Accelerometer Structure Research Articles

Design and fabrication of an accelerometer structure using glass fiber reinforced epoxy resin for seismic P-wave early warning

Earthquake early warning represents a vital and effective strategy for mitigating earthquake-related losses. Among the existing sensors for earthquake early warning, MEMS accelerometers involve complex manufacturing process, leading to high research and development costs and long cycles. Traditional mechanical sensors are bulky, costly, hence not suitable for large-scale, high-density monitoring network. In this study, a low-cost accelerometer using glass fiber reinforced epoxy resin is proposed for longitudinal seismic waves (P-waves) early warning. Both theorical and finite element analysis are carried out to define and optimize the initial structure of the accelerometer. A pre-deformation structure is implemented into the spring suspension system to offset the influence of the sensor’s gravity, so that a self-balanced state in the direction of gravity is achieved. The simulation results show that the accelerator can achieve an eigenfrequency of 12.67 Hz, a Q-value of 49.2, and mechanical thermal noise of 1.72×10-9g/Hz. Based on the simulation results, the accelerometer’s structure is processed using a computer numerical control (CNC) milling machine, and tested by collecting the voltage signals when the accelerometer’s structure undergoes an impact in the direction of the gravity. The measured eigenfrequency is around 10 Hz, and the signal attenuation rate closely aligns with the simulation results. The accelerometer structure has dimensions within 6 cm and a relatively simplified manufacturing process, making it a cost-effective solution for the development of large-scale, high-density earthquake early warning systems.

A novel design of a MEMS resonant accelerometer with adjustable sensitivity

This paper presents the design and experimental evaluation of a silicon micro-machined resonant accelerometer featuring adjustable sensitivity. By integrating an electrostatic tuning module into the fundamental accelerometer structure, dynamic sensitivity adjustment becomes feasible, leveraging the softening effect of electrostatic negative stiffness to optimize range, noise, and bandwidth. Notably, the electrostatic tuning module integrates seamlessly with the core accelerometer structure, minimizing structural alterations. Through theoretical analysis and finite element simulation of the electrostatic negative stiffness principle, we have designed a novel accelerometer with adjustable sensitivity, which can enhance the sensitivity and reduces the bias-instability of the accelerometer with a relatively small adjustment voltage, without increasing structural complexity. The performance of the accelerometer was assessed through open-loop, closed-loop, and dynamic experiments, revealing that sensitivity increased from 843 Hz/g to 2611 Hz/g within a linear range of ±1 g when employing a sensitivity-enhancing bias voltage of 9 V. Moreover, the bias-instability is lowered down from 17.3 μg to 6.8 μg. This design offers a promising avenue for sensitivity tuning in MEMS resonant accelerometers.

New parameters for the capacitive accelerometer to reduce its measurement error and power consumption

Capacitive accelerometers are essential components in a wide range of electronic devices, enabling crucial functionalities such as touch sensitivity and proximity detection. Ensuring optimal accuracy is crucial for their effective performance in various applications. A key factor in this accuracy is the frequency margin, a parameter that significantly influences the sensor's ability to detect and respond to changes in capacitance.In this article, we will delve deeply into strategies aimed at optimizing capacitive sensors with a focus on improving their frequency margin. By exploring the methodologies and techniques that enhance the sensor's ability to operate within an ideal frequency range, we aim to improve the measurement accuracy of capacitive accelerometers by reducing measurement errors and power consumption. This optimization process involves meticulous calibration of sensor parameters such as sensitivity, resonance frequency, and damping factors to maximize performance under various environmental conditions. The new capacitive accelerometer structure improves sensitivity, linearity, and accuracy through advanced measurement setups and design, offering high-performance acceleration measurements suitable for various applications and reliable data collection and calibration.

Highly stabilized fiber Bragg grating accelerometer based on cross-type diaphragm

A fiber Bragg grating (FBG) accelerometer based on cross-type diaphragm was proposed and designed, in which the cross-beam acts as a spring element. To balance the sensitivity and stability, the accelerometer structure was optimized. The experimental results show that the designed device has a resonant frequency of 556 Hz with a considerable wide frequency bandwidth of up to 200 Hz, which is consistent with the simulation. The sensitivity of the device is 12.35 pm/g@100 Hz with a linear correlation coefficient of 0.99936. The proposed FBG accelerometer has simple structure and strong anti-interference capability with a maximal cross-error less than 3.26%, which can be used for mechanical structural health monitoring.

