Performance Of Accelerometer Research Articles

Effect of Electroplated Gold Film on the Performance of a Piezoresistive Accelerometer with Stress Concentrated Tiny Beams

Background/Objective: In the recent times, piezoresistive accelerometers have been extensively explored with the primary focus on the optimization of its sensitivity and measurement bandwidth. In this paper, the design of an in-plane deflection mode accelerometer sensor has been devised with selective deposition of gold metal on the top and both the sides of the proof mass. Methods/Statistical Analysis: The micromachined silicon accelerometer constitutes of stress concentrated tiny piezoresistor beams and a central cantilever beam to support the proof mass. In order to improve the electromechanical response of the sensor, selective deposition of the gold metal layer was performed on the top and both the sides of the proof mass. The design and modeling of the sensor has been performed utilizing a Finite Element Model (FEM) software simulation tool IntelliSuite®. Findings: Compared to the conventional designs reported in the literature, accelerometer sensors with stress concentrated tiny beams and gold layer selectively deposited on the proof mass have shown an improvement in the electrical sensitivity and the FOM (product of the sensitivity and square of the resonant frequency). Simulation results demonstrate that the accelerometer structure with gold layer atop of the proof mass has a better sensitivity and FOM than the conventional design without gold by 28.26% and 27.43% respectively. Similarly, the accelerometer structure with gold on both sides of the proof mass has shown an improvement in the sensitivity by 57.82% and the Figure Of Merit (FOM) by 29.70% compared to the structure without gold layer. Conclusion/Improvements: It has been demonstrated that the performance metrics of piezoresistive accelerometer sensors with stress concentrated tiny beams can further be improved by selective deposition of metal gold layer on the proof mass of the accelerometer structure.

Pulse detection with a single accelerometer placed at the carotid artery: Performance in a real-life diagnostic test during acute hypotension.

Pulse detection via palpation is a basic and essential procedure in daily medical practice. We have been investigating the performance of a single accelerometer placed above the carotid artery, which is one of the recommended locations for manual palpation. A low-cost sensor attached by an adhesive measures accelerations due to carotid dilatations and whole body vibrations. A real-time demonstrator has been developed to classify 10 second- windows in "Pulse", "Motion" and "No Pulse" and to infer pulse rate. Data were obtained during a scheduled head-up tilt table test (HUTT). Our results show for a subgroup of 10 patients with acute hypotension a wide spread of "good" signal coverage ranging from as low as 37% up to 100%. Key factors compromising the performance in HUTT are motion artifacts, arrhythmias, sensor placement and sensor-skin coupling. In conclusion, pulse detection with a single accelerometer is sufficiently accurate, if good signal coverage can be achieved.

Cantilever Fiber-Optic Accelerometer Based on Modal Interferometer

A cantilever fiber-optic accelerometer using modal interferometer, with a large fringe visibility of up to 30 dB, is proposed and demonstrated. In the system, an electrical testing replaces optical-spectrum detection to achieve fast acceleration measurement of the cantilever fiber-optic accelerometer, and the performance of the cantilever fiber-optic accelerometer is studied experimentally. Experimental results show that the minimum detectable acceleration is 1.36 mg, and the resonance frequency is 520 Hz. Meanwhile, the angular dependence of the fiber accelerometer is also analyzed in the article and the result shows that the output intensity difference is up to 18 dB for different angles. This fiber-optic accelerometer can be used to detect underwater acoustic and seismic wave.

Performance enhancement for piezoresistive microaccelerometer by geometrical design: a focused review

Purpose – This paper aims to provide a focused review on the geometrical designs for performance enhancement of piezoresistive microaccelerometers. Design/methodology/approach – By analyzing working principle and conventional geometries, the improved research proposals are sorted into three groups in terms of their anticipated objectives, including sensitivity, resonant frequency and cross-axis sensitivity. Accessible methods are outlined and their merits and demerits are described. Findings – Novel geometries obviously enhance the performance of accelerometers, and the efficacy can be further elevated by newer materials and fabrication processes. Research limitations/implications – This paper mainly focused on the improved geometrical designs for sensitivity, resonant frequency and cross-axis sensitivity. Other performance parameters or design schemes are not included in this paper. Originality/value – This paper generalizes the available geometries and methods for the enhancement of sensitivity, resonant frequency and cross-axis sensitivity in piezoresistive accelerometers design.

