Types Of Accelerometers Research Articles

Monolithic Multi Degree of Freedom (MDoF) Capacitive MEMS Accelerometers.

With the continuous advancements in microelectromechanical systems (MEMS) fabrication technology, inertial sensors like accelerometers and gyroscopes can be designed and manufactured with smaller footprint and lower power consumption. In the literature, there are several reported accelerometer designs based on MEMS technology and utilizing various transductions like capacitive, piezoelectric, optical, thermal, among several others. In particular, capacitive accelerometers are the most popular and highly researched due to several advantages like high sensitivity, low noise, low temperature sensitivity, linearity, and small footprint. Accelerometers can be designed to sense acceleration in all the three directions (X, Y, and Z-axis). Single-axis accelerometers are the most common and are often integrated orthogonally and combined as multiple-degree-of-freedom (MDoF) packages for sensing acceleration in the three directions. This type of MDoF increases the overall device footprint and cost. It also causes calibration errors and may require expensive compensations. Another type of MDoF accelerometers is based on monolithic integration and is proving to be effective in solving the footprint and calibration problems. There are mainly two classes of such monolithic MDoF accelerometers, depending on the number of proof masses used. The first class uses multiple proof masses with the main advantage being zero calibration issues. The second class uses a single proof mass, which results in compact device with a reduced noise floor. The latter class, however, suffers from high cross-axis sensitivity. It also requires very innovative layout designs, owing to the complicated mechanical structures and electrical contact placement. The performance complications due to nonlinearity, post fabrication process, and readout electronics affects both classes of accelerometers. In order to effectively compare them, we have used metrics such as sensitivity per unit area and noise-area product. This paper is devoted to an in-depth review of monolithic multi-axis capacitive MEMS accelerometers, including a detailed analysis of recent advancements aimed at solving their problems such as size, noise floor, cross-axis sensitivity, and process aware modeling.

MICRO-VIBRATION TEST AND ANALYSIS FOR HIGH-TECH WORKSHOP

In this paper, micro-vibration tests at a display driver chips production workshop in Hefei were carried out lasting 24 hours. Vibration accelerations of each testing point on three directions were simultaneously recorded by a high-sensitivity type accelerometer. Internationally accepted one-third octave band analysis method was adopted to process the field test data. The variation of vibration over time was analyzed, and the attenuation characteristics of vibrations induced by traffic loads with distance were also studied by one-third octave band spectra. Results show that, vibration accelerations alter smoothly within 24 hours, and it should be noted that the peak acceleration in the daytime is slightly higher than that at night. Vibration amplitudes swing between 10-5 gal and 10-2 gal. In the low frequency ranges(2~8 Hz),the peak of vibration acceleration is 0.015gal. In the medium-high frequency ranges(8~250 Hz),the maximum value of vertical velocity reaches 0.5013ms-1,while the velocity touches higher to 0.6636ms-1 in horizontal direction. One-third octave band spectra of testing vibrations locate below the VC-B curve totally indicating that design requirements are satisfied. Besides, ground vibrations caused by traffic loads decay apparently with distance in the frequency from 15 to 60 Hz, which are regarded that ground layers play a role in the attenuation of vibration caused by traffic load.

Development of vector hydrophone using thickness–shear mode piezoelectric single crystal accelerometer

In this study, a vector hydrophone was developed for a towed array sonar system using a shear type accelerometer. In general, inertia type vector hydrophones using accelerometers have higher sensitivity than multimode vector hydrophones. However, the sensitivity still needs to be enhanced as much as possible for practical application. For the purpose, the effect of the structural parameters of a shear type accelerometer on the receiving voltage sensitivity (RVS) of the vector hydrophone was rigorously analyzed, and the structure of the vector hydrophone was optimized to maximize the RVS. The developed vector hydrophone has an external diameter of 23 mm and the minimum RVS over the given frequency range of -201.4 dB. It was also verified that the designed vector hydrophone exhibits the characteristic of a dipole mode beam pattern. Furthermore, a prototype of the vector hydrophone was fabricated with the optimal dimensions, and its acoustic characteristics were measured to verify the validity of the design. The vector hydrophone developed in this work has the highest feasible RVS over the desired frequency range in comparison with other types of vector hydrophone like the multimode hydrophone.