Study on the influence of pendulum convex plate on the partial value of quartz flexible accelerometer

The partial value is an essential performance index for assessing the stability of quartz flexible accelerometers. By analyzing the structure of the quartz flexural accelerometer and the impact of the pendulum convex plate, the influence of the convex plate on the partial value of the accelerometer is studied by theoretical derivation and modeling simulation methods. The results show that the barycentric coordinate shifts by approximately 10.7678 × 10-12 µm with the change of the coplanarity of the convex plate, which causes mechanical zero position errors, increases the partial value, and affects the stability of the quartz flexural accelerometer. Therefore, the coplanarity of the convex plate should be maintained at ≤0.3 µm and the partial value should be within the error range of ≤ |±2| mg and provide improvement measures to establish a basis for further improving the stability of the quartz flexible accelerometer.

High-Sensitivity Piezoelectric MEMS Accelerometer for Vector Hydrophones.

In response to the growing demand for high-sensitivity accelerometers in vector hydrophones, a piezoelectric MEMS accelerometer (PMA) was proposed, which has a four-cantilever beam integrated inertial mass unit structure, with the advantages of being lightweight and highly sensitive. A theoretical energy harvesting model was established for the piezoelectric cantilever beam, and the geometric dimensions and structure of the microdevice were optimized to meet the vibration pickup conditions. The sol-gel and annealing technology was employed to prepare high-quality PZT thin films on silicon substrate, and accelerometer microdevices were manufactured by using MEMS technology. Furthermore, the MEMS accelerometer was packaged for testing on a vibration measuring platform. Test results show that the PMA has a resonant frequency of 2300 Hz. In addition, there is a good linear relationship between the input acceleration and the output voltage, with V = 8.412a - 0.212. The PMA not only has high sensitivity, but also has outstanding anti-interference ability. The accelerometer structure was integrated into a vector hydrophone for testing in a calibration system. The results show that the piezoelectric vector hydrophone (PVH) has a sensitivity of -178.99 dB@1000 Hz (0 dB = 1 V/μPa) and a bandwidth of 20~1100 Hz. Meanwhile, it exhibits a good "8" shape directivity and consistency of each channel. These results demonstrate that the piezoelectric MEMS accelerometer has excellent capabilities suitable for use in vector hydrophones.

Thermal Stress Resistance for the Structure of MEMS-Based Silicon Differential Resonant Accelerometer

Due to material mismatch, silicon differential resonant accelerometers (SDRA) experience unpredictable thermal stress that is challenging to account for. An SDRA with a stress-isolated frame that is co-faced with the sensitive structural layer is shown in this study. Analytical construction is used to create the stress transmission model of SDRA, which incorporates the equivalent stiffness of a stress-isolated frame. It offers a technique to balance the scale factor of the device with thermal stress resistance. Then, from -40°C to 85°C, the proposed SDRA devices’ temperature behavior with and without a stress-isolated frame were examined theoretically, numerically, and experimentally. The measured temperature sensitivities of the device with the stress-isolated structure were around -1.15Hz /°C, 0.19mg/°C, and 37.23ppm /°C for the frequency, bias, and scale factors, respectively. The bias instability of the novel device is 0.72μg. Under the identical experimental conditions, each of these metrics outperformed the device without stress isolation by one to two orders of magnitude, demonstrating the efficiency of the novel stress-isolated structure.

Design and simulation of micro piezoelectric fiber triaxial acceleration sensor

Aiming at the demand for passive sonar systems for medium and low-frequency detection, low cost, and small working platform working sensor, a three-axis pressure piezoelectric accelerometer based on piezoelectric ceramic fiber is designed. Firstly, based on the acoustic vibration pick-up principle and extended Hamilton, the action mode of the accelerometer is analyzed theoretically to determine the accelerometer structure size. The accelerometer with a special mass structure is designed by using axially polarized piezoelectric ceramic fiber. The characteristic frequency and frequency domain analysis of the accelerometer are simulated by the FEM method. The results show that the overall size of the piezoelectric accelerometer is 20 mm ×20 mm×35 mm, the first-order natural frequency is 410 Hz, the external field directivity is standard “8” type, and the acceleration sensitivity reaches 112.2 mV/g, which verifies the great potential of the three-axis accelerometer designed by piezoelectric ceramic fiber material in the field of medium and low frequency.

