Micromachines

5 pages, 154 KiB

Open AccessEditorial

Editorial for the Applications and Challenges for Gas Sensors

by Zhaohui Lei, Yinglin Wang and Pengfei Cheng

Micromachines 2025, 16(5), 493; https://doi.org/10.3390/mi16050493 - 23 Apr 2025

Gas sensors, widely used in various fields, are devices used to detect the presence of a specific gas within a certain area or to continuously measure the concentration of gas components [...] Full article

(This article belongs to the Section C：Chemistry)

14 pages, 4712 KiB

Open AccessArticle

Nonlinear Hysteresis Parameter Identification of Piezoelectric Actuators Using an Improved Gray Wolf Optimizer with Logistic Chaos Initialization and a Levy Flight Variant

by Yonggang Yan, Kangqiao Duan, Jianjun Cui, Shiwei Guo, Can Cui, Yongsheng Zhou, Junjie Huang, Geng Wang, Dengpan Zhang and Fumin Zhang

Micromachines 2025, 16(5), 492; https://doi.org/10.3390/mi16050492 - 23 Apr 2025

Abstract

Piezoelectric tilt mirrors are crucial components of precision optical systems. However, the intrinsic hysteretic nonlinearity of the piezoelectric actuator severely restricts the control accuracy of these mirrors and the overall performance of the optical system. This paper proposes an improved Gray Wolf Optimization [...] Read more.

Piezoelectric tilt mirrors are crucial components of precision optical systems. However, the intrinsic hysteretic nonlinearity of the piezoelectric actuator severely restricts the control accuracy of these mirrors and the overall performance of the optical system. This paper proposes an improved Gray Wolf Optimization (GWO) algorithm for high-accuracy identification of hysteresis model parameters based on the Bouc–Wen (BW) differential equation. The proposed algorithm accurately describes the intrinsic hysteretic nonlinear behavior of piezoelectric tilt mirrors. A logistic chaotic mapping method is introduced for population initialization, while a nonlinear convergence factor and a Levy flight strategy are incorporated to enhance global search capabilities during the later stages of optimization. These modifications enable the algorithm to effectively identify BW model parameters for piezoelectric nonlinear systems. Compared to conventional Particle Swarm Optimization (PSO) and standard GWO, the improved algorithm demonstrates faster convergence, higher accuracy, and superior ergodicity, making it a promising tool for solving optimization problems, such as parameter identification in piezoelectric hysteresis systems. This work provides a robust approach for improving the precision and reliability of piezoelectric-driven optical systems. Full article

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12 pages, 2211 KiB

Open AccessArticle

Electrostatic Field Modification Enhances the Electrocatalytic Oxygen Evolution Reaction Stability of CoFe₂O₄ Catalysts

by Liwen Liang, Jiatong Miao, Xiyuan Feng, Yunlei Zhong and Wei Wang

Micromachines 2025, 16(5), 491; https://doi.org/10.3390/mi16050491 - 22 Apr 2025

Abstract

Enhancing the stability of oxygen evolution reaction (OER) catalysts is a critical challenge for realizing efficient water splitting. In this work, we introduce an innovative approach by applying an electric field during the annealing of a CoFe₂O₄/C catalyst. By [...] Read more.

Enhancing the stability of oxygen evolution reaction (OER) catalysts is a critical challenge for realizing efficient water splitting. In this work, we introduce an innovative approach by applying an electric field during the annealing of a CoFe₂O₄/C catalyst. By controlling the electric field strength (100 mV) and treatment duration (1 h), we achieved dual optimization of the catalyst’s microstructure and electronic environment, resulting in a significant improvement in catalytic stability. The experimental results demonstrate that the electric field-treated catalyst exhibits a reduced overpotential decay (only 0.8 mV) and enhanced stability (retaining 89.1% of its initial activity after 24 h) during extended OER testing. This performance significantly surpasses that of the untreated sample, which showed an overpotential decay of 1.5 mV and retained only 72.5% of its activity after 24 h. X-ray photoelectron spectroscopy (XPS) analysis confirmed that the electric field treatment promoted the formation of oxygen vacancies, substantially improved electron transfer efficiency, and optimized the local electronic environment of Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺, leading to a decrease in charge transfer resistance (Rct) from 58.2 Ω to 42.9 Ω. This study not only presents a novel strategy for modulating catalyst stability via electric fields but also broadens the design concepts for OER catalytic materials by establishing a structure–activity relationship between electric field strength, microstructure, and catalytic performance, ultimately providing a theoretical foundation and experimental guidance for the development of highly efficient and stable water splitting catalysts. Full article

