can effectively reduce the output noise of the circuit while increasing the input impedance, thus improving the accuracy of the feed-through compensation coefficient. By establishing the equivalent circuit model of the sensor and analyzing the influence of the feed-through effect on the sensor test, the feed-through compensation circuit is designed to suppress the feed-through signal. Experimental testing of the sensor proves that the designed circuit can effectively suppress the feed-through effect of the sensor. The noise power spectral density of the improved charge amplifier is tested to be 26.74 nV/√Hz, which is a 65% reduction in noise density. The feed-through compensation circuit eliminates the interference frequency of 34,919 Hz introduced by the feed-through capacitor. Additionally, the resonance peak of the intrinsic resonance frequency of the pressure sensor is −40.75 dBV, which is reduced by 8 dBV compared with that before the feed-through compensation. The feed-through compensation circuit effectively reduces the feed-through interference signal of the sensor, improves the measurement accuracy of the test system, and provides technical support for the design of a low-noise, high-precision, stable, and reliable sensor test system.

Micromachines doi: 10.3390/mi16040399

Authors: Dong Hyun Kim Wonhwa Lee Jung Bin Park Jea Uk Lee

Recently, there has been an increasing emphasis on improving the performance of metal components across various industries, such as automotive, aerospace, electronics, medical devices, and military applications. However, the challenges related to efficient heat generation and transfer in equipment and devices are becoming increasingly critical. A solution to these issues involves the adoption of a metal–composite hybrid structure, designed to efficiently manage heat, while substituting conventional metal components with polymer–carbon composites. In this study, nanopores were formed on the metal surface using an anodization process, serving as the basis for creating 3D-printed polymer/metal hybrid constructions. Various surface treatments, including plasma treatment, mixed electrolyte anodization, and etching, were applied to the metal surface to enhance the bonding strength between the 3D-printed polymer and the aluminum alloy. These processes were essential for developing lightweight polymer/metal hybrid structures utilizing a range of 3D-printed polymer filaments, such as polylactic acid, thermoplastic polyurethane, acrylonitrile butadiene styrene, polypropylene, thermoplastic polyester elastomer, and composite materials composed of polymer and carbon. In particular, the hybrid structures employing polymer–carbon composite materials demonstrated excellent heat dissipation characteristics, attributed to the remarkable conductive properties of carbon fibers. These technologies have the potential to effectively address the device heat problem by facilitating the development of lightweight hybrid structures applicable across various fields, including automotive, mobile electronics, medical devices, and military applications.

Micromachines doi: 10.3390/mi16040398

Authors: Chanyoung Son Seok-Tae Koh Hyuntak Jeon

This paper presents a low-power photoplethysmography (PPG) readout system designed for wearable health monitoring. The system employs a differential current mirror (DCM) to convert single-ended PPG currents into differential voltages, inherently suppressing DC components. A wide common-mode input range (WCMIR) SAR ADC processes the differential signals, ensuring accurate analog-to-digital conversion. The DCM eliminates the need for DC cancelation loops, simplifying the design and reducing power consumption. Implemented in a 0.18 µm CMOS process, the system occupies only 0.30 mm2, making it suitable for multi-channel applications. The system achieves over 60 dB DC dynamic range and consumes only 9.6 µW, demonstrating its efficiency for portable devices. The simulation results validate its ability to process PPG signals across various conditions, offering a scalable solution for advanced biomedical sensing platforms.

Micromachines doi: 10.3390/mi16040397

Authors: Tongtian Zhang Junhui Wu Guangya Zhou

MEMS stiffness-tunable devices, owing to their low resonant frequency and high sensitivity, have been widely adopted in fields such as biological force sensing, vibration sensing, and inertial sensing. However, traditional stress-effect-based stiffness-adjustment methods offer limited tuning range. This paper introduces a novel stiffness-tuning mechanism based on the principle of stiffness compensation, integrating positive stiffness springs with V-shaped negative stiffness springs in a parallel configuration. A self-locking mechanism enables precise control of the mechanical preloading on the negative stiffness structures to realize stiffness adjustment. This design is prototyped by microscale fabrication techniques and is suitable for miniaturization. The experimental results confirm a stiffness reduction of over 90% and demonstrate bistability. These findings highlight the potential of the design for high-sensitivity MEMS accelerometers and dual-mode optical switches with low switching voltage.

Micromachines doi: 10.3390/mi16040396

Authors: George Mamin Ekaterina Dmitrieva Fadis Murzakhanov Margarita Sadovnikova Sergey Nagalyuk Marat Gafurov

Quantum technologies are currently being explored for various applications, including computing, secure communication, and sensor technology. A critical aspect of achieving high-fidelity spin manipulations in quantum devices is the controlled optical initialization of electron spins. This paper introduces a low-cost programming scheme based on a 32-bit STM32F373 microcontroller, aimed at facilitating high-precision measurements of optically active solid-state spin centers within semiconductor crystals (SiC, hBN, and diamond) utilizing a multi-pulse sequence. The effective shaping of short optical pulses across semiconductor and solid-state lasers, covering the visible to near-infrared range (405–1064 nm), has been validated through photoinduced electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies. The application of pulsed laser irradiation influences the EPR relaxation parameters associated with spin centers, which are crucial for advancements in quantum computing. The presented experimental approach facilitates the investigation of weak electron–nuclear interactions in crystals, a key factor in the development of quantum memory utilizing nuclear qubits.

Micromachines doi: 10.3390/mi16040394

Authors: Xiaowen Wang Yingnan Gao Yueze Yuan Yaping Wang Anqin Liu Sen Jia Wenguang Yang

Electronic skin (E-skin) refers to a portable medical or health electronic device that can be worn directly on the human body and can carry out perception, recording, analysis, regulation, intervention and even treatment of diseases or maintenance of health status through software support. Its main features include wearability, real-time monitoring, convenience, etc. E-skin is convenient for users to wear for a long time and continuously monitors the user’s physiological health data (such as heart rate, blood pressure, blood glucose, etc.) in real time. Health monitoring can be performed anytime and anywhere without frequent visits to hospitals or clinics. E-skin integrates multiple sensors and intelligent algorithms to automatically analyze data and provide health advice and early warning. It has broad application prospects in the medical field. With the increasing demand for E-skin, the development of multifunctional integrated E-skin with low power consumption and even autonomous energy has become a common goal of many researchers. This paper outlines the latest progress in the application of E-skin in physiological monitoring, disease treatment, human–computer interaction and other fields. The existing problems and development prospects in this field are presented.

Micromachines doi: 10.3390/mi16040395

Authors: Abdulelah S. Alrebaish Layla O. Alnami Joud M. Alshraim Razan A. Alnghemshi Alanoud A. Aljammaz Amir Altinawi Kholood K. Alhuthali Hend Alfadul Abdulaziz K. Assaifan

Interleukin-8 (IL-8) is a critical biomarker associated with inflammation and disability in both adults and newborns. Conventional detection methods are often labor-intensive, time-consuming, and require highly trained personnel. Non-Faradaic impedimetric biosensors offer a label-free, rapid, and direct approach for IL-8 detection. While previous studies have primarily focused on capacitance and phase changes, the potential of other impedimetric parameters remains underexplored. In this study, a gold interdigitated electrode (Au-IDE)-based non-Faradaic biosensor was developed for IL-8 detection, evaluating multiple impedimetric parameters, including capacitance, impedance magnitude (Zmod), real impedance (Zreal), and imaginary impedance (Zimag). Among these, Zimag exhibited the lowest limit of detection (LoD) at 90 pg/mL, followed by Zmod at 120 pg/mL, and capacitance at 140 pg/mL, all significantly below the clinical threshold of 600 pg/mL. In contrast, Zreal displayed the highest LoD at 1.3 ng/mL. Sensitivity analysis revealed that Zimag provided the highest sensitivity at 13.1 kΩ/log (ng/mL), making it the most effective parameter for detecting IL-8 at low concentrations. The sensitivity of Zmod and Zreal was lower, while capacitance sensitivity was measured at 20 nF/log (ng/mL). These findings highlight the importance of investigating alternative impedimetric parameters beyond capacitance to optimize biosensor performance for biomarker detection. This study demonstrates that non-Faradaic biosensors, despite their capacitive-based nature, can achieve enhanced sensitivity and detection limits by leveraging additional impedimetric parameters, offering a promising approach for rapid and effective IL-8 detection.

Micromachines doi: 10.3390/mi16040392

Authors: Yajun Sun Yi Quan Jie Xing Zhi Tan Xinhao Sun Lifei Lou Chunlong Fei Jianguo Zhu Yintang Yang

Ultrasound is one of the most promising methods for blood pressure monitoring due to its harmless, non-invasive, and high-precision characteristics. To further enhance the biocompatibility of ultrasound blood pressure monitors, this work reports wearable ultrasonic patches for blood pressure monitoring based on lead-free KNN (potassium sodium niobate)-based materials. The patches are designed and fabricated with a center frequency of 5 MHz and dimensions of 2.8 mm × 2.8 mm, optimized for both electrical impedance matching and vascular detection. Moreover, biocompatible silicone rubber is used for the packaging. The wearable ultrasonic patches are demonstrated to effectively transmit and receive signals. The diameter of artificial blood vessels is measured to validate the vascular diameter detection capability of the patches. The relationship between blood pressure and vascular diameter is then calculated. A radial artery vascular system platform is built to simulate changes in human blood pressure. Finally, the patches are shown to successfully measure the variation in vessel diameters on this platform. These patches exhibit sufficient detection ability, good biocompatibility, and can adhere tightly to human skin without coupling agents, providing the possibility for safe, sustainable, comfortable, and wearable long-term blood pressure monitoring.

