A method to measure the equivalent acoustic impedance of a scatterer

The procedures of simplifying scatterers’ geometry and finding its equivalent acoustic impedance are proposed by using scattering holography and multiple multipole expansions. The scattered sound field depends on the incident field, the geometry, and the physical property of the scatterer, which can be measured by using tools such as a set of microphones and a 3‐D scanner. Once the sound field over a surface is measured, the whole sound field of 3‐D space can be reconstructed by acoustic holography. However, predicting near‐field sound by holography is inefficient in practice, because huge numbers of measurement points are required to describe the complex sound field in the vicinity of a scatterer. With this regard, multiple multipole expansions are employed to reduce the number and the size of elements of a scatterer necessary to express the measured scattered field. Therefore it is equivalent to simplifying the geometry of a scatterer, and enables us to predict the sound pressure and velocity, as well as acoustic impedance, on the scatterers’ surface. Using the proposed method, it is demonstrated that the equivalent acoustic impedance can be obtained. [Work supported by the BK21 project initiated by the Ministry of Education and Human Resources Development of Korea.]