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Micromachines
Volume 16
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Micromachines, Volume 16, Issue 6 (June 2025) – 123 articles

Cover Story (view full-size image): The controllable transport of droplets on solid surfaces is crucial for many applications, from water harvesting to bio-analysis. This study proposes reconfigurable orbital electrowetting (ROEW) on inclined slippery liquid-infused porous surfaces (SLIPSs) for controllable droplet transport and dynamic handling. The flexible reconfigurability is attributed to the non-contact wettability modulation and reversibly deformable flexible electrodes. ROEW enables reconfiguration of the wetting pathways by designing the electrode shapes and dynamically switching electrode configurations, achieving the controllable transport of various pathways and the dynamic handling of droplet sorting and mixing. ROEW provides a new approach for reconfigurable, electrode-free arrays and reusable microfluidics. View this paper
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15 pages, 5625 KiB  
Article
Compact Frequency-Agile and Mode-Reconfigurable Antenna for C-Band, Sub-6-GHz-5G, and ISM Applications
by Esraa Mousa Ali, Wahaj Abbas Awan, Anees Abbas, Syed Mujahid Abbas and Heba G. Mohamed
Micromachines 2025, 16(6), 724; https://doi.org/10.3390/mi16060724 - 19 Jun 2025
Viewed by 352
Abstract
This article presents the design and evaluation of a compact-sized antenna targeting heterogenous applications working in the C-band, 5G-sub-6GHz, and the ISM band. The antenna offers frequency reconfigurability along with multi-operational modes ranging from wideband to dual-band and tri-band. A compact-sized antenna is [...] Read more.
This article presents the design and evaluation of a compact-sized antenna targeting heterogenous applications working in the C-band, 5G-sub-6GHz, and the ISM band. The antenna offers frequency reconfigurability along with multi-operational modes ranging from wideband to dual-band and tri-band. A compact-sized antenna is designed initially to cover a broad bandwidth that ranges from 4 GHz to 7 GHz. Afterwards, various multiband antennas are formed by loading various stubs. Finally, the wideband antenna along with multi-stub loaded antennas are combined to form a single antenna. Furthermore, PIN diodes are loaded between the main radiator and stubs to activate the stubs on demand, which consequently generates various operational modes. The last stage of the design is optimization, which helps in achieving the desired bandwidths. The optimized antenna works in the wideband mode covering the C-band, Wi-Fi 6E, and the ISM band. Meanwhile, the multiband modes offer the additional coverage of the LTE, LTE 4G, ISM lower band, and GSM band. The various performance parameters are studied and compared with measured results to show the performance stability of the proposed reconfigurable antenna. In addition, an in-depth literature review along with comparison with proposed antenna is performed to show its potential for targeted applications. The utilization of FR4 as a substrate of the antenna along with its compact size of 15 mm × 20 mm while having multiband and multi-mode frequency reconfigurability makes it a strong candidate for present as well as for future smart devices and electronics. Full article
(This article belongs to the Special Issue Microwave Passive Components, 3rd Edition)
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11 pages, 1929 KiB  
Article
Influence of Nonlinear Effects Induced by Mode Coupling on Vibration Trajectories of MEMS Micromirrors
by Zhen Chen, Dayong Qiao and Anjie Peng
Micromachines 2025, 16(6), 723; https://doi.org/10.3390/mi16060723 - 19 Jun 2025
Viewed by 278
Abstract
Detection of the vibration trajectories of MEMS micromirrors is crucial for ensuring their application performance. This study investigates key factors influencing micromirror vibration trajectories. When actuated by a square-wave signal containing high-frequency components, micromirrors exhibit mode coupling vibrations. By incorporating a mode coupling [...] Read more.
Detection of the vibration trajectories of MEMS micromirrors is crucial for ensuring their application performance. This study investigates key factors influencing micromirror vibration trajectories. When actuated by a square-wave signal containing high-frequency components, micromirrors exhibit mode coupling vibrations. By incorporating a mode coupling mechanism, this paper establishes a comprehensive vibration trajectory model for micromirrors. Numerical simulations were performed to obtain trajectory solutions. Both the experimental and simulation results demonstrate that the mode coupling leads to deviations between the actual trajectory and the expected sinusoidal pattern. These deviations compromise the accuracy of trajectory prediction systems, which typically assume that the trajectory follows a sinusoidal pattern. To mitigate the deviations caused by mode coupling, this study proposes structural parameter optimization during the micromirror design process. Full article
(This article belongs to the Special Issue Recent Advances in MEMS Mirrors)
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20 pages, 5284 KiB  
Article
Experimental Study of a Broadband Vibration Energy Harvester Based on Orthogonal Magnetically Coupled Double Cantilever Beam
by Yanhao Feng, Jianhua Wang, Xiangye Chen and Peng Liu
Micromachines 2025, 16(6), 722; https://doi.org/10.3390/mi16060722 - 19 Jun 2025
Viewed by 325
Abstract
Purpose: The aim of this study is to achieve automated energy capture and charging for the ADXL355 accelerometer, enhance the vibration energy collection efficiency, and widen the energy trapping frequency band of a system in a working environment for bridge health state [...] Read more.
Purpose: The aim of this study is to achieve automated energy capture and charging for the ADXL355 accelerometer, enhance the vibration energy collection efficiency, and widen the energy trapping frequency band of a system in a working environment for bridge health state detection. Methods: A vibration energy harvester based on a magnetic coupling cantilever beam in an orthogonal direction was proposed. The harvester works by adjusting the angle and magnetic spacing between the two cantilever-beam piezoelectric oscillators, enabling the oscillators to produce large-scale and stable vibrations when excited by an external broadband vibration source. Results: Sinusoidal frequency sweep experiments showed that, under an excitation amplitude of 0.2 g, the proposed broadband vibration energy harvester based on orthogonal magnetic coupling double cantilever beams achieved the best energy harvesting performance when the magnetic angle of the double cantilever beam system was 130°, and the radius was 16 mm. In the frequency range of 5–20 Hz, the system can effectively capture higher effective voltages across all frequency bands, with a total captured voltage value of approximately 15.3 V. Compared with the control group, the system’s energy harvesting capacity under this working condition increases by 770%. Additionally, the effective frequency band of the system was broadened by 3.7 Hz. Conclusions: Unlike previous studies, which often limited the angles of the magnetic fields generated by the magnets at the ends of piezoelectric beams to specific values, this study explores the influence of rotating these magnetic fields to general angles on the working frequency band of the structure. The findings provide a new perspective and theoretical basis for the optimal design of broadband vibration energy harvesters. Full article
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18 pages, 5278 KiB  
Article
Integrated Electrochemical and Computational Elucidation of Nitro Blue Tetrazolium Chloride as an Efficient Leveler for Copper Microvia Superfilling
by Dong Xing, Xiangfu Wei, Jinge Ye, Mingsong Lin, Shengchang Tang and Hui You
Micromachines 2025, 16(6), 721; https://doi.org/10.3390/mi16060721 - 19 Jun 2025
Viewed by 315
Abstract
Levelers are indispensable additives for achieving void-free, bottom-up superconformal copper filling of microvias. Establishing the molecular-level correlation between leveler structure and performance is therefore essential to the continued advancement of microelectronic copper-plating technology. Herein, nitro blue tetrazolium chloride (NBT) is identified as an [...] Read more.