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11 pages, 3791 KiB

Open AccessArticle

Rapid Synthesis of Fast-Charging TiNb₂O₇ for Lithium-Ion Storage via Ultrafast Carbothermal Shock

by Xianyu Hu, Yunlei Zhong, Xiaosai Hu, Xiyuan Feng and Fengying Ye

Micromachines 2025, 16(5), 490; https://doi.org/10.3390/mi16050490 - 22 Apr 2025

Abstract

The development of fast-charging lithium-ion batteries urgently requires high-performance anode materials. In this paper, through an ultrafast carbothermal shock (CTS) strategy, titanium niobium oxide (TiNb₂O₇, TNO) with an optimized structure was successfully synthesized within 30 s. By regulating the [...] Read more.

The development of fast-charging lithium-ion batteries urgently requires high-performance anode materials. In this paper, through an ultrafast carbothermal shock (CTS) strategy, titanium niobium oxide (TiNb₂O₇, TNO) with an optimized structure was successfully synthesized within 30 s. By regulating the synthesis temperature to 1200 °C, the TNO-1200 material was obtained. Its lattice parameters (a-axis: 17.6869 Å) and unit-cell volume (796.83 Å³) were significantly expanded compared to the standard structure (a-axis: 17.51 Å, volume ~790 Å³), which widened the lithium-ion migration channels. Rietveld refinement and atomic position analysis indicated that the partial overlap of Ti/Nb atoms and the cooperative displacement of oxygen atoms induced by CTS reduced the lithium-ion diffusion energy barrier. Meanwhile, the cation disorder suppressed the polarization effect. Electrochemical tests showed that after 3000 cycles at a current density of 10 C, the specific capacity of TNO-1200 reached 125 mAh/g, with a capacity retention rate of 98%. EDS mapping confirmed the uniform distribution of elements and the absence of impurity phases. This study provides an efficient synthesis strategy and theoretical basis for the design of high-performance fast-charging battery materials through atomic-scale structural engineering. Full article

(This article belongs to the Section C：Chemistry)

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16 pages, 4503 KiB

Open AccessArticle

A Single-Field Finite Difference Time-Domain Method Verified Using a Novel Antenna Design with an Artificial Magnetic Conductor Enhanced Structure

by Yongjun Qi, Weibo Liang, Yilan Hu, Liang Zhang, Cheng You, Yuxiang Zhang, Tianrun Yan and Hongxing Zheng

Micromachines 2025, 16(4), 489; https://doi.org/10.3390/mi16040489 - 21 Apr 2025

Abstract

The Finite Difference Time-Domain (FDTD) method is a powerful tool for electromagnetic field analysis. In this work, we develop a variation of the algorithm to accurately calculate antenna, microwave circuit, and target scattering problems. To improve efficiency, a single-field (SF) FDTD method is [...] Read more.

The Finite Difference Time-Domain (FDTD) method is a powerful tool for electromagnetic field analysis. In this work, we develop a variation of the algorithm to accurately calculate antenna, microwave circuit, and target scattering problems. To improve efficiency, a single-field (SF) FDTD method is proposed as a numerical solution to the time-domain Helmholtz equations. New formulas incorporating resistors and voltage sources are derived for the SF-FDTD algorithm, including hybrid implicit–explicit and weakly conditionally stable SF-FDTD methods. The correctness of these formulas is verified through numerical simulations of a newly designed dual-band wearable antenna with an artificial magnetic conductor (AMC) structure. A novel antenna fed by a coplanar waveguide with a compact size of 15.6 × 20 mm² has been obtained after being optimized through an artificial intelligent method. A double-layer, dual-frequency AMC structure is designed to improve the isolation between the antenna and the human body. The simulation and experiment results with different bending degrees show that the antenna with the AMC structure can cover two frequency bands, 2.4 GHz–2.48 GHz and 5.725 GHz–5.875 GHz. The gain at 2.45 GHz and 5.8 GHz reaches 5.3 dBi and 8.9 dBi, respectively. The specific absorption rate has been reduced to the international standard range. In particular, this proposed SF-FDTD method can be extended to analyze other electromagnetic problems with fine details in one or two directions. Full article

