Fiber Optic Hydrophone Research Articles

Experimental Study of Surface Microtexture Formed by Laser-Induced Cavitation Bubble on 7050 Aluminum Alloy

In order to study the feasibility of forming microtexture at the surface of 7050 aluminum alloy by laser-induced cavitation bubble, and how the density of microtexture influences its tribological properties, the evolution of the cavitation bubble was captured by a high-speed camera, and the underwater acoustic signal of evolution was collected by a fiber optic hydrophone system. This combined approach was used to study the effect of the cavitation bubble on 7050 aluminum alloy. The surface morphology of the microtexture was analyzed by a confocal microscope, and the tribological properties of the microtexture were analyzed by a friction testing machine. Then the feasibility of the preparation process was verified and the optimal density was obtained. The study shows that the microtexture on the surface of a sample is formed by the combined results of the plasma shock wave and the collapse shock wave. When the density of microtexture is less than or equal to 19.63%, the diameters of the micropits range from 478 μm to 578 μm, and the depths of the micropits range from 13.56 μm to 18.25 μm. This shows that the laser-induced cavitation bubble is able to form repeatable microtexture. The friction coefficient of the sample with microtexture is lower than that of the untextured sample, with an average friction coefficient of 0.16. This indicates that the microtexture formed by laser-induced cavitation bubble has a good lubrication effect. The sample with a density of 19.63% is uniform and smooth, having the minimum friction coefficient, with an average friction coefficient of 0.14. This paper provides a new approach for microtexture processing of metal materials.

GA-BP-Based Low-Noise FBG Hydroacoustic Monitoring System with Reference Sensor.

To address the issue of harsh marine background noise impacting the monitoring signal of fiber-optic hydrophones, we propose a low-noise fiber Bragg grating (FBG) hydroacoustic monitoring system with a reference sensor based on genetic algorithm backpropagation (GA-BP). Through theoretical analysis, we deduce the noise suppression steps of the GA-BP algorithm based on the reference sensor and construct train and test sets based on the data from the reference sensor and monitoring sensor at different times, optimizing the GA-BP algorithm to find the best fitting results and thereby obtaining the low-noise monitoring signal. Experimental results from the anechoic tank show that the proposed method can suppress background noise interference on effective signals and that the suppression effect improves as the background noise increases. The sound pressure sensitivity ranges from -173.76 dB to -171.33 dB at frequencies of 8 kHz to 12 kHz, with a response flatness of less than 2.43 dB. The noise suppression effect is obvious under the condition of poor signal-to-noise ratio (SNR), which can reach more than 18.3 dB. The advantages of the proposed algorithm in array signal processing are further demonstrated by the directivity experiment, which proves that the algorithm has a great potential for engineering applications in harsh marine environment.

Simulations of the optical diffraction patterns produced by the pressure field of a clinical shock wave source

Today, shock waves are used to treat a wide variety of ailments. Consequently, there is a need to develop efficient methodologies for comparing and evaluating the pressure fields generated by different equipment. Hydrophones are commonly utilized for accurate pressure measurements although they can be damaged by pitting due to acoustic cavitation. Furthermore, the range of measurement is limited by the position of the device. Optical methods have also been proposed since the presence of a disturbing device in the wave propagation medium is not necessary, and they provide a broader registering field. Nevertheless, these methods do not provide accurate measurements compared with those obtained with polyvinylidene difluoride or fiber-optic hydrophones. Herein, an optical method for shock wave characterization based on diffraction analysis, that can lead to more precise results, is proposed. The phase fluctuations of a light wave produced when it traverses the shock wave pressure field are calculated. The diffraction patterns produced by this perturbed wave at an observation plane at different propagation distances are presented. Considering the state of the art of high-speed cameras, we conclude that an experimental setup, based on the results reported here, can contribute to the evaluation and comparison of shock wave generators for medical applications.

Influence of carrier signal frequency error on the demodulation phase of the fiber optic hydrophone

This paper investigates the influence of carrier signal frequency error on the demodulation phase of the fiber optic hydrophone with the demodulation algorithm of the phase generated carrier (PGC) and heterodyne. The proposed theory is demonstrated experimentally, with results showing that the frequency error between the carrier wave and local oscillator signal will influence the demodulated phase signal of the fiber optic hydrophone, which is consistent with the theory proposed. When the PGC algorithm is adopted, the error leads to a time-varying amplitude of the demodulated signal while a linear trend is superimposed on the signal demodulated by the heterodyne method.