Levelers are indispensable additives for achieving void-free, bottom-up superconformal copper filling of microvias. Establishing the molecular-level correlation between leveler structure and performance is therefore essential to the continued advancement of microelectronic copper-plating technology. Herein, nitro blue tetrazolium chloride (NBT) is identified as an efficient leveler for copper microvia superfilling. A multiscale strategy—combining electrochemical measurements, X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and molecular dynamics (MD) simulations—is employed to elucidate the action mechanism of NBT and pinpoint its electroactive sites. Electrochemical tests show that NBT markedly suppresses copper deposition and, together with polyethylene glycol (PEG), effectively resists competitive adsorption by bis-(3-sulfopropyl) disulfide (SPS), thereby enhancing the microvia superfilling performance of the PEG–SPS–NBT additive system. DFT results reveal that the nitro groups and tetrazolium rings constitute the primary adsorption centers on the copper surface; the nitro groups additionally strengthen intermolecular interactions between NBT and PEG. MD simulations further confirm that NBT anchors onto the Cu(111) surface predominantly through these NO2 groups and the tetrazolium ring, while co-adsorbed PEG enhances the overall adsorption strength of NBT. The electroplating experiment demonstrates that NBT can act as an effective leveler for microvia superfilling. Moreover, XPS analyses further confirm the synergistic co-adsorption of NBT and PEG and verify that the NO2 groups and tetrazolium rings are the dominant adsorption sites of NBT. Collectively, the electroplating, XPS, electrochemical, DFT, and MD findings clarify the structure–activity relationship of NBT and provide rational guidelines for designing next-generation copper-plating levelers. Full article
(This article belongs to the Special Issue Microelectronics Assembly and Packaging: Materials and Technologies, 2nd Edition)
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20 pages, 10112 KiB  
Article
Radomizing an Antenna for a SAR-Based ETA Radar System While Ensuring Imaging Accuracy: A Focus on Phase Shifts
by María Elena de Cos Gómez, Alicia Flórez Berdasco, Jaime Laviada Martínez and Fernando Las-Heras Andrés
Micromachines 2025, 16(6), 720; https://doi.org/10.3390/mi16060720 - 17 Jun 2025
Viewed by 453
Abstract
The impact of radomization on the radiation pattern of a millimeter-wave antenna for an ETA system utilizing synthetic aperture radar (SAR) is examined with special emphasis placed on the phase shift across both the beamwidth and the bandwidth, rather than the amplitude. Three [...] Read more.
The impact of radomization on the radiation pattern of a millimeter-wave antenna for an ETA system utilizing synthetic aperture radar (SAR) is examined with special emphasis placed on the phase shift across both the beamwidth and the bandwidth, rather than the amplitude. Three different radomization approaches, including one based on metasurfaces, are evaluated for a radar antenna operating within the 24.05–24.25 GHz frequency range. Fabricated prototypes, both of the standalone antenna and the radomized version, are tested and compared in terms of electromagnetic image quality. The metasurface-based radome provides the best results among the radomization options analyzed. Full article
(This article belongs to the Special Issue RF MEMS and Microsystems)
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15 pages, 6545 KiB  
Article
A X-Band Integrated Passive Device Structure Based on TMV-Embedded FOWLP
by Jiajie Yang, Lixin Xu, Xiangyu Yin and Ke Yang
Micromachines 2025, 16(6), 719; https://doi.org/10.3390/mi16060719 - 17 Jun 2025
Viewed by 223
Abstract
In this paper, the fabrication and testing of an integrated passive device (IPD) structure for X-band FMCW radar based on the fan-out wafer-level packaging (FOWLP) process are discussed. First, a transition line structure is added to the IPD structure to increase the upper [...] Read more.
In this paper, the fabrication and testing of an integrated passive device (IPD) structure for X-band FMCW radar based on the fan-out wafer-level packaging (FOWLP) process are discussed. First, a transition line structure is added to the IPD structure to increase the upper impedance limit of the substrate, so as to reduce the process implementation difficulty and development cost. Second, the vertical soldered SubMiniature Push-On Micro (SMPM) interfaces testing method is proposed, reducing the testing difficulty of the dual-port structure with the antenna. Finally, the process fabrication as well as testing of the IPD structure are completed. The dimensions of the fabricated structure are 16.983 × 24.099 × 0.56 mm3. Test results show that, with a center frequency of 8.5 GHz, the actual operational bandwidth of the structure reaches 7.66% (8.095–8.74 GHz), with a maximum isolation of 33.9 dB. The bandwidth with isolation greater than 20 dB is 1.76% (8.455–8.605 GHz). The maximum gain at the center frequency is 2.02 dBi. Additionally, experimental uncertainty analysis is performed on different IPD structures, and the measurement results are basically consistent. These results validate the feasibility of the FOWLP process in the miniaturization of X-band FMCW radar antenna and other passive devices. Full article
(This article belongs to the Special Issue Micro/Nano Sensors: Fabrication and Applications)
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13 pages, 2983 KiB  
Article
Impact of Reset Pulse Width on Gradual Conductance Programming in Al2O3/TiOx-Based RRAM
by Hyeonseong Lim, Wonbo Shim and Tae-Hyeon Kim
Micromachines 2025, 16(6), 718; https://doi.org/10.3390/mi16060718 - 17 Jun 2025
Viewed by 310
Abstract
This work investigates the impact of reset pulse width on multilevel conductance programming in Al2O3/TiOx-based resistive random access memory. A 32 × 32 cross-point array of Ti (12 nm)/Pt (62 nm)/Al2O3 (3 nm)/TiOx [...] Read more.
This work investigates the impact of reset pulse width on multilevel conductance programming in Al2O3/TiOx-based resistive random access memory. A 32 × 32 cross-point array of Ti (12 nm)/Pt (62 nm)/Al2O3 (3 nm)/TiOx (32 nm)/Ti (14 nm)/Pt (60 nm) devices (2.5 µm × 2.5 µm active area) was fabricated via e-beam evaporation, atomic layer deposition, and reactive sputtering. Following an initial forming step and a stabilization phase of five DC reset–set cycles, devices were programmed using an incremental step pulse programming (ISPP) scheme. Reset pulses of fixed amplitude were applied with widths of 100 µs, 10 µs, 1 µs, and 100 ns, and the programming sequence was terminated when the read current at 0.2 V exceeded a 45 µA target. At a 100 µs reset pulse width, most cycles exhibited abrupt current jumps that exceeded the target current, whereas at a 100 ns width, the programmed current increased gradually in all cycles, enabling precise conductance tuning. Cycle-to-cycle variation decreased by more than 50% as the reset pulse width was reduced, indicating more uniform filament disruption and regrowth. These findings demonstrate that controlling reset pulse width offers a straightforward route to reliable, linear multilevel operation in Al2O3/TiOx-based RRAM. Full article
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12 pages, 2514 KiB  
Article
Designed Omnidirectional Antenna of Quarter-Mode Substrate-Integrated Waveguide Element with Characteristic Mode Analysis
by Wei Hu, Liangfu Peng, Tao Tang, Maged A. Aldhaeebi, Thamer S. Almoneef and Jaouhar Mouine
Micromachines 2025, 16(6), 717; https://doi.org/10.3390/mi16060717 - 17 Jun 2025
Viewed by 333
Abstract
This study investigates the design of omnidirectional antennas, using a characteristic mode analysis (CMA), and explores two distinct feeding methods. The first method employs equal-amplitude and in-phase excitation across all ports, whereas the second method utilizes equal-amplitude excitation with a 180° phase difference [...] Read more.