Micromachines doi: 10.3390/mi16040393

Authors: Ghazaleh Ramezani Ixchel Ocampo Silva Ion Stiharu Theo G. M. van de Ven Vahe Nerguizian

This study explores the use of citric acid and L-ascorbic acid as reducing agents in CNC/CNF/rGO nanocomposite fabrication, focusing on their effects on electrical conductivity and mechanical properties. Through comprehensive analysis, L-ascorbic acid showed superior reduction efficiency, producing rGO with enhanced electrical conductivity up to 2.5 S/m, while citric acid offered better CNC and CNF dispersion, leading to higher mechanical stability. The research employs an advanced optimization framework, integrating regression models and a neural network with 30 hidden layers, to provide insights into composition–property relationships and enable precise material tailoring. The neural network model, trained on various input variables, demonstrated excellent predictive performance, with R2 values exceeding 0.998. A LASSO model was also implemented to analyze variable impacts on material properties. The findings, supported by machine learning optimization, have significant implications for flexible electronics, smart packaging, and biomedical applications, paving the way for future research on scalability, long-term stability, and advanced modeling techniques for these sustainable, multifunctional materials.

Micromachines doi: 10.3390/mi16040391

Authors: Yin Qing Lu Wang Yu Zheng

For Measurement While Drilling (MWD), the redundant Micro-Electro-Mechanical Systems Inertial Measurement Unit (MEMS-IMU) navigation system significantly enhances the reliability and accuracy of drill string attitude measurements. Such an enhancement enables precise control of the wellbore trajectory and enhances the overall quality of drilling operations. But installation errors of the redundant MEMS-IMUs still degrade the accuracy of drill string attitude measurements. It is essential to calibrate these errors to ensure measurement precision. Currently, the commonly used calibration method involves mounting the carrier on a horizontal plane and performing calibration through rotation. However, when the carrier rotates on the horizontal plane, the gravity acceleration component sensed by the horizontal axis of the IMU accelerometer in the carrier is very small, which leads to a low signal-to-noise ratio, so that the measured matrix obtained by the solution is dominated by noise. As a result, the accuracy of the installation is insufficient, and, finally, the effectiveness of the installation error compensation is reduced. In order to solve this problem, this study proposes a 45°-inclined six-position calibration method based on the selected hexagonal prism redundant structure for redundant MEMS-IMUs in MWD. Firstly, the compensation matrices and accelerometer measurement errors were analyzed, and the new calibration method was proposed; the carrier of the IMUs should be installed at an inclined position of 45°. Then, six measuring points were identified for the proposed calibration approach. Finally, simulation and laboratory experiments were conducted to verify the effectiveness of the proposed method. The simulation results showed that the proposed method reduced installation errors by 40.4% compared with conventional methods. The experiments’ results demonstrated reductions of 83% and 68% in absolute measurement errors for the x and y axes, respectively. As a result, sensor accuracy after compensation improved by over 25% compared with traditional methods. The calibration method proposed by this study effectively improves the accuracy of redundant systems, providing a new approach for the precise measurement of downhole trajectories.

Micromachines doi: 10.3390/mi16040390

Authors: Khairul Mohd Arshad Muhamad Mat Noor Asrulnizam Abd Manaf Hiroshi Kawarada Shaili Falina Mohd Syamsul

In the original publication [...]

Micromachines doi: 10.3390/mi16040389

Authors: Yulin Hou Mengdan Hu Dongke Sun Yueming Sun

This study employs numerical techniques to investigate the motion characteristics of red blood cells (RBCs) and drug carriers (DCs) within microvessels. A coupled model of the lattice Boltzmann method (LBM) and immersed boundary method (IBM) is proposed to investigate the migration of particles in blood flow. The lattice Bhatnagar–Gross–Krook (LBGK) model is utilized to simulate the flow dynamics of blood. While the IBM is employed to simulate the motion of particles, using a membrane model based on the finite element method. The present model was validated and demonstrated good agreements with previous theoretical and numerical results. Our study mainly examines the impact of the Reynolds number, DC size, and stiffness. Results suggest that these factors would influence particles’ equilibrium regions, motion stability and interactions between RBCs and DCs. Within a certain range, under a higher Reynolds number, the motion of DCs remains stable and DCs can swiftly attain their equilibrium states. DCs with smaller sizes and softer stiffness demonstrate a relatively stable motion state and their interactions with RBCs are weakened. The findings would offer novel perspectives on drug transport mechanisms and the impact of drug release, providing valuable guidance for the design of DCs.

Micromachines doi: 10.3390/mi16040388

Authors: Haibo Guo Na Pang Xu Hu Rui Wang Guo Li Fei Li

With the widespread application of RTD-fluxgate sensors in UAV aeromagnetic measurements, improving sensor sensitivity is essential for aeromagnetic gradient detection. The excitation waveform is one of the key factors affecting sensitivity. Under sinusoidal excitation, the output model shows poor linearity, and the time-difference expression needs to consider coercivity. Additionally, when triangular and trapezoidal waves are used, sensitivity improvement is limited. To address these issues, this paper proposed using a sawtooth wave as the excitation waveform for RTD-fluxgate sensors. The expressions for output time difference ΔT and sensitivity S were derived, and the sensor’s output characteristics under different excitations were compared. It was found that the time-difference expression under sawtooth wave excitation was independent of coercivity. The simulation results showed that under identical frequency and amplitude conditions, the time difference ΔT produced by sawtooth wave excitation was 2 times that of the triangular wave and 3.3 times that of the trapezoidal wave, significantly enhancing sensitivity. This excitation waveform offers advantages, providing new technical support for UAV aeromagnetic gradient detection and demonstrating broad application potential.

Micromachines doi: 10.3390/mi16040387

Authors: Lihui Ke Hang Zhao Hongbo Shan Yicheng Chen Yongsheng Cai Yang Wang Bo Wei Minghua Du

Sensitive and specific detection of DNA methylation is crucial for the early diagnosis of various human diseases, particularly cancers. However, conventional methylation detection methods often face challenges in balancing both sensitivity and specificity. In this study, we present a novel approach that integrates the high specificity of methylation-dependent restriction endonuclease (GlaI) digestion with the amplification efficiency of specific terminal-mediated polymerase chain reaction (STEM-PCR). This combination enables selective amplification of methylated DNA, which is then detected through lateral flow detection (LFD), providing a simple, visual readout. As a proof of concept, a STEM-PCR-LFD assay was applied to detect methylated Septin 9, a biomarker for colorectal cancer. The assay demonstrated a sensitivity of approximately 0.1% (10 copies of methylated template per reaction), with no cross-reactivity observed when 10,000 copies of unmethylated DNA were included as background. Furthermore, the assay was validated with ten formalin-fixed paraffin-embedded (FFPE) tissue samples, achieving 100% consistency with standard real-time STEM-PCR. This method offers a highly sensitive, specific, and accessible platform for DNA methylation detection, with potential for early disease diagnosis.

Micromachines doi: 10.3390/mi16040386

Authors: Nadia Ahbab Sidra Naz Tian-Bing Xu Shihai Zhang

Polyvinylidene fluoride (PVDF) polymer films, renowned for their exceptional piezoelectric, pyroelectric, and ferroelectric properties, offer a versatile platform for the development of cutting-edge micro-scale functional devices, enabling innovative applications ranging from energy harvesting and sensing to medical diagnostics and actuation. This paper presents an in-depth review of the material properties, fabrication methodologies, and characterization of PVDF films. Initially, a comprehensive description of the physical, mechanical, chemical, thermal, electrical, and electromechanical properties is provided. The unique combination of piezoelectric, pyroelectric, and ferroelectric properties, coupled with its excellent chemical resistance and mechanical strength, makes PVDF a highly valuable material for a wide range of applications. Subsequently, the fabrication techniques, phase transitions and their achievement methods, and copolymerization and composites employed to improve and optimize the PVDF properties were elaborated. Enhancing the phase transition in PVDF films, especially promoting the high-performance β-phase, can be achieved through various processing techniques, leading to significantly enhanced piezoelectric and pyroelectric properties, which are essential for diverse applications. This concludes the discussion of PVDF material characterization and its associated techniques for thermal, crystal structure, mechanical, electrical, ferroelectric, piezoelectric, electromechanical, and pyroelectric properties, which provide crucial insights into the material properties of PVDF films, directly impacting their performance in applications. By understanding these aspects, researchers and engineers can gain valuable insights into optimizing PVDF-based devices for various applications, including energy-harvesting, sensing, and biomedical devices, thereby driving advancements in these fields.