High-G MEMS Accelerometer Calibration Denoising Method Based on EMD and Time-Frequency Peak Filtering.

In order to remove noise generated during the accelerometer calibration process, an accelerometer denoising method based on empirical mode decomposition (EMD) and time-frequency peak filtering (TFPF) is proposed in this paper. Firstly, a new design of the accelerometer structure is introduced and analyzed by finite element analysis software. Then, an algorithm combining EMD and TFPF is proposed for the first time to deal with the noise of the accelerometer calibration process. Specific steps taken are to remove the intrinsic mode function (IMF) component of the high frequency band after the EMD decomposition, and then to use the TFPF algorithm to process the IMF component of the medium frequency band; meanwhile, the IMF component of the low frequency band is reserved, and finally the signal is reconstructed. The reconstruction results show that the algorithm can effectively suppress the random noise generated during the calibration process. The results of spectrum analysis show that EMD + TFPF can effectively protect the characteristics of the original signal and that the error can be controlled within 0.5%. Finally, Allan variance is used to analyze the results of the three methods to verify the filtering effect. The results show that the filtering effect of EMD + TFPF is the most obvious, being 97.4% higher than the original data.

Retraction Note: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

Retraction Note: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

Study on stress isolation structure of piezoresistive high-g accelerometer

We put forward a novel thermal stress isolation structure with five anchors, which greatly suppresses the zero offset of piezoresistive high-g accelerometer. In this paper, the parameters of the thermal stress isolation structure are optimized by finite element simulation to ensure that the sensor has lower zero offset and a good natural frequency. A high natural frequency can prevent the sensor from being damaged due to resonance when it is subjected to shock. Finally, the zero offset of the sensor with thermal stress isolation is reduced to 10% of that without thermal stress isolation. Natural frequency of the sensor is 264.18 kHz. Its sensitivity is 1.1μV/G/5V according to shock simulation of 100,000 g.

DISPOSABLE PIEZOELECTRIC SENSOR OF ACCELERATIONS (ACCELEROMETER) FOR DESTRUCTIVE TESTS

The paper presents designing specifications and structure of cheap piezoelectric accelerometers on the range up to ca. 4000g developed and made in the AFIT (Air Force Institute of Technology) for destructive tests. Piezoelectric 455 kHz resonating plates were used for the units. Their calibration was described and sensitivity determined on 0.37 - 0.72 mV/g at accuracy < 10%.

Design, fabrication and test of a bulk SiC MEMS accelerometer

The application of micro accelerometer in extremely high temperature environment has become an urgent problem to be solved. However, current microelectromechanical system (MEMS) Si-based accelerometer cannot adapt to higher temperatures than 500 °C. Because of its excellent properties in high temperature environments, silicon carbide (SiC) shows promising potential in development of high temperature MEMS sensors, and it is a good alternative to Si for developing accelerometers. Due to the difficulty of bulk-SiC fabrication process and the complex structure of MEMS accelerometers, there are few studies on bulk SiC accelerometers and few test data of the performance. In this study, in order to solve the problem of fabrication, a MEMS accelerometer based on bulk SiC processing technology is designed, and fabricated. The sensor is fabricated using a 4H-SiC wafer and adopts the classic elastic beam-proof mass structure. The top surface of the wafer is a doped N-type SiC epitaxial layer that is used as piezoresistive material to develop sensitive resistance. Ultra-thin (20 μm) elastic beams obtained using dry etching form the sensitive mechanical structure to realize a high-sensitivity output in low/medium-g-value environments. The static flip and dynamic vibration experiments show that the final sensor can test low/medium-g-value acceleration signals precisely. Finally, the dynamic sensitivity obtained is 0.21 mV/g under 5 V input voltage and the linearity is 99.8%. This work has potential value for promoting the practical application of fabrication of bulk micromachined SiC in accelerometer, and the test data can provide guidance for future design of bulk SiC piezoresistive sensors.

