Capacitive Accelerometer Research Articles

An accurate Verilog-A based model for MEMS capacitive accelerometer

This paper presents an accurate macro model for a capacitive micro accelerometer using Verilog-A tool. For this purpose, first the accelerometer is simulated in COMSOL software. Then, considering the simplified physics of the accelerometer, a preliminary Verilog-A model is derived, which is not accurate enough. This initial model has been modified by using mathematical tools and adapting to the results of COMSOL. Furthermore, a switched-capacitor based capacitance to voltage converter (CVC) is used as a readout circuit to validate the proposed model. The CVC is designed, simulated and optimized in the Cadence software by using a 65 nm CMOS technology. In order to reduce low-frequency non-idealities such as flicker noise and DC offsets, a chopper-stabilization technique is used. The power consumption for a 1.2 V supply is 140 μW. Simulation results show a good agreement between COMSOL results and simulation of the proposed model in the Cadence.

An aerosol deposition based MEMS piezoelectric accelerometer for low noise measurement

Potentially applied in low-noise applications such as structural health monitoring (SHM), a 1-axis piezoelectric MEMS accelerometer based on aerosol deposition is designed, fabricated, simulated, and measured in this study. It is a cantilever beam structure with a tip proof mass and PZT sensing layer. To figure out whether the design is suitable for SHM, working bandwidth and noise level are obtained via simulation. For the first time, we use aerosol deposition method to deposit thick PZT film during the fabrication process to achieve high sensitivity. In performance measurement, we obtain the charge sensitivity, natural frequency, working bandwidth and noise equivalent acceleration of 22.74 pC/g, 867.4 Hz, 10–200 Hz (within ±5% deviation) and 5.6 mu {{{rm{g}}}}/sqrt{{{{rm{Hz}}}}} (at 20 Hz). To demonstrate its feasibility for real applications, vibrations of a fan are measured by our designed sensor and a commercial piezoelectric accelerometer, and the results match well with each other. Moreover, shaker vibration measurement with ADXL1001 indicates that the fabricated sensor has a much lower noise level. In the end, we show that our designed accelerometer has good performance compared to piezoelectric MEMS accelerometers in relevant studies and great potential for low-noise applications compared to low-noise capacitive MEMS accelerometers.

A High-Linearity Closed-Loop Capacitive Micro-Accelerometer Based on Ring-Diode Capacitance Detection.

This paper presents an implementation scheme and experimental evaluation of a high-linearity closed-loop capacitive accelerometer based on ring-diode capacitance detection. By deducing the capacitance detection model of the ring-diode considering the influence of the diode, the existing theoretical model error of the ring-diode is corrected and a closed-loop scheme of reusing the detection electrode and the control electrode of the MEMS die is designed to apply this detection scheme to the parallel-plate accelerometer, which only has three independent electrodes. After analyzing the non-linear problems in the existing closed-loop control schemes, a theoretically absolute linear closed-loop control scheme is proposed, and an integrated closed-loop accelerometer is realized by combining the closed-loop diode detection. The experimental results of the ring-diode detection model are in agreement with the theoretical formula. The non-linearity of the accelerometer within ±1 g after the closed-loop is 130 ppm, compared with 1500 ppm when the open-loop is used.

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

Design of MEMS capacitive comb accelerometer with perforated proof mass for seismic applications

Micro Electro Mechanical System (MEMS) sensors are characterized by their small size, but their performances exceed that of their macro-scale counterparts. The small size of MEMS devices and their integration with microelectronics proves a major advantage. In this paper, a design of MEMS capacitive comb accelerometer for seismology application using COMSOL Multiphysics platform is presented. A seismometer (also known as a seismograph) is a device that is used to measure and record the behavior of seismic waves. With this data, the location and measure of earthquakes can be detected. This seismic device has a large frequency band, compared to traditional geophones and seismographs. In this paper, a study to measure amplitudes and frequencies of vibrations is presented, and the results are analyzed and compared for perforated mass and solid proof mass. The effect of the size of etch hole for perforation is also studied.The displacement sensitivity and capacitive sensitivity of accelerometer are found to be 1.188 × 10-9m/g and 1.093 × 10-21F, respectively.

