Acoustics Division, Naval Research Laboratory, Washington, DC 20375, USA.
J Acoust Soc Am. 2010 Feb;127(2):773-83. doi: 10.1121/1.3278591.
A technique is described to image the vector intensity in the near field of a spherical array of microphones flush mounted in a rigid sphere. The spatially measured pressure is decomposed into Fourier harmonics in order to reconstruct the volumetric vector intensity outside the sphere. The theory for this reconstruction is developed in this paper. The resulting intensity images are very successful at locating and quantifying unknown exterior acoustic sources, ideal for application in noise control problems in interior spaces such as automobiles and airplanes. Arrays of varying numbers of microphones and radii are considered and compared and errors are computed for both theory and experiment. It is demonstrated that this is an ill-posed problem below a cutoff frequency depending on array design, requiring Tikhonov regularization below cutoff. There is no low frequency limit on operation, although the signal-to-noise ratio is the determining factor for high-spatial resolution at low frequencies. It is shown that the upper frequency limit is set by the number of microphones in the array and is independent of noise. The accuracy of the approach is assessed by considering the exact solution for the scattering of a point source by a rigid sphere. Several field experiments are presented to demonstrate the utility of the technique. In these experiments, the partial field decomposition technique is used and holograms of multiple exterior sources are separated and their individual volumetric intensity fields imaged. In this manner, the intensity fields of two uncorrelated tube sources in an anechoic chamber are isolated from one another and separated intensity maps are obtained from over a broad frequency range. In a practical application, the vector intensity field in the interior of an automobile cabin is mapped at the fundamental of the engine vibration using the rigid sphere positioned at the driver's head. The source regions contributing to the interior cabin noise are identified.
介绍了一种用于对紧密安装在刚性球中的球形微阵列近场中的矢量强度进行成像的技术。为了重建球体外部的体积矢量强度，将空间测量的压力分解为傅里叶谐波。本文发展了这种重建的理论。所得的强度图像非常成功地定位和量化了未知的外部声源，非常适合应用于汽车和飞机等内部空间的噪声控制问题。考虑了不同数量的麦克风和半径的阵列，并对其进行了比较，并计算了理论和实验的误差。结果表明，这是一个依赖于阵列设计的截止频率以下的不适定问题，需要在截止频率以下进行 Tikhonov 正则化。操作没有低频限制，尽管信噪比是低频高空间分辨率的决定因素。结果表明，上限频率由阵列中的麦克风数量决定，与噪声无关。通过考虑刚性球散射的精确解来评估该方法的准确性。提出了几个现场实验来演示该技术的实用性。在这些实验中，使用了部分场分解技术，并分离了多个外部源的全息图，并对其各自的体积强度场进行成像。通过这种方式，可以将消声室中两个不相关的管声源的强度场彼此分离，并从宽频带获得分离的强度图。在实际应用中，使用位于驾驶员头部的刚性球在发动机振动的基频下绘制汽车机舱内部的矢量强度场。确定了导致机舱内部噪声的源区域。