This study investigates the design of omnidirectional antennas, using a characteristic mode analysis (CMA), and explores two distinct feeding methods. The first method employs equal-amplitude and in-phase excitation across all ports, whereas the second method utilizes equal-amplitude excitation with a 180° phase difference between adjacent ports. Both designs achieve operating bandwidths of 2.45–2.58 GHz and 2.42–2.45 GHz, respectively, with peak gains of 4.1 dBi and 4.4 dBi at 2.45 GHz. The proposed antennas exhibited high gain and low-profile characteristics, making them well-suited for applications in wireless energy harvesting. Full article
(This article belongs to the Section E：Engineering and Technology)
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22 pages, 9047 KiB  
Article
Miniaturized Dual and Quad Port MIMO Antenna Variants Featuring Elevated Diversity Performance for UWB and 5G-Midband Applications
by Karthikeyan Ramanathan, Srivatsun Gopalakrishnan and Thrisha Chandrakanthan
Micromachines 2025, 16(6), 716; https://doi.org/10.3390/mi16060716 - 17 Jun 2025
Viewed by 381
Abstract
The growing demand for high-speed and high-capacity wireless communication has intensified the need for compact, wideband, and efficient MIMO antenna systems, particularly for 5G mid-band and UWB applications. This article presents a miniaturized dual and quad port MIMO antenna design optimized for 5G [...] Read more.
The growing demand for high-speed and high-capacity wireless communication has intensified the need for compact, wideband, and efficient MIMO antenna systems, particularly for 5G mid-band and UWB applications. This article presents a miniaturized dual and quad port MIMO antenna design optimized for 5G mid-band (n77/n78/n79/n96/n102) and Ultra-Wideband (UWB) applications without employing any decoupling structures between the radiating elements. The 2-port configuration features two closely spaced symmetric monopole elements (spacing < λmax/2), promoting efficient use of space without degrading performance. An FR4 substrate (εr = 4.4) is used for fabrication with a compact size of 30 × 41 × 1.6 mm3. This layout is extended orthogonally and symmetrically to form a compact quad-port variant with dimensions of 60 × 41 × 1.6 mm3. Both designs offer a broad operational bandwidth from 2.6 GHz to 10.8 GHz (8.2 GHz), retaining return loss (SXX) below −10 dB and strong isolation (SXY < −20 dB at high frequencies, <−15 dB at low frequencies). The proposed MIMO antennas demonstrate strong performance and excellent diversity characteristics. The two-port antenna achieves an average envelope correlation coefficient (ECC) of 0.00204, diversity gain (DG) of 9.98 dB, and a mean effective gain difference (MEGij) of 0.3 dB, with a total active reflection coefficient (TARC) below −10 dB and signal delay variation under 0.25 ns, ensuring minimal pulse distortion. Similarly, the four-port design reports an average ECC of 0.01432, DG of 9.65 dB, MEGij difference below 0.3 dB, and TARC below −10 dB, confirming robust diversity and MIMO performance across both configurations. Full article
(This article belongs to the Section E：Engineering and Technology)
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14 pages, 1745 KiB  
Article
Investigation of Efficient Mixing Enhancement in a Droplet Micromixer with Short Mixing Length at Low Reynolds Number
by Yuanfang Qiu, Xueze Zhang, Mengzhen Hao, Xu Yin, Mengling Zhou, Shichao Ma, Yuanting Zhang, Naiqian Jiang, Li Xie, Xichen Yuan and Honglong Chang
Micromachines 2025, 16(6), 715; https://doi.org/10.3390/mi16060715 - 16 Jun 2025
Viewed by 326
Abstract
Rapid mixing is widely prevalent in the field of microfluidics, encompassing applications such as biomedical diagnostics, drug delivery, chemical synthesis, and enzyme reactions. Mixing efficiency profoundly impacts the overall performance of these devices. However, at the micro-scale, the flow typically presents as laminar [...] Read more.
Rapid mixing is widely prevalent in the field of microfluidics, encompassing applications such as biomedical diagnostics, drug delivery, chemical synthesis, and enzyme reactions. Mixing efficiency profoundly impacts the overall performance of these devices. However, at the micro-scale, the flow typically presents as laminar flow due to low Reynolds numbers, rendering rapid mixing challenging. Leveraging the vortices within a droplet of the Taylor flow and inducing chaotic convection within the droplet through serpentine channels can significantly enhance mixing efficiency. Based on this premise, we have developed a droplet micromixer that integrates the T-shaped channels required for generating Taylor flow and the serpentine channels required for inducing chaotic convection within the droplet. We determined the range of inlet liquid flow rate and gas pressure required to generate Taylor flow and conducted experimental investigations to examine the influence of the inlet conditions on droplet length, total flow rate, and mixing efficiency. Under conditions where channel dimensions and liquid flow rates are identical, Taylor flow achieves a nine-fold improvement in mixing efficiency compared to single-phase flow. At low Reynolds number (0.57 ≤ Re ≤ 1.05), the chip can achieve a 95% mixing efficiency within a 2 cm distance in just 0.5–0.8 s. The mixer proposed in this study offers the advantages of simplicity in manufacturing and ease of integration. It can be readily integrated into Lab-on-a-Chip devices to perform critical functions, including microfluidic switches, formation of nanocomposites, synthesis of oxides and adducts, velocity measurement, and supercritical fluid fractionation. Full article
(This article belongs to the Collection Micromixers: Analysis, Design and Fabrication)
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10 pages, 3193 KiB  
Article
Optical Film with Microstructures to Regulate Viewing Angle of HUDs
by Qibin Feng, Xiangjun Li, Chunhui Chen, Guoqiang Lv and Zi Wang
Micromachines 2025, 16(6), 714; https://doi.org/10.3390/mi16060714 - 16 Jun 2025
Viewed by 239
Abstract
Head-up displays (HUDs) can effectively enhance driving safety by projecting information—such as speed and maps—onto the windshield, thereby reducing blind spots caused by drivers looking down. As drivers need to observe road conditions within a wider horizontal viewing field, and considering that the [...] Read more.