Long-Term Degradation Evaluation of the Mismatch of Sensitive Capacitance in MEMS Accelerometers.

During long-term use, MEMS accelerometers will experience degradation, such as bias and scale factor changes. Bias of MEMS capacitive accelerometers usually comes from the mismatch of parasitic capacitance and sensitive capacitance. This paper focuses on the mismatch of sensitive capacitance and analyzes the mechanism of long-term degradation of MEMS accelerometers. Firstly, the effect of sensitive capacitance mismatch on the performance of a MEMS accelerometer was investigated. Secondly, a method of measuring the mismatch of sensitive capacitance was proposed, and the validation experiment shows that the accuracy of this measurement can be less than 1.10×10-5 of the sensitive capacitance. For the samples in this experiment, the measurement error of this method can be less than 0.36 fF. Finally, a high-temperature acceleration experiment was performed. The mismatch of the sensitive capacitance during the experiment was monitored based on the proposed method, and the experimental results are analyzed. The experimental result demonstrates that the mismatch of sensitive capacitance varies linearly with time. The change rates of sensitive capacitance mismatch for the two samples are 2.95×10-7 C0/h and 2.66×10-7 C0/h in the high-temperature acceleration experiment at 145 °C, respectively. The change in sensitive capacitance mismatch seems small, but it is not to be ignored during long-term use. The rate of change is similar for the same batch of samples. This could imply that the adverse effects due to the mismatch of sensitive capacitance changes can be reduced by compensating for this variation.

Capacitive accelerometers at low frequency for infrastructure monitoring

In this paper, we would like to present a research activity with the purpose of a design carried out to develop a monitoring system capable of integrating a wired or wireless network of dynamic accelerometers. This activity involves the design of a new low-cost sensor capable of measuring three-axis dynamic acceleration from a sub Hz to a hundred Hz regime (0.01 to 100 Hz) and linking them multiple sensors in a network in order to get to monitor large infrastructures such as bridges, viaducts, and tunnels capable of measuring significant physical quantities of the structural response to the actions and environmental conditions of the infrastructure being monitored.

Simulation and analysis of suspension based single axis mems capacitive accelerometer

This paper reports a comparison of different types of springs used in MEMS based capacitive accelerometers. In this work MEMS based Single-axis accelerometers are designed using different Suspension systems. Analysis of the structure is done for resonant frequency of 2kHz. Analytical modeling of the different suspensions is presented for the specified frequency. Stress, displacement and capacitive analysis of the accelerometer is done. The sensitivity of the accelerometer with parallel beam suspension is 70nm/g, 50nm/g for folded beam suspension and 35nm/g for serpentine beam suspension. Hence parallel beam suspension has 0.7 times improved sensitivity than folded beam and 2 times better than serpentine suspension accelerometer. Whereas the stress obtained for folded beam is better than the other two. Hence Parallel beam suspension is preferred for higher sensitivity and accuracy whereas Folded beam suspension is preferred for greater structural stability By comparing these devices, it is concluded that a compromise on certain parameters is required in order meet the requirements. If there is higher displacement sensitivity then there is lower mechanical stability and vice versa. The simulations are carried out using COMSOL Multiphysics.

Studying the Functioning of the Sensitive Element of a Capacitive Accelerometer with a Sandwich Structure under the Conditions of Parasitic Effects along the Nonworking Axes and Random Vibration

Studying the Functioning of the Sensitive Element of a Capacitive Accelerometer with a Sandwich Structure under the Conditions of Parasitic Effects along the Nonworking Axes and Random Vibration

MEMS İvme Ölçerler için Analog Yapay Sinir Ağı Temelli Kontrolcü Tasarımı

Bu çalışmada tek eksenli kapasitif MEMS ivme ölçer için yeni bir analog yapay sinir ağı temelli bir kontrolcü önerilmektedir. Bu kontrolcü giriş katmanında bir, gizli katmanda altı ve çıkış katmanında iki nöron olacak şekilde tasarlanmıştır. Bu kontrolcü, AMI C5N 0,6 μm CMOS üretim teknolojisi kullanılarak Electric serim editörü ile tasarlanmıştır. Tasarlanan kontrolcünün başarısı çeşitli bilgisayar benzetimleriyle PID kontrolcüyle karşılaştırılmıştır. Benzetim sonuçları önerilen kontrolcünün tepki süresi, aşım ve ölçüm aralığı açısından PID kontrolcüden daha başarılı olduğunu göstermiştir.