Micromachines doi: 10.3390/mi16040385

Authors: Zengliang Hu Minghai Li Xiaohui Jia

Microfluidic technology is an emerging interdisciplinary field that uses micropipes to handle or manipulate tiny fluids in chemistry, fluid physics, and biomedical engineering. As one of the rapid prototyping methods, the three-dimensional (3D) printing technique, which is rapid and cost-effective and has integrated molding characteristics, has become an important manufacturing technology for microfluidic chips. Polymethyl-methacrylate (PMMA), as an exceptional thermoplastic material, has found widespread application in the field of microfluidics. This paper presents a comprehensive process study on the fabrication of fused deposition modeling (FDM) 3D-printed PMMA microfluidic chips (chips), encompassing finite element numerical analysis studies, orthogonal process parameter optimization experiments, and the application of 3D-printed integrated microfluidic reactors in the reaction between copper ions and ammonium hydroxide. In this work, a thermal stress finite element model shows that the printing platform temperature was a significant printing parameter to prevent warping and delamination in the 3D printing process. A single printing molding technique is employed to fabricate microfluidic chips with square cross-sectional dimensions reduced to 200 μm, and the microchannels exhibited no clogging or leakage. The orthogonal experimental method of 3D-printed PMMA microchannels was carried out, and the optimized printing parameter resulted in a reduction in the microchannel profile to Ra 1.077 μm. Finally, a set of chemical reaction experiments of copper ions and ammonium hydroxide are performed in a 3D-printed microreactor. Furthermore, a color data graph of copper hydroxide is obtained. This study provides a cheap and high-quality research method for future research in water quality detection and chemical engineering.

Micromachines doi: 10.3390/mi16040384

Authors: Sukrut Prashant Phansalkar Roshith Mittakolu Bongtae Han Taehwa Kim

Dynamic mechanical analysis (DMA) is routinely practiced in the semiconductor industry to measure the viscoelastic properties of various thermosetting polymers. Modern commercial DMA test machines are highly-advanced systems which enable users to perform automatic testing and post-processing of the experimental data. When highly filled thermosets like epoxy-based molding compound (EMC) are tested, unique challenges are encountered during measurements due to the extremely large change in modulus over the testing temperature range. An advanced procedure is proposed to cope with these problems. The first part is the use of different oscillation strain amplitudes so that the variations in stress amplitudes across the testing domain remain consistent. The second part is the conducting of two monotonic tests at the lowest and highest temperatures to obtain the glassy modulus and equilibrium modulus, which can guide the master curve construction accurately. The results of the proposed procedure are presented. The relaxation modulus master curve is used to conduct a virtual testing to verify the accuracy of the generalized Maxwell model constants determined from the frequency data using the proposed procedure.

Micromachines doi: 10.3390/mi16040383

Authors: Minsu Park

Thermal technologies that effectively deliver thermal stimulation through skin-integrated systems and enable temperature perception via the activation of cutaneous thermoreceptors are key to enhancing immersive experiences in virtual and augmented reality (VR/AR) through multisensory engagement. However, recent advancements and commercial adoption have predominantly focused on haptic rather than thermal technology. This review provides an overview of recent advancements in wearable thermal devices (WTDs) designed to reconstruct artificial thermal sensations for VR/AR applications. It examines key thermal stimulation parameters, including stimulation area, magnitude, and duration, with a focus on thermal perception mechanisms and thermoreceptor distribution in the skin. Input power requirements for surpassing thermal perception thresholds are discussed based on analytical modeling. Material choices for WTDs, including metal nanowires, carbon nanotubes, liquid metals, thermoelectric devices, and passive cooling elements, are introduced. The functionalities, device designs, operation modes, fabrication processes, and electrical and mechanical properties of various WTDs are analyzed. Representative applications illustrate how flexible, thin WTDs enable immersive VR/AR experiences through spatiotemporal, programmable stimulation. A concluding section summarizes key challenges and future opportunities in advancing skin–integrated VR/AR systems.

Micromachines doi: 10.3390/mi16040382

Authors: S. Haghgooye Shafagh Imran Deen Dhilippan Mamsapuram Panneerselvam Muthukumaran Packirisamy

Polydimethylsiloxane (PDMS) and poly(3,4-ethylene dioxythiophene):poly(4-styrene-sulfonate) (PEDOT:PSS) composites were tested to determine their suitability for charging small-scale batteries in conjunction with a piezoelectric actuator as an energy harvester. Two different PEDOT:PSS patterns (zigzag and serpentine) were tested, and the maximum DC voltage of a system incorporating PEDOT:PSS was determined. The aim of this work is to study the effect of soft corners in the electrical routing of aircraft and IoT sensors. The zigzag and serpentine patterns were considered for this study because of their simplicity in design. Without the polymer, 2.3 V was produced by the actuator, while adding PEDOT:PSS resulted in the voltage being reduced to 1.7 V. The piezoelectric actuator was connected to a 3.6 V rechargeable Li-ion battery, and the battery’s voltage was recorded over 1 h. The voltage from the piezoelectric actuator was 3.8 V. Without PEDOT:PSS, the battery was charged to a maximum of 3 V. Adding the PEDOT:PSS to the circuit reduced the maximum charge to a voltage of 2 V. The results indicate that while PEDOT:PSS composites can be used in conjunction with piezoelectric energy harvesters, more work is still needed to optimize the system to increase efficiency and charging rates.

Micromachines doi: 10.3390/mi16040381

Authors: Jiacheng Li Junpeng Wang Chunrong Peng Wenjie Liu Jiahao Luo Zhengwei Wu Ren Ren Yao Lv

To mitigate the three-dimensional (3D) coupling interference of electric field sensors, a novel MEMS 3D electric field sensor with a dual-orthogonal induction structure and its spatial decoupling method is proposed. The sensor is designed with a cylindrical structure, in which two pairs of induction electrodes are orthogonally arranged to suppress common-mode interference. MEMS electric field sensing chips are utilized to achieve 3D electric field measurement. Furthermore, a spatial decoupling calibration model is established based on the structural characteristics of the sensor. The Cramér–Rao lower bound of the linear model is calculated to obtain the optimal decoupled calibration matrix, enabling precise 3D electric field decoupling. Experimental results showed that within an electric field range of 0–50 kV/m, the linearity of the three decoupled electric field components was 2.60%, 1.20%, and 1.78%, respectively, while the synthesized electric field achieved a linearity of 0.74% with a maximum full-scale error of 0.80%. Under varying angles and field intensities, the maximum and average relative errors of the decoupled synthesized electric field were 1.20% and 0.43%, respectively, representing reductions of 61.8% and 56.1% compared to the conventional matrix inversion method. These results confirmed that the proposed method effectively suppressed coupling interference and enhanced 3D electric field measurement accuracy.

Micromachines doi: 10.3390/mi16040380

Authors: Zijuan Han Bo Ran Jisheng Pan Rongji Zhuang

The third-generation semiconductor single-crystal silicon carbide (SiC), as a typical difficult-to-machine material, improves the chemical reaction rate on the SiC surface during the polishing process, which is key to realizing efficient chemical mechanical polishing (CMP). In this paper, a new core-shell structure Fe3O4@MIL-100(Fe) magnetic catalyst was successfully synthesized, which can effectively improve the reaction rate during the SiC polishing procesSs. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), and was used as a heterogeneous photocatalyst for chemical mechanical polishing, and the polishing results of SiC were optimized using response surface methodology (RSM). The experimental results show that the surface roughness of SiC can reach the minimum value of 0.78 nm when the polishing pressure is 0.06 MPa, the polishing speed is 60 rpm, and the polishing flow rate is 12 mL/min. The results of the study provide theoretical support for the visible photocatalysis-assisted CMP of SiC.

Micromachines doi: 10.3390/mi16040379

Authors: Xinyu Gao Zihao Gao Zhen Sun Ping Song Xiyuan Feng Zhixin Jin

Lead halide perovskite solar cells (PSCs) have shown tremendous progress in the last few years. However, highly toxic Pb and its instability have restricted their further development. On the other hand, antimony-based perovskites such as cesium antimony iodide (Cs3Sb2I9) have shown high stability but low power conversion efficiency (PCE) due to the limited transfer of photocarriers and the poor quality of films. Here, we present a novel method to improve the performance of Cs3Sb2I9 PSCs through a FACl-modified buried interface. FACl acts as a bi-functional additive, and FA incorporation enhances the crystallinity and light absorption of films. Furthermore, treatment with FACl optimizes the level position of Cs3Sb2I9. In addition, transient photovoltage and transient photocurrent were employed to confirm the reduction of charge recombination and superior carrier transportation. By using a planar device structure, we found the PCE of a FACl–Cs3Sb2I9-based device to be 1.66%. The device, stored for 2 months under N2 conditions, showed a negligible loss in PCE. Overall, this study provides a new strategy to further enhance the performance of Sb-based PSCs.

Micromachines doi: 10.3390/mi16040378

Authors: Xuhong Fan Chongming Zhao Wenan Jiang

To address the low electromechanical conversion efficiency associated with traditional single-degree-of-freedom (SDOF) piezoelectric energy harvesters, this study proposes a two-degree-of-freedom (2-DOF) cut-out piezoelectric beam for wind-induced vibration energy harvesting. Experimental comparisons conducted on four bluff bodies indicated that the triangular column exhibits superior aerodynamic stability, achieving an output voltage of 11.6 V at a wind speed of 7.0 m/s. Furthermore, the cut-out piezoelectric beam demonstrated a 1.9-fold increase in output voltage compared to its non-cut-out counterpart. These results underscore the potential of the 2-DOF cut-out piezoelectric beam design as an autonomous power solution for IoT nodes operating in complex environments.

