Low-frequency Accelerometer Research Articles

Optical interferometry implementation considerations for sinusoidal low frequency accelerometer measurements and calibrations

Vibration metrology utilizing sine excitation stimulus, based either on fringe counting or minimum point methods, employs Michelson interferometers for the calibration of accelerometers. The former method combines the optical reference and measurements arms from a static mirror and reflected by the accelerometer respectively which are then directed to a suitable photodiode for processing. The stroking motion due to the oscillation of the accelerometer will contribute to the misalignment of the two optical paths and there are three methods to compensate for this. The first requires the mounting of a mirror on the accelerometer itself and the effect of the added mass from the mirror can be accounted for and corrected. The second requires the mounting of three mirrors on the mounting surface of the accelerometer but this requires the alignment of the Michelson interferometer for each mirror. The third is to use two retro reflectors so that the returning measurement beams are always along the same path with the reference; however, this requires the alignment of the interferometer for each retro-reflector. This paper will discuss such considerations on the optical systems, their components and associated instrumentation and discuss the design of an alternative approach that can overcome certain limitations.

Development of a Fiber Bragg Grating accelerometer based on a tandem single-notched hinge structure

A Fiber Bragg Grating low-frequency accelerometer with a single-notched hinge in series is proposed to improve the hinge structure’s sensitivity and the cross-sensitivity of the accelerometer of low-frequency seismic waves. The sensitivity and the cross-sensitivity of the accelerometer are improved by connecting the single-notched hinge structure in series and experimentally verified. Based on the theoretical analysis, the resonance frequency and sensitivity formula of the accelerometer are derived. At the same time, the accelerometer is simulated by finite element analysis software to simulate and analyze the characteristics of the accelerometer in terms of resonance frequency, strain distribution, and amplitude-frequency response. The structural parameters of the accelerometer are optimized by numerical analysis software, and the effects of the structural parameters on the sensitivity and resonance frequency of the accelerometer are analyzed. The experimental results show that the resonance frequency of the accelerometer is 110 Hz, the flat region is 0.6–50 Hz, the linearity is as high as 98.9%, the sensitivity is 1040.41 pm/g, and the cross-sensitivity of the accelerometer in the flat interval is 4.94%. This indicates that the accelerometer shows good linearity and cross-sensitivity in the flat interval, which well meets the needs of seismic wave signal monitoring in low-frequency oil and gas exploration.

Fiber Bragg Grating low-frequency accelerometer based on spring structure

To meet the needs of accelerometers for seismic wave monitoring in the field of low-frequency oil exploration, a Fiber Bragg Grating (FBG) low-frequency accelerometer based on spring structure is proposed. The accelerometer consists of two FBGs, two semi-profile metal capillaries, a spring, and a mass block. In addition, the accelerometer is encapsulated in a cylindrical housing to enhance its stability. Firstly, the working principle of the accelerometer is introduced in detail and the theoretical model of the accelerometer is established, then the accelerometer is simulated by finite element analysis software and the dimensional parameters of the accelerometer are optimized by numerical analysis software. Finally, the experimental study of the accelerometer is carried out to test the shock response, amplitude-frequency response, and sensitivity response of the accelerometer. The experimental results show that the proposed new accelerometer has a resonant frequency of 115 Hz, dynamic resolution up to 0.123 mg/Hz in the operating range 0.5–60 Hz, the sensitivity is 932.25 pm/g, the linearity is up to 99.9 %, the higher sensitivity, and sufficient operating range, so that the accelerometer is expected to be used in the field of low-frequency oil exploration.

Development of a low-frequency accelerometer based on symmetric multi-stage triangular beam fiber Bragg grating

In order to meet the needs of accelerometers for low-frequency seismic exploration, a fiber-optic grating accelerometer based on a symmetric multi-stage triangular hinge is proposed. The sensitivity of the accelerometer is improved by the symmetrical multi-stage triangular beam structure, and experimental verification is carried out. The resonant frequency and sensitivity equations of the accelerometer are given based on theoretical analysis, while the finite element analysis software is used to simulate and analyze the characteristics of the accelerometer such as resonant frequency, stress distribution, and amplitude-frequency response. The structural parameters of the accelerometer are optimized by numerical analysis software, and the influence of the structural parameters on the sensitivity and resonant frequency of the accelerometer is analyzed. The experimental results show that the accelerometer has a resonant frequency of 140 Hz and a linearity of 99.9 % in the flat region of 1–70 Hz, a sensitivity of 337.325 pm/g, and an interference immunity of 5.39 % in the lateral direction in the working axis direction. This indicates that the accelerometer shows good linearity and lateral interference immunity in the flat interval, which well meets the needs of seismic wave signal monitoring in the field of low-frequency oil and gas exploration.

