Micromachines

17 pages, 4312 KiB

Open AccessArticle

Study on Electrical Characteristics and ECG Signal Acquisition Performance of Fabric Electrodes Based on Organizational Structure and Wearing Pressure

by Ming Wang, Jinli Zhou and Ge Zhang

Micromachines 2025, 16(7), 821; https://doi.org/10.3390/mi16070821 - 17 Jul 2025

Abstract

Obtaining stable ECG signals under both static and dynamic conditions, while ensuring comfortable wear, is a prerequisite for fabric-electrode applications. It is necessary to study the wearing pressure of fabric electrodes as well as their organizational structure. In this study, fabric electrodes with [...] Read more.

Obtaining stable ECG signals under both static and dynamic conditions, while ensuring comfortable wear, is a prerequisite for fabric-electrode applications. It is necessary to study the wearing pressure of fabric electrodes as well as their organizational structure. In this study, fabric electrodes with different organizational structures (plain weave, twill weave, and satin weave) were prepared using silver-plated nylon conductive yarns as weft yarns and polyester yarns as warp yarns. The electrical characteristics of these structures of fabric electrodes were analyzed under different wearing pressures (2 kPa, 3 kPa, 4 kPa, and 5 kPa), and their effects on the quality of static and dynamic ECG signals acquired from human body were examined. The results showed that the contact impedance of the twill and satin weave structured electrodes with the skin was smaller and more stable than that of the plain weave structured electrodes. Furthermore, when a wearing pressure of 3–4 kPa was applied to the satin-structured electrodes, they not only provided satisfactory comfort but also collected stable static and dynamic ECG signals during daily exercise. These results can provide a reference for the application of fabric electrodes in ECG monitoring devices and an important basis for the design of intelligent ECG clothing. Full article

(This article belongs to the Special Issue Advances in Flexible and Wearable Electronics: Devices and Systems)

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27 pages, 5856 KiB

Open AccessReview

MXene-Based Gas Sensors for NH₃ Detection: Recent Developments and Applications

by Yiyang Xu, Yinglin Wang, Zhaohui Lei, Chen Wang, Xiangli Meng and Pengfei Cheng

Micromachines 2025, 16(7), 820; https://doi.org/10.3390/mi16070820 (registering DOI) - 17 Jul 2025

Abstract

Ammonia, as a toxic and corrosive gas, is widely present in industrial emissions, agricultural activities, and disease biomarkers. Detecting ammonia is of vital importance to environmental safety and human health. Sensors based on MXene have become an effective means for detecting ammonia gas [...] Read more.

Ammonia, as a toxic and corrosive gas, is widely present in industrial emissions, agricultural activities, and disease biomarkers. Detecting ammonia is of vital importance to environmental safety and human health. Sensors based on MXene have become an effective means for detecting ammonia gas due to their unique hierarchical structure, adjustable surface chemical properties, and excellent electrical conductivity. This study reviews the latest progress in the use of MXene and its composites for the low-temperature detection of ammonia gas. The strategies for designing MXene composites, including heterojunction engineering, surface functionalization, and active sites, are introduced, and their roles in improving sensing performance are clarified. These methods have significantly improved the ability to detect ammonia, offering high selectivity, rapid responses, and ultra-low detection limits within the low-temperature range. Successful applications in fields such as industrial safety, food quality monitoring, medical diagnosis, and agricultural management have demonstrated the multi-functionality of this technology in complex scenarios. The challenges related to the material’s oxidation resistance, humidity interference, and cross-sensitivity are also discussed. This study aims to briefly describe the reasonable design based on MXene sensors, aiming to achieve real-time and energy-saving environmental and health monitoring networks in the future. Full article

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14 pages, 4871 KiB

Open AccessArticle

Study on Laser Surface Texturing and Wettability Control of Silicon Nitride Ceramic

by Hong-Jian Wang, Jing-De Huang, Bo Wang, Yang Zhang and Jin Wang

Micromachines 2025, 16(7), 819; https://doi.org/10.3390/mi16070819 - 17 Jul 2025

Abstract

Silicon nitride (Si₃N₄) ceramic is widely used in the production of structural components. The surface wettability is closely related to the service life of materials. Laser surface texturing is considered an effective method for controlling surface wettability by processing [...] Read more.

Silicon nitride (Si₃N₄) ceramic is widely used in the production of structural components. The surface wettability is closely related to the service life of materials. Laser surface texturing is considered an effective method for controlling surface wettability by processing specific patterns. This research focused on the laser surface texturing of a Si₃N₄ ceramic, employing rectangular patterns instead of the typical dimple designs, as these had promising applications in heat transfer and hydrodynamic lubrication. The effects of scanning speed and number of scans on the change of the morphologies and dimensions of the grooves were investigated. The results indicated that the higher scanning speed and fewer number of scans resulted in less damage to the textured surface. As the scanning speed increased, the width and depth of the grooves decreased significantly first, and then fluctuated. Conversely, increasing the number of scans led to an increase in the width and depth of the grooves, eventually stabilizing. The analysis of the elemental composition of different areas on the textured surface presented a notable increase in oxygen content at the grooves, while Si and N levels decreased. It was mainly caused by the chemical reaction between Si₃N₄ ceramic and oxygen during laser surface texturing in an air environment. This study also assessed the wettability of the textured surface, finding that the contact angle of the water droplet was significantly affected by the groove dimensions. After laser surface texturing, the contact angle increased from 35.51 ± 0.33° to 57.52 ± 1.83°. Improved wettability was associated with smaller groove volume, indicating better hydrophilicity at lower scanning speed and enhanced hydrophobicity with a fewer number of scans. Full article

(This article belongs to the Special Issue Advances in Digital Manufacturing and Nano Fabrication)

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41 pages, 2729 KiB

Open AccessReview

Memristor Emulator Circuits: Recent Advances in Design Methodologies, Healthcare Applications, and Future Prospects

by Amel Neifar, Imen Barraj, Hassen Mestiri and Mohamed Masmoudi

Micromachines 2025, 16(7), 818; https://doi.org/10.3390/mi16070818 - 17 Jul 2025

Abstract

Memristors, as the fourth fundamental circuit element, have attracted significant interest for their potential in analog signal processing, computing, and memory storage technologies. However, physical memristor implementations still face challenges in reproducibility, scalability, and integration with standard CMOS processes. Memristor emulator circuits, implemented [...] Read more.

