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Keywords = MEMS accelerometer

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20 pages, 7741 KiB  
Article
A Mode-Localized Micro-Electromechanical System Accelerometer with Force Rebalance Closed-Loop Control
by Bowen Wang, Zhenxiang Qi, Kunfeng Wang, Zhaoyang Zhai, Zheng Wang and Xudong Zou
Micromachines 2025, 16(3), 248; https://doi.org/10.3390/mi16030248 - 21 Feb 2025
Viewed by 201
Abstract
This article proposes a force rebalance control scheme based on a mode-localized resonant accelerometer (ML-RXL), which is applied to address the limited measurement range problem of the ML-RXL. For the first time, an empirical response model of the weakly coupling resonators for the [...] Read more.
This article proposes a force rebalance control scheme based on a mode-localized resonant accelerometer (ML-RXL), which is applied to address the limited measurement range problem of the ML-RXL. For the first time, an empirical response model of the weakly coupling resonators for the amplitude ratio output is established. Based on this, this paper builds an overall model of the force rebalance control system to analyze the sensitivity characteristics by simulations, which demonstrates that the scheme can effectively broaden the linear measurement range. It is demonstrated that the sensor exhibits a highly linear output within a measurement range of ±1 g, with a sensitivity of the feedback-control voltage output measured at 2.94 V/g. The measurement range is expanded by at least 6.7 times. Moreover, the results show that the minimum input-referred acceleration noise density of the sensor for the force rebalance control scheme is 3.29 μg/rtHz, and that the best bias instability is optimized to 5.34 μg with an integral time of 0.64 s. Full article
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Figure 1
<p>The schematic diagram of the force rebalance scheme for the ML-RXL.</p>
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<p>(<b>a</b>) Schematic diagram of the ML-RXL, (<b>b</b>) Mode shapes of 2DoF for WCRs under different perturbation conditions.</p>
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<p>Mass-spring-damper model of the 2DoF for WCRs.</p>
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<p>The feedback-control voltage (<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>V</mi> </mrow> <mrow> <mi>t</mi> </mrow> </msub> </mrow> </semantics></math>) application method for the force-rebalance control scheme.</p>
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<p>The loop diagrammatic sketch of the force rebalance control scheme.</p>
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<p>Perspective view of the device structure of the ML-RXL.</p>
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<p>The output metrics characterization of both the IP mode and the OOP mode for the ML-RXL with <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">κ</mi> <mo>=</mo> <mo>−</mo> <mn>3.2</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>4</mn> </mrow> </msup> </mrow> </semantics></math>, (<b>a</b>) the resonant frequencies, (<b>b</b>) the ARs.</p>
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<p>The simulation response results of the WCRs. (<b>a</b>) Varying frequency differences between the two modes when the PLL bandwidth is set at 500 Hz and the peak of the AC acceleration signal is 0.010 g; (<b>b</b>) Varying bandwidths of the PLL when the frequency difference of the two modes is set at 64.6 Hz and the peak of the AC acceleration signal is 0.010 g; (<b>c</b>) Varying peaks of the AC acceleration signal when the frequency difference of the two modes is set at 64.6 Hz and the PLL bandwidth is set at 500 Hz.</p>
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<p>The limit surface of the system where the variable parameters are <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>L</mi> <mi>P</mi> <mi>F</mi> </mrow> </msub> </mrow> </semantics></math>,<math display="inline"><semantics> <mrow> <msub> <mrow> <mo> </mo> <mi>K</mi> </mrow> <mrow> <mi>p</mi> </mrow> </msub> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>K</mi> </mrow> <mrow> <mi>i</mi> </mrow> </msub> </mrow> </semantics></math>. The * marked the parameters for a set of stable solutions of the system, specifically <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>ω</mi> </mrow> <mrow> <mi>L</mi> <mi>P</mi> <mi>F</mi> </mrow> </msub> <mo>=</mo> <mn>2</mn> <mi mathvariant="sans-serif">π</mi> <mo>×</mo> </mrow> </semantics></math>1000 rad/s,<math display="inline"><semantics> <mrow> <msub> <mrow> <mo> </mo> <mi>K</mi> </mrow> <mrow> <mi>p</mi> </mrow> </msub> <mo>=</mo> <mn>0.01</mn> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>K</mi> </mrow> <mrow> <mi>i</mi> </mrow> </msub> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math>.</p>
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<p>Voltage output characteristics of different OPs.</p>
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<p>Fabrication process flow of the ML-RXL. (<b>a</b>) Prepare an SOI wafer; (<b>b</b>) etch shallow cavity; (<b>c</b>) pattern the bottom electrode; (<b>d</b>) deposite the silicon oxide in the shallow cavity; (<b>e</b>) prepare the second SOI wafer and bond two wafers together by the silicon-to-silicon bonding process; (<b>f</b>) remove the substrate layer and the oxygen layer, deposite and pattern the metal layer; (<b>g</b>) etch the device layer structure; (<b>h</b>) package in a vacuum environment by the glass slurry bonding process.</p>
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<p>Schematic diagram of the force-rebalance control scheme for the ML-RXL.</p>
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<p>(<b>a</b>) The optical micro-graph of the packaged ML-RXL and the details of bonding wires. (<b>b</b>) Analog front-end signal processing circuit board. (<b>c</b>) Digital control system circuit board. (<b>d</b>) The experimental setup.</p>
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<p>(<b>a</b>) The amplitude-frequency response and the phase-frequency response of both the modes for the device without perturbation. (<b>b</b>) The frequency shifts of both the modes tested in the open-loop measurement. (<b>c</b>) The AR shift of the IP mode tested in the measurement for the closed-loop excitation scheme.</p>
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<p>(<b>a</b>) The feedback-control voltage-output characteristics of the device for the single-electrode control method. (<b>b</b>) The feedback-control voltage output characteristics of different AR setups for the double-electrode control method of the force rebalance control scheme.</p>
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<p>The Allan variance results of the ML-RXL for (<b>a</b>) a closed-loop excitation scheme and (<b>b</b>) a force-rebalance control scheme.</p>
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<p>The PSD analysis results of the ML-RXL for (<b>a</b>) a closed-loop excitation scheme and (<b>b</b>) a force rebalance control scheme.</p>
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29 pages, 22165 KiB  
Article
Shake Table Tests on Scaled Masonry Building: Comparison of Performance of Various Micro-Electromechanical System Accelerometers (MEMS) for Structural Health Monitoring
by Giuseppe Occhipinti, Francesco Lo Iacono, Giuseppina Tusa, Antonio Costanza, Gioacchino Fertitta, Luigi Lodato, Francesco Macaluso, Claudio Martino, Giuseppe Mugnos, Maria Oliva, Daniele Storni, Gianni Alessandroni, Giacomo Navarra and Domenico Patanè
Sensors 2025, 25(4), 1010; https://doi.org/10.3390/s25041010 - 8 Feb 2025
Viewed by 499
Abstract
This study presents the results of an experimental investigation conducted on a 2:3 scale model of a two-story stone masonry building. We tested the model on the UniKORE L.E.D.A. lab shake table, simulating the Mw 6.3 earthquake ground motion that struck L’Aquila, Italy, [...] Read more.
