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Research on Low-Profile Directional Flexible Antenna with 3D Coplanar Waveguide for Partial Discharge Detection
Multi-Nozzles 3D Bioprinting Collagen/Thermoplastic Elastomer Scaffold with Interconnect Pores
Rapid and Sensitive Detection of Thrombospondin-2 Using Nanoparticle Sensors Towards Cancer Screening and Prognosis

Journal Description

Micromachines

Micromachines is a peer-reviewed, open access journal on the science and technology of small structures, devices and systems, published monthly online by MDPI. The Chinese Society of Micro-Nano Technology (CSMNT) is affiliated with Micromachines and its members receive discounts on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), PubMed, PMC, Ei Compendex, dblp, and other databases.
Journal Rank: JCR - Q2 (Instruments and Instrumentation) / CiteScore - Q1 (Mechanical Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 17.2 days after submission; acceptance to publication is undertaken in 1.9 days (median values for papers published in this journal in the first half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Testimonials: See what our editors and authors say about Micromachines.
Companion journal: Micro.

Impact Factor: 3.0 (2024); 5-Year Impact Factor: 3.1 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2072-666X

Latest Articles

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

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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22 pages, 3866 KiB

Open AccessArticle

Evaluating the Accuracy of Low-Cost Wearable Sensors for Healthcare Monitoring

by Tatiana Pereira Filgueiras, Pedro Bertemes-Filho and Fabrício Noveletto

Micromachines 2025, 16(7), 791; https://doi.org/10.3390/mi16070791 - 2 Jul 2025

This study evaluates the accuracy of a low-cost wearable system for the continuous monitoring of vital signs, including heart rate, blood oxygen saturation (SpO

_{2}

), blood pressure trend (BPT), and body temperature. The prototype was built using the nRF52840 microcontroller, which integrates [...] Read more.

This study evaluates the accuracy of a low-cost wearable system for the continuous monitoring of vital signs, including heart rate, blood oxygen saturation (SpO

_{2}

), blood pressure trend (BPT), and body temperature. The prototype was built using the nRF52840 microcontroller, which integrates photoplethysmography and infrared sensors. The heart rate and SpO

_{2}

data were collected under three body positions (Rest, Sitting, and Standing), while all measurements were performed using both anatomical configurations: BPT-Finger and BPT-Earlobe. Results were compared against validated commercial devices: UT-100 for heart rate and SpO

_{2}

, G-TECH LA800 for blood pressure, and G-TECH THGTSC3 for body temperature. Ten participants were monitored over a ten-day period. Bland–Altman analysis revealed clinically acceptable agreement thresholds of ±5 mmHg for blood pressure, ±5–10 bpm for heart rate, ±4% for SpO

_{2}

, and ±0.5 °C for temperature. Both wearable configurations demonstrated clinically acceptable agreement across all vital signs. The BPT-Earlobe configuration exhibited superior stability and lower variability in the Rest and Sitting positions, likely due to reduced motion artifacts. Conversely, the BPT-Finger configuration showed higher SpO

_{2}

accuracy in the Standing position, with narrower limits of agreement. These findings highlight the importance of sensor placement in maintaining measurement consistency across physiological conditions. With an estimated cost of only ~USD 130—compared to ~USD 590 for the commercial alternatives—the proposed system presents a cost-effective, scalable, and accessible solution for decentralized health monitoring, particularly in underserved or remote environments. Full article

(This article belongs to the Special Issue Advanced Flexible Electronic Devices for Biomedical Application)

9 pages, 3091 KiB

Open AccessArticle

Microwave Detection of Carbon Monoxide Gas via a Spoof Localized Surface Plasmons-Enhanced Cavity Antenna

by Meng Wang, Wenjie Xu and Shitao Sun

Micromachines 2025, 16(7), 790; https://doi.org/10.3390/mi16070790 - 2 Jul 2025

This paper presents a carbon monoxide (CO) detection mechanism achieved through further improvement of the sensing antenna based on hybrid spoof localized surface plasmons (SLSPs) and cavity resonance. Unlike conventional approaches relying on chemical reactions or photoelectric effects, the all-metal configuration detects dielectric [...] Read more.

