This paper proposes two distinct methods for estimating the surface impedance Z_s of acoustic materials using a spherical microphone array. The first method is based on the spherical ambisonic representation of sound fields to estimate the normal particle velocity and the sound pressure at the surface of the material. The second method uses an optimization process, where the measured sound pressure field is constrained to match a theoretical model. These two methods are compared to two existing methods: the equivalent source approach and the two-microphone measurement technique. The results show a clear advantage of the microphone array methods compared to the classical two-microphone method. The measurements show an accurate reconstruction of surface impedance and absorption coefficient between 120 and 5000 Hz for various sound incidences but also show edge effect perturbations due to the limited size of the tested samples. In addition, two criteria are proposed, one estimating the noise floor level allowing the optimization of the measurement results, the other evaluating the area of accurate impedance reconstruction on the surface of the material.

中文翻译：

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使用球形麦克风阵列对倾斜入射的声学材料进行表征。

本文提出了两种不同的方法来估计表面阻抗Z _s使用球形麦克风阵列的声学材料。第一种方法是基于声场的球形双歧声表示，以估计材料表面的正常粒子速度和声压。第二种方法使用优化过程，在此过程中，测得的声压场被约束为与理论模型匹配。将这两种方法与两种现有方法进行了比较：等效信号源方法和双麦克风测量技术。结果表明，与经典的两麦克风方法相比，麦克风阵列方法具有明显的优势。这些测量结果表明，对于各种声音入射，表面阻抗和吸收系数在120至5000 Hz之间均可得到精确的重建，但由于受测样品的尺寸有限，还显示出边缘效应扰动。