Optimization of corner compensations in wet etching of silicon for a MEMS Z-axis accelerometer

Fabrication of planar MEMS accelerometers using micromachining and wet etching of surface structures on monocrystalline silicon wafer substrates poses several problems. One such problem is the preferential undercut of convex corners in the structure during chemical etch of silicon wafers. Resultant structures after etching are no longer the same as the design structure, leading to degradation in the performance of the device. The preferential undercut arises due to ‘wet anisotropic etching’ wherein the etchant has different etch rates along different crystal planes of the substrate. One of the methods to minimise this preferential undercut is to use compensation extension structures in the planar geometry of the device. In this paper, an accelerometer structure using a square extension has been studied in detail and the resulting dimensions are experimentally validated through fabrication and tests. Design steps and selection of optimal dimensions of the square compensation geometry are discussed considering etch depth with minimal undercut using KOH etching solution. Several samples of structures with three different dimensions of square extensions were fabricated and resultant device geometry was studied to establish the optimal extension dimensions with minimal undercut for the desired depth of etch.

Cold Starting Temperature Drift Modeling and Compensation of Micro-Accelerometer Based on High-Order Fourier Transform.

The traditional temperature modeling method is based on the full heating of the accelerometer to achieve thermal balance, which is not suitable for the cold start-up phase of the micro-accelerometer. For decreasing the complex temperature drift of the cold start-up phase, a new temperature compensation method based on a high-order Fourier transform combined model is proposed. The system structure and repeatability test of the micro digital quartz flexible accelerometer are provided at first. Additionally, we analyzed where the complex temperature drift of the cold start-up phase comes from based on the system structure and repeatability test. Secondly, a high-order temperature compensation model combined with K-means clustering and the symbiotic organisms search (SOS) algorithm is established with repeatability test data as training data. To verify the proposed temperature compensation model, a test platform was built to transmit the measured values before and after compensation with the proposed Fourier-related model and the other time-related model, which is also a model aiming at temperature compensation in the cold start-up phase. The experimental results indicate that the proposed method achieves better compensation accuracy compared with the traditional temperature compensation methods and the time-related compensation model. Furthermore, the compensation for the cold start-up phase has no effect on the original accuracy over the whole temperature range. The stability of the accelerometer can be significantly improved to about 30 μg in the start-up phase of different temperatures after compensation.

Analysis of the Scale Factor Nonlinearity of MEMS Differential Silicon Resonant Accelerometer Caused by the DETF’s Force-Frequency Nonlinear Characteristic

The scale factor nonlinearity of MEMS differential silicon resonant accelerometer(DSRA) structure is mainly due to the force-frequency nonlinear characteristic of DETF. This paper presents a detailed analysis of the relationship between the structural parameters, measurement range and the scale factor nonlinearity, which will provide a reference for the parameter design of DETF and overall structure. The inherent force-frequency nonlinearity of DETFs is analyzed, and the effects of structural parameters of DETF and axial force on nonlinearity of frequency variation are revealed. Combining the working principle of MEMS DSRA introduced first, the scale factor nonlinearity is studied. The results show that the structural parameters of the proof mass (determines the conversion between acceleration and inertial force), the support mechanism and the lever mechanism (determines the transfer coefficient of inertial force), and the DETF (determines the inherent force-frequency nonlinearity and affect the transfer coefficient of inertial force), as well as the measurement range, can all affect the scale factor nonlinearity. Moreover, the scale factor nonlinearity is directly proportional to the square of the measurement range and the square of the nominal scale factor, and inversely proportional to the square of the natural frequency of DETF. The finite element simulation is carried out, and the simulation results are in good agreement with the theoretical analysis values. Finally, the experiment on the scale factor nonlinearity of a prototype is carried out. The measured scale factor nonlinearity of the prototype is 1994.09ppm, which is consistent with the theoretical analysis value of 1737.30ppm.

