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A Sensor Employing an Array of Silicon Photomultipliers for Detection of keV Ions in Time-of-Flight Mass Spectrometry
On-Line Monitoring of Vitamin C in Fruit Juice in Processing Plants by PEDOT-Modified Electrochemical Sensor
Resonant Drive Techniques for Electrostatic Microelectromechanical Systems (MEMS): A Comparative Study
Acquisition and Modeling of Material Appearance Using a Portable, Low Cost, Device
Super Learner Calibration of Low-Cost IoT Air Quality Sensors for Accurate PM Monitoring

Journal Description

Sensors

Sensors is an international, peer-reviewed, open access journal on the science and technology of sensors. Sensors is published semimonthly online by MDPI. The Polish Society of Applied Electromagnetics (PTZE), Japan Society of Photogrammetry and Remote Sensing (JSPRS), Spanish Society of Biomedical Engineering (SEIB), International Society for the Measurement of Physical Behaviour (ISMPB) and Chinese Society of Micro-Nano Technology (CSMNT) and more are affiliated with Sensors and their members receive a discount 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, MEDLINE, PMC, Ei Compendex, Inspec, Astrophysics Data System, and other databases.
Journal Rank: JCR - Q2 (Instruments and Instrumentation) / CiteScore - Q1 (Instrumentation)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 19.7 days after submission; acceptance to publication is undertaken in 2.4 days (median values for papers published in this journal in the first half of 2025).
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Companion journals for Sensors include: Chips, Targets and AI Sensors.
Journal Cluster of Instruments and Instrumentation: Actuators, AI Sensors, Instruments, Micromachines and Sensors.

Impact Factor: 3.5 (2024); 5-Year Impact Factor: 3.7 (2024)

Imprint Information Journal Flyer Open Access ISSN: 1424-8220

Latest Articles

21 pages, 2347 KB

Open AccessArticle

EAFormer: Edge-Aware Guided Adaptive Frequency-Navigator Network for Image Restoration

by Wenjie Xie, Dong Zhou, Wenshuai Zhang and Wenrui Wang

Sensors 2025, 25(18), 5912; https://doi.org/10.3390/s25185912 (registering DOI) - 22 Sep 2025

Although many deep learning-based image restoration networks have emerged in various image restoration tasks, most can only perform well in a specific type of restoration task and still face challenges in the general performance of image restoration. The fundamental reason for this problem [...] Read more.

Although many deep learning-based image restoration networks have emerged in various image restoration tasks, most can only perform well in a specific type of restoration task and still face challenges in the general performance of image restoration. The fundamental reason for this problem is that different types of degradation require different frequency features, and the image needs to be adaptively reconstructed according to the characteristics of input degradation. At the same time, we noticed that the previous image restoration network ignored the reconstruction of the edge contour details of the image, resulting in unclear contours of the restored image. Therefore, we proposed an edge-aware guided adaptive frequency navigation network, EAFormer, which extracts edge information in the image by applying different edge detection operators and reconstructs the edge contour details of the image more accurately during the restoration process. The adaptive frequency navigation perceives different frequency components in the image and interactively participates in the subsequent restoration process with high- and low-frequency feature information, better retaining the global structural information of the image and making the restored image more visually coherent and realistic. We verified the versatility of EAFormer in five classic image restoration tasks, and many experimental results also show that our model has advanced performance. Full article

(This article belongs to the Section Navigation and Positioning)

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11 pages, 856 KB

Open AccessArticle

Feasibility of a Markerless Motion Capture System for Balance Function Assessment in Children with Cerebral Palsy

by Xiaoxia Yan, Nichola Wilson, Chengyan Sun and Yanxin Zhang

Sensors 2025, 25(18), 5911; https://doi.org/10.3390/s25185911 (registering DOI) - 21 Sep 2025

Children with cerebral palsy (CP) have impaired standing balance ability, caused by increased muscle tone, muscle weakness, and joint deformity. It is necessary to investigate standing balance for children with CP. Compared with postural stability assessment using force plates, OpenCap has the potential [...] Read more.

Children with cerebral palsy (CP) have impaired standing balance ability, caused by increased muscle tone, muscle weakness, and joint deformity. It is necessary to investigate standing balance for children with CP. Compared with postural stability assessment using force plates, OpenCap has the potential to be used utilized as a cost-effective standing balance assessment tool, providing details about the center of mass (CoM) and joint angles. This study aims to evaluate the feasibility of using OpenCap for standing balance assessment in children with CP by (i) examining the validity of OpenCap-based CoM parameters against force plate center of pressure (CoP) measures and (ii) exploring associations between joint angles and CoM displacement. Twenty-two children with CP completed standing balance trials on a force plate-based balance tester while two smartphones recorded synchronized videos for OpenCap processing. For the correlation between CoM parameters and CoP parameters, Pearson’s R values were from 0.39 to 0.94 between the two systems. After correcting the CoM parameters, the R² values ranged from 0.98 to 1.00. Regarding the relationship between the joint angles and CoM, maximum and minimum sagittal angles in the ankle were corrected with CoM displacement along the x-axis. These findings suggest that OpenCap may be a potential, cost-effective tool for standing balance assessment in children with CP. Full article

