Fiber Vibration Research Articles

Polarization-Interference-Based Fiber Vibration Sensor Incorporating Polarization-Diversity Loop Structure

We demonstrate a polarization-interference-based fiber vibration sensor by incorporating a Sagnac interferometer based on a polarization-diversity loop structure composed of a polarization beam splitter, polarization-maintaining photonic crystal fiber, and polarization controllers. A laser diode and a photodetector were used to implement a high-speed intensity-based sensor. By using a piezoelectric transducer, we performed single frequency vibration measurement over 1-3000 Hz, resulting in a cutoff frequency of ~2100 Hz, a phase shift per unit length and unit strain of ~3.48 mrad/(με · m), and a minimum detectable strain perturbation of ~0.46 nε/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 2000 Hz. Naturally, damped vibration response was also investigated using a metal cantilever, and the relationship between the sensor output and applied impulse was analyzed.

A conceptual design of spacers with hairy structures for membrane processes

Abstract The development of membrane technology requires spacers that can significantly enhance the mass-transfer rate while avoiding a severe pressure drop across the membrane module. A potential solution to this challenge is to introduce some flexible and dynamic structures into the spacer mesh. The current work was motivated to explore a conceptual design of spacers with hairy structures. The hairy structures were simulated using highly flexible nylon fibers that were fixed on a well-designed framework. The effects of fiber asymmetry and spacing on the vibrations were discussed in terms of the observations via a high speed camera. A variety of spacer prototypes were employed in a forward osmosis process to examine the performance of the hairy structures. The experimental results indicate that fiber vibrations could have a great impact on the mass transfer in the vicinity of the membrane surface and enhance the filtration flux (up to ~20%). This fundamental study not only provides insight into the mechanisms underlying the complex fiber-flow interactions but also charts the direction for future hairy spacer design.

Long-Range Distributed Fiber Vibration Sensor Using an Asymmetric Dual Mach–Zehnder Interferometers

An asymmetric dual Mach–Zehnder interferometry (ADMZI) design is proposed to achieve distributed fiber vibration sensing at long range. In this structure, we utilized two distributed feedback laser beams and dense wavelength-division multiplexing to significantly reduce the influence of Rayleigh backscattering noise, which will seriously deteriorate the signal noise ratio (SNR) in traditional dual Mach–Zehnder interferometer (DMZI) sensor. At the sensing length of 61 km, the SNR achieved using the ADMZI design is 20 dB higher than that using the DMZI design. Using a positioning algorithm based on the time–frequency analysis, the positioning mean square error can reach 52.5 m at this distance.

基于3×3迈克耳孙干涉仪的分布式光纤振动传感器

A distributed fiber vibration sensor based on 3 * 3 Michelson interferometer is proposed, and a 3 * 3 interferometer is used to build the structure of a phase sensitive optical time domain reflectometer (phi-OTDR) based on homodyne coherent detection. With transfer matrix phase demodulation algorithm and through the basic parameters of the 3*3 interferometer transmission matrix, the corresponding relationship between differential phase and interferometer output light intensity is established. The simple and efficient software computing programs are used to demodulate the differential phase of Rayleigh scattering light in optical fiber, so as to realize the optical fiber distributed disturbance detection. The system is also used to detect the vibration along the fiber, and the experimental results show that the sensing system can accurately locate for the vibration and restore the frequencies of audio and radio frequency drivers, of which the effective sensing distance is 10 km.

具有温度补偿功能的光纤振动测量系统

具有温度补偿功能的光纤振动测量系统

Distributed fiber-optic vibration sensing based on phase extraction from time-gated digital OFDR.

A novel distributed fiber vibration sensing technique based on phase extraction from time-gated digital optical frequency domain reflectometry (TGD-OFDR) which can achieve quantitative vibration measurement with high spatial resolution and long measurement range is proposed. A 90 degree optical hybrid is used to extract phase information. By increasing frequency sweeping speed, the influence of environmental phase disturbance on TGD-OFDR is mitigated significantly, which makes phase extraction in our new scheme more reliable than that in conventional OFDR-based method, leading to the realization of long distance quantitative vibration measurement. By using the proposed technique, a distributed vibration sensor that has a measurement range of 40 km, a spatial resolution of 3.5 m, a measurable vibration frequency up to 600 Hz, and a minimal measurable vibration acceleration of 0.08g is demonstrated.