This study presents the results of an experimental investigation conducted on a 2:3 scale model of a two-story stone masonry building. We tested the model on the UniKORE L.E.D.A. lab shake table, simulating the Mw 6.3 earthquake ground motion that struck L’Aquila, Italy, on 6 April 2009, with progressively increasing peak acceleration levels. We installed a network of accelerometric sensors on the model to capture its structural behaviour under seismic excitation. Medium-to lower-cost MEMS accelerometers (classes A and B) were compared with traditional piezoelectric sensors commonly used in Structural Health Monitoring (SHM). The experiment assessed the structural performance and damage progression of masonry buildings subjected to realistic earthquake inputs. Additionally, the collected data provided valuable insights into the effectiveness of different sensor types and configurations in detecting key vibrational and failure patterns. All the sensors were able to accurately measure the dynamic response during seismic excitation. However, not all of them were suitable for Operational Modal Analysis (OMA) in noisy environments, where their self-noise represents a crucial factor. This suggests that the self-noise of MEMS accelerometers must be less than 1 µg/√Hz, or preferably below 0.5 µg/√Hz, to obtain good results from the OMA. Therefore, we recommend ultra-low-noise sensors for detecting differences in the structural behaviour before and after seismic events. Our findings provide valuable insights into the seismic vulnerability of masonry structures and the effectiveness of sensors in detecting damage. The management of buildings in earthquake-prone areas can benefit from these specifications. Full article
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<p>Design dimensions of the four facades of the specimen (units: mm).</p>
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<p>Plan view (units: mm) and construction of the wooden floors.</p>
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<p>Shaking table system at L.E.D.A. Research Institute: (<b>a</b>) single tables; (<b>b</b>) connected tables.</p>
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<p>Specimen under test placed on the shaking table. From left to right: (<b>a</b>) facades 1 and 4; (<b>b</b>) facades 3 and 2.</p>
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<p>Comparison of the power spectral densities (PSDs) of self-noise for the three MEMS accelerometers used: Analog Device ADXL355 (red line), Safran-Colibrys VS1002 (blue line), and Seiko-Epson M-A352 QMEMS (orange line). The PSDs of self-noises for the Safran-Colibrys SI1003 (grey line) and of the Episensor ES-T force balance accelerometer (grey line), commonly used for seismology and SHM measurements, are also shown. Lastly, the seismic low-noise model and seismic high-noise model curves (thick black lines) are shown, along with the spectra of earthquakes of different sizes that were measured 10 km from the epicentre (point lines) (modified after Patanè et al. 2024 [<a href="#B2-sensors-25-01010" class="html-bibr">2</a>]).</p>
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<p>Distribution of the sensors installed on the individual facades of the building under testing: (<b>a</b>) facade 1; (<b>b</b>) facade 2; (<b>c</b>) facade 3; (<b>d</b>) facade 4. Refer to <a href="#sensors-25-01010-t004" class="html-table">Table 4</a> for the sensor codes.</p>
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<p>Scaled reference accelerograms for a seismic input at 50% of ZPA and the associated Fourier Amplitude Spectra (FAS).</p>
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<p>Average HVSR curves at the nine accelerometric stations equipped with Seiko-Epson M-A352 sensors.</p>
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<p>Stabilization diagram of estimation state space models of sensors with (<b>a</b>) 0.2 µg/√Hz, (<b>b</b>) 18-6-2 µg/√Hz @ 1-10-100 Hz, (<b>c</b>) 7 µg/√Hz, and (<b>d</b>) 25 µg/√Hz during the hydraulic pumps’ activation.</p>
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<p>Stabilization diagram of estimation state space models of sensors with 0.2 µg/√Hz and modal shape.</p>
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<p>Comparison of the first frequency (<b>a</b>) before shaking test, and (<b>b</b>) at the end of shaking test.</p>
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<p>Seismic signal recorded during the experiment with different inputs from 10% to 50% (<b>a</b>). Stockwell transform, non-normalized (<b>b</b>) and normalized (<b>c</b>), for the signal inputs of 10%, 30%, and 50% recorded at accelerometer M5.</p>
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<p>PFAs and PSAs measured at the stations installed at the first (<b>a</b>) and second (<b>b</b>) levels of the structure, normalized with respect to the ground-level PGAs (measured at station M8), for the different percentages of ZPA (%g) experienced during the shaking table test.</p>
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<p>Elastic response spectra calculated for increasing seismic input at the stations installed along the vertical V1 of the structure and for the three directions of motion. In each plot, the values of the period corresponding to the PSA at stations M5 and M6 (arbitrarily chosen as the reference for levels 2 and 1, respectively) are also shown.</p>
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<p>Normalized response spectra with respect to the values measured at the M8 station installed at the ground level.</p>
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<p>Qualitative damage distribution on all four facades.</p>
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<p>Details of two damaged areas: (<b>a</b>) the lower right corner of facade 3, and (<b>b</b>) the right masonry wall of facade 4.</p>
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<p>Planar seismic response for each sensor type on vertical V1 at each level.</p>
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<p>Planar seismic response for each sensor type on vertical V1 at each level.</p>
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14 pages, 4601 KiB  
Article
Modeling and Analysis of Vibration Coupling in Differential Common-Based MEMS Resonators
by Jing Zhang, Zhuo Yang, Tianhao Wu, Zhichao Yao, Chen Lin and Yan Su
Micromachines 2025, 16(2), 169; https://doi.org/10.3390/mi16020169 - 30 Jan 2025
Viewed by 556
Abstract
In differential MEMS resonant sensors, a pair of resonators are interconnected with other structural components while sharing a common substrate. This leads to mutual coupling of vibration energy between resonators, interfering with their frequency outputs and affecting the sensor’s static performance. This paper [...] Read more.
In differential MEMS resonant sensors, a pair of resonators are interconnected with other structural components while sharing a common substrate. This leads to mutual coupling of vibration energy between resonators, interfering with their frequency outputs and affecting the sensor’s static performance. This paper aims to model and analyze the vibration coupling phenomena in differential common-based MEMS resonators (DCMR). A mechanical model of the DCMR structure was established and refined through finite element simulation analysis. Theoretical calculations yielded vibration coupling curves for two typical silicon resonant accelerometer (SRA) structures containing DCMR: SRA-V1 and SRA-V2, with coupling stiffness values of 2.361 × 10−4 N/m and 1.370 × 10−2 N/m, respectively. An experimental test system was constructed to characterize the vibration coupling behavior. The results provided coupling amplitude-frequency characteristic curves and coupling stiffness values (7.073 × 10−4 N/m and 1.068 × 10−2 N/m for SRA-V1 and SRA-V2, respectively) that validated the theoretical analysis and computational model. This novel approach enables effective evaluation of coupling intensity between 5resonators and provides a theoretical foundation for optimizing device structural designs. Full article
(This article belongs to the Special Issue Advances in MEMS Inertial Sensors)
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<p>Schematic diagram of the differential common-based MEMS resonator system.</p>
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<p>Spring-mass model of two-DOF micromechanical resonator system.</p>
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<p>Schematic diagram of amplitude-frequency response curves for the two resonators.</p>
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<p>Schematic diagram of SRA structure.</p>
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<p>(<b>a</b>) Three-dimensional model of SRA-V1. (<b>b</b>) Mesh of SRA-V1. (<b>c</b>) Three-dimensional model of SRA-V2. (<b>d</b>) Mesh of SRA-V2.</p>
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<p>Simulation cloud diagrams of resonator vibrations under applied forces: (<b>a</b>) SRA-V1; (<b>b</b>) SRA-V2.</p>
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<p>Displacement amplitude–frequency curves of the accelerometer under simulation: (<b>a</b>) SRA-V1; (<b>b</b>) SRA-V2.</p>
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<p>Displacement amplitude–frequency curves of the accelerometer under simulation: (<b>a</b>) SRA-V1; (<b>b</b>) SRA-V2.</p>
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<p>Schematic diagram of driving and detection test system for DCMR.</p>
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<p>Test instruments and experimental environment.</p>
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<p>Experimental voltage amplitude-frequency curves of the accelerometer: (<b>a</b>) SRA-V1; (<b>b</b>) SRA-V2.</p>
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14 pages, 3285 KiB  
Article
Design of Interface ASIC with Power-Saving Switches for Capacitive Accelerometers
by Juncheng Cai, Yongbin Cai, Xiangyu Li, Shanshan Wang, Xiaowei Zhang, Xinpeng Di and Pengjun Wang
Micromachines 2025, 16(1), 96; https://doi.org/10.3390/mi16010096 - 15 Jan 2025
Viewed by 735
Abstract
High-precision, low-power MEMS accelerometers are extensively utilized across civilian applications. Closed-loop accelerometers employing switched-capacitor (SC) circuit topologies offer notable advantages, including low power consumption, high signal-to-noise ratio (SNR), and excellent linearity. Addressing the critical demand for high-precision, low-power MEMS accelerometers in modern geophones, [...] Read more.