(This article belongs to the Section Intelligent Sensors)

22 pages, 4786 KB

Open AccessArticle

Multi-Signal Acquisition System for Continuous Blood Pressure Monitoring

by Naiwen Zhang, Yu Zhang, Jintao Chen, Shaoxuan Qiu, Jinting Ma, Lihai Tan and Guo Dan

Sensors 2025, 25(18), 5910; https://doi.org/10.3390/s25185910 (registering DOI) - 21 Sep 2025

Continuous blood pressure (BP) monitoring is essential for the early detection and prevention of cardiovascular diseases like hypertension. Recently, interest in continuous BP estimation systems and algorithms has grown. Various physiological signals reflect BP variations from different perspectives, and combining multiple signals can [...] Read more.

Continuous blood pressure (BP) monitoring is essential for the early detection and prevention of cardiovascular diseases like hypertension. Recently, interest in continuous BP estimation systems and algorithms has grown. Various physiological signals reflect BP variations from different perspectives, and combining multiple signals can enhance the accuracy of BP measurements. However, research integrating electrocardiogram (ECG), photoplethysmography (PPG), and impedance cardiography (ICG) signals for BP monitoring remains limited, with related technologies still in early development. A major challenge is the increased system complexity associated with acquiring multiple signals simultaneously, along with the difficulty of efficiently extracting and integrating key features for accurate BP estimation. To address this, we developed a BP monitoring system that can synchronously acquire and process ECG, PPG, and ICG signals. Optimizing the circuit design allowed ECG and ICG modules to share electrodes, reducing components and improving compactness. Using this system, we collected 400 min of signals from 40 healthy subjects, yielding 4390 records. Experiments were conducted to evaluate the system’s performance in BP estimation. The results demonstrated that combining pulse wave analysis features with the XGBoost model yielded the most accurate BP predictions. Specifically, the mean absolute error for systolic blood pressure was 3.76 ± 3.98 mmHg, and for diastolic blood pressure, it was 2.71 ± 2.57 mmHg, both of which achieved grade A performance under the BHS standard. These results are comparable to or better than existing studies based on multi-signal methods. These findings suggest that the proposed system offers an efficient and practical solution for BP monitoring. Full article

(This article belongs to the Special Issue Wearable Medical Sensors and AI-Driven Signal Processing for Next-Generation Healthcare)

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16 pages, 4189 KB

Open AccessArticle

Experimental Study of Liquid and Gas Gate Valve Internal Leakage Testing Based on Ultrasonic Signal

by Tingwei Wang, Xinjia Ma, Shiqiang Zhang, Qiang Feng, Xiaomei Xiang and Hui Xia

Sensors 2025, 25(18), 5909; https://doi.org/10.3390/s25185909 (registering DOI) - 21 Sep 2025

This study presents an experimental analysis of high-pressure liquid and gas gate valve leakage under multiple operating conditions, based on the variation patterns of ultrasonic signals. Focusing on a multi-physics field analysis of gate valve internal leakage and corresponding experiments, this research illustrates [...] Read more.

This study presents an experimental analysis of high-pressure liquid and gas gate valve leakage under multiple operating conditions, based on the variation patterns of ultrasonic signals. Focusing on a multi-physics field analysis of gate valve internal leakage and corresponding experiments, this research illustrates the acoustic wave characteristics of gate valves across diverse working media, pressures, internal leakage defect sizes, and valve diameters. By drawing upon both fluid mechanics and acoustics theory, an analytical approach suited to high-pressure gate valve leakage issues is devised. Separate high-pressure gate valve leakage test platforms for liquid and gas environments were designed and constructed, enabling 126 groups of tests under varying conditions, which include one measurement per condition of the valve size, defect size, and pressure value. These experiments examine the quantitative correlation of internal leakage flow rates and ultrasonic signal measurements under different situations. In addition, the distinct behaviors and principles exhibited by high-pressure liquid gate valves and gas gate valves are compared. The findings provide theoretical and technical support for quantifying high-pressure gate valve leakage. The study analyzes the theoretical basis for the generation of ultrasonic signals from valve internal leakage, providing specific experimental data under various operating conditions. It explains the various observations during the experiments and their principles. The conclusions of this research have practical engineering value and provide important references for future studies. Full article

(This article belongs to the Section Industrial Sensors)

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23 pages, 14935 KB

Open AccessArticle

Robust Pedestrian Detection and Intrusion Judgment in Coal Yard Hazard Areas via 3D LiDAR-Based Deep Learning

by Anxin Zhao, Yekai Zhao and Qiuhong Zheng

Sensors 2025, 25(18), 5908; https://doi.org/10.3390/s25185908 (registering DOI) - 21 Sep 2025

Pedestrian intrusion in coal yard work areas is a major cause of accidents, posing challenges for the safe supervision of coal yards. Existing visual detection methods suffer under poor lighting and a lack of 3D data. To overcome these limitations, this study introduces [...] Read more.

