Noise Equivalent Acceleration Research Articles

Monolithic integrated cavity optomechanical accelerometer based on push-pull photonic crystal zipper cavity

We propose a monolithic integrated cavity optomechanical accelerometer based on push-pull photonic crystal zipper cavity. The accelerometer integrates grating couplers, phase modulators, acceleration sensing unit, and electrostatic force feedback module on a chip. We use push-pull structure to eliminate the coupling crosstalk caused by paraxial acceleration and extend its range using electrostatic force feedback module. The transmissive photonic crystal zipper cavity structure is adopted to improve the integration and stability of the system. Accurate results are demonstrated as follows: the bandwidth is larger than 20 kHz, the mechanical sensitivity is 369 pm/g, the measuring range is ±100 g, and the noise equivalent acceleration is 5.06 μg / Hz. With its advantages, the accelerometer can be used in consumer electronics, aerospace, resource exploration, and other fields.

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 Systematic Design Optimization Approach for Multiphysics MEMS Devices Based on Combined Computer Experiments and Gaussian Process Modelling.

This paper presents a systematic and efficient design approach for the two degree-of-freedom (2-DoF) capacitive microelectromechanical systems (MEMS) accelerometer by using combined design and analysis of computer experiments (DACE) and Gaussian process (GP) modelling. Multiple output responses of the MEMS accelerometer including natural frequency, proof mass displacement, pull-in voltage, capacitance change, and Brownian noise equivalent acceleration (BNEA) are optimized simultaneously with respect to the geometric design parameters, environmental conditions, and microfabrication process constraints. The sampling design space is created using DACE based Latin hypercube sampling (LHS) technique and corresponding output responses are obtained using multiphysics coupled field electro–thermal–structural interaction based finite element method (FEM) simulations. The metamodels for the individual output responses are obtained using statistical GP analysis. The developed metamodels not only allowed to analyze the effect of individual design parameters on an output response, but to also study the interaction of the design parameters. An objective function, considering the performance requirements of the MEMS accelerometer, is defined and simultaneous multi-objective optimization of the output responses, with respect to the design parameters, is carried out by using a combined gradient descent algorithm and desirability function approach. The accuracy of the optimization prediction is validated using FEM simulations. The behavioral model of the final optimized MEMS accelerometer design is integrated with the readout electronics in the simulation environment and voltage sensitivity is obtained. The results show that the combined DACE and GP based design methodology can be an efficient technique for the design space exploration and optimization of multiphysics MEMS devices at the design phase of their development cycle.

Multi-Function Microelectromechanical Systems Implementation with an ASIC Compatible CMOS 0.18 μm Process.

A multi-function microelectromechanical system (MEMS) with a three-axis magnetometer (MAG) and three-axis accelerometer (ACC) function was implemented with an application-specific integrated circuit (ASIC)-compatible complementary metal-oxide-semiconductor (CMOS) 0.18 μm process. The readout circuit used the nested chopper, correlated double-sampling (CDS), noise reduction method; the frequency division multiplexing method; the time-division multiplexing method; and the calibration method. Sensing was performed by exciting the MEMS three-axis magnetometer at X/Y/Z axes mechanical resonant frequencies of 3.77/7.05/7.47 kHz, respectively. A modest die-level vacuum packaging resulted in in-plane and out-of-plane mechanical quality factors of 471–500 and 971–1000, respectively. The sensitivities of both the three-axis magnetometer with 2 mA driving current and the three-axis accelerometer were 7.1–10.7 uV/uT and 58.37–88.87 uV/ug. The resolutions of both the three-axis magnetometer with 2 mA driving current and three-axis accelerometer resolution were 44.06–87.46 nT/√Hz and 5.043–7.5 ng/√Hz. The resolution was limited by circuit noise equivalent acceleration (CNEM) and Brownian noise equivalent magnetic field (BNEM).

