Minimum Detectable Acceleration Research Articles

Optical micro/nano fiber enabled accelerometer

Abstract Highly sensitive and miniaturized accelerometers play an important role in structural health, earthquakes, and body motion monitoring. Herein, an optical micro/nanofiber (MNF) enabled accelerometer is proposed. The structural parameters of the MNF accelerometer are optimized based on theoretical simulation. The accelerometer shows excellent linear relationship between displacement and force, and achieves a minimum detectable acceleration of 0.15 m/s2. For vibration sensing, the natural frequency of the sensor can be as high as 753 Hz.

Optical micro/nanofiber enabled wearable accelerometer

Highly sensitive and miniaturized accelerometers are of importance in many areas. Herein, an optical micro/nanofiber (MNF) enabled accelerometer is proposed. The structural parameters of the MNF accelerometer are optimized based on theoretical simulation. The accelerometer shows excellent linear relationship between displacement and force in a force range of 0–40 nN and achieves a minimum detectable acceleration of 0.15m/s2. For vibration sensing, the natural frequency of the sensor can be as high as 753 Hz; the vibrations of the tuning fork and human arm are recorded with high fidelity.

A real time digital vibration acceleration fiber sensing system based on a multi-carrier modulation/demodulation technique

A multi-longitudinal mode fiber laser sensor (MLMFLS) system based on digital modulation/demodulation technique for vibration acceleration detection is proposed. To the best of the authors’ knowledge, this is the first digital vibration acceleration demodulation system ever reported by a MLMFLS system. A few beat frequency signals (BFS) generated by the MLMFLS are used as signal carriers of applied vibration signals. Based on multi-channel digital down-conversion technique, the weak vibration signals modulated on the BFS are superposed by utilizing the digital universal software radio peripheral (USRP). The signal-to-noise ratio (SNR) of the output vibration signal is greatly enhanced. A spectral subtraction method is also utilized to improve the SNR of the demodulated vibration signal. The acceleration of the vibration signal is obtained after second order differential of the time domain vibration signal. By simply changing the position of window function of short-time Fourier transform, a real-time vibration frequency and acceleration sensing system is achieved. The measurement results demonstrated a minimum detectable acceleration of 0.03 g at vibration frequency of 1.0 Hz by the designed sensing system. It also has a simple structure, high signal-to-noise ratio and stability.

A High-Sensitivity MEMS Accelerometer Using a Sc0.8Al0.2N-Based Four Beam Structure.

In this paper, a high-sensitivity microelectromechanical system (MEMS) piezoelectric accelerometer based on a Scandium-doped Aluminum Nitride (ScAlN) thin film is proposed. The primary structure of this accelerometer is a silicon proof mass fixed by four piezoelectric cantilever beams. In order to enhance the sensitivity of the accelerometer, the Sc0.2Al0.8N piezoelectric film is used in the device. The transverse piezoelectric coefficient d31 of the Sc0.2Al0.8N piezoelectric film is measured by the cantilever beam method and found to be -4.7661 pC/N, which is approximately two to three times greater than that of a pure AlN film. To further enhance the sensitivity of the accelerometer, the top electrodes are divided into inner and outer electrodes; then, the four piezoelectric cantilever beams can achieve a series connection by these inner and outer electrodes. Subsequently, theoretical and finite element models are established to analyze the effectiveness of the above structure. After fabricating the device, the measurement results demonstrate that the resonant frequency of the device is 7.24 kHz and the operating frequency is 56 Hz to 2360 Hz. At a frequency of 480 Hz, the sensitivity, minimum detectable acceleration, and resolution of the device are 2.448 mV/g, 1 mg, and 1 mg, respectively. The linearity of the accelerometer is good for accelerations less than 2 g. The proposed piezoelectric MEMS accelerometer has demonstrated high sensitivity and linearity, making it suitable for accurately detecting low-frequency vibrations.

A flexible hinge accelerometer based on dual short fiber Bragg grating

Fiber Bragg gratings (FBGs) are a type of optical element with several advantages. In this study, we propose a vibration monitoring system consisting of a flexible hinge and a dual FBG. The novel design enables the dual short FBG to be tensile and compressed separately during vibration, while achieving sensitivity enhancement and self-temperature compensation. Through theoretical analysis and experiments, the resonant frequency was 150 Hz. The working frequency bandwidth of the accelerometer ranged from 10 to 100 Hz with a sensitivity of 1711 pm/g. The minimum resolution and detectable acceleration of the proposed system were 0.584 mg and 3 mg, respectively, which are significantly better than similar systems with a single FBG.