Pedestrian intrusion in coal yard work areas is a major cause of accidents, posing challenges for the safe supervision of coal yards. Existing visual detection methods suffer under poor lighting and a lack of 3D data. To overcome these limitations, this study introduces a robust pedestrian intrusion detection method based on 3D LiDAR. Our approach consists of three main components. First, we propose a novel pedestrian detection network called EFT-RCNN. Based on Voxel-RCNN, this network introduces an EnhancedVFE module to improve spatial feature extraction, employs FocalConv to reconstruct the 3D backbone network for enhanced foreground–background distinction, and utilizes TeBEVPooling to optimize bird’s eye view (BEV) generation. Second, a precise 3D hazardous area is defined by combining a polygonal base surface, determined through on-site exploration, with height constraints. Finally, a point–region hierarchical judgment method is designed to calculate the spatial relationship between pedestrians and the hazardous area for graded warning. When evaluated on the public KITTI dataset, the EFT-RCNN network improved the average precision for pedestrian detection by 4.39% in 3D and 4.68% in BEV compared with the baseline, while maintaining a real-time processing speed of 28.56 FPS. In practical tests, the pedestrian detection accuracy reached 92.9%, with an average error in distance measurement of 0.054 m. The experimental results demonstrate that the proposed method effectively mitigates complex environmental interference, enables robust detection, and provides a reliable means for the proactive prevention of pedestrian intrusion accidents. Full article

(This article belongs to the Special Issue Intelligent Point Cloud Processing, Sensing and Understanding—Third Edition)

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18 pages, 4035 KB

Open AccessArticle

Application of a Multi-Frequency Electromagnetic Method for Boundary Detection of Isolated Permafrost

by Yi Wu, Changlei Dai, Yunhu Shang, Lei Yang, Kai Gao and Wenzhao Xu

Sensors 2025, 25(18), 5907; https://doi.org/10.3390/s25185907 (registering DOI) - 21 Sep 2025

Isolated permafrost is widely distributed in freeze–thaw transition zones, characterized by blurred boundaries and strong spatial variability. Traditional methods such as drilling and electrical resistivity surveys are often limited in achieving efficient and continuous boundary identification. This study focuses on a typical isolated [...] Read more.

Isolated permafrost is widely distributed in freeze–thaw transition zones, characterized by blurred boundaries and strong spatial variability. Traditional methods such as drilling and electrical resistivity surveys are often limited in achieving efficient and continuous boundary identification. This study focuses on a typical isolated permafrost region in Northeast China and proposes a boundary detection strategy based on multi-frequency electromagnetic (EM) measurements using the GEM-2 sensor. By designing multiple frequency combinations and applying joint inversion, a boundary identification framework was developed and validated against borehole data. Results show that the multi-frequency joint inversion method improves the spatial identification accuracy of permafrost boundaries compared to traditional point-based techniques. In areas lacking boreholes, the method still demonstrates coherent boundary imaging and strong adaptability to geomorphological conditions. The multi-frequency joint inversion strategy significantly enhances imaging continuity and effectively captures electrical variations in complex freeze–thaw transition zones. Overall, this study establishes a complete non-invasive technical workflow—“acquisition–inversion–validation–imaging”—providing an efficient and scalable tool for engineering site selection, foundation design, and permafrost degradation monitoring. It also offers a methodological paradigm for electromagnetic frequency optimization and subsurface electrical boundary modeling. Full article

(This article belongs to the Section Electronic Sensors)

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14 pages, 2211 KB

Open AccessCommunication

Large-Area Nanostructure Fabrication with a 75 nm Half-Pitch Using Deep-UV Flat-Top Laser Interference Lithography

by Kexin Jiang, Mingliang Xie, Zhe Tang, Xiren Zhang and Dongxu Yang

Sensors 2025, 25(18), 5906; https://doi.org/10.3390/s25185906 (registering DOI) - 21 Sep 2025

Micro- and nanopatterning is crucial for advanced photonic, electronic, and sensing devices. Yet achieving large-area periodic nanostructures with a 75 nm half-pitch on low-cost laboratory systems remains difficult, because conventional near-ultraviolet laser interference lithography (LIL) suffers from Gaussian-beam non-uniformity and a narrow exposure [...] Read more.