Micromachines doi: 10.3390/mi16040377

Authors: En-Chih Chang Yeong-Jeu Sun Chun-An Cheng

A new and improved sliding mode control (NISMC) with a grey linear regression model (GLRM) facilitates the development of high-quality pure sine wave inverters in photovoltaic (PV) energy conversion systems. SMCs are resistant to variations in internal parameters and external load disturbances, resulting in their popularity in PV power generation. However, SMCs experience a slow convergence time for system states, and they may cause chattering. These limitations can result in subpar transient and steady-state performance of the PV system. Furthermore, partial shading frequently yields a multi-peaked power-voltage curve for solar panels that diminishes power generation. A traditional maximum power point tracking (MPPT) algorithm in such a case misclassifies and fail to locate the global extremes. This paper suggests a GLRM-based NISMC for performing MPPT and generating a high-quality sine wave to overcome the above issues. The NISMC ensures a faster finite system state convergence along with reduced chattering and steady-state errors. The GLRM represents an enhancement of the standard grey model, enabling greater accuracy in predicting global state points. Simulations and experiments validate that the proposed strategy gives better tracking performance of the inverter output voltage during both steady state and transient tests. Under abrupt load changing, the proposed inverter voltage sag is constrained to 10% to 90% of the nominal value and the voltage swell is limited within 10% of the nominal value, complying with the IEEE (Institute of Electrical and Electronics Engineers) 1159-2019 standard. Under rectified loading, the proposed inverter satisfies the IEEE 519-2014 standard to limit the voltage total harmonic distortion (THD) to below 8%.

Micromachines doi: 10.3390/mi16040376

Authors: Claudia Cirillo Mariagrazia Iuliano Francesca Fierro Claudia Florio Gaetano Maffei Andrea Loi Todor Batakliev Maria Sarno

This study focuses on preparing and characterizing functionalized silver nanoparticle-based (Ag-F NPs) finishing agents for leather treatment. Ag-F NPs were synthesized and functionalized through a ligand exchange process with citric acid, enhancing their dispersion stability in aqueous media. The nanoparticles were incorporated into polyurethane- and nitroemulsion-based finishing formulations and applied to ovine and bovine leather via a spray coating process. Morphological (SEM, TEM), structural (XRD), thermal (TGA), and spectroscopic (FT-IR) analyses confirmed successful functionalization and uniform dispersion within the finishing layer. Leather samples treated with Ag-F NPs exhibited a significant improvement in antibacterial properties, with microbial growth reduction of up to 90% after 72 h. Additionally, accelerated aging tests demonstrated enhanced UV resistance, with a 30% lower color change (∆E) compared to control samples. The Ag-F NPs-based finishing layers also exhibited superior abrasion and micro-scratch resistance, maintaining a stable coefficient of friction over time. These findings demonstrate the potential of Ag-F NPs as multifunctional leather-finishing agents, making them highly suitable for applications in the automotive, footwear, and leather goods industries.

Micromachines doi: 10.3390/mi16040375

Authors: Rui Chen Liming Wang Ruizhe Han Keqin Liao Xinlong Shi Peijian Zhang Huiyong Hu

To address the severe gate-induced drain leakage (GIDL) issue in fully depleted germanium-on-insulator (FD-GeOI) multi-subchannel tunneling field-effect transistors (MS TFETs), this paper proposes a stepped gate oxide (SGO) structure. In the off-state, the SGO structure effectively suppresses GIDL by reducing the electric field intensity at the channel/drain interface while simultaneously decreasing gate capacitance to reduce static power consumption. Based on an accurate device model, a systematic investigation was conducted into the effects of varying the thickness and length of the SGO structure on TFET performance, enabling the optimization of the SGO design. The simulation results demonstrate that, compared to normal MS TFETs, the SGO MS TFET reduces the off-state GIDL current (Ioff) from 4.6×10−7 A to 2.6×10−11 A, achieving a maximum improvement of 4.22 orders of magnitude in the on-state-to-off-state current ratio (Ion/Ioff) and a 28% reduction in subthreshold swing (SS). Furthermore, compared to lightly doped drain (LDD) MS TFETs, the SGO MS TFET achieves a 32% reduction in total gate capacitance and a 23% enhancement in carrier mobility at the channel/drain interface. This study demonstrates that SGO provides an effective solution for GIDL suppression.

Micromachines doi: 10.3390/mi16040374

Authors: Huixin Yuan Chunyu Zhang Chengwei Song Zhibing He Guo Li Leyao Li

Nanocrystalline diamond (NCD) is regarded as a highly promising composite engineering material owing to its superior mechanical properties. Surface texturing significantly enhances the surface performance of NCD. Given the unique inherent combination of hardness and brittleness in NCD, laser ablation emerges as a critical method for fabricating surface microstructures. However, the research on laser-induced surface texturing of NCD remains limited. This study experimentally investigated the characteristics of nanosecond laser-ablation-induced graphitization in NCD and provided an in-depth analysis of the laser ablation mechanism, aiming to guide the optimization of NCD surface microtexture manufacturing. Specifically, we conducted systematic nanosecond pulse laser ablation experiments on NCD samples and utilized Raman spectroscopy to qualitatively characterize the graphitization within microgrooves and across the entire ablated surface. The effects of the laser scanning speed, power, defocus level, and scanning interval on the graphitization extent and morphological characteristics were systematically investigated, identifying the single-factor optimal parameter set for maximizing graphitization. Through single-factor experimental analysis, the findings of this study provide foundational data for subsequent multivariate-coupled optimization and offer theoretical support for enhancing the surface properties of NCD through microtexturing via laser ablation.

Micromachines doi: 10.3390/mi16040373

Authors: Xinpeng Shi Yongge Li Kheder Suleiman

This study investigates the complex dynamic behavior of three-tailed helical microrobots operating in confined spaces. A stochastic dynamic model has been developed to analyze the effects of input angular velocity, current, fluid viscosity, and channel width on their motion trajectories, velocity, mean squared displacement (MSD), and wobbling rate. The results indicate that Gaussian white noise exerts a dispersive driving effect on the motion characteristics of the microrobots, leading to a 49% reduction in their velocity compared to deterministic conditions. Additionally, the time required for microrobots to traverse from the initial position to the bifurcation point decreases by 65% when the current is increased and by 39% when the fluid viscosity is reduced. These findings underscore the importance of optimizing control parameters to effectively mitigate noise impacts, enhancing the practical performance of the microrobots in real-world applications. This research offers solid theoretical support and guidance for the deployment of microrobots in complex environments.

Micromachines doi: 10.3390/mi16040372

Authors: Yunbin Kuang Xiaoyan Huo Weitao Guo Xiaoxing Li Jiangyan He Qiong Mao Xiaolin Ma Jie Liu

Thermal stress is one of the most important factors damaging the temperature-dependent performance of MEMS gyroscopes. To reduce thermal stress and improve their performance, this paper deduced the production and effects of thermal stress on a high-precision MEMS butterfly gyroscope theoretically, which provided a basis for optimization and experiments. A novel cantilever plate structure was designed based on the working modes of the MEMS butterfly gyroscope and optimized based on our simulation to achieve stress isolation. The simulation results showed that after integrating the cantilever plate structure, the stress acting on the MEMS butterfly gyroscope was reduced by 346 times, while the average capacitance gap error was also reduced by 36 times within the same variable temperature range. In addition, the cantilever plate structure was fabricated and integrated with the MEMS butterfly gyroscope. Experiments were also conducted to demonstrate the effect of reducing the thermal stress, and the results showed that the frequency variation was reduced by 28.6% and the bias stability increased by about 2 times over the full temperature range after integrating the cantilever plate structure into the gyroscope. This demonstrated that the cantilever plate structure can effectively reduce thermal stress and improve the performance of the MEMS butterfly gyroscope.

Micromachines doi: 10.3390/mi16040371

Authors: Monikuntala Bhattacharya Michael Jin Hengyu Yu Shiva Houshmand Jiashu Qian Marvin H. White Atsushi Shimbori Anant K. Agarwal

This work introduces a novel temperature-triggered threshold voltage shift (T3VS) method to study the energy-dependent Dit distribution close to the conduction band edge in commercial 1.2 kV 4H-SiC MOSFETs with planar and trench gate structures. Traditional Dit extraction methodologies are complicated and require sophisticated instrumentation, complex analysis, and/or prior information related to the device design and fabrication, which is generally unavailable to the consumers of commercial devices. This methodology merely utilizes the transfer characteristics of the device and is straightforward to implement. The Dit analysis using the T3VS method shows that trench devices have significantly lower Dit in comparison to the planar devices, making them more reliable and efficient in practical applications. Furthermore, this study examines the impact of a novel room temperature gate oxide screening methodology called screening with adjustment pulse (SWAP) on the Dit distribution in commercial planar MOSFETs, utilizing the proposed T3VS method. The result demonstrates that the SWAP technique is aggressive in nature and can introduce new defect states close to the conduction band edge. Hence, additional care is needed during screening optimization to ensure the reliability and usability of the screened devices in the consequent applications.