Miniature tri-axis accelerometer based on fiber optic Fabry-Pérot interferometer

A fiber optic accelerometer with a high sensitivity, low noise, and compact size is proposed for low-frequency acceleration sensing. The sensor is composed of a 20 mm diameter spherical outer frame and a three-dimensional spring-mass structure as the inertial sensing element. Three Fabry-Pérot interferometers (FPI) are formed between flat fiber facets and cubic mass surfaces to measure the FPI cavity length change caused by acceleration. The dynamic signal sensing of the designed accelerometer is performed, which shows a high acceleration sensitivity of 42.6 dB re rad/g with a working band of 1-80 Hz. An average minimum detectable acceleration of 4.5 µg/Hz1/2 can be obtained. The sensor features simple assembling, small size, light weight, and good consistency. Its transverse sensitivity is measured to be less than 3% (-30 dB) of the sensitive axis. The experimental result indicates that the proposed accelerometer has application potential in areas such as seismic wave detection and structural health monitoring.

Design and Experimental Assessment of Low-Noise Piezoelectric Microelectromechanical Systems Vibration Sensors.

The ubiquity of vibration sensors and accelerometers, as well as advances in microfabrication technologies, have led to the development of implantable devices for biomedical applications. This work describes a piezoelectric microelectromechanical systems accelerometer designed for potential use in auditory prostheses. The design includes an aluminum nitride bimorph beam with a silicon proof mass. Analytic models of the device sensitivity and noise are presented. These lead to a minimum detectable acceleration cost function for the sensor that can be used to optimize sensor designs more effectively than typical sensitivity maximizing or electrical noise minimizing approaches. A fabricated device with a 1 μm thick, 100 μm long, and 700 μm wide beam and a 400 μm thick, 63 μm long, and 740 μm wide proof mass is tested experimentally. Results indicate accurate modeling of the system sensitivity up to the first resonant frequency (1420 Hz). The low-frequency sensitivity of the device is 1.3 mV/g, and the input referred noise is 36.3 at 100 Hz and 11.8 at 1 kHz. The resulting minimum detectable acceleration at 100 Hz and 1 kHz is 28 and 9.1 , respectively. A brief explanation of the use of the validated cost function for sensor design is provided, as well as an example comparing the piezoelectric sensor design to another from the literature. It is concluded that a traditional single-resonance design cannot compete with the performance of acoustic sensors; therefore, novel device designs must be considered for implantable auditory prosthesis applications.

A Case Study on Fiber Optic Interferometric Seafloor Seismic and Tsunami Monitoring System in South China Sea

A seafloor seismic and tsunami monitoring system based on fiber optic interferometric technology was developed and installed in the nearby waters at the Chinese State Oceanic Administration's (SOA) Wuchang (Hainan Province, China) monitoring site. The developed tricomponent fiber optic interferometric seismometer has a sensitivity of 57 dB (re: 0 dB = 1 rad/g), within the operation frequency range of 0.005-50 Hz, and a minimum detectable acceleration of 43.4 ng/√(Hz); while the fiber optic interferometric water-level monitor has an accuracy of ±1 cm, a measurement range of 0-110 m. The system has been operating continuously since its installation in October of 2017, and has been collecting data ever since during this long-term field trial. To date, there were 55 earthquakes with M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> 6.0+ in the Northeast Asia area, and 39 earthquakes were recorded by our system. As examples, the detailed measurement results of two M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> 6.0+ earthquakes in Indonesia are given.