High-precision, low-power MEMS accelerometers are extensively utilized across civilian applications. Closed-loop accelerometers employing switched-capacitor (SC) circuit topologies offer notable advantages, including low power consumption, high signal-to-noise ratio (SNR), and excellent linearity. Addressing the critical demand for high-precision, low-power MEMS accelerometers in modern geophones, this work focuses on the design and implementation of closed-loop interface ASICs (Application-Specific Integrated Circuits). The proposed interface circuit, based on switched-capacitor modulation technology, incorporates a low-noise charge amplifier, sample-and-hold circuit, integrator, and clock divider circuit. To minimize average power consumption, a switched operational amplifier (op-amp) technique is adopted, which temporarily disconnects idle op-amps from the power supply. Additionally, a class-AB output stage is employed to enhance the dynamic range of the circuit. The design was realized using a standard 0.35 μm CMOS process, culminating in the completion of layout design and small-scale engineering fabrication. The performance of the MEMS accelerometers was evaluated under a 3.3 V power supply, achieving a power consumption of 3.3 mW, an accelerometer noise density below 1 μg/√Hz, a sensitivity of 1.65 V/g, a measurement range of ±1 g, a nonlinearity of 0.15%, a bandwidth of 300 Hz, and a bias stability of approximately 36 μg. These results demonstrate the efficacy of the proposed design in meeting the stringent requirements of high-precision MEMS accelerometer applications. Full article
(This article belongs to the Special Issue MEMS Inertial Device, 2nd Edition)
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<p>Overall circuit structure.</p>
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<p>Switched-op-amp with switched output stage.</p>
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<p>System schematic simulation results. (<b>a</b>) Detection results when the acceleration signal is 1 g. (<b>b</b>) Detection results when the acceleration signal is 100 mg.</p>
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<p>Switched-op-amp topology.</p>
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<p>The transistor circuit in switched-op-amp.</p>
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<p>Simulation result of the whole circuit.</p>
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<p>Chip photos and MEMS accelerometer test board.</p>
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<p>The transient test for micro-accelerometers.</p>
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<p>Frequency response and noise spectrum closed-loop micro-accelerometers.</p>
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<p>The linearity test.</p>
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<p>The bias instability test.</p>
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20 pages, 18281 KiB  
Article
IMU Sensor-Based Worker Behavior Recognition and Construction of a Cyber–Physical System Environment
by Sehwan Park, Minkyo Youm and Junkyeong Kim
Sensors 2025, 25(2), 442; https://doi.org/10.3390/s25020442 - 13 Jan 2025
Viewed by 661
Abstract
According to South Korea’s Ministry of Employment and Labor, approximately 25,000 construction workers suffered from various injuries between 2015 and 2019. Additionally, about 500 fatalities occur annually, and multiple studies are being conducted to prevent these accidents and quickly identify their occurrence to [...] Read more.
According to South Korea’s Ministry of Employment and Labor, approximately 25,000 construction workers suffered from various injuries between 2015 and 2019. Additionally, about 500 fatalities occur annually, and multiple studies are being conducted to prevent these accidents and quickly identify their occurrence to secure the golden time for the injured. Recently, AI-based video analysis systems for detecting safety accidents have been introduced. However, these systems are limited to areas where CCTV is installed, and in locations like construction sites, numerous blind spots exist due to the limitations of CCTV coverage. To address this issue, there is active research on the use of MEMS (micro-electromechanical systems) sensors to detect abnormal conditions in workers. In particular, methods such as using accelerometers and gyroscopes within MEMS sensors to acquire data based on workers’ angles, utilizing three-axis accelerometers and barometric pressure sensors to improve the accuracy of fall detection systems, and measuring the wearer’s gait using the x-, y-, and z-axis data from accelerometers and gyroscopes are being studied. However, most methods involve use of MEMS sensors embedded in smartphones, typically attaching the sensors to one or two specific body parts. Therefore, in this study, we developed a novel miniaturized IMU (inertial measurement unit) sensor that can be simultaneously attached to multiple body parts of construction workers (head, body, hands, and legs). The sensor integrates accelerometers, gyroscopes, and barometric pressure sensors to measure various worker movements in real time (e.g., walking, jumping, standing, and working at heights). Additionally, incorporating PPG (photoplethysmography), body temperature, and acoustic sensors, enables the comprehensive observation of both physiological signals and environmental changes. The collected sensor data are preprocessed using Kalman and extended Kalman filters, among others, and an algorithm was proposed to evaluate workers’ safety status and update health-related data in real time. Experimental results demonstrated that the proposed IMU sensor can classify work activities with over 90% accuracy even at a low sampling rate of 15 Hz. Furthermore, by integrating internal filtering, communication modules, and server connectivity within an application, we established a cyber–physical system (CPS), enabling real-time monitoring and immediate alert transmission to safety managers. Through this approach, we verified improved performance in terms of miniaturization, measurement accuracy, and server integration compared to existing commercial sensors. Full article
(This article belongs to the Special Issue Sensor-Based Human Activity Recognition)
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<p>Fabrication of the prototype IMU sensor: (<b>a</b>) appearance of the fabricated IMU sensor; (<b>b</b>) diagram of the IMU sensor and the positions of the included sensors.</p>
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<p>Algorithm flowchart for worker status assessment.</p>
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<p>Results of applying the forward gaze algorithm: (<b>a</b>) when only the head turns; (<b>b</b>) when both body and head turn together (during directional change).</p>
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<p>Results of applying the forward gaze algorithm: (<b>a</b>) when only the head turns; (<b>b</b>) when both body and head turn together (during directional change).</p>
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<p>Results of applying the Kalman filter and walking detection: (<b>a</b>) result of applying the Kalman filter to raw data; (<b>b</b>) walking detection results (1 when there is no foot movement; 0 when there is foot movement).</p>
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<p>Results of applying the Kalman filter and walking detection: (<b>a</b>) result of applying the Kalman filter to raw data; (<b>b</b>) walking detection results (1 when there is no foot movement; 0 when there is foot movement).</p>
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<p>Results of applying the energy detection algorithm during jumping.</p>
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<p>Results of applying the extended Kalman filter to barometric data and estimation of altitude changes.</p>
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<p>IMU sensor placement by body part.</p>
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<p>IMU sensor application integration screen and database connection screen.</p>
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<p>Dashboard and environment setup for CPS implementation: (<b>a</b>) CPS dashboard screen layout; (<b>b</b>) CPS environment construction scene.</p>
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<p>Dashboard and environment setup for CPS implementation: (<b>a</b>) CPS dashboard screen layout; (<b>b</b>) CPS environment construction scene.</p>
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<p>Worker icons and UI in CPS operation.</p>
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<p>Example of CPS application for multiple workers.</p>
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7 pages, 633 KiB  
Communication
Improved Analysis for Intrinsic Properties of Triaxial Accelerometers to Reduce Calibration Uncertainty
by Jon Geist, Hany Metry, Aldo Adrian Garcia Gonzalez, Arturo Ruiz Rueda, Giancarlo Barbosa Micheli, Ronaldo da Silva Dias and Michael Gaitan
Micromachines 2024, 15(12), 1494; https://doi.org/10.3390/mi15121494 - 14 Dec 2024
Viewed by 4125
Abstract
We describe a modification of a previously described measurement–analysis protocol to determine the intrinsic properties of triaxial accelerometers by using a measurement protocol based on angular stepwise rotation in the Earth’s gravitational field. This study was conducted with MEMS triaxial accelerometers that were [...] Read more.