Head-up displays (HUDs) can effectively enhance driving safety by projecting information—such as speed and maps—onto the windshield, thereby reducing blind spots caused by drivers looking down. As drivers need to observe road conditions within a wider horizontal viewing field, and considering that the observed angle in a vertical direction is relatively small, it becomes reasonable for an HUD to present a larger horizontal viewing angle than vertical viewing angle. This paper proposes a method to independently regulate the horizontal and vertical viewing angles. The original microstructure morphology is modeled as an ellipsoid, and the curvatures of the ellipsoid’s major and minor axes are calculated according to the required viewing angles. The simulation results show that the horizontal viewing angle corresponding to 85% of the maximum luminance increases from 2° without the film to 20° with the film, while the vertical viewing angle increases from 2° to 8°. The optical film with the designed microstructures is prepared and measured. The practical measurement results indicate that the tested horizontal and vertical viewing angles exhibit significant differentiation. At 85% of the maximum luminance, the horizontal viewing angle increases from 2° without the film to 23° with the film, while the vertical viewing angle increases from 2° to 10°. These results meet the requirements for independently regulating horizontal and vertical viewing angles and widening the horizontal viewing angle. Full article
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15 pages, 2341 KiB  
Article
Roll-to-Roll (R2R) High-Throughput Manufacturing of Foil-Based Microfluidic Chips for Neurite Outgrowth Studies
by Nihan Atak, Martin Smolka, Anja Haase, Alexandra Lorenz, Silvia Schobesberger, Stephan Ruttloff, Christian Wolf, Ana Ayerdi-Izquierdo, Peter Ertl, Nerea Briz Iceta, Jan Hesse and Martin Frauenlob
Micromachines 2025, 16(6), 713; https://doi.org/10.3390/mi16060713 - 16 Jun 2025
Viewed by 534
Abstract
Microfluidic devices have emerged as a pivotal in vitro technology for axon outgrowth studies, facilitating the separation of the cell body from the neurites by geometric constraints. However, traditional microfabrication techniques fall short in terms of scalability for large-scale production, hindering widespread application. [...] Read more.
Microfluidic devices have emerged as a pivotal in vitro technology for axon outgrowth studies, facilitating the separation of the cell body from the neurites by geometric constraints. However, traditional microfabrication techniques fall short in terms of scalability for large-scale production, hindering widespread application. This study presents the development of foil-based cell culture chips, made of polyethylene terephthalate and in-house formulated ultraviolet curable liquid resin by high-throughput roll-to-roll (R2R) manufacturing. Here, two microchannel designs were tested to optimize manufacturing quality and assess the neurite outgrowth behavior. The fabricated neuron-foil chips demonstrated biocompatibility and supported neurite outgrowth within microchannels under static cell culture conditions. Furthermore, fluidic flow, oriented either perpendicular or parallel to the microchannel direction, was applied to enhance the biological reproducibility within the neuron-foil chips. These findings suggest that R2R manufacturing offers a promising approach for the high-throughput production of biocompatible microfluidic devices, advancing their potential application in modeling neurological diseases within the biomedical industry. Full article
(This article belongs to the Section B2: Biofabrication and Tissue Engineering)
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23 pages, 2579 KiB  
Review
From Micro to Marvel: Unleashing the Full Potential of Click Chemistry with Micromachine Integration
by Zihan Chen, Zimo Ren, Carmine Coluccini and Paolo Coghi
Micromachines 2025, 16(6), 712; https://doi.org/10.3390/mi16060712 - 15 Jun 2025
Viewed by 531
Abstract
Micromachines, small-scale engineered devices prepared to carry out exact tasks at the micro level, have garnered great interest across different fields such as drug delivery, chemical synthesis, and biomedical applications. In emerging applications, micromachines have indicated great potential in advancing click chemistry, a [...] Read more.
Micromachines, small-scale engineered devices prepared to carry out exact tasks at the micro level, have garnered great interest across different fields such as drug delivery, chemical synthesis, and biomedical applications. In emerging applications, micromachines have indicated great potential in advancing click chemistry, a highly selective and efficient chemical technique widely applied in materials science, bioconjugation, and pharmaceutical development. Click chemistry, distinguished by its rapid reaction rates, high efficiency, and bioorthogonality, serves as a robust method for molecular assembly and functionalization. Incorporating micromachines into click chemistry processes paves the way for precise, automated, and scalable chemical synthesis. These tiny devices can effectively transport reactants, boost reaction efficiency through localized mixing, and enable highly exact site-specific modifications. Moreover, micromachines driven by external forces such as magnetic fields, ultrasound, or chemical fuels provide exceptional control over reaction conditions, significantly enhancing the selectivity and efficiency of click reactions. In this review, we explore the interaction between micromachines and click chemistry, showcasing recent advancements, potential uses, and future prospects in this cross-disciplinary domain. By leveraging micromachine-supported click chemistry, scientists can surpass conventional reaction constraints, opening doors to groundbreaking innovations in materials science, drug discovery, and beyond. Full article
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13 pages, 4379 KiB  
Article
A Broadband Millimeter-Wave Circularly Polarized Folded Reflectarray Antenna Based on Transmissive Linear-to-Circular Polarization Converter
by Yue Cao, Zhuwei Wang, Qing Wang, Mingzhu Du and Miaojuan Zhang
Micromachines 2025, 16(6), 711; https://doi.org/10.3390/mi16060711 - 14 Jun 2025
Viewed by 355
Abstract
In this paper, a wideband circularly polarized folded reflectarray antenna (CPFRA) based on a transmissive linear-to-circular polarization converter is proposed. The CPFRA consists of a primary reflector and a sub-reflector. To achieve broadband performance, a metasurface-based RA element on the primary reflector surface [...] Read more.
In this paper, a wideband circularly polarized folded reflectarray antenna (CPFRA) based on a transmissive linear-to-circular polarization converter is proposed. The CPFRA consists of a primary reflector and a sub-reflector. To achieve broadband performance, a metasurface-based RA element on the primary reflector surface and a transmissive linear-to-circular polarization converter on the sub-reflector surface are applied. Moreover, the transmissive linear-to-circular polarization converter on the sub-reflector surface helps convert linear polarization to circular polarization. To verify the proposed CPFRA, a prototype is designed, fabricated, and tested. The measured results exhibit that the proposed CPFRA presents a 3 dB gain bandwidth of 27.4% and a 3 dB axial ratio bandwidth of 23%. The CPFRA achieves a peak gain of 21.2 dBi with an aperture efficiency of 27.2%. The proposed CPFRA is a promising candidate for millimeter-wave (mm-W) satellite communication applications because of its advantages of high gain, low cost, low profile, and broad bandwidth. Full article
(This article belongs to the Special Issue Microwave Passive Components, 3rd Edition)
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14 pages, 3967 KiB  
Article
Influence of Homoepitaxial Layer Thickness on Flatness and Chemical Mechanical Planarization Induced Scratches of 4H-Silicon Carbide Epi-Wafers
by Chi-Hsiang Hsieh, Chiao-Yang Cheng, Yi-Kai Hsiao, Zi-Hao Wang, Chang-Ching Tu, Chao-Chang Arthur Chen, Po-Tsung Lee and Hao-Chung Kuo
Micromachines 2025, 16(6), 710; https://doi.org/10.3390/mi16060710 - 13 Jun 2025
Viewed by 332
Abstract
The integration of thick homoepitaxial layers on silicon carbide (SiC) substrates is critical for enabling high-voltage power devices, yet it remains challenged by substrate surface quality and wafer geometry evolution. This study investigates the relationship between substrate preparation—particularly chemical mechanical planarization (CMP)—and the [...] Read more.