Fiber Optic Dual-Ring Michelson Interferometer-Based Detection Scheme for the Measurement of Dynamic Signals

A fiber optic dual-ring Michelson interferometer (DRMI) based detection scheme for the measurement of dynamic signals is proposed and experimentally demonstrated. The fiber optic sensor is a single mode fiber between two broadband fiber Bragg gratings (FBGs) with different center wavelengths. The two FBGs are connected to two output ports of a 3 × 3 coupler to compose a DRMI. High responsivity and wide frequency response range can be achieved at the same time. The scheme has high reliability, in which the undesirable external perturbation applied to interferometric arms is removed. A DRMI-based vibration sensor and a DRMI-based acoustic sensor are fabricated and experimentally investigated. For the DRMI-based vibration sensor, a responsivity of minimum detectable acceleration is 54 μg/√Hz at 300 Hz. The 12.8 rad/g is obtained, and the resonant frequency is 825 Hz. The acoustic sensor is used to detect signals in the frequency range of 0.5-19 kHz. The detection scheme has properties of wide frequency response range, high responsivity, and high reliability.

Design and Analysis of a Novel Dual FBG Accelerometer Based on Lantern Shape Metallic Shells

A novel dual FBG (DFBG) accelerometer based on lantern shape metallic shells is designed and analyzed. The DFBG accelerometer is based on the push-pull structure, which is used to eliminate common noises and disturbances. The axial size of the DFBG accelerometer is shortened by special combination of the mass and the elastic shells. The size of the optimized DFBG accelerometer is only 24 mm×24 mm×24 mm. Vibration trial results show that the average acceleration sensitivity is about 9.4 pm/g between 30 and 300 Hz, the resonant frequency is about 1175 Hz, the orthogonal crosstalk beyond 100 Hz is -20.6 dB, and the background phase noise is -70 dB re rad/√(Hz) for interferometric detection method, which corresponds to a minimum detectable acceleration 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> g. This DFBG accelerometer has great superiority in composing small 3-D FBG accelerometers and ultra-large scale vector sensor arrays.

A Fiber-Optic Interferometric Tri-Component Geophone for Ocean Floor Seismic Monitoring.

For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 Hz to 150 Hz for acceleration detection, employing a phase generated carrier demodulation scheme, with a responsivity above 50 dB re rad/g for the whole frequency range. The transverse suppression ratio is about 30 dB. The system noise at low frequency originated mainly from the 1/f fluctuation, with an average system noise level −123.55 ranging from 0 Hz to 500 Hz. The minimum detectable acceleration is about 2 , and the dynamic range is above 116 dB.

Design and application of fiber Bragg grating (FBG) geophone for higher sensitivity and wider frequency range

The fiber Bragg grating geophone sensor with higher sensitivity and wider frequency range was reported. The methods to increase the sensitivity of the FBG cantilever sensor were presented. The acceleration sensitivity of the optimized FBG geophone is 220pm/g, and the resonant frequency can reach to 295Hz. The experiments show that the FBG geophone system has the minimum detectable acceleration of 1mm/s2. Some factual application examples of using this fiber Bragg grating geophone monitoring system for micro seismic monitoring in coal mine were presented.

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.

Fiber-optic accelerometer based on a modal interferometer using a thin-core fiber

A compact fiber-optic accelerometer based on a modal interferometer, which is fabricated by misaligned splicing of a short section of a thin-core fiber between two sections of a standard single-mode fiber, is demonstrated experimentally. A spectrum analysis method is used to detect an acceleration signal rapidly. The experimental results show that the thin-core fiber-based fiber-optic accelerometer has a minimum detectable acceleration of 3.3×10–3g (g – gravitational acceleration), and a wide frequency response range from 10 to 1200 Hz. Moreover, the proposed accelerometer exhibits the advantages of low cost, simple structure and easy fabrication.

Fiber optic 3-component seismometer

An all-metal 3-component optical fiber seismometer was proposed and experimentally demonstrated. The theoretical analysis was given based on the electro-mechanical theory. Calibration results showed that the axis sensitivity was about 41 dB (re: 0 dB=1 rad/g) with a fluctuation ±2 dB in the frequency bandwidth of 5 Hz–400 Hz. A transverse sensitivity of about −40 dB was achieved. The fluctuation of the acceleration sensitivity for the three accelerometers in the seismometer was within ±2.5 dB. The minimum phase demodulation detection accuracy of the phase-generated carrier (PGC) was 10−5 rad/√Hz, and the minimum detectable acceleration was calculated to be 90 ng/√Hz.