This paper presents a carbon monoxide (CO) detection mechanism achieved through further improvement of the sensing antenna based on hybrid spoof localized surface plasmons (SLSPs) and cavity resonance. Unlike conventional approaches relying on chemical reactions or photoelectric effects, the all-metal configuration detects dielectric variations through microwave-regime resonance frequency shifts, enabling CO/air differentiation with theoretically enhanced robustness and environmental adaptability. The designed system achieves measured figures of merit (FoMs) of 183.2 RIU⁻¹, resolving gases with dielectric contrast below 0.1%. Experimental validation successfully discriminated CO (ε_r = 1.00262) from air (ε_r = 1.00054) under standard atmospheric pressure at 18 °C. Full article

(This article belongs to the Special Issue Current Research Progress in Microwave Metamaterials and Metadevices)

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18 pages, 3665 KiB

Open AccessArticle

Analytical Device and Prediction Method for Urine Component Concentrations

by Zhe Wang, Jianbang Huang, Qimeng Chen, Yuanhua Yu, Xuan Yu, Yue Zhao, Yan Wang, Chunxiang Shi, Zizhao Zhao and Dachun Tang

Micromachines 2025, 16(7), 789; https://doi.org/10.3390/mi16070789 - 2 Jul 2025

To tackle the low-accuracy problem with analyzing urine component concentrations in real time, a fully automated dipstick analysis device of urine dry chemistry was designed, and a prediction method combining an image acquisition system with a whale optimization algorithm (WOA) for BP neural [...] Read more.

To tackle the low-accuracy problem with analyzing urine component concentrations in real time, a fully automated dipstick analysis device of urine dry chemistry was designed, and a prediction method combining an image acquisition system with a whale optimization algorithm (WOA) for BP neural network optimization was proposed. The image acquisition system, which comprised an ESP32S3 chip and a GC2145 camera, was used to collect the urine test strip images, and then color data were calibrated by image processing and color correction on the upper computer. The correlations between reflected light and concentrations were established following the Kubelka–Munk theory and the Beer–Lambert law. A mathematical model of urine colorimetric value and concentration was constructed based on the least squares method. The WOA algorithm was applied to optimize the weight and threshold of the BP neural network, and substantial data were utilized to train the neural network and perform comparative analysis. The experimental results show that the MAE, RMSE and R² of predicted versus actual urine protein values were, respectively, 3.1415, 4.328 and approximately 1. The WOA-BP neural network model exhibited high precision and accuracy in predicting the urine component concentrations. Full article

(This article belongs to the Section B：Biology and Biomedicine)

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21 pages, 4997 KiB

Open AccessArticle

3D-Printed Multi-Stimulus-Responsive Hydrogels: Fabrication and Characterization

by Jinzhe Wu, Zhiyuan Ma, Qianqian Tang and Runhuai Yang

Micromachines 2025, 16(7), 788; https://doi.org/10.3390/mi16070788 - 1 Jul 2025

Stimulus-responsive hydrogels have broad applications in the biomedical, sensing, and actuation fields. However, conventional fabrication methods are often limited to 2D structures, hindering the creation of complex, personalized 3D hydrogel architectures. Furthermore, hydrogels responding to only a single stimulus and delays in fabrication [...] Read more.

Stimulus-responsive hydrogels have broad applications in the biomedical, sensing, and actuation fields. However, conventional fabrication methods are often limited to 2D structures, hindering the creation of complex, personalized 3D hydrogel architectures. Furthermore, hydrogels responding to only a single stimulus and delays in fabrication techniques restrict their practical utility in biomedicine. In this study, we developed two novel multi-stimuli-responsive hydrogels (based on Gelatin/Sodium Alginate and Tannic Acid/EDTA-FeNa complexes) specifically designed for direct ink writing (DIW) 3D printing. We systematically characterized the printed properties and optimized component ratio, revealing sufficient mechanical strength (e.g., tensile modulus: Gel/SA-TA ≥ 0.22854 ± 0.021 MPa and Gel/SA-TA@Fe³⁺ ≥ 0.35881 ± 0.021 MPa), high water content (e.g., water absorption rate Gel/SA-TA ≥ 70.21% ± 1.5% and Gel/SA-TA@Fe³⁺ ≥ 64.86% ± 1.28%), excellent biocompatibility (e.g., cell viability: Gel/SA-TA and Gel/SA-TA@Fe³⁺ ≥ 90%) and good shape memory performance (e.g., the highest shape recovery rate of Gel/SA-TA reaches 74.85% ± 4.776%). Furthermore, we explored electrical characteristics, showing that the impedance value of Gel/SA-TA@Fe³⁺ hydrogel changes significantly under finger bending and NIR irradiation. This investigation demonstrates the potential of these 3D-printed multi-stimuli hydrogels for applications such as wearable flexible strain sensors. Full article

(This article belongs to the Section D3: 3D Printing and Additive Manufacturing)

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15 pages, 2580 KiB

Open AccessArticle

Observation of a Fano Resonance at 92 MeV (13.5 µm) in Al_0.2Ga_0.8N/GaN-Based Quantum Cascade Emitters

by Daniel Hofstetter, Andreas D. Wieck, Hans Beck and David P. Bour

Micromachines 2025, 16(7), 787; https://doi.org/10.3390/mi16070787 - 30 Jun 2025

We report on asymmetrically shaped Fano resonances in Al_0.2Ga_0.8N/GaN-based quantum cascade structures. In order to observe this type of resonance in electro-luminescence, a spectrally narrow feature must interact with a broad, quasi-continuous emission. While the narrow waveform is provided [...] Read more.