Accelerometer adherence and performance in a cohort study of US Hispanic adults.

This study described participant adherence to wearing the accelerometer and accelerometer performance in a cohort study of adults. From 2008 to 2011, 16,415 US Hispanic/Latino adults age 18-74 yr enrolled in the Hispanic Community Health Study/Study of Latinos. Immediately after the baseline visit, participants wore an Actical accelerometer for 1 wk. This study explored correlates of accelerometer participation and adherence, defined as wearing it for at least three of a possible six days for ≥10 h·d. Accelerometer performance was assessed by exploring the number of different values of accelerometer counts per minute for each participant. Overall, 92.3% (n = 15,153) had at least 1 d with accelerometer data and 77.7% (n = 12,750) were adherent. Both accelerometer participation and adherence were higher among participants who were married or partnered, reported a higher household income, were first-generation immigrants, or reported lower sitting time. Participation was also higher among those with no stair limitations. Adherence was higher among participants who were male, older, employed or retired, not US born, preferred Spanish over English, reported higher work activity or lower recreational activity, and with a lower body mass index. Among the sample that met the adherence definition, the maximum recorded count per minute was 12,000, and there were a total of 5846 different counts per minute. On average, participants had 112.5 different counts per minute over 6 d (median, 106; interquartile range, 91-122). The number of different counts per minute was higher among men, younger ages, normal weight, and those with higher accelerometer-assessed physical activity. Several correlates differed between accelerometer participation and adherence. These characteristics could be targeted in future studies to improve accelerometer wear. The performance of the accelerometer provided insight into creating a more accurate nonwear algorithm.

Study of self-calibrating MEMS accelerometers

Micro-electromechanical System(MEMS) accelerometers are widely used in a number of inertial navigation systems and vibration detection system thanks to their small size, low cost and low power consumption. In order to improve their performance, the accelerometers have been designed to compensate the zero-bias caused by process variations. A new method of self-calibration sensitivity applies a self-test structure to simulate standard acceleration; depending on the standard and real-time values of the accelerometer’s output and by adjustment of the time division feedback, the scale factor of capacitive accelerometers can be flexibly adjusted to achieve sensitivity in self-calibrating MEMS accelerometers. Moreover, this research also uses the following: a PID feedback structure to improve the stability of the closed-loop system; a correlated double sampling (CDS) circuit to attenuate noise, which can eliminate zero drift caused by offset voltage of the pre-amplifier; a time division multiplexing electrostatic force feedback circuit to achieve the operation of a closed-loop micro-accelerometer. The structure can completely avoid electrostatic feedback coupling with a capacitance change detection circuit, which can also improve the bandwidth and stability of the accelerometer. By means of capacitance compensation array the zero-bias performance of accelerometers can be improved. The bias stability of the accelerometer can be reduced from 173mg to 31mg by testing.

A phenomenological contact‐element model considering slight non‐uniform contact for pounding analysis of highway bridges under seismic excitations

SummaryImpact stiffness is an important parameter of the contact‐element models for the analysis and prediction of the pounding responses of highway bridges subjected to seismic excitations. This paper presents a pounding experiment to investigate the inconsistencies between the theoretical and experimental values of the impact stiffness both for the linear impact model and Kelvin impact model presented in literature. The analysis of the impact acceleration and acoustic emission signals indicates that accelerometer performance and the non‐uniform pounding are two important factors that affect the pounding responses. Based on this observation, a phenomenological contact‐element model is proposed based on the actual contact state of highway bridges during the impact. To evaluate the effectiveness of the proposed impact model, a numerical simulation is subsequently conducted. A comparison of the results indicates that the proposed impact model can effectively predict the pounding responses of highway bridges. Copyright © 2015 John Wiley & Sons, Ltd.

