Research On The Application Of Acoustic Vector-sensor With Acoustic Baffle

The emergence of acoustic vector sensor, broke through the restrictions that measuringthe underwater acoustic signal for the sonar equipment has long relied on scalar pressuresensor, opens up a new way for the development of sonar technology. The acoustic vectorsensor is combined by omnidirectional pressure sensor and dipole particle velocity sensor,which co-locating and simultaneously measures acoustic pressure and all the three orthogonalcompotents of particle velocity in acoustic field. Using that information, it can obtain theintensity and direction of sources, and can have equivalent performance of a four elementssonar system with omnidirectional pressure sensor. This compact configuration of theacoustic sensors provides a very good solution to solve the problem of limited of the layoutspace of the small scale underwater platform. The directivity of acoustic vector sensor is notdependent on the frequency of sound. This advantage is particularly prominent in thelow-frequency trend of development of sonar systems. And it can make the sonar systemswhich base on the acoustic vector sensor have better low-frequency adaptability. The vectorsensor provides more information than a pressure sensor as it contains three dipole channelsin addition to a monopole channel. Hence, an array of N vector sensors can achieve betterperformance than a conventional array of N pressure sensors. Likewise, a given level ofperformance may be attained with fewer vector sensors. Due to these attractive characteristics,the acoustic vector sensor has been successfully applied to low-noise measurement system,marine sonar buoys, towed array sonar and other acoustic devices. These works have onlyconsidered the acoustic vector sensors in free space; however, when the acoustic vectorsensors are mounted on a ship, due to the scattering of the acoustic baffle, it will result in asignificant decline in the performance of the vector sensor. Therefore, how to use the acousticvector sensor in the presence of an acoustic baffle and obtain good performance as the marinesonar buoys have become urgent problems. In this paper, the three typical sonar baffles--rectangular, cylindrical and spherical baffle are taken as research objects, acoustic vectorcharacteristics of near fields scattered by the three typical sonar baffles as well as thecorresponding vector signal processing methods are studied.For the rectangular baffle, an elastic rectangular air chamber baffle which is usedcommonly in practical engineering is taked as research object. The elastic rectangular airchamber baffle is modeled as a baffled, simply supported plate. The both sides of the plate arewater and air respectively. The analytical expressions for the scattered pressure and particle velocity are derived. Then the rationality of the model and the correctness of the formula areverified. Calculations are presented for the scattered near fields of the pressure, the particlevelocity and the intensity. Because the expression of sound pressure field and particle velocityis quite complex, is not conducive to the signal processing, the scattering field were simplymodeled based on the reflection coefficient. In this way, we can establish a measurementmodel of vector sensor linear array with rectangular air chamber baffle based on the reflectioncoefficient. Based on this measurement model, vector signal processing methods for thevector sensor linear array with rectangular air chamber baffle is studied. Coherent signalprocessing of pressure and particle velocity is achieved in the direct element space.Simulation and experimental results show that the vector sensor linear array with rectangularair chamber baffle still can take full advantage of the vector sensor.Considering the engineering practice, a closed finite length cylindrical air chamber shellis used as a cylindrical baffle. Firstly, the acoustic scaterring from finite length cylindricalshell is studied. On the basis of previous studies, we use the elastic thin shell theory (Donnellequation) describe the motion of cylindrical shell, and under some approximation assumptionsanalytical expressions are derived for the total acoustic pressure field and the total particlevelocity field scattering from the cylindrical shell. The acoustic vector characteristics ofspatial distribution are discussed based on the analytical expressions. Phase modal domainsignal processing method for a traditional scalar circular array is introduced into the acousticvector sensor circular array mounted around a cylindrical baffle. The complex interferencepattern near the surface of cylindrical baffle, which is provoked by the far-field plane wave,can be decomposed into regular phase modal patterns. Then the modal vector-sensor arraysignal processing algorithm, which is based on the wavefield decomposition techniques, forthe acoustic vector sensor circular array mounted around the cylindrical baffle is proposed.Coherent signal processing of pressure and particle velocity is achieved in phase modal space.It is concluded that the vector sensor can be used under the condition of the cylindrical baffleand that the acoustic vector sensor circular array mounted around the cylindrical baffle canalso combine subspace DOA (direction of arrival) estimation algorithm with phase modalspace array signal processing technology. The scope of application of vector hydrophone isextended to the cylindrical baffle condition.The article also studied applications of vector sensor under the conditions of sphericalbaffle. Firstly, the analytic expressions for the scattered pressure and particle velocity arederived using the elastic thin shell theory. Calculations are presented for the scattered nearfields of the pressure, the particle velocity and the intensity. Based on the Wavefield decomposition techniques, the element domain signal were represented for some orderquadrature phase modes, and then gives the preconditioning matrix of the pressure, the radialvelocity and tangential velocity. The array signals are converted from element space to phasemodal space using the preconditioning matrix, and then estimate direction of arrival in phasemodal space. The algorithm is based on the principle of coherency between pressure andparticle velocity, which can suppress interference in isotropic noise field. The scope ofapplication of vector hydrophone is extended to the spherical baffle condition.Two experimental sonar systems, the three elements linear acoustic vector-sensor arraywith a rectangular air chamber baffle and the eight elements circular acoustic vector-sensorarray with cylindrical air chamber baffle, were designed to carry out the Songhua Lakeexperiment. The test results and the simulation results were in good agreement, to verify thecorrectness of the theory in this paper and provide the experimental basis for the engineeringapplication of acoustic vector-sensor with acoustic baffle.