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13 pages, 5333 KiB

Open AccessPerspective

Interposer-Based ESD Protection: A Potential Solution for μ-Packaging Reliability of 3D Chips

by Xunyu Li, Zijin Pan, Weiquan Hao, Runyu Miao, Zijian Yue and Albert Wang

Micromachines 2025, 16(4), 488; https://doi.org/10.3390/mi16040488 - 21 Apr 2025

Abstract

The ending of Moore’s Law calls for innovations in integrated circuit (IC) technologies and chip designs. Heterogeneous integration (HI) emerges as a pathway towards smart future chips for more Moore time and for beyond-Moore time, featuring systems-on-integrated-chiplets (SoICs) and advanced micro-packaging (μ-packaging). Reliability, [...] Read more.

The ending of Moore’s Law calls for innovations in integrated circuit (IC) technologies and chip designs. Heterogeneous integration (HI) emerges as a pathway towards smart future chips for more Moore time and for beyond-Moore time, featuring systems-on-integrated-chiplets (SoICs) and advanced micro-packaging (μ-packaging). Reliability, particularly with regard to electrostatic charge (ESD) failure, is a major challenge for 3D SoIC chips in μ-packaging, which is an emerging design-for-reliability challenge for future chips. This perspective article articulates that interposer-based ESD protection will be an important potential solution for 3D SoIC chips in μ-packaging against the devastating ESD failure problem. Full article

(This article belongs to the Special Issue Microelectronics Assembly and Packaging: Materials and Technologies, 2nd Edition)

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18 pages, 20007 KiB

Open AccessArticle

Design and Driving Characteristics of a Bidirectional Micro-Device Based on Multi-Electrothermal Co-Actuation

by Yujuan Tang, Zihao Guo, Yujiao Ding and Xinjie Wang

Micromachines 2025, 16(4), 487; https://doi.org/10.3390/mi16040487 - 21 Apr 2025

Abstract

In this paper, a bidirectional micro-device based on multi-electrothermal co-actuation is proposed for a fuze safety system, combining the advantages of the simple structure, small size, low input voltage, large output, and absence of electromagnetic interference in electrothermal actuators. Based on the working [...] Read more.

In this paper, a bidirectional micro-device based on multi-electrothermal co-actuation is proposed for a fuze safety system, combining the advantages of the simple structure, small size, low input voltage, large output, and absence of electromagnetic interference in electrothermal actuators. Based on the working principle of the multi-electrothermal co-actuation device and the mathematical model of the single V-shaped electrothermal actuator established in this paper, the temperature distribution of the V-shaped electrothermal actuator is simulated. In addition, the dynamic response and the effect of geometric factors on the output performance of the multi-electrothermal co-actuation device are analyzed in detail. Furthermore, driving characteristics tests of the electrothermal micro-device are carried out. The experimental findings indicate that a displacement of approximately 258.95 μm with a response time of about 156.51 ms can be achieved by the V-shaped electrothermal actuator when the applied voltage is 1.2 V. In a single cycle, a total displacement of 340 μm is obtained by the co-actuation device in around 1.28 s. Full article

(This article belongs to the Special Issue MEMS Actuators and Their Applications)

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16 pages, 37103 KiB

Open AccessArticle

Mechano-Filtering Encapsulation: A Stitching-Based Packaging Strategy Implementing Active Noise Suppression in Piezoresistive Pressure Sensors

by Yi Yu, Yingying Zhao, Tao Xue, Xinyi Wang and Qiang Zou

Micromachines 2025, 16(4), 486; https://doi.org/10.3390/mi16040486 - 20 Apr 2025

Abstract

Flexible pressure sensors face the dual challenges of weak signal extraction and environmental noise suppression in wearable electronics and human-machine interfaces. This research proposes an intelligent pressure sensor utilizing chitosan/carbon nanotube/melamine sponge (CS/CNT/MS) composites, achieving high-performance sensing through a dual-stage noise reduction architecture [...] Read more.

