Capacitive Accelerometer Research Articles

Editorial: Special Section on Human-Centered Artificial Intelligence with Big Data Applications

Editorial: Special Section on Human-Centered Artificial Intelligence with Big Data Applications

Development of a Self-Powered Piezo-Resistive Smart Insole Equipped with Low-Power BLE Connectivity for Remote Gait Monitoring.

The evolution of low power electronics and the availability of new smart materials are opening new frontiers to develop wearable systems for medical applications, lifestyle monitoring, and performance detection. This paper presents the development and realization of a novel smart insole for monitoring the plantar pressure distribution and gait parameters; indeed, it includes a piezoresistive sensing matrix based on a Velostat layer for transducing applied pressure into an electric signal. At first, an accurate and complete characterization of Velostat-based pressure sensors is reported as a function of sizes, support material, and pressure trend. The realization and testing of a low-cost and reliable piezoresistive sensing matrix based on a sandwich structure are discussed. This last is interfaced with a low power conditioning and processing section based on an Arduino Lilypad board and an analog multiplexer for acquiring the pressure data. The insole includes a 3-axis capacitive accelerometer for detecting the gait parameters (swing time and stance phase time) featuring the walking. A Bluetooth Low Energy (BLE) 5.0 module is included for transmitting in real-time the acquired data toward a PC, tablet or smartphone, for displaying and processing them using a custom Processing® application. Moreover, the smart insole is equipped with a piezoelectric harvesting section for scavenging energy from walking. The onfield tests indicate that for a walking speed higher than 1 ms−1, the device’s power requirements (i.e., ) was fulfilled. However, more than 9 days of autonomy are guaranteed by the integrated 380-mAh Lipo battery in the total absence of energy contributions from the harvesting section.

A rapid fabrication approach for the capacitive accelerometer based on 3D printing and a silver particle-free ink

A rapid fabrication approach for the capacitive accelerometer based on 3D printing and a silver particle-free ink

A Capacitive 3-Axis MEMS Accelerometer for Medipost: A Portable System Dedicated to Monitoring Imbalance Disorders.

The constant development and miniaturization of MEMS sensors invariably provides new possibilities for their use in health-related and medical applications. The application of MEMS devices in posturographic systems allows faster diagnosis and significantly facilitates the work of medical staff. MEMS accelerometers constitute a vital part of such systems, particularly those intended for monitoring patients with imbalance disorders. The correct design of such sensors is crucial for gathering data about patient movement and ensuring the good overall performance of the entire system. This paper presents the design and measurements of a three-axis accelerometer dedicated for use in a device which tracks patient movement. Its main focus is the characterization of the sensor, comparing different designs and evaluating the impact of the packaging and readout circuit integration on sensor operation. Extensive testing and measurements confirm that the designed accelerometer works correctly and allows identifying the best design in terms of sensitivity/stability. Moreover, the response of the proposed sensor as a function of the applied acceleration demonstrates very good linearity only if the readout circuit is integrated in the same package as the MEMS sensor.

Characterization of SOI MEMS capacitive accelerometer under varying acceleration shock pulse durations

Characterization of SOI MEMS capacitive accelerometer under varying acceleration shock pulse durations

Lightweight Thermal Compensation Technique for MEMS Capacitive Accelerometer Oriented to Quasi-Static Measurements.

The application of MEMS capacitive accelerometers is limited by its thermal dependence, and each accelerometer must be individually calibrated to improve its performance. In this work, a light calibration method based on theoretical studies is proposed to obtain two characteristic parameters of the sensor’s operation: the temperature drift of bias and the temperature drift of scale factor. This method requires less data to obtain the characteristic parameters, allowing a faster calibration. Furthermore, using an equation with fewer parameters reduces the computational cost of compensation. After studying six accelerometers, model LIS3DSH, their characteristic parameters are obtained in a temperature range between 15 °C and 55 °C. It is observed that the Temperature Drift of Bias () is the parameter with the greatest influence on thermal drift, reaching 1.3 mg/°C. The Temperature Drift of Scale Factor () is always negative and ranges between 0 and −400 ppm/°C. With these parameters, the thermal drifts are compensated in tests with 20 °C of thermal variation. An average improvement of 47% was observed. In the axes where the thermal drift was greater than 1 mg/°C, the improvement was greater than 80%. Other sensor behaviors have also been analyzed, such as temporal drift (up to 1 mg/h for three hours) and self-heating (2–3 °C in the first hours with the corresponding drift). Thermal compensation has been found to reduce the effect of the latter in the first hours after power-up of the sensor by 43%.