We report on asymmetrically shaped Fano resonances in Al_0.2Ga_0.8N/GaN-based quantum cascade structures. In order to observe this type of resonance in electro-luminescence, a spectrally narrow feature must interact with a broad, quasi-continuous emission. While the narrow waveform is provided by the GaN-based LO-phonon at 92 MeV (13.5 µm, 741 cm⁻¹), the broad peak consists of overlapping inter-subband transitions between several higher-order excited states ranging from 80 to 300 MeV and the ground state. Through the interference of these spectrally dissimilar peaks, a typical, asymmetric Fano line shape is generated. Full article

(This article belongs to the Special Issue III-V Optoelectronics and Semiconductor Process Technology, Second Edition)

22 pages, 25204 KiB

Open AccessArticle

An Improved NSGA-II Algorithm for Multi-Objective Optimization of Irregular Polygon Patch Antennas

by Zhenyang Ma and Jiahao Liu

Micromachines 2025, 16(7), 786; https://doi.org/10.3390/mi16070786 - 30 Jun 2025

This paper presents an improved NSGA-II algorithm for the multi-objective optimization of irregular polygon patch antennas (IPPAs), improving convergence efficiency and Pareto front quality. The algorithm integrates adaptive mechanisms that dynamically adjust crossover and mutation rates based on generational progression, accelerating convergence while [...] Read more.

This paper presents an improved NSGA-II algorithm for the multi-objective optimization of irregular polygon patch antennas (IPPAs), improving convergence efficiency and Pareto front quality. The algorithm integrates adaptive mechanisms that dynamically adjust crossover and mutation rates based on generational progression, accelerating convergence while preserving solution diversity. Furthermore, a simulated annealing-inspired acceptance criterion is embedded during offspring generation to mitigate local optima trapping and enhance evolutionary robustness. A dual-objective formulation simultaneously minimizes antenna volume and maximizes operational bandwidth within the X-band. Optimization is executed via HFSS co-simulation, with detailed electromagnetic models ensuring physical realizability and design fidelity. The optimized antenna achieves a compact volume of 2807.6 mm³ and an operational bandwidth of 2.7 GHz. Experimental validation of fabricated prototypes demonstrates agreement with simulations, confirming the accuracy and reliability of the proposed method. These results demonstrate the effectiveness of the improved NSGA-II algorithm in addressing complex multi-objective design challenges and underscore its potential in advanced broadband antenna applications. Full article

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

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14 pages, 1681 KiB

Open AccessArticle

Automated Antithrombin Activity Detection with Whole Capillary Blood Based on Digital Microfluidic Platform

by Dongshuo Li, Hanqi Hu, Hanzhi Zhang, Lei Shang, Tao Zhao, Qingchen Zhao, Shuhao Zhang, Fucun Ma, Guowei Liang, Rongxin Fu and Xuekai Liu

Micromachines 2025, 16(7), 785; https://doi.org/10.3390/mi16070785 - 30 Jun 2025

Antithrombin (AT) plays a crucial role in the human anticoagulant system and has extensive clinical applications. However, traditional detection methods often require large sample volumes, complex procedures, and lengthy processing times. Methods: We integrated digital microfluidics technology with AT detection to develop a [...] Read more.

Antithrombin (AT) plays a crucial role in the human anticoagulant system and has extensive clinical applications. However, traditional detection methods often require large sample volumes, complex procedures, and lengthy processing times. Methods: We integrated digital microfluidics technology with AT detection to develop a point-of-care testing (POCT) device that is user-friendly and fully automated for real-time AT testing. Results: This device allows for automation and enhanced adaptability to various settings, requiring only a minimal sample volume (whole capillary blood), thereby omitting steps such as plasma separation to save time and improve clinical testing efficiency. Comparisons with conventional AT activity detection methods demonstrate a high degree of consistency in the results obtained with this device. Conclusion: The AT detection system we developed exhibits significant effectiveness and holds substantial research potential, positioning it to evolve into a clinically impactful POCT solution for AT assessment. Full article

(This article belongs to the Special Issue Advances in Microfluidic Chips for Chemical and Biomedical Applications)