We describe a modification of a previously described measurement–analysis protocol to determine the intrinsic properties of triaxial accelerometers by using a measurement protocol based on angular stepwise rotation in the Earth’s gravitational field. This study was conducted with MEMS triaxial accelerometers that were co-integrated in four consumer-grade wireless microsensors. The measurements were carried out on low-cost rotation tables in different laboratories in different countries to simulate the reproducibility environment encountered in inter-comparisons of calibration capabilities. We used a previously described calibration–uncertainty metric to independently characterize the overall uncertainty of the calibration and analysis process. The intrinsic property analysis suggested, and the uncertainty metric confirmed, an unacceptably large error in one combination of microsystem and low-cost rotation table. A simple modification of the analysis protocol provided a substantial improvement in the reproducibility of the protocol with all combinations of microsystem and rotation table. Later, measurements with a high-performance triaxial accelerometer using a significantly more expensive rotation table carried out at one location further validated the usefulness of this modification. The results reported here also demonstrate the existence of unidentified defects in one microsystem and one low-cost rotation table that interact with each other in ways not currently understood to produce anomalously large errors with the old protocol but not with the new protocol. Full article
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<p>Experimental set up for measuring <math display="inline"><semantics> <mrow> <msub> <mrow> <mi mathvariant="bold-italic">T</mi> </mrow> <mrow> <mi mathvariant="bold-italic">k</mi> <mi mathvariant="bold-italic">j</mi> </mrow> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi mathvariant="bold-italic">C</mi> </mrow> <mrow> <mi mathvariant="bold-italic">j</mi> </mrow> </msub> </mrow> </semantics></math> for the microsensor system shown in <a href="#micromachines-15-01494-f001" class="html-fig">Figure 1</a>. The microsensor system was glued to a battery (silver), which is mounted on the <span class="html-italic">z</span>-axis rotation platform of a two-axis rotation table. The local gravitational coordinate system is shown in white. The triaxial–accelerometer axes of maximum responsivity are shown in red, and the axes of rotation of the rotation table are shown in blue. A red wire connects the battery to the microsensor.</p>
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24 pages, 6400 KiB  
Article
Innovative Modeling of IMU Arrays Under the Generic Multi-Sensor Integration Strategy
by Benjamin Brunson, Jianguo Wang and Wenbo Ma
Sensors 2024, 24(23), 7754; https://doi.org/10.3390/s24237754 - 4 Dec 2024
Viewed by 922
Abstract
This research proposes a novel modeling method for integrating IMU arrays into multi-sensor kinematic positioning/navigation systems. This method characterizes sensor errors (biases/scale factor errors) for each IMU in an IMU array, leveraging the novel Generic Multisensor Integration Strategy (GMIS) and the framework for [...] Read more.
This research proposes a novel modeling method for integrating IMU arrays into multi-sensor kinematic positioning/navigation systems. This method characterizes sensor errors (biases/scale factor errors) for each IMU in an IMU array, leveraging the novel Generic Multisensor Integration Strategy (GMIS) and the framework for comprehensive error analysis in Discrete Kalman filtering developed through the authors’ previous research. This work enables the time-varying estimation of all individual sensor errors for an IMU array, as well as rigorous fault detection and exclusion for outlying measurements from all constituent sensors. This research explores the feasibility of applying Variance Component Estimation (VCE) to IMU array data, using separate variance components to characterize the performance of each IMU’s gyroscopes and accelerometers. This analysis is only made possible by directly modeling IMU inertial measurements under the GMIS. A real land-vehicle kinematic dataset was used to demonstrate the proposed technique. The a posteriori positioning/attitude standard deviations were compared between multi-IMU and single IMU solutions, with the multi-IMU solution providing an average accuracy improvement of ca. 14–16% in the estimated position, 30% in the estimated roll and pitch, and 40% in the estimated heading. The results of this research demonstrate that IMUs in an array do not generally exhibit homogeneous behavior, even when using the same model of tactical-grade MEMS IMU. Furthermore, VCE was used to compare the performance of three IMU sensors, which is not possible under other IMU array data fusion techniques. This research lays the groundwork for the future evaluation of IMU array sensor configurations. Full article
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<p>Flowchart of the traditional sensor integration strategy for a simple GPS/IMU sensor integration. This workflow was adapted from those used in [<a href="#B17-sensors-24-07754" class="html-bibr">17</a>,<a href="#B18-sensors-24-07754" class="html-bibr">18</a>,<a href="#B19-sensors-24-07754" class="html-bibr">19</a>,<a href="#B20-sensors-24-07754" class="html-bibr">20</a>].</p>
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<p>The general workflow of integrating positioning sensors in the GMIS.</p>
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<p>The top-down view of the trajectory of the kinematic dataset. The coordinates presented are local geodetic coordinates relative to the starting location.</p>
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<p>The velocity profile of the kinematic dataset. Velocity values are expressed in the navigation frame of local geodetic coordinates.</p>
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<p>The acceleration profile of the kinematic dataset. Acceleration values are expressed in the navigation frame of local geodetic coordinates.</p>
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<p>The roll, pitch, and heading profiles for the kinematic dataset. Attitude is presented in the local navigation frame.</p>
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<p>The estimated time derivatives for the roll, pitch, and heading values over the kinematic dataset. These values are presented in the local navigation frame.</p>
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<p>The estimated accelerometer-specific force residuals of each IMU in the array for the kinematic dataset.</p>
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<p>The estimated gyroscope angular rate residuals of each IMU in the array for the kinematic dataset.</p>
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<p>Histograms of the gyroscope standardized residuals for all three constituent IMUs. Standard normal distribution superimposed for reference.</p>
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<p>Histograms of the accelerometer standardized residuals for all three constituent IMUs. Standard normal distribution superimposed for reference.</p>
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<p>The estimated accelerometer bias for (<b>a</b>) the first IMU in the array, (<b>b</b>) the second IMU in the array, and (<b>c</b>) the third IMU in the array.</p>
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<p>The estimated accelerometer scale factor errors for (<b>a</b>) the first IMU in the array, (<b>b</b>) the second IMU in the array, and (<b>c</b>) the third IMU in the array.</p>
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<p>The estimated gyroscope bias for (<b>a</b>) the first IMU in the array, (<b>b</b>) the second IMU in the array, and (<b>c</b>) the third IMU in the array.</p>
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<p>The estimated gyroscope scale factor errors for (<b>a</b>) the first IMU in the array, (<b>b</b>) the second IMU in the array, and (<b>c</b>) the third IMU in the array.</p>
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<p>The estimated overall standard error of unit weight for the MIMU-integrated system (moving window: 20 s).</p>
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<p>The estimated standard errors of unit weight for the specific force measurements of three sets of IMU accelerometers in the MIMU-integrated system (moving window: 20 s).</p>
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<p>The estimated standard errors of unit weight for the angular rate measurements of three sets of IMU gyroscopes in the MIMU-integrated system (moving window: 20 s).</p>
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<p>The ratio of the a posteriori MIMU position standard deviations to the a posteriori SIMU position standard deviations (Note: the dashed lines plot the average ratios for each sensor axis).</p>
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<p>The ratio of the a posteriori MIMU attitude standard deviations to the a posteriori SIMU attitude standard deviations (Note: the dashed lines plot the average ratios for each sensor axis).</p>
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<p>The ratio of the a posteriori MIMU attitude time-derivative standard deviations to the a posteriori SIMU attitude time-derivative standard deviations (Note: the dashed lines plot the average ratios for each sensor axis).</p>
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<p>The estimated standard errors of unit weight for the SIMU-integrated system (moving window: 20 s).</p>
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18 pages, 8935 KiB  
Article
Use of Attitude and Heading Reference System (AHRS) to Analyze the Impact of Safety Nets on the Accelerations Occurring in the Human Body During a Collision
by Mariusz Gołkowski, Jerzy Kwaśniewski, Maciej Roskosz, Paweł Mazurek, Szymon Molski and Józef Grzybowski
Sensors 2024, 24(23), 7431; https://doi.org/10.3390/s24237431 - 21 Nov 2024
Viewed by 724
Abstract
The article presents accelerations occurring in the human body when falling onto a safety net. An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for objects, including pitch, roll, and yaw. These sensors are made [...] Read more.