Memristors, as the fourth fundamental circuit element, have attracted significant interest for their potential in analog signal processing, computing, and memory storage technologies. However, physical memristor implementations still face challenges in reproducibility, scalability, and integration with standard CMOS processes. Memristor emulator circuits, implemented using analog, digital, and mixed components, have emerged as practical alternatives, offering tunability, cost effectiveness, and compatibility with existing fabrication technologies for research and prototyping. This review paper provides a comprehensive analysis of recent advancements in memristor emulator design methodologies, including active and passive analog circuits, digital implementations, and hybrid approaches. A critical evaluation of these emulation techniques is conducted based on several performance metrics, including maximum operational frequency range, power consumption, and circuit topology. Additional parameters are also taken into account to ensure a comprehensive assessment. Furthermore, the paper examines promising healthcare applications of memristor and memristor emulators, focusing on their integration into biomedical systems. Finally, key challenges and promising directions for future research in memristor emulator development are outlined. Overall, the research presented highlights the promising future of memristor emulator technology in bridging the gap between theoretical memristor models and practical circuit implementations. Full article

(This article belongs to the Section E：Engineering and Technology)

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10 pages, 2486 KiB

Open AccessArticle

Performance of Miniature Carbon Nanotube Field Emission Pressure Sensor for X-Ray Source Applications

by Huizi Zhou, Wenguang Peng, Weijun Huang, Nini Ye and Changkun Dong

Micromachines 2025, 16(7), 817; https://doi.org/10.3390/mi16070817 - 17 Jul 2025

Abstract

There is a lack of an effective approach to measure vacuum conditions inside sealed vacuum electronic devices (VEDs) and other small-space vacuum instruments. In this study, the application performance of an innovative low-pressure gas sensor based on the emission enhancements of multi-walled carbon [...] Read more.

There is a lack of an effective approach to measure vacuum conditions inside sealed vacuum electronic devices (VEDs) and other small-space vacuum instruments. In this study, the application performance of an innovative low-pressure gas sensor based on the emission enhancements of multi-walled carbon nanotube (MWCNT) field emitters was investigated, and the in situ vacuum performance of X-ray tubes was studied for the advantages of miniature dimension and having low power consumption, extremely low outgassing, and low thermal disturbance compared to conventional ionization gauges. The MWCNT emitters with high crystallinity presented good pressure sensing performance for nitrogen, hydrogen, and an air mixture in the range of 10⁻⁷ to 10⁻³ Pa. The miniature MWCNT sensor is able to work and remain stable with high-temperature baking, important for VED applications. The sensor monitored the in situ pressures of the sealed X-ray tubes successfully with high-power operations and a long-term storage of over two years. The investigation showed that the vacuum of the sealed X-ray tube is typical at a low 10⁻⁴ Pa level, and pre-sealing degassing treatments are able to make the X-ray tube work under high vacuum levels with less outgassing and keep a stable high vacuum for a long period of time. Full article

(This article belongs to the Section D：Materials and Processing)

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14 pages, 7197 KiB

Open AccessArticle

Study on Self-Sharpening Mechanism and Polishing Performance of Triethylamine Alcohol on Gel Polishing Discs

by Yang Lei, Lanxing Xu and Kaiping Feng

Micromachines 2025, 16(7), 816; https://doi.org/10.3390/mi16070816 - 16 Jul 2025

Viewed by 53

Abstract

To address the issue of surface glazing that occurs during prolonged polishing with gel tools, this study employs a triethanolamine (TEA)-based polishing fluid system to enhance the self-sharpening capability of the gel polishing disc. The inhibitory mechanism of TEA concentration on disc glazing [...] Read more.

To address the issue of surface glazing that occurs during prolonged polishing with gel tools, this study employs a triethanolamine (TEA)-based polishing fluid system to enhance the self-sharpening capability of the gel polishing disc. The inhibitory mechanism of TEA concentration on disc glazing is systematically analyzed, along with its impact on the gel disc’s frictional wear behaviour. Furthermore, the synergistic effects of process parameters on both surface quality and material removal rate (MRR) of SiC are examined. The results demonstrate that TEA concentration is a critical factor in regulating polishing performance. At an optimal concentration of 4 wt%, an ideal balance between chemical chelation and mechanical wear is achieved, effectively preventing glazing while avoiding excessive tool wear, thereby ensuring sustained self-sharpening capability and process stability. Through orthogonal experiment optimization, the best parameter combination for SiC polishing is determined: 4 wt% TEA concentration, 98 N polishing pressure, and 90 rpm rotational speed. This configuration delivers both superior surface quality and desirable MRR. Experimental data confirm that TEA significantly enhances the self-sharpening performance of gel discs through its unique complex reaction. During the rough polishing stage, the MRR increases by 34.9% to 0.85 μm/h, while the surface roughness S_a is reduced by 51.3% to 6.29 nm. After subsequent CMP fine polishing, an ultra-smooth surface with a final roughness of 2.33 nm is achieved. Full article

(This article belongs to the Special Issue Ultra-Precision Surface Abrasive Micro-Machining: Advances and Applications)

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16 pages, 11669 KiB

Open AccessArticle

Design and Electromagnetic Performance Optimization of a MEMS Miniature Outer-Rotor Permanent Magnet Motor

by Kaibo Lei, Haiwang Li, Shijia Li and Tiantong Xu

Micromachines 2025, 16(7), 815; https://doi.org/10.3390/mi16070815 - 16 Jul 2025

Viewed by 137

Abstract

In this study, we present the design and electromagnetic performance optimization of a micro-electromechanical system (MEMS) miniature outer-rotor permanent magnet motor. With increased attention towards higher torque density and lower torque pulsations in MEMS micromotor designs, an adaptation of an external rotor can [...] Read more.

In this study, we present the design and electromagnetic performance optimization of a micro-electromechanical system (MEMS) miniature outer-rotor permanent magnet motor. With increased attention towards higher torque density and lower torque pulsations in MEMS micromotor designs, an adaptation of an external rotor can be highly attractive. However, with the design complexity involved in such high-performance MEMS outer-rotor motor designs, the ultra-miniature 3D coil structures and the thin-film topology surrounding the air gap have been one of the main challenges. In this study, an ultra-thin outer-rotor motor with 3D MEMS silicon-based coils and a MEMS-compatible manufacturing method for the 3D coils is presented. Additionally, finite element simulations are conducted for the thin-film topology around the air gap to optimize performance characteristics such as torque developed, torque pulsations, and back electromotive force amplitude. Ultimately, the average magnetic flux density increased by 37.1%, from 0.361 T to 0.495 T. The root mean square (RMS) value of the back EMF per phase rises by 14.4%. Notably, the average torque is improved by 11.3%, while the torque ripple is significantly reduced from 1.281 mNm to 0.74 mNm, corresponding to a reduction of 49.9% in torque ripple percentage. Full article

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19 pages, 4958 KiB

Open AccessArticle

Understanding the Nanoindentation Edge Effect of Single-Crystal Silicon Using Molecular Dynamics Simulations

by Chao Long, Ruihan Li, Pengyue Zhao, Ziteng Li, Shuhao Kang, Duo Li and Huan Liu

Micromachines 2025, 16(7), 814; https://doi.org/10.3390/mi16070814 - 16 Jul 2025

Viewed by 105

Abstract

The edge effect refers to what occurs when an object undergoes elastic contact with the edge of a material. This is common in practical applications, but the understanding of this phenomenon is not yet mature enough, and understanding the microscopic characteristics of the [...] Read more.