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18 pages, 6398 KiB

Open AccessArticle

Assessment of SiO₂ Nanotube Activity to Modify DL α-Tocopherol via ¹O₂ Generation Under Visible Light Irradiation

by Mihai Anastasescu, Radu Socoteanu, Veronica Bratan, Silviu Preda, Crina Anastasescu, Ioana Cătălina Gîfu, Cristina Lavinia Nistor, Rica Boscencu, Emilian Chifor, Catalin Negrila, Ion Bordeianu, Maria Zaharescu and Ioan Balint

Micromachines 2025, 16(7), 784; https://doi.org/10.3390/mi16070784 - 30 Jun 2025

Abstract [...] Full article

(This article belongs to the Special Issue Emerging Trends in Optoelectronic Device Engineering)

11 pages, 7781 KiB

Open AccessArticle

The Impact of Single-Event Radiation on Latch-Up Effect in High-Temperature CMOS Devices and Its Mechanism

by Bin Wang, Jianguo Cui, Ling Lv and Longsheng Wu

Micromachines 2025, 16(7), 783; https://doi.org/10.3390/mi16070783 - 30 Jun 2025

This paper investigates the latch-up effect in CMOS devices based on a 28 nm CMOS process within the temperature range of 200 K to 450 K using Sentaurus Technology Computer-Aided Design (TCAD) simulation, with a particular focus on the single-event latch-up (SEL) effect [...] Read more.

This paper investigates the latch-up effect in CMOS devices based on a 28 nm CMOS process within the temperature range of 200 K to 450 K using Sentaurus Technology Computer-Aided Design (TCAD) simulation, with a particular focus on the single-event latch-up (SEL) effect in the high-temperature range of 300 K to 450 K. The physical mechanism underlying the triggering of SEL in CMOS devices at high temperatures is revealed. The results show that when the linear energy transfer (LET) value is 75 MeV cm²/mg, the CMOS devices do not exhibit SEL effects at 300 K and 350 K. However, when the temperature rises to 400 K, a significant latch-up effect occurs, which becomes more pronounced with increasing temperature. Additionally, at a supply voltage of 1.2 V and a temperature of 450 K, the LET threshold for triggering SEL in CMOS devices decreases by 91.4% compared to 75 MeV cm²/mg at 300 K, dropping to 6 MeV cm²/mg. As the temperature increases, the latch-up trigger current of the CMOS devices decreases from 1.18 × 10⁻⁴ A/μm at 300 K to 4.65 × 10⁻⁵ A/μm at 450 K, and the hold voltage decreases from 1.48 V at 300 K to 1.07 V at 450 K. Full article

(This article belongs to the Special Issue Advanced Nano-Semiconductor Devices: Design, Modeling and Next-Generation AI Applications)

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18 pages, 9801 KiB

Open AccessArticle

Structural Optimization Design of the Dual-Layer CMUT with Low Power Consumption and High Ultrasonic Reception Performance

by Jie Li, Zhaohui Xiao, Zutang Wu, Xiong Hu, Zhikang Li, Yihe Zhao, Min Li, Jiawei Yuan, Shaohui Qin and Libo Zhao

Micromachines 2025, 16(7), 782; https://doi.org/10.3390/mi16070782 - 30 Jun 2025

Capacitive micromachined ultrasonic transducers (CMUTs) have been widely applied in fields such as air-coupled ultrasonic nondestructive testing, gesture recognition, and 3D imaging. However, most current CMUTs struggle to simultaneously achieve both low power consumption and high performance, which limits their application in relevant [...] Read more.

Capacitive micromachined ultrasonic transducers (CMUTs) have been widely applied in fields such as air-coupled ultrasonic nondestructive testing, gesture recognition, and 3D imaging. However, most current CMUTs struggle to simultaneously achieve both low power consumption and high performance, which limits their application in relevant fields. In this paper, a dual-layer CMUT is proposed, and its structural optimization design is also analyzed. The dual-layer CMUT consists of a top-layer circular CMUT cell and a bottom-layer annular CMUT cell. A movable pillar connects the top and bottom cells of the double-layer CMUT. This design increases the total deflection and reduces the stiffness, making the membrane more susceptible to deformation under external forces, thereby achieving low power consumption and high reception performance. The finite element method (FEM) results showed that, compared with conventional CMUTs, the structural optimization design of the dual-layer CMUT had a 13.7% reduction in collapse voltage. The improvements in the maximum deflection, average deflection, electromechanical coupling coefficient, transmitting sensitivity, and receiving sensitivity were 41.2%, 68.0%, 84.6%, 17.7%, and 101.6%, respectively. Therefore, the dual-layer CMUT has low power consumption and high reception performance while maintaining transmission performance, and it has potential for applications in portable, low-power devices and air-coupled ultrasonic nondestructive testing. Full article