The integration of thick homoepitaxial layers on silicon carbide (SiC) substrates is critical for enabling high-voltage power devices, yet it remains challenged by substrate surface quality and wafer geometry evolution. This study investigates the relationship between substrate preparation—particularly chemical mechanical planarization (CMP)—and the impact on wafer bow, total thickness variation (TTV), local thickness variation (LTV), and defect propagation during epitaxial growth. Seven 150 mm, 4° off-axis, prime-grade 4H-SiC substrates from a single ingot were processed under high-volume manufacturing (HVM) conditions and grown with epitaxial layers ranging from 12 μm to 100 μm. Metrology revealed a strong correlation between increasing epitaxial thickness and geometric deformation, especially beyond 31 μm. Despite initial surface scratches from CMP, hydrogen etching and buffer layer deposition significantly mitigated scratch propagation, as confirmed through defect mapping and SEM/FIB analysis. These findings provide a deeper understanding of the substrate-to-epitaxy integration process and offer pathways to improve manufacturability and yield in thick-epilayer SiC device fabrication. Full article
(This article belongs to the Section D：Materials and Processing)
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16 pages, 5187 KiB  
Article
Optimization and Experimental Analysis of Electroless Nickel Plating on the Diamond Surface
by Qingming Fan, Guokang Su, Congmin Zhu, Hui Qi, Pengfan Li, Xiumei Shen, Chuanyun Zhang and Kai Cheng
Micromachines 2025, 16(6), 709; https://doi.org/10.3390/mi16060709 - 13 Jun 2025
Viewed by 345
Abstract
Coating diamond particle surfaces with a layer of high-temperature resistant nickel, which possesses weldability, effectively enhances the bonding strength between diamond particles and substrates in pre-grinding tools. This improves their stability and strength at high temperatures, thereby enhancing the performance, lifespan, and efficiency [...] Read more.
Coating diamond particle surfaces with a layer of high-temperature resistant nickel, which possesses weldability, effectively enhances the bonding strength between diamond particles and substrates in pre-grinding tools. This improves their stability and strength at high temperatures, thereby enhancing the performance, lifespan, and efficiency of grinding tools. This paper explores the electroless nickel plating process on diamond surfaces, analyzes the working principle of electroless nickel plating on diamond surfaces, and proposes the use of 2 g/L AgNO3 solution and 2 g/L AgNO3 + 10 mL/L NH3·H2O solution as Pd-free activating solutions. Experimental studies have demonstrated the feasibility of using silver nitrate as an activator, and it has been found that the 2 g/L AgNO3 + 10 mL/L NH3·H2O solution achieves a higher surface plating ratio when used as an activator for electroless nickel plating on diamond surfaces. Based on this, through orthogonal and single-factor experimental methods, the effects of ammonia solution concentration, sodium hypophosphite concentration, plating temperature, and diamond particle size on electroless nickel plating on diamond surfaces were investigated. The optimal process for electroless nickel plating on diamond surfaces was obtained: ammonia solution concentration of 17.5 mL/L, sodium hypophosphite concentration of 33 g/L, and plating temperature of 80 °C. Under this process, using diamond particles with a size of 120/140 for electroless nickel plating, a surface plating ratio of 10.75% electroless nickel-plated diamond can be achieved. Full article
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22 pages, 8548 KiB  
Article
Study on the Motion Trajectory of Abrasives and Surface Improvement Mechanism in Ultrasonic-Assisted Diamond Wire Sawing Monocrystalline Silicon
by Honghao Li, Yufei Gao, Shengtan Hu and Zhipu Huo
Micromachines 2025, 16(6), 708; https://doi.org/10.3390/mi16060708 - 13 Jun 2025
Viewed by 309
Abstract
The surface quality of diamond wire sawing (DWS) wafers directly affects the efficiency and yield of subsequent processing steps. This paper investigates the motion trajectory of abrasives in ultrasonic-assisted diamond wire sawing (UADWS) and its mechanism for improving surface quality. The influence of [...] Read more.
The surface quality of diamond wire sawing (DWS) wafers directly affects the efficiency and yield of subsequent processing steps. This paper investigates the motion trajectory of abrasives in ultrasonic-assisted diamond wire sawing (UADWS) and its mechanism for improving surface quality. The influence of ultrasonic vibration on the cutting arc length, cutting depth, and interference of multi-abrasive trajectories was analyzed through the establishment of an abrasive motion trajectory model. The ultrasonic vibration transforms the abrasive trajectory from linear to sinusoidal, thereby increasing the cutting arc length while reducing the cutting depth. A lower wire speed was found to be more conducive to exploiting the advantages of ultrasonic vibration. Furthermore, the intersecting interference of multi-abrasive trajectories contributes to enhanced surface quality. Experimental studies were conducted on monocrystalline silicon (mono-Si) to verify the effectiveness of ultrasonic vibration in improving surface morphology and reducing wire marks during the sawing process. The experimental results demonstrate that, compared with DWS, UADWS achieves a significantly lower surface roughness Ra and generates micro-pits. The ultrasonic vibration induces a micro-grinding effect on both peaks and valleys of wire marks, effectively reducing their peak–valley (PV) height. This study provides a theoretical basis for optimizing UADWS process parameters and holds significant implications for improving surface quality in mono-Si wafer slicing. Full article
(This article belongs to the Section D：Materials and Processing)
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18 pages, 908 KiB  
Article
Diffusiophoresis of a Weakly Charged Dielectric Fluid Droplet in a Cylindrical Pore
by Lily Chuang, Sunny Chen, Nemo Chang, Jean Chien, Venesa Liao and Eric Lee
Micromachines 2025, 16(6), 707; https://doi.org/10.3390/mi16060707 - 13 Jun 2025
Viewed by 387
Abstract
Diffusiophoresis of a weakly charged dielectric droplet in a cylindrical pore is investigated theoretically in this study. The governing fundamental electrokinetic equations are solved with a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to take care of [...] Read more.
Diffusiophoresis of a weakly charged dielectric droplet in a cylindrical pore is investigated theoretically in this study. The governing fundamental electrokinetic equations are solved with a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to take care of the irregular solution domain. The impact of the boundary confinement effect upon the droplet motion is explored in detail, which is most profound in narrow channels. We found, among other things, that the droplet moving direction may reverse with varying channel widths. Enhanced motion-inducing double-layer polarization due to the presence of a nearby channel wall is found to be responsible for it. In particular, an interesting and seemingly peculiar phenomenon referred to as the “solidification phenomenon” is observed here at some specific critical droplet sizes or electrolyte strengths in narrow channels, under which all the droplets move at identical speeds regardless of their viscosities. They move like a rigid particle without the surface spinning motions and the induced interior recirculating vortex flows. As the corresponding shear rate is zero at this point, the droplet is resilient to undesirable exterior shear stresses tending to damage the droplet in motion. This provides a helpful guideline in the fabrication of liposomes in drug delivery in terms of the optimal liposome size, as well as in the microfluidic and nanofluidic manipulations of cells, among other potential practical applications. The effects of other parameters of electrokinetic interest are also examined. Full article
(This article belongs to the Special Issue Electrokinetic Particle and Fluid Transport Driven by Solute Concentration and Thermal Gradients)
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13 pages, 2748 KiB  
Article
Additive–Subtractive Manufacturing Based on Water-Soluble Sacrificial Layer: High-Adhesion Metal Patterning via Inkjet Printing
by Mengyang Su, Jin Huang, Hongxiao Gong, Zihan Zhu, Pan Li, Huagui Wang, Pengbing Zhao, Jianjun Wang and Jie Zhang
Micromachines 2025, 16(6), 706; https://doi.org/10.3390/mi16060706 - 13 Jun 2025
Viewed by 819
Abstract
Inkjet printing has become a primary technique for manufacturing flexible and conformal electronics due to its digital control, design flexibility, and material compatibility. However, its direct deposition nature results in weak adhesion between metal films and substrates, as it mainly relies on van [...] Read more.