An ultra-efficient recycling folded cascode OTA based on GAA-CNTFET technology for MEMS/NEMS capacitive readout applications

This paper demonstrates an ultra-efficient recycling folded cascode (RFC) operational transconductance amplifier (OTA) as one of the cardinal blocks in most analog microsystems. Two positive feedbacks are utilized in the proposed RFC OTA to enhance the input transconductance and the output impedance. All GAA-CNTFETs are biased in the near-threshold region (VT≈0.37 V and VDD=±0.2 V) to reduce power consumption. The simulation results indicate that with CLoad = 5pF, the proposed RFC OTA shows 102 dB open-loop gain and 17.2 MHz unit gain-bandwidth with an ultra-low power consumption of 111.5nW and a reasonable slew rate response (17.3 V/µs). A capacitive readout circuit for micro-and nano-electromechanical systems (MEMS/NEMS) applications is suggested to assess the proposed RFC OTA's performance in practical applications. By utilizing an RC sensing feedback structure, the proposed transimpedance amplifier presents 155dBΩ gain with a 400 MHz bandwidth. Compared to the other counterparts, the proposed GAA-CNTFET-based TIA presents fascinating power savings 86% total average improvement) and 1.6 times total average gain improvement. Our simulation results accentuate that the proposed GAA-CNTFET-based RFC OTA is a powerful candidate for designing ultra-efficient MEMS/NEMS capacitive accelerometers readout circuits.

Design and implementation of an optical fiber sensing based vibration monitoring system

Vibration analysis is generally used in the industries for condition monitoring of various electromechanical equipment. For the predictive maintenance of the industry equipment, several techniques have been applied which are based on capacitive and piezoelectric accelerometers. However, they possess several real time problems due to the negative influence of electromagnetic interference. The major problem lies in the detection and transmission of various physical parameters in the noisy and harsh environment. In order to solve the weak points of commonly used structural vibration detection sensors that are easily affected by the harsh environment of the engineering site, the principle of optical fiber sensing is studied, and the system optical path is designed based on MZ interference technology. In this work, a special data acquisition and processing software is developed to acquire the sensed data and the vibration detection is carried out on the steel cantilever structure pasted with fiber optic sensors. Extraction using FFT and pattern recognition through bp neural network yields the system accuracy rate of 96.7 %. The proposed interference type optical fiber technology provides a novel approach for real-time monitoring of engineering structure vibration laying the foundation for the research of intelligent buildings.

Design and implementation for the PWM closed-loop feedback interface circuit of a sandwich capacitive accelerometer based on ARM

Owing to the advantages of small size and high integration that accelerometers made by MEMS technology, the Pulse Width Modulation (PWM) closed-loop feedback interface circuit of a sandwich capacitive accelerometer based on ARM is designed. Based on the design, a simulation by SIMULINK and a PCB board-level circuit are conducted. Simulation and measurement are provided to support the design. The realization of Proportion Integral Differential (PID) control algorithm and the generation of PWM are performed by STM32 microcontroller instead of the circuit in the design. The output form of the interface circuit is PWM with different duty cycle and filtered DC voltage. According to the measurement results, the output of the PWM duty cycle change is 16.9%/g, and the sensitivity is 1.045 V/g.

