Fiber-optic Acoustic Sensor Research Articles

Use of 2D In2Se3 Single Crystal as a Diaphragm Material for Fabry-Perot Fiber Optic Acoustic Sensors

Use of 2D In₂Se₃ Single Crystal as a Diaphragm Material for Fabry-Perot Fiber Optic Acoustic Sensors

Miniature Fiber Optic Acoustic Pressure Sensors With Air-Backed Graphene Diaphragms.

Graphene has been known to possess exceptional mechanical properties, including its extremely high Young's modulus and atomic layer thickness. Although there are several reported fiber optic pressure sensors using graphene film, a key question that is not well understood is how the suspended graphene film interacts with the backing air cavity and affects the sensor performance. Based on our previous analytical model, we will show that the sensor performance suffers due to the significantly reduced mechanical sensitivity by the backing cavity. To remedy this limitation, we will, through experimental and numerical methods, investigate two approaches to enhance the sensitivity of fiber optic acoustic pressure sensors using graphene film. First, a graphene-silver composite diaphragm is used to enhance the optical sensitivity by increasing the reflectivity. Compared with a sensor with pure graphene diaphragm, graphene-silver composite can enhance the sensitivity by threefold, while the mechanical sensitivity is largely unchanged. Second, a fiber optic sensor is developed with enlarged backing air volume through the gap between an optical fiber and a silica capillary tube. Experimental results show that the mechanical sensitivity is increased by 10× from the case where the gap side space is filled. For both approaches, signal-to-noise ratio (SNR) is improved due to the enhanced sensitivity, and COMSOL Thermoviscous acoustics simulation compares well with the experimental results. This study is expected to not only enhance the understanding of fluid-structural interaction in sensor design but also benefit various applications requiring high-performance miniature acoustic sensors.

Performance analysis of distributed optical fiber acoustic sensors based on φ-OTDR.

The performance of distributed optical fiber acoustic sensor as a function of parameters such as the linewidth of the laser, the probe pulse width, and the amplitude and frequency of perturbation is experimentally studied. The aim of this study is to experimentally confirm the outcome of the simulation results obtained previously. It is shown that the experimental and simulation results are in good agreement, and the precision of the sensing system depends on the pulse width and linewidth of the probe pulse, as well as the frequency and amplitude of the perturbation. It is shown that the sensing precision of the system can be enhanced by reducing the width of the probe pulse while increasing the linewidth of the laser.

Distributed acoustic sensor based on improved minimum control recursive average algorithm

Abstract An optical fiber acoustic sensor based on the combination of generalized cross-correlation and improved minimum control recursive average algorithms is proposed. The sensing system consists of a double Sagnac interference structure that picks up acoustic signals along the sensing fiber. The improved minimum control recursive average algorithm is used to preprocess the acquired signal to improve the signal-to-noise ratio, then the time-delay information is obtained through the correlation operation on the processed signal, and the acoustic source is located through the time delay information. Experiments show that under the condition of high signal-to-noise ratio of the acquired signal, the accuracy of acoustic source localization can be improved.

Miniature fiber optic acoustic pressure sensors with air-backed graphene diaphragms

Graphene has been known to possess exceptional mechanical properties, including its extremely high Young’s modulus and atomic-layer thickness. Although there are several reported fiber optic pressure sensors using a graphene film, a key question that is not well understood is how the suspended graphene film interacts with the backing air cavity and affects sensor performance. Based on our previously analytical model, we will show that sensor performance suffers due to the significantly reduced mechanical sensitivity by the backing cavity. To remedy this limitation, we will, through experimental and numerical methods, investigate two approaches to enhance the sensitivity of fiber optic acoustic pressure sensors using the graphene film. First, a graphene-silver composite diaphragm is used to enhance the optical sensitivity by increasing the reflectivity. Compared with a sensor with pure graphene diaphragm, a graphene-silver composite can enhance the sensitivity by three-fold, while the mechanical sensitivity is largely unchanged. Second, a fiber optic sensor is developed with enlarged backing air volume through the gap between an optical fiber and a silica capillary tube. Experimental results show that the mechanical sensitivity is increased by 10xfrom the case where the gap side space is filled.

On-Line Registration of Damages in Composite Materials with Fiber-Optic Acoustic Emission Sensors

This paper presents the results of the analysis of acoustic emission signals registered by using fiber-optic sensors during the propagation of ultrasonic waves in a polymer composite material. Fiber-optical sensors for acoustic emission were constructed according to the scheme of an adaptive holographic interferometer. Unlike piezoelectric sensors, fiber-optic sensors are distributed type sensors. This imposes certain features on the detection of signals in plates in which fiber-optic sensors are embedded. It is established that the difference of the spectrum of acoustic emission signals is registered in different directions of wave propagation. The local maximums of the spectrum are determined by the mode of wave propagation in the plate in different directions and the location of fiber-optic sensors.