Monitoring the behavior of freely moving lobsters with accelerometers

Accelerometers are useful devices for monitoring the activity of a variety of lobster species, both in the laboratory and the field. While the method has proven beneficial for determining when animals are active, it is more difficult to determine the actual distance animals travel or the intensity of their movements based on accelerometry. To achieve this goal, we monitored American lobsters, Homarus americanus H. Milne-Edwards, 1837, fitted with HOBO accelerometer dataloggers and Vemco V13AP accelerometer transmitters in the laboratory and simultaneously obtained time-lapse digital videos of their behavior. We used these data to convert accelerometer outputs to distances moved per unit time. The outputs of both types of accelerometers were well correlated with distance traveled. We then used this information to analyze data obtained in a previous study, using the same HOBO accelerometers. This made it possible to calculate to what extent activity and the distance traveled per hour changed on a seasonal basis over a year. This analysis also revealed that lobster activity in the field was significantly greater than activity in the lab at the same time of year, within similar enclosures. Overall, these results demonstrate that accelerometry is a suitable and accurate method for monitoring the relative activity of lobsters over long periods in the laboratory and field and the results compare favorably with other published studies of lobster movements. Document Type: Research Article

Calibration of tri-axial MEMS accelerometers in the low-frequency range – Part 2: Uncertainty assessment

Abstract. A comparison among three methods for the calibration of tri-axial accelerometers, in particular MEMS, is presented in this paper, paying attention to the uncertainty assessment of each method. The first method is performed according to the ISO 16063 standards. Two innovative methods are analysed, both suitable for in-field application. The effects on the whole uncertainty of the following aspects have been evaluated: the test bench performances in realizing the reference motion, the vibration reference sensor, the geometrical parameters and the data processing techniques. The uncertainty contributions due to the offset and the transverse sensitivity are also studied, by calibrating two different types of accelerometers, a piezoelectric one and a capacitive one, to check their effect on the accuracy of the methods under comparison. The reproducibility of methods is demonstrated. Relative uncertainty of methods ranges from 3 to 5 %, depending on the complexity of the model and of the requested operations. The results appear promising for low-cost calibration of new tri-axial accelerometers of MEMS type.

Self-Referenced Accelerometer Array Multiplexed on a Single Fiber Using a Dual-Pulse Heterodyne Phase-Sensitive OTDR

We report a new type of multiplexed fiber-optic accelerometer array based on a dual-heterodyne-pulse phase-sensitive OTDR technique. This scheme significantly simplifies the structure of fiber accelerometer and can greatly benefit its practical applications. The sensitivity model for the new type accelerometer based on the Rayleigh backscattering is developed for the first time, which shows a great difference from the transmission-type interferometric accelerometer. On a single piece of telecommunication fiber, we demonstrate the multiplexing of three accelerometers separated by 20 m, each with a measured sensitivity of ∼36 rad/g that agrees well with the theoretical analysis. The connecting fiber between accelerometers simultaneously acts as a distributed acoustic sensor, which under proper vibration isolation can be used as a self-reference to suppress system noises. We show that the common-mode noises of the sensor can be suppressed by 35 dB at a frequency of 100 Hz without using additional reference interferometers.

Digital platform for Sigma-Delta accelerometer assessment and test

A digital platform for fast assessment and testing of multiple order architectures of electromechanical Sigma-Delta modulators for MEMS capacitive accelerometers is introduced in this paper. It is well known that the introduction of a negative feedback loop on sensors presents significant advantages to improve important characteristics, such as precision, linearity, speed, and dynamic range over open-loop operation (Borovic et al. in J Micromech Microeng 15(10):1917–1924, 2005; Chen et al. in IEEE Sens J 16(17):6476–6495, 2016). In a closed-loop system, the controller is responsible for the aforementioned improvements, enabling the relaxation on the manufactured device specifications. Consequently, it demands better and more complex electronic circuits for the controller. A configurable multi-order (2nd, 3rd, 4th and 5th) ΣΔ module was developed in field-programmable gate array, along with the necessary signal acquisition and actuation modules, using a processor-centric approach, ensuring real-time performance, simple reconfiguration, and fast assessment of different orders and gains for the ΣΔ modulator with real MEMS devices. The system is capable of a measuring cycle lower than 100 ms. The platform was used to perform a comparison between two different types of MEMS accelerometers, evaluating the results obtained with second, third, fourth and fifth modulation orders for two bandwidth values—200 and 1000 Hz. The best noise figure achieved was 4.4 µg/√Hz, using a fifth order ΣΔ modulator and the device with the larger seismic mass. A comparison between three similar devices is also performed, as well as a comparison between simulated and experimental results.

