Vector Hydrophone Research Articles

Signal Denoising Based on Wavelet Threshold Denoising and Optimized Variational Mode Decomposition

To eliminate the noise from the signals received by MEMS vector hydrophone, a joint algorithm is proposed in this paper based on wavelet threshold (WT) denoising, variational mode decomposition (VMD) optimized by a hybrid algorithm of Multiverse Optimizer (MVO) and Particle Swarm Optimization (PSO), and correlation coefficient (CC) judgment to perform the signal denoising of MEMS vector hydrophone, named as MVO‐PSO‐VMD‐CC‐WT, whose fitness function is the root mean square error (RMSE) and whose individual is the parameters of VMD. For every individual, the original signal is decomposed by VMD into pure components, noisy components, and noise components in terms of CC judgment, where the pure components are directly retained, the noisy components are denoised by WT denoising, and the noise components are discarded, and then, the denoised noisy components and the pure components are reconstructed to be the denoised signal of the original signal. Then, the obtained optimal individual is utilized to perform the signal denoising by MVO‐PSO‐VMD‐CC‐WT by the use of the above repeated signal processing. Two simulated experimental results show that the MVO‐PSO‐VMD‐CC‐WT algorithm which has the highest signal‐to‐noise ratio and the least RMSE is superior to the other compared algorithms. And the proposed MVO‐PSO‐VMD‐CC‐WT algorithm is effectively applied to perform the signal denoising of the actual lake experiments. Therefore, the proposed MVO‐PSO‐VMD‐CC‐WT is suitable for the signal denoising and can be applied into the actual experiments in signal processing.

Vector Hydrophone Array Design Based on Off-Grid Compressed Sensing.

Array design is the primary consideration for array signal processing, and sparse array design is an important and challenging task. In underwater acoustic environments, the vector hydrophone array contains more information than the scalar hydrophone array, but there are few articles focused on the design of the vector hydrophone array. The difference between the vector hydrophone array and the scalar hydrophone array is that each vector hydrophone has three or four channels. When designing a sparse vector hydrophone array, these channels need to be optimized at the same time to ensure the sparsity of the array elements’ number. To solve this problem, this paper introduced the compressed sensing (CS) theory into the vector hydrophone array design, constructed the vector hydrophone array design problem into a globally solvable optimization problem, proposed a CS-based algorithm with the L1 norm suitable for vector hydrophone array, and realized the simultaneous optimization of multiple channels from the same vector hydrophone. At the same time, the off-grid algorithm was added to obtain higher design accuracy. Two design examples verify the effectiveness of the proposed method. The theoretical analysis and simulation results show that compared with the conventional compressed sensing algorithm with the same aperture, the algorithm proposed in this paper used fewer vector hydrophone elements to obtain better fitting of the desired beam pattern.

A Data Fusion Orientation Algorithm Based on the Weighted Histogram Statistics for Vector Hydrophone Vertical Array.

In this paper, we propose a data fusion algorithm based on the weighted histogram statistics (DF-WHS) to improve the performance of direction-of-arrival (DOA) estimation for the vector hydrophone vertical array (VHVA). The processing frequency band is firstly divided into multiple sub-bands, and the high-resolution multiple signal classification (MUSIC) algorithm is applied to estimate the azimuth of each sub-band for each vector hydrophone. Then, the weighted least square (WLS) data fusion technique is used to fuse the sub-band estimation results of multiple sensors. Finally, the weighted histogram statistics method is employed to obtain the synthesis results in the frequency domain. We carried out a simulation and sea trial of the 16-element VHVA to evaluate the performance of the proposed algorithm. Compared to several traditional processing algorithms, the beam width of the proposed approach is significantly narrower, the side lobes are considerably lower, and the mean square error (MSE) is effectively smaller. In addition, the DF-WHS method is more suitable to accurately estimate the target azimuth with a low signal-to-noise ratio (SNR) because the noise sub-band is suppressed in the weighted histogram statistics step. The DF-WHS method in this article provides a new approach to improve the performance of deep-sea target detection for the VHVA.