Angular dependence of screen speckle and fiber speckle of coupled output of nine high-power blue laser diodes through a multi-mode fiber

Angular dependence of speckle contrast of speckle pattern projected out of a multi-mode fiber connected to a high-power blue laser module is investigated. The laser module has nine high-power InGaN/GaN blue laser diodes arranged in a three-by-three array. Each of the arrayed laser diodes have slightly different incident angle to the fiber. We have successfully extracted the fine screen speckle pattern from the projected pattern mixed up with the coarse fiber speckle pattern by processing the measured data. It is found that the speckle contrast of the both screen and fiber speckles are larger around the center area where the guided-light component closest to the paraxial direction is projected. This is because the output of the center laser in the array is likely to couple into the paraxial mode more than the rest. Speckle contrast behaviors when applying the speckle reduction methods, fiber vibration, diffuser, and spinning diffuser are also investigated.

Development of a low-cost 3 × 3 coupler Mach–Zehnder interferometric optical fibre vibration sensor

In this paper, a low-cost 3 × 3 coupler Mach–Zehnder interferometric optical fibre vibration sensor is proposed. Unlike the traditional Mach–Zehnder interferometer with a strain free reference arm, two parallel optical fibres with different strain transfer sensitivities are adopted. With the proper demodulation algorithm, the time rate of change in strain can be computed from the light signal of the outputs of a 3 × 3 coupler. The proposed optical fibre vibration sensor is verified by experiment. The vibrating frequency spectrum of a two-layer metal frame is measured by both the proposed optical fibre vibration sensor and micro-electro-mechanical system (MEMS)-based accelerometers. It was found that the proposed vibration sensor is more sensitive compared to the MEMS-based accelerometer, unless it is located near a zero-strain region. Several proposed sensors can easily be multiplexed to minimise the overall cost.

Distributed Strain and Vibration Sensing System Based on Phase-Sensitive OTDR

A system based on phase-sensitive optical time domain reflectometry is proposed for simultaneously strain and vibration sensing. The strain of fiber is detected by comparing the patterns of signal for different laser frequencies, and the vibration of fiber is detected simultaneously from the signals for any certain laser frequency. During the measurement, frequencies of the probe optical pulses are modulated sequentially in ascending or descending order. Using the signals generated by optical pulses with the same frequency, the vibration of fiber is detected with fast response speed; using that with different frequencies, the strain of fiber is detected with high resolution. In our experiment, a sensing system with 2-m spatial resolution, up to 1-kHz frequency measurement range and 10- $\text{n}{{\varepsilon }}$ strain resolution is realized for a 9-km sensing fiber length.

A two-level detection algorithm for optical fiber vibration

Optical fiber vibration is detected by the coherent optical time domain reflection technique. In addition to the vibration signals, the reflected signals include clutters and noises, which lead to a high false alarm rate. The “cell averaging” constant false alarm rate algorithm has a high computing speed, but its detection performance will be declined in nonhomogeneous environments such as multiple targets. The “order statistics” constant false alarm rate algorithm has a distinct advantage in multiple target environments, but it has a lower computing speed. An intelligent two-level detection algorithm is presented based on “cell averaging” constant false alarm rate and “order statistics” constant false alarm rate which work in serial way, and the detection speed of “cell averaging” constant false alarm rate and performance of “order statistics” constant false alarm rate are conserved, respectively. Through the adaptive selection, the “cell averaging” is applied in homogeneous environments, and the two-level detection algorithm is employed in nonhomogeneous environments. Our Monte Carlo simulation results demonstrate that considering different signal noise ratios, the proposed algorithm gives better detection probability than that of “order statistics”.

