Title: Measurement of the absorption coefficient for acoustical coating samples using multi-channel inverse filter

Author(s): SONG Hao; MA Xiaochen; LI Jun; LI Jianlong;

Affiliation(s): Systems Engineering Research Institute of Chinese Shipbuilding Industry; College of Information Science and Electronic Engineering, Zhejiang University; Key Laboratory of Ocean Observation-Imaging Testbed of Zhejiang Province

Abstract: A method of measuring the absorption coefficient for acoustical coating samples by use of the multi-channel inverse filter based on the least square method was proposed. First, the responses of the circuit channels and the underwater acoustical channels are estimated, the retransmitted inverse signals for the multiple transducers can be estimated using the least square method, and the cost function constructed by the multi-channel inverse filtering theory can be solved. Then, by retransmitting the inverse signals, the incident signal at the position of the acoustical coating sample is focused with high resolution, low level of side lobes and a narrow pulse signal in temporal domain, which improves the measurement accuracy of the absorption coefficient for acoustical coating samples at low frequencies. The performance of the spatio-temporal focusing for the proposed method is demonstrated by simulations. The validity of the method is verified by experiments carried out in a cylindrical tank for a steel plate sample in the frequency range 0.8-5.0 kHz. The experimental results show that the proposed method is effective to the measurement of the absorption coefficient for acoustical coating samples in non-free field, and is especially applicable to low-frequency measurements.