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

12 pages, 1086 KiB

Open AccessArticle

Research on High-Precision Measurement Technology of the Extinction Ratio Based on the Transparent Element Mueller Matrix

by Ruiqi Xu, Mingpeng Hu, Xuedong Cao and Jiahui Ren

Micromachines 2025, 16(7), 781; https://doi.org/10.3390/mi16070781 - 30 Jun 2025

With the widespread application of optical technology in numerous fields, the polarization performance of transmissive optical components has become increasingly crucial. The extinction ratio, an important indicator for evaluating their polarization characteristics, holds great significance for its precise detection. Aiming at the measurement [...] Read more.

With the widespread application of optical technology in numerous fields, the polarization performance of transmissive optical components has become increasingly crucial. The extinction ratio, an important indicator for evaluating their polarization characteristics, holds great significance for its precise detection. Aiming at the measurement of the extinction ratio of a transparent component, this study proposes a measurement method for solving the extinction ratio based on measuring the Mueller matrix of the transparent component. The purpose is to analyze the worst position of the extinction ratio of the transmissive component. The extinction ratio of the sample is obtained according to the phase retardation derived from the Stokes vector of the incident light and the Mueller matrix of the optical component, and a theoretical analysis and simulation of this method are carried out. The simulation results verify the feasibility of the theoretical derivation of this method. To further verify the accuracy of the measurement method, experimental verification is conducted. A standard transparent sample with a phase retardation of 13 nm is selected for actual measurement. The data of independent experiments on the transparent sample under different powers are analyzed, and the extinction ratio of the transparent sample is further obtained. When using this method, the relative error is less than 2%, indicating good accuracy. Full article

(This article belongs to the Special Issue Micro/Nano Optical Devices and Sensing Technology)

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38 pages, 7348 KiB

Open AccessReview

Artificial Intelligence Control Methodologies for Shape Memory Alloy Actuators: A Systematic Review and Performance Analysis

by Stefano Rodinò, Giuseppe Rota, Matteo Chiodo, Antonio Corigliano and Carmine Maletta

Micromachines 2025, 16(7), 780; https://doi.org/10.3390/mi16070780 - 30 Jun 2025

Shape Memory Alloy (SMA) actuators are pivotal in modern engineering due to their unique thermomechanical properties, but their inherent non-linearities, hysteresis, and temperature sensitivity pose significant control challenges. This systematic review evaluates artificial intelligence (AI)-based control methodologies to address these limitations, analyzing their [...] Read more.

Shape Memory Alloy (SMA) actuators are pivotal in modern engineering due to their unique thermomechanical properties, but their inherent non-linearities, hysteresis, and temperature sensitivity pose significant control challenges. This systematic review evaluates artificial intelligence (AI)-based control methodologies to address these limitations, analyzing their efficacy in enhancing precision, adaptability, and reliability for SMA and Magnetic SMA (MSMA) systems. A PRISMA-guided literature review (2003–2025) identified 24 studies, which were categorized by control architectures (hybrid AI-linear, pure AI, adaptive, and model predictive control) and evaluated through quantitative metrics, including Root Mean Square Error (RMSE%) and a weighted scoring system for experimental rigor. Results revealed hybrid AI-linear controllers as the dominant approach (36%), with online-trained neural networks achieving superior accuracy (+2.4%) over offline methods. Feedforward neural networks outperformed recurrent architectures (+3.1%), while Model Predictive Control (MPC) excelled for SMA actuators (+5.8% accuracy) but underperformed for MSMAs (−7.7%). Sensorless strategies proved advantageous for MSMAs (+5.0%), leveraging intrinsic material properties like electrical resistance for state estimation. The analysis underscores AI’s capacity to mitigate hysteresis and non-linear dynamics, though material-specific optimization is critical: SMA systems favor dynamic control and MPC, whereas MSMAs benefit from sensorless AI and pure neural networks. Challenges persist in computational demands for online training and reinforcement learning’s exploration–exploitation trade-offs. Future research should prioritize adaptive algorithms for fatigue compensation, lightweight AI models for embedded deployment, and standardized benchmarking to bridge material-specific performance gaps. This synthesis establishes AI as a transformative paradigm for SMA actuation, enabling precise control in aerospace, biomedical, and soft robotics applications. Full article

(This article belongs to the Special Issue Design and Real Time Implementation of Intelligent Control Schemes for Actuators)

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9 pages, 1793 KiB

Open AccessArticle

Improved DC and RF Characteristics of GaN HEMT Using a Back-Barrier and Locally Doped Barrier Layer

by Shuxiang Sun, Lulu Liu, Gangchuan Qu, Xintong Xie and J. Ajayan

Micromachines 2025, 16(7), 779; https://doi.org/10.3390/mi16070779 - 30 Jun 2025

To enhance the DC and RF performance of AlGaN/GaN HEMTs, a novel device structure was proposed and investigated through simulation. The key innovation of this new structure lies in the incorporation of an Al_0.7In_0.15Ga_0.15N back-barrier layer and [...] Read more.