An adaptive model for the location of low-frequency sound sources in shallow sea environments

At present, mathematical models applicable to the localization of shallow sea low-frequency sound source targets are usually complicated, and some environmental parameters need to be set in advance. This poses a great challenge to the scope of the application of this technology. To solve this problem, we propose an adaptive sound source localization model (ASSL) based on data driving, which only needs to input the vector hydrophone signal to output the two-dimensional coordinates of the sound source in real time. First, the four-channel sound source signal received by the single vector hydrophone is fused into a single-channel sound intensity signal and dynamically divided into suitable lengths based on Shannon entropy; then, the built deep bidirectional long short-term memory (DBiLSTM) network is used for a priori training; finally, the results are cross-validated, and the location of the target sound source is output. Experimental results show that the model can quickly estimate the position of the low-frequency sound source in the shallow sea environment using only a 1 s signal collected by a single vector hydrophone. The error between the estimated position and the actual position is approximately 35 m. Even with large samples, the method also showed great potential for application.

Design and implementation of hollow cilium cylinder MEMS vector hydrophone

The cilium MEMS vector hydrophone (CVH) plays an important role in detecting underwater acoustic targets, but there are still problems of low sensitivity and insufficient working bandwidth. In this paper, hollow cilium cylinder vector hydrophone (HCVH) is presented, which can improve sensitivity and working bandwidth within a certain range. Acting as the received acoustic signal structure, a hollow cylinder can not only ensure that sensitivity is improved by increasing the size of area which receives sound, but also reduce its weight to improve the stability of hydrophone. Through the theoretical analysis and the simulation, the relationship between the structure parameters and working performance of the hydrophone is obtained, and the specific size of the sensitive structure is determined. The experimental results show that the sensitivity of HCVH is increased by 8.7 dB in 20–1000 Hz, reaching up to −185.6 dB (re 1 V/µPa) at 1250 Hz. In addition, HCVH has a good directivity.

Design and fabrication of a novel MEMS piezoelectric hydrophone

Hydrophone, serving as a part of sonar, has a significant effect on the performance of acoustic sensors such as frequency characteristics and sensitivity, however, some limitation such as high cost and complexity in SOI manufacturing technique hinder the industrial application of hydrophones. Therefore, a novel Micro-Electro-Mechanical Systems (MEMS) piezoelectric vector hydrophone based on PZT (lead zirconate titanate) film has been adopted in obtaining vector information of underwater sound field. The piezoelectric hydrophone sensor was analyzed, designed and fabricated with PZT-on-Si substrate, and the structure consists of a four-cantilevers and an acoustics columnar cilium fixed on the center micro mass. According to the simulation results, the piezoelectric films are optimally distributed at the tip of the four beams, where the maximum strain locates. Finally, the piezoelectric vector hydrophone was characterized by comparative calibration experiments in a standing wave bucket. This passive MEMS piezoelectric hydrophone has the characteristics of receiving sensitivity with −189.3 dB at 920 Hz (0dB = 1 V/μPa) and a typical directional pattern of "8" shape, low noise output and high dynamic test range, which is suitable for high precision passive underwater detection.

Design and realization of dumbbell-shaped ciliary MEMS vector hydrophone

An excellent hydrophone should have higher sensitivity in its working frequency-band to provide signal with better quality for direction of arrival (DOA). Aiming at the centralized distribution of radiation noise from ships generally below 1KHz, a Dumbbell-shaped ciliary MEMS vector hydrophone (DCVH) with better sensitivity below 1KHz is designed in this paper. When detecting the submarine sound signal, Dumbbell-shaped ciliary can obtain the area of receiving sound waves larger than common ciliary structure in the same mass, increase the center of gravity position and increase the moment of force, so as to improve the high sensitivity of hydrophone under the premise of meeting the working frequency-band. In addition, the use of resin as the material for making cilia can bring better performance to hydrophone. Through theoretical analysis and simulation verification by COMSOL5.4, the design is feasible. Finally, DCVH is verified by hydrophone test calibration system, with the sensitivity of -186.1dB (1KHz, 0dB=1V/μPa), 10.8dB higher than bionic ciliary MEMS vector hydrophone (CVH), the working frequency-band of 20Hz-1KHz, the excellent “8″ character directivity, and concave point depth exceeding 30dB, which is consistent with theory and simulation results and meets the design requirements.