Gyro-Free Inertial Navigation Systems Based on Linear Opto-Mechanical Accelerometers.

High-sensitivity uniaxial opto-mechanical accelerometers provide very accurate linear acceleration measurements. In addition, an array of at least six accelerometers allows the estimation of linear and angular accelerations and becomes a gyro-free inertial navigation system. In this paper, we analyze the performance of such systems considering opto-mechanical accelerometers with different sensitivities and bandwidths. In the six-accelerometer configuration adopted here, the angular acceleration is estimated using a linear combination of accelerometers' read-outs. The linear acceleration is estimated similarly but requires a correcting term that includes angular velocities. Accelerometers' colored noise from experimental data is used to derive, analytically and through simulations, the performance of the inertial sensor. Results for six accelerometers, separated by 0.5 m in a cube configuration show noise levels of 10-7 m s-2 and 10-5 m s-2 (in Allan deviation) for time scales of one second for the low-frequency (Hz) and high-frequency (kHz) opto-mechanical accelerometers, respectively. The Allan deviation for the angular velocity at one second is 10-5 rad s-1 and 5×10-4 rad s-1. Compared to other technologies such as MEMS-based inertial sensors and optical gyroscopes, the high-frequency opto-mechanical accelerometer exhibits better performance than tactical-grade MEMS for time scales shorter than 10 s. For angular velocity, it is only superior for time scales less than a few seconds. The linear acceleration of the low-frequency accelerometer outperforms the MEMS for time scales up to 300 s and for angular velocity only for a few seconds. Fiber optical gyroscopes are orders of magnitude better than the high- and low-frequency accelerometers in gyro-free configurations. However, when considering the theoretical thermal noise limit of the low-frequency opto-mechanical accelerometer, 5×10-11 m s-2, linear acceleration noise is orders of magnitude lower than MEMS navigation systems. Angular velocity precision is around 10-10 rad s-1 at one second and 5×10-7 rad s-1 at one hour, which is comparable to fiber optical gyroscopes. While experimental validation is yet not available, the results shown here indicate the potential of opto-mechanical accelerometers as gyro-free inertial navigation sensors, provided the fundamental noise limit of the accelerometer is reached, and technical limitations such as misalignments and initial conditions errors are well controlled.

Transfer-Learning-Based Estimation of the Remaining Useful Life of Heterogeneous Bearing Types Using Low-Frequency Accelerometers.

Deep learning approaches are becoming increasingly important for the estimation of the Remaining Useful Life (RUL) of mechanical elements such as bearings. This paper proposes and evaluates a novel transfer learning-based approach for RUL estimations of different bearing types with small datasets and low sampling rates. The approach is based on an intermediate domain that abstracts features of the bearings based on their fault frequencies. The features are processed by convolutional layers. Finally, the RUL estimation is performed using a Long Short-Term Memory (LSTM) network. The transfer learning relies on a fixed-feature extraction. This novel deep learning approach successfully uses data of a low-frequency range, which is a precondition to use low-cost sensors. It is validated against the IEEE PHM 2012 Data Challenge, where it outperforms the winning approach. The results show its suitability for low-frequency sensor data and for efficient and effective transfer learning between different bearing types.

Reduction of gravity effect on the results of low-frequency accelerometer calibration

This paper describes a study on the possible sources of systematic errors during the calibration of accelerometers at low-frequencies. This study was carried out on a primary calibration system that uses an air-bearing vibration exciter APS Dynamics 129 and applying the sine-approximation method. Tests performed and actions taken to reduce the effect on experimental results are presented.