Simulation and experimental investigation about interferometric optical fiber acoustic sensor for sensitivity enhancement

In this paper, the results of simulation and experimental investigation of interferometric optical fiber acoustic sensing are primarily presented, and the main area of interest is studying the different algorithms for enhancement of sensor sensitivity. In fact, when light propagates through optical fiber, in a Michelson interferometer, the phase of light changes due to effect of external perturbation as acoustic wave on optical path length and this phase change is detected by demodulation algorithm. It is strived to present the Phase Generated Carrier (PGC) demodulation algorithm based on Differential-Cross-Multiplying (DCM), Arctangentfunction (ATAN) and ATAN based on Coordinate Rotation Digital Computer CORDIC algorithm. Simulation results reveal that PGC demodulation method based on ATAN CORDIC algorithm has better result (signal to noise ratio) than DCM and ATAN without using CORDIC algorithm. On this account, PGC demodulation algorithm based on ATAN method with CORDIC algorithm is applied in the experimental investigation due to simulation results and simpler digital implementation on Field Programmable Gate Array (FPGA). Moreover, acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies. The sensitivity of digital circuit is 5μradHz-0.5 and the minimum detectable phase is 50μrad Acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies, and consequently, the system allows detecting the sinusoidal acoustic wave with different frequencies. It is also detected acoustic frequency by measurement of the reflected optical power. Moreover, in this part, it is packaged sensing arm of interferometer with polymer material (polyurethane) for investigation the effect of polymer on sensitivity enhancement of sensor. It is observed with applying of acoustic wave, the reflected optical power decreases and this reduction is more, when sensing arm is packaged with polymer.

Localization of partial discharge in transformer oil using Fabry-Pérot optical fiber sensor array

Partial discharge is the main reason for insulation deterioration and failure of high voltage electrical asset. Thus, the online detection and localization of partial discharge can provide the information on the equipment degradation characteristics, and moreover, is of great value for improving the safe operation of the power grid and the developing of optimal maintenance. Accounting for the good sensitivity, the high immunity to electromagnetic interference, the compact size with outstanding insulation level, the Fabry-Perot optical fiber sensor is attracting increasing attention as a promising way for online acoustic partial discharge localization. In this study, the partial discharge localization in the transformer oil is realized by an ultrasonic detection system, which is consisting of 2×2 Fabry-Perot optical fiber sensor array with steered response power algorithm. In general, the Fabry-Perot optical fiber acoustic sensor array shows good direction sharpness, and achieves accurate localization. This detection and localization system is further applied to a 35 kV transformer single-phase winding and verified with partial discharges on the outer winding.

Speech detection enhancement in optical fiber acoustic sensor via adaptive threshold function

Abstract In this paper, we demonstrate a novel speech enhancement method for improving detection performance of optical fiber acoustic sensor. The proposed method is based on a novel threshold function with adaptive threshold for wavelet analysis. For a certain speech signal, the adaptive threshold in the function is set lower in speech presence region and higher in speech absence region, which ensures more speech details preserved as well as noise reduced. At the same time, the new threshold function guarantees the continuity and no deviation of speech signal. Experimental results show that the proposed method is more suitable for optical fiber acoustic sensor to extract speech signal compared with universal wavelet packet method, and it improves speech quality significantly. The clear speech can be obtained via the optical fiber acoustic sensor even if work surroundings of sensing unit is noisy.

Optical fiber acoustic sensors

Optical fiber acoustic sensors are a kind of acoustic sensors that use optical fibers as light-propagating media or detection units. Compared to traditional electro-acoustic sensors, it features high sensitivity, broad-band frequency response, anti-electromagnetic interference etc, thus very promising for national security, industrial non-destructive testing, medical diagnostics, consumer electronics etc. Optical fiber acoustic sensors are classified, in terms of the coupling mode between acoustic field and light, as indirect and direct coupling types. The former presents some problems such as uneven frequency response, narrower bandwidth, and smaller dynamic range due to the frequency response features of the acoustic coupling materials, while the latter has overcome these shortcomings and thus possesses broad development potential.

Ultrathin graphene diaphragm-based extrinsic Fabry-Perot interferometer for ultra-wideband fiber optic acoustic sensing.