Experimental Study on Near-Wall Laser-Induced Cavitation Bubble Micro-Dimple Formation on 7050 Aluminum Alloy

To investigate the feasibility and formation laws of fabricating micro-dimples induced by near-wall laser-induced cavitation bubble (LICB) on 7050 aluminum alloy. A high-speed camera and a fiber-optic hydrophone system were used to capture pulsation evolution images and acoustic signals of LICB. Meanwhile, a three-dimensional profilometer was employed to examine the contour morphology of the surface micro-dimple on the specimen. The results show that at an energy level of 500 mJ, the total pulsation period for the empty bubble is 795 μs, with individual pulsation periods of 412.5 μs, 217 μs, and 165 μs for the first, second, and third cycles, respectively, with most energy of the laser and bubble being consumed during the first evolution period. Under the synergy of the plasma shock wave and collapse shock wave, a spherical dimple with a diameter of 450 μm is formed on the sample surface with copper foil as the absorption layer. A model of micro-dimple formed by LICB impact is established. As the energy increases, the depth of the surface micro-dimple peaks at an energy of 400 mJ and then decreases. The depth of the surface micro-dimple increases with the increase in the number of impacts; the optimal technology parameters for the micro-dimple formation by LICB impact are as follows: the absorption layer is copper foil, the energy is 400 mJ, and the number of impacts is three.

Experimental Study of Laser-Induced Cavitation Bubbles near Wall: Plasma Shielding Observation

To investigate the plasma shielding of laser-induced cavitation bubbles near a wall, a pulsed laser with different energies was selected to induce cavitation bubbles on the surface of 7050-T7451 aluminum alloy. A high-speed camera captured the evolution of the cavitation bubble, while a fiber-optic hydrophone system collected the acoustic signals during the evolution. Finally, a confocal microscope was used to view and analyze the surface morphology of 7050 aluminum alloy. The experimental results indicate that as the laser energy increases, the diameter, the evolution time, the pressure of the bubble, and both the pit diameter and depth all increase. Beyond an energy level of 1.4 J, the maximum diameter and the evolution time of the laser-induced cavitation bubble begin to decrease; the maximum diameter decreases by 2.04%, and the first evolution time decreases by 3.26%. Plasma shielding was observed in this experiment. Considering that the essence of a laser-induced cavitation bubble is the interaction between a high-energy laser and a liquid medium, the abnormal decrease in the maximum diameter, evolution time, and sound pressure epitomizes the manifestation of plasma shielding.

Thin Fiber-Optic Hydrophone Towed Array for Autonomous Underwater Vehicle

Thin Fiber-Optic Hydrophone Towed Array for Autonomous Underwater Vehicle

Stability-enhanced low-frequency fiber optic hydrophone based on an extrinsic Fabry-Perot interferometer

Fiber optic hydrophones (FOHs) offer the notable advantage of electromagnetic interference resistance. Nevertheless, overcoming the challenge of sustaining stable, high-performance operation in intricate underwater settings at a low cost remains a considerable obstacle for them. To circumvent the restrictions noted above, we employed a miniaturized FOH, utilizing an easily fabricated extrinsic Fabry-Perot interferometer (EFPI) which is made up of a composite chromium-aluminum (Cr-Al) membrane and fiber. The linear demodulation also suppresses the drift issue in the output spectrum. The average sound pressure sensitivity of the sensor, according to experimental findings, is around -139.15 dB re 1 V/µPa, while the equivalent noise sound pressure at 1 kHz is 51.52 dB re 1 µPa/Hz1/2. This sensor has a lot of potential because of features like sensitive low-frequency response and noise performance.

A spatiotemporal deconvolution approach for measurements of therapeutic ultrasound pressures, intensities, and beamwidths

Complete characterization of high intensity focused ultrasound (HIFU) systems includes measurements of transmitted pressure at the focal plane with a hydrophone. However, highly focused, nonlinear HIFU beams can result in considerable spatial averaging artifacts due to finite area of the hydrophone active element. Spatiotemporal deconvolution (STD) can correct for hydrophone spatial averaging (Wear, IEEE Trans. UFFC 69, 1243–1256 (2021)]. The objective of the present work is to extend validation of STD from diagnostic levels (6 MPa) to therapeutic levels (49 MPa). Three HIFU transducers (1.45 MHz F/1, 1.53 MHz F/1.5, and 3.91 MHz F/1) were driven in tone bursts (Agilent HP3314A function generator, ENI 240L amplifier) to generate HIFU fields in a degassed, deionized water tank with focal compressional pressures of 49, 16, and 29 MPa. Fields were measured in focal planes with two hydrophones (Onda HFO 100-μm fiber-optic; Onda HNA-0400 400-μm robust needle). STD reduced inter-hydrophone differences from −18 ± 11% to 0 ± 8% (peak compressional pressure), −8 ± 4% to −5 ± 5% (peak rarefactional pressure), −20% ± 7% to −3 ± 8% (pulse intensity integral), and 21 ± 12% to −2 ± 3% (beam FWHM). STD reduces dependence of measurements on hydrophone active element size. STD reduces reliance on fiber optic hydrophones, which can be expensive, difficult to use, and prone to radiation-force-induced sensor misalignment.