Micro- and nanopatterning is crucial for advanced photonic, electronic, and sensing devices. Yet achieving large-area periodic nanostructures with a 75 nm half-pitch on low-cost laboratory systems remains difficult, because conventional near-ultraviolet laser interference lithography (LIL) suffers from Gaussian-beam non-uniformity and a narrow exposure latitude. Here, we report a cost-effective deep-ultraviolet (DUV) dual-beam LIL system based on a 266 nm laser and diffractive flat-top beam shaping, enabling large-area patterning of periodical nanostructures. At this wavelength, a moderate half-angle can be chosen to preserve a large beam-overlap region while still delivering 150 nm period (75 nm half-pitch) structures. By independently tuning the incident angle and beam uniformity, we pattern one-dimensional (1D) gratings and two-dimensional (2D) arrays over a Ø 1.0 cm field with critical-dimension variation < 5 nm (1σ), smooth edges, and near-vertical sidewalls. As a proof of concept, we transfer a 2D pattern into Si to create non-metal-coated nanodot arrays that serve as surface-enhanced Raman spectroscopy (SERS) substrates. The arrays deliver an average enhancement factor of ~1.12 × 10⁴ with 11% intensity relative standard deviation (RSD) over 65 sampling points, a performance near the upper limit of all-dielectric SERS substrates. The proposed method overcomes the uneven hotspot distribution and complex fabrication procedures in conventional SERS substrates, enabling reliable and large-area chemical sensing. Compared to electron-beam lithography, the flat-top DUV-LIL approach offers orders-of-magnitude higher throughput at a fraction of the cost, while its centimeter-scale uniformity can be scaled to full wafers with larger beam-shaping optics. These attributes position the method as a versatile and economical route to large-area photonic metasurfaces and sensing devices. Full article

(This article belongs to the Section Nanosensors)

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22 pages, 5746 KB

Open AccessArticle

AGSK-Net: Adaptive Geometry-Aware Stereo-KANformer Network for Global and Local Unsupervised Stereo Matching

by Qianglong Feng, Xiaofeng Wang, Zhenglin Lu, Haiyu Wang, Tingfeng Qi and Tianyi Zhang

Sensors 2025, 25(18), 5905; https://doi.org/10.3390/s25185905 (registering DOI) - 21 Sep 2025

The performance of unsupervised stereo matching in complex regions such as weak textures and occlusions is constrained by the inherently local receptive fields of convolutional neural networks (CNNs), the absence of geometric priors, and the limited expressiveness of MLP in conventional ViTs. To [...] Read more.

The performance of unsupervised stereo matching in complex regions such as weak textures and occlusions is constrained by the inherently local receptive fields of convolutional neural networks (CNNs), the absence of geometric priors, and the limited expressiveness of MLP in conventional ViTs. To address these problems, we propose an Adaptive Geometry-aware Stereo-KANformer Network (AGSK-Net) for unsupervised stereo matching. Firstly, to resolve the conflict between the isotropic nature of traditional ViT and the epipolar geometry priors in stereo matching, we propose Adaptive Geometry-aware Multi-head Self-Attention (AG-MSA), which embeds epipolar priors via an adaptive hybrid structure of geometric modulation and penalty, enabling geometry-aware global context modeling. Secondly, we design Spatial Group-Rational KAN (SGR-KAN), which integrates the nonlinear capability of rational functions with the spatial awareness of deep convolutions, replacing the MLP with flexible, learnable rational functions to enhance the nonlinear expression ability of complex regions. Finally, we propose a Dynamic Candidate Gated Fusion (DCGF) module that employs dynamic dual-candidate states and spatially aware pre-enhancement to adaptively fuse global and local features across scales. Experiments demonstrate that AGSK-Net achieves state-of-the-art accuracy and generalizability on Scene Flow, KITTI 2012/2015, and Middlebury 2021. Full article

(This article belongs to the Special Issue Deep Learning Technology and Image Sensing: 2nd Edition)

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24 pages, 3004 KB

Open AccessArticle

Slot-Coupled Fed 256-Element Planar Microstrip Array with Beam Stability for K-Band Water Level Sensing

by Kuang-Hsuan Huang and Yen-Sheng Chen

Sensors 2025, 25(18), 5904; https://doi.org/10.3390/s25185904 (registering DOI) - 21 Sep 2025

Radar-based water-level monitoring requires antennas with narrow beams, high gain, and low sidelobes. Existing horn and series-fed microstrip arrays either lack compactness or suffer from frequency-dependent beam deviation that reduces sensing accuracy. This paper presents a 256-element slot-coupled planar microstrip array operating in [...] Read more.

Radar-based water-level monitoring requires antennas with narrow beams, high gain, and low sidelobes. Existing horn and series-fed microstrip arrays either lack compactness or suffer from frequency-dependent beam deviation that reduces sensing accuracy. This paper presents a 256-element slot-coupled planar microstrip array operating in the K-band for water-level radar. The array combines large-scale integration with slot-coupled feeding, which provides inherent 180° phase correction and stabilizes the main beam across frequency. The fabricated array has overall dimensions of 140 mm × 160 mm × 1.12 mm. Simulated results show a peak gain of 22.8 dBi with beamwidths of 5.2° (E-plane) and 4.2° (H-plane), while beam deviation remains within 0.5° across 25.9–27.0 GHz. In comparison, a series-fed array of identical aperture exhibits up to 7.5° deviation and only 15.8 dBi broadside gain. These results demonstrate that the proposed slot-coupled array provides a compact antenna solution meeting regulatory requirements and improving the accuracy of radar-based water-level monitoring systems. Full article

(This article belongs to the Special Issue Advanced Millimeter Wave Antenna Systems for 5G and beyond 5G Wireless Communications)

15 pages, 3006 KB

Open AccessArticle

An Improved Ratiometric FRET Biosensor with Higher Affinity for Extracellular ATP

by Autumn Cholger, Jason M. Conley, Elaine Colomb, Olivia de Cuba, Jacob Kress and Mathew Tantama

Sensors 2025, 25(18), 5903; https://doi.org/10.3390/s25185903 (registering DOI) - 21 Sep 2025

Adenosine triphosphate (ATP) is readily released into the extracellular space as an autocrine and paracrine purinergic signaling molecule. We originally reported a genetically encoded, fluorescent protein-based Förster Resonance Energy Transfer (FRET) biosensor that can detect micromolar levels of extracellular ATP. Through mutagenesis of [...] Read more.

