Department of Power Mechanical Engineering, National Tsing-Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
J Acoust Soc Am. 2012 Aug;132(2):862-71. doi: 10.1121/1.4734238.
Conventional near-field acoustical holography (NAH) is generally based on the free-field assumption, which can cause errors when interfering sources are present in practical environments. To cope with this problem, previous research suggested a combined pressure-velocity approach for NAH that provides certain advantages to rejection of interferences. This paper revisits this idea in a broader context of optimal array design and examines the feasibility of using unidirectional microphones in each channel of the array such that the robustness of inverse reconstruction is enhanced against interfering sources. As indicated in the simulation, the numerical noise in finite difference estimation of particle velocity can nullify the advantage of the well-conditioned velocity-based reconstruction. In the proposed approach, the characteristics of each array channel consisting of two microphones are tailored by taking into account not only the directivity, but also the robustness against self-noise. An objective function based on directivity index and white noise gain is exploited in a linear quadratic optimization of a two-element end-fire array. The proposed optimal array is validated in conjunction with the equivalent source model (ESM) -based NAH through numerical simulations, with an interfering source positioned behind the array. The results have shown the directive optimal array has yielded improved quality of images in comparison with conventional approaches in the presence of an interfering source and sensor noise.
传统的近场声全息（NAH）通常基于自由场假设，当存在干扰源时，该假设会导致误差。为了应对这个问题，之前的研究提出了一种用于 NAH 的压力-速度组合方法，该方法对干扰的抑制具有一定的优势。本文在更广泛的最优阵列设计背景下重新审视了这一想法，并研究了在阵列的每个通道中使用单向麦克风的可行性，以便增强逆重建对干扰源的鲁棒性。如仿真所示，粒子速度有限差分估计中的数值噪声可能会抵消基于速度的良好条件重建的优势。在提出的方法中，通过考虑方向性和对自噪声的鲁棒性，对由两个麦克风组成的每个阵列通道的特性进行了调整。在一个两元素端射阵的线性二次优化中，利用基于指向性指数和白噪声增益的目标函数。通过数值模拟，结合基于等效源模型（ESM）的 NAH 对所提出的最优阵列进行了验证，其中干扰源位于阵列后面。结果表明，与存在干扰源和传感器噪声时的传统方法相比，指向性最优阵列在图像质量方面有了显著提高。