Laser adaptive holographic hydroacoustic intensimeter

A new type of a vector hydrophone, a laser adaptive hydroacoustic intensimeter, is investigated. Two identical, spatially separated coil-type sensors are used as a primary receiver of the acoustic signal. The signals received at the sensor output are phase demodulated in a two-channel adaptive holographic interferometer based on two dynamic holograms multiplexed in a CdTe photorefractive crystal. Using a laser intensimeter, the acoustic field formed in a limited volume is studied. The performance characteristics of the intensimeter are determined experimentally; its threshold sensitivity, according to the acoustic field intensity, constitutes 0.1 × 10−13 W m−2.

A study on MEMS vector hydrophone and its orientation algorithm

Purpose The problem of port and starboard ambiguity will exist when only utilize the vector or scalar parameters. Meanwhile, the amplitude-phase error between the vector and scalar can also cause this problem. In this paper, a compound MEMS vector hydrophone which contains cilia vector microstructure and piezoelectric ceramic tube has been presented to solve the problem. Compared with traditional MEMS vector hydrophone, the compound MEMS vector hydrophone can realize the measurement of sound pressure and vibration velocity simultaneously. Design/methodology/approach A compound MEMS vector hydrophone has been presented. The unipolar directivity of the combined signal which combine the acoustic pressure and vibration velocity is used to achieve the direction of arrival (DOA). This paper introduced the working principle and the target detection mechanism of the compound vector hydrophone. The amplitude and phase error are analyzed and corrected in the standing wave tube. After that, the authors use beam-forming algorithm to estimate the DOA. Findings The experimental results in the standing wave tube and the external field verified the vector hydrophone's directional accuracy up to 1 and 5 degrees, respectively. Practical implications The research of compound vector hydrophone plays an important role in marine acoustic exploration and engineering applications. Originality/value This research provides a basis for MEMS hydrophone directivity theory. The compound vector hydrophone has been applied in the underwater location, with a huge market potential in underwater detection systems.

Optimization of Shell packaging for cilium MEMS bionic vector hydrophone

Packaging of vector hydrophone influences its engineering application scope. However, the sensitivity of vector hydrophone is greatly reduced after packaging in previous works. Moreover, the vector hydrophone with dipole directivity has the problem of left-right ambiguity. To solve these problems, the shell packaging of cilium MEMS bionic vector hydrophone is optimized in terms of sound-transparent cap and the capability of underwater localization. A blue nitrile butadiene rubber is used as the material for the sound-transparent cap to solve the problem of poor sensitivity after packaging. And in order to solve the problem of left-right ambiguity of a single vector hydrophone, a piezoelectric ceramic tube is integrated into the shell to obtain sound pressure information. In this paper, the packaging process of optimized shell is introduced in detail. Then, the sensitivity test, directivity test and pressure-resisting test of optimized shell are finished. The testing results show that sensitivity of vector information part is increased average 5.6 dB after packaging. And the sensitivity curve depicts that the sensitivity increases 6 dB per octave in the working bandwidth in the range of 63−1000 Hz. Therefore, the optimized vector hydrophone shows a good performance in engineering application.

Off-Grid DOA Estimation Based on Alternating Iterative Weighted Least Squares for Acoustic Vector Hydrophone Array

In this paper, an alternating iterative weighted least squares method is proposed to handle the off-grid issue in sparsity-based direction of arrival (DOA) estimation for acoustic vector hydrophone (AVH) array. Firstly, the off-grid model via AVH array is formulated by introducing a bias parameter into the signal model. Secondly, the reconstructed interference plus noise covariance matrix is calculated as the weighting term. Then, a novel objective function with respect to the sparse signal and the unknown bias parameter is developed based on weighted least squares. Finally, the closed-form solutions of the sparse signal and the unknown bias parameter are deduced. Simulation results reveal that compared with the state-of-the-art algorithms, the proposed method improves the DOA estimation accuracy in the presence of a coarse sample grid and has a faster convergence speed. Furthermore, the effectiveness and robustness of the proposed method are verified by the underwater experimental results.