Flexible pressure sensors face the dual challenges of weak signal extraction and environmental noise suppression in wearable electronics and human-machine interfaces. This research proposes an intelligent pressure sensor utilizing chitosan/carbon nanotube/melamine sponge (CS/CNT/MS) composites, achieving high-performance sensing through a dual-stage noise reduction architecture that combines mechanical pre-filtration and electrical synergistic regulation. An innovative compressed-stitching encapsulation technique creates pressure sensors with equivalent mechanical low-pass filtering characteristics, actively eliminating interference signals below 3 kPa while maintaining linear response within the 3–20 kPa effective loading range (sensitivity: 0.053 kPa⁻¹). The synergistic effects of CS molecular cross-linking and CNTs’ three-dimensional conductive network endow the device with a 72 ms response time, 24 ms recovery speed, and over 3500-cycle compression stability. Successful applications in smart sport monitoring and tactile interactive interfaces demonstrate a material-structure-circuit co-design paradigm for mechanical perception in complex environments. Full article

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21 pages, 16024 KiB

Open AccessArticle

Posture Detection of Dual-Hemisphere Capsule Robot Based on Magnetic Tracking Effects and ORB-AEKF Algorithm

by Xu Liu, Yongshun Zhang and Qiancheng Wang

Micromachines 2025, 16(4), 485; https://doi.org/10.3390/mi16040485 - 20 Apr 2025

Abstract

Posture detection is essential for capsule robots to be manipulated in a relatively closed gastrointestinal (GI) tract and to fulfill some medical operations. In this paper, a posture detection technique for a magnetic-actuated dual-hemisphere capsule robot (DHCR) is proposed. In this method, the [...] Read more.

Posture detection is essential for capsule robots to be manipulated in a relatively closed gastrointestinal (GI) tract and to fulfill some medical operations. In this paper, a posture detection technique for a magnetic-actuated dual-hemisphere capsule robot (DHCR) is proposed. In this method, the DHCR realizes fixed-point posture adjustment based on tracking effects, and feature points are recognized and matched with the help of the ORB algorithm on the GI image acquired by a vision sensor. The system model is derived from the dynamic model and feature point information. Then, the posture is optimized by using the adaptive extended Kalman filter (AEKF) algorithm. As a result, the posture detection method based on the tracking effects and the ORB-AEKF algorithm is formed. The effectiveness and superiority of the proposed method are verified through experiments, which provide a good foundation for the subsequent, accurate closed-loop control of the DHCR. Full article

(This article belongs to the Special Issue Advanced Applications in Microrobots)

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19 pages, 14110 KiB

Open AccessArticle

A 3D DC Electric Field Meter Based on Sensor Chips Packaged Using a Highly Sensitive Scheme

by Pengfei Yang, Xiaolong Wen, Xiaonan Li, Zhaozhi Chu, Chunrong Peng and Shuang Wu

Micromachines 2025, 16(4), 484; https://doi.org/10.3390/mi16040484 - 20 Apr 2025

Abstract

This study presents a 3D DC electric field meter (EFM) that uses three identical 1D MEMS chips. The shielding electrodes and sensing electrodes of the MEMS chips employ a combination of rigid frames and short strip-type beams to improve vibrational stability. To enhance [...] Read more.

This study presents a 3D DC electric field meter (EFM) that uses three identical 1D MEMS chips. The shielding electrodes and sensing electrodes of the MEMS chips employ a combination of rigid frames and short strip-type beams to improve vibrational stability. To enhance sensitivity, our MEMS chips feature inner convex packaging covers. Moreover, the integrated design and wireless transmission efficiently eradicate the impact of ground potential on detection results. Detailed simulations have been conducted to analyze the electric field distribution within the chip package and the electric field distribution on the EFM’s surface. A prototype was then developed, calibrated, and validated. The test results indicate that the sensitivity of our proposed 3D EFM is at least 4.64 times higher than the highest sensitivity observed in previously reported MEMS 3D EFMs. The maximum relative deviation is a mere 2.2% for any rotation attitude. Remarkably, even in high humidity conditions, the EFM’s linearity remains within 1%. Additionally, the resolution of any single axis is less than 10 V/m. Full article

(This article belongs to the Special Issue MEMS/NEMS Devices and Applications, 3rd Edition)

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17 pages, 20569 KiB

Open AccessArticle

A Slanted-Finger Interdigitated Transducer Microfluidic Device for Particles Sorting

by Baoguo Liu, Xiang Ren, Tao Xue and Qiang Zou

Micromachines 2025, 16(4), 483; https://doi.org/10.3390/mi16040483 - 20 Apr 2025

Abstract

Sorting particles or cells of specific sizes in complex systems has long been a focus of many researchers. Acoustic surface waves, which generate acoustic radiation forces on particles or cells and, thus, influence their motion, are commonly used for the non-destructive separation of [...] Read more.

