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Research On Vector Hydrophone And Combined Signal Processing

Posted on:2003-09-07Degree:MasterType:Thesis
Country:ChinaCandidate:H MengFull Text:PDF
GTID:2132360092966458Subject:Underwater Acoustics
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With the development of the acoustic stealth technique, the noise-level radiated by underwater moving targets becomes lower and lower. This is the new challenge for noise measurement technology, and particularly for the low frequency long-range detection. Towed line array technique is an effective way to solve this problems, however the conventional line arrays with omni-directional hydrophones suffer from the inherent left /right bearing ambiguity. The emergence of vector hydrophone, may change this present condition.A vector hydrophone is using to measuring the vector of sound field, it consists of two or three spatially collocated but orthogonally oriented velocity sensors (pressure gradient sensors, accelerometer or displacement sensors) plus an optional collocated pressure hydrophone. A single vector hydrophone thus has an intrinsic "8"or cardioid-like directivity pattern and therefore is very attractive for many applications in acoustics . One of these applications is the measurement of ambient noise directionally at low or infrasonic frequencies. The use of vector hydrophone in towed line arrays is to solve the left /right ambiguity without ship maneuvers by steering the hydrophone response to port and starboard.The left /right bearing resolution technique for a towed line array is presented in this thesis. By the comparison of various vector sensors' measurement principle and operating characteristics, we choose the combined vector hydrophones based on omnidirectional sound pressure hydrophone and accelerometer, which act as the elements of the acoustic vector-sensor line array in our special topic. The bending stresses in a cantilever beam of piezoelectric material is exploited for the accelerometer to obtain wide bandwidth and high sensitivity. The core of the vector hydrophone-the accelerometer and its measurement principle is analyzed with the scattering theory of a rigid body. The analysis of the stubby beam associated with the accelerometer requires the application of Timoshenko cantilever beam theory. Hence we predict the acceleration sensitivity, pressure sensitivity. In addition, we use the L.Rayleighmethod to derive the theoretical estimates of natural frequency that presented in this paper.The development of acoustic vector hydrophones, result in new signal processing techniques their corresponding - technology for pressure-particle velocity combined signal processing.Then for the benefit of the left /right target bearing resolution technique, we combine the pressure-velocity processing with the information provided by the multi-dimensional combined vector hydrophone which is composed of sound pressure hydrophones and particle velocity sensors in different ways. The combined processing researches include theoretical and simulation research on the pressure-velocity signal pre-processing, general linear beamforming of various vector hydrophones, vector-sensing line arrays and vertical arrays. Finally some meaningful conclusion care made, such as without a corresponding measurement of pressure, the triaxial velocity-sensing line array whose elements are placed along either the x -axis or z -axis still suffer from the left /right ambiguity.In order to compare the performance of vector-sensing arrays with that of conventional scalar-sensing arrays, we not only establish the measurement models, but also obtain the integral and closed form expressions for the auto- and cross-correlations between the components of an acoustic vector hydrophone in the wideband noise field, with the following assumptions concerning its spatial distribution: 1) azimuth independence; 2) azimuth independence and elevation symmetry; and 3) spherical isotropy. At the same time we derive expressions for the cross-covariances between all components of two spatially displaced elements of vector-sensing arrays in the narrowband noise field with the same assumptions. Comparisons are made from DI(directivity index) and AG(array gain) for each type of individual vector hydrophone and for vector-sensing arrays .Finall...
Keywords/Search Tags:acoustic vector hydrophone, left /right bearing resolution, cantilever beam, acoustic vector-sensor line array, combined signal processing
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