A comparison of low-shock and centrifuge calibrations using piezoresistive accelerometers

This paper describes the degree of equivalence between low-shock and centrifuge calibrations up to 10 000 m s−2 against three types of piezoresistive accelerometer: an undamped sputter gauge type, a damped sputter gauge type and an undamped semiconductive type. The complex sensitivity in the low-shock calibration and the DC sensitivity in the centrifuge calibration are well consistent within each expanded uncertainty in the frequency domain, together with the vibration calibration using the second-order transfer function. In addition, the preliminary uncertainty budget in the centrifuge calibration facility is also indicated, and distinctly estimated from the viewpoint of the mechanical parts and accelerometers.

Modelling and hardware co-simulation of a Quadrotor unmanned aerial vehicle

This paper deals with the modelling and hardware (HW) co-simulation of a Quadrotor vertical take-off and landing (VTOL) type of unmanned aerial vehicle (UAV). The developed HW co-simulation platform is based on a reconfigurable I/O (RIO) board of National Instruments (NI) Company, called sbRIO-9636, and a host PC with a real-time operating system (RTOS). The control design and simulation (CDSim) module of LabVIEW environment as well as an established network streams data communication protocol are used to emulate and co-simulate all flight dynamics' within a processor-in-the-loop (PIL) framework. The flight motion principle of the Quadrotor, i.e. lift, rotation and translation, is firstly described as function of changes in the angular speed of the rotors. All aerodynamic forces and moments of such a vehicle are then described within an inertial earth frame and a nonlinear dynamical model is established thanks to the Newton-Euler formalism. The dynamics of the propellers' brushless DC motors, accelerometer and gyroscope types of sensors are also modelled and co-simulated in order to complete the established model of the studied VTOL rotorcraft. HW simulations are carried out and compared to those obtained with software (SW) simulations in order to show the effectiveness of the proposed PIL co-simulation strategy.

Modelling and hardware co-simulation of a Quadrotor unmanned aerial vehicle

This paper deals with the modelling and hardware (HW) co-simulation of a Quadrotor vertical take-off and landing (VTOL) type of unmanned aerial vehicle (UAV). The developed HW co-simulation platform is based on a reconfigurable I/O (RIO) board of National Instruments (NI) Company, called sbRIO-9636, and a host PC with a real-time operating system (RTOS). The control design and simulation (CDSim) module of LabVIEW environment as well as an established network streams data communication protocol are used to emulate and co-simulate all flight dynamics' within a processor-in-the-loop (PIL) framework. The flight motion principle of the Quadrotor, i.e. lift, rotation and translation, is firstly described as function of changes in the angular speed of the rotors. All aerodynamic forces and moments of such a vehicle are then described within an inertial earth frame and a nonlinear dynamical model is established thanks to the Newton-Euler formalism. The dynamics of the propellers' brushless DC motors, accelerometer and gyroscope types of sensors are also modelled and co-simulated in order to complete the established model of the studied VTOL rotorcraft. HW simulations are carried out and compared to those obtained with software (SW) simulations in order to show the effectiveness of the proposed PIL co-simulation strategy.

An optimization technique for performance improvement of gap-changeable MEMS accelerometers

This paper demonstrates the design and optimization of single- and dual-axis capacitive accelerometers. Detailed analysis together with fabrication and characterization results are reported. The designs utilize a simplified comb structure to detect capacitance change between rotor and stator fingers. By optimizing the gap spacing (finger gap and anti-finger gap), the devices are designed to yield high capacitance change as a function of the proof mass displacement. It was found that there is a critical anti-gap spacing for a selected finger gap at which the device sensitivity is the highest (ratio of 3.45: 1). Designs are first optimized using Finite Element Analysis (FEA) tools. Initial simulation results indicated a differential capacitive sensitivity of 80fF/g and 68fF/g for single- and dual -axis accelerometers, respectively. The capacitance-voltage (CV) measurements exhibited a parabolic behavior which is an important characteristic for these type of accelerometers. Furthermore, results show a rest capacitance of 16.42 pF and sensitivity of 35 fF/g for single-axis accelerometer. Overall, the devices have excellent sensitivity, high linearity, and low cross-axis sensitivity. The accelerometers are fabricated using GlobalFoundries’ Inertial Measurement Unit (IMU) platform and have a compact footprint of 1.8 mm × 1.8 mm.

Eddy-Current Sensing Principle in Inertial Sensors

The eddy-current displacement sensing principle is, to the best of our knowledge, not yet used in inertial sensors. The main reasons for this are the important performance limitations of the existing eddy-current sensor solutions, such as low sensitivity, poor stability, high-power consumption, and bulkiness. Our novel high-frequency eddy-current displacement sensor (ECDS), however, has significantly improved performance with respect to these limitations and allows the use of planar, stable coils, making it a viable candidate for the use in inertial sensors. An implementation example of an ECDS-based inertial sensor with a bandwidth of 370 Hz and a noise floor of $13\,\mu {\text{g}/ \surd \text{Hz}}$ is proposed. Although not yet competitive with state-of-the-art inertial sensors, it performs better than other types of inductive accelerometers and offers the inherent advantages of ECDSs, such as insensitivity to the environment.