Downhole Microseismic Monitoring Using Time-Division Multiplexed Fiber-Optic Accelerometer Array

Microseismic monitoring is of importance for several geoscience research aspects and for applications in oil and gas industry. For signals generated by the ultra-weak microseismic events, conventional moving-coil geophone systems have reached their limit in detection sensitivity especially at high frequency range. Here we for the first time present a specially tailored fiber-optic sensing system targeting at downhole microseismic monitoring. The system contains 30 individual interferometric accelerometers and 2 reference sensors, which are time-division multiplexed into a 12-level vector seismic sensor array. The multiplexed accelerometers can achieve ~50 ng/ $\sqrt {\mathrm{Hz}} $ noise equivalent acceleration, which is superior to the commercial available moving-coil geophone systems at frequencies above 200 Hz. The measured sensitivity of the accelerometers can reach ~200 rad/g from 10 Hz to 1 kHz. The dynamic range is above 134 dB over the same frequency range and is higher than its electronic counterpart in the low frequency band. Moreover, the sensors can function properly under the harsh condition of 120 °C temperature and 40 MPa pressure over the 4-hour test duration. The sensor array along with the interrogator has been running uninterruptedly over 3 weeks in a multi-stage hydraulic fracturing stimulation field test. On-site results show that our system can clearly resolve the vector nature of both compressional and shear waves generated by the microseismic events.

DBR Fiber Laser Based High-Resolution Accelerometer Network

In this paper, we report a high-resolution and precision acceleration sensor network with potential large sensing capacity, which is based on distributed Bragg reflector fiber lasers. To start with, a transducer based on a T-shaped cantilever beam and an adjustable bearing is theoretically designed and experimentally employed to achieve high sensitivity and wideband frequency response. Second, the beat frequency interrogation system that utilizes super-heterodyne receiver and digital orthogonal phase identifying technology is developed to improve the resolution of the sensors. In addition, assisted with the wavelength/time division multiplexing technology, hundreds of sensing units could be potentially multiplexed in the prototype system. A proof-of-concept sensing network with three acceleration sensor units is established for experimental validation. The sensor network demonstrates a sensitivity of 1.16064 GHz/g with a flat frequency response region from 20 to 200 Hz, corresponding to a noise equivalent acceleration of 17.99 ng/√Hz at 90 Hz. In particular, the measurement precision of the prototype system has been calibrated as high as 1.305 μg. The proposed acceleration sensor network could benefit potential applications in smart unmanned platforms and seismic monitoring.

A 10 mW, 0.4 $\mu \text{g}/\surd $ Hz, 700 Hz $\Sigma \Delta $ High-Order Electromechanical Modulator for a High-Q Micromechanical Capacitive Accelerometer

A switched-capacitor sigma–delta ( $\Sigma \Delta $ ) CMOS interface circuit for the closed-loop operation of a micromechanical capacitive accelerometer is presented in this paper. A distributed-feedback and feedforward topology is proposed to combine with a high-Q sensor element to obtain a sub- $\mu \text{g}/\surd $ Hz noise floor. The loop stability is implemented by damping the high-Q sensor element in the operation of electrostatic feedback force and heavy phase compensation, which introduces an extra zero to compensate the loop. Besides, the low-frequency loop gain is controlled by off-chip adjusting of distributed-feedback factor to keep the balance between the loop stability and noise shaping ability. The interface circuit is designed and fabricated in a standard 0.5- $\mu \text{m}$ CMOS process. The chip consumes 10 mW from a single 5-V supply. The measurement results show that the noise level is lower than 400 ng/ $\surd $ Hz, and the average noise equivalent acceleration density is 200 ng/ $\surd $ Hz over a 700-Hz bandwidth. The input range of the accelerometer is ±0.7 g resulting in a dynamic range of 125 dB over 1-Hz bandwidth. The measured sensitivity of 2.5 V/g is shown with a dc nonlinearity of 0.17%, and the bias instability is $19~\mu \text{g}$ .

A 4 mm² Double Differential Torsional MEMS Accelerometer Based on a Double-Beam Configuration.