Inkjet printing has become a primary technique for manufacturing flexible and conformal electronics due to its digital control, design flexibility, and material compatibility. However, its direct deposition nature results in weak adhesion between metal films and substrates, as it mainly relies on van der Waals or capillary forces, which severely limits its broader application in these fields. To address this limitation, we proposed an additive–subtractive manufacturing method based on a water-soluble sacrificial layer. First, the sacrificial material is inkjet-printed onto the substrate. Then, ion sputtering is employed to bombard the surface with high-energy ions, enabling metal atoms to embed into the substrate and form a strongly adhered conductive layer. Finally, the substrate is immersed in water, dissolving the sacrificial layer and detaching the undesired metal, thereby achieving selective retention of the conductive pattern. Experimental results demonstrate that the optimized water-soluble material, with tailored viscosity and surface tension, enables a patterning resolution of ±10 μm. The adhesion strength of the sputtered metal layer is 5.2 times greater than that of inkjet-printed silver nanoparticles. This method was further applied to fabricate conductive patterns on a curved surface with a 91 mm radius confirming its feasibility and adaptability for complex 3D surfaces. Full article
(This article belongs to the Section D3: 3D Printing and Additive Manufacturing)
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17 pages, 2382 KiB  
Article
Hydrothermally Synthesized PPy/VO2 Nanorod Composites for High-Performance Aqueous Zinc-Ion Battery Cathodes
by Taoyun Zhou, Shilin Li, Dong Xie, Yi Liu, Yun Cheng and Xinyu Li
Micromachines 2025, 16(6), 705; https://doi.org/10.3390/mi16060705 - 13 Jun 2025
Viewed by 374
Abstract
The rapid development of energy storage technologies has led to an increasing demand for high-performance electrode materials that can enhance both the energy density and the cycling stability of batteries. In this study, polypyrrole (PPy) nanorods with partial hollow features are utilized as [...] Read more.
The rapid development of energy storage technologies has led to an increasing demand for high-performance electrode materials that can enhance both the energy density and the cycling stability of batteries. In this study, polypyrrole (PPy) nanorods with partial hollow features are utilized as a conductive and flexible framework for the in situ growth of VO2 nanospheres via a simple hydrothermal method, forming a well-defined core–shell PPy/VO2 nanocomposite. This hierarchical nanostructure combines the excellent electrical conductivity and mechanical flexibility of PPy with the high theoretical capacity of VO2, creating a synergistic effect that significantly enhances the electrochemical performance. The well-integrated interface between PPy and VO2 reduces interfacial resistance, promotes efficient electron and ion transport, and improves the overall energy conversion efficiency. Electrochemical testing reveals that the PPy/VO2 nanocomposite delivers a high specific capacity of 413 mAh g−1 at 100 mA g−1 and retains 87.2% of its initial capacity after 1200 cycles, demonstrating exceptional rate capability and long-term cycling stability. This work provides a versatile strategy for designing high-performance cathode materials and highlights the promising potential of PPy/VO2 nanocomposites for next-generation high-energy-density aqueous zinc-ion batteries. Full article
(This article belongs to the Section E：Engineering and Technology)
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12 pages, 6408 KiB  
Article
Automatic Mode-Matching Method for MEMS Gyroscope Based on Fast Mode Reversal
by Feng Bu, Bo Fan, Rui Feng, Ming Zhou and Yiwang Wang
Micromachines 2025, 16(6), 704; https://doi.org/10.3390/mi16060704 - 12 Jun 2025
Viewed by 570
Abstract
Processing errors can result in an asymmetric stiffness distribution within a microelectromechanical system (MEMS) disk resonator gyroscope (DRG) and thereby cause a mode mismatch and reduce the mechanical sensitivity and closed-loop scale factor stability. This paper proposes an automatic mode-matching method that utilizes [...] Read more.
Processing errors can result in an asymmetric stiffness distribution within a microelectromechanical system (MEMS) disk resonator gyroscope (DRG) and thereby cause a mode mismatch and reduce the mechanical sensitivity and closed-loop scale factor stability. This paper proposes an automatic mode-matching method that utilizes mode reversal to obtain the true resonant frequency of the operating state of a gyroscope for high-precision matching. This method constructs a gyroscope control system that contains a drive closed loop, sense force-to-rebalance (FTR) closed loop, and quadrature error correction closed loop. After the gyroscope was powered on and started up, the x- and y-axes were quickly switched to obtain the resonant frequencies of the two axes through a phase-locked loop (PLL), and the x-axis tuning voltage was automatically adjusted to match the two-axis frequency. The experimental results show that the method takes only 5 s to execute, the frequency matching accuracy reaches 0.01 Hz, the matching state can be maintained in the temperature range of −20 to 60 °C, and the fluctuation of the frequency split does not exceed 0.005 Hz. Full article
(This article belongs to the Special Issue Advances in MEMS Inertial Sensors)
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19 pages, 6385 KiB  
Review
An Updated Review of BiCuSeO-Based Thermoelectric Materials
by Haitao Zhang, Bo Feng, Suoluosu Yang, Ruolin Ruan, Rong Zhang, Tongqiang Xiong, Biyu Xu, Zhipeng Zheng, Guopeng Zhou, Yang Zhang, Kewei Wang, Yin Zhong, Yanhua Fan and Xiaoqiong Zuo
Micromachines 2025, 16(6), 703; https://doi.org/10.3390/mi16060703 - 12 Jun 2025
Viewed by 355
Abstract
Since 2010, BiCuSeO has emerged as a captivating subject of investigation within the realm of thermoelectric materials. Its allure lies in a remarkable confluence of characteristics: a distinctive natural super-lattice structure, an elevated Seebeck coefficient, and a low thermal conductivity, all of which [...] Read more.