Low‐offset differential output switched‐capacitor interface for micro‐capacitive acceleration sensors

This paper presents two simple but effective switched capacitor based differential output capacitive sensor interfaces, designed and fabricated in United Microelectronics Corporation 180 nm complementary metal oxide semiconductor (CMOS) process technology. The first configuration combines chopper modulation and switched capacitor based correlated double sampling, while the second configuration utilises chopper modulation with a modified demodulation scheme to reduce noise and offset. The proposed designs utilise a fully differential operational amplifier (op-amp) with single-feedback loop, which reduces the mismatch between the single-ended outputs in the differential configuration. The proposed configurations are analysed in perspective of noise to achieve high accuracy with less noise and integrated with supporting circuitry. The fabricated application specific integrated circuit (ASIC) is first characterised with the internal on-chip capacitors and then integrated with micro-electro-mechanical systems (MEMS) based differential capacitive accelerometer sensor on a printed circuit board (PCB) for dynamic testing. The integrated PCB and a commercially available accelerometer (ADXL335) is mounted on a sub-woofer system and the dynamic testing is carried out. The measurement results show that the sensor interface is capable of measuring sub-fF capacitance change with zero offset less than 2 mV. The first configuration provides sensitivity of 720 mV/g, whereas the second configuration attains sensitivity of 385 mV/g. The noise floors are 400 μ g / Hz , 325 μ g / Hz , whereas the capacitance resolutions are 70 and 60 aF, respectively.

A Novel Fabrication Method for a Capacitive MEMS Accelerometer Based on Glass-Silicon Composite Wafers.

In this paper, we report a novel teeter-totter type accelerometer based on glass-silicon composite wafers. Unlike the ordinary micro-electro-mechanical systems (MEMS) accelerometers, the entire structure of the accelerometer, includes the mass, the springs, and the composite wafer. The composite wafer is expected to serve as the electrical feedthrough and the fixed capacitance plate at the same time, to simplify the fabrication process, and to save on chip area. It is manufactured by filling melted borosilicate glass into an etched silicon wafer and polishing the wafer flat. A sensitivity of 51.622 mV/g in the range of ±5 g (g = 9.8 ), a zero-bias stability under 0.2 mg, and the noise floor with 11.28 µg/√Hz were obtained, which meet the needs of most acceleration detecting applications. The micromachining solution is beneficial for vertical interconnection and miniaturization of MEMS devices.

Stress analysis in new improved differential vertical comb capacitive micro accelerometer using SOI technology

Stress analysis in new improved differential vertical comb capacitive micro accelerometer using SOI technology

Design and optimization of differential capacitive micro accelerometer for vibration measurement

Abstract This paper deals with the design and optimization of a differential capacitive micro accelerometer for better displacement since other types of micro accelerometer lags in sensitivity and linearity. To overcome this problem, a capacitive area-changed technique is adopted to improve the sensitivity even in a wide acceleration range (0–100 g). The linearity is improved by designing a U-folded suspension. The movable mass of the accelerometer is designed with many fingers connected in parallel and suspended over the stationary electrodes. This arrangement gives the differential comb-type capacitive accelerometer. The area changed capacitive accelerometer is designed using Intellisuite 8.6 Software. Design parameters such as spring width and radius, length, and width of the proof mass are optimized using Minitab 17 software. Mechanical sensitivity of 0.3506 μm/g and Electrical sensitivity of 4.706 μF/g are achieved. The highest displacement of 7.899 μm is obtained with a cross-axis sensitivity of 0.47%.

Low-Noise Readout Circuit for an Automotive MEMS Accelerometer

This paper presents a charge-balanced readout circuit for MEMS capacitive accelerometers. The focus of this work is a design with a low-noise and low area consumption while ensuring the essential linearity and electromagnetic compatibility (EMC) for automotive applications. The readout circuit is composed of a charge-balanced single-ended input C/V stage followed by a second order sigma-delta modulator. The C/V stage uses a Gm stage combined with an integrator to reduce its noise contribution. The measurement results of the readout circuit show a noise floor of 62 $\mu g/{\sqrt {\mathrm{ Hz}}}$ and a temperature dependent offset smaller than ±0.6 mg after compensation. The measured dynamic range of the complete interface, including readout circuit and sensor, is 95.5 dB. The measured EMC is below 2 mg. The accelerometer readout circuit has been designed in a 130nm technology. Its power and area consumption is 1.4 mW and 0.26mm2.