Sorting particles or cells of specific sizes in complex systems has long been a focus of many researchers. Acoustic surface waves, which generate acoustic radiation forces on particles or cells and, thus, influence their motion, are commonly used for the non-destructive separation of particles or cells of specific sizes. In previous studies, the frequency of acoustic surface wave generation has been limited by the interdigitated transducer (IDT). To extend the effective operating frequency range of the IDT, a slanted-finger interdigitated transducer (SFIT) with a wide acoustic path and multiple operating frequencies was designed. Compared with traditional acoustic sorting devices, which suffer from a limited frequency range and narrow acoustic paths, this new design greatly expands both the operating frequency range and acoustic path width, and enables adjustable operating frequencies, providing a solution for sorting particles or cells with uneven sizes in complex environments. The optimal resonance frequency is distributed within the 32–42 MHz range, and the operating frequencies within this range can generate a standing wave acoustic path of approximately 200

μ

m, thus enhancing the effectiveness of the operating frequencies. The microfluidic sorting device based on SFIT can efficiently and accurately sort polystyrene (PS) with particle sizes of 20

μ

m, 30

μ

m, and 50

μ

m from mixed PS microspheres (5, 10, 20

μ

m), (5, 10, 30

μ

m), and (5, 10, 50

μ

m), with a sorting efficiency and purity exceeding 96%. Additionally, the device is capable of sorting other types of mixed microspheres (5, 10, 20, 30, 50

μ

m). This new wide-acoustic-path, multi-frequency sorting device demonstrates the ability to sort particlesin a high-purity, label-free manner, offering a more alternative to traditional sorting methods. Full article

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44 pages, 9568 KiB

Open AccessReview

MEMS Varifocal Optical Elements for Focus Control

by Chen Liu, Tong Wang, Xin Wang, Manpeng Chang, Yu Jian and Weimin Wang

Micromachines 2025, 16(4), 482; https://doi.org/10.3390/mi16040482 - 19 Apr 2025

Abstract

As microelectronic devices become more prevalent daily, miniaturization is emerging as a key trend, particularly in optical systems. Optical systems with volume scanning and imaging capabilities heavily rely on focus control. The traditional focus tuning method restricts the miniaturization of optical systems due [...] Read more.

As microelectronic devices become more prevalent daily, miniaturization is emerging as a key trend, particularly in optical systems. Optical systems with volume scanning and imaging capabilities heavily rely on focus control. The traditional focus tuning method restricts the miniaturization of optical systems due to its complex structure and large volume. The recent rapid development of MEMS varifocal optical elements has provided sufficient opportunities for miniaturized optical systems. Here, we review the literature on MEMS varifocal optical elements over the past two decades. Based on light control mechanisms, MEMS varifocal optical elements are divided into three categories: reflective varifocal mirrors, varifocal microlenses, and phased varifocal mirrors. A novel indicator is introduced to evaluate and compare the performance of MEMS varifocal optical elements. A wide range of applications is also discussed. This review can serve as a reference for relevant researchers and engineers. Full article

(This article belongs to the Section A1: Optical MEMS and Photonic Microsystems)

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17 pages, 6680 KiB

Open AccessArticle

Research on Machining Parameter Optimization and an Electrode Wear Compensation Method of Microgroove Micro-EDM

by Xiaodong Zhang, Wentong Zhang, Peng Yu and Yiquan Li

Micromachines 2025, 16(4), 481; https://doi.org/10.3390/mi16040481 - 18 Apr 2025

Abstract

In the process of micro-EDM, tool electrode wear is inevitable, especially for complex three-dimensional cavities or microgroove structures. Tool electrode wear accumulates during machining, which will finally affect machining accuracy and machining quality. It is necessary to reduce electrode wear and compensate it [...] Read more.

