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

A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed,which is called "virtual end-fire array technology".To damage the coherence of the same frequency reflection interference of each path,signal of different phase 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.Signals all at the above positions were superimposed to eliminate the clutter.The insertion loss of the material was finally calculated by the desired waveform.In the measured frequency range of 3~20 kHz,the aluminum panel with size of 1.1 m×1.0 m×8 mm and the round aluminum panel 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 technology compared with the conventional method.Measuring round aluminum panel and rectangular aluminum panel,error in the effective measurement band was less than 0.5 dB and the interference of the acoustic multipath propagation effects was reduced effectively.Ability of one single transducer in reverberant tanks to measure acoustic materials is improved after this method implemented.