Vector Hydrophone Research Articles

Bearing estimation for optical fiber vector hydrophone with in-band resonance

The accelerometer-type optical fiber vector hydrophone (OFVH) shows resonance in its frequency response due to the mass-spring structure of the accelerometer. To avoid signal distortion, the usable frequency band of an OFVH is usually limited to far below the resonant frequency. Increasing the resonant frequency would extend the frequency band but at the expense of decreased hydrophone sensitivity. This paper points out that for bearing estimation, the out-of-band frequency components of the OFVH output are usable, which leads to efficient utilization of the OFVH signal and enhancement of target detection performance in some circumstances. A modification of the intensity-based algorithm, along with calibrations based on the simple oscillator model, are given for the bearing estimation in this paper. The analysis are confirmed by results of lake experiments using an acoustic source, a fixed pump and a small ship.

New insight into contradictive relationship between sensitivity and working bandwidth of cilium MEMS bionic vector hydrophone

Sensitivity and working bandwidth are two important features of cilium MEMS bionic vector hydrophone. However, in previous studies, they were mutually inhibited so that they could not be optimized simultaneously, which means that the method of increasing sensitivity would reduce the working bandwidth. This paper presents an efficient solution to this contradictive relationship. First of all, this paper makes a theoretical analysis of device structure through the two-degree of freedom mechanics system instead of previous single degree of freedom. Then, theoretical analysis, theoretical simplified model simulation analysis and actual model simulation analysis are performed by mathematical modeling and ANSYS 17.0 software. Moreover, four hydrophones of different cilium diameters are fabricated and comparison calibration test is performed. The results demonstrate that the sensitivity and working bandwidth can be increased simultaneously. Besides, their concave points of directivity curves are almost equal to each other. Finally, the sensitivity of the optimal structure can reach up to −185.9dB (1250 Hz 0 dB at 1 V µPa−1) and its working bandwidth is in the range of 20–1250 Hz which is the widest among all previous optimized structures.

A bionic micro-electromechanical system piezo-resistive vector hydrophone that suppresses vibration noise

For piezo-resistive sensors have outstanding low-frequency response, micro-electro-mechanical system (MEMS) piezo-resistive vector hydrophones play an important role in low-frequency sound waves measurements. However, their signal-noise ratio can be decreased by vibration noise. The conventional solution is to suspend the hydrophone elastically, which can reduce the influence of vibration with frequencies higher than the natural frequency of the elastic element used for suspension. However, this approach has little effect on reducing low-frequency vibration noise. To overcome this problem, a novel hydrophone structure with a large-volume supporting block is proposed in this study. When the hydrophone is subject to vibration, the actions of the supporting block and cilium on the piezo-resistors counteract each other. Therefore, the proposed hydrophone can effectively reduce output voltages caused by vibration. Mathematical models of this new hydrophone are established to verify the feasibility of the method. Simulations are performed and found to be in accordance with the mathematical models. The experimental results clearly demonstrate that the proposed hydrophone can dramatically reduce vibration noise without reducing sensitivity to sound.

Design and fabrication of a multipurpose cilia cluster MEMS vector hydrophone

The previous cilia MEMS vector hydrophone were mainly aimed at monitoring the noises of remote ships due to the limitation of frequency band. Moreover, the methods of adding appendants to cilia were usually used to improve the sensitivity, which increased the difficulty of fabrication, secondary integration and the consistency of production. In this paper, based on the bionic principle of multiple cilia on fishes’ sense cells, a cilia cluster MEMS vector hydrophone(CCVH) is designed. This micro-structure not only improves the sensitivity of hydrophone without adding appendants to cilia, but also designs a suitable frequency band to monitor ships and some valuable marine species. Firstly, a mathematical model is established for theoretical analysis. Then, simulation analysis is carried out to verify the correctness of theoretical analysis, and the optimal size of cilia is found simultaneously. Secondly, the fabrication of cilia cluster MEMS vector hydrophone is more simpler because the cilia have the same properties and integrated process. Finally, test results show that the sensitivity of hydrophone has been increased by 9.6 dB, which can reach up to -183.3 dB@1600 Hz(0 dB ref.1 V/uPa) with the frequency band in the range of 20 Hz-1 kHz. Besides, the sensitivity is increased by 6 dB per octave. Concave point depth of 8-shaped directivity is beyond 30 dB, which indicates that CCVH is promising in underwater application.