The edge effect refers to what occurs when an object undergoes elastic contact with the edge of a material. This is common in practical applications, but the understanding of this phenomenon is not yet mature enough, and understanding the microscopic characteristics of the material regarding this phenomenon is necessary. This article investigates the edge effects of single-crystal silicon at different indentation positions through molecular dynamics simulations. The results indicate that the edge effect of the indentation is influenced by the indentation position and depth. The closer the indentation head is to the edge of the workpiece, the more particles are extruded from the side of the workpiece and the wider the collapse range of the indentation surface. At the same time, the indentation position also affects the distribution of the von Mises stress and phase transition area. When the edge effect occurs, the von Mises stress and phase transition region tend to be concentrated near the workpiece edge. This study demonstrates the atomic-scale deformation mechanism of single-crystal silicon under varying indentation positions. Full article

(This article belongs to the Special Issue Recent Advances in Nanoindentation Techniques)

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38 pages, 5046 KiB

Open AccessReview

Photonics on a Budget: Low-Cost Polymer Sensors for a Smarter World

by Muhammad A. Butt

Micromachines 2025, 16(7), 813; https://doi.org/10.3390/mi16070813 - 15 Jul 2025

Viewed by 230

Abstract

Polymer-based photonic sensors are emerging as cost-effective, scalable alternatives to conventional silicon and glass photonic platforms, offering unique advantages in flexibility, functionality, and manufacturability. This review provides a comprehensive assessment of recent advances in polymer photonic sensing technologies, focusing on material systems, fabrication [...] Read more.

Polymer-based photonic sensors are emerging as cost-effective, scalable alternatives to conventional silicon and glass photonic platforms, offering unique advantages in flexibility, functionality, and manufacturability. This review provides a comprehensive assessment of recent advances in polymer photonic sensing technologies, focusing on material systems, fabrication techniques, device architectures, and application domains. Key polymer materials, including PMMA, SU-8, polyimides, COC, and PDMS, are evaluated for their optical properties, processability, and suitability for integration into sensing platforms. High-throughput fabrication methods such as nanoimprint lithography, soft lithography, roll-to-roll processing, and additive manufacturing are examined for their role in enabling large-area, low-cost device production. Various photonic structures, including planar waveguides, Bragg gratings, photonic crystal slabs, microresonators, and interferometric configurations, are discussed concerning their sensing mechanisms and performance metrics. Practical applications are highlighted in environmental monitoring, biomedical diagnostics, and structural health monitoring. Challenges such as environmental stability, integration with electronic systems, and reproducibility in mass production are critically analyzed. This review also explores future opportunities in hybrid material systems, printable photonics, and wearable sensor arrays. Collectively, these developments position polymer photonic sensors as promising platforms for widespread deployment in smart, connected sensing environments. Full article

(This article belongs to the Section A：Physics)

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9 pages, 2576 KiB

Open AccessArticle

Novel Debris Material Identification Method Based on Impedance Microsensor

by Haotian Shi, Yucai Xie and Hongpeng Zhang

Micromachines 2025, 16(7), 812; https://doi.org/10.3390/mi16070812 - 14 Jul 2025

Viewed by 107

Abstract

Oil condition monitoring can ensure the safe operation of mechanical equipment. Metal debris is full of friction information, and the identification of debris material helps to locate wear of parts. A method based on impedance analysis is proposed to identify debris material in [...] Read more.

Oil condition monitoring can ensure the safe operation of mechanical equipment. Metal debris is full of friction information, and the identification of debris material helps to locate wear of parts. A method based on impedance analysis is proposed to identify debris material in this article. The differences in permeability and conductivity result in the nonlinear variation trend of inductance–resistance amplitude with debris volume. By establishing a database of amplitude–size curves, debris information (material and size) can be obtained through impedance analysis. Based on experimental and simulation results, iron, stainless steel, aluminum, copper, and brass particles are effectively distinguished. This method is not affected by oil’s light transmittance, other impurities, and debris surface dirt and can be used to distinguish metals with similar colors. This work provides a novel solution for debris material identification, which is expected to promote the development of fault diagnosis. Full article

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

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25 pages, 10123 KiB

Open AccessArticle

Fabrication of Micro-Holes with High Aspect Ratios in C_f/SiC Composites Using Coaxial Waterjet-Assisted Nanosecond Laser Drilling

by Chenhu Yuan, Zenggan Bian, Yue Cao, Yinan Xiao, Bin Wang, Jianting Guo and Liyuan Sheng

Micromachines 2025, 16(7), 811; https://doi.org/10.3390/mi16070811 - 14 Jul 2025

Viewed by 88

Abstract

In the present study, the coaxial waterjet-assisted nanosecond laser drilling of micro-holes in C_f/SiC composites, coupled with nanosecond laser drilling in air for fabricating micro-holes with high aspect ratios, were investigated. The surface morphology, reaction products, and micro-hole shapes were thoroughly [...] Read more.

In the present study, the coaxial waterjet-assisted nanosecond laser drilling of micro-holes in C_f/SiC composites, coupled with nanosecond laser drilling in air for fabricating micro-holes with high aspect ratios, were investigated. The surface morphology, reaction products, and micro-hole shapes were thoroughly examined. The results reveal that, for the coaxial waterjet-assisted nanosecond laser drilling of micro-holes in the C_f/SiC composite, the increasing of waterjet velocity enhances the material removal rate and micro-hole depth, but reduces the micro-hole diameter and taper angle. The coaxial waterjet isolates the laser-ablated region and cools down the corresponding region rapidly, leading to the formation of a mixture of SiC, SiO₂, and Si on the surface. As the coaxial waterjet velocity increases, the morphology of residual surface products changes from a net-like structure to individual spheres. Coaxial waterjet-assisted nanosecond laser drilling, with a waterjet velocity of 9.61 m/s, achieves micro-holes with a good balance between efficiency and quality. For the fabrication of micro-holes with a high aspect ratio in C_f/SiC composites, micro-holes fabricated by nanosecond laser drilling in air exhibit obvious taper features, which should be ascribed to the combined effects of spattering slag, plasma, and energy dissipation. The application of coaxial waterjet-assisted nanosecond laser drilling on micro-holes fabricated by laser drilling in air effectively expands the hole diameter. The fabricated micro-holes have very small taper angles, with clean wall surfaces and almost no reaction products. This approach, combining nanosecond laser drilling in air followed by coaxial waterjet-assisted nanosecond laser drilling, offers a promising technique for fabricating high-quality micro-holes with high aspect ratios in C_f/SiC composites. Full article

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

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11 pages, 2799 KiB

Open AccessArticle

Development of LPFG-Based Seawater Concentration Monitoring Sensors Packaged by BFRP

by Zhe Zhang, Tongchun Qin, Yuping Bao and Jianping He

Micromachines 2025, 16(7), 810; https://doi.org/10.3390/mi16070810 - 14 Jul 2025

Viewed by 147

Abstract

Leveraging the sensitivity of long-period fiber grating (LPFG) to changes in the environmental refractive index, an LPFG-based seawater concentration monitoring sensor is proposed. Considering the highly saltine and alkali characteristics of the sensor’s operating environment, the proposed sensor is packaged by basalt fiber-reinforced [...] Read more.