An ultra-wideband fiber optic acoustic sensor based on graphene diaphragm with a thickness of 10nm has been proposed and experimentally demonstrated. The two reflectors of the extrinsic Fabry-Perot interferometer is consist of fiber endface and graphene diaphragm, and the cavity is like a horn-shape. The radius of the effective area of the ultrathin graphene diaphragm is 1mm. Attributed to the strong van der Waals force between the diaphragm and the ceramic ferrule, the sensor head can be applied not only in the air but also underwater. Experimental results illustrate that ultra-wideband frequency response is from 5Hz to 0.8MHz, covering the range from infrasound to ultrasound. The noise-limited minimum detectable pressure level of 0.77Pa/Hz1/2@5Hz and 33.97μPa/Hz1/2@10kHz can be achieved, and the applied sound pressure is 114dB and 65.8dB, respectively. The fiber optic acoustic sensor may have a great potential in seismic wave monitoring, photoacoustic spectroscopy and photoacoustic imaging application due to its compact structure, simple manufacturing, and low cost.

High-fidelity distributed fiber-optic acoustic sensor with fading noise suppressed and sub-meter spatial resolution.

In order to solve fading problem and realize sub-meter spatial resolution in DAS, this paper proposes a novel configuration of time-gated digital optical frequency domain reflectometry (TGD-OFDR) based on optical intensity modulator (IM). IM has a large modulation bandwidth and the positive and negative harmonics can be fully used to suppress fading while the spatial resolution remains unchanged. In experiments, with fading suppressed, the spatial resolution of DAS is 0.8 m and the strain resolution is about 245.6 pε√Hz along the total 9.8-km sensing fiber. The response bandwidth of vibration is 5 kHz, only/limited by the fiber length.

Phase Interrogation of Diaphragm-Based Optical Fiber Acoustic Sensor Assisted by Wavelength-Scanned Spectral Coding

In this paper, we proposed a phase interrogation method for diaphragm-based interferometric optical fiber acoustic sensor based on the spectral coding process. The information of the sound wave is coded on the optical spectrum of the sensor head by wavelength scanning, which builds a map between time and wavelength. The acoustic signal can be reconstructed from the sound-encoded spectrum. The sound-induced phase variation of the sensor can be interrogated by comparing the sound-encoded spectrum with the initial spectrum curve, which can be acquired from the sinusoidal fitting method. In order to eliminate the phase ambiguity, a diaphragm-based Michelson interferometer is set up using a commercial 3 × 3 fiber coupler and two synchronized channels with 120° phase difference are employed for the interrogation. Experimental results indicate that the proposed method can provide stable demodulation results under random environmental fluctuations, while the commonly used edge filtering technique shows fluctuations of more than 10 dB under the same condition.

Composite Materials Monitoring by Fiber Optic Sensors

The paper presents methods for testing the composite materials using two types of fiber-optic sensors as well as a method for using radiation of the vertical-cavity emitting laser radiation (VCSEL) for checking the material deformation and its performances. The deformation checking sensor is a fiber Bragg grating (FBG) with a spectrum width of 50 pm, which is interrogated by the VCSEL. A new algorithm for modulating the laser diode current is proposed for the FBG interrogation providing a dynamic range of at least 3 nm. A new interrogation method of impulse Fabry-Perot interferometer was proposed. The interrogation method was applied for a fiber-optic acoustic emission sensor manufacturing. The sensor was experimentally investigated by the impact of a 6 mm diameter steel ball and compared to a reference piezoelectric acoustic emission transducer.

Deformation control method of composite structural elements by fiber-optic acoustic emission sensor

Subject of Research.The paper presents the study of a graphite-epoxy composite plate strain detection possibility by the fiber-optic acoustic emission sensor mounted on its surface. Method. The proposed method consisted in additional low-frequency phase-generated carrier implementation in the impulse Fabry-Perot interferometer and its amplitude evaluation. The phase-generated carrier amplitude depends on the interferometer optical path difference, therefore, its value change can be used for the studied composite strain estimation. VCSEL with a wavelength of 1550 nm was used as a light source. The phase carrier was generated by current modulation of the light source that caused center wavelength shift of the VCSEL. Main Results. The low-frequency phase-generated carrier signal amplitude dependence on the interferometer optical path difference and wavelength shift of the light source were obtained. According to simulation results the sensitivity of the proposed method is 1.6 urad×ppm, 5.3 urad×ppm and 13.3 urad×ppm at different values of the coefficient Kd 30, 100 and 250 pm, respectively. Experimental study of the proposed method and results analysis were performed. According to experimental results, the accuracy of the proposed method was about 1´10–3% that corresponds to the sensor relative stretch of 10 me, while the accuracy of the market available fiber optic systems based on fiber Bragg grating sensors equals to 4 ppm. Practical Relevance.The proposed method can be used for strain detection of the graphite-epoxy composite constructions along with its acoustic emission control by one fiber-optic sensor.