Normal Mode Based MUSIC Method for DOA Estimation in Shallow Water Using a Single Vector Sensor

Sound field in the shallow water can be modeled as a superposition of multiple normal modes. Traditional underwater DOA estimation methods assume the sound wavefront to be plane, which will lead to relatively large estimation errors. To solve this problem, a normal mode based MUSIC (NM-MUSIC) method using a single vector hydrophone is presented. The orthogonality between the steering vector and the noise subspace in classic MUSIC method is replaced by that between the steering matrix and the noise subspace. Elements of the steering matrix are functions of the azimuth angles and the modal wavenumbers, and the azimuth angles can be estimated through minimal optimization searching. Computer simulation results verify that the proposed algorithm outperforms the traditional MUSIC method from the perspective of both estimation bias and root mean square error.

Modeling and Simulation of MEMS Vector Hydrophone for Suppressing Vibration Output

The influence of vibration on the output of hydrophone having a serious disturbance on the measurement of sound. To suppress the output of hydrophone caused by vibration promoting its engineering application, a crafty piezoresistive eight beams vector hydrophone with thick thickness of mass block was designed. The models of presented hydrophone were established. Based on the models, a method optimizing the thickness of mass block to suppress the output caused by vibration, but hardly no influence on the output of hydrophone resulted by sound. The FEM simulation results demonstrate the practicality of this method. The output caused by vibration is minimum and output resulted by sound has hardly influence when the thickness of mass block is 230 μm for the designed hydrophone. This is beneficial to the engineering application of vector hydrophone.

A Monolithic Integration Bio-Inspired Three-Dimensional MEMS Vector Hydrophone

Three-dimensional vector hydrophone plays an important role in underwater spatial location. In order to solve the problems of monolithic integration and linearity of previous three-dimensional vector hydrophones, a three-dimensional micro-electro-mechanical system (MEMS) vector hydrophone based on the piezoresistive effect and bio-inspired principle is proposed in this paper. Different from previous three-dimensional vector hydrophone, this three-dimensional MEMS vector hydrophone is monolithically integrated. It has the characteristics of high consistency and batch production. Acoustic pressure gradients in xand y-directions are detected by the cilium, and acoustic pressure gradient in the z direction is detected by the supporting block and beams. Mathematical models of longitudinal stress on the surface of beams and the first three-order natural frequencies of the hydrophone are established. The simulation results prove the accuracy of the mathematical models. Specific structure parameters of hydrophone are determined and then the designed hydrophone is fabricated on a silicon-on-insulator (SOI) wafer. Finally, the sensitivities and directivities of designed hydrophone are tested. The sensitivities of X-channel and Z-channel are -187 dB and -163 dB (0 dB referring to 1 VμPa -1 ) at 400 Hz, respectively. The test results show that the hydrophone promising in spatial location.

Design and research on impact resistance characteristics of vector hydrophone application platform

On the basis of the analysis of the impact resistance of the application platform of the vector hydrophone is analysed , this paper designed single-stage and two-stage vibration isolation system based on rubber damper by using its characteristics of large viscous damping coefficient, low mass and easy installation and disassembly. By comparing the output signal of vector hydrophones in the state of rigid connection and with single-stage vibration isolation system, it can be seen that under different connection conditions, the signal amplitude of the impact response of the hydrophone are also different. The results of the experiment verified the effect of vibration isolation system on impact signal and the accuracy of theoretical analysis results.

