Vibration Sensor System Research Articles

A Vibration Sensor System based on Distributed Feedback Fiber Lasers and Digital Phase Generated Carrier Demodulation

A vibration sensor system based on Distributed Feedback Fiber Lasers (DFB-FL) and digital Phase Generated Carrier (PGC) demodulation is presented in this paper. The external sound signals is collected by DFB-FL, and then the signal is gathered into the computer and is processed. The sensing of the system need no power supply, so the system can deal with unexpected disasters. Moreover, the system can be used for remote warning.

Balanced polarization maintaining fiber Sagnac interferometer vibration sensor

To achieve a nearly zero-delay operating point in a polarization-maintaining (PM) fiber Sagnac interferometer, two identical PM fibers were incorporated so that their two main axes were orthogonally coupled to each other. A simple fiber vibration sensor system was constructed with a light emitting diode and a balanced PM fiber Sagnac interferometer, in which one of the PM fibers was used as a sensing cable and the other as a reference cable. The vibration sensor was confirmed to be temperature-compensated and generated a phase shift per unit length and unit strain of the sensor of 4.7 milliradian/(m·με) when mechanical vibrations with 1 kHz sinusoidal and triangular waves were stably observed under an input power of 10 μW.

Wavelength Division Multiplexing/Spectral Amplitude Coding Applications in Fiber Vibration Sensor Systems

This paper presents a wavelength division multiplexing/spectral amplitude coding system with optical code-division multiple-access, for applications using fiber vibration sensors. The device makes use of fiber Bragg grating (FBG) etching on optical fibers to provide encoding/decoding functionality. According to the orthogonal properties of spectral amplitude coding (SAC) using m-sequence code, the encoding- decoding devices that employ FBG filters provide a considerable reduction in multiple access interference in optical code division multiple access systems. The proposed fiber vibration sensor located between the encoder and optical circulator enables the measurement of multiple points. Experimental results reveal that the proposed sensor detects a variety of vibrational signals.

VCSEL-Based Tilted Fiber Grating Vibration Sensing System

A fiber-optic vibration sensing system that uses a tilted fiber Bragg grating (TFBG) and a vertical-cavity surface-emitting laser (VCSEL) has been demonstrated. The backward-propagating low-order cladding modes excited by the TFBG can be effectively recoupled to the fiber core via a lateral-offset-splice upstream the TFBG and the amount of recoupling varies strongly with fiber curvature, providing the sensing mechanism. VCSEL with matched wavelength enables the recoupling to work at a high power level and an improved optical signal-to-noise ratio better than 40 dB is achieved. Meanwhile, VCSEL provides a high-speed continuous wavelength tuning over 1 ~ 2 nm which perfectly covers the strongest recoupling band, making the demodulation filter unnecessary. Dynamic vibration measurement up to 200 Hz has been achieved via cost-effective normalized power detection.

Fiber Bragg grating vibration-sensing system, insensitive to Bragg wavelength and employing fiber ring laser

A fiber Bragg grating (FBG) vibration-sensing system employing a fiber ring laser utilizing an FBG sensor as the ring cavity mirror was designed and developed herein. The fiber ring laser emitted lasing light at the Bragg wavelength of the FBG sensor, and the intensity of the lasing light varied with vibrations applied to the FBG sensor. Experiments demonstrated that this system could detect, with good sensitivity, vibrations over a broad band, ranging from just a few hertz up to ultrasound. This sensing system should be able to detect vibrations regardless of both the strain and temperature applied to the FBG sensor.

Distributed optical fiber perturbation sensing system based on Mach-Zehnder interferometer

A novel distributed optical fiber vibrationsensing system based on Mach-Zehnder interferometer has been designed and experimentally demonstrated. Firstly, the principle of Mach-Zehnder optical path interferometer technique is clarified. The output of the Mach-Zehnder interferometer is proportional to the phase shift induced by the perturbation. Secondly, the system consists of the laser diode (LD) as the light source, fiber, Mach-Zehnder optical interferometers as the sensing units, a 1×N star fiber-optic coupler, an N×1 fiber-optic coupler, a photodiode (PD) detector, and a computer used in signal processing. The entire monitoring region of this system is divided into several small zones, and each small monitoring zone is independent from each other. All of the small monitoring zones have their own sensing unit, which is defined by Mach-Zehnder optical interferometer. A series of sensing units are connected by the star fiber-optic couplers to form a whole sensing net. Thirdly, signal-processing techniques are subsequently used to calculate the phase shift to estimate whether intruders appear. The sensing system is able to locate the vibration signal simultaneously, including multiple vibrations at different positions, by employing the time-division multiplexed (TDM) technique. Finally, the operation performance of the proposed system is tested in the experiment lab with the conditions as follows: the number of the sensing units is 3, the length of the sensing fiber is 50 m, and the wavelength of the light diode is 1550 nm. Based on these investigations, the fiber surrounding alert system is achieved. We have experimentally demonstrated that the sensing system can measure both the frequency and position of the vibration in real time, with a spatial positional resolution better than 50 m in an area of 1 km2.