This paper reports the design and simulation of a 4 mm2 double differential torsional MEMS accelerometer based on a double-beam configuration. Based on the structure of conventional torsional accelerometers, normally composed of one pair of proof masses and one torsional beam, this work explores the double differential configuration: a torsional accelerometer with two pairs of unbalanced proof masses rotating in reverse. Also, the torsional beam is designed as a double-beam structure, which is a symmetrical structure formed by two torsional beams separated by a certain distance. The device area of the novel accelerometer is more than 50 times smaller than that of a traditional double differential torsional MEMS accelerometer. The FEM simulation results demonstrate that the smaller device does not sacrifice other specifications, such as mechanical sensitivity, nonlinearity and temperature robustness. The mechanical sensitivity and nonlinearity of a ±15 g measuring range is 59.4 fF/g and 0.88%, respectively. Compared with traditional single-beam silicon structures, the novel structure can achieve lower maximum principle stress in critical regions and reduce the possibility of failure when high-g acceleration loading is applied along all three axes. The mechanical noise equivalent acceleration is about in the theoretical calculations and the offset temperature coefficient is 0.25 mg/ in the full temperature range of to .

Design, simulation and fabrication of a MEMS accelerometer by using sequential and pulsed-mode DRIE processes

A sensitive half-bridge MEMS accelerometer fabricated by sequential and pulsed-mode processes is presented in this paper. The proposed accelerometer is analyzed by using conventional equations and the finite element method. The micromachining technology used in this work relies on two processes: sequential and pulsed-mode. In the sequential deep reactive ion etching process, a mixture of hydrogen and oxygen with a trace value of SF6 is used instead of polymeric material in the passivation step. The pulsed-mode process employs periodic hydrogen pulses in continuous fluorine plasma. Because of the continuous nature of this process, plus the in situ passivation caused by the hydrogen pulses, scallop-free sidewalls are achieved and the etch rate is also relatively high.Furthermore, the functional characteristics of the fabricated accelerometer sensor are measured and reported. Measurement results, which are in good agreement with simulations, show that the functional characteristics of the fabricated sensor are as follows: resonance frequency of about 2 kHz, sensitivity of 76 mV g−1 and Brownian noise equivalent acceleration of g .

Low-frequency vibration sensors based on a cascaded gapped cantilever

This paper reports the development of low-cost high-performance vibration sensors based on a cascaded asymmetric-gapped cantilever for low-frequency sensing. The cascaded structure is implemented to reduce the spring constant for a high sensitivity and simultaneously avoid the undesirable shear bending. A prototype with a proof mass of 40 g and an overall size of 124 mm × 39 mm × 5.1 mm (l × w × t) has been successfully constructed. The sensor body was made of aluminum and two lead zirconate titanate sheets were implemented as the sensing element. Based on a coherence method, a noise equivalent acceleration close to the theoretical value has been achieved at 35 Hz (~3 ng/√Hz). Finally, the prototype has been successfully demonstrated for ballistocardiogaph monitoring for both sitting and lying positions.

Noise behaviors of a closed-loop micro-electromechanical system capacitive accelerometer

The noise of closed loop micro-electromechanical systems (MEMS) capacitive accelerometer is treated as one of the significant performance specifications. Traditional optimization of noise performance often focuses on designing large capacitive sensitivity accelerometer and applying closed loop structure to shape total noise, but different noise sources in closed loop and their behaviors at low frequencies are seldom carefully studied, especially their behaviors with different electronic parameters. In this work, a thorough noise analysis is established focusing on the four noise sources transfer functions near 0 Hz with simplified electronic parameters in closed loop, and it is found that the total electronic noise equivalent acceleration varies differently at different frequency points, such that the noise spectrum shape at low frequencies can be altered from 1/f noise-like shape to flat spectrum shape. The bias instability changes as a consequence. With appropriate parameters settings, the 670 Hz resonant frequency accelerometer can reach resolution of \(2.6 \mu g/\sqrt {Hz}\) at 2 Hz and 6 μg bias instability, and 1300 Hz accelerometer can achieve \(5 \mu g/\sqrt {Hz}\) at 2 Hz and 31 μg bias instability. Both accelerometers have flat spectrum profile from 2 Hz to 15 Hz.