Adenosine triphosphate (ATP) is readily released into the extracellular space as an autocrine and paracrine purinergic signaling molecule. We originally reported a genetically encoded, fluorescent protein-based Förster Resonance Energy Transfer (FRET) biosensor that can detect micromolar levels of extracellular ATP. Through mutagenesis of the ATP binding site and optimization of cell-surface display, here we report the development of a second-generation biosensor called ECATS2 with greater than three-fold higher affinity for extracellular ATP. We found that the tether length between the FRET biosensor and the cell surface anchor is critical to optimization of its performance. Furthermore, we demonstrate that the improved sensor can detect extracellular ATP release upon hypoosmotic stress in cultured astrocytes. This new sensor contributes an improved tool for the ratiometric detection of extracellular ATP dynamics and purinergic signaling. Full article

(This article belongs to the Section Biosensors)

26 pages, 1627 KB

Open AccessReview

Nanomaterial-Mediated Electrochemical and Optical Biosensors and Their Application in Tumour Marker Detection

by Xinlan Wang, Jingyi Hei, Tao Zhao, Xiyu Liu and Yong Huang

Sensors 2025, 25(18), 5902; https://doi.org/10.3390/s25185902 (registering DOI) - 21 Sep 2025

Cancer constitutes a category of diseases with high mortality rates, where early and precise detection plays a crucial role in diagnosis and treatment. Tumour markers are biomolecules produced during cancer progression, predominantly inert molecules that prove difficult to detect at low concentrations. Traditional [...] Read more.

Cancer constitutes a category of diseases with high mortality rates, where early and precise detection plays a crucial role in diagnosis and treatment. Tumour markers are biomolecules produced during cancer progression, predominantly inert molecules that prove difficult to detect at low concentrations. Traditional detection methods, however, exhibit shortcomings in sensitivity and convenience. Biosensors, with their portability and high sensitivity, hold broad application prospects for detecting tumour markers. Nanomaterials, enhancing detection performance through signal amplification mechanisms, have increasingly become the primary choice for improving sensor analytical capabilities. This review retrieved 60 relevant publications from the Web of Science and PubMed databases (2018–2024) covering “nanomaterials, biosensors, tumour markers”, focusing on those employing signal amplification mechanisms and providing clinical sample validation. It summarises signal amplification mechanisms in nanomaterial-mediated electrochemical and optical biosensors, contrasting the differences between these two sensor types. This review focuses on the relationship between “nanomaterial functionality, signal amplification, and clinical application”. It systematises and presents the latest advances in nanomaterial-mediated biosensors for detecting tumour markers, analysing the challenges encountered in their clinical implementation. While providing guidance for the clinical translation of nanomaterial-mediated biosensors from laboratory research, their practical application still requires validation through further multicentre, large-scale studies. Full article

(This article belongs to the Section Biosensors)

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25 pages, 1704 KB

Open AccessArticle

Interior Point-Driven Throughput Maximization for TS-SWIPT Multi-Hop DF Relays: A Log Barrier Approach

by Yang Yu, Xiaoqing Tang and Guihui Xie

Sensors 2025, 25(18), 5901; https://doi.org/10.3390/s25185901 (registering DOI) - 21 Sep 2025

This paper investigates a simultaneous wireless information and power transfer (SWIPT) decode-and-forward (DF) relay network, where a source node transmits data to a destination node through the assistance of multi-hop passive relays. We employ the time-switching (TS) protocol, enabling the relays to harvest [...] Read more.

This paper investigates a simultaneous wireless information and power transfer (SWIPT) decode-and-forward (DF) relay network, where a source node transmits data to a destination node through the assistance of multi-hop passive relays. We employ the time-switching (TS) protocol, enabling the relays to harvest energy from the received previous hop signal to support data forwarding. We first prove that the system throughput monotonically increases with the transmit power of the source node. Next, by employing logarithmic transformations, we convert the non-convex problem of obtaining optimal TS ratios at each relay to maximize the system throughput into a convex optimization problem. Comprehensively taking into account the convergence rate, computational complexity per iteration, and robustness, we selected the log barrier method—a type of interior point method—to address this convex optimization problem, along with providing a detailed implementation procedure. The simulation results validate the optimality of the proposed method and demonstrate its applicability to practical communication systems. For instance, the proposed scheme achieves 1437.3 bps throughput at 40 dBm maximum source power in a 2-relay network—278.6% higher than that of the scheme with TS ratio fixed at 0.75 (379.68 bps). On the other hand, it converges within a 1.36 ms computation time for 5 relays, 6 orders of magnitude faster than exhaustive search (1730 s). Full article