Design of a MEMS bionic vector hydrophone with piezo-gated MOSFET readout

A new design of a MEMS bionic vector hydrophone based on piezoelectric transduction has been proposed. The designed hydrophone has a higher sensitivity in comparison to its previous counterparts. Readout electronics includes embedded MOSFETs and external operational amplifiers. MOSFETs with piezoelectric gates are integrated to the beams and have been used as the strain to electrical current transducers. The drains of the MOSFETs have been connected to operational amplifiers that convert the transistor currents to the voltage and also amplify the output. The changes in the channel length and mobility are negligible and the transistor current is merely under the influence of the pressure induced charges on the piezoelectric surface which directly produce the vertical electric field. Designed hydrophone characterized with the sensitivity up to −146.2 ​dB (Ref. 1 ​V/μPa) for frequencies up to about 3 ​kHz. The results verify the possibility of utilizing the proposed design as an underwater acoustic sensor with a high sensitivity and a wide frequency range.

Iterative Sparse Covariance Matrix Fitting Direction of Arrival Estimation Method Based on Vector Hydrophone Array

Aiming at the direction of arrival (DOA) estimation of coherent signals in vector hydrophone array, an iterative sparse covariance matrix fitting algorithm is proposed. Based on the fitting criterion of weighted covariance matrix, the objective function of sparse signal power is constructed, and the recursive formula of sparse signal power iteration updating is deduced by using the properties of Frobenius norm. The present algorithm uses the idea of iterative reconstruction to calculate the power of signals on discrete grids, so that the estimated power is more accurate, and thus more accurate DOA estimation can be obtained. The theoretical analysis shows that the power of the signal at the grid point solved by the present algorithm is preprocessed by a filter, which allows signals in specified directions to pass through and attenuate signals in other directions, and has low sensitivity to the correlation of signals. The simulation results show that the average error estimated by the present method is 39.4% of the multi-signal classification high resolution method and 73.7% of the iterative adaptive sparse signal representation method when the signal-to-noise ratio is 15 dB and the non-coherent signal. Moreover, the average error estimated by the present method is 12.9% of the iterative adaptive sparse signal representation method in the case of coherent signal. Therefore, the present algorithm effectively improves the accuracy of target DOA estimation when applying to DOA estimation with highly correlated targets.

Measurement of the Acoustic Reflection Coefficient of Materials Based on Signal Subspace Decomposition Using a Single Vector Hydrophone

A method is presented for measuring the reflection coefficient of underwater acoustic materials in the free field with a single vector hydrophone. The main advantage of this method is that the incident and reflected signals are separated in the signal subspace without considering the aliasing of direct and reflected signals in the time domain. The postprocessing inverse filter technology is introduced into the measurement. The signal distortion caused by the transfer function of the measurement system is compensated for the postprocessing inverse filter, which is conducive to eliminating the interference of the edge diffraction. The basic mechanism is based on signal subspace decomposition and postprocessing inverse filter technology. Numerical simulations are presented to demonstrate the advantages of the method. The findings are confirmed by an underwater experiment conducted with a single vector hydrophone. The experimental results show that a satisfactory reflection coefficient can be obtained using this method, and the results agree well with the numerical predictions. The relative error of the measurement results is no more than 20%.

MEMS Hydrophone Signal Denoising and Baseline Drift Removal Algorithm Based on Parameter-Optimized Variational Mode Decomposition and Correlation Coefficient.

Underwater acoustic technology is an important means of detecting the ocean. Due to the complex influence of the marine environment, there is a lot of noise and baseline drift in the signals collected by hydrophones. In order to solve this problem, this paper proposes a denoising and baseline drift removal algorithm for MEMS vector hydrophone based on whale-optimized variational mode decomposition (VMD) and correlation coefficient (CC). Firstly, the power spectrum entropy (PSE), which reflects the variation characteristics of the signal frequency is selected as the fitness function of the whale-optimization algorithm to find the parameters (K,α) of the VMD. It is easier to find the global optimal solution of the parameters by combining the whale-optimization algorithm. Then, using the VMD algorithm after obtaining the parameters, the original signal is decomposed to obtain the intrinsic mode functions (IMFs), and calculating the correlation coefficients (CCs) between the IMFs and the original signal. Finally, the CC threshold is used to remove the noise IMFs, and the rest of the useful IMFs are reconstructed to complete the denoising and baseline drift removal process of the original signals. In the simulation experiments, the algorithm proposed in this paper shows better performance by comparing conventional digital signal-processing methods and the related algorithms proposed recently. Applied in the experiments of a MEMS hydrophone, the effectiveness of the proposed algorithm is also verified. This algorithm can provide new ideas for signal denoising and baseline drift removal.