Toward acceleration sensing based on topological gyroscopic metamaterials

In this paper, the equation of motion of graphenelike topological gyroscopic metamaterials under acceleration is derived, and the influence of the external acceleration on the band structure is investigated. The calculated results of band structure under acceleration of $1g$ are in good agreement with the experimental results reported in the literature and the numerical simulations show that the edge states are highly confined to the boundary, which is significantly different from the bulk states. Hence, an acceleration sensing method based on topological gyroscopic metamaterials is proposed by detecting the acceleration-induced bandwidth variation of the edge bands. Moreover, it is found that the proposed sensing approach shows extremely high sensitivity in a small acceleration range compared to the traditional capacitive accelerometers. And arising from its topological properties, the robustness of the proposed sensing method against local defects is numerically verified. Finally, some possible electronic methods are proposed to read the output signal of the sensing system.

Reset Noise Sampling Feedforward Technique (RNSF) for Low Noise MEMS Capacitive Accelerometer

The reset noise sampling feedforward (RNSF) technique is proposed in this paper to reduce the noise floor of the readout circuit for micro-electromechanically systems (MEMS) capacitive accelerometer. Because of the technology-imposed size restriction on the sensing element, the sensing capacitance and the capacitance variation are reduced to the femto-farad level. As a result, the reset noise from the parasitic capacitance, which is pico-farad level, becomes significant. In this work, the RNSF technique focuses on the suppression of the parasitic-capacitance-induced noise, thereby improving the noise performance of MEMS capacitive accelerometer. The simulation results show that the RNSF technique effectively suppresses the thermal noise from the parasitic capacitance. Compared with the traditional readout circuit, the noise floor of the readout circuit with the RNSF technique is reduced by 9 dBV. The presented circuit based on the RNSF technique is fabricated by a commercial 0.18-μm BCD process and tested with a femto-farad MEMS capacitive accelerometer. The physical measurement results show that, compared with the readout circuit without the RNSF technique, the RNSF technique reduces the noise floor of the readout circuit for MEMS capacitive accelerometer from −72 dBV to −80 dBV. Compared with other similar works, the proposed readout circuit achieves better FoM (FoM=(power×noise floor)/system bandwidth=490 μW·μg/Hz) among the switched-capacitor readout circuits.

Simplified Analytical Damping Constant Model for Design of MEMS Capacitive Accelerometer With Gold Perforated Proof-Mass Structure

This paper describes a simplified analytical model of a damping constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula> to design a MEMS capacitive accelerometer using the multi-layer metal technology. The proposed model is introduced by combining the theoretical equation with the approximate form factor obtained by the measured data. In order to create the model, we fabricated several types of MEMS capacitive accelerometers with different structure parameters such as the etching hole area, the perforated proof-mass area, and the gap. The calculation results show that by the proposed model, the damping constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula> was in accord with the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula> . We also confirmed that the relative error between the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula> and the damping constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula> by the proposed model could be improved to one-half of the conventional model. Moreover, the Brownian noise <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${B}_{\text {N}}$ </tex-math></inline-formula> calculated by the proposed model was also consistent with the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${B}_{\text {N}}$ </tex-math></inline-formula> . In addition, to confirm the suitability of the proposed model for CMOS-MEMS multi-physics simulation, we performed the simulation of the ring-down characteristics of a gold perforated proof-mass differential MEMS capacitive accelerometer. The simulated results suggested that the ring-down characteristics by the proposed model coincided with those of the measured data. Therefore, we verified that the proposed model would be effective for the analysis and the design of the MEMS capacitive accelerometer with the gold perforated proof-mass.

Study on the Dynamic Characteristics of a SiC-Based Capacitive Micro-Accelerometer in Rarefied Air.

