边界元法循环平稳近场声全息理论研究

Research on the cyclostationary nearfield acoustic holography based on boundary element method

循环平稳声场是工程中经常遇到的一种特殊非平稳声场,声压信号受到调制作用,导致频谱出现边带现象,经典的近场声全息技术重建得到的声场无法反映声场的调制特性。在平面循环平稳近场声全息基础上,提出一种边界元法的循环平稳近场声全息技术,用二阶循环统计量理论代替传统的傅里叶分析,并以声压的循环谱密度取代其频谱及功率谱密度作为重建量,可用于循环平稳声场中具有复杂表面声源的辐射声场。由于循环谱密度对循环平稳信号具有解调功能,用该方法重建得到的循环谱密度能有效地反映调制和载波信号的信息。仿真分析与实验表明了本理论的有效性和精度能满足工程要求。

Cyclostationary sound field is a special kind of nonstationary sound field, in which pressure signal is modulated seriously and sidebands exist in its spectrum. The reconstructed sound field can＇t figure the cyclostationary features in original Nearfield Acoustic Holography （NAH） procedure. On the basis of planar cyclostationary NAH, the cyclostationary NAH based on boundary element method is proposed which can be utilized to radiators with complicated surface in cyclostationary sound field. Replacing the Fourier＇s transform with the second-order cyclic statistics, the Cyclic Spectral Density （CSD） functions is used as the reconstructed physical quantity in the proposed NAH technique, instead of the spectrum or power spectral density of pressure signal. By virtue of the demodulation ability of CSD function, the reconstructed CSD holograph can effectively express the information of modulating and carrier wave solely. The simulation and experiment illustrate that the validity and accuracy of this cyclostationary NAH technique satisfy the request of engineering.