To enhance the DC and RF performance of AlGaN/GaN HEMTs, a novel device structure was proposed and investigated through simulation. The key innovation of this new structure lies in the incorporation of an Al_0.7In_0.15Ga_0.15N back-barrier layer and an N-type locally doped AlGaN barrier layer (BD-HEMT), based on conventional device architecture. The Al_0.7In_0.15Ga_0.15N back-barrier layer effectively confines electrons within the channel, thereby increasing the electron concentration. Simultaneously, the N-type locally doped AlGaN barrier layer introduced beneath the gate supplies additional electrons to the channel, further enhancing the electron density. These modifications collectively lead to improved DC and RF characteristics of the device. Compared to the conventional AlGaN/GaN HEMT, BD-HEMT achieves a 24.8% increase in saturation drain current and a 10.4% improvement in maximum transconductance. Furthermore, the maximum cutoff frequency and maximum oscillation frequency are enhanced by 14.8% and 21.2%, respectively. Full article

(This article belongs to the Special Issue Advances in GaN- and SiC-Based Electronics: Design and Applications)

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21 pages, 2896 KiB

Open AccessArticle

Annealing-Driven Modifications in ZnO Nanorod Thin Films and Their Impact on NO₂ Sensing Performance

by Sandip M. Nikam, Tanaji S. Patil, Nilam A. Nimbalkar, Raviraj S. Kamble, Vandana R. Patil, Uttam E. Mote, Sadaf Jamal Gilani, Sagar M. Mane, Jaewoong Lee and Ravindra D. Mane

Micromachines 2025, 16(7), 778; https://doi.org/10.3390/mi16070778 - 30 Jun 2025

This research examines the effect of annealing temperature on the growth orientation of zinc oxide (ZnO) nanorods and its subsequent influence on NO₂ gas sensing efficiency. Zinc oxide (ZnO) nanorods were synthesized using the chemical bath deposition method, followed by annealing at [...] Read more.

This research examines the effect of annealing temperature on the growth orientation of zinc oxide (ZnO) nanorods and its subsequent influence on NO₂ gas sensing efficiency. Zinc oxide (ZnO) nanorods were synthesized using the chemical bath deposition method, followed by annealing at 300, 400, and 500 °C. Diffraction analysis confirmed that both non-annealed and annealed ZnO nanorods crystallize in a hexagonal wurtzite structure. However, increasing the annealing temperature shifts the growth orientation from the c-axis (002) toward the (100) and (101) directions. Microscopy images (FE-SEM) revealed a reduction in nanorod diameter as the annealing temperature increases. Optical characterization using UV–visible and photoluminescence spectroscopy indicated shifts in the band gap energy and emission properties. Contact angle measurements demonstrated the hydrophobic nature of the films. Gas sensing tests at 200 °C revealed that the ZnO thin film annealed at 400 °C achieved the highest NO₂ response of 5.88%. The study highlights the critical role of annealing in modifying the crystallinity, growth orientation, and defect states of ZnO thin films, ultimately enhancing their NO₂ detection capability. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for High-Performance Gas Sensors)

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21 pages, 4979 KiB

Open AccessArticle

Reconfigurable Memristive Quasi-Lumped Dual-Band Bandpass Filters

by Dejan Miljanović, Milka Potrebić Ivaniš and Ivo Marković

Micromachines 2025, 16(7), 777; https://doi.org/10.3390/mi16070777 - 30 Jun 2025

This paper presents a dual-band bandpass filter with passband switchability controlled by using memristors. The memristor is a good choice as a control element due to its characteristics, such as low-power consumption, no bias needed, good electrical characteristics, and no moving parts. The [...] Read more.