A 200 μg/√Hz, 2.7 milli-g Offset Differential Interface for Capacitive Micro Accelerometer

This brief presents a switched-capacitor based low offset differential output sensor interface for MEMS capacitive accelerometers. The proposed interface employs an improved demodulation scheme by using a fully differential op-amp and a modified clocking scheme to reduce the zero-g offset. The interfacing Application Specific Integrated Circuit (ASIC) is designed and fabricated using UMC 180 nm CMOS process technology. The fabricated ASIC is integrated with a MEMS capacitive acceleration sensor and the measured results are presented. The proposed configuration achieves maximum sensitivity of 1.45 V/g with less than 2% non-linearity error. The zero-g offset is less than 3 milli-g while the noise floor is 200 μg/√{Hz} approximately.

Capacitive Accelerometers with Beams Based on Alternated Segments of Different Widths

Microelectromechanical (MEM) Accelerometers measure the accelerations or vibrations experienced by objects due to inertial forces or mechanical excitations. To improve their proof mass displacement, several alternatives have been used, such as the design of different shapes of suspension beams. In this work, a new shape of beam is proposed based on alternated segments of different widths. To analyze its performance, one-quarter, middle and complete accelerometers were calculated and simulated; the results were compared with similar cases using conventional uniform-shaped beams. A notable improvement in the proof mass displacement was obtained in all cases, especially with the proposed symmetrical-shaped beam. Harmonic response and explicit dynamic analysis were also considered to discover performance when they are subjected to structural load. An improvement in amplitude displacement was also observed, as well as operation frequency reduction. From the explicit dynamic analysis, a faster performance of the accelerometer with uniform arms can be observed; however, it responds at a lower range of input velocities. A performance comparison of the proposed beam is presented considering the two reported accelerometers. Finally, from the variation in the width of the thinner segment of the symmetrical arms, it can be observed that it is possible to obtain an increment in the displacement of the proof mass of 39.57% and a decrement in natural frequency of 15.30%, with respect to the case of the uniform arm. Other advantages of the symmetric beam are the stress distribution, reducing its effect on the proof mass, as well as their low cross-axis sensitivity. Simulations were performed with ANSYS.

Моделирование и исследование различных типов подвесов инерционной массы в чувствительных элементах микромеханических приборов

In microelectromechanical devices and systems (MEMS), capacitive micromechanical accelerometers (MMA) are used in airbag systems, machine vibration monitoring, navigation, seismology, microgravity measurements, etc. The most important structural elements of the sensing element are suspensions, through which the inertial mass is connected to a fixed frame. To ensure reliable operation and stability of sensor parameters, it is necessary to take into account the results of external factors already at the design stage of the sensor structure, especially its sensitive element, and at subsequent stages of the life cycle. In this work, the characteristic structures of suspension elements, which are made of silicon with different crystallographic orientations, are investigated and the results of modeling their most important parameters are presented. The simulation has been performed using the ANSYS program. The natural frequencies of inertial mass oscillations, residual mechanical stresses in the structural elements of silicon sensitive element with different crystallographic orientations have been calculated upon impact (up to 10 000 g). The natural vibration frequency changes and the dynamics of the change in the residual mechanical stress in the suspension elements with a temperature change in the range from +150 to –150 °C for a short time interval of 10 s, which corresponds to thermal shock, investigated. The results of studies of residual mechanical stresses arising upon impact and natural frequencies of inertial mass oscillations have been made it possible to develop recommendations on the choice of the design of suspension elements made of silicon, providing high sensitivity and stability of MMA parameters. It has been established that the use of folded springs with a rectangular or round cross-sectional shape with a suspension element thickness of 40 μm provides the highest temperature stability of the parameters. The results obtained are useful for developing real designs of MMA and other micromechanical devices