Leveraging the sensitivity of long-period fiber grating (LPFG) to changes in the environmental refractive index, an LPFG-based seawater concentration monitoring sensor is proposed. Considering the highly saltine and alkali characteristics of the sensor’s operating environment, the proposed sensor is packaged by basalt fiber-reinforced polymer (BFRP), and the sensor’s sensitivities were studied by sodium chloride and calcium chloride solution concentration experiments and one real-time sodium chloride solution concentration monitoring experiment. The test results show the wavelength of LPFG, a 3 dB bandwidth and a peak loss of LPFG’s spectrogram change with changes in the concentration of sodium chloride or calcium chloride solutions, but only the wavelength has a good linear relationship with the change in solution concentration, and the sensing coefficient is −0.160 nm/% in the sodium chloride solution and −0.225 nm/% in the calcium chloride solution. The real-time monitoring test further verified the sensor’s sensing performance, with an absolute measurement error of less than 1.8%. The BFRP packaged sensor has good corrosion resistance and a simple structure, and it has a certain application value in the monitoring of salinity in the marine environment and coastal soil. Full article

(This article belongs to the Special Issue MEMS Sensors and Actuators: Design, Fabrication and Applications, 2nd Edition)

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20 pages, 23222 KiB

Open AccessArticle

A Multi-View Three-Dimensional Scanning Method for a Dual-Arm Hand–Eye System with Global Calibration of Coded Marker Points

by Tenglong Zheng, Xiaoying Feng, Siyuan Wang, Haozhen Huang and Shoupeng Li

Micromachines 2025, 16(7), 809; https://doi.org/10.3390/mi16070809 - 13 Jul 2025

Viewed by 257

Abstract

To achieve robust and accurate collaborative 3D measurement under complex noise conditions, a global calibration method for dual-arm hand–eye systems and multi-view 3D imaging is proposed. A multi-view 3D scanning approach based on ICP (M3DHE-ICP) integrates a multi-frequency heterodyne coding phase solution with [...] Read more.

To achieve robust and accurate collaborative 3D measurement under complex noise conditions, a global calibration method for dual-arm hand–eye systems and multi-view 3D imaging is proposed. A multi-view 3D scanning approach based on ICP (M3DHE-ICP) integrates a multi-frequency heterodyne coding phase solution with ICP optimization, effectively correcting stitching errors caused by robotic arm attitude drift. After correction, the average 3D imaging error is 0.082 mm, reduced by 0.330 mm. A global calibration method based on encoded marker points (GCM-DHE) is also introduced. By leveraging spatial geometry constraints and a dynamic tracking model of marker points, the transformation between multi-coordinate systems of the dual arms is robustly solved. This reduces the average imaging error to 0.100 mm, 0.456 mm lower than that of traditional circular calibration plate methods. In actual engineering measurements, the average error for scanning a vehicle’s front mudguard is 0.085 mm, with a standard deviation of 0.018 mm. These methods demonstrate significant value for intelligent manufacturing and multi-robot collaborative measurement. Full article

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19 pages, 5491 KiB

Open AccessArticle

Design of an Angled Single-Excitation Elliptical Vibration System

by Qiang Liu, Xiping He, Weiguo Wang and Yanning Yang

Micromachines 2025, 16(7), 808; https://doi.org/10.3390/mi16070808 - 13 Jul 2025

Viewed by 123

Abstract

An angled single-excitation elliptical vibration system for ultrasonic-assisted machining was developed in this paper, which was composed of a giant magnetostrictive transducer and an angled horn. Based on the continuous boundary conditions between the components, the frequency equation of the angled vibration system [...] Read more.

An angled single-excitation elliptical vibration system for ultrasonic-assisted machining was developed in this paper, which was composed of a giant magnetostrictive transducer and an angled horn. Based on the continuous boundary conditions between the components, the frequency equation of the angled vibration system was derived, and the resonant frequencies of vibration systems with different angles were theoretically calculated. The finite element method was employed to investigate the impact of varying angles on the resonant frequency, elliptical trajectory, phase difference, and output amplitude of the vibration systems. The electrical impedance of the vibration system and the longitudinal and transverse vibration amplitudes at the end face of the horn were tested experimentally. The results show that the resonant frequency and phase difference in the vibration system decreased, the transverse amplitude of the output elliptical trajectory increased, and the longitudinal amplitude decreased with the increase in the included angle. The elliptical trajectories obtained from the test were generally consistent with the calculated results, and the calculated values of the resonant frequencies of the three angled vibration systems were in good agreement with the experimental test values. Full article

(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)

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18 pages, 3047 KiB

Open AccessArticle

A Rotary Piezoelectric Electromagnetic Hybrid Energy Harvester

by Zhiyang Yao and Chong Li

Micromachines 2025, 16(7), 807; https://doi.org/10.3390/mi16070807 - 11 Jul 2025

Viewed by 156

Abstract

To collect the energy generated by rotational motion in the natural environment, a piezoelectric electromagnetic hybrid energy harvester (HEH) based on a planetary gear system is proposed. The harvester combines piezoelectric and electromagnetic effects and is mainly used for collecting low-frequency rotational energy. [...] Read more.

To collect the energy generated by rotational motion in the natural environment, a piezoelectric electromagnetic hybrid energy harvester (HEH) based on a planetary gear system is proposed. The harvester combines piezoelectric and electromagnetic effects and is mainly used for collecting low-frequency rotational energy. The HEH has a compact structure and contains four sets of piezoelectric energy harvesters (PEHs) and electromagnetic energy harvesters (EMHs) inside. The working principle of the energy harvester is analyzed, its theoretical model is established, and a simulation analysis is conducted. To verify the effectiveness of the design, an experimental device is constructed. The results indicate that the HEH can generate an average output power of 250 mW under eight magnets and an external excitation frequency of 7 Hz. In actual power supply testing, the HEH can light up 60 LEDs and provide stable power supply for the temperature–humidity meter. Full article

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

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14 pages, 4427 KiB

Open AccessArticle

Numerical Investigation of Mixing Performance in Microfluidic Chip via Structural Micro-Rotors

by Yongliang Dong, Liqiu Wang and Xing Han

Micromachines 2025, 16(7), 806; https://doi.org/10.3390/mi16070806 - 11 Jul 2025

Viewed by 151

Abstract

Microfluidics is a powerful tool with extensive applications, including chemical synthesis and biological detection. However, the limited channel size and high viscosity of samples/reagents make it difficult to fully mix liquids and improve the reaction efficiency inside microfluidic chips. Active mixing by rotors [...] Read more.

