Measurement of the absorption coefficient for acoustical coating samples using multichannel inverse filter

A method of measuring the absorption coefficient for acoustical coating samples using multichannel inverse filter using the least square method is proposed.First,the responses of the circuit channels and the underwater acoustical channels are estimated,and the retransmitted inverse signals for multiple transducers can be estimated with the least square method for solving the cost function constructed by the multichannel inverse filtering theory.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 based on the multichannel inverse filtering theory.The focus improves the measurement accuracy of the absorption coefficient for acoustical coating samples in low frequencies.The effect 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 specimen at the frequency 0.8-5 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.