This paper presents a dual-band bandpass filter with passband switchability controlled by using memristors. The memristor is a good choice as a control element due to its characteristics, such as low-power consumption, no bias needed, good electrical characteristics, and no moving parts. The filter’s reconfigurability is achieved by using memristors to selectively connect filter elements to ground. For the filter realization, multilayer technology with quasi-lumped elements has been chosen because of filter size miniaturization. Circuit-level simulations were initially used for quick analysis, followed by 3D EM simulations to validate the expected functionality of the proposed design concept. The results confirm the feasibility of a very small dual-band bandpass filter with independently controllable passbands. The frequency response of each of the two passbands (3.5 GHz and 5.8 GHz) can be tuned with negligible impact on the other passband by controlling the states of the memristors. The filter footprint area is equal to 0.10 λ_g × 0.12 λ_g, where λ_g is the guided wavelength at 3.5 GHz. Full article

(This article belongs to the Special Issue Future of RF/Microwave Filtering and Memristive Devices in Nowadays Mobile Networks)

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28 pages, 63037 KiB

Open AccessReview

Advances in 2D Photodetectors: Materials, Mechanisms, and Applications

by Ambali Alade Odebowale, Andergachew Mekonnen Berhe, Dinelka Somaweera, Han Wang, Wen Lei, Andrey E. Miroshnichenko and Haroldo T. Hattori

Micromachines 2025, 16(7), 776; https://doi.org/10.3390/mi16070776 - 30 Jun 2025

Two-dimensional (2D) materials have revolutionized the field of optoelectronics by offering exceptional properties such as atomically thin structures, high carrier mobility, tunable bandgaps, and strong light–matter interactions. These attributes make them ideal candidates for next-generation photodetectors operating across a broad spectral range—from ultraviolet [...] Read more.

Two-dimensional (2D) materials have revolutionized the field of optoelectronics by offering exceptional properties such as atomically thin structures, high carrier mobility, tunable bandgaps, and strong light–matter interactions. These attributes make them ideal candidates for next-generation photodetectors operating across a broad spectral range—from ultraviolet to mid-infrared. This review comprehensively examines the recent progress in 2D material-based photodetectors, highlighting key material classes including graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), MXenes, chalcogenides, and carbides. We explore their photodetection mechanisms—such as photovoltaic, photoconductive, photothermoelectric, bolometric, and plasmon-enhanced effects—and discuss their impact on critical performance metrics like responsivity, detectivity, and response time. Emphasis is placed on material integration strategies, heterostructure engineering, and plasmonic enhancements that have enabled improved sensitivity and spectral tunability. The review also addresses the remaining challenges related to environmental stability, scalability, and device architecture. Finally, we outline future directions for the development of high-performance, broadband, and flexible 2D photodetectors for diverse applications in sensing, imaging, and communication technologies. Full article

(This article belongs to the Special Issue Emerging Nanomaterials and Novel Structures for Photodetectors and Their Applications)

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20 pages, 23523 KiB

Open AccessArticle

A Wrist Brace with Integrated Piezoelectric Sensors for Real-Time Biomechanical Monitoring in Weightlifting

by Sofia Garcia, Ethan Ortega, Mohammad Alghamaz, Alwathiqbellah Ibrahim and En-Tze Chong

Micromachines 2025, 16(7), 775; https://doi.org/10.3390/mi16070775 - 30 Jun 2025

This study presents a self-powered smart wrist brace integrated with a piezoelectric sensor for real-time biomechanical monitoring during weightlifting activities. The system was designed to quantify wrist flexion across multiple loading conditions (0 kg, 0.5 kg, and 1.0 kg), leveraging mechanical strain-induced voltage [...] Read more.

This study presents a self-powered smart wrist brace integrated with a piezoelectric sensor for real-time biomechanical monitoring during weightlifting activities. The system was designed to quantify wrist flexion across multiple loading conditions (0 kg, 0.5 kg, and 1.0 kg), leveraging mechanical strain-induced voltage generation to capture angular displacement. A flexible PVDF film was embedded within a custom-fitted wrist brace and tested on male and female participants performing controlled wrist flexion. The resulting voltage signals were analyzed to extract root-mean-square (RMS) outputs, calibration curves, and sensitivity metrics. To interpret the experimental results analytically, a lumped-parameter cantilever beam model was developed, linking wrist flexion angles to piezoelectric voltage output based on mechanical deformation theory. The model assumed a linear relationship between wrist angle and induced strain, enabling theoretical voltage prediction through simplified material and geometric parameters. Model-predicted voltage responses were compared with experimental measurements, demonstrating a good agreement and validating the mechanical-electrical coupling approach. Experimental results revealed consistent voltage increases with both wrist angle and applied load, and regression analysis demonstrated strong linear or mildly nonlinear fits with high

R^{2}

values (up to 0.994) across all conditions. Furthermore, surface plots and strain sensitivity analyses highlighted the system’s responsiveness to simultaneous angular and loading changes. These findings validate the smart wrist brace as a reliable, low-power biomechanical monitoring tool, with promising applications in injury prevention, rehabilitation, and real-time athletic performance feedback. Full article

