Title: A restraining multipath effect method for the measurement of insertion loss of underwater acoustic materials

Author(s): SUN Min; WANG Yuebing; ZHENG Huifeng; ZHAO Peng; WU Lizhuo;

Affiliation(s): College of Metrological Technology and Engineering, China Jiliang University

Abstract: A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed, which is called "virtual end-fire array method". To weaken the coherence of the same-frequency reflection interference of each path, signal of different phases at different positions was transmitted by a single transducer in the simulation design, and a sharp directionality in the direction of the array length was formed. All signals at the above positions were superimposed to eliminate the clutters. The insertion loss (IL) of the material was finally calculated by extracting the desired waveforms. In the measured frequency range of 3–20 k Hz, the aluminum plate with size of 1.1 m × 1.0 m × 8 mm and the round aluminum plate with 0.5 m in diameter and 8 mm in thickness were measured in a reverberant tank with size of 5.5 m × 3.5 m × 3.5 m. Results showed the measured lowest effective frequency limit can be reduced by the virtual end-fire array technique compared with the conventional method. In the measurement of round aluminum plate and rectangular aluminum plate, errors in the effective measurement band was less than 0.5 d B and the interference of the acoustic multipath propagation effects was reduced effectively. The ability of the transducer in reverberant tank to measure acoustic materials has been improved after implementing this method.