基于多层石墨烯材料的光纤声波传感器

基于多层石墨烯材料的光纤声波传感器

Fiber-Optic Acoustic-Based Disturbance Prediction in Pipelines Using Deep Learning

The problem of detecting nonstationary disturbances in a pipeline is demonstrated using a predictive framework based on high spatial resolution fiber-optic acoustic sensors. We show that the root-mean-square (RMS) acoustic power is related to flow and density changes in the fluid. However, in practice, fluid parameters are not known at the resolution of the acoustics. In an experimental study, we trained long-short-term memory (LSTM) networks to exploit hidden patterns in an acoustic time series to predict the RMS acoustic power. We found LSTM perform efficiently and shows improvement over baseline neural network predictor, and its strength lies in discriminating sequential order from spatial input data. The system is verified on 25 m resolution fiber-optic acoustic data. Results show promise in predicting anomalous disturbances despite unknown pipe and fluid parameters..

Ultrafast laser ablation of silica optical fibers for fabrication of diaphragm/cantilever-based acoustic sensors

We present our recent progress in fiber optic acoustic sensors formed by using a Fabry–Perot (FP) interferometer with a silica diaphragm/cantilever on the tip of a single-mode fiber, fabricated by the femtosecond (fs) laser ablation technique. The directivity of an acoustic sensor with a silica diaphragm was improved by packaging the sensor head in a capillary tube coated with an acoustically absorbing wax film. The measurement results demonstrated a substantial increase in directivity with this packaging method. A cantilever beam diaphragm based FP tip was further investigated to improve the sensor performance. This sensor structure is insensitive to Q-point drift. In addition, the sensing frequency range can be flexibly controlled by designing the dimension of the cantilever beam, indicating the flexibility of sensor fabrication by fs laser micromachining.

Highly Sensitive Optical Fiber Curvature and Acoustic Sensor Based on Thin Core Ultralong Period Fiber Grating

A novel fiber sensor for curvature and acoustic wave measurement, which is based on a thin core ultralong period fiber grating (TC-ULPFG), has been proposed and experimentally demonstrated. By tracking the power variation of different resonant wavelength caused by TC-ULPFG, high curvature sensitivity of 97.77 dB/m–1 is achieved, to best of our knowledge, which is the highest than other structures at the same measurement range. Thus, the desired curvature property of the TC-ULPFG is used for acoustic measurement. The polyethylene terephthalate film is selected as a transducer, on which TC-ULPFG is tightly pasted. The acoustic pressure sensitivity of 1.89 V/Pa is two orders higher than other structures based on the diaphragm transducer, and the noise-limited minimum detectable pressure is 1.94 mPa/Hz1/2 at 200 Hz. In addition, the frequency fluctuations are nearly ±0.4 dB from 70 to 200 Hz and ±0.2 dB from 1 to 3 kHz. Therefore, the proposed optical fiber acoustic sensor has a flat frequency response at a relatively lower frequency. The TC-ULPFG shows many advantages, including high sensitivities of curvature, high acoustic pressure sensitivity, easy fabrication, simple structure, and low cost.

Phase Demodulation of Short-Cavity Fabry–Perot Interferometric Acoustic Sensors With Two Wavelengths

A phase interrogation method for a fiber-optic acoustic sensor based on a short-cavity extrinsic Fabry–Perot interferometer (EFPI) is proposed with two wavelengths. A multichannel tunable optical filter is employed, which selects out two monochromatic beams from the broadband interference spectrum of EFPI with fixed wavelength interval. The influence of the wavelength interval on the recovery of the phase signal has been theoretically and experimentally analyzed. To get the best sensitivity, the wavelength interval is fixed at one quarter of the period of sensor interference fringes. An optimized differential cross multiplication algorithm is utilized to demodulate the acoustic signal, which can eliminate the impact of optical power imbalance between the two light paths. This system may be a universal phase demodulation unit for short-cavity EFPI acoustic sensors. The EFPI acoustic sensing head is formed by an aluminum-attached polyethylene terephthalate membrane and a cleaved fiber tip. The sensor interrogated by the proposed demodulation system demonstrated large dynamic range in low-frequency domain under high sound pressure. A signal-to-noise ratio (SNR) of ∼53 dB is obtained at 80 Hz. These features make the sensor especially suitable for noise detection.