A feedback control method for phase signal demodulation in fiber-optic hydrophones

A feedback control method for phase signal demodulation in fiber-optic hydrophones

Multimode Microstructured Optical Fiber Hydrophone

Multimode Microstructured Optical Fiber Hydrophone

Low-Noise Stabilization of Demodulation in Fiber-Optic Hydrophones Using Heterodyne Algorithm with Non-Polarization-Maintaining Optical Path and Serial Acousto-Optic Modulation

Low-Noise Stabilization of Demodulation in Fiber-Optic Hydrophones Using Heterodyne Algorithm with Non-Polarization-Maintaining Optical Path and Serial Acousto-Optic Modulation

Fiber-optic acoustic-velocity hydrophone based on castor-oil-loaded fiber-laser cantilever

Fiber-optic acoustic-velocity hydrophone based on castor-oil-loaded fiber-laser cantilever

A Multi-Phase Phase-Generated Carrier Demodulation Algorithm for Stability Improvement of Noise Transfer Coefficient for Fiber Optic Hydrophone

A Multi-Phase Phase-Generated Carrier Demodulation Algorithm for Stability Improvement of Noise Transfer Coefficient for Fiber Optic Hydrophone

Research and Application Progress of Distributed Fiber Optic Hydrophone Technology

Research and Application Progress of Distributed Fiber Optic Hydrophone Technology

Large-Scale Distributed Fiber-Optic Hydrophone Towing Array and Lake Trial Performance Test

Large-Scale Distributed Fiber-Optic Hydrophone Towing Array and Lake Trial Performance Test

Hydroacoustic communications in the field of countering underwater robots

The tasks of countering potential threats in the form of maritime terrorism and ensuring the safety of marine waters play an important role for our country. This article proposes technologies for the use of fiber-optic hydrophones for detecting underwater robots.

Depth Spatial Characterization of Marine Environmental Noise in the Zengmu Basin

Based on the measured data obtained from an array of optical fiber hydrophones, this paper analyzes and interprets the depth spatial spectrum characteristics, correlation characteristics, and vertical directionality of marine environmental noise in the Zengmu Basin. The analysis is conducted within the frequency range of 20 Hz to 2500 Hz. Additionally, the statistical characteristics of the probability density distribution of environmental noise in the Zengmu Basin were studied and analyzed. The findings indicate that the predominant ambient noise in the low-frequency range (less than 400 Hz) in the Zengmu Basin is primarily attributed to distant sources, commonly identified as ship radiation noise. In the high-frequency band (greater than 400 Hz), the marine ambient noise is primarily derived from the sea surface, predominantly in the form of wind-generated noise. In the frequency range of 25–1600 Hz, examined in this study, the power spectral density exhibits an average decrease of over 3 dB and a maximum decrease of over 5 dB with each doubling of frequency. When the frequency is below 400 Hz, there is a higher vertical spatial correlation to ambient noise. The vertical directivity of the noise energy is horizontal, meaning that it is perpendicular to the vertical array direction. Additionally, the probability distribution of the noise level approximately follows the Burr distribution. When the frequency exceeds 400 Hz, there is a low vertical spatial correlation to noise. The vertical directivity of environmental noise exhibits distinct grooves in the horizontal direction, and the probability distribution of the noise spectrum level generally follows a normal distribution.

A light-weight neural network for marine acoustic signal recognition suitable for fiber-optic hydrophones

Fiber-optic hydrophones based on optical fiber sensing and communication technology have developed rapidly in recent years. With the advantages of high sensitivity, small size, and large dynamic range, they are easy to detect underwater acoustic signals, showing great potential in the field of marine ecological protection. Researchers can monitor the marine ecological environment by recognizing underwater optical fiber sensing signals collected by fiber-optic hydrophones in real-time. Deep learning models can achieve high recognition accuracy, but they usually have large amounts of parameters that makes them difficult to be deployed in mobile terminals of marine survey ships. To solve the key problem, this paper discussed the design of the Deep Light-Weight Attention Residual Network (DLA-ResNet). It introduces the depth-wise separable convolution (DSC) and the convolutional block attention module (CBAM) into ResNet18 to make its performance better. ResNet18 is a two-dimensional convolutional network (CNN) model applying residual blocks. Experiments verify that the accuracy of DLA-ResNet improved from ResNet18 is increased by about 2.04% and its size is reduced by 85.67%. The proposed scheme in this paper realizes an average recognition rate of 96.50% for eight types of underwater optical fiber sensing signals in the application of marine ecological environment monitoring. Moreover, its model size is only 6.12 MB and it only takes 27.90 ms, which is available to meet the needs of reliability and effectiveness.

A Novel PMDI Fiber Optic Hydrophone Incorporating IOC-Based Phase Modulator

Fiber-optic hydrophone (FOH) has significant potential in many applications of hydroacoustic sensing and underwater communication. A novel path-matched differential interferometer fiber optic hydrophone (PMDI-FOH) approach incorporating an integrated-optic component (IOC) is presented in this paper. It is presented to meet the demands for high-quality dynamic measurements, which solves the problems with the conventional homodyne detection system’s low modulation frequency. The IOC functions as a phase-generated carrier (PGC) component. The scheme is investigated both in theory and experiments. The theoretical and experimental results verify the effectiveness of the proposed scheme. It achieves a high SNR of up to 20.29 dB demodulations. The proposed system is cost-effective and has excellent potential in building next-generation underwater sensing and communication networks.