Application of femtosecond laser etching in the fabrication of bulk SiC accelerometer

Silicon carbide (SiC) is a promising material to fabricate MEMS accelerometers used in extreme environments for vibration monitoring. However, with ultra-high hardness and corrosion resistance, it is difficult to etch bulk SiC by traditional MEMS processing methods. Here, we presented a bulk SiC accelerometer structure and its femtosecond laser deep etching method. Combined with the sensor design and femtosecond laser etching method, the sensitivity of the sensor could be improved and the processing difficulty could be reduced. The sensitive beams and mass block of the designed accelerometer were fabricated by femtosecond laser and high size accuracy with the maximum size error of about 3.1% was achieved. A fillet transition on the sensitive beam can eliminate crack propagation during laser etching and improve the quality of the etched gap. The cross-section of the etched sensitive beam can be regarded as an isosceles trapezoid with a steepness of 84.76°. The laser etching sidewall surface of the beam is smooth with a surface roughness (Sa) of 0.255 μm. The piezoresistors on the beam of the accelerometer remain stable before and after laser etching. Generally, the results show that femtosecond laser etching is a feasible method to fabricate bulk SiC accelerometers.

High-Stability Quartz Resonant Accelerometer With Micro-Leverages

This study proposes a highly stable differential resonant accelerometer that is monolithically micro-machined from a piece of ultrapure, single z-cut crystal quartz. The overall structure of quartz accelerometer is centrally symmetrical, which comprises two double-ended tuning forks (DETFs), two link beams, two micro-leverages, a proof mass, and a quartz frame. Micro-leverages and DETFs are perpendicular to each other and are located around the chip, which maximizes the utilization of the sensor area and is conducive to the miniaturization of the sensor. The effectiveness of the structure was verified by theoretical analysis, simulation, and experiment. The structure with differential arrangement can eliminate common mode disturbances, such as temperature, to improve sensitivity to acceleration. Within the measurement range of ±100 g, the sensor's sensitivity, which is measured by experiments, is 17.72 Hz/g, with a velocity random walk of 0.84 μg/√ Hz and bias instability of 3.05 μg, which is consistent with the theoretical analysis results. [2020-0309]

RETRACTED ARTICLE: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

In this paper, a three-axis capacitor accelerator has been analyzed, modeled and optimized using micro-electromechanical systems technology. In the proposed structure, acceleration measurements are carried out on all three axes simultaneously using a mass and spring system, which makes it possible to achieve a high sensitivity at a low occupancy level without losing other accelerator factors. In this structure, it is shown that each axis acceleration has a very low impact on the acceleration of the other two axes. If any external factor (e.g., electromagnetic waves) changes the value of a single capacitor, the original output of the capacitor does not change for detecting acceleration. In this paper, first the model is extracted for the proposed accelerometer structure and then to prove the validity of the model, the proposed structure is simulated using Intellisuite software. Moreover, a multi-objective genetic optimization algorithm which is made of NSGA2 and SPEA algorithms has been used to determine the dimensions of the constituents of the spring and the weight. This algorithm is implemented in MATLAB software. This study covers a dynamic range up to 1000 g and an operating frequency up to 20 kHz. The accelerometer sensitivity is 4fF/g in the z axis direction while it is 9fF/g in the x and y axes directions.

Electrical equivalent modeling of MEMS differential capacitive accelerometer

The paper presents an electrical equivalent model of Micro-Electro-Mechanical Systems (MEMS) differential capacitive accelerometer. The accelerometer structure is symmetrically suspended using folded beam springs. An electrical equivalent circuit is proposed for the mechanical structure using Force-Current analogy. Electrical circuit model of squeeze air film damping is also taken into account. The simulation results of temperature and pressure variations on the accelerometer for both mechanical and electrical domains are analyzed and compared using MATLAB®, and the results for both the domains are found to be closely matching. The results are compared with the analytical mechanical model of MEMS differential capacitive accelerometer recently reported by Mukhiya et al. (2019) [23]; and are found to be closely matching. The optimum pressure range for operation is found to be 200 ​Pa–300 ​Pa. Settling time is found to be less than 10 ​ms, which also verifies a bandwidth of 100 ​Hz. The proposed model has reasonably good accuracy and requires less computational time in comparison to FEM-based numerical models.