Micromachines doi: 10.3390/mi16040370

Authors: Yong Tang Yuxin Wei Tong Sun Jingjing Bai Fangqiong Luo Huarong Qiu Yiming Li Wei Yuan Shiwei Zhang

The evolution of 5G technology necessitates effective thermal management strategies for compact, high-power devices. The potential of aluminum-based vapor chambers (VCs) as thermal management solutions is recognized, yet the heat transfer performance is limited by the capillary constraints of the wick structures. This study proposes a laser-sintered composite wick to address this limitation. Experimental evaluations were conducted on microgroove wicks (MW) and groove–spiral woven mesh composite wicks (GSCW), utilizing ethanol and acetone as the working fluids. The MW, characterized by a laser spacing of 0.2 mm and two passes, demonstrated a capillary rise of 52.90 mm, while the spiral woven mesh (SWM) achieved a rise of 61.48 mm. Notably, the GSCW surpassed both configurations, reaching a capillary height of 84.57 mm and a capillary parameter (K/Reff) of 2.769 μm, which corresponds to increases of 90.15% and 43.76% over the MW and SWM, respectively. This study demonstrates an effective approach to enhancing the capillary performance of aluminum wicks, which provides valuable insights for the design of composite wicks, particularly for applications in ultra-thin aluminum VC.

Micromachines doi: 10.3390/mi16040369

Authors: Lei Xie Tao Zhang Shengrui Xu Huake Su Hongchang Tao Yuan Gao Xu Liu Jincheng Zhang Yue Hao

In this work, the electrical properties of the Ga2O3 Schottky barrier diodes (SBDs) using W/Au as the Schottky metal were investigated. Due to the 450 °C post-anode annealing (PAA), the reduced oxygen vacancy defects on the β-Ga2O3 surface resulted in the improvement in the forward characteristics of the W/Au Ga2O3 Schottky diode, and the breakdown voltage was significantly enhanced, increasing by 56.25% from 400 V to 625 V after PAA treatment. Additionally, the temperature dependence of barrier heights and ideality factors was analyzed using the thermionic emission (TE) model combined with a Gaussian distribution of barrier heights. Post-annealing reduced the apparent barrier height standard deviation from 112 meV to 92 meV, indicating a decrease in barrier height fluctuations. And the modified Richardson constants calculated for the as-deposited and annealed samples were in close agreement with the theoretical value, demonstrating that the barrier inhomogeneity of the W/Au Ga2O3 SBDs can be accurately explained using the TE model with a Gaussian distribution of barrier heights.

Micromachines doi: 10.3390/mi16040367

Authors: Yuanxin Li Jinjie Zhou Jiabo Wen Zehao Wang Liu Li

High-temperature pipelines, as core facilities in the fields of petrochemical and power, are constantly exposed to extreme working conditions ranging from 450 to 600 °C, facing risks of stress corrosion, creep damage, and other defects. Traditional shutdown inspections are time-consuming and costly. Meanwhile, existing electromagnetic acoustic transducers (EMATs) are restricted by their high-temperature tolerance (≤500 °C) and short-term stability (effective working duration < 5 min). This paper proposes a high-frequency circumferential guided wave (CLamb wave) EMAT based on a Halbach permanent magnet array. Through magnetic circuit optimization (Halbach array) and multi-layer insulation design, it enables continuous and stable detection on the surface of 600 °C pipelines for 10 min. The simulations revealed that the Halbach array increased the magnetic flux density by 1.4 times and the total displacement amplitude by 2 times at a magnet’s large lift-off (9 mm). The experimental results show that the internal temperature of the sensor remained stable below 167 °C at 600 °C. It was capable of detecting the smallest defect of a φ3 mm half-hole (depth half of the wall thickness), with a signal attenuation rate of only 0.32%/min. The signal amplitude of Q235 pipelines under high-temperature short-term detection (<5 min) was 1.5 times higher than that at room temperature. However, material degradation under high temperature led to insufficient long-term stability. This study breaks through the bottleneck of long-term detection of high-temperature EMATs, providing a new scheme for efficient online detection of high-temperature pipelines.

Micromachines doi: 10.3390/mi16040368

Authors: Shengtao Niu Ru Li

The effective measurement method plays a vital role in the structural health monitoring (SHM) field, which provides accurate and real-time information concerning structural conditions and performance. The innovative measurement approach based on strain sensors, referred to as the inverse finite element method (iFEM), has been considered the most promising and versatile technology for meeting the requirements of the SHM system. However, the existing iFEM for shape sensing of thick plate structures has the drawback that the transverse shear effect makes no contribution to the three-dimensional deformation of thick plate structures. Therefore, this study proposed an enhanced inverse finite element method (iFEM) based on single-surface fiber Bragg grating strain sensors for reconstructing thick plate structures coupled with an analytical formulation. The method characterized the explicit relationship between transverse shear and bending displacement field on the mid-plane, which presents the sixth-order differential equation based on a variational approach. The three-dimensional deformation field can be obtained along the thickness direction, expanding the SHM application of iFEM for composite structures based on strain measurement. By performing shape sensing analysis of the thick plate model, the exactness and applicability of the present method are numerically and experimentally validated for different loading cases.

Micromachines doi: 10.3390/mi16040366

Authors: Hadi Beitollahi Somayeh Tajik

In the present work, we designed a straightforward and disposable voltammetric sensor utilizing a molybdenum disulfide/multi-walled carbon nanotube nanostructure-modified screen-printed carbon electrode (MoS2/MWCNTs/SPCE) for 4-nitrophenol (4-NP) determination. The successful synthesis of the MoS2/MWCNT nanostructure was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EXD) mapping. The electrochemical behavior of 4-NP at the MoS2/MWCNTs/SPCE was examined using differential pulse voltammetry (DPV), cyclic voltammetry (CV), and chronoamperometry techniques. The MoS2/MWCNTs/SPCE exhibited outstanding electro-catalytic activity for the voltammetric detection of 4-NP. Under optimized conditions, the reduction peak current showed a linear dependence with the concentration of 4-NP in the range of 0.05 to 800.0 µM, and a detection limit (LOD) of 0.01 µM was determined. In addition, the MoS2/MWCNTs/SPCE sensor has advantages including repeatability, reproducibility, stability, inexpensiveness, and practical application. The MoS2/MWCNTs/SPCE-based sensor was also utilized for the determination of 4-NP in real water specimens.

Micromachines doi: 10.3390/mi16040365

Authors: Yi Liu Shunyi Zhao

Trajectory tracking is a critical component of autonomous driving and robotic motion control. This paper proposes a novel robust finite impulse response (FIR) filter for linear time-invariant systems, aimed at enhancing the accuracy and robustness of trajectory tracking. To address the limitations of infinite impulse response (IIR) filters in complex environments, we integrate a cumulative risk–sensitive criterion with an FIR structure. The proposed filter effectively mitigates model mismatches and temporary modeling uncertainties, making it highly suitable for trajectory tracking in dynamic and uncertain environments. To validate its performance, a comprehensive vehicle trajectory tracking experiment is conducted. The experimental results demonstrate that, compared to the Kalman filter (KF), risk–sensitive filter (RSF), and unbiased FIR (UFIR) filter, the proposed algorithm significantly reduces the average tracking error and exhibits superior robustness in complex scenarios. This work provides a new and effective solution for trajectory tracking applications, with broad potential for practical implementation.

Micromachines doi: 10.3390/mi16040364

Authors: Zhibo Huang Kunpeng Xu Hongguang Dai Zhanxia Wu Xiaopeng Yu Guoqiang Zhang

A novel low-power delay time cancellation (LPDTC) technique and a current ratio adjustment (CRA) method are proposed for designing high-precision relaxation oscillators. These methods effectively reduce the impacts of comparator delay time, offset voltage, and temperature-induced variations in resistors. To validate these methods, we have designed and simulated an 8 MHz open-loop relaxation oscillator using a 40 nm CMOS process. The oscillator, incorporating these advanced methods, achieves a line sensitivity of 0.38%/V and a temperature sensitivity of 43 ppm/°C over a temperature range of −40 °C to 125 °C.

Micromachines doi: 10.3390/mi16040363

Authors: Majid Roshanfar Mohammadhossein Salimi Amir Hossein Kaboodrangi Sun-Joo Jang Albert J. Sinusas Shing-Chiu Wong Bobak Mosadegh

With an increasing number of elderly individuals, the demand for advanced technologies to treat cardiac diseases has become more critical than ever. Additionally, there is a pressing need to reduce the learning curve for cardiac interventionalists to keep pace with the rapid development of new types of procedures and devices and to expand the adoption of established procedures in more hospitals. This comprehensive review aims to shed light on recent advancements in novel robotic systems for cardiac interventions. To do so, this review provides a brief overview of the history of previously developed robotic systems and describes the necessity for advanced technologies for cardiac interventions to address the technological limitations of current systems. Moreover, this review explores the potential of cutting-edge technologies and methods in developing the next generation of intra-procedure autonomous navigation. Each highlighted topic undergoes a critical analysis to evaluate its technical limitations and the challenges that must be addressed for successful clinical implementation.

Micromachines doi: 10.3390/mi16040362

Authors: Wenbo Li Anthony Mercader Sung Kwon Cho

Piezoelectric acoustic energy harvesting within the human body has traditionally faced challenges due to insufficient energy levels for biomedical applications. Existing acoustic resonators are often much larger in size, making them impractical for microscale applications. This study investigates the use of acoustically oscillated microbubbles as energy-harvesting resonators. A comparative study was conducted to determine the energy harvested by a freestanding diaphragm and a diaphragm coupled with an oscillating microbubble. The experimental results demonstrated that incorporating a microbubble enabled the flexible piezoelectric diaphragm to harvest seven times more energy than the freestanding diaphragm. These findings were further validated using Laser Doppler Vibrometer (LDV) measurements and stress calculations. Additional experiments with a phantom tissue tank confirmed the feasibility of this technology for biomedical applications. The results indicate that acoustically resonating microbubbles are a promising design for microscale acoustic energy-harvesting resonators in implantable biomedical devices.