Experimental Analysis of Transition Metal (Ni-V) Codoped ZnO Nanorods for Piezoelectric Accelerometer Application

Growth of Nickel (Ni) and Vanadium (V) codoped Zinc Oxide (ZVN) nanorods (NRs) using the hydrothermal method, and its application in low-frequency accelerometer have been explored in this study. Poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) is spin-coated on ZVN NRs grown on a rigid substrate to establish p-n junction. Structural analysis exhibited dominant (002) plane revealing the c-axis orientation and improved quality of ZVN NRs. Morphological examination showed growth of NRs with the hexagonal top surface. Study about the optical properties evinced a bandgap of ∼3.03 eV with decreased defects. Electrical properties evidenced a typical p-n junction rectifying behavior with less turn-on voltage and internal resistance of 0.1 V and ∼158 Ω respectively depicting increased conductivity. Experimental accelerometer performance evaluation manifested a maximum output voltage of 2.9 V and 3.6 V at resonant frequency 7 Hz and 1 g acceleration respectively. The sensitivity calculated is ∼6.9 V/g which is considerable in comparison with the literature reported. The fabricated ZNV accelerometer has been reported to have satisfactory linearity.

Monocular Vision-Based Earth’s Graviation Method Used for Low-Frequency Vibration Calibration

At present, the sensitivity phase of low-frequency accelerometer is commonly calibrated by time synchronization (TS), which needs to strictly align its input excitation acceleration signal and output signal in the time domain. However, TS is very difficult to be implemented and has severely restricted the improvement of the measurement accuracy. A novel calibration method that combines the monocular vision method and time-spatial synchronization technique is investigated to achieve the high-accuracy sensitivity phase calibration. The sensitivity phase is accurately calibrated by determining the aligned spatial position between the excitation acceleration signal and the output signal with the monocular vision method. The sensitivity magnitude can also be simultaneously calibrated. Experimental results show that the calibrated sensitivity phase and magnitude by the investigated method agree well with those by the laser interferometry in the range from 0.3 Hz to 2 Hz. The calibration accuracy of the investigated method is especially superior to that of the laser interferometry in the range from 0.01 Hz to 0.3 Hz.

COMPLEX OF SPECIALIZED STAND EQUIPMENT FOR MONITORING THE CHARACTERISTICS OF LOW FREQUENCY ACCELEROMETERS

При вирішенні задач дослідження вібростійкості будівель, споруд та малих інженерних конструкцій, основним елементом системи контролю, що забезпечує проведення таких досліджень, є віброперетворювачі, від достовірності показів яких суттєво залежить працездатність системи в цілому. Перевірка функціювання та визначення параметрів таких приладів здійснюється за допомогою вібростендів. З урахуванням особливостей низькочастотних акселерометрів, для перевірки їх функціонального стану необхідні випробувальні стенди з діапазоном переміщень до 200 мм і частотним діапазоном у межах 0.1 – 10 Гц, такі стенди, зазвичай, мають великі розміри і вимагають стаціонарного встановлення в лабораторіях. Після транспортування на місце проведення випробувань, необхідно також провести перевірку працездатності віброперетворювачів і їх первинне калібрування. Але при перевірці портативних віброперетворювачів, особливо в польових умовах, виникає низка проблем, пов’язаних і з заданням необхідних параметрів вібрації, і з необхідністю проводити дослідження віброперетворювачів масою 5 -10 кілограмів, що також потребує наявності випробувальних стендів, які частіше відсутні. В роботі представлені два розроблені стенди для перевірки працездатності та контролю характеристик низькочастотних віброперетворювачів. Перший з них – двокомпонентний, переносний, автономний. Може бути використаний в польових умовах за відсутності мережевого електроживлення в місці проведення досліджень. Конструкція стенда дозволяє проводити перевірку акселерометрів як з горизонтальною, так і вертикальною осями чутливості. Особливістю стенду є, з одного боку його портативність, а з іншого – можливість перевірки датчиків масою до 7 кілограмів в частотному діапазоні до 10 Гц. Другий стенд – лабораторний маятниковий великих переміщень. Може бути використаний для визначення параметрів вібродатчиків з динамічним діапазоном переміщень до 200 мм, масою до 20 кілограмів, в частотному діапазоні до 2 Гц. Обидва стенди обладнані універсальним інформаційно-вимірювальним модулем, що забезпечує збір, візуалізацію і первинний аналіз отриманих даних та їх збереження на ПК, для чого було розроблене спеціальне програмне забезпечення у середовищі NI LabVIEW. Для універсального автономного стенду реалізована функція керування частотою вібрації платформи.

