The Application Of Planar Near-filed Acoustical Holography In Noise Source Identification

Near-field acoustic holography is a very important technology in acoustic researching, which can reconstruct and predict acoustic quantities in the whole 3-D field by recording the sound pressure in the near-field of radiator. By using this method, we can not only identify the noise sources in the near-field, but also predict acoustic quantities in the far-filed.This thesis states the basic theory of planar near-filed acoustical holography and its actualization method. The discrete methods of K-space Green's function and the errors of each method are described in detail. The program for NAH is made by using the software -Matlab. The affection of parameters, such as discrete methods of k-space Green's function, reconstructing distance, filter windows and the error of reconstructed filed are analyzed by means of numerical simulation.A rough experiment is designed according to the basal theory of NAH. The parameters in the experiment are calculated after the transmit frequency of the source is confirmed. The measure system of the linear array is also set up. In the end, the whole system is adjusted to fit the requirement of the experiment. By the results of rough experiment, an advanced experiment is designed and the new parameters are set .After the advanced experiment, the results are analyzed.The results enunciate that positions of noise sources and distribution of sound field can be reconstructed accurately when the reconstruction distance is very small. The precision of sound field reconstruction will fall down when the reconstruction distance increases.