Microfluidics is a powerful tool with extensive applications, including chemical synthesis and biological detection. However, the limited channel size and high viscosity of samples/reagents make it difficult to fully mix liquids and improve the reaction efficiency inside microfluidic chips. Active mixing by rotors has been proven to be an effective method to promote mixing efficiency via a magnetic field. Here, we numerically investigated the mixing performance of rotors with different shapes (bar-shaped, Y-shaped, and cross-shaped). We systematically studied the influence of the arrangement of multiple cross-rotors and the rotation rate on mixing performance. The results are promising for instructing the design and manipulation of rotors for in-channel mixing. Full article

(This article belongs to the Special Issue Preparation, Manipulation, and Biomedical Applications of Micro/Nanodroplets/Fluids)

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22 pages, 5230 KiB

Open AccessArticle

Integrated CAD/CAM Approach for Parametric Design and High Precision Fabrication of Planar Curvilinear Structures

by Jonas T. Churchill-Baird, O. Remus Tutunea-Fatan and Evgueni V. Bordatchev

Micromachines 2025, 16(7), 805; https://doi.org/10.3390/mi16070805 - 11 Jul 2025

Viewed by 188

Abstract

Curvilinear V-grooves are increasingly employed in functional surfaces with applications ranging from fluidics to tribology and optics. Despite their widespread use, the accurate and repeatable fabrication of curvilinear V-grooves remains challenging due to their inherent geometric complexity and the lack of relevant commercial [...] Read more.

Curvilinear V-grooves are increasingly employed in functional surfaces with applications ranging from fluidics to tribology and optics. Despite their widespread use, the accurate and repeatable fabrication of curvilinear V-grooves remains challenging due to their inherent geometric complexity and the lack of relevant commercial CAD/CAM systems. To address this, the present study proposes a CAD/CAM integrated framework capable of automating the design and fabrication of functional surfaces comprising curvilinear V-grooves generated by multi-axis single-point diamond cutting (SPDC). The framework is organized into three main functional blocks supported by seven secondary modules that encompass the entire process from V-groove geometry definition to cutting. The developed framework was practically validated by fabricating sinusoidal V-grooves on a flat surface and testing the capillary flow functionality of a curvilinear pattern. These results demonstrate the relevance of the integrated framework to curvilinear V-groove fabrication, thereby offering a versatile solution for certain types of surface engineering applications. Full article

(This article belongs to the Special Issue Advances in Digital Manufacturing and Nano Fabrication)

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17 pages, 5309 KiB

Open AccessArticle

Application of Carbon Nanotube-Based Elastomeric Matrix for Capacitive Sensing in Diabetic Foot Orthotics

by Monisha Elumalai, Andre Childs, Samantha Williams, Gabriel Arguello, Emily Martinez, Alaina Easterling, Dawn San Luis, Swaminathan Rajaraman and Charles M. Didier

Micromachines 2025, 16(7), 804; https://doi.org/10.3390/mi16070804 - 11 Jul 2025

Viewed by 311

Abstract

Diabetic foot ulcers (DFUs) represent a critical global health issue, necessitating the development of advanced smart, flexible, and wearable sensors for continuous monitoring that are reimbursable within foot orthotics. This study presents the design and characterization of a pressure sensor implemented into a [...] Read more.

Diabetic foot ulcers (DFUs) represent a critical global health issue, necessitating the development of advanced smart, flexible, and wearable sensors for continuous monitoring that are reimbursable within foot orthotics. This study presents the design and characterization of a pressure sensor implemented into a shoe insole to monitor diabetic wound pressures, emphasizing the need for a high sensitivity, durability under cyclic mechanical loading, and a rapid response time. This investigation focuses on the electrical and mechanical properties of carbon nanotube (CNT) composites utilizing Ecoflex and polydimethylsiloxane (PDMS). Morphological characterization was conducted using Transmission Electron Microscopy (TEM), Laser Confocal Microscopy, and Scanning Electron Microscopy (SEM). The electrical and mechanical properties of the CNT/Ecoflex- and the CNT/PDMS-based sensor composites were then investigated. CNT/Ecoflex was then further evaluated due to its lower variability performance between cycles at the same pressure, as well as its consistently higher capacitance values across all trials in comparison to CNT/PDMS. The CNT/Ecoflex composite sensor showed a high sensitivity (2.38 to 3.40 kPa⁻¹) over a pressure sensing range of 0 to 68.95 kPa. The sensor’s stability was further assessed under applied pressures simulating human weight. A custom insole prototype, incorporating 12 CNT/Ecoflex elastomeric matrix-based sensors (as an example) distributed across the metatarsal heads, midfoot, and heel regions, was developed and characterized. Capacitance measurements, ranging from 0.25 pF to 60 pF, were obtained across N = 3 feasibility trials, demonstrating the sensor’s response to varying pressure conditions linked to different body weights. These results highlight the potential of this flexible insole prototype for precise and real-time plantar surface monitoring, offering an approachable avenue for a challenging diabetic orthotics application. Full article

(This article belongs to the Special Issue Bioelectronics and Its Limitless Possibilities)

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14 pages, 4288 KiB

Open AccessArticle

The Impact of Acoustic Synthetic Jet Actuator Parameters on the Generated Noise

by Emil Smyk and Michał Stopel

Micromachines 2025, 16(7), 803; https://doi.org/10.3390/mi16070803 - 10 Jul 2025

Viewed by 186

Abstract

Synthetic jet actuators are becoming increasingly popular for enhancing electronic heat transfer. However, their use is currently limited due to the high noise they generate. This article examines how actuator parameters (orifice diameter, orifice length and cavity height) affect synthetic jet velocity and [...] Read more.

Synthetic jet actuators are becoming increasingly popular for enhancing electronic heat transfer. However, their use is currently limited due to the high noise they generate. This article examines how actuator parameters (orifice diameter, orifice length and cavity height) affect synthetic jet velocity and noise generation. Hot-wire anemometry was used to measure velocity, and noise was measured with a sound meter. The actuator was supplied with constant power at different frequencies ranging from 50 to 500 Hz. Observation of the velocity showed that it decreased with an increasing orifice diameter and increased with a decreasing orifice length. No relationship was observed between cavity height and synthetic jet velocity. This article indicates that increasing the orifice diameter or reducing the orifice length causes an increase in the noise generated by SJAs, provided we remain in the vicinity of the characteristic frequency. It was demonstrated that higher actuator chambers produce higher noise levels, although this was not a consistent trend across the entire tested frequency range. Full article

(This article belongs to the Special Issue Novel Electromagnetic and Acoustic Devices)

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13 pages, 4900 KiB

Open AccessArticle

Comparative Noise Analysis of Readout Circuit in Hemispherical Resonator Gyroscope

by Zhihao Yu, Libin Zeng, Changda Xing, Lituo Shang, Xiuyue Yan and Jingyu Li

Micromachines 2025, 16(7), 802; https://doi.org/10.3390/mi16070802 - 9 Jul 2025

Viewed by 216

Abstract

In high-precision Hemispherical Resonator Gyroscope (HRG) control systems, readout circuit noise critically determines resonator displacement detection precision. Addressing noise issues, this paper compares the noise characteristics and contribution mechanisms of the Transimpedance Amplifier (TIA) and Charge-Sensitive Amplifier (CSA). By establishing a noise model [...] Read more.