Micromachines doi: 10.3390/mi16040361

Authors: Qiyun Liu Jinjie Zhou Ziliang Jia Pengfei Zhou

An epoxy/glass microbeads-based 1-3 piezoelectric composite is proposed, to enhance electromechanical conversion efficiency. Firstly, based on the series-parallel theory, the theoretical model is established. Secondly, the epoxy resin/glass microbeads-based 1-3 piezoelectric composite is simulated by finite element software. The effects of polymers with different acoustic impedances, the thicknesses of piezoelectric composites, and ceramic volume fractions are analyzed systematically. After parameter optimization, the epoxy/glass microbeads-based 1-3 piezoelectric composite is prepared. The experimental results agree well with the theoretical and simulation results. When the ceramic volume fraction is 60.0%, its electromechanical coupling factor is the largest, which is 0.714. Compared with the prepared traditional 1-3 piezoelectric composites with the same parameters, its electromechanical coupling factor is increased by 7.8%. Therefore, the epoxy/glass microbeads-based 1-3 piezoelectric composite can enhance the sensitivity and resolution of the transducers, which has potential advantages for improving the performance of transducers.

Micromachines doi: 10.3390/mi16040360

Authors: Yuan Xi Yan Gu Jieqiong Lin Zisu Xu Zhiduo Fan Tianyu Gao Xiaoming Zhang Yuanshuo Liu

Aluminum-based silicon carbide (SiCp/Al) is a hard-to-process material. SiC particles are randomly distributed and have a unique structure, thus posing challenges during processing. These distinctions considerably affect the overall quality of machining. As the volume fraction increases, the machinability continues to decline. Understanding the removal mechanism of SiCp/Al composites is essential for improving their machined surface quality. This study explores the influence of vibration frequency on the removal mechanism and plastic deformation in high-volume fraction SiCp/Al composites using non-resonant vibration-assisted scratching (NVAS) experiments combined with molecular dynamics (MD) simulations. The experimental results show that compared with conventional scraping (CS), increasing the vibration frequency in the NVAS process significantly expands the plastic removal area and reduces the scraping force. The simulation results indicate that as vibration frequency rises, the smoothness of the scratched groove improves, leading to a more uniform distribution of dislocations and a significant reduction in dislocation loops and HCP structures, promoting plastic deformation of the material. The simulation explains and clarifies the occurrence of plastic deformation observed during the scratching experiments. This study can provide a potential understanding of non-resonant vibration-assisted high-volume SiCp/Al composites machining.

Micromachines doi: 10.3390/mi16040359

Authors: Azam Arefi Abhilash Sreekumar Dimitrios Chronopoulos

Growing demands for self-powered, low-maintenance devices—especially in sensor networks, wearables, and the Internet of Things—have intensified interest in capturing ultra-low-frequency ambient vibrations. This paper introduces a hybrid energy harvester that combines elastic buckling with magnetically induced forces, enabling programmable transitions among monostable, bistable, and multistable regimes. By tuning three key parameters—buckling amplitude, magnet spacing, and polarity offset—the system’s potential energy landscape can be selectively shaped, allowing the depth and number of potential wells to be tailored for enhanced vibrational response and broadened operating bandwidths. An energy-based modeling framework implemented via an in-house MATLAB® R2024B code is presented to characterize how these parameters govern well depths, barrier heights, and snap-through transitions, while an inverse design approach demonstrates the practical feasibility of matching industrially relevant target force–displacement profiles within a constrained design space. Although the present work focuses on systematically mapping the static potential landscape, these insights form a crucial foundation for subsequent dynamic analyses and prototype validation, paving the way for advanced investigations into basins of attraction, chaotic transitions, and time-domain power output. The proposed architecture demonstrates modularity and tunability, holding promise for low-frequency energy harvesting, adaptive vibration isolation, and other nonlinear applications requiring reconfigurable mechanical stability.

Micromachines doi: 10.3390/mi16040358

Authors: Netzahualcóyotl Palomera Peter Feng

Different materials are studied for environmental gas sensors as well as photodetection prototypes. A ZnO/MoS2 p-n junction was synthetized to act as a multifunctional sensor prototype. After the ZnO was prepared on a silicon substrate by using DC sputtering at room temperature, molybdenum disulfide layers were spin-coated on a nanostructured zinc oxide flake-shaped surface to form an active layer. The heterostructure’s composite surface was examined using scanning electron microscopy, energy-dispersed X-ray, and Raman spectroscopy. Responses to light frequencies, light intensities, and gas chemical tracing were characterized, revealing an enhanced multifunctional performance of the prototype. Characterizations of light-induced photocurrents indicted that the obtained response strength (photocurrent/illumination light power) was up to 0.01 A/W, and the response time was less than 5 ms. In contrast, the gas-sensing measurements showed that its response strength (variation in resistance/original resistance) was up to 3.7% and the response time was down to 150 s when the prototype was exposed to ammonia gas, with the concentration down to 168 ppm. The fabricated prototype appears to have high stability and reproducibility, quick response and recovery times, as well as a high signal-to-noise ratio.

Micromachines doi: 10.3390/mi16040357

Authors: Xiaocong Zhou Jiaqiang Wen Shasha Han Chong Li

To address the bias drift problem and hysteresis phenomenon of hemispherical resonator gyroscope (HRG) under temperature change, a temperature drift compensation method based on internal parameters is proposed. The influence model of zero-rate output bias is established with the parameters such as resonance frequency, driving signal amplitude and quadrature suppression voltage amplitude during HRG operation. The temperature cycle experiment is carried out in the range of −20 to 60 °C, and the relationship between internal parameters and working temperature is revealed. Using KAN neural network combined with time series data as input features, a real-time compensation model is designed to effectively improve the prediction accuracy of hysteresis phenomenon. The experimental results show that the model significantly reduces the output stability performance of HRG, from 0.022°/h to 0.013°/h, and the stability decreases from 1.1392°/h to 0.0651°/h, which improves the stability and reliability of HRG.

Micromachines doi: 10.3390/mi16030356

Authors: Kairui Zhang Haifeng Sun Dajie Yu Song Hu Junbo Liu Ji Zhou

Alignment systems are core subsystems of lithography, which directly affect the overlay accuracy of the lithography process. The Moiré fringe-based alignment method has the advantages of high precision and low complexity. However, the precision of this method is highly sensitive to variations in the gap between the wafer and the mask. To enhance the performance of Moiré fringe-based alignment, this paper proposes a novel method in which the multi-wavelength approach is used to enhance the imaging depth of focus (DOF). We use a multi-wavelength light to illuminate the alignment marks on the wafer and mask, which is combined with different sources. Then, we use the improved phase analysis algorithm to analyze the contrast of the Moiré fringe and calculate the Moiré fringe displacement. Experiments show that, in an alignment range of 1000 μm, the effective DOF can exceed 400 μm. It is evidenced that the accuracy of the Moiré fringe alignment is unaffected and remains at the nanometer level. Otherwise, with parameter optimization, the alignment DOF is expected to be further extended.

Micromachines doi: 10.3390/mi16030355

Authors: Quoc-Viet Luong Quang-Ngoc Le Jai-Hyuk Hwang Thi-My-Nu Ho

This manuscript presents a new approach to describe aircraft landing gear systems equipped with magnetorheological (MR) dampers, integrating a reinforcement learning-based neural network control strategy. The main target of the proposed system is to improve the shock absorber efficiency in the touchdown phase, in addition to reducing the vibration due to rough ground in the taxing phase. The dynamic models of the aircraft landing system in the taxing phase with standard landing ground roughness, one-point touchdown, two-point touchdown, and third-point touchdown are built as the first step. After that, Q-learning-based reinforcement learning is developed. In order to verify the effectiveness of the controller, the co-simulations based on RECURDYN V8R4-MATLAB R2019b of the proposed system and the classical skyhook controller are executed. Based on the simulation results, the proposed controller provides better performance compared to the skyhook controller. The proposed controller provided a maximum improvement of 16% in the touchdown phase and 10% in the taxing phase compared to the skyhook controller.

Micromachines doi: 10.3390/mi16030354

Authors: Maziyar Kalateh Mohammadi Seyedsina Mirjalili Md Ashif Ikbal Hao Xie Chao Wang

Thrombospondin-2 (THBS2) is a prevailing prognostic biomarker implicated in different cancer types, such as deadly colorectal, pancreas, and triple-negative breast cancers. While the current methods for cancer-relevant protein detection, such as enzyme-linked immunosorbent assay (ELISA), mass spectrometry, and immunohistochemistry, are feasible at advanced stages, they have shortcomings in sensitivity, specificity, and accessibility, particularly at low concentrations in complex biological fluids for early detection. Here, we propose and demonstrate a modular, in-solution assay design concept, Nanoparticle-Supported Rapid Electronic Detection (NasRED), as a versatile cancer screening and diagnostic platform. NasRED utilizes antibody-functionalized gold nanoparticles (AuNPs) to capture target proteins from a minute amount of sample (<10 µL) and achieve optimal performance with a short assay time by introducing active fluidic forces that act to promote biochemical reaction and accelerate signal transduction. This rapid (15 min) process serves to form AuNP clusters upon THBS2 binding and subsequently precipitate such clusters, resulting in color modulation of the test tubes that is dependent on the THBS2 concentration. Finally, a semiconductor-based, portable electronic device is used to digitize the optical signals for the sensitive detection of THBS2. High sensitivity (femtomolar level) and a large dynamic range (five orders of magnitude) are obtained to analyze THBS2 spiked in PBS, serum, whole blood, saliva, cerebrospinal fluids, and synovial fluids. High specificity is also preserved in differentiating THBS2 from other markers such as cancer antigen (CA) 19-9 and bovine serum albumin (BSA). This study highlights NasRED’s potential to enhance cancer prognosis and screening by offering a cost-effective, accessible, and minimally invasive solution.

