Virtual End-fire Array Technology And Its Applied Research In The Measurement Of Underwater Acoustic Materials

With the increasing demand for underwater stealth and sonar technology,the main development trend of underwater acoustic materials is to develop toward broadband and low-frequency.However,the multipath effect of sound waves is the main reason for impacting the accuracy of measurement results when measuring underwater acoustic materials in the low-frequency range.Therefore,