In high-precision Hemispherical Resonator Gyroscope (HRG) control systems, readout circuit noise critically determines resonator displacement detection precision. Addressing noise issues, this paper compares the noise characteristics and contribution mechanisms of the Transimpedance Amplifier (TIA) and Charge-Sensitive Amplifier (CSA). By establishing a noise model and analyzing circuit bandwidth, the dominant role of feedback resistor thermal noise in the TIA is revealed. These analyses further demonstrate the significant suppression of high-frequency noise by the CSA capacitive feedback network. Simulation and experimental results demonstrate that the measured noise of the TIA and CSA is consistent with the theoretical model. The TIA output noise is 25.8

μ V_{rms}

, with feedback resistor thermal noise accounting for 99.8%, while CSA output noise is reduced to 13.2

μ V_{rms}

, a reduction of 48.8%. Near resonant frequency, the equivalent displacement noise of the CSA is

1.69 \times 10^{- 14} m / \sqrt{Hz}

, a reduction of 86.7% compared to the TIA’s

1.27 \times 10^{- 13} m / \sqrt{Hz}

, indicating the CSA is more suitable for high-precision applications. This research provides theoretical guidance and technical references for the topological selection and parameter design of HRG readout circuits. Full article

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24 pages, 4771 KiB

Open AccessArticle

Constant High-Voltage Triboelectric Nanogenerator with Stable AC for Sustainable Energy Harvesting

by Aso Ali Abdalmohammed Shateri, Salar K. Fatah, Fengling Zhuo, Nazifi Sani Shuaibu, Chuanrui Chen, Rui Wan and Xiaozhi Wang

Micromachines 2025, 16(7), 801; https://doi.org/10.3390/mi16070801 - 9 Jul 2025

Viewed by 278

Abstract

Triboelectric nanogenerators (TENGs) hold significant potential for decentralized energy harvesting; however, their dependence on rotational mechanical energy often limits their ability to harness ubiquitous horizontal motion in real-world applications. Here, a single horizontal linear-to-rotational triboelectric nanogenerator (SHLR-TENG) is presented, designed to efficiently convert [...] Read more.

Triboelectric nanogenerators (TENGs) hold significant potential for decentralized energy harvesting; however, their dependence on rotational mechanical energy often limits their ability to harness ubiquitous horizontal motion in real-world applications. Here, a single horizontal linear-to-rotational triboelectric nanogenerator (SHLR-TENG) is presented, designed to efficiently convert linear motion into rotational energy using a robust gear system, enabling a high voltage and reliable full cycle of alternating current (AC). The device features a radially patterned disk with triboelectric layers composed of polyimide. The SHLR-TENG achieves a peak-to-peak voltage of 1420 V, a short-circuit current of 117 µA, and an average power output of 41.5 mW, with a surface charge density of 110 µC/m². Moreover, it demonstrates a power density per unit volume of 371.2 W·m⁻³·Hz⁻¹. The device retains 80% efficiency after 1.5 million cycles, demonstrating substantial durability under mechanical stress. These properties enable the SHLR-TENG to directly power commercial LEDs and low-power circuits without the need for energy storage. This study presents an innovative approach to sustainable energy generation by integrating horizontal motion harvesting with rotational energy conversion. The compact and scalable design of the SHLR-TENG, coupled with its resilience to humidity (20–90% RH) and temperature fluctuations (10–70 °C), positions it as a promising next-generation energy source for Internet of Things (IoT) devices and autonomous systems. Full article

(This article belongs to the Special Issue Micro-Energy Harvesting Technologies and Self-Powered Sensing Systems)

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23 pages, 3253 KiB

Open AccessReview

Overcoming Challenges in Silicon Anodes: The Role of Electrolyte Additives and Solid-State Electrolytes

by Jinsik Nam, Hanbyeol Lee and Oh B. Chae

Micromachines 2025, 16(7), 800; https://doi.org/10.3390/mi16070800 - 9 Jul 2025

Viewed by 440

Abstract

Silicon-based anodes have emerged as promising candidates for advanced lithium-ion batteries (LIBs) owing to their outstanding lithium storage capacity; however, the commercial implementation of silicon-based anodes is hindered primarily by their significant volumetric changes and the resulting solid electrolyte interphase (SEI) instability during [...] Read more.

Silicon-based anodes have emerged as promising candidates for advanced lithium-ion batteries (LIBs) owing to their outstanding lithium storage capacity; however, the commercial implementation of silicon-based anodes is hindered primarily by their significant volumetric changes and the resulting solid electrolyte interphase (SEI) instability during the lithiation/delithiation process. To overcome these issues, electrolyte optimization, particularly through the use of functional additives and solid-state electrolytes, has attracted significant research attention. In this paper, we review the recent developments in electrolyte additives, such as vinylene carbonate, fluoroethylene carbonate, and silane-based additives, and new additives, such as dimethylacetamide, that improve the SEI stability and overall electrochemical performance of silicon-based anodes. We also discuss the role of solid electrolytes, including oxides, sulfides, and polymer-based systems, in mitigating the volume changes in Si and improving safety. Such approaches can effectively enhance both the longevity and capacity retention of silicon-based anodes. Despite significant progress, further studies are essential to optimize electrolyte formulation and solve interfacial problems. Integrating these advances with improved electrode designs and anode materials is critical for realizing the full potential of silicon-based anodes in high-performance LIBs, particularly in electric vehicles and portable electronics. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices, 2nd Edition)

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15 pages, 3428 KiB

Open AccessArticle

An Enhanced Circularly Polarized Textile Antenna Using a Metasurface and Slot-Patterned Ground for Off-Body Communications

by Yong-Deok Kim, Tu Tuan Le and Tae-Yeoul Yun

Micromachines 2025, 16(7), 799; https://doi.org/10.3390/mi16070799 - 9 Jul 2025

Viewed by 242

Abstract

This paper presents an enhanced circularly polarized (CP) all-textile antenna using a metasurface (MS) and slot-patterned ground (SPG) for 5.8 GHz industry, scientific, and medical (ISM)-band applications in off-body communications. The 3 × 3 MS, capable of converting the incident wave into an [...] Read more.

This paper presents an enhanced circularly polarized (CP) all-textile antenna using a metasurface (MS) and slot-patterned ground (SPG) for 5.8 GHz industry, scientific, and medical (ISM)-band applications in off-body communications. The 3 × 3 MS, capable of converting the incident wave into an orthogonal direction with equal magnitude and a 90° phase difference, converts the linearly polarized (LP) wave, radiated from the fundamental radiator with a corner-truncated slot square-patch configuration, into being CP. The SPG, consisting of periodic slots with two different sizes of corner-truncated slots, redistributes the surface current on the ground plane, enhancing the axial ratio bandwidth (ARBW) of the proposed antenna. The novel combination of MS and SPG not only enables the generation and enhancement of CP characteristics but also significantly improves the impedance bandwidth (IBW), gain, and radiation efficiency by introducing additional surface wave resonances. The proposed antenna is composed of a conductive textile and a felt substrate, offering comfort and flexibility for applications where the antenna is placed in close proximity to the human body. The proposed antenna is simulated under bending in various directions, showing exceptionally similar characteristics to a flat condition. The proposed antenna is fabricated and is then verified by measurements in both free space and a human body environment. The measured IBW is 36.3%, while the ARBW is 18%. The measured gain and radiation efficiency are 6.39 dBic and 64.7%, respectively. The specific absorption rate (SAR) is simulated, and the results satisfy both US and EU safety standards. Full article

(This article belongs to the Special Issue Metasurface-Based Devices and Systems)

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15 pages, 1607 KiB

Open AccessArticle

A Hierarchical Inverse Lithography Method Considering the Optimization and Manufacturability Limit by Gradient Descent

by Haifeng Sun, Qingyan Zhang, Jie Zhou, Jianwen Gong, Chuan Jin, Ji Zhou and Junbo Liu

Micromachines 2025, 16(7), 798; https://doi.org/10.3390/mi16070798 - 8 Jul 2025

Viewed by 246

Abstract

Inverse lithography technology (ILT) based on the gradient descent (GD) algorithm, which is a classical local optimal method, can effectively improve the lithographic imaging fidelity. However, due to the low-pass filtering effect of the lithography imaging system, GD, although able to converge quickly, [...] Read more.

