Experimental Study Of The ARM9—based Near-field Acoustical Holography Based On Wave Superpose Approach Of Multiple Virtual Fields

Near-field acoustical holography is a technology applicable for near field low-frequency sound source identification. By obtaining the object’s near field holographic data, using acoustic field transform relation between the holography surface and the surface of the sound source, using the holographic data as a known quantity, space sound field transfer coefficient were obtained through the inverse transformation. Then the sound field radiation has been reconstructed. Combined with the Fast Fourier Transform algorithm and the equivalent source method, a new source simulation extrapolation technique is proposed to solve hologram data extrapolation problem. This technique obtains advantages of both equivalent source method and FFT algorithm, such as easy to implement, fast computing speed, suitable for sound source in any shape. As a result, this technique is more suitable for engineering practice.In this paper, using the holography technique based on FFT algorithm and equivalent source method, combined with characteristics of ARM9 architecture such as small volume, low power consumption, low cost, high performance, developed a holographic system that can realize holographic data acquisition and holographic transformation. Set up a complete set of experiment platform. This platform obtains the holographic information by array scanning acquisition under the condition of a small number of channels. In order to obtain the phase of complex sound pressure using cross spectra method. Use MATLAB calculation program of near-field acoustical holography acoustic to realize reconstruction and prediction of the sound field.This paper first introduces the theory and method of experiment and hardware and software design plan of data acquisition system. Then use the data acquisition system to conduct the study of the sound source identification. The experimental procedure involves many aspects. Firstly, it involves the arrangement of the holographic surface measure-nodes in the near-field of the sound field and the arrangement of microphones’ channel. Secondly, when microphones were on the right position sound pressure data can be collected through reference channel and holographic surface measure-nodes’ channel and then complex sound pressure can be computed. Thirdly, in order to compensate the time lag between microphone channels a phase shift must be added to the phase of complex sound pressure. After that procedure, combined with using the holography technique based on FFT algorithm and equivalent source method make a study of the sound source identification. Finally make a comparison of the reconstruction results and the measuring results and find the causes of the differences. Adjust the position of the reference microphone according to the analysis, made an extended experiment. Study the validity of the algorithm and the experimental scheme and the validity of the data acquisition system.