스마트 구조물의 동시다점 진동 취득용 안정화된 광섬유 브래그 격자 센서 시스템의 개발

For the application of structural health monitoring such as AE detection, a stabilized FBG sensor system with wide dynamic range was proposed. A tunable Fabry-Perot filter with narrow free spectral range(FSR) was used to simplify the multiplexing demodulator for FBG vibration sensors. Stabilization controlling system was also developed for the maintenance of maximum sensitivity of the sensors. In order to verify the performance of the proposed FBG vibration sensor system, we measured sensitivity, and the system showed the average sensitivity of 256 . Finally, multi-points vibration tests using in-line FBG sensors were conducted to validate the multiplexing performance of the FBG system.က€

Vertical Seismic Prospecting System Using Super Elastic Alloy

For tunneling, it is very important to understand the characteristic of the-rock around the tunnel. A new method of rock property investigation by using a compact vertical seismic prospecting system is proposed. This system consists of a probe attached vibration sensor, computer and trigger system. A superelastic alloy plate is used to press the probe flexibly against borehole surface.

Detecting impact damage in a composite material with an optical fibre vibration sensor system

This paper proposes a vibration monitoring system for detecting damage in a material. The system consists of an intensity-based fibre-optic vibration sensor, a fast Fourier transform pre-processing stage and a neural network. The response of the vibration sensor to sinusoidal acceleration is compared with that of a piezoelectric accelerometer. The vibration sensor was fixed to carbon-fibre composite panels and its response to acoustic transients was investigated. The system was trained to distinguish between the sensor responses to dropping a ball bearing on undamaged panels and panels with various levels of either real or simulated impact damage. The trained networks were capable of identifying previously unseen examples of these types of vibration sensor signals. Two types of network were compared, back- propagation and learning vector quantization.

Extrinsic Fabry–Perot interferometer vibration and acoustic sensor systems for airport ground traffic monitoring

The authors describe new fibre optic vibrational and acoustic sensor systems developed for airport ground traffic monitoring. The theoretical background of the extrinsic Fabry–Perot interferometer (EFPI) sensors is derived, and results of laboratory experiments as well as initial field tests in an experimental surface movement guidance and control system (ESMGCS) at the Braunschweig airport are reported.

Simple intensity type fiber optic vibration sensors and sensor systems

Research is continuing on the development of simple intensity type fiber optic vibration sensors suitable for use in hostile environments, such as automotive and aircraft engine cavities. The transduction element consists of a single or a pair of optical fibers mounted on a cantilever reed. The intensity of the optical output signal is directly proportional to the reed displacement and, therefore, to acceleration at frequencies well below the reed fundamental. Using readily available materials an operating temperature range of −40 ° to +225 °C has been achieved. In addition, by employing simple multiplexing techniques, small groups of these sensors may be addressed with a single optical source and/or detector. The basic design of the sensors and the results of extensive laboratory tests are presented in detail. [Work supported in part by NASA.]

The effect of environmental acoustic noise on optical fibre based velocity and vibration sensor systems

Interferometric fibre optic sensors are increasingly finding applications 'in the field'. Examples are provided by the use of fibre-based laser Doppler velocimetry (LDV) systems for wind tunnels and by laser vibrometry systems used for example in the monitoring of machine tool wear. Both the wind tunnel, and the factory floor are harsh environments for interferometric sensors. In particular the pick-up of acoustic noise from the air or from vibrating surfaces is a potentially serious problem, broadening and distorting the signal spectrum. A new broadening mechanism, called environmental noise broadening, is discussed and the magnitude of this effect is estimated for typical LDV systems. For flow velocity measurements in wind tunnels, this broadening leads to an overestimate of the turbulence intensity which is more serious for low-speed flows. The statistical formalism introduced here is applicable to any type of fibre-linked extrinsic interferometric sensor.