Computational study of granular shear flows of dry flexible fibres using the discrete element method

In this study, shear flows of dry flexible fibres are numerically modelled using the discrete element method (DEM), and the effects of fibre properties on the flow behaviour and solid-phase stresses are explored. In the DEM simulations, a fibre is formed by connecting a number of spheres in a straight line using deformable and elastic bonds. The forces and moments induced by the bond deformation resist the relative normal, tangential, bending and torsional movements between two bonded spheres. The bond or deforming stiffness determines the flexibility of the fibres and the bond damping accounts for the energy dissipation in the fibre vibration. The simulation results show that elastically bonded fibres have smaller effective coefficients of restitution than rigidly connected fibres. Thus, smaller solid-phase stresses are obtained for flexible fibres, particularly with bond damping, compared with rigid fibres. Frictionless fibres tend to align with a small angle from the flow direction as the solid volume fraction increases, and fibre deformation is minimized due to the alignment. However, jamming, with a corresponding sharp stress increase, large fibre deformation and dense contact force network, occurs for fibres with friction at high solid volume fractions. It is also found that jamming is more prevalent in dense flows with larger fibre friction coefficient, rougher surface, larger stiffness and larger aspect ratio.

Study the effect of fiber-dia on the alongside dual-plastic optical fiber vibration sensor

An alongside dual-plastic optical fiber vibration sensor is designed based on the reflection intensity modulation and study the effect of transmitting fiber (TF) and receiving fiber (RF) diameter on the sensor response is studied. Three fibers of 0.75, 1 and 1.5 mm diameter are chosen with nine pair combinations for vibration measurement. From displacement response, it is observed that the sensitivity of the sensor increases as the diameter of the RF decreases and vice versa. The test results show that the frequency range increases when the RF diameter is less than the TF and vice versa. The resolution of the sensor also increases when the difference in diameters of the TF and RF decreases and vice versa. Moreover it is evident from the results that the dynamic range, range of frequency can be optimized by choosing the suitable diameter of the TF or RF as for the application.

Study on the algorithm of vibration source identification based on the optical fiber vibration pre-warning system

One of the key technologies for optical fiber vibration pre-warning system (OFVWS) refers to identifying the vibration source accurately from the detected vibration signals. Because of many kinds of vibration sources and complex geological structures, the implement of identifying vibration sources presents some interesting challenges which need to be overcome in order to achieve acceptable performance. This paper mainly conducts on the time domain and frequency domain analysis of the vibration signals detected by the OFVWS and establishes attribute feature models including an energy information entropy model to identify raindrop vibration source and a fundamental frequency model to distinguish the construction machine and train or car passing by. Test results show that the design and selection of the feature model are reasonable, and the rate of identification is good.

Ultra-weak FBG and its refractive index distribution in the drawing optical fiber.

For the online writing of ultra-weak fiber Bragg gratings (FBGs) in the drawing optical fibers, the effects of the intensity profile, pulse fluctuation and pulse width of the excimer laser, as well as the transverse and longitudinal vibrations of the optical fiber have been investigated. Firstly, using Lorentz-Loren equation, Gladstone-Dale mixing rule and continuity equation, we have derived the refractive index (RI) fluctuation along the optical fiber and the RI distribution in the FBG, they are linear with the gradient of longitudinal vibration velocity. Then, we have prepared huge amounts of ultra-weak FBGs in the non-moving optical fiber and obtained their reflection spectra, the measured reflection spectra shows that the intensity profile and pulse fluctuation of the excimer laser, as well as the transverse vibration of the optical fiber are little responsible for the inconsistency of ultra-weak FBGs. Finally, the effect of the longitudinal vibration of the optical fiber on the inconsistency of ultra-weak FBGs has been discussed, and the vibration equations of the drawing optical fiber are given in the appendix.