High-Performance Closed-Loop Interface Circuit for High-Q Capacitive Microaccelerometers

High-Q sensory microsystems are desirable especially in low noise applications. However this makes implementation of the closed-loop control a great challenge. An in-depth investigation into high-performance closed-loop interface circuit design for high-Q capacitive microaccelerometers is presented. Focus is placed on an analogue force feedback scheme with proportional-derivative compensation. Such an approach is differing from the commonly used electromechanical Δ Σ technique, since the latter one often suffers severe problems in balancing between the loop stability and other essential characteristics in the presence of high-Q sensing element. A comprehensive analysis concerning the system linearity and bandwidth is conducted, aiming for performance optimization. The adverse impact arising from several electronic noise sources in the system is studied in order for minimization. Accordingly, a prototype interface circuit is designed and fabricated in a commercial 0.35-μm CMOS process. The chip measures 2.5×2.5 mm2 and operates from a single 5 V supply. The quiescent current is about 10 mA. The test results show that it offers a full scale acceleration of ±1.2 g correspondingly with integrated non-linearity (INL) of 6.6%, wide-band noise equivalent acceleration of nearly 1 μg/√Hz over a signal bandwidth of about 1.2 kHz.

Design and simulation of a high-performance Z-axis SOI-MEMS accelerometer

This paper presents a new micromachined z-axis accelerometer as well as a new method to sense the out-of-plane displacement capacitively via comb finger arrays. The new design built the z-accelerometer using eight folded beam suspension to minimize the off axis sensitivities in both the x- and y- directions. The proposed method implements the sensing electrode as a comb finger arrays surrounding the sensor. This method enables the realization of the sensor by bulk micromachining process, increases the sense capacitance and reduces the off-axis sensitivity. This process allows building the micromachined accelerometer with large inertial mass. This work introduces the design and simulation for this accelerometer. The introduced method results in a high sense capacitance as well as high sensitivity. The simulated sense capacitance is 19.6627 pF. The sensor sensitivity is 2.037 μm/g with a very small total noise equivalent acceleration of 3.096 μg/$$ \sqrt {Hz} $$.

Coupled effects of gold electroplating and electrochemical discharge machining processes on the performance improvement of a capacitive accelerometer

Coupled effects of an electroplated gold layer and damper holes drilled by Electro Chemical Discharge Machining (ECDM) process on the performance improvement of a quad beam capacitive accelerometer is presented in this paper. A simple quad beam-proof mass configuration with its beams located symmetrically at the centre of all the edges of the proof mass and connected to an outer supporting frame is considered in the present study. For a fixed damping ratio, prime-axis sensitivity of the sensor is increased by the damper holes whereas an electroplated gold layer improves the prime-axis sensitivity, cross-axis sensitivity, and Brownian Noise Equivalent Acceleration (BNEA). Moreover, the increased weight of the proof mass due to an electroplated gold layer further reduces the damping of the device which in turn helps to increase the prime-axis sensitivity more. A new figure of merit called Performance Factor (PF), defined as the ratio of the product of the prime-axis sensitivity and resonant frequency to the cross-axis sensitivity at a fixed damping ratio of 0.7 is used as a quantitative index to evaluate the performance improvement caused by the coupled effects of gold electroplating and ECDM processes. Simulation results show that for a device with damper holes of 8 μm diameter and electroplated gold layer of dimensions 3,000 μm × 3,000 μm × 20 μm, the prime-axis sensitivity is increased by more than 500 times, rotational cross-axis sensitivity and BNEA are reduced by around 10 and 30%, respectively and the PF is improved by around 482 times at a fixed damping ratio of 0.7.

Continuous-time interface for a micromachined capacitive accelerometer with NEA of 4 [formula omitted]g and bandwidth of 300 Hz

A continuous-time accelerometer interface is feasible when a high dynamic range together with a wide signal band is required. In this paper the implementation of a continuous-time force-feedback loop for a capacitive sensor element with a full-scale signal of ± 1.5 g is presented. The interface is measured to attain a noise equivalent acceleration (NEA) density of 500 ng / Hz at 30 Hz for the on-chip digitized output and 300 ng / Hz at 30 Hz for the analog output using a capacitive half-bridge sensor element with a single pair of electrodes. The essential circuit structures of the closed-loop sensor will be presented and analyzed in detail.