The article presents accelerations occurring in the human body when falling onto a safety net. An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for objects, including pitch, roll, and yaw. These sensors are made of microelectromechanical systems (MEMS) gyroscopes, accelerometers, and magnetometers. Usually, they are used in aircraft flight instruments due to their high precision. In the present article, these sensors were used to test safety nets, protecting people or objects falling from heights. The measurement was made for two heights: 6 m and 3.5 m. During the research, a type of mannequin that is a representative model of the human body for the largest segment of the adult population was used. The measurement was carried out using two independent measurement systems. One recorded the accelerations at the chest of the tested object, while the sensors of the second system were placed at the head, arms, and legs. The compiled measurement results were related to the permissible acceleration values that do not threaten human health and life. Full article
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<p>Detailed view of the safety system with safety nets.</p>
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<p>General view of the safety system with safety nets.</p>
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<p>Hybrid III 95th test dummy.</p>
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<p>View of a set of modules connected by the CAN bus of the PRP-W2 system. From the left: data recorder, AHRS system, air data computer, GPS module, analogue input module, PWM input module.</p>
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<p>View of the PCDL-01 data recorder.</p>
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<p>View of the PCAI-01 analogue input module.</p>
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<p>GUARDA recorder placed on the parachute jumper’s chest.</p>
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<p>Arrangement of the elements of the PRP-W2 measurement system.</p>
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<p>Installation of the GUARDA recorder on the chest.</p>
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<p>Measurement conditions.</p>
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<p>Acceleration variation distribution for the center of gravity.</p>
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<p>Acceleration variation distribution for the head sensor.</p>
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<p>Acceleration variation distribution for the center of gravity.</p>
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<p>Acceleration variation distribution for the head sensor.</p>
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<p>Results of the PRP-W2 system tests—dump no. 1; H = 6.0 m.</p>
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<p>Results of the PRP-W2 system tests—dump no. 2; H = 3.5 m.</p>
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<p>Results of the PRP-W2 system tests—comparison for center of gravity and head.</p>
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<p>Acceleration variation distribution for the GUARDA system—dump no. 1; H = 6.0 m.</p>
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<p>Acceleration variation distribution for the GUARDA system—dump no. 2; H = 3.5 m.</p>
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<p>Modulus of acceleration variation a<sub>tot</sub> distribution for the GUARDA system.</p>
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26 pages, 1397 KiB  
Article
Inertial Measurement Unit Self-Calibration by Quantization-Aware and Memory-Parsimonious Neural Networks
by Matteo Cardoni, Danilo Pietro Pau, Kiarash Rezaei and Camilla Mura
Electronics 2024, 13(21), 4278; https://doi.org/10.3390/electronics13214278 - 31 Oct 2024
Viewed by 2522
Abstract
This paper introduces a methodology to compensate inertial Micro-Electro-Mechanical System (IMU-MEMS) time-varying calibration loss, induced by stress and aging. The approach relies on a periodic assessment of the sensor through specific stimuli, producing outputs which are compared with the response of a high-precision [...] Read more.
This paper introduces a methodology to compensate inertial Micro-Electro-Mechanical System (IMU-MEMS) time-varying calibration loss, induced by stress and aging. The approach relies on a periodic assessment of the sensor through specific stimuli, producing outputs which are compared with the response of a high-precision sensor, used as ground truth. At any re-calibration iteration, differences with respect to the ground truth are approximated by quantization-aware trained tiny neural networks, allowing calibration-loss compensations. Due to the unavailability of aging IMU-MEMS datasets, a synthetic dataset has been produced, taking into account aging effects with both linear and nonlinear calibration loss. Also, field-collected data in conditions of thermal stress have been used. A model relying on Dense and 1D Convolution layers was devised and compensated for an average of 1.97 g and a variance of 1.07 g2, with only 903 represented with 16 bit parameters. The proposed model can be executed on an intelligent signal processing inertial sensor in 126.4 ms. This work represents a step forward toward in-sensor machine learning computing through integrating the computing capabilities into the sensor package that hosts the accelerometer and gyroscope sensing elements. Full article
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<p>Design schema of silicon comb-like structure, used for accelerometers and gyroscopes.</p>
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<p>Compensation block incorporating the tiny neural network. The subtraction block indicates the element-wise subtraction of the compensation error to the uncompensated output.</p>
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<p>Golden Reference and MEMS response data collection procedure. Element-wise subtraction of each couple of responses (from the MEMS and from the GR) is used to compute the compensation error for each response.</p>
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<p>Tiny neural network inference procedure, with MEMS uncompensated responses as input and compensation error as output.</p>
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<p>Re-calibration system architecture featuring periodic network updates. The compensation block is the one from <a href="#electronics-13-04278-f002" class="html-fig">Figure 2</a>. The subtraction operator indicates the element-wise subtraction of each response in output from the compensation block to the Golden Reference responses.</p>
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<p>Architectural diagram of the Neural Network training implemented inside a Microcontroller or a Microprocessor.</p>
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<p>Simulated MEMS model illustration.</p>
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<p>Example MEMS and GR model responses to impulse, square and sine training functions. The MEMS model for these measurements is the resulting model after 3 days of simulated time.</p>
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<p>One of the LSM6DSV IMU device under test acceleration readings on the X, Y, and Z axes, along with the measured temperature during a thermal cycle. Acceleration measurement error is visibly temperature dependent.</p>
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<p>The calibration and re-calibration process. Stimuli could be applied at the beginning of each period (of 1 day of duration) to perform calibration and/or re-calibration.</p>
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<p>MCP of the models as the number of re-calibration iterations changes, from <a href="#sec8dot2dot1-electronics-13-04278" class="html-sec">Section 8.2.1</a>. The error bars represent the maximum and minimum compensation percentage.</p>
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<p>MCP, separately for each model, as the number of re-calibration iterations changes, from <a href="#sec8dot2dot1-electronics-13-04278" class="html-sec">Section 8.2.1</a>. The error bars represent the maximum and minimum compensation percentages.</p>
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<p>An example of the MEMS, GR, and calibrated responses to the test sequence of 4 days and 5 s of <span class="html-italic">X</span>-axis data utilizing Quantized Conv1D-Dense as the (re-)calibration model.</p>
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40 pages, 22416 KiB  
Article
In-Depth Analysis of Low-Cost Micro Electromechanical System (MEMS) Accelerometers in the Context of Low Frequencies and Vibration Amplitudes
by Piotr Emanuel Srokosz, Ewa Daniszewska, Jakub Banach and Michał Śmieja
Sensors 2024, 24(21), 6877; https://doi.org/10.3390/s24216877 - 26 Oct 2024
Viewed by 1082
Abstract
Shock and vibration hazards to civil structures are common and come not only from earthquakes but most often from mining operations or foundation work involving the installation of piles using hammer-driving and vibrating technology. The purpose of this study is to present test [...] Read more.