In the process of micro-EDM, tool electrode wear is inevitable, especially for complex three-dimensional cavities or microgroove structures. Tool electrode wear accumulates during machining, which will finally affect machining accuracy and machining quality. It is necessary to reduce electrode wear and compensate it through micro-EDM. Therefore, based on an established L27 orthogonal experiment, this paper uses the grey relational analysis (GRA) method to realize multi-objective optimization of machining time and electrode wear, so as to achieve the shortest machining time and the minimum electrode wear during machining under the optimal machining parameter combination. Then, the orthogonal experiment results are used as dataset of artificial neural networks (ANNs), and an ANN prediction model is established. Combined with image processing technology, the bottom profile of the machined microgroove is extracted and then an electrode axial wear compensation equation is fitted, and a fixed-length nonlinear compensation method for electrode axial wear is proposed. Finally, the GRA optimal experiment shows that machining time, electrode axial wear and radial wear are reduced by 13.89%, 3.31%, and 10.80%, respectively, compared with the H17 orthogonal experiment with the largest grey relational grade. For the study of electrode axial wear compensation methods, the consistency of the depth and width of the machined microgroove structure with compensation is significantly better than that of the microgroove structure without compensation. This result shows that the proposed fixed-length nonlinear compensation method can effectively compensate electrode axial wear in micro-EDM and improve machining quality to a certain extent. Full article

(This article belongs to the Special Issue Emerging Micro Manufacturing Technologies and Applications, 3rd Edition)

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18 pages, 6869 KiB

Open AccessArticle

A Trimming Strategy for Mass Defects in Hemispherical Resonators Based on Multi-Harmonic Analysis

by Yimo Chen, Fanrui Kong, Kai Zeng, Xiang Xi, Yan Shi, Dingbang Xiao and Xuezhong Wu

Micromachines 2025, 16(4), 480; https://doi.org/10.3390/mi16040480 - 18 Apr 2025

Abstract

This study investigates the impact of etching trimming parameters on the multiple harmonics of the mass distribution in hemispherical resonators and proposes a novel 1st harmonic trimming scheme. As mass balancing technology advances, the extension of identification and trimming from frequency split to [...] Read more.

This study investigates the impact of etching trimming parameters on the multiple harmonics of the mass distribution in hemispherical resonators and proposes a novel 1st harmonic trimming scheme. As mass balancing technology advances, the extension of identification and trimming from frequency split to multiple harmonics remains a challenge. Initially, a multi-harmonic identification scheme based on spurious mode detection was established, considering the influence of the first three harmonics of the mass distribution on the dynamic characteristics of hemispherical resonators. Finite element method modeling and analysis revealed that common structural geometric errors significantly introduce the 1st harmonic. By integrating a rectangular pulse function into the mass distribution function to simulate etching grooves, spectral analysis revealed that groove depth and width determine the amplitude and gradient of introduced harmonics. This research introduces an innovative discrete trimming scheme aimed at addressing the frequency split and mode mismatch issues associated with traditional single-point trimming of the 1st harmonic. By decomposing the trimming task into primary and auxiliary etching grooves, the 4th harmonic introduced by the primary etching is compensated by the secondary 4th harmonic introduced by the auxiliary etching, achieving decoupling of the 1st harmonic from frequency split during the trimming process. The scheme was verified through finite element simulations and experimental testing. Results demonstrate that, for a similar reduction in the 1st harmonic, the variation in frequency split during the discrete trimming process is only 11% of that observed in single-point trimming, facilitating efficient and low-damage trimming of the 1st harmonic. Full article

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14 pages, 2091 KiB

Open AccessArticle

Influence of Oil Viscosity on Hysteresis Effect in Electrowetting Displays Based on Simulation

by Wei Li, Linwei Liu, Taiyuan Zhang, Lixia Tian, Li Wang, Cheng Xu, Jianwen Lu, Zichuan Yi and Guofu Zhou

Micromachines 2025, 16(4), 479; https://doi.org/10.3390/mi16040479 - 18 Apr 2025

Abstract

As the most promising new reflective display technology, electrowetting displays (EWDs) have the advantages of a simple structure, fast response, high contrast, and rich colors. However, due to the hysteresis effect, the grayscales of EWDs cannot be accurately controlled, which seriously restricts the [...] Read more.