In this study, we investigated the viscosity, squeeze-film damping, and a SiC-based capacitive micro-accelerometer in rarefied air. A specific expression for the effective viscosity coefficient of the air was derived, and when the air pressure drops from the standard atmospheric pressure, the viscosity of the air will decrease accordingly. Decreases in the air pressure and the viscosity of the air lead to the change in the squeeze-film air damping in the micro-accelerometer, and both the viscous damping force and the elastic damping force of the air film between the moving electrode plate and the fixed electrode plate will also decrease. The damping coefficient and relative damping ratio of the micro-accelerometer in rarefied air were calculated, which was also confirmed by simulations. The changes of the damping coefficient and the relative damping ratio of the system will directly affect the dynamic characteristics of the micro-accelerometer. When the air pressure in the working environment is below the standard atmospheric pressure, the micro-accelerometer will be in an underdamping state. With the decrease in the air pressure, the working bandwidth of the micro-accelerometer will decrease significantly, and the resonant phenomenon may appear. However, the decrease in the air pressure will not have a notable impact on the response time of the micro-accelerometer. Therefore, this work provides a theoretical basis for the study of the performance characteristics of a SiC-based capacitive accelerometer in rarefied air.

Characterization of Distant and Moderate Earthquakes with Inexpensive MEMS Sensors: Application to the Mw 6.3, 29th December 2020, Petrinja Event.

In this work, we evaluate the suitability of a new MEMS sensor prototype, called ASX1000 (ADEL s.r.l., Modena, Italy), for the monitoring of distant and moderate seismic events. This device is an inexpensive capacitive accelerometer with a relatively low level of instrumental noise; it can record both local and far seismic events. An experimental network built with ASX1000 MEMS, located in northern Italy, was able to record the Mw 6.3 Petrinja earthquake that occurred in December 2020; it had an epicentral distance of more than 350 km. We retrieved the strong motion parameters (PGA, pseudo-absolute velocity, and pseudo-absolute spectral acceleration) from the acceleration time histories recorded by the MEMS sensors. The obtained parameters were compared with the ones obtained by the closer high-quality seismometers, belonging to the INGV National Seismic Network. The comparison to the highest-quality sensors confirms a reasonable agreement of the inferred parameters. This work suggests that—in the near future—MEMS sensors could be adopted to integrate the existing seismic network. A denser coverage of sensors can sample more accurately the seismic wavefield, taking into account the large spatial variability of local geology and the relative differences in seismic response.

Very low frequency IEPE accelerometer calibration and application to a wind energy structure

Abstract. In this work, we present an experimental setup for very low frequency calibration measurements of low-noise integrated electronics piezoelectric (IEPE) accelerometers and a customised signal conditioner design for using IEPE sensors down to 0.05 Hz. AC-response IEPE accelerometers and signal conditioners have amplitude and phase deviations at low frequencies. As the standard calibration procedure in the low-frequency range is technically challenging, IEPE accelerometers with standard signal conditioners are usually used in frequency ranges above 1 Hz. Vibrations on structures with low eigenfrequencies like wind turbines are thus often monitored using DC-coupled micro-electro-mechanical system (MEMS) capacitive accelerometers. This sensor type suffers from higher noise levels compared to IEPE sensors. To apply IEPE sensors instead of MEMS sensors, in this work the calibration of the entire measurement chain of three different IEPE sensors with the customised signal conditioner is performed with a low-frequency centrifuge. The IEPE sensors are modelled using infinite impulse response (IIR) filters to apply the calibration to time-domain measurement data of a wind turbine support structure. This procedure enables an amplitude and phase-accurate vibration analysis with IEPE sensors in the low-frequency range down to 0.05 Hz.

A Novel Route to Optimize Placement Equipment Kinematics by Coupling Capacitive Accelerometers.

Machine end-effector kinematic analysis is critical to optimizing transporting components where inertial forces are the main loads. While displacements may be measured with relatively high accuracy in transportation equipment motors, the inertial forces in the transported components are seldom optimized. This is especially relevant in electronic component placement systems, where the components have a wide range of configurations (i.e., geometry and mass) and the deployment dimensional/geometric tolerances are remarkably good. The optimization of these systems requires the monitoring of the real position of the accelerometers relative to the measurement point of interest with sufficient accuracy that allows the assembly position to be predicted instantaneously. This study shows a novel method to calibrate this equipment using triaxial accelerometers on a surface mount machine to measure the end-effector accelerations and velocities in its planar motion. The dynamic equations of the system and the method for integration are presented to address the uncertainty on the exact position of the accelerometer sensors relative to the measuring point of interest exist and allow the position correction to optimize response and accuracy.