An Improved Squirrel Search Algorithm for Maximum Likelihood DOA Estimation and Application for MEMS Vector Hydrophone Array

Maximum likelihood (ML) method for direction of arrival (DOA) estimation achieves an excellent performance in array signal processing, but the complexity and computational load of searching the multidimensional nonlinear function prevented it from practical application. Based on squirrel search algorithm (SSA), an improved SSA (ISSA) for ML DOA estimation is proposed in this paper, which can reduces the computational complexity. The idea of spatial variation and diffuse inspired by the invasive weed optimization(IWO) algorithm is applied to ISSA. The simulation experiments compared ISSA with SSA, IWO, seeker optimization algorithm(SOA), sine cosine algorithm (SCA), genetic algorithm (GA), particle swarm optimization (PSO) and differential evolution (DE) method for ML DOA estimator show that the proposed algorithm has faster convergence speed, fewer iterations and lower root mean square error(RMSE) under different number of signal sources, different signal to noise ratio(SNR) and different population size. Therefor the proposed algorithm does not only ensure the estimation accuracy, but also greatly reduce the computation complexity of multidimensional nonlinear optimization for the ML method. Finally, the test experiment using Micro Electronic Mechanical Systems(MEMS) vector hydrophone array in Fenhe lake show the engineering practicability of proposed ML DOA estimator with ISSA.The results obtained will be valuable in the application of engineering.

A Hybrid Algorithm Based on Squirrel Search Algorithm and Invasive Weed Optimization for Optimization

This paper proposes a hybrid algorithm called ISSA based on the combination of squirrel search algorithm (SSA) proposed in 2019 and invasive weed optimization (IWO) proposed in 2006. About 36 benchmark functions are employed to test the performances of ISSA. Then, ISSA is combined with support vector machine (SVM) and deterministic maximum-likelihood (DML) algorithm, respectively, and the two corresponding models ISSA-SVM and ISSA-DML are established for performing the grade classifications of air quality and the direction of arrival (DOA) estimation of MEMS vector hydrophone, respectively. The results of 36 benchmark functions prove that the proposed ISSA is able to provide very competitive results in terms of the average values, the standard derivation, and the convergence curves. The average accuracy rate of classification of ISSA-SVM model is the best and reaches 87.91971%, and the DOA estimations of ISSA-DML have the least root mean square error (RMSE) and the closest to the actual angles. Therefore, it is concluded that the proposed ISSA is an effective algorithm for function optimizations and is suitable to be combined with other algorithms and machine learning for classification and estimation.

Denoising and Baseline Drift Removal Method of MEMS Hydrophone Signal Based on VMD and Wavelet Threshold Processing

Aiming at the problem that the signals received by MEMS vector hydrophones are mixed with a large amount of external environmental noise, and inevitably produce baseline drift and other distortion phenomenons which made it difficult for the further signal detection and recognition, a joint denoising method (VMD-NWT) based on variational mode decomposition (VMD) and nonlinear wavelet threshold (NWT) processing is proposed. The main frequency of the noisy signal is first obtained by Fourier transform. Then the noisy signal is decomposed by VMD to obtain the IMF components. The center frequency and correlation coefficient of each IMF component further determine that the IMF components belong to noise IMF components, noisy IMF components or pure IMF components. Then the pure IMF components are reserved, the noise IMF components are removed, and the noisy IMF components are denoised by NWT processing method with new threshold function as a whole. Finally, the denoised IMF components and the pure IMF components are reconstructed to obtain the denoised signal to realize the extraction of useful signals and baseline drift removal. Compared with complete ensemble empirical mode decomposition with adaptive noise combined with wavelet threshold processing method (CEEMDAN-WT), ensemble empirical mode decomposition combined with wavelet threshold processing method (EEMD-WT), and single wavelet threshold processing method with compromised function between hard and soft threshold (ZWT), the VMD-NWT in this paper has the advantages of less calculation and simple implementation. The simulation comparison experiments verify that the VMD-NWT is superior to CEEMDAN-WT, EEMD-WT, and ZWT. Then VMD-NWT is applied to process the measured data obtained from the Fenji experiment conducted by the North University of China. Simulation and lake trial results show that VMD-NWT has better denoising effect and can realize baseline drift removal. So the proposed VMD-NWT has certain practical research value.