Shock and vibration hazards to civil structures are common and come not only from earthquakes but most often from mining operations or foundation work involving the installation of piles using hammer-driving and vibrating technology. The purpose of this study is to present test methods for low-cost MEMS accelerometers in terms of their selection for low-amplitude acceleration vibration-prone object-monitoring systems. Tests of 24 commercially available digital accelerometers were carried out on a custom-built test bench, selecting four models for detailed tests conducted on a specially built precision vibration table capable of inflicting accelerations at frequencies of 1–2 Hz, using displacements as small as a few micrometers. The analysis of the results was based, among other things, on a modified method of determining the signal-to-noise ratio (SNR) and also on the idea of the effective number of bits (ENOB). The results of the analysis showed that among low-cost MEMS accelerometers, there are some that are successfully suitable for the monitoring and warning of excessive vibration hazards in situations where objects are extremely sensitive to such impacts (e.g., treatment rooms in hospitals). Examples of accelerometers capable of detecting harmonic vibrations with amplitudes as small as 10 mm/s2 or impulsive shocks with amplitudes of at least 70 mm/s2 are indicated. Full article
(This article belongs to the Section Fault Diagnosis & Sensors)
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<p>Allan variance interpretation (S—slope factor) [<a href="#B38-sensors-24-06877" class="html-bibr">38</a>].</p>
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<p>Experimental setup for AV measurements. 1—accelerometer; 2—dual-channel data acquisition unit; 3—power supply; 4—wooden board; 5—polyurethane foam. The resonant frequency of the system as a mass-spring model is about 44.7 Hz.</p>
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<p>Block diagram of a single MEMS sensor data acquisition unit.</p>
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<p>Harmonic signal with linearly decreasing amplitude (S1).</p>
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<p>Harmonic signal with linearly decreasing amplitude (S2).</p>
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<p>Step signal with linearly decreasing amplitude (P1).</p>
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<p>Step signal with linearly decreasing amplitude (P2).</p>
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<p>Exciter scheme (modified 200 W wideband loudspeaker). 1—NdFeB magnet; 2—hall sensor; 3—aluminum support frame; 4—base (steel ballast braced with plaster); 5—steel frame; 6—accelerometer mounting platform (plastic composite covered with shielding copper); 7—copper coil; 8—ferrite magnet; 9—loudspeaker diaphragm.</p>
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<p>Vibration table with various MEMS placement configurations.</p>
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<p>Block diagram of exciter driver.</p>
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<p>Example modules with MEMS accelerometers.</p>
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<p>Allan variance for grade A accelerometers (x-axis).</p>
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<p>Allan variance for grade A accelerometers (y-axis).</p>
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<p>Allan variance for grade A accelerometers (z-axis).</p>
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<p>S1 signal recorded by ADXL313.</p>
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<p>S2 signal recorded by ADXL313.</p>
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<p>P1 signal recorded by ADXL313.</p>
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<p>P2 signal recorded by ADXL313.</p>
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<p>Filtered S1 signal recorded by LSM6DSVX16.</p>
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<p>Filtered S2 signal recorded by LSM6DSVX16.</p>
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<p>SNR for S1 signal.</p>
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<p>SNR for S2 signal.</p>
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<p>MSNR for S1 signal.</p>
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<p>MSNR for S2 signal.</p>
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<p>ENOB evaluated for S2 signal.</p>
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<p>DR evaluated for S2 signal.</p>
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<p>P1 signal recorded by LSM6DSVX16.</p>
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<p>P2 signal recorded by LSM6DSVX16.</p>
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<p>P2 signal recorded by MMA8452Q.</p>
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<p>P1 signal recorded by ISM330DHCX (y-axis excitation; pulses recorded in the z-axis).</p>
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<p>Construction of the Trauma Center of the Regional Specialized Hospital in Olsztyn (Poland); event recorder module installed on the wall of the hospital building adjacent to the construction site.</p>
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<p>Allan variance for grade B accelerometers (x-axis).</p>
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<p>Allan variance for grade B accelerometers (y-axis).</p>
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<p>Allan variance for grade B accelerometers (z-axis).</p>
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<p>Allan variance for grade C accelerometers (x-axis).</p>
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<p>Allan variance for grade C accelerometers (y-axis).</p>
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<p>Allan variance for grade C accelerometers (z-axis).</p>
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<p>S1 signal recorded by BMI270.</p>
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<p>S2 signal recorded by BMI270.</p>
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<p>S1 signal recorded by IIM42352.</p>
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<p>S2 signal recorded by IIM42352.</p>
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<p>S1 signal recorded by ISM330DHCX.</p>
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<p>S2 signal recorded by ISM330DHCX.</p>
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<p>S1 signal recorded by KX132.</p>
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<p>S2 signal recorded by KX132.</p>
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<p>S1 signal recorded by LIS2DW12.</p>
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<p>S2 signal recorded by LIS2DW12.</p>
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<p>S1 signal recorded by LSM6DSVX16.</p>
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<p>S2 signal recorded by LSM6DSVX16.</p>
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<p>S1 signal recorded by MMA8452Q.</p>
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<p>S2 signal recorded by MMA8452Q.</p>
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<p>P1 signal recorded by BMI270.</p>
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<p>P2 signal recorded by BMI270.</p>
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<p>P1 signal recorded by IIM42352.</p>
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<p>P2 signal recorded by IIM42352.</p>
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<p>P1 signal recorded by ISM330DHCX.</p>
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<p>P2 signal recorded by ISM330DHCX.</p>
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<p>P1 signal recorded by KX132.</p>
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<p>P2 signal recorded by KX132.</p>
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<p>P1 signal recorded by LIS2DW12.</p>
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<p>P2 signal recorded by LIS2DW12.</p>
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<p>P1 signal recorded by LSM6DSVX16.</p>
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<p>P2 signal recorded by LSM6DSVX16.</p>
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<p>P1 signal recorded by MMA8452Q.</p>
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<p>P2 signal recorded by MMA8452Q.</p>
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21 pages, 8060 KiB  
Article
Total Least Squares In-Field Identification for MEMS-Based Inertial Measurement Units
by Massimo Duchi and Edoardo Ida’
Robotics 2024, 13(11), 156; https://doi.org/10.3390/robotics13110156 - 23 Oct 2024
Viewed by 3298
Abstract
Inertial Measurement Units are widely used in various applications and, hardware-wise, they primarily consist of a tri-axial accelerometer and a tri-axial gyroscope. For low-end commercial employments, the low cost of the device is crucial: this makes MEMS-based sensors a popular choice in this [...] Read more.
Inertial Measurement Units are widely used in various applications and, hardware-wise, they primarily consist of a tri-axial accelerometer and a tri-axial gyroscope. For low-end commercial employments, the low cost of the device is crucial: this makes MEMS-based sensors a popular choice in this context. However, MEMS-based transducers are prone to significant, non-uniform and environmental-condition-dependent systematic errors, that require frequent re-calibration to be eliminated. To this end, identification methods that can be performed in-field by non-expert users, without the need for high-precision or costly equipment, are of particular interest. In this paper, we propose an in-field identification procedure based on the Total Least Squares method for both tri-axial accelerometers and gyroscopes. The proposed identification model is linear and requires no prior knowledge of the parameters to be identified. It enables accelerometer calibration without the need for specific reference surface orientation relative to Earth’s gravity and allows gyroscope calibration to be performed independently of accelerometer data, without requiring the sensor’s sensitive axes to be aligned with the rotation axes during calibration. Experiments conducted on NXP sensors FXOS8700CQ and FXAS21002 demonstrated that using parameters identified by our method reduced cross-validation standard deviations by about two orders of magnitude compared to those obtained using manufacturer-provided parameters. This result indicates that our method enables the effective calibration of IMU sensor parameters, relying only on simple 3D-printed equipment and significantly improving IMU performance at minimal cost. Full article
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<p>Fixed frame (F-frame) and Mobile frame (M-frame) at the beginning of the calibration procedure.</p>
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<p>3D-printed equipment used for the tests, including a rectangular prism housing (<b>a</b>), an 18-faced housing (<b>b</b>), a non-sloped reference (<b>c</b>) and a sloped reference (<b>d</b>).</p>
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<p>First six orientations of the re-orientation scheme for the prismatic housing.</p>
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<p>IMU mounted inside the prismatic housing (<b>a</b>) and inside the 18-faced housing (<b>b</b>).</p>
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<p>Experimental equipment in the initial orientation of the procedure for the <span class="html-italic">Sloped 18-faced</span> setup.</p>
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<p>Flowchart illustrating the key steps of the calibration procedure.</p>
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17 pages, 7212 KiB  
Article
Zigbee-Based Wireless Sensor Network of MEMS Accelerometers for Pavement Monitoring
by Nicky Andre Prabatama, Mai Lan Nguyen, Pierre Hornych, Stefano Mariani and Jean-Marc Laheurte
Sensors 2024, 24(19), 6487; https://doi.org/10.3390/s24196487 - 9 Oct 2024
Cited by 1 | Viewed by 3555
Abstract
In this paper, we propose a wireless sensor network for pavement health monitoring exploiting the Zigbee technology. Accelerometers are adopted to measure local accelerations linked to pavement vibrations, which are then converted into displacements by a signal processing algorithm. Each device consists of [...] Read more.