As the most promising new reflective display technology, electrowetting displays (EWDs) have the advantages of a simple structure, fast response, high contrast, and rich colors. However, due to the hysteresis effect, the grayscales of EWDs cannot be accurately controlled, which seriously restricts the industrialization process of this technology. In this paper, the oil movement process in an EWD pixel cell was simulated, and the influence of oil viscosity on the hysteresis effect was studied based on the proposed simulation model. Firstly, the cause of the hysteresis effect was analyzed through the hysteresis curve of an EWD. Then, based on the COMSOL Multiphysics simulation environment, the oil movement process in an EWD pixel cell was simulated by coupling the phase field of laminar two-phase flow and electrostatic field. Finally, based on the simulation model, the influence of oil viscosity on the hysteresis effect in an EWD pixel cell was studied. We observed that the maximum hysteresis difference in the hysteresis effect increased with the increase in oil viscosity and decreased with the decrease in oil viscosity. The oil viscosity had little effect on the maximum aperture ratio of EWD. The pixel-on response time and pixel-off response time increased with the increase in oil viscosity. Full article

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30 pages, 9650 KiB

Open AccessArticle

Kinetostatic Modeling and Workspace Analysis of Redundant Actuated n-4R Compliant Parallel Pointing Mechanism

by Jun Ren, Yikang Shu and Youwei Lin

Micromachines 2025, 16(4), 478; https://doi.org/10.3390/mi16040478 - 18 Apr 2025

Abstract

The workspace of the compliant parallel mechanism (CPM) is generally limited due to the small deformation range of flexible hinges, which are usually at the micro/nano scale. This paper takes the 2-DOFs n-4R compliant parallel pointing mechanism (n-4R CPPM) as [...] Read more.

The workspace of the compliant parallel mechanism (CPM) is generally limited due to the small deformation range of flexible hinges, which are usually at the micro/nano scale. This paper takes the 2-DOFs n-4R compliant parallel pointing mechanism (n-4R CPPM) as the object and optimizes the workspace performance of the mechanism through redundant actuation, aiming to maximize the workspace. First, the kinetostatic model and the flexible hinge displacement model of the redundant actuated n-4R CPPM are established, successively. The former model reveals the relationships between the output displacements and the input forces/displacements, while the latter relates the flexible hinge deformation and the input forces/displacements. Second, a space pointing trajectory is chosen to validate the accuracy of the kinetostatic model of the redundant actuated 3-4R CPPM through finite element (FE) simulation. The results show that the relative error between the analytical and the FE results does not exceed 2.1%, and the high consistency indicates the accuracy of the kinetostatic model. Finally, the workspace performance of the 3-4R and 4-4R CPPMs is successively optimized through redundant actuation. The results indicate that, compared with the non-redundant actuation case, the workspace can be effectively enlarged and become more symmetric by means of the redundant actuation. The maximum achievable pitch angle ψ_a and the y-direction motion range of the mobile platform both increase by 100%. Moreover, it is shown that the workspace in the non-redundant actuated case is a subset of the workspace in the redundant actuated case, and the position-workspace shape changes from planar to 3-D. Full article

(This article belongs to the Special Issue Advanced Applications in Microrobots)

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14 pages, 19446 KiB

Open AccessArticle

Wide-Range, Washable Piezoresistive Pressure Sensor Based on MCNT-PDMS Dip-Coated PDMS Sponge

by Kun Luo, Xinyi Wang, Tao Xue, Yingying Zhao and Qiang Zou

Micromachines 2025, 16(4), 477; https://doi.org/10.3390/mi16040477 - 17 Apr 2025

Abstract

Flexible pressure sensors have great potential for wearable applications such as human health monitoring and human–computer interaction, which require different trade-offs between the sensitivity and operating range. However, preparing washable and wide-range piezoresistive pressure sensors remains a great challenge. Here, we developed a [...] Read more.