(This article belongs to the Special Issue Next-Generation Wearable Technologies: Integrating Smart Sensing, Biomedical Innovation, and Sustainable Energy Solutions)

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19 pages, 4761 KiB

Open AccessArticle

An Open-Type Crossflow Microfluidic Chip for Deformable Droplet Separation Driven by a Centrifugal Field

by Zekun Li, Yongchao Cai, Xiangfu Wei, Cuimin Sun, Wenshen Luo and Hui You

Micromachines 2025, 16(7), 774; https://doi.org/10.3390/mi16070774 - 30 Jun 2025

This study presents an innovative wedge-shaped inlet weir-type microfluidic chip designed to address common issues of clogging and inefficiency in microfiltration processes. Driven solely by centrifugal force, the chip integrates a crossflow separation mechanism and enables selective droplet sorting based on size, without [...] Read more.

This study presents an innovative wedge-shaped inlet weir-type microfluidic chip designed to address common issues of clogging and inefficiency in microfiltration processes. Driven solely by centrifugal force, the chip integrates a crossflow separation mechanism and enables selective droplet sorting based on size, without the need for external pumps. Fabricated from PMMA, the device features a central elliptical chamber, a wedge-shaped inlet, and spiral microchannels. These structures leverage shear stress and Dean vortices under centrifugal fields to achieve high-throughput separation of droplets with different diameters. Using water-in-oil emulsions as a model system, we systematically investigated the effects of geometric parameters and rotational speed on separation performance. A theoretical model was developed to derive the critical droplet size based on force balance, accounting for centrifugal force, viscous drag, pressure differentials, and surface tension. Experimental results demonstrate that the chip can effectively separate droplets ranging from 0 to 400 μm in diameter at 200 rpm, achieving a sorting efficiency of up to 72% and a separation threshold (cutoff accuracy) of 98.2%. Fluorescence analysis confirmed the absence of cross-contamination during single-chip operation. This work offers a structure-guided, efficient, and contamination-free droplet sorting strategy with broad potential applications in biomedical diagnostics and drug screening. Full article

(This article belongs to the Special Issue Advances in Microfluidic Chips for Chemical and Biomedical Applications)

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16 pages, 2521 KiB

Open AccessArticle

A Multimodal CMOS Readout IC for SWIR Image Sensors with Dual-Mode BDI/DI Pixels and Column-Parallel Two-Step Single-Slope ADC

by Yuyan Zhang, Zhifeng Chen, Yaguang Yang, Huangwei Chen, Jie Gao, Zhichao Zhang and Chengying Chen

Micromachines 2025, 16(7), 773; https://doi.org/10.3390/mi16070773 - 30 Jun 2025

This paper proposes a dual-mode CMOS analog front-end (AFE) circuit for short-wave infrared (SWIR) image sensors, which integrates a hybrid readout circuit (ROIC) and a 12-bit two-step single-slope analog-to-digital converter (TS-SS ADC). The ROIC dynamically switches between buffered-direct-injection (BDI) and direct-injection (DI) modes, [...] Read more.

This paper proposes a dual-mode CMOS analog front-end (AFE) circuit for short-wave infrared (SWIR) image sensors, which integrates a hybrid readout circuit (ROIC) and a 12-bit two-step single-slope analog-to-digital converter (TS-SS ADC). The ROIC dynamically switches between buffered-direct-injection (BDI) and direct-injection (DI) modes, thus balancing injection efficiency against power consumption. While the DI structure offers simplicity and low power, it suffers from unstable biasing and reduced injection efficiency under high background currents. Conversely, the BDI structure enhances injection efficiency and bias stability via an input buffer but incurs higher power consumption. To address this trade-off, a dual-mode injection architecture with mode-switching transistors is implemented. Mode selection is executed in-pixel via a low-leakage transmission gate and coordinated by the column timing controller, enabling low-current pixels to operate in low-noise BDI mode, whereas high-current pixels revert to the low-power DI mode. The TS-SS ADC employs a four-terminal comparator and dynamic reference voltage compensation to mitigate charge leakage and offset, which improves signal-to-noise ratio (SNR) and linearity. The prototype occupies 2.1 mm × 2.88 mm in a 0.18 µm CMOS process and serves a 64 × 64 array. The AFE achieves a dynamic range of 75.58 dB, noise of 249.42 μV, and 81.04 mW power consumption. Full article

(This article belongs to the Special Issue High-Reliability Semiconductor Devices and Integrated Circuits, 3rd Edition)

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