Large-Stroke Capacitive MEMS Accelerometer Without Pull-In

In this study, the feasibility of obtaining electrical read-out data from a capacitive MEMS accelerometer that employs repulsive electrode configuration is demonstrated. This configuration allows for large-stroke vibrations of microstructures without suffering from pull-in failure that exists in conventional accelerometers based on the parallel-plate configuration. With initial fabrication gap of 2.75μm, the accelerometer can reach a 4.2μm dynamical displacement amplitude. The accelerometer is tested up to 95(V) without exhibiting pull-in failure. For comparison, the pull-in voltage of an accelerometer with same dimensions but with conventional parallel-plate electrode configuration is 0.8(V). The MEMS device is fabricated using the POLYMUMPs fabrication standard. An electrical circuit is built to measure the capacitance change due to motion of the accelerometer proof-mass. The accelerometer has a mechanical sensitivity of 35nm/g and electrical sensitivity of 5.3mV/g. The ability to use large bias voltages without the typical adverse effects on the stability of the moving electrode will enable the design of capacitive MEMS accelerometers with enhanced resolution and tunable frequency range.

A Low-Power Low-Noise Monolithic Accelerometer with Automatic Sensor Offset Calibration

This work presents a monolithically integrated CMOS-MEMS capacitive accelerometer that uses background self-calibration in analog mode to compensate for sensor offset. Background analog calibration maintains sensor accuracy at all times, thus improving upon traditional digital calibration methods. When powered on, the calibration process automatically initiates without the need for an external controller like a microcontroller. The design requires no physical trimming techniques on the MEMS structure, and the worst zero-gram offset can be reduced to ±50 ​mg. The single-axis accelerometer was fabricated by the UMC 0.18 ​μm CMOS-MEMS process. The chip area containing the sensors and the integrated circuit is 1.94 ​mm ​× ​1.23 ​mm. Within the sensing range of ±8 ​g, the measured output noise density is around 100 μg/rtHz. This total power consumption from the 1.8 ​V supply voltage is 45 ​μW.

MEMS-based wave buoy: Towards short wind-wave sensing

Low-cost commercial micro-electro-mechanical system (MEMS)-based inertial motion unit is used for sea surface wave measurements. A buoy is developed based on the capacitive silicon-based accelerometer–gyroscope–magnetometer sensor with radically simplified architecture allowing a significant reduction of the buoy hull size down to 14-cm diameter and hence increased high-frequency sensitivity. The proposed buoy design is suitable for short-term manual wave measurements with minimal deployment–recovery efforts and/or experiments where knowledge of the high-frequency part of the spectrum is preferable. The buoy data is validated in a field experiment at the Black Sea stationary research platform using reference measurements of the six-wire resistive wave gauge. The strapped-down buoy measurements are transformed into the georeferenced buoy tilts and vertical acceleration using small wave slope approximation. The classical (Longuet-Higgins et al., 1961) approach is used for directional wave spectra estimation. Under 1 to 15 m/s wind speed, pure wind and mixed sea conditions, the significant wave height, wave peak period, wave direction, and spectral width are well reproduced by the buoy. The buoy geometric cut-off frequency, about 2.5 Hz, corresponding to wavelength twice the hull diameter, is at least 2.5 times better than that of commercially available buoys. The sub-peak low-frequency noise, typical for accelerometer-derived spectra, is wind-dependent and thus is clearly not the intrinsic sensor noise, but rather results from the buoy non-linear response to the waves. The detected high-frequency (4<f<80Hz) spectrum tail also depends on the wind speed in accord with the short-wave wind-driven wave spectrum model. The observed high-frequency sensitivity may be useful for short-wave sensing beyond the geometric cut-off frequency with MEMS-based sensors.