Micromachines doi: 10.3390/mi16030353

Authors: Wei-Ting Shih Wan-Hsin Tsou Dejan Vasic François Costa Wen-Jong Wu

In this study, we present two configurations of piezo-actuated microspeakers, which were fabricated by combining a self-developed aerosol deposition method with the metal MEMS microfabrication process. The stainless steel used was structurally designed to enhance the displacement amplitude of the speaker, which is related to its sound pressure level. The two packaged speakers were measured using the IEC 60318-4 standard. The package around the speaker contains a printed circuit board with the dimensions in 20.0 mm × 13.0 mm × 3.0 mm. In an enclosed field test, the bimorph single-layer (BSL) configuration reached sound levels of 98.4 dB and 92.4 dB using driving voltages of 30 Vpp and 15 Vpp at 1 kHz, respectively; however, the bimorph multi-layer (BML) configuration reached higher levels of 108.2 dB and 102.2 dB under the same conditions.

Micromachines doi: 10.3390/mi16030352

Authors: Yang Gou Shenhai Ye Xin Fu Fanghua Zheng Xuzhong Zha Cong Li

The bandwidth and output power of underwater acoustic transmitters are important for high-performance sonar detection systems. A mismatch between the impedance of the transducer and the transmitting circuit results in a low power factor, significantly limiting the sonar’s operating bandwidth and detection range. In addition, the radial head structure of the Tonpilz transducer plays an important role in determining the radiation characteristics of the sound field. This paper proposes a new radiation head structure along with an impedance-matching network circuit. First, a mathematical model of active power is established based on the Krimholtz–Leedom–Matthaei (KLM) model of the transducer. The adaptive Gauss–Newton algorithm is then used to calculate the parameters of the broadband impedance-matching network components, ultimately determining the network parameters and the structure of the transducer’s radiation head. Experimental results indicate that the transmitter voltage response of the proposed transducer is 6 dB higher than that of a conventional transducer and can be further increased by 5 dB with impedance matching. The impedance-matching network enhances the power factor of the transducer by 3.2 times, expands the frequency band by a factor of 1.6, and significantly enhances the acoustic field radiation characteristics of the underwater acoustic transducer.

Micromachines doi: 10.3390/mi16030351

Authors: Shashwat S. Agarwal Jacob C. Holter Travis H. Jones Brendan T. Fuller Joseph W. Tinapple Joseph M. Barlage Jonathan W. Song

Continuous perfusion is necessary to sustain microphysiological systems and other microfluidic cell cultures. However, most of the established microfluidic perfusion systems, such as syringe pumps, peristaltic pumps, and rocker plates, have several operational challenges and may be cost-prohibitive, especially for laboratories with no microsystems engineering expertise. Here, we address the need for a cost-efficient, easy-to-implement, and reliable microfluidic perfusion system. Our solution is a modular pumpless perfusion assembly (PPA), which is constructed from commercially available, interchangeable, and aseptically packaged syringes and syringe filters. The total cost for the components of each assembled PPA is USD 1–2. The PPA retains the simplicity of gravity-based pumpless flow systems but incorporates high resistance filters that enable slow and sustained flow for extended periods of time (hours to days). The perfusion characteristics of the PPA were determined by theoretical calculations of the total hydraulic resistance of the assembly and experimental characterization of specific filter resistances. We demonstrated that the PPA enabled reliable long-term culture of engineered endothelialized 3-D microvessels for several weeks. Taken together, our novel PPA solution is simply constructed from extremely low-cost and commercially available laboratory supplies and facilitates robust cell culture and compatibility with current microfluidic setups.

Micromachines doi: 10.3390/mi16030350

Authors: Jung-Pin Lai Shane Lin Vito Lin Andrew Kang Yu-Po Wang Ping-Feng Pai

Thermal analysis is an indispensable aspect of semiconductor packaging. Excessive operating temperatures in integrated circuit (IC) packages can degrade component performance and even cause failure. Therefore, thermal resistance and thermal characteristics are critical to the performance and reliability of electronic components. Machine learning modeling offers an effective way to predict the thermal performance of IC packages. In this study, data from finite element analysis (FEA) are utilized by machine learning models to predict thermal resistance during package testing. For two package types, namely the Quad Flat No-lead (QFN) and the Thin Fine-pitch Ball Grid Array (TFBGA), data derived from finite element analysis, are employed to predict thermal resistance. The thermal resistance values include θJA, θJB, θJC, ΨJT, and ΨJB. Five machine learning models, namely the light gradient boosting machine (LGBM), random forest (RF), XGBoost (XGB), support vector regression (SVR), and multilayer perceptron regression (MLP), are applied as forecasting models in this study. Numerical results indicate that the XGBoost model outperforms the other models in terms of forecasting accuracy for almost all cases. Furthermore, the forecasting accuracy achieved by the XGBoost model is highly satisfactory. In conclusion, the XGBoost model shows significant promise as a reliable tool for predicting thermal resistance in packaging design. The application of machine learning techniques for forecasting these parameters could enhance the efficiency and reliability of IC packaging designs.

Micromachines doi: 10.3390/mi16030348

Authors: Hexiang Guo Junya Wang Zheng You

A MEMS scanning mirror is a beam scanning device based on MEMS technology, which plays an important role in the fields of Lidar, medical imaging, laser projection display, and so on. The accurate measurement of the scanning mirror index can verify its performance and application scenarios. This paper designed and built a scanning mirror benchmark platform based on a two-dimensional position-sensitive detector (PSD), which can accurately measure the deflection angle, resonance frequency, and angular resolution of the scanning mirror, and described the specific test steps of the scanning mirror parameters, which can meet the two-dimensional measurement. Secondly, this paper analyzed and calculated the angular test uncertainty of the designed test system. After considering the actual optical alignment error and PSD measurement error, when the distance between the PSD and MEMS scanning mirror is 100 mm, the range of mechanical deflection angle that can be measured is (−6.34°, +6.34°). When the mechanical deflection angle of the scanning mirror is 0.01°, the accuracy measured by the test system is 0.00097°, and when the mechanical deflection of the scanning mirror is 6.34°, the accuracy measured by the test system is 0.011°. The test platform has high accuracy and can measure the parameters of the scanning mirror accurately.

Micromachines doi: 10.3390/mi16030349

Authors: Eda Ozyilmaz Gamze Gediz Ilis

Accurate separation in microfluidic devices is crucial for biomedical applications; however, enhancing their performance remains challenging due to computational and experimental constraints. This study aims to optimize microfluidic devices by systematically refining spiral microchannel configurations for the segregation of circulating tumor cells (CTCs) and red blood cells (RBCs) through detailed variable analysis and resource-efficient techniques. The spiral design was developed into six variations, considering loop numbers (2, 3, and 4), aspect ratios (2.333, 3.333, and 5), spiral radii (5, 6, and 7 mm), flow rates (1.5, 2, and 3 mL/min), surface roughness levels (0, 0.5, and 1 μm), and particle sizes (12, 18, and 24 μm). Simulations were conducted in COMSOL Multiphysics and evaluated using the Taguchi method to determine the optimal configuration, reducing the analysis set from 216 to 27 through an efficient experimental design approach. The results identified the optimal structure as having an aspect ratio of 3.333, four loops, a spiral radius of 6–7 mm, a flow rate of 3 mL/min, a surface roughness of 1 μm, and a particle diameter of 24 μm. Among the evaluated parameters, aspect ratio (61.2%) had the most significant impact, followed by the number of loops (13.9%) and flow rate (9.4%). The optimized design demonstrated high separation efficiency and purity, achieving 97.5% and 97.6%, respectively. The fabrication process involved 3D-printing the channel mold, followed by polydimethylsiloxane (PDMS) casting, validating the durability and scalability of the proposed design. This study integrates simulation and experimental results, providing a robust framework for developing next-generation microfluidic devices and advancing diagnostic and targeted therapeutic applications.

Micromachines doi: 10.3390/mi16030347

Authors: Shaoyu Liu Yan Tang Xiaolong Cheng Yuliang Long Jinfeng Jiang Yu He Lixin Zhao

This paper introduces a method for improving the measurement performance of single wavelength overlay errors by incorporating higher diffraction orders. In this method, to enhance the accuracy and robustness of overlay error detection between layers, the measurement errors introduced by empirical formulas are corrected by incorporating higher diffraction orders, based on the differences in the light intensity difference curves for different diffraction orders. This method also expands the range of available wavelengths for selection. The introduction of specially designed overlay error measurement markers enhances the diffraction efficiency of higher diffraction orders to overcome the issue of their weak light intensity, making them difficult to utilize effectively. This paper first conducts a theoretical analysis using scalar diffraction theory, and then demonstrates the feasibility of the design through vector diffraction simulations and optical path simulations. The resulting two-layer marker structure is simple and compatible with existing measurement systems, showing tremendous potential for application at advanced process nodes.