Protection System of Communication Line based on Distributed Interference Fiber Sensing Network

On the issue of security and protection of communication line, this study designed and realized a new distribut- ed fiber vibration sensing and warning system for hazardous events. Based on M-Z interference principle, the system real- ized the real-time detecting and accurate locating of the vibration signals by means of cross-correlation calculation of the fiber signals, restrained effectively the sensing signal noise and extracted accurately the vibration signals of various haz- ardous events with the methods of wavelet threshold shrinkage and Hilbert transform. In the meantime, the study pro- posed multi-dimensional features including wavelet decomposition, MFCC coefficients and time-domain envelope to de- scribe the vibration signals and established multi-level classifier models with BP neural network and SVM methods to re- alize the classification and recognition of various hazardous events. After the applications and experiments of the system on 7 hazardous events, we obtained experimental results of the locating accuracy of <100 meters and classifying accuracy rate of 94.35% on hazardous events, which verified the effectiveness of the study.

Finite Element Analysis of Anchor Impacting the Buried SOFC

It is imminent to establish an early-warning SOFC monitoring system for anchor damage, the gravest threat to the SOFC communication, while the key to build the monitoring system is to correctly grasp anchor the response law of embedded submarine cable caused by anchor impact; ANSYS/LS-DYNA is used to perform the finite element analysis of SOFC and make the length-shape variables differences between signal fiber and reference fiber caused by anchor impact clearly, besides, combining with the sensing model of distributed optical fiber vibration sensing system, the current wave is acquired, based on what the monitoring system warn the anchoring incidents near the submarine route, which is significant to guide the design of forecasting monitoring system of SOFC.

The Effect of Induced Vibration on Thermoplastic Composite System

Thermoplastic composite manufacturing is often difficult due to high viscosity of the matrix materials. Coupling a high level of mechanical properties with simple, low-cost processing technique is a difficult subject, but an important task for any state-of-the-art impregnation processes. In this paper, Thermoplastic Prepreg Fabrication Technology is utilized to prepare thermoplastic tapes and the technology's effect on strain energy absorption was investigated. The tape was prepared under three categories: first, with induced vibration and no fiber preheat (NV), second, without vibration and fiber preheat (HN) and last, with both fiber preheat and vibration (HV). For the purpose of comparison, all other variables such as pulling speed, fiber tension, fiber preheat and processing temperature were kept constant. The HV category showed improvement in the strain energy absorption by 10 and 23% when compared to HN and NV, respectively. In addition, HV had better wetting, fiber spread and dispersion. Fiber preheating is important as it worked well with vibration possibly due to good fiber spread on the HV category (widest tape). Also, HV had the least fiber volume fraction as it takes more matrix volume when exiting the die plate.

Collimator‐based sensor for remote vibration monitoring

ABSTRACTIntensity‐based fiber vibration sensor using optical collimators for remote vibration monitoring is investigated. The sensor is proposed for its rigidity and ability to be used in place of fiber Brags grating and interferometry sensor which are subjected to impairment in dynamic sensing due to their fragile nature. The result shows the proposed sensor having good linear response over the measured value and stability when tested over 1 h. The low frequency range of 0–180 Hz measured shows the suitability of the proposed sensor for remote vibration monitoring in bridge, electrical power generator, machines, and structures that exhibit low vibration. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:38–41, 2015

A Design Technique and Structure for Optical Fibre Vibration Sensor

This paper reviewed techniques of vibration sensors, studied structure and working principle of phase modulated optical fiber vibration sensor, and designed a new structure of non-contact optical vibration sensor. Use this structure, expect accuracy of 0.1um can be obtained in the range of 1mm. At the same time, this system is simple, anti-interference ability, high reliability and ease of practical.

Improved configuration and reduction of phase noise in a narrow linewidth ultrawideband optical RF source.

In this Letter, we report on the improved configuration of a widely tunable optical RF generation system, particularly for the generation of low-frequency RF, as well as the reduction of phase noise in that same system. Using an amplitude modulator, a simplified system design was demonstrated with fewer components and improved phase noise performance, especially at RF frequencies below ∼36 GHz. Excess phase noise due to acoustic vibrations of the optical fibers was also successfully eliminated by mechanical isolation. A minimum phase noise of -124 dBc/Hz at 10 kHz offset was demonstrated at 4 GHz.