Design of a high SNR electronic heart sound sensor based on a MEMS bionic hydrophone

Since most of the contact conduction type of heart sound sensors don’t take into account the acoustic signal attenuation problem caused by the heart sound signal transmitting to a sensor whose filling materials’ impedance is different to human soft tissue, the signal-to-noise ratio (SNR) of the heart sound sensors is not very well. Human heart is immersed in blood. If the sensor’s core sensitive element can be immersed in fluid, the attenuation of heart sound signal may be decreased greatly. Inspired by the principle of hydroacoustic signal’s detection, this paper proposes the design of heart sound sensor based on the bionic vector hydrophone. Then theoretical analysis and finite element method (FEM) simulation about the sensor have been carried out. Combined sensitivity with resonant frequency, the optimum dimension of the sensor’s structure has been determined. The sensor’s micro-structure has been fabricated by using Micro-Electro-Mechanical System (MEMS) technology and coupling encapsulated by choosing a kind of medical coupling agent as the filling material. Finally, the performance of the proposed sensor is tested. The fact is that the proposed sensor can work well with either healthy people or patients with heart disease. The obtained data clearly show that: the SNR of the proposed heart sound sensor is superior to 3200-type of 3M Littmann 8.2 dB.

Steering Acoustic Intensity Estimator Using a Single Acoustic Vector Hydrophone

Azimuth angle estimation using a single vector hydrophone is a well-known problem in underwater acoustics. In the presence of multiple sources, a conventional complex acoustic intensity estimator (CAIE) cannot distinguish the azimuth angle of each source. In this paper, we propose a steering acoustic intensity estimator (SAIE) for azimuth angle estimation in the presence of interference. The azimuth angle of the interference is known in advance from the global positioning system (GPS) and compass data. By constructing the steering acoustic energy fluxes in the x and y channels of the acoustic vector hydrophone, the azimuth angle of interest can be obtained when the steering azimuth angle is directed toward the interference. Simulation results show that the SAIE outperforms the CAIE and is insensitive to the signal-to-noise ratio (SNR) and signal-to-interference ratio (SIR). A sea trial is presented that verifies the validity of the proposed method.

Optimal tone detection for optical fibre vector hydrophone

An optimal tone detector based on the Neyman-Pearson criterion is proposed for the optical fibre vector hydrophone (OFVH). The detector takes account of the difference between noise levels on the acoustic pressure channel and the three particle acceleration channels of an OFVH. Explicit expressions for the impulse responses of pre-filters that are central to the proposed detector are given. Analyses show that the proposed detector is equivalent to the minimum variance distortionless response beamformer for the OFVH. In the case of identical noise on all particle acceleration channels, the signal-to-noise ratio (SNR) gain of the detector is 101g(1 + μ) dB (μ is the noise power ratio of OFVH channels at the tone frequency), whereas the SNR gain also depends on target direction and is bounded by 101g(1 + μ min ) and 101g(1 + μ max ) dB when noise on all particle acceleration channels are different. Results from both simulations and lake experiment data show that the proposed detector outperforms tone detectors that use (i) the acoustic pressure signal, (ii) the particle acceleration signals and (iii) equally the combination of acoustic pressure signal and particle acceleration signals.

Three-component homovibrational vector hydrophone based on fiber Bragg grating F-P interferometry.

A fiber optic vector hydrophone is an interesting topic for many applications. Using a fiber Bragg grating (FBG) as a reflection unit, the vector hydrophone combines the advantages of miniaturization, high reliability, and low cost. In this paper, the interferometric vector sensing, multiplexing design, and cross-talk suppression of a fiber optic vector hydrophone based on FBG-based Fabry-Perot interferometry are discussed and validated. The average cross talk of the channels is reduced by 20dB than that of a high-reflectivity grating by using 1% reflectivity fiber gratings. A three-component homovibrational vector hydrophone with a low-reflection FBG was developed and tested. The working band of the hydrophone is extended to 20Hz, and the sensitivity of each vector channel is about -132.5 dB at 500Hz and its directivity index is more than 30dB at 100Hz.