A high precision time-multiplexed fully differential interface ASIC for capacitive MEMS accelerometer

A high precision time-multiplexed fully differential interface Application specific integrated circuit (ASIC) for micromechanical capacitive accelerometer is presented in this paper. A time-multiplexed fully differential capacitor-to-voltage (C-V) converter employs the half-bridge sensing structure and two paralleled single-end charge integrators to substitute the full-bridge or fully differential sensing element and restrain the influence of the common-mode voltage. A time-multiplexed fully differential switch-capacitor (SC) programmable gain amplifier (PGA) with continuous output is proposed, providing continuous signals to the following circuits. The proposed interface is fabricated in a 0.18 [Formula: see text]m CMOS process, occupying an area of [Formula: see text]. The measured results indicate that the total power dissipation is 8.25 mW from a 3.3 V power supply. The noise floor of the accelerometer is 10.5 [Formula: see text]g/Hz1/2, and the achieved figure of merit (FOM, 5.5 pW/Hz) is better than the previously reported works.

High Sensitivity MEMS Accelerometer Using PZT-Based Four L-Shaped Beam Structure

Piezoelectric accelerometers present higher sensitivities and better signal-to-noise ratios in comparison with piezoresistive and capacitive accelerometers. A micro-electromechanical system (MEMS) piezoelectric accelerometer was designed and manufactured with four L-shaped beams covered by Lead Zirconate Titanate (PZT) thin film with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{m}$ </tex-math></inline-formula> in thickness which was deposited using sol-gel methods. The micro devices, whose size and the optimized PZT distribution were determined by theoretical and simulation analysis, were fabricated on the silicon substrate using PZT films working in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${d}_{31}$ </tex-math></inline-formula> mode. Different from the conventional vertical crossbeam accelerometers, the designed structure devotes to the larger area piezoelectric film laid on L-shaped supporting beams with higher energy transferring efficiency for sensing. Then the chips of accelerometer were fabricated, and the proposed sensor was packaged on the printed circuit board (PCB). In addition, the microsphere was integrated in the center of the beams. Finally, the properties of the accelerometer were measured by vibration measurement system. The measuring results show that the initial sensitivity of the accelerometer is 28.14mV/g at 500Hz. The proposed piezoelectric accelerometer has high sensitivity and low resonance frequency, and the frequency response on each beam is consistent, providing a new structure for high-performance accelerometer.

Self-Calibration Technique with Lightweight Algorithm for Thermal Drift Compensation in MEMS Accelerometers.

Capacitive MEMS accelerometers have a high thermal sensitivity that drifts the output when subjected to changes in temperature. To improve their performance in applications with thermal variations, it is necessary to compensate for these effects. These drifts can be compensated using a lightweight algorithm by knowing the characteristic thermal parameters of the accelerometer (Temperature Drift of Bias and Temperature Drift of Scale Factor). These parameters vary in each accelerometer and axis, making an individual calibration necessary. In this work, a simple and fast calibration method that allows the characteristic parameters of the three axes to be obtained simultaneously through a single test is proposed. This method is based on the study of two specific orientations, each at two temperatures. By means of the suitable selection of the orientations and the temperature points, the data obtained can be extrapolated to the entire working range of the accelerometer. Only a mechanical anchor and a heat source are required to perform the calibration. This technique can be scaled to calibrate multiple accelerometers simultaneously. A lightweight algorithm is used to analyze the test data and obtain the compensation parameters. This algorithm stores only the most relevant data, reducing memory and computing power requirements. This allows it to be run in real time on a low-cost microcontroller during testing to obtain compensation parameters immediately. This method is aimed at mass factory calibration, where individual calibration with traditional methods may not be an adequate option. The proposed method has been compared with a traditional calibration using a six tests in orthogonal directions and a thermal chamber with a relative error difference of 0.3%.