Jiang Laixu, Xi Yingqi, Hu Yingying, Wang Guo, Liu Jingqiao
Marine Design and Research Institute of China, Shanghai 200011, China.
Sensors (Basel). 2024 Jul 17;24(14):4651. doi: 10.3390/s24144651.
In practical conditions, near-field acoustic holography (NAH) requires the measurement environment to be a free sound field. If vibrating objects are located above the reflective ground, the sound field becomes non-free in the presence of a reflecting surface, and conventional NAH may not identify the sound source. In this work, two types of half-space NAH techniques based on the Helmholtz equation least-squares (HELS) method are developed to reconstruct the sound field above a reflecting plane. The techniques are devised by introducing the concept of equivalent source in HELS-method-based NAH. Two equivalent sources are tested. In one technique, spherical waves are used as the equivalent source, and the sound reflected from the reflecting surface is regarded as a linear superposition of orthogonal spherical wave functions of different orders located below the reflecting surface. In the other technique, some monopoles are considered equivalent sources, and the reflected sound is considered a series of sounds generated by simple sources distributed under the reflecting surface. The sound field is reconstructed by matching the pressure measured on the holographic surface with the orthogonal spherical wave source in the vibrating object and replacing the reflected sound with an equivalent source. Therefore, neither technique is related to the surface impedance of the reflected plane. Compared with the HELS method, both methods show higher reconstruction accuracy for a half-space sound field and are expected to broaden the application range of HELS-method-based NAH techniques.
在实际情况下，近场声全息（NAH）要求测量环境为自由声场。如果振动物体位于反射地面上方，在存在反射面的情况下，声场就会变成非自由声场，传统的NAH可能无法识别声源。在这项工作中，基于亥姆霍兹方程最小二乘法（HELS）开发了两种半空间NAH技术，用于重建反射平面上方的声场。这些技术是通过在基于HELS方法的NAH中引入等效源的概念而设计的。测试了两种等效源。在一种技术中，使用球面波作为等效源，将从反射面反射的声音视为位于反射面下方不同阶次的正交球面波函数的线性叠加。在另一种技术中，一些单极子被视为等效源，反射声被视为由分布在反射面下方的简单源产生的一系列声音。通过将全息面上测量的压力与振动物体中的正交球面波源进行匹配，并用等效源代替反射声来重建声场。因此，这两种技术都与反射平面的表面阻抗无关。与HELS方法相比，这两种方法对半空间声场都具有更高的重建精度，有望拓宽基于HELS方法的NAH技术的应用范围。