Since 2010, BiCuSeO has emerged as a captivating subject of investigation within the realm of thermoelectric materials. Its allure lies in a remarkable confluence of characteristics: a distinctive natural super-lattice structure, an elevated Seebeck coefficient, and a low thermal conductivity, all of which have collectively piqued the intense interest of scientists worldwide. Over the subsequent eight-year period, an extensive array of research endeavors has been meticulously carried out, delving deep into the multifaceted properties of BiCuSeO and exploring avenues for performance enhancement. In this comprehensive review, we embark on a detailed exploration of the fundamental properties of BiCuSeO, encompassing its preparation methodologies, as well as its thermoelectric and mechanical attributes. A thorough synthesis of diverse strategies for optimizing the composition and structure of BiCuSeO is presented, elucidating how these modifications contribute to the enhancement of its thermoelectric and mechanical performance. Finally, the current state of research on N-type BiCuSeO is systematically summarized, offering a panoramic view of the advancements and challenges in this particular area. Full article
(This article belongs to the Special Issue Functional Materials and Microdevices, 2nd Edition)
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10 pages, 2060 KiB  
Article
Passive Frequency Tunability in Moiré-Inspired Frequency Selective Surfaces Based on Full-Wave Simulation
by Jieun Hwang and Sungcheol Hong
Micromachines 2025, 16(6), 702; https://doi.org/10.3390/mi16060702 - 12 Jun 2025
Viewed by 512
Abstract
This paper presents a simulation-based investigation of passive frequency tunability in frequency-selective surfaces (FSSs) enabled by Moiré pattern interference. By overlapping two identical hexagonal FSS layers and introducing rotational misalignment between them, we demonstrate that the resulting Moiré patterns induce significant shifts in [...] Read more.
This paper presents a simulation-based investigation of passive frequency tunability in frequency-selective surfaces (FSSs) enabled by Moiré pattern interference. By overlapping two identical hexagonal FSS layers and introducing rotational misalignment between them, we demonstrate that the resulting Moiré patterns induce significant shifts in the resonance frequency without any external bias or active components. Using full-wave simulations in HFSS, we show that rotating the second layer from 0° to 30° can shift the resonant frequency from 4.4 GHz down to 1.2 GHz. This tunable behavior emerges solely from geometrical manipulation, offering a low-complexity alternative to active tuning methods that rely on varactors or micro-electromechanical systems (MEMSs). We discuss the theoretical basis for this tuning mechanism based on effective periodicity modulation via rotational interference and highlight potential applications in passive reconfigurable filters and refractive index sensors. The proposed approach provides a promising route for implementing tunable electromagnetic structures without compromising simplicity, power efficiency, or integration compatibility. Full article
(This article belongs to the Special Issue Novel Electromagnetic and Acoustic Devices)
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20 pages, 12065 KiB  
Article
Design and Optimization of a Tapered Magnetic Soft Continuum Robot for Enhanced Navigation in Cerebral Vasculature
by Jiahang Wang, Yuhang Liu, Xiwen Lu, Yunlong Zhu and Chenyao Bai
Micromachines 2025, 16(6), 701; https://doi.org/10.3390/mi16060701 - 12 Jun 2025
Viewed by 666
Abstract
Magnetic soft continuum robots (MSCRs) have broad application advantages in vascular intervention; however, current MSCRs still face challenges in navigating the narrower and tortuous structure of the cerebral vasculature. To address this challenge, we propose a tapered MSCR (T-MSCR), which is designed to [...] Read more.
Magnetic soft continuum robots (MSCRs) have broad application advantages in vascular intervention; however, current MSCRs still face challenges in navigating the narrower and tortuous structure of the cerebral vasculature. To address this challenge, we propose a tapered MSCR (T-MSCR), which is designed to facilitate smooth navigation through microvascular structures via its miniature tip. Specifically, to optimize its bending ability, we combine the Gray Wolf Optimizer (GWO) with the Euler–Bernoulli beam theory and introduce a Discrete GWO (DGWO) approach to optimize the distribution of magnetic particles within the T-MSCR. We then demonstrate the optimization process of the T-MSCR’s bending ability, comparing and analyzing its deflection angle and deformation characteristics, highlighting its capability to enter microvasculars. Furthermore, we demonstrate the magnetic steering and path selection capabilities of T-MSCR in a two-dimensional vascular model and its navigation performance in real-scale human vascular models. Finally, biocompatibility tests confirm that T-MSCR exhibits no toxicity to human cells, thereby laying a solid foundation for its clinical application. The proposed T-MSCR design and optimization are expected to provide a more efficient and feasible solution for future cerebrovascular interventions. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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12 pages, 5712 KiB  
Article
The Study of the Transient Dose Rate Effect on ROIC Pixels in Ultra-Large-Scale Infrared Detectors
by Yuan Liu, Bin Wang, Ziyuan Tang, Mengwei Chen, Hui Wang, Weitao Yang and Longsheng Wu
Micromachines 2025, 16(6), 700; https://doi.org/10.3390/mi16060700 - 12 Jun 2025
Viewed by 333
Abstract
Infrared image sensors are crucial across various industries. However, with technological advancements, the growing scale of infrared image sensors has made the impact of transient dose rate effects increasingly significant. It is necessary to conduct relevant radiation effect studies to provide the theoretical [...] Read more.
Infrared image sensors are crucial across various industries. However, with technological advancements, the growing scale of infrared image sensors has made the impact of transient dose rate effects increasingly significant. It is necessary to conduct relevant radiation effect studies to provide the theoretical and data basis for future radiation-hardened design. This study explores the response of large-area N-wells in the readout circuit of infrared detectors to transient dose rate effects. The TCAD simulation results indicate that the expansive N-well area in the merged-design pixel units generates significant current pulses when exposed to gamma-ray irradiation. Specifically, at dose rates of 3 × 1011 rad/s, 5 × 1011 rad/s, 7 × 1011 rad/s, and 9 × 1011 rad/s, the pulse currents measured are 39 nA, 64 nA, 89 nA, and 119 nA, respectively. Due to the spatial constraints of the 55 nm merged design, the close proximity of the GND to the N-well creates a high potential barrier near the N-well, obstructing the path between the GND and the substrate, which results in the pulse current exhibiting a stepped-like characteristic. Full article
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22 pages, 1159 KiB  
Article
Compaction-Aware Flash Memory Remapping for Key–Value Stores
by Jialin Wang, Zhen Yang, Yi Fan and Yajuan Du
Micromachines 2025, 16(6), 699; https://doi.org/10.3390/mi16060699 - 11 Jun 2025
Viewed by 1053
Abstract
With the rapid development of big data and artificial intelligence, the demand for memory has exploded. As a key data structure in modern databases and distributed storage systems, the Log-Structured Merge Tree (LSM-tree) has been widely employed (such as LevelDB, RocksDB, etc.) in [...] Read more.
With the rapid development of big data and artificial intelligence, the demand for memory has exploded. As a key data structure in modern databases and distributed storage systems, the Log-Structured Merge Tree (LSM-tree) has been widely employed (such as LevelDB, RocksDB, etc.) in systems based on key–value pairs due to its efficient writing performance. In LSM-tree-based KV stores, typically deployed on systems with DRAM-SSD storage, the KV items are first organized into MemTable as buffer for SSTables in main memory. When the buffer size exceeds the threshold, MemTable is flushed to the SSD and reorganized into an SSTable, which is then passed down level by level through compaction. However, the compaction degrades write performance and SSD endurance due to significant write amplification. To address this issue, recent proposals have mostly focused on redesigning the structure of LSM trees. We discover the prevalence of unchanged data blocks (UDBs) in the LSM-tree compaction process, i.e., UDBs are written back to SSD the same as they are read into memory, which induces extra write amplification and degrades I/O performance. In this paper, we propose a KV store design in SSD, called RemapCom, to exploit remapping on these UDBs. RemapCom first identifies UDBs with a lightweight state machine integrated into the compaction merge process. In order to increase the ratio of UDBs, RemapCom further designs a UDB retention method to further develop the benefit of remapping. Moreover, we implement a prototype of RemapCom on LevelDB by providing two primitives for the remapping. Compared to the state of the art, the evaluation results demonstrate that RemapCom can reduce write amplification by up to 53% and improve write throughput by up to 30%. Full article
(This article belongs to the Special Issue State-of-the-Art Memristor and Optoelectronic Memristor: Materials, Fabrication, Mechanism and Applications)
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15 pages, 2930 KiB  
Article
Energy Harvesting from Ankle Flexion During Gait Using Flexible CdS and PVDF Sensors
by Kimberly Trevizo, Luis Santana, Manuel Chairez, Amanda Carrillo and Rafael Gonzalez-Landaeta
Micromachines 2025, 16(6), 698; https://doi.org/10.3390/mi16060698 - 11 Jun 2025
Viewed by 363
Abstract
In this work, energy was harvested from ankle flexion during gait. For this, two piezoelectric thin films were tested: PVDF and CdS. The PVDF film was a commercial option, and the CdS film was fabricated in our laboratory. Deposition of the CdS film [...] Read more.