All-Metal Optical Fiber Accelerometer With Low Transverse Sensitivity for Seismic Monitoring

An all-metal double metal diaphragm-based optical fiber accelerometer with low transverse sensitivity is proposed and experimentally demonstrated. The theoretical analysis is given based on the electro-mechanical theory. Finite element modal analysis shows that the proposed accelerometer has low transverse sensitivity. Calibration results show that axis responsivity is 41 dB (re: 0 dB = 1 rad/g) with a fluctuation ±2 dB in frequency bandwidth of 5-400 Hz. The transverse sensitivity is ~ 3 dB (re: 0 dB = 1 rad/g) with a fluctuation ±1.5 dB. A transverse sensitivity of about -40 dB is achieved. The fluctuation of the acceleration responsivity for the three accelerometers is within ±2.5 dB, which shows good consistency of the proposed accelerometer. The minimum phase demodulation detection accuracy of the phase-generated carrier is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> rad/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , and the minimum detectable acceleration can be 90 ng/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> theoretically. With an all-metal structure, the proposed accelerometer is expected to improve the reliability of long-term use in harsh environment. These desirable features show that the proposed optical fiber accelerometer is promising for seismic wave monitoring in oil and gas exploration.

Deep-well seismic monitoring based on fiber laser seismometer

We present a downhole seismic monitoring system and the field test results using a fiber laser seismometer (FLS). The distributed feedback fiber laser is used as the sensing element of the seismometer. Using the interferometric demodulation system, a minimum detectable acceleration of ~ng is achieved. The FLS is installed in a 400-m-depth well in Puer city, Yunnan Province. A micro-earthquake (M=1.2) in Puer area is detected. Compared with the existing underground electrical seismometer, FLS shows a higher signal-to-noise ratio and good reliability, which indicates that the FLS provides a new approach to deep-well seismic monitoring.

Design and analysis of an intensity modulated micro-opto-electro-mechanical accelerometer based on nonuniform cantilever beam proof mass

Micro-opto-electro-mechanical (MOEM) accelerometers using principle of optical coupling between two waveguide structures is proposed. It consists of an antiresonant reflecting optical waveguide structure combined with a cantilever beam. Under acceleration, the output waveguide optical power changes, which is a function of acceleration. The mathematical model of the mechanical sensing element in terms of proof mass, damping, and spring constant is formulated. Here, different aspects such as beam deflection, bending stress, and breakdown acceleration are incorporated into the formulation. Based on the analysis, the optimum mechanical structure for intensity modulated MOEM accelerometers are designed. We report for a typical uniform cantiliver beam of type I (3 mm×3 mm×0.38 µm) accelerometer, mechanical sensitivity of 0.15 µm/g, minimum detectable acceleration of 4.7 µg/ at an optimum power of 500 µW, range of ±25 g, a bandwidth of 1.59 kHz, breakdown acceleration of 5.1×104 g and cross-axis sensitivity of 0.001%. The results in the case of nonuinform beam cantiliver accelerations are sensitivity of 2.15 µm/g, minimum detectable acceleration of 0.27 µg/ range of ±1.8 g, bandwidth of 0.411 kHz, breakdown acceleration of 2987 g and cross-axis sensitivity of 0.001%.

Vibration monitoring in electrical engines using an in-line fiber etalon

In this work a new scheme for condition monitoring of electrical engines using a fiber optic sensor is proposed. The in-line fiber etalon scheme, specifically designed for the detection of damages in large electrical machines, provides high robustness and stability. In general, these large systems are characterized by a low speed operation, and when a new mechanical or electrical fault appears, it can be monitored through the vibration spectrum in the low frequency range, with a maximum bandwidth of 500 Hz. The proposed sensor has been optimized to achieve minimum detectable acceleration amplitude of 0.05 g in the frequency range of interest, although the preliminary scheme can be customized to the specific motion system. The vibration sensor has been tested using laboratory induction motor test-rigs, showing a particularly good performance both in the detection of magnetic and mechanical nature vibrations.

High performance torsional silicon accelerometer for automotive air bags

A high-sensitive torsional silicon accelerometer for automotive air bags systems has been developed using the wet etching of a single crystal silicon and silicon–glass bonding technique. The fabricated accelerometer yields a sensitivity of 100 mV/G, and a nonlinearity of 1.13% over a range of −22 G to 22 G. The minimum detectable acceleration measured by readout electronics is 25 mG.