Study on Performance Evaluation of MEMS Sensors and Data Integration Methods for Expected Use to Determine Damage Degrees of Existing Structures

The shake table test of small-scaled steel frame structure was conducted using large-scale earthquake simulator at the National Research Institute for Earth Science and Disaster Resilience (NIED) in Tsukuba, Ibaragi. This paper presents the performance evaluation of Micro Electro Mechanical Systems (MEMS) type accelerometers, which are recently being used in various fields, comparing with the conventional servo type accelerometers. In addition, this paper discussed the integration method of the measured acceleration into displacements, which is suitable for structural damage evaluation due to strong earthquakes.

P 083 - The effect of a bespoke home based physical activity intervention on markers of oxidative stress and markers of general health in older adults

Home-based unsupervised exercise training has been shown to improve health in older adults. Assessing adherence, especially using a self-report format, in unsupervised exercise interventions is problematic. The aim of this pilot study was to objectively assess the effect of an unsupervised home-based exercise intervention in community dwelling older adults. Markers of oxidative stress and measures of health were assessed, including cerebral hemodynamics and cognitive function. Physical activity was measured continuously using a wrist watch type accelerometer with optical heart rate monitoring. A secondary aim of the study was to test the feasibility of a wrist activity monitor as a tool to assess physical activity in this population. The intervention failed to increase the level of physical activity in all the participants, although changes were observed. No significant changes were observed in markers of oxidative stress or other measures of health in response to the exercise intervention. Progressive goals, based on adherence measurement, are potentially important for the success of an unsupervised exercise intervention. Wrist-based accelerometers may be useful tools for the assessment of physical activity in sedentary older adults, but further development of specialist software may be necessary.

Sensitivity improvement of a dual axis thermal accelerometer with modified cavity structure

An improved dual axis thermal accelerometer is proposed in this paper. The thermal accelerometer consists of a centrally placed micro-heater, temperature detectors (placed symmetrically opposite of the heater) and silicon islands. A cavity is etched in silicon bulk to create thermal insulation between heater and the temperature detectors. The islands enhance the accelerometer sensitivity significantly. 3D structures of both types of accelerometers (with and without island) were designed and simulated in an FEM simulator. The results show that, the sensitivity of the accelerometer increases from 0.335 to 0.657 K/g by adding two pairs of silicon islands along two axes (where g is the gravitational acceleration i.e. 9.8 m/s2 and K is the unit of temperature in Kelvin scale). The improvement of sensitivity is observed over a wide range of acceleration.

Automated Detection of Stereotypical Motor Movements in Autism Spectrum Disorder Using Recurrence Quantification Analysis.

A number of recent studies using accelerometer features as input to machine learning classifiers show promising results for automatically detecting stereotypical motor movements (SMM) in individuals with Autism Spectrum Disorder (ASD). However, replicating these results across different types of accelerometers and their position on the body still remains a challenge. We introduce a new set of features in this domain based on recurrence plot and quantification analyses that are orientation invariant and able to capture non-linear dynamics of SMM. Applying these features to an existing published data set containing acceleration data, we achieve up to 9% average increase in accuracy compared to current state-of-the-art published results. Furthermore, we provide evidence that a single torso sensor can automatically detect multiple types of SMM in ASD, and that our approach allows recognition of SMM with high accuracy in individuals when using a person-independent classifier.

SisFall: A Fall and Movement Dataset.

Research on fall and movement detection with wearable devices has witnessed promising growth. However, there are few publicly available datasets, all recorded with smartphones, which are insufficient for testing new proposals due to their absence of objective population, lack of performed activities, and limited information. Here, we present a dataset of falls and activities of daily living (ADLs) acquired with a self-developed device composed of two types of accelerometer and one gyroscope. It consists of 19 ADLs and 15 fall types performed by 23 young adults, 15 ADL types performed by 14 healthy and independent participants over 62 years old, and data from one participant of 60 years old that performed all ADLs and falls. These activities were selected based on a survey and a literature analysis. We test the dataset with widely used feature extraction and a simple to implement threshold based classification, achieving up to 96% of accuracy in fall detection. An individual activity analysis demonstrates that most errors coincide in a few number of activities where new approaches could be focused. Finally, validation tests with elderly people significantly reduced the fall detection performance of the tested features. This validates findings of other authors and encourages developing new strategies with this new dataset as the benchmark.