Inverse lithography technology (ILT) based on the gradient descent (GD) algorithm, which is a classical local optimal method, can effectively improve the lithographic imaging fidelity. However, due to the low-pass filtering effect of the lithography imaging system, GD, although able to converge quickly, is prone to fall into the local optimum for the information in the corner region of complex patterns. Considering the high-frequency information of the corner region during the optimization process, this paper proposes a resolution layering method to improve the efficiency of GD-based ILT algorithms. A corner-rounding-inspired target retargeting strategy is used to compensate for the over-optimization defect of GD for inversely optimizing the complex pattern layout. Furthermore, for ensuring the manufacturability of masks, differentiable top-hat and bottom-hat operations are employed to improve the optimization efficiency of the proposed method. To confirm the superiority of the proposed method, multiple optimization methods of ILT were compared. Numerical experiments show that the proposed method has higher optimization efficiency and effectively avoids the over-optimization. Full article

(This article belongs to the Section E：Engineering and Technology)

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18 pages, 16017 KiB

Open AccessArticle

Design and Fabrication of Multi-Frequency and Low-Quality-Factor Capacitive Micromachined Ultrasonic Transducers

by Amirhossein Moshrefi, Abid Ali, Mathieu Gratuze and Frederic Nabki

Micromachines 2025, 16(7), 797; https://doi.org/10.3390/mi16070797 - 8 Jul 2025

Viewed by 366

Abstract

Capacitive micromachined ultrasonic transducers (CMUTs) have been developed for air-coupled applications to address key challenges such as noise, prolonged ringing, and side-lobe interference. This study introduces an optimized CMUT design that leverages the squeeze-film damping effect to achieve a low-quality factor, enhancing resolution [...] Read more.

Capacitive micromachined ultrasonic transducers (CMUTs) have been developed for air-coupled applications to address key challenges such as noise, prolonged ringing, and side-lobe interference. This study introduces an optimized CMUT design that leverages the squeeze-film damping effect to achieve a low-quality factor, enhancing resolution and temporal precision for imaging as one of the suggested airborne application. The device was fabricated using the PolyMUMPs process, ensuring high structural accuracy and consistency. Finite element analysis (FEA) simulations validated the optimized parameters, demonstrating improved displacement, reduced side-lobe artifacts, and sharper main lobes for superior imaging performance. Experimental validation, including Laser Doppler Vibrometer (LDV) measurements of membrane displacement and mode shapes, along with ring oscillation tests to assess Q-factor and signal decay, confirmed the device’s reliability and consistency across four CMUT arrays. Additionally, this study explores the implementation of multi-frequency CMUT arrays, enhancing imaging versatility across different air-coupled applications. By integrating multiple frequency bands, the proposed CMUTs enable adaptable imaging focus, improving their suitability for diverse diagnostic scenarios. These advancements highlight the potential of the proposed design to deliver a superior performance for airborne applications, paving the way for its integration into advanced diagnostic systems. Full article

(This article belongs to the Special Issue MEMS Ultrasonic Transducers)

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13 pages, 2818 KiB

Open AccessArticle

Leveling Method of Working Platform Based on PZT Electromechanical Coupling Effect

by Aiqun Xu, Jianhui Yuan and Jinxuan Gao

Micromachines 2025, 16(7), 796; https://doi.org/10.3390/mi16070796 - 8 Jul 2025

Viewed by 241

Abstract

Lead zirconate titanate (PZT) piezoelectric ceramics are widely used functional materials due to their strong and stable piezoelectric properties. A leveling method based on lead zirconate titanate piezoelectric ceramics is proposed for the high level of accuracy required in microelectromechanical fields such as [...] Read more.

Lead zirconate titanate (PZT) piezoelectric ceramics are widely used functional materials due to their strong and stable piezoelectric properties. A leveling method based on lead zirconate titanate piezoelectric ceramics is proposed for the high level of accuracy required in microelectromechanical fields such as aerospace, industrial robotics, biomedical, and photolithography. A leveling mechanism consisting of core components such as piezoelectric ceramic actuators and sensors is designed. The closed-loop leveling of the working platform is performed using the electromechanical coupling effect of the PZT piezoelectric material. Combined with the theory of the dielectric inverse piezoelectric effect in electric fields, a simulation is used to analyze the four force and deformation cases generated by the drive legs when the load is attached at different positions of the working platform, and the leveling is realized by applying the drive voltage to generate micro-motion displacement. Simulation and calculation results show that the leveling method can reduce the tilt angle of the working platform by 60% when the driving voltage is in the range of 10~150 V. The feasibility of the leveling method and the uniformity of the theoretical calculation and simulation are verified. Full article

(This article belongs to the Section E：Engineering and Technology)

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17 pages, 3483 KiB

Open AccessArticle

A Novel Triboelectric–Electromagnetic Hybrid Generator with a Multi-Layered Structure for Wind Energy Harvesting and Wind Vector Monitoring

by Jiaqing Niu, Ribin Hu, Ming Li, Luying Zhang, Bei Xu, Yaqi Zhang, Yi Luo, Jiang Ding and Qingshan Duan

Micromachines 2025, 16(7), 795; https://doi.org/10.3390/mi16070795 - 8 Jul 2025

Viewed by 331

Abstract

High-efficiency wind energy collection and precise wind vector monitoring are crucial for sustainable energy applications, smart agriculture, and environmental management. A novel multi-layered triboelectric–electromagnetic hybrid generator (TEHG) for broadband wind energy collection and wind vector monitoring was built. The TEHG comprises three functional [...] Read more.