(This article belongs to the Section Communications)

18 pages, 13021 KB

Open AccessArticle

EMPhone: Electromagnetic Covert Channel via Silent Audio Playback on Smartphones

by Yongjae Kim, Hyeonjun An and Dong-Guk Han

Sensors 2025, 25(18), 5900; https://doi.org/10.3390/s25185900 (registering DOI) - 21 Sep 2025

Covert channels enable hidden communication that poses significant security risks, particularly when smartphones are used as transmitters. This paper presents the first end-to-end implementation and evaluation of an electromagnetic (EM) covert channel on modern Samsung Galaxy S21, S22, and S23 smartphones (Samsung Electronics [...] Read more.

Covert channels enable hidden communication that poses significant security risks, particularly when smartphones are used as transmitters. This paper presents the first end-to-end implementation and evaluation of an electromagnetic (EM) covert channel on modern Samsung Galaxy S21, S22, and S23 smartphones (Samsung Electronics Co., Ltd., Suwon, Republic of Korea). We first demonstrate that a previously proposed method relying on zero-volume playback is no longer effective on these devices. Through a detailed analysis of EM emissions in the 0.1–2.5 MHz range, we discovered that consistent, volume-independent signals can be generated by exploiting the hardware’s recovery delay after silent audio playback. Based on these findings, we developed a complete system comprising a stealthy Android application for transmission, a time-based modulation scheme, and a demodulation technique designed around the characteristics of the generated signals to ensure reliable reception. The channel’s reliability and robustness were validated through evaluations of modulation time, probe distance, and message length. Experimental results show that the maximum error-free bit rate (bits per second, bps) reached 0.558 bps on Galaxy S21 and 0.772 bps on Galaxy S22 and Galaxy S23. Reliable communication was feasible up to 0.5 cm with a near-field probe, and a low alignment-aware bit error rate (BER) was maintained even for 100-byte messages. This work establishes a practical threat, and we conclude by proposing countermeasures to mitigate this vulnerability. Full article

(This article belongs to the Section Electronic Sensors)

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17 pages, 7102 KB

Open AccessArticle

Behavioral Biometrics in VR: Changing Sensor Signal Modalities

by Aleksander Sawicki, Khalid Saeed and Wojciech Walendziuk

Sensors 2025, 25(18), 5899; https://doi.org/10.3390/s25185899 (registering DOI) - 20 Sep 2025

The rapid evolution of virtual reality systems and the broader metaverse landscape has prompted growing research interest in biometric authentication methods for user verification. These solutions offer an additional layer of access control that surpasses traditional password-based approaches by leveraging unique physiological or [...] Read more.

The rapid evolution of virtual reality systems and the broader metaverse landscape has prompted growing research interest in biometric authentication methods for user verification. These solutions offer an additional layer of access control that surpasses traditional password-based approaches by leveraging unique physiological or behavioral traits. Current literature emphasizes analyzing controller position and orientation data, which presents challenges when using convolutional neural networks (CNNs) with non-continuous Euler angles. The novelty of the presented approach is that it addresses this limitation. We propose a modality transformation approach that generates acceleration and angular velocity signals from trajectory and orientation data. Specifically, our work employs algebraic techniques—including quaternion algebra—to model these dynamic signals. Both the original and transformed data were then used to train various CNN architectures, including Vanilla CNNs, attention-enhanced CNNs, and Multi-Input CNNs. The proposed modification yielded significant performance improvements across all datasets. Specifically, F1-score accuracy increased from 0.80 to 0.82 for the Comos subset, from 0.77 to 0.82 for the Quest subset, and notably from 0.83 to 0.92 for the Vive subset. Full article

(This article belongs to the Special Issue Sensor-Based Behavioral Biometrics)

21 pages, 5539 KB

Open AccessArticle

Multimodal Large Language Model-Enabled Machine Intelligent Fault Diagnosis Method with Non-Contact Dynamic Vision Data

by Zihan Lu, Cuiying Sun and Xiang Li

Sensors 2025, 25(18), 5898; https://doi.org/10.3390/s25185898 (registering DOI) - 20 Sep 2025

Smart manufacturing demands ever-increasing equipment reliability and continuous availability. Traditional fault diagnosis relies on attached sensors and complex wiring to collect vibration signals. This approach suffers from poor environmental adaptability, difficult maintenance, and cumbersome preprocessing. This study pioneers the use of high-temporal-resolution dynamic [...] Read more.