Flexible pressure sensors have great potential for wearable applications such as human health monitoring and human–computer interaction, which require different trade-offs between the sensitivity and operating range. However, preparing washable and wide-range piezoresistive pressure sensors remains a great challenge. Here, we developed a porous flexible elastomer sponge based on a carbon nanotube composite network coating for pressure sensors with extremely high stability and washability over a wide range. Specifically, a sugar template was used to fabricate a homogeneous macroporous PDMS sponge as a substrate, and a dip-coated MCNT-PDMS composite was used as a conductive layer. The high degree of adhesion formed between the substrate and the conductive layer resulted in a sponge with greatly enhanced mechanical properties and stability, while improving the operating range. The pressure sensors exhibited a broad operating range of 0–650 kPa, demonstrating excellent sensitivity (0.0049 kPa⁻¹ in the range of 0–74 kPa, 0.0010 kPa⁻¹ in the range of 74–310 kPa, and 0.0004 kPa⁻¹ in the range of 310–650 kPa), as well as a fast response time of 143 ms and recovery time of 73 ms, long-term cycling stability of over 10,000 cycles, and excellent washable stability. Finally, we demonstrate that the sensors can be applied to gesture monitoring, human motion gait monitoring, and cycling pressure monitoring. Full article

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17 pages, 9262 KiB

Open AccessArticle

Infrared Absorption of Laser Patterned Sapphire Al₂O₃ for Radiative Cooling

by Nan Zheng, Daniel Smith, Soon Hock Ng, Hsin-Hui Huang, Dominyka Stonytė, Dominique Appadoo, Jitraporn Vongsvivut, Tomas Katkus, Nguyen Hoai An Le, Haoran Mu, Yoshiaki Nishijima, Lina Grineviciute and Saulius Juodkazis

Micromachines 2025, 16(4), 476; https://doi.org/10.3390/mi16040476 - 16 Apr 2025

Abstract

The reflectance (R) of linear and circular micro-gratings on c-plane sapphire Al₂O₃ ablated by a femtosecond (fs) laser were spectrally characterised for thermal emission

\propto (1 - R)

in the mid-to-far infrared (IR) spectral range. An [...] Read more.

The reflectance (R) of linear and circular micro-gratings on c-plane sapphire Al₂O₃ ablated by a femtosecond (fs) laser were spectrally characterised for thermal emission

\propto (1 - R)

in the mid-to-far infrared (IR) spectral range. An IR camera was used to determine the blackbody radiation temperature from laser-patterned regions, which showed (3–6)% larger emissivity dependent on the grating pattern. The azimuthal emission curve closely followed the Lambertian angular profile

\propto cos θ_{a}

at the 7.5–13 μm emission band. The back-side ablation method on transparent substrates was employed to prevent debris formation during energy deposition as it applies a forward pressure of >0.3 GPa to the debris and molten skin layer. The back-side ablation maximises energy deposition at the exit interface where the transition occurs from the high-to-low refractive index. Phononic absorption in the Reststrahlen region 20–30 μm can be tailored with the fs laser inscription of sensor structures/gratings. Full article

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17 pages, 12485 KiB

Open AccessArticle

Research and Experimentation on Acoustic Monitoring Technology for Laser Drilling Penetration

by Bowen Lian, Kewen Pan, Liqun Wang, Liwu Shi, Jianhua Yao and Wei Guo

Micromachines 2025, 16(4), 475; https://doi.org/10.3390/mi16040475 - 16 Apr 2025

Abstract

To prevent back wall damage in cavity workpieces during laser drilling, it is crucial to monitor hole penetration status in real time. This study proposes a laser drilling penetration monitoring method based on acoustic principles. First, the acoustic module parameters of the system [...] Read more.

To prevent back wall damage in cavity workpieces during laser drilling, it is crucial to monitor hole penetration status in real time. This study proposes a laser drilling penetration monitoring method based on acoustic principles. First, the acoustic module parameters of the system were simulated and calibrated using COMSOL Multiphysics (version 6.1) software, resulting in an optimal sound source frequency of 35 kHz and an incident angle of 30° for the acoustic waves. Next, a nickel-based alloy laser drilling acoustic monitoring platform was designed and constructed, and the system’s upper computer control software was developed. Subsequent drilling trials were performed on the validated platform. During the experiments, the threshold for hole penetration signals under the specified experimental parameters was determined, enabling the acquisition of acoustic signals and the identification of hole penetration status. Furthermore, a correlation between the intensity of the acoustic signals and the exit aperture of the drilled holes was established. The results demonstrate the feasibility of using acoustic principles to monitor hole penetration status and measure machining aperture, providing both theoretical and experimental foundations for active laser drilling to prevent back wall damage. Full article

(This article belongs to the Special Issue Optical and Laser Material Processing, 2nd Edition)

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