Micromachines doi: 10.3390/mi16030346

Authors: Honghong Wang Jingli Du Yi Mao

Traditional tendon-driven continuum robot (TDCR) models based on Cosserat rod theory often assume that tendon tension is a continuous wrench along the backbone. However, this assumption overlooks critical factors, including the discrete arrangement of disks, the segmented configuration of tensioned tendons, and the friction between tendons and guide holes. Additionally, tendon forces are not continuous but discrete, concentrated wrenches, with the frictional force magnitude and direction varying based on the TDCR’s bending configuration. We propose a TDCR modeling method that integrates Cosserat rod theory with a finite element approach to address these limitations. We construct a Cosserat rod model for the robot’s backbone, discretize the tendon geometry using the finite element method (FEM), and incorporate friction modeling between tendons and guide holes. Furthermore, we introduce an algorithm to determine the direction of friction forces, enhancing modeling accuracy. This approach results in a more realistic and comprehensive mathematical representation of TDCR behavior. Numerical simulations under various tendon-routing scenarios are conducted and compared with classical TDCR models. The results indicate that our friction-inclusive model improves accuracy, yielding an average configuration deviation of only 0.3% across different tendon routings. Experimental validation further confirms the model’s accuracy and robustness.

Micromachines doi: 10.3390/mi16030345

Authors: Xiyao Liu Kuihua Han

To enhance the safety of lithium ternary battery cases in new energy vehicles, this study designed a temperature monitoring and fault warning system based on NiCr/NiSi thin-film thermocouples. The system integrates six modules—sensor, amplifier, data acquisition, microprocessor (using the KPCA nonlinear dimensionality reduction algorithm), communication and monitoring, and alarm control—to monitor temperature, voltage, and humidity changes in real time. Multi-level warning thresholds are established (e.g., Level 1: initial temperature 35–55 °C rising to 42–65 °C after 10 min; initial voltage 400–425 V dropping to 398–375 V after 10 min). Experimental results demonstrate that the NiCr/NiSi thermocouple exhibits high sensitivity (average Seebeck coefficient: 41.42 μV/°C) and low repeatability error (1.04%), with a dense and uniform surface structure (roughness: 3.2–5.75 nm). The warning logic, triggered in four levels based on dynamic temperature and voltage changes, achieves an 80% accuracy rate and a low false/missed alarm rate of 4%. Long-term operation tests show stable monitoring deviations (±0.2 °C for temperature and ±0.02 V for voltage over 24 h). The system also adapts to varying humidity environments, with peak sensitivity (41.3 μV/°C) at 60% RH. This research provides a highly reliable solution for battery safety management in new energy vehicles.

Micromachines doi: 10.3390/mi16030344

Authors: Yuri D. Ivanov Ivan D. Shumov Andrey F. Kozlov Alexander N. Ableev Angelina V. Vinogradova Ekaterina D. Nevedrova Oleg N. Afonin Dmitry D. Zhdanov Vadim Y. Tatur Andrei A. Lukyanitsa Nina D. Ivanova Evgeniy S. Yushkov Dmitry V. Enikeev Vladimir A. Konev Vadim S. Ziborov

Low-frequency electromagnetic fields, induced by alternating current (AC)-based equipment such as transformers, are known to influence the physicochemical properties and function of enzymes, including their catalytic activity. Herein, we have investigated how incubation near a 50 Hz AC autotransformer influences the physicochemical properties of horseradish peroxidase (HRP), by atomic force microscopy (AFM) and spectrophotometry. We found that a half-hour-long incubation of the enzyme above the coil of a loaded autotransformer promoted the adsorption of the monomeric form of HRP on mica, enhancing the number of adsorbed enzyme particles by two orders of magnitude in comparison with the control sample. Most interestingly, the incubation of HRP above the switched-off transformer, which was unplugged from the mains power supply, for the same period of time was also found to cause a disaggregation of the enzyme. Notably, an increase in the activity of HRP against ABTS was observed in both cases. We hope that the interesting effects reported will emphasize the importance of consideration of the influence of low-frequency electromagnetic fields on enzymes in the design of laboratory and industrial equipment intended for operation with enzyme systems. The effects revealed in our study indicate the importance of proper shielding of AC-based transformers in order to avoid the undesirable influence of low-frequency electromagnetic fields induced by these transformers on humans.

Micromachines doi: 10.3390/mi16030343

Authors: Milica Govedarica Ivana Milosevic Vesna Jankovic Radmila Mitrovic Ivana Kundacina Ivan Nastasijevic Vasa Radonic

Biosensors as advanced analytical tools have found various applications in food safety, healthcare, and environmental monitoring in rapid and specific detection of target analytes in small liquid samples. Up to now, planar electrochemical electrodes have shown the highest potential for biosensor applications due to their simple and compact construction and cost-effectiveness. Although a number of commercially available electrodes, manufactured from various materials on different substrates, can be found on the market, their high costs for single use and low reproducibility persist as major drawbacks. In this study, we present an innovative, cost-effective approach for the rapid fabrication of electrodes that combines lamination of 24-karat gold leaves with low-cost polyvinyl chloride adhesive sheets followed by laser ablation. Laser ablation enables the creation of electrodes with customizable geometries and patterns with microlevel resolutions. The developed electrodes are characterized by cyclic voltammetry and electrochemical impedance spectroscopy, scanning electronic microscopy, and 3D profiling. To demonstrate the manufacturing and biosensing potential, different geometries and shapes of electrodes were realized as the electrochemical transducing platform and applied for the realization of magnetic bead (MB)-labeled biosensors for quantitative detection of food-borne pathogens of Salmonella typhimurium (S. typhimurium) and Listeria monocytogenes (L. monocytogenes).

Micromachines doi: 10.3390/mi16030342

Authors: Ching-Feng Yu Jr-Wei Peng Chih-Cheng Hsiao Chin-Hung Wang Wei-Chung Lo

This study presents an artificial intelligence (AI) prediction platform driven by deep learning technologies, designed specifically to address the challenges associated with predicting warpage behavior in fan-out wafer-level packaging (FOWLP). Traditional electronic engineers often face difficulties in implementing AI-driven models due to the specialized programming and algorithmic expertise required. To overcome this, the platform incorporates a graphical user interface (GUI) that simplifies the design, training, and operation of deep learning models. It enables users to configure and run AI predictions without needing extensive coding knowledge, thereby enhancing accessibility for non-expert users. The platform efficiently processes large datasets, automating feature extraction, data cleansing, and model training, ensuring accurate and reliable predictions. The effectiveness of the AI platform is demonstrated through case studies involving FOWLP architectures, highlighting its ability to provide quick and precise warpage predictions. Additionally, the platform is available in both uniform resource locator (URL)-based and standalone versions, offering flexibility in usage. This innovation significantly improves design efficiency, enabling engineers to optimize electronic packaging designs, reduce errors, and enhance the overall system performance. The study concludes by showcasing the structure and functionality of the GUI platform, positioning it as a valuable tool for fostering further advancements in electronic packaging.

Micromachines doi: 10.3390/mi16030341

Authors: Eleftheria Babaliari Paraskevi Kavatzikidou Dionysios Xydias Sotiris Psilodimitrakopoulos Anthi Ranella Emmanuel Stratakis

Considering that neurological injuries cannot typically self-recover, there is a need to develop new methods to study neuronal outgrowth in a controllable manner in vitro. In this study, a precise flow-controlled microfluidic system featuring custom-designed chambers that integrate laser-microstructured polyethylene terephthalate (PET) substrates comprising microgrooves (MGs) was developed to investigate the combined effect of shear stress and topography on Neuro-2a (N2a) cells’ behavior. The MGs were positioned parallel to the flow direction and the response of N2a cells was evaluated in terms of growth and differentiation. Our results demonstrate that flow-induced shear stress could inhibit the differentiation of N2a cells. This microfluidic system could potentially be used as a new model system to study the impact of shear stress on cell differentiation.

Micromachines doi: 10.3390/mi16030340

Authors: Sefa Aydin Mesut Melek Levent Gökrem

Nowadays, brain–computer interface (BCI) systems are frequently used to connect individuals who have lost their mobility with the outside world. These BCI systems enable individuals to control external devices using brain signals. However, these systems have certain disadvantages for users. This paper proposes a novel approach to minimize the disadvantages of visual stimuli on the eye health of system users in BCI systems employing visual evoked potential (VEP) and P300 methods. The approach employs moving objects with different trajectories instead of visual stimuli. It uses a light-emitting diode (LED) with a frequency of 7 Hz as a condition for the BCI system to be active. The LED is assigned to the system to prevent it from being triggered by any involuntary or independent eye movements of the user. Thus, the system user will be able to use a safe BCI system with a single visual stimulus that blinks on the side without needing to focus on any visual stimulus through moving balls. Data were recorded in two phases: when the LED was on and when the LED was off. The recorded data were processed using a Butterworth filter and the power spectral density (PSD) method. In the first classification phase, which was performed for the system to detect the LED in the background, the highest accuracy rate of 99.57% was achieved with the random forest (RF) classification algorithm. In the second classification phase, which involves classifying moving objects within the proposed approach, the highest accuracy rate of 97.89% and an information transfer rate (ITR) value of 36.75 (bits/min) were achieved using the RF classifier.