Comparative study on hydrothermally synthesized undoped and Vanadium doped Zinc Oxide nanorods for nanoelectromechanical systems low-frequency accelerometer application

Lead-free undoped and Vanadium (V) doped Zinc Oxide (ZnO) nanorods were grown on rigid Fluorine-doped Tin Oxide substrates using a simple hydrothermal method. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate was coated on the grown nanorods to form a p-n junction. The optical, crystalline and morphological analysis were done using X-ray diffraction, Ultraviolet-Visible spectroscopy, Field Emission Scanning Electron Microscope and Spectrofluorescence. The decrease in bandgap from 3.1 eV (undoped) to 3 eV (V doped) showed increased conductivity. Current-Voltage analysis depicted an improvement in the electrical properties of V doped device in terms of a low turn-on voltage, rectification ratio and reverse leakage current density. The RC time constant was analyzed using Impedance analysis. A decrease in RC time constant value and internal resistance of 0.06 msec and 1.61 kΩ respectively for V doped ZnO device compared with undoped one showed an improved piezoelectric property. The maximum output voltages of 1.6 V and 1.9 V for 9 Hz and 1 g input respectively were observed in the V doped device. The sensitivity of undoped and V doped device was 1.71 V/g and 1.93 V/g respectively. It is evident that ~12.9% of improved sensitivity is obtained when V is doped into ZnO nanorods.

Low-frequency Accelerometer Based on DVD Pick-up Head and Cantilever

Low-frequency Accelerometer Based on DVD Pick-up Head and Cantilever

Sensor Fusion Algorithm by Complementary Filter for Attitude Estimation of Quadrotor with Low-Cost IMU

This paper proposes a sensor fusion algorithm by complementary filter technique for attitude estimation of quadrotor UAV using low-cost MEMS IMU. Angular rate from gyroscope tend to drift over a time while accelerometer data is commonly effected with environmental noise. Therefore, high frequency gyroscope signal and low frequency accelerometer signal is fused using complementary filter algorithm. The complementary filter scaling factor K1=0.98 and K2=0.02 are used to merge both gyro and accelerometer. The results show that the smooth roll, pitch and yaw attitude angle can be obtained from the low cost IMU by using proposed sensor fusion algorithm.

Low frequency accelerometer calibration using an optical encoder sensor

Low frequency accelerometer calibration is generally a time consuming process and requires special considerations as well as excitation techniques due to the low frequency and low acceleration levels encountered. A limited work has been reported on this aspect so far. The paper discusses the measurement considerations associated with the implementation of optical encoder technology in low frequency accelerometer calibration. The method may be considered as primary one as reference is displacement rather than acceleration. The paper provides comparison of the optical encoder reference technique to manufacturer’s accredited primary calibration of an artifact as per ISO 16063-11. The work also discusses the measurement uncertainty associated with low frequency accelerometer calibration using an optical encoder sensor.

Experiments with the DAKON-M convection sensor

We have described an express technique for processing the results of experiments with a DAKON-M convection sensor on board the Service Module of the International Space Station (ISS) in 2011. The technique uses a certain rule to compare the sensor measurements with the calculated data on the quasistatic component of microacceleration at the point of installation. The sensor experiments have been conducted during shuttle docking and undocking, when low-frequency microaccelerations on the ISS were significant. The microaccelerations have been calculated using measurement data of the MAMS low-frequency accelerometer installed in the Lab module and the telemetry data on the ISS rotational motion. This has made it possible to convert the MAMS measurement data to the DAKON-M convection sensor installation point. A comparison of sensor readings with calculated microaccelerations has revealed fairly good agreement between them.