In this work, energy was harvested from ankle flexion during gait. For this, two piezoelectric thin films were tested: PVDF and CdS. The PVDF film was a commercial option, and the CdS film was fabricated in our laboratory. Deposition of the CdS film is also reported in this work. Energy harvested during gait from heel strike and ankle flexion was compared. Tests were performed with 10 healthy volunteers walking on a treadmill at 1.2–1.5 km/h. The volunteers wore a sock with piezoelectric films incorporated in the heel and ankle joint (talocrural joint). Tests were performed first with the PVDF film and then with the CdS film. The CdS thin film obtained a d33 coefficient of 1.4928 nm/V, indicating high electrical energy generated from strain-stress. The talocrural joint generated the most energy: 11.359 μJ for the PVDF film and 0.854 μJ for the CdS film. Although the CdS film generated less energy than the commercial option, it was shown that harvesting energy from ankle flexion increased the energy harvested by more than 700% during gait compared to the energy harvested from heel-to-ground impact. Full article
(This article belongs to the Special Issue Flexible and Wearable Devices for Health Monitoring and Energy Harvesting)
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18 pages, 13463 KiB  
Article
Investigating the Characteristics of the Laser Powder Bed Fusion of SiCp/AlSi10Mg Composites: From a Single Track to a Cubic Block
by Ying He, Gang Xue, Haifeng Xiao and Haihong Zhu
Micromachines 2025, 16(6), 697; https://doi.org/10.3390/mi16060697 - 11 Jun 2025
Viewed by 601
Abstract
Laser powder bed fusion (LPBF) of SiCp/AlSi10Mg is promising in many industrial fields. In this paper, the characteristics of a 15 wt.% 1200 mesh SiCp/AlSi10Mg metal matrix composite fabricated by LPBF were investigated systematically, i.e., from a single track to a block. It [...] Read more.
Laser powder bed fusion (LPBF) of SiCp/AlSi10Mg is promising in many industrial fields. In this paper, the characteristics of a 15 wt.% 1200 mesh SiCp/AlSi10Mg metal matrix composite fabricated by LPBF were investigated systematically, i.e., from a single track to a block. It was found that when the laser energy input was high enough, the single track was continuous and not distorted; when the laser energy input was low, the single track was unstable and wrinkled. The densification of the LPBFed composite sample was influenced significantly by the surface morphologies and geometric dimensions of the single tracks. As high as 98.9% relative density was achieved when the optimized processing parameters were used. Because of the good wettability and the interfacial reaction during the process, the interface of SiC and the matrix showed good bonding. Near the interface of SiC and the matrix, needle-shaped phase Al4SiC4 could be found both in the single track and block, and the faceted particle Si was formed in the block because of the interfacial reaction. The microhardness of the LPBFed SiCp/AlSi10Mg composites was much higher than that of the LPBFed unreinforced AlSi10Mg. A coefficient of friction of 0.178 and wear rate of 2.02 × 10−4 mm3/(N⋅m) were achieved for the LPBFed composites. The main wear mechanism was delamination wear, accompanied by abrasive wear. The maximum yield strength and ultimate compressive strength were 566.6 MPa and 764.1 MPa, respectively. The fracture mode of the LPBFed composites is mainly brittle fracture. This study provides a theoretical and technical basis for LPBFed SiCp/AlSi10Mg 3D parts. Full article
(This article belongs to the Special Issue 3D/4D Printing of Multifunctional Composites with Multifunctional Applications)
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12 pages, 3480 KiB  
Article
Laser Micromachining for the Nucleation Control of Nickel Microtextures for IR Emission
by Tatsuhiko Aizawa, Hiroki Nakata and Takeshi Nasu
Micromachines 2025, 16(6), 696; https://doi.org/10.3390/mi16060696 - 11 Jun 2025
Viewed by 545
Abstract
Femtosecond laser micromachining was utilized to build up a micro-through-hole array into a sacrificial film, which was coated onto a copper specimen. This micro-through hole was shaped in the paraboloidal profile, with its micro-dimple on the interface between the copper substrate and the [...] Read more.
Femtosecond laser micromachining was utilized to build up a micro-through-hole array into a sacrificial film, which was coated onto a copper specimen. This micro-through hole was shaped in the paraboloidal profile, with its micro-dimple on the interface between the copper substrate and the film. This profile was simply in correspondence with the laser energy profile. The array was used as a nucleation and growth site for nickel cluster deposition during wet plating. The micro-pillared unit cells nucleated at the micro-dimple and grew on the inside of the micro-through hole. After removing the sacrificial film, cleansing, and polishing, the nickel micro-pillar array was obtained, standing on the copper substrate. These unit cells and their alignments were measured through scanning electron microscopy and laser microscopy. Thermographic microscopy with FT-IR was utilized to measure the IR emittance as a function of wavelength. The focused areas were varied by controlling the aperture to analyze the effects of arrayed microtextures on the IR emittance. Full article
(This article belongs to the Special Issue Laser Micro/Nano Fabrication, Second Edition)
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12 pages, 1707 KiB  
Article
Research on Simulation Optimization of MEMS Microfluidic Structures at the Microscale
by Changhu Wang and Weiyun Meng
Micromachines 2025, 16(6), 695; https://doi.org/10.3390/mi16060695 - 11 Jun 2025
Viewed by 306
Abstract
Microfluidic systems have become a hot topic in Micro-Electro-Mechanical System (MEMS) research, with micropumps serving as a key element due to their role in determining structural and flow dynamics within these systems. This study aims to analyze the influence of different structural obstacles [...] Read more.
Microfluidic systems have become a hot topic in Micro-Electro-Mechanical System (MEMS) research, with micropumps serving as a key element due to their role in determining structural and flow dynamics within these systems. This study aims to analyze the influence of different structural obstacles within microfluidics on micropump efficiency and offer guidance for improving microfluidic system designs. In this context, a MEMS-based micropump valve structure was developed, and simulations were conducted to examine the effects of the valve on microfluidic oscillations. The research explored various configurations, including valve positions and quantities, yielding valuable insights for optimizing microfluidic transport mechanisms at the microscale. Full article
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