Novel two-dimensional micromachined accelerometer based on thermocapillary heat transfer

We report a novel prototype of a two-dimensional micromachined accelerometer based on thermocapillary heat transfer. The only moving element in this accelerometer is a thermal bubble generated by vaporizing the working liquid in the microchamber. The accelerometer consists of two key components, a heating resistor for creating symmetrical temperature profiles and two pairs of temperature detectors placed symmetrically and orthogonally to each other. The prototype devices demonstrate that a sensitivity of 1.5°C/g for an operating power of 60 mW can be realized. The frequency response of the accelerometer containing deionized water is 200 Hz, and the corresponding noise equivalent acceleration is ~1 mg/Hz1/2.

HDL modeling of convective accelerometers for system design and optimization

This study concerns the integration of convective accelerometers on CMOS. The design approach is based on an HDL modeling of the sensing cell. The development of a monolithic system is then undertaken, using multi-domain simulations, within the microelectronics design environment. For illustration, the sensor equivalent input noise (i.e. the resolution) is computed for various readout circuitry configurations: a simple instrumentation amplifier, a customized low-noise amplifier and a chopper-stabilized amplifier with a track-and-hold signal demodulator. Finally, a noise equivalent acceleration below 1 mg/√Hz has been reached, which is interesting for applications in consumer electronics.

Wafer-level hermetic packaged microaccelerometer with fully differential BiCMOS interface circuit

This paper presents a microaccelerometer with wafer-level packaged MEMS sensing element with fully differential, continuous-time BiCMOS interface circuit. The MEMS sensing element is fabricated on a (1 1 1)-oriented SOI wafer by using the sacrificial bulk micromachining (SBM) process. To protect the silicon structure of the sensing element and to enhance the reliability, a wafer level hermetic packaging process is achieved, using silicon–glass anodic bonding. The fabricated sensing element gives the improved noise performance and low bias instability by the inherent high-aspect-ratio, large sacrificial gap and footing-free advantages of the SBM process. The interface circuit is fabricated using a 0.8 μm Polarfab BiCMOS process. The continuous-time, fully-differential transconductance input amplifier and the chopper-stabilization architecture is adopted to reduce low-frequency noise. The fabricated microaccelerometer has a total noise equivalent acceleration of 0.23 μg/(Hz) 1/2, bias instability of 490 μg, input range of ±10 g, and output non-linearity of ±0.5% FSO.

Two-dimensional optical accelerometer based on commercial DVD pick-up head

This study develops a low-cost, highly sensitive two-dimensional optical accelerometer based on a commercially available DVD optical pick-up head. Vibrations of the structure of interest cause a change in the angle of the seismic mass within the accelerometer. The relative movement between the seismic mass and the base produces a change in the distribution of a focused light spot on the surface of a four-quadrant photodetector. The resulting change in the output of the voltage signals by the photodetector is then used to calculate the corresponding acceleration of the base. The experimental results indicate that the resonant frequencies of the accelerometer in the X- and Y-axis directions are 92.75 Hz and 92.87 Hz, respectively. Furthermore, the useful frequency range of the accelerometer is found to be approximately 20% of its resonant frequency. The sensitivities of the accelerometer in the X- and Y-axis directions are 22.9 V/g and 21.3 V/g, respectively. Finally, the noise equivalent acceleration (NEA) of the accelerometer is found to be less than 30 µg Hz−1/2 over the frequency range 0.5–50 Hz.

High Performance Microaccelerometer with Wafer-level Hermetic Packaged Sensing Element and Continuous-time BiCMOS Interface Circuit

A microaccelerometer with highly reliable, wafer-level packaged MEMS sensing element and fully differential, continuous time, low noise, BiCMOS interface circuit is fabricated. The MEMS sensing element is fabricated on a (111)-oriented SOI wafer by using the SBM (Sacrificial/Bulk Micromachining) process. To protect the silicon structure of the sensing element and enhance the reliability, a wafer level hermetic packaging process is performed by using a silicon-glass anodic bonding process. The interface circuit is fabricated using 0.8 µm BiCMOS process. The capacitance change of the MEMS sensing element is amplified by the continuous-time, fully-differential transconductance input amplifier. A chopper-stabilization architecture is adopted to reduce low-frequency noise including 1/f noise. The fabricated microaccelerometer has the total noise equivalent acceleration of 0.89 µg/√Hz, the bias instability of 490 µg, the input range of ±10 g, and the output nonlinearity of ±0.5 %FSO.