Widely Linear Adaptive Instantaneous Frequency Estimation in Vector Hydrophones

To solve the problem that the time-frequency resolution of Short-Time Fourier Transform (STFT) is constrained by the window length and the moving step of the short time window, and to utilize the merits of a widely linear method, a novel instantaneous frequency estimation method in vector hydrophone was proposed. In this paper, a complex variable was constructed. It is composed of sound pressure and particle velocity as its real part and imaginary part, respectively. The constructed variable was approved to be second order noncircular (improper). For the modelling of noncircular signals, the standard linear estimation is not adequate and the pseudo-covariance matrix should also be taken into consideration. As a result, a widely linear adaptive instantaneous frequency estimation algorithm and its three solutions based on the augmented complex least mean square (ACLMS) method are presented to estimate the instantaneous frequency in vector hydrophones. The results of simulations and laboratory experiments prove that this approach based on a widely linear model performs better compared to STFT and strict linear filter methods.

Development of vector hydrophone using thickness–shear mode piezoelectric single crystal accelerometer

In this study, a vector hydrophone was developed for a towed array sonar system using a shear type accelerometer. In general, inertia type vector hydrophones using accelerometers have higher sensitivity than multimode vector hydrophones. However, the sensitivity still needs to be enhanced as much as possible for practical application. For the purpose, the effect of the structural parameters of a shear type accelerometer on the receiving voltage sensitivity (RVS) of the vector hydrophone was rigorously analyzed, and the structure of the vector hydrophone was optimized to maximize the RVS. The developed vector hydrophone has an external diameter of 23 mm and the minimum RVS over the given frequency range of -201.4 dB. It was also verified that the designed vector hydrophone exhibits the characteristic of a dipole mode beam pattern. Furthermore, a prototype of the vector hydrophone was fabricated with the optimal dimensions, and its acoustic characteristics were measured to verify the validity of the design. The vector hydrophone developed in this work has the highest feasible RVS over the desired frequency range in comparison with other types of vector hydrophone like the multimode hydrophone.

A primer on vector hydrophones

Vector hydrophones are used by the military to track submarines, and, more recently, by scientists attempting to measure the influence of particle velocity on the behaviour of fish. Despite being in use for decades, vector hydrophones remain poorly understood by both communities. The problem is particularly acute for those aiming to measure particle velocity because vector hydrophones do not measure particle velocity directly; rather they measure pressure difference, the force that creates particle velocity. Topics covered will be the two types of vector hydrophone and why only one works well at low frequencies, the importance of knowing the phase of the directional channels relative to each other and to the pressure hydrophone, how bearings are determined, calibration of vector hydrophones and near-field effects, the magnitude of particle velocity for typical sound pressure levels, why bigger is better for mechanical noise, why neutral buoyancy is unnecessary and undesirable, and best practice for mounting.

Effect of acoustic horizontal refraction on DOA estimation with a single vector hydrophone

The effect of horizontal refraction (HR) on DOA estimation with a single vector hydrophone is studied. It has been demonstrated in a previous study that HR may bring about a significant deviation between the true bearing of the source and the direction of time-averaged sound flux at the receiver point, i.e., DOA estimation error. [J. Tang et al., 2018, 43(2), ACTA ACUSTICA (in Chinese)]. In the present work, the DOA estimation error in a more realistic scenario is studied, more precisely, source signals are considered to be wide-band instead of time-harmonic, and meanwhile ambient noise is added to the received signal. The ocean waveguide used in simulations is a 3D version of the standard ASA wedge, which implies that the HR considered in this work is raised from multiple reflections between a horizontal sea surface and a sloping sea bottom. The results of this work shall offer some reference to DOA estimation in circumstances with strong HR effects.

Design and analysis of a multiple sensor units vector hydrophone

Inspired by the hairy structure of fish neuromast, a multiple sensor units (multi-unit) vector hydrophone is proposed in the paper, which integrates multiple sensor units on one chip according to bionics. Its sensitivity and signal noise ratio (SNR) are theoretically analyzed compared with the hydrophone which has only one sensor unit. In order to verify the correctness of the theory, a 4-unit vector hydrophone has been fabricated. For experiments, the comparative calibration experiment is used to validate the theoretical analysis of sensitivity and fast fourier transform algorithm (FFT) is used to process the experiment data to verify the theoretical analysis of SNR. The results show that the sensitivity of the 4-unit hydrophone is improved by 11.8 dB and the SNR is improved by 1.9 dB on average, which is correlated with the theoretical analysis.