Selective modal control for vibration reduction in flexible structures

The design of a controller for selective reduction of vibrations in flexible low-damped structures is presented. The objective of the active feedback control law is to increase damping of selected modes only, in frequency regions where a disturbance is likely to produce largest effect. Moreover, the stabilizing controller is required to be band-pass, in order to filter out high-frequency sensor noise and low-frequency accelerometer drift, and stable to increase robustness to uncertain parameters. The control design is based on the Inverse Optimal Design approach, through the solution of a matrix Stein equation, resulting in the solution of an optimal H∞ control problem. A grey-box identification approach of the authors is employed for obtaining the model from experimental data or from detailed Finite Element Model (FEM) simulators. The problem of optimal actuator/sensor location is also addressed. Detailed simulation results are provided to show the effectiveness of the strategy.

Design and Analysis of MEMS Comb Drive Capacitive Accelerometer for SHM and Seismic Applications

Abstract This work presents the design of a MEMS accelerometer that is specifically intended for Structural Health Monitoring (SHM) applications where sensing low frequency low amplitude accelerations with high resolution is essential. The surface micromachined comb drive capacitance accelerometer structure has been considered in this design. The simulation experiments conducted on these devices using IntelliSuite MEMS design tool show that it has excellent displacement sensitivity of 21.39 μm/g, a capacitive sensitivity of 1.22 pF/g and voltage sensitivity of 1783 mV/g/V when it is designed to measure 0–0.1 g. Further, it is seen that it has a very low noise floor of 1.32 μg/√Hz and therefore high resolution. Since the accelerations can be as low as 0.04 g in SHM applications, excellent resolution is the primary goal in this design. Further, one more sensor specifically meant for strong motion seismic application has also been reported. This device has a bandwidth of 0–250 Hz and a noise floor of 5.612 μg/√Hz in addition to a sensor level voltage sensitivity of 97.9 mV/g/V. Finally, the comparison of these results with other similar devices reported in the past clearly illustrates the comparable performance of the present devices. Further, these devices, unlike the commercial low frequency accelerometers and other similar devices reported in the past can be fabricated by surface micromachining and CMOS compatible processes.

Correction of shaker flatness deviations in very low frequency primary accelerometer calibration

This paper describes the influence of a constant curvature of the shaker’s air bearing guidance on a low frequency primary accelerometer calibration. Based on the mathematical model, three different methods are developed that allow a quantitative evaluation of this disturbing effect and thus the correction of the resulting systematic deviation.All three methods are applied to the example of a primary low frequency accelerometer calibration performed at PTB, and the results are given in comparison to the original uncorrected magnitude of sensitivity results.

Dynamic calibration uncertainty of three-axis low frequency accelerometers

In this paper a methodology concerning the static and dynamic calibration of three-axis low-cost accelerometers in the (0 to 10) Hz frequency range is described, to be used for evaluation of existing civil infrastructures. <br /> Main and cross sensitivities of the accelerometers have been experimentally estimated by means of the matrix sensitivity concept. <br />The standard deviation of accelerations obtained along all three axes using different calibration data sets in repeatability conditions has been calculated and intended as dynamic calibration uncertainty. <br />The method has been validated by using reference accelerations accurately realized, in order to evaluate the residual bias error. <br />Static and dynamic calibration test benches have been used to realize reference accelerations. In order to create a three-axis acceleration field, a mechanical arm is used in static calibration; a rotary device is used in order to test the accelerometers in dynamic conditions. <br />According to the procedure described in this paper, a great improvement of the low cost accelerometers' metrological characterization could be achieved, especially in dynamic working conditions.

An experimental study on a new air-eddy current damper for application in low-frequency accelerometers

This paper discusses the new concept of a hybrid damper for application in low-frequency accelerometers. A hybrid damping structure is proposed in which an air damping principle and an eddy current damping principle are integrated into one damping structure. A prototype of the hybrid damper was fabricated and applied to a low-frequency accelerometer structure. A free-vibration test was conducted on the accelerometer structure in various damping configurations: air-damped, eddy-current-damped and hybrid-damped. The experimental results indicate that the proposed hybrid damper exhibits good damping performance in comparison with single-damped cases while still maintaining their original advantages, such as their low cost, simple structure and nonsealing, nonelectric system. The proposed hybrid damping system will be useful for other small machinery devices in real applications.