In this paper, we propose a wireless sensor network for pavement health monitoring exploiting the Zigbee technology. Accelerometers are adopted to measure local accelerations linked to pavement vibrations, which are then converted into displacements by a signal processing algorithm. Each device consists of an on-board unit buried in the roadway and a roadside unit. The on-board unit comprises a microcontroller, an accelerometer and a Zigbee module that transfers acceleration data wirelessly to the roadside unit. The roadside unit consists of a Raspberry Pi, a Zigbee module and a USB Zigbee adapter. Laboratory tests were conducted using a vibration table and with three different accelerometers, to assess the system capability. A typical displacement signal from a five-axle truck was applied to the vibration table with two different displacement peaks, allowing for two different vehicle speeds. The prototyped system was then encapsulated in PVC packaging, deployed and tested in a real-life road situation with a fatigue carousel featuring rotating truck axles. The laboratory and on-road measurements show that displacements can be estimated with an accuracy equivalent to that of a reference sensor. Full article
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<p>(<b>a</b>) System Architecture; (<b>b</b>) prototype tested in the laboratory.</p>
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<p>(<b>a</b>) Block diagram of the embedded unit; (<b>b</b>) embedded unit prototype.</p>
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<p>(<b>a</b>) Block diagram of the roadside unit; (<b>b</b>) roadside unit system.</p>
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<p>Five-axle truck displacement signals used for the vibrating table.</p>
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<p>(<b>a</b>) Vibrating pot test; (<b>b</b>) vibrating table test.</p>
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<p>Description of the five steps adopted to extract the displacement time histories from raw acceleration data.</p>
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<p>Vibrating table tests: (<b>a</b>) example of raw acceleration signal; (<b>b</b>) velocity history after the first integration; (<b>c</b>) displacement history after the second time integration; (<b>d</b>) final displacement history provided by the Hilbert transform.</p>
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<p>Vibrating table tests featuring a peak displacement of 0.25 mm and a vehicle speed of 45 km/h: (<b>a</b>) exemplary raw ADXL355 acceleration signal; (<b>b</b>–<b>d</b>) displacement histories obtained with the adopted signal processing procedure applied to measurements collected with the three MEMS accelerometers.</p>
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<p>Vibrating table tests featuring a peak displacement of 0.5 mm and a vehicle speed of 45 km/h: (<b>a</b>) exemplary raw MS1002 acceleration signal; (<b>b</b>–<b>d</b>) displacement histories obtained with the adopted signal processing procedure applied to measurements collected with the three MEMS accelerometers.</p>
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<p>Vibrating table tests featuring a peak displacement of 0.25 mm and a vehicle speed of 18 km/h: (<b>a</b>) raw ADXL355 acceleration signal; (<b>b</b>–<b>d</b>) displacement histories obtained with measurements collected with the three MEMS accelerometers.</p>
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<p>Vibrating table tests featuring a peak displacement of 0.25 mm and a vehicle speed of 92 km/h: (<b>a</b>) raw ADXL355 acceleration signal; (<b>b</b>–<b>d</b>) displacement histories obtained with measurements collected with the three MEMS accelerometers.</p>
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<p>Designed and fabricated PVC packaging, and assembly of the embedded unit.</p>
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<p>(<b>a</b>) Device installation scheme; (<b>b</b>) installation of the device in the pavement.</p>
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<p>(<b>a</b>) Position of the roadside unit on the test track; (<b>b</b>) accelerated pavement testing setup.</p>
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<p>(<b>a</b>) Raw acceleration, and (<b>b</b>) displacement time history obtained with the reported signal processing strategy.</p>
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18 pages, 18528 KiB  
Article
Data Poisoning Attack against Neural Network-Based On-Device Learning Anomaly Detector by Physical Attacks on Sensors
by Takahito Ino, Kota Yoshida, Hiroki Matsutani and Takeshi Fujino
Sensors 2024, 24(19), 6416; https://doi.org/10.3390/s24196416 - 3 Oct 2024
Viewed by 3400
Abstract
In this paper, we introduce a security approach for on-device learning Edge AIs designed to detect abnormal conditions in factory machines. Since Edge AIs are easily accessible by an attacker physically, there are security risks due to physical attacks. In particular, there is [...] Read more.
In this paper, we introduce a security approach for on-device learning Edge AIs designed to detect abnormal conditions in factory machines. Since Edge AIs are easily accessible by an attacker physically, there are security risks due to physical attacks. In particular, there is a concern that the attacker may tamper with the training data of the on-device learning Edge AIs to degrade the task accuracy. Few risk assessments have been reported. It is important to understand these security risks before considering countermeasures. In this paper, we demonstrate a data poisoning attack against an on-device learning Edge AI. Our attack target is an on-device learning anomaly detection system. The system adopts MEMS accelerometers to measure the vibration of factory machines and detect anomalies. The anomaly detector also adopts a concept drift detection algorithm and multiple models to accommodate multiple normal patterns. For the attack, we used a method in which measurements are tampered with by exposing the MEMS accelerometer to acoustic waves of a specific frequency. The acceleration data falsified by this method were trained on an anomaly detector, and the result was that the abnormal state could not be detected. Full article
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<p>Autoencoder-based anomaly detector.</p>
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<p>Overview of ELM.</p>
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<p>Overview of concept drift detection algorithm. (<b>a</b>) Trained centroids are sequentially calculated during training. (<b>b</b>) Test centroids are sequentially calculated during inference. (<b>c</b>) When concept drift occurs, the test centroid moves away from the train centroid. (<b>d</b>) When the test centroid exceeds the threshold, a concept drift is detected and a new instance is created. The new instance computes its own train centroid from the latest data (training data).</p>
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<p>Expected drift rate behavior. (<b>a</b>) Concept drift does not occur; (<b>b</b>) Concept drift occurs.</p>
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<p>Behavior of multi-instance on-device learning anomaly detector.</p>
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<p>Behavior of anomaly detector without attack.</p>
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<p>Behavior of anomaly detector with data poisoning attack.</p>
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<p>Experimental setup. (<b>a</b>) Overall setup; (<b>b</b>) Cooling fan and speaker.</p>
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<p>Block diagram of experimental setup.</p>
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<p>Observed frequency spectrum while both cooling fans are stopped.</p>
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<p>Relationship between irradiated acoustic wave frequency (in audible range), observed peak frequency, and amplitude.</p>
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<p>Relationship between irradiated acoustic wave frequency (in ultrasonic range), observed peak frequency, and amplitude.</p>
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<p>Effects of sound pressure for observed peak amplitude (frequency of acoustic waves: 3000 Hz).</p>
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<p>Samples of observed data. (<b>a</b>) Normal state; (<b>b</b>) Abnormal state; (<b>c</b>) Poisoned state.</p>
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<p>Error and drift rate without data poisoning attack.</p>
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<p>Error and drift rate with data poisoning attack.</p>
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14 pages, 4775 KiB  
Article
A Micromachined Silicon-on-Glass Accelerometer with an Optimized Comb Finger Gap Arrangement
by Jiacheng Li, Rui Feng, Xiaoyi Wang, Huiliang Cao, Keru Gong and Huikai Xie
Micromachines 2024, 15(9), 1173; https://doi.org/10.3390/mi15091173 - 22 Sep 2024
Viewed by 1309
Abstract
This paper reports the design, fabrication, and characterization of a MEMS capacitive accelerometer with an asymmetrical comb finger arrangement. By optimizing the ratio of the gaps of a rotor finger to its two adjacent stator fingers, the sensitivity of the accelerometer is maximized [...] Read more.