High-efficiency wind energy collection and precise wind vector monitoring are crucial for sustainable energy applications, smart agriculture, and environmental management. A novel multi-layered triboelectric–electromagnetic hybrid generator (TEHG) for broadband wind energy collection and wind vector monitoring was built. The TEHG comprises three functional layers corresponding to three modules: a soft-contact rotary triboelectric nanogenerator (S-TEHG), an electromagnetic generator (EMG), and eight flow-induced vibration triboelectric nanogenerators (F-TENGs), which are arranged in a circular array to enable low-wind-speed energy harvesting and multi-directional wind vector monitoring. The TEHG achieves broadband energy harvesting and demonstrates exceptional stability, maintaining a consistent electrical output after 3 h of continuous operation. The EMG charges a 1 mF capacitor to 1.5 V 738 times faster than conventional methods by a boost converter. The TEHG operates for 17.5 s to power a thermohygrometer for 103 s, achieving an average output power of 1.87 W with a power density of 11.2 W/m³, demonstrating an exceptional power supply capability. The F-TENGs can accurately determine the wind direction, with a wind speed detection error below 4.5%. This innovative structure leverages the strengths of both EMG and TENG technologies, offering a durable, multifunctional solution for sustainable energy and intelligent environmental sensing. Full article

(This article belongs to the Special Issue Self-Tuning and Self-Powered Energy Harvesting Devices)

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32 pages, 6074 KiB

Open AccessReview

High-Quality Manufacturing with Electrochemical Jet Machining (ECJM) for Processing Applications: A Comprehensive Review, Challenges, and Future Opportunities

by Yong Huang, Yi Hu, Xincai Liu, Xin Wang, Siqi Wu and Hanqing Shi

Micromachines 2025, 16(7), 794; https://doi.org/10.3390/mi16070794 - 7 Jul 2025

Viewed by 270

Abstract

The enduring manufacturing goals are increasingly shifting toward ultra-precision manufacturing and micro-nano fabrication, driven by the demand for sophisticated products. Unconventional machining processes such as electrochemical jet machining (ECJM), electrical discharge machining (EDM), electrochemical machining (ECM), abrasive water jet machining (AWJM), and laser [...] Read more.

The enduring manufacturing goals are increasingly shifting toward ultra-precision manufacturing and micro-nano fabrication, driven by the demand for sophisticated products. Unconventional machining processes such as electrochemical jet machining (ECJM), electrical discharge machining (EDM), electrochemical machining (ECM), abrasive water jet machining (AWJM), and laser beam machining (LBM) have been widely adopted as feasible alternatives to traditional methods, enabling the production of high-quality engineering components with specific characteristics. ECJM, a non-contact machining technology, employs electrodes on the nozzle and workpiece to establish an electrical circuit via the jet. As a prominent special machining technology, ECJM has demonstrated significant advantages, such as rapid, non-thermal, and stress-free machining capabilities, in past research. This review is dedicated to outline the research progress of ECJM, focusing on its fundamental concepts, material processing capabilities, technological advancements, and its variants (e.g., ultrasonic-, laser-, abrasive-, and magnetism-assisted ECJM) along with their applications. Special attention is given to the application of ECJM in the semiconductor and biomedical fields, where the demand for ultra-precision components is most pronounced. Furthermore, this review explores recent innovations in process optimization, significantly boosting machining efficiency and quality. This review not only provides a snapshot of the current status of ECJM technology, but also discusses the current challenges and possible future improvements of the technology. Full article

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

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26 pages, 5512 KiB

Open AccessArticle

Optimal Design for a Novel Compliant XY Platform Integrated with a Hybrid Double Symmetric Amplifier Comprising One-Lever and Scott–Russell Mechanisms Arranged in a Perpendicular Series Layout for Vibration-Assisted CNC Milling

by Minh Phung Dang, Anh Kiet Luong, Hieu Giang Le and Chi Thien Tran

Micromachines 2025, 16(7), 793; https://doi.org/10.3390/mi16070793 - 3 Jul 2025

Viewed by 415

Abstract

Compliant mechanisms are often utilized in precise positioning systems but have not been thoroughly examined in vibration-aided fine CNC machining. This study aims to develop a new 02-DOF flexure stage for vibration-aided fine CNC milling. A hybrid displacement amplifier, featuring a two-lever mechanism, [...] Read more.

Compliant mechanisms are often utilized in precise positioning systems but have not been thoroughly examined in vibration-aided fine CNC machining. This study aims to develop a new 02-DOF flexure stage for vibration-aided fine CNC milling. A hybrid displacement amplifier, featuring a two-lever mechanism, two Scott–Russell mechanisms, and a parallel leading mechanism, was integrated into a symmetric perpendicular series configuration to create an innovative design. The pseudo-rigid body model (PRBM), Lagrangian approach, finite element analysis (FEA), and Firefly optimization algorithm were employed to develop, verify, and optimize the quality response of the new positioner. The PRBM and Lagrangian methods were used to construct an analytical model, while finite element analysis was used to validate the theoretical solution. The primary natural frequency results from theoretical and FEM methods were 318.16 Hz and 308.79 Hz, respectively. The difference between these techniques was 3.04%, demonstrating a reliable modelling strategy. The Firefly optimization approach applied mathematical equations to enhance the key design factors of the mechanism. The prototype was then built, revealing an error of 7.23% between the experimental and simulated frequencies of 331.116 Hz and 308.79 Hz, respectively. The specimen was subsequently mounted on the fabricated optimization positioner, and vibration-assisted fine CNC milling was performed at 100–1000 Hz. At 400 Hz, the specimen achieved ideal surface roughness with a Ra value of 0.187 µm. The developed design is a potential structure that generates non-resonant frequency power for vibration-aided fine CNC milling. Full article

(This article belongs to the Section E：Engineering and Technology)

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19 pages, 4423 KiB

Open AccessReview

Laser Active Optical Systems (LAOSs) for Material Processing

by Vladimir Chvykov

Micromachines 2025, 16(7), 792; https://doi.org/10.3390/mi16070792 - 2 Jul 2025

Viewed by 374

Abstract

The output energy of Laser Active Optical Systems (LAOSs), in which image brightness is amplified within the laser-active medium, is always higher than the input energy. This contrasts with conventional optical systems (OSs). As a result, a LAOS enables the creation of laser [...] Read more.

The output energy of Laser Active Optical Systems (LAOSs), in which image brightness is amplified within the laser-active medium, is always higher than the input energy. This contrasts with conventional optical systems (OSs). As a result, a LAOS enables the creation of laser beams with tailored energy distribution across the aperture, making them ideal for material processing applications. This concept was first successfully implemented using metal vapor lasers as the gain medium. In these systems, material processing was achieved by using a laser beam that either carried the required energy profile or the image of the object itself. Later, other laser media were utilized for LAOSs, including barium vapor, strontium vapor, excimer XeCl lasers, and solid-state media. Additionally, during the development of these systems, several modifications were introduced. For example, Space-Time Light Modulators (STLMs) and CCD cameras were incorporated, along with the use of multipass amplifiers, disk-shaped or thin-disk (TD) solid-state laser amplifiers, and other advancements. These techniques have significantly expanded the range of power, energy, pulse durations, and operating wavelengths. Currently, TD laser amplifiers and STLMs based on Digital Light Processor (DLP) technology or Digital Micromirror Devices (DMDs) enhance the potential to develop LAOS devices for Subtractive and Additive Technologies (ST, AT), applicable in both macromachining (cutting, welding, drilling) and micro-nano processing. This review presents comparable characteristics and requirements for these various LAOS applications. Full article

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

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