Array MEMS Vector Hydrophone Oriented at Different Direction Angles

A new type of array MEMS (Microelectro Mechanical Systems) vector hydrophone has been proposed to solve the left-right ambiguity problem that is commonly found in current ones. Meanwhile, the advantages of good sensitivity and low fabrication cost are maintained. The array MEMS vector hydrophone is integrated by four units oriented at different direction angles. By the aid of this kind of vector hydrophone, not only the exact direction of the sound source can be measured, but also the position obtained. The working principle of the array microstructure has been analyzed and simulated. The result shows that the position of the sound source can be well determined. The prototype of the hydrophone is fabricated based on standard MEMS technology, and its performance is tested in a standing wave tube and an anechoic tank. The testing results show that the array hydrophone exhibits a good consistency of all the four units and satisfactory performance. More importantly, this array hydrophone exhibits excellent ability of positioning with the relatively small angle error. Thus, a MEMS hydrophone with multiple functions and relatively high performance is realized, which has important theoretical and practical significance in relevant applications such as the small-size underwater vehicles.

The Reflection Coefficients Measurement Method for the Underwater Acoustic Materials Based on the Single Vector Hydrophone

In order to obtain the normal acoustic reflection coefficients of underwater acoustic materials in the free field with the wideband pulse signal, a new measuring method with a single vector hydrophone and the post-processing inverse filtering is put forward. Numerical simulations had been conducted to comparatively analyze the measurement performances of the measuring method. The simulation results show that the present method should be established on the high ratio of signal to the noise and it is not sensitive to the system error. The experiment result shows that the post-processing inverse filtering measuring method is more effective comparing with the method without the post-processing inverse filtering, especially the measurement consequence of the post-processing inverse filtering measurement method tends to the theoretical value when the frequency is higher than 2.5 kHz, because limitation of the transducer.

Analysis for approach of passive measurement based on waveguide invariant

Nowadays, the development of underwater acoustic positioning and measuring direction technology becomes more and more important. A method which belongs to a passive direction based on waveguide invariant, could be used to measure a heading angle of a target source with guide source technology, combined with a single acoustic vector hydrophone at a low frequency in the epicontinental. At first, in the epicontinental ocean, at a low frequency, simulating the channel of ocean according to normal mode theory using the software called KrakenC. Then, the vector acoustic pressure field could be calculated, getting the schematic diagram about a stable interference structure of epicontinental ocean in a low frequency. Waveguide invariant could describe the situation about that. To pick up, waveguide invariant becomes the most important part of this paper. This process get with the movement of the guide source and the target source; also, an image processing method called Hough transform is essential. Finally, waveguide invariant is acquired. At the same time, by that, the heading angle of the target source is easy to be estimated. When detailed information of the ocean have not acquired enough, this method still works well, and simulation data for the experiment prove the feasibility of the model.

Mixed near field and far field sources localization algorithm based on MEMS vector hydrophone array

A mixed near and far field sources localization algorithm is proposed which applied to the uniform linear MEMS vector hydrophone array. The algorithm includes three steps: firstly, the steering vector contains common azimuthal information in both near and far field, direction-of-arrival (DOA) can be obtained by using the MUSIC algorithm. Secondly, the direction vector array is decomposed into different matrices and DOA and range are separated efficiently. All DOAs can be obtained through searching for a feature matrix. Thirdly, one-dimensional spectrum search in Fresnel zone is carried out to realize the accurate estimation of range in near-field. Finally, the performance of the algorithm was simulated. The results verify that the proposed algorithm can achieve DOA estimation within the range of [0:2*π] and solve the problem of port and starboard ambiguity. The vector matrix algorithm does not require construction the high-order cumulants and multi-dimensional search, and can avoid parameter matching procedure.

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.