A new type of tri-axial accelerometers with high dynamic range MEMS for earthquake early warning

Earthquake Early Warning System (EEWS) has shown its efficiency for earthquake damage mitigation. As the progress of low-cost Micro Electro Mechanical System (MEMS), many types of MEMS-based accelerometers have been developed and widely used in deploying large-scale, dense seismic networks for EEWS. However, the noise performance of these commercially available MEMS is still insufficient for weak seismic signals, leading to the large scatter of early-warning parameters estimation. In this study, we developed a new type of tri-axial accelerometer based on high dynamic range MEMS with low noise level using for EEWS. It is a MEMS-integrated data logger with built-in seismological processing. The device is built on a custom-tailored Linux 2.6.27 operating system and the method for automatic detecting seismic events is STA/LTA algorithms. When a seismic event is detected, peak ground parameters of all data components will be calculated at an interval of 1s, and τc-Pd values will be evaluated using the initial 3s of P wave. These values will then be organized as a trigger packet actively sent to the processing center for event combining detection. The output data of all three components are calibrated to sensitivity 500 counts/cm/s2. Several tests and a real field test deployment were performed to obtain the performances of this device. The results show that the dynamic range can reach 98dB for the vertical component and 99dB for the horizontal components, and majority of bias temperature coefficients are lower than 200μg/°C. In addition, the results of event detection and real field deployment have shown its capabilities for EEWS and rapid intensity reporting.

Measurement of Surface Vibration Accelerations Propagated in the Environment

The paper presents the analysis of the influence of the method of accelerometers attachment to the ground on the recorded level of vibration acceleration. Measurements of vibrations were conducted using two types of accelerometers with various weights and measuring accuracy. Accelerometers were mounted to the ground in four different methods using various mounting bases anchored in the ground with one, three and four rods. The vibrations were generated using Light Falling Weight Deflectometer (LFWD) and recorded in longitudinal, transversal and vertical directions at the distance of 5 and 10 m from the source of vibrations. Measurements of vibration accelerations were carried out using 32-channel and 24-bit mobile data acquisition system - SIEMENS LMS SCADAS Recorder, as well as a set of 18 low-frequency, seismic piezoelectric accelerometers type 8340, manufactured by Brüel&Kjær, and two triaxial, high sensitivity accelerometers type TLD356B18 manufactured by PCB Piezotronics. The comparative analysis of Peak Particle Accelerations (PPA) has demonstrated that the method of attaching of accelerometers to the ground is crucial for the credibility of measurements. The best way of attaching transducers to the ground was shown in the paper. The resulting values of vibration acceleration may constitute a basis for a reliable analysis of vibration in the subsoil, which is particularly important in terms of the credibility of assessment of the impact of physical pollution in a form of vibrations propagated in the environment on the newly designed buildings and their future users.

Seismogeodesy Using GPS and Low‐Cost MEMS Accelerometers: Perspectives for Earthquake Early Warning and Rapid Response

Abstract The seismogeodetic method computes accurate displacement and velocity waveforms by optimally extracting high‐frequency information from strong‐motion accelerometers and low‐frequency information from collocated Global Positioning System (GPS) instruments. These broadband observations retain the permanent (static) displacement, are immune to clipping and magnitude saturation for large earthquakes, and are sensitive enough to record P ‐wave arrivals. These characteristics make seismogeodesy suitable for real‐time applications such as earthquake early warning. The Scripps Institution of Oceanography (SIO) has developed an inexpensive microelectromechanical systems (MEMS) accelerometer package to upgrade established GPS stations. We compare the performance of our MEMS accelerometer with an observatory‐grade accelerometer using an experiment at the University of California San Diego Large High‐Performance Outdoor Shake Table. We show that the two types of accelerometers agree in frequency ranges of seismological and engineering interest and produce equivalent seismogeodetic estimates of displacement and velocity. To date, 27 SIO MEMS packages have been installed at GPS monitoring stations in southern California and the San Francisco Bay area and have recorded four earthquakes ( M 4.2, M 4.1, and two of M 4.0). The P ‐wave arrivals are distinguishable in the seismogeodetic observations at distances of up to ∼25 km away but not in the GPS‐only displacements. There is no significant permanent deformation for these small events. This study demonstrates the lower limit of detectability and that seismogeodetic waveforms can also be a reliable early confirmation that an event is not large or hazardous. It also raises the possibility of rapid magnitude estimation through scaling relationships.