Performance of the ActiGraph accelerometer using a national population-based sample of youth and adults.

BackgroundAccelerometer output may be semi-continuous or continuous in nature, which has implications on discerning non-wear and defining physical activity intensity levels. This study described field-based accelerometer performance from a surveillance sample of youth and adults.MethodsUsing 2003–2006 National Health and Nutrition Examination Survey data, 4,028 youth ages 6 to 17 years and 7,931 adults age > =18 years wore an ActiGraph AM7164 accelerometer for one week, providing at least 3 days of wear for > =8 hours/day. Accelerometer performance was assessed by exploring the number of different values of accelerometer counts/minute for each participant.ResultsOn average, youth participants had 1381 different counts/minute over 7 days (median 1360, interquartile range 1127–1623) and adult participants had 1101 different counts/minute over 7 days (median 1085, interquartile range 874–1313). For both youth and adults, when restricting to counts/minute between 0 to 4999, every possible value (in counts/minute) occurred at least once.ConclusionThe field-based data confirmed that the accelerometer used in this study allowed for continuous counts/minute through which all but the most vigorous activities would usually occur.

Performance and Modeling of a Micro-Grating Accelerometer

We design a packaged micro-optical–electromechanical system (MOEMS) – micro-grating accelerometer – that measures the interference of light resulting from its passage through a diffraction grating and reflection from the proof mass. In the present glass–silicon–glass embodiment, the diffraction optical element made of gold and the sensing proof mass supported by eight aluminum symmetrical cantilevers are fabricated on glass and silicon, respectively. Additional system components include a semiconductor laser, photodiodes, and the necessary electronics. First, we analyze the optical model to achieve high optical sensitivity. Then we optimize the structure parameters using the finite element method. Finally, we successfully fabricated the micro-grating accelerometer and packaged it in a small surface-mount package (12 × 12 × 3.6 mm). Our experiments show that the micro-grating accelerometer has a sensitivity of 5.6 V/G in the linear operating region, a bias stability of 0.94 μG, a resolution of 5.6 μG, and a dynamic range of 82.5 dB. Such a MOEMS accelerometer integrates the micro-grating with the proof mass through an anodic bonding procedure with the advantages of small size and high resolution.

Process development of an all-silicon capacitive accelerometer with a highly symmetrical spring-mass structure etched in TMAH + Triton-X-100

This paper reports a fabrication process of a capacitive microelectromechanical system (MEMS) accelerometer with a highly symmetrical spring-mass structure for the high device performance, which is composed of eight springs and a central mass. The sandwich accelerometer is constituted by top layer, middle layer and bottom layer. The suspended spring-mass structure in the middle silicon layer is formed simply by double thermally grown oxide layers and the mask–maskless wet anisotropic etching, avoiding the generally adopted deep-groove photolithography when fabricating the thin spring. Moreover, the gap between electrodes can be determined by the thickness of the oxide layer in this process. The surfactant-modified TMAH is selected as the etchant because it not only provides the minimum undercutting at the mass corner, thus saving much space of the compensation parts, but also allows the good control of spring thickness at the low etch rate. The spring shape evolution during etching in surfactant-modified TMAH is simulated and the obtained rhombic cross-section has the advantage of easily identifying the thickness of the spring from its width according to their crystal orientation relation. The three silicon layers are bonded through silicon fusion bonding (SFB) at temperature >1000°C to relax surface stresses that could be present in the material prior bonding. Preliminary test result shows the sensitivity of 60mV/g with good linearity of R2=0.99979 in a closed-loop interface circuit. The advanced accelerometer performance could be expected due to the symmetrical structure, the large proof mass, controllable spring shape, the narrow uniform capacitive gap, and the IC-compatible process.