Smart manufacturing demands ever-increasing equipment reliability and continuous availability. Traditional fault diagnosis relies on attached sensors and complex wiring to collect vibration signals. This approach suffers from poor environmental adaptability, difficult maintenance, and cumbersome preprocessing. This study pioneers the use of high-temporal-resolution dynamic visual information captured by an event camera to fine-tune a multimodal large model for the first time. Leveraging non-contact acquisition with an event camera, sparse pulse events are converted into event frames through time surface processing. These frames are then reconstructed into a high-temporal-resolution video using spatiotemporal denoising and region of interest definition. The study introduces the multimodal model Qwen2.5-VL-7B and employs two distinct LoRA fine-tuning strategies for bearing fault classification. Strategy A utilizes OpenCV to extract key video frames for lightweight parameter injection. In contrast, Strategy B calls the model’s built-in video processing pipeline to fully leverage rich temporal information and capture dynamic details of the bearing’s operation. Classification experiments were conducted under three operating conditions and four rotational speeds. Strategy A and Strategy B achieved classification accuracies of 0.9247 and 0.9540, respectively, successfully establishing a novel fault diagnosis paradigm that progresses from non-contact sensing to end-to-end intelligent analysis. Full article

(This article belongs to the Special Issue Applications of Sensors in Condition Monitoring and Fault Diagnosis)

14 pages, 1440 KB

Open AccessArticle

Sex Differences in Cortical Hemodynamic Responses During Interactive and Passive Tasks: An fNIRS Study Using the Nefroball System

by Karolina Jezierska, Agnieszka Turoń-Skrzypińska, Iwona Rotter, Anna Syroka and Aleksandra Rył

Sensors 2025, 25(18), 5897; https://doi.org/10.3390/s25185897 (registering DOI) - 20 Sep 2025

The present study aimed to investigate sex differences in the hemodynamic response of the cerebral cortex during interactive and passive tasks using functional near-infrared spectroscopy fNIRS. Ninety-seven healthy adults (63 women, 34 men) participated in the study. Participants performed two tasks: an interactive [...] Read more.

The present study aimed to investigate sex differences in the hemodynamic response of the cerebral cortex during interactive and passive tasks using functional near-infrared spectroscopy fNIRS. Ninety-seven healthy adults (63 women, 34 men) participated in the study. Participants performed two tasks: an interactive motor game and a passive hand movement, and activation was measured in five cortical regions. Statistically significant differences in the amplitude of the hemodynamic response of oxygenated haemoglobin ΔHbO levels were observed, particularly in the parietal cortex, where men showed higher activation levels. The differences remained significant in the parietal, prefrontal, left hemisphere, and visual cortex. The differences were more pronounced in the passive task, which may indicate different processing strategies in women and men. Although no significant group differences were found in the latency time of maximum reaction t_max, men tended to have longer times in the visual cortex. Additionally, a moderate positive correlation between ΔHbO and t_max was observed among men, particularly in the prefrontal cortex. These results highlight the importance of considering biological sex in neuroimaging studies and suggest directions for further analysis. Full article

(This article belongs to the Section Biomedical Sensors)

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18 pages, 2774 KB

Open AccessArticle

Partial Discharge Activity Inductive Sensors and the Application of Magnetic Materials

by Ján Zbojovský, Ardian Hyseni and Jaroslav Petráš

Sensors 2025, 25(18), 5896; https://doi.org/10.3390/s25185896 (registering DOI) - 20 Sep 2025

The monitoring of partial discharge activity is part of very basic methods used to determine the status of insulation systems in high-voltage electric power devices. These methods use direct galvanic coupled measurement, measurement by inductive offline methods, or other non-electric methods. The inductive [...] Read more.

The monitoring of partial discharge activity is part of very basic methods used to determine the status of insulation systems in high-voltage electric power devices. These methods use direct galvanic coupled measurement, measurement by inductive offline methods, or other non-electric methods. The inductive method requires sensitive inductive sensors, which detect the partial discharge pulses occurring in high-voltage circuits. The sensitivity of such sensors strongly depends on the design, construction, and materials of the sensor core. Therefore, knowledge of the magnetic material parameters of a sensor is crucial for obtaining optimal values in terms of the sensor’s final sensitivity. In this experiment, experimental sensor cores were constructed using different magnetic materials and different sensor construction processes. For the laboratory experiments, two types of magnetic material were selected: a magnetic material based on Fe-Ni (Permalloy) and a magnetic material based on MO.Fe₂O₃. As a reference level for sensitivity, the minimum acceptable sensitivity was defined as the equivalent measuring sensitivity obtained using the direct galvanic measurement method. The optimal construction type and magnetic material for the sensor core of inductive sensors were determined. Full article

(This article belongs to the Special Issue Electronic Test and Measurement Instrumentation: Design and Applications (2nd Edition))

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18 pages, 4306 KB

Open AccessArticle

Creation of Low-Loss Triple-Ring Optical Filter via Direct Binary Search Inverse Design

by Yuchen Hu, Tong Wang, Wen Zhou and Bo Hu

Sensors 2025, 25(18), 5895; https://doi.org/10.3390/s25185895 (registering DOI) - 20 Sep 2025

This paper presents a triple-ring optical filter designed through direct binary search inverse design, comprising three cascaded rings in an add–drop configuration. We established a physical model using temporal coupled-mode theory to derive theoretical spectra and analyze key transmission parameters. Subsequently, we encoded [...] Read more.

This paper presents a triple-ring optical filter designed through direct binary search inverse design, comprising three cascaded rings in an add–drop configuration. We established a physical model using temporal coupled-mode theory to derive theoretical spectra and analyze key transmission parameters. Subsequently, we encoded the target transmission performance into a figure of merit to optimize the coupling coefficients between ring resonators and waveguides. We verify the theoretical parameters using three-dimensional finite-difference time-domain simulations. The optimized filter achieves a free spectral range of 86 nm, an insertion loss of 0.4 dB, an extinction ratio of 20 dB, and a narrow spectral linewidth of 0.2 nm within a compact footprint of

29 μ m \times 46.5 μ m

. This device demonstrates significant application potential, particularly in laser external cavities, dense wavelength division multiplexing systems, and sensing applications. Furthermore, this work provides a systematic design framework for the precision design of photonic devices. Full article

(This article belongs to the Section Optical Sensors)

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27 pages, 4710 KB

Open AccessArticle

Impact of Force Scaling on Physician Fatigue in a Bilateral Tele-Ultrasound System

by Eleonora Storto, Valerio Novelli, Antonio Frisoli and Francesco Porcini

Sensors 2025, 25(18), 5894; https://doi.org/10.3390/s25185894 (registering DOI) - 20 Sep 2025

Tele-ultrasound systems enable remote diagnostic imaging by transmitting both motion commands and haptic feedback between a sonographer and a robotic probe. While these systems aim to replicate conventional ultrasound procedures, they rarely address the physical strain typically experienced by sonographers. In this study, [...] Read more.

Tele-ultrasound systems enable remote diagnostic imaging by transmitting both motion commands and haptic feedback between a sonographer and a robotic probe. While these systems aim to replicate conventional ultrasound procedures, they rarely address the physical strain typically experienced by sonographers. In this study, the effect of applying a force scaling strategy to haptic feedback on reducing muscular fatigue and task-induced stress during a realistic tele-ultrasound task is studied. First, a thorough operational and biomechanical analysis of the abdominal US procedure was performed to reconstruct a representative task in the laboratory. Then, a bilateral position–force tele-ultrasound architecture was implemented, and a total of 11 subjects performed the reconstructed remote ultrasound task under two randomized conditions: with and without force scaling. Surface electromyography (sEMG) signals were acquired from seven upper-limb muscles (posterior deltoid, trapezius, anterior deltoid, biceps, triceps, wrist flexors, and wrist extensors). Teleoperation-related stress was also assessed using a seven-item Likert-scale self-report questionnaire administered after each trial. Statistical significance was tested using Repeated Measures ANOVA for EMG data and the Wilcoxon signed-rank test for stress scores. The results showed a statistically significant reduction in muscle activation in 5 out of 7 muscles, and a clear mitigation of fatigue progression over time in the scaled condition. Additionally, perceived stress levels were significantly lower in the presence of force scaling in overall stress scores. These findings support the effectiveness of force scaling as a tool to enhance ergonomics in tele-ultrasound procedures without compromising the operator’s ability to perform the task. The proposed methodology proved robust and generalizable, offering valuable insight into the integration of human-centered design in tele-operated diagnostic systems. Full article

(This article belongs to the Section Sensors and Robotics)

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37 pages, 9456 KB

Open AccessArticle

Diffusion-Based Frequency Hopping for Collision Mitigation in Dense Bluetooth Networks

by Giwon Yang, Hyungjoon Shin and Hyogon Kim

Sensors 2025, 25(18), 5893; https://doi.org/10.3390/s25185893 (registering DOI) - 20 Sep 2025

This paper challenges the conventional wisdom of using uniform random resource selection for collision resolution in distributed scheduling, particularly in wireless protocols. Bluetooth, being one such technology, is analyzed through its frequency hopping mechanism to explore for a better alternative in random access [...] Read more.

This paper challenges the conventional wisdom of using uniform random resource selection for collision resolution in distributed scheduling, particularly in wireless protocols. Bluetooth, being one such technology, is analyzed through its frequency hopping mechanism to explore for a better alternative in random access MAC (medium access control). Using diffusion theory, we characterize Bluetooth’s original frequency hopping as exhibiting maximum diffusivity, which correlates with unnecessarily high collision rates and a short mean first encounter time (MFET) between nodes. MFET, defined as the expected time until two independent hopping sequences first collide on the same channel, serves as an intuitive metric for evaluating collision likelihood. This insight leads to the proposal of a new collision avoidance mechanism with reduced diffusivity, effectively increasing MFET while maintaining efficient spectrum utilization. Our analysis and simulation results demonstrate that it can significantly lower packet collisions, outperforming existing techniques such as adaptive frequency hopping. The results are further corroborated by a real-life prototype implementation that closely replicates the predicted performance. The proposed diffusion-based MAC, by explicitly targeting longer MFETs, is expected to better handle dense Bluetooth environments, which are becoming increasingly common. Full article

(This article belongs to the Special Issue Empowering the IoT: Scalable, Sustainable, and Ultra-Low Power Solutions)

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