This paper reports the design, fabrication, and characterization of a MEMS capacitive accelerometer with an asymmetrical comb finger arrangement. By optimizing the ratio of the gaps of a rotor finger to its two adjacent stator fingers, the sensitivity of the accelerometer is maximized for the same comb finger area. With the fingers’ length, width, and depth at 120 μm, 4 μm, and 45 μm, respectively, the optimized finger gap ratio is 2.5. The area of the proof mass is 750 μm × 560 μm, which leads to a theoretical thermomechanical noise of 9 μg/√Hz. The accelerometer has been fabricated using a modified silicon-on-glass (SOG) process, in which a groove is pre-etched into the glass to hold the metal electrode. This SOG process greatly improves the silicon-to-glass bonding yield. The measurement results show that the resonant frequency of the accelerometer is about 2.05 kHz, the noise floor is 28 μg/√Hz, and the nonlinearity is less than 0.5%. Full article
(This article belongs to the Special Issue MEMS Sensors and Actuators: Design, Fabrication and Applications)
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<p>(<b>a</b>) Stereo structures of the accelerometer; (<b>b</b>) detail of the accelerometer structures.</p>
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<p>(<b>a</b>) The accelerometer structure topology; (<b>b</b>) equivalent circuit diagram of the accelerometer.</p>
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<p>The relationship between the capacitive sensitivity and the parameters <span class="html-italic">d</span> and <span class="html-italic">p</span> in the case of a certain chip area.</p>
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<p>(<b>a</b>) Block diagram of the phase-locked amplifier circuit; (<b>b</b>) actual manufactured PCB board.</p>
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<p>SOG process flow chart: (<b>a</b>) etching of the back cavity of the silicon wafer; (<b>b</b>) etching of the groove of the glass wafer; (<b>c</b>) fabrication of metal electrode; (<b>d</b>) the anodic bonding step; (<b>e</b>) thinning of the silicon wafer; (<b>f</b>) Etching of comb finger and spring structures.</p>
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<p>(<b>a</b>) SEM photograph of the accelerometer; (<b>b</b>) SEM photograph of comb fingers.</p>
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<p>Dynamic test system.</p>
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<p>Frequency response of the accelerometer.</p>
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<p>Quasi-static test system.</p>
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<p>Quasi-static response of the accelerometer.</p>
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<p>Spectrogram of the accelerometer output.</p>
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<p>Allan standard deviation curve.</p>
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18 pages, 6172 KiB  
Article
Integrated Amorphous Carbon Film Temperature Sensor with Silicon Accelerometer into MEMS Sensor
by Qi Zhang, Xiaoya Liang, Wenzhe Bi, Xing Pang and Yulong Zhao
Micromachines 2024, 15(9), 1144; https://doi.org/10.3390/mi15091144 - 12 Sep 2024
Viewed by 3546
Abstract
Amorphous carbon (a-C) has promising potential for temperature sensing due to its outstanding properties. In this work, an a-C thin film temperature sensor integrated with the MEMS silicon accelerometer was proposed, and a-C film was deposited on the fixed frame of the accelerometer [...] Read more.
Amorphous carbon (a-C) has promising potential for temperature sensing due to its outstanding properties. In this work, an a-C thin film temperature sensor integrated with the MEMS silicon accelerometer was proposed, and a-C film was deposited on the fixed frame of the accelerometer chip. The a-C film was deposited by DC magnetron sputtering and linear ion beam, respectively. The nanostructures of two types of films were observed by SEM and TEM. The cluster size of sp2 was analyzed by Raman, and the content of sp2 and sp3 of the carbon film was analyzed by XPS. It showed that the DC-sputtered amorphous carbon film, which had a higher sp2 content, had better temperature-sensitive properties. Then, an integrated sensor chip was designed, and the structure of the accelerometer was simulated and optimized to determine the final sizes. The temperature sensor module had a sensitivity of 1.62 mV/°C at the input voltage of 5 V with a linearity of 0.9958 in the temperature range of 20~150 °C. The sensitivity of the sensor is slightly higher than that of traditional metal film temperature sensors. The accelerometer module had a sensitivity of 1.4 mV/g/5 V, a nonlinearity of 0.38%, a repeatability of 1.56%, a total thermomechanical noise of 509 μg over the range of 1 to 20 Hz, and an average thermomechanical noise density of 116 µg/√Hz, which is smaller than the input acceleration amplitude for testing sensitivity. Under different temperatures, the performance of the accelerometer was tested. This research provided significant insights into the convenient procedure to develop a high-performance, economical temperature–accelerometer-integrated MEMS sensor. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators, 3rd Edition)
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<p>The SEM image of the amorphous carbon. (<b>a</b>) Prepared by DC sputtering; (<b>b</b>) prepared by ion beam.</p>
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<p>The Raman spectrum of the amorphous carbon. (<b>a</b>) Prepared by DC sputtering; (<b>b</b>) prepared by ion beam.</p>
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<p>The XPS spectrum of the amorphous carbon. (<b>a</b>) Prepared by DC sputtering; (<b>b</b>) prepared by ion beam.</p>
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<p>Test results of temperature-resistance characteristics of amorphous carbon thin films. (<b>a</b>) Prepared by DC sputtering (Sample A); (<b>b</b>) prepared by ion beam (Sample B).</p>
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<p>Temperature dependence of electrical conductivity of a-C and a-C:H films. (<b>a</b>) Prepared by DC sputtering (Sample A); (<b>b</b>) prepared by ion beam (Sample B) at the temperature range of 0~50 °C. (<b>c</b>) Prepared by ion beam (Sample B) at the temperature range of 50~100 °C. (<b>d</b>) Prepared by ion beam (Sample B) at the temperature range of 100~120 °C.</p>
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<p>(<b>a</b>) Theoretical Wheatstone bridge circuit for temperature sensors; (<b>b</b>) actual Wheatstone bridge circuit for temperature sensors.</p>
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<p>Design parameters of a-C temperature sensor.</p>
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<p>Temperature sensor processing flow diagrams. (<b>a</b>) Photolithography; (<b>b</b>) a-C deposition; (<b>c</b>) lift off.</p>
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<p>(<b>a</b>) Schematic of accelerometer; (<b>b</b>) zoomed-in view of R<sub>2</sub>; (<b>c</b>) zoomed-in view of R<sub>1</sub>; (<b>d</b>) zoomed-in view of temperature sensor; (<b>e</b>) TEM picture of the surface of the a-C temperature sensor. (<b>f</b>) read-out circuit.</p>
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<p>(<b>a</b>) Finite element simulation analysis of embedded cross-beam sensitive structures; (<b>b</b>) Stress simulation of sensitive beams with different sizes of accelerometer.</p>
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<p>Integrated temperature sensor and accelerometer processing flow diagrams. (<b>a</b>) Ion injection; (<b>b</b>) resistor etching; (<b>c</b>) deposited insulation layer; (<b>d</b>) back cavity etching; (<b>e</b>) glass corrosion; (<b>f</b>) silicon-glass bonding; (<b>g</b>) thermistor deposition; (<b>h</b>) metal wire etching; (<b>i</b>) electrode sputtering; (<b>j</b>) front structure release.</p>
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<p>Test results of a-C temperature sensor modules with integrated sensor. (<b>a</b>) Read-out circuit of temperature sensor modules; (<b>b</b>) the output voltage versus temperature of temperature sensor modules.</p>
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<p>Static test results of the accelerometer.</p>
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<p>The noise power density spectrum of accelerometer modules of integrated sensor.</p>
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<p>Temperature effect on the accelerometer of the integrated sensor. (<b>a</b>) The output voltage versus acceleration in the temperature range of 20 °C to 150 °C; (<b>b</b>) the sensitivity and linearity of the accelerometer in the temperature range of 20 °C to 150 °C.</p>
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<p>Sensor output after temperature compensation.</p>
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