This paper focuses on the deduction of surface impedance and absorption coefficient of locally and non-locally reactive materials in free field. A sound wave model based on the complex image theory is introduced and used for deducing the characteristics of both locally and non-locally reactive materials. For the locally reactive material, the method based on the complex image model is compared with the other two existing deduction methods based on the Q-term model and the F-term model. The comparisons are made through numerical experiment in which the sound field above an impedance plane is simulated by the boundary element method. The results show that, considering both the accuracy and the efficiency, the complex image model-based method would be an optimal choice. For the non-locally reactive material, the method based on the complex image model is then compared with the existing deduction method based on the sound wave model proposed by Allard. The numerical experiment shows that, the method based on the complex image model can obtain almost the same result as that of the method based on the Allard’s model but cost less time.
Zhang et al. (Wed,) studied this question.