A design of order-adjustable Σ∆ modulator for high performance micro-machined accelerometers

Sigma-delta modulation has been widely used in micro-machined accelerometers. Previous researches are mainly focused on increasing the order of the sigma-delta modulator for the mechanical sensor to improving the performance of the micro-machined accelerometers. These designs performed well in high resolution acceleration measurement, but they are insufficient in balancing the proof mass quickly while the micro-machined accelerometer is working. In this paper, the design of order-adjustable micro-machined accelerometer is proposed. It employs a mechanical sensor to balance the proof mass, and a fifth order MEMS accelerator to measure the acceleration with high resolution. Furthermore, this work shows an optimized design with a SQNR of 156.5 and 73.6 dB which can accurately measure the acceleration input and quickly balance the proof mass, respectively.

A Novel Fiber Bragg Grating Accelerometer Based on Fiber Vibrating Wire

Abstract A fiber Bragg grating (FBG) accelerometer based on fiber vibrating wire is presented. Finite element analysis has been done and experiments are carried out to demonstrate the performance of this FBG accelerometer. The seismic simulation experimental results indicate that the system has a good response to the 50–400 Hz vibration signal. What more, the accelerometer has a high sensitivity which can reach 108.6 pm/G at 100Hz. The linear responsivity and repeatability are also tested. The responsivity error is less than 2.5% and repeatability error is less than 0.03%. There is an extremely linear relationship between amplitude of detected signal and acceleration.

Performance of Several Low-Cost Accelerometers

Several groups are implementing low-cost host-operated systems of strong-motion accelerographs to support the somewhat divergent needs of seismologists and earthquake engineers. The Advanced National Seismic System Technical Implementation Committee (ANSS TIC, 2002), managed by the U.S. Geological Survey (USGS) in cooperation with other network operators, is exploring the efficacy of such systems if used in ANSS networks. To this end, ANSS convened a working group to explore available Class C strong-motion accelerometers (defined later), and to consider operational and quality control issues, and the means of annotating, storing, and using such data in ANSS networks. The working group members are largely coincident with our author list, and this report informs instrument-performance matters in the working group’s report to ANSS. Present examples of operational networks of such devices are the Community Seismic Network (CSN; csn.caltech.edu), operated by the California Institute of Technology, and Quake-Catcher Network (QCN; Cochran et al., 2009; qcn.stanford.edu; November 2013), jointly operated by Stanford University and the USGS. Several similar efforts are in development at other institutions. The overarching goals of such efforts are to add spatial density to existing Class-A and Class-B (see next paragraph) networks at low cost, and to include many additional people so they become invested in the issues of earthquakes, their measurement, and the damage they cause.

Analysis of the natural frequency and phase sensitivity of an optical fiber accelerometer coated with a rigid package

The operation frequency band and the output signal-to-noise ratio of the optical fiber accelerometer are decided by the natural frequency and phase sensitivity of the accelerometer, respectively. Until now, existing theoretical models have been incapable of analyzing the performance of the accelerometer coated with the rigid package. In this paper, an improved model is presented to explain the interreaction between the rigid package and the mass spring assembly inside. The natural frequency and phase sensitivity are affected by both the package mass and the damping of the surrounding medium. With the increase of the package mass, the natural frequency becomes lower and the phase sensitivity becomes higher. The damping of the surrounding medium induces the additional mass added on the package, which increases with the density of the medium. Further, the performance of the three-component vector accelerometer is analyzed by using the improved model. Experiments on the unpackaged and packaged accelerometers in different surrounding mediums indicate that our method is efficient. The improved model is also useful for the traditional piezoelectric accelerometer.

Design and validation of a high-voltage levitation circuit for electrostatic accelerometers

A simple high-voltage circuit with a voltage range of 0 to 900 V and an open-loop bandwidth of 11 kHz is realized by using an operational amplifier and a MOSFET combination. The circuit is used for the levitation of a test mass of 71 g, suspended below the top-electrodes with a gap distance of 57 μm, so that the performance of an electrostatic accelerometer can be tested on the ground. The translation noise of the accelerometer, limited by seismic noise, is about 4 × 10(-8) m/s(2)/Hz(1/2) at 0.1 Hz, while the high-voltage coupling noise is one-order of magnitude lower.

Performance evaluation of high g accelerometers

A numerical model for the split Hopkinson bar fly-away technique is presented to evaluate the performance of accelerometers measuring large amplitude pulses. Simulation results based on the numerical model indicate that the rise time of the incident stress pulse in the incident bar and the disk length are of appropriate lengths for the disk response to be accurately approximated as a rigid-body motion. Strain-time histories demonstrate that the incident strain pulse is non-dispersive. The rigid-body acceleration of the disk is derived from analytical models with stress at the incident bar/disk interface, incident strain-time data, and particle velocity on the free end of the disk calculated from numerical results. Thus, accelerations measured using the accelerometer and those derived from the models can be compared. These acceleration-time pulses show good agreement. The numerical model of the split Hopkinson bar fly-away technique can be used to calibrate high g accelerometers.

System Simulation and Test of a Field Emission Accelerometer

Field emission accelerometer work in vacuum environment, the negative exponential relationship between the current and the distance of the cathode and anode electrode make the accelerometer has high sensitivity and serious non-linearity. A system simulation method by using SIMULINK tools was put forward, and the system simulation model was proposed. The system simulation was carried out under low vacuum and high vacuum environment. On the guidance of the simulation result, the circuit was designed and the performance of accelerometer was tested. The result indicated that the accelerometer have good linearity and sensitivity.

Intensity-Encoded Polymer Optical Fiber Accelerometer

In this paper, we report the development and experimental implementation of a low-cost, compact, intensity-encoded accelerometer based on polymer optical fibers (POF). The proposed accelerometer sensor element relies on the misalignment between two POFs, being the external acceleration encoded in the optical signal intensity. The accelerometer performance was optimized by simulation, resulting in a coupling efficiency and modulation index values of 0.38 and 1.78, respectively. The implemented device has a sensitivity of ${\rm 33.5}\pm{\rm 0.1}~{\rm mV}/{\rm g}$ and a resonant frequency of ${\rm 51.44}\pm{\rm 0.1}~{\rm Hz}$ , obtained for a signal to noise ratio of 20 dB. This value for the resonant frequency is suitable for applications in several fields, such as structural health monitoring of civil engineering structures.

Study on Packaging Thermal Stress of Micromechanical Silicon Resonant Accelerometer

Packaging thermal stress is harmful to the performance of the micromechanical silicon resonant accelerometer. In order to decrease the packaging thermal stress, correlations of packaging thermal stress with the material properties, curing temperature and geometrical size of adhesive layers of adhesive materials were discussed. A finite element model of package was developed to analyze the influence of surface mounting technology (SMT） on the micromechanical silicon resonant accelerometer. The simulation results show that the Young’s modulus, thermal expansion coefficient, curing temperature and geometrical sizes of adhesive layers are important influencing factors for packaging thermal stress and the warpage of the chip. The thermal stresses during the process of SMT will cause the resonant frequency shift.

MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp

In this paper, a novel polymer MOEMS (micro-opto-electro-mechanical systems) accelerometer is reported. Low cost, photopatternable epoxies, EpoClad and EpoCore, are lithographically patterned through a 2 masks process to form this accelerometer in a simple and robust fabrication process. EpoClad is used for the cladding layer and EpoCore for the waveguides, fiber optic clamps and the seismic mass. Fiber optic clamping structures are presented that can be fabricated without extra process steps, and still assure both in-plane and out-of-plane clamping. The acceleration sensing principle is based on light intensity modulation by the seismic mass's position. A laser diode light source and a photodiode, connected to the sensor core through optical fibers, are used to extract the intensity variation as a function of acceleration. A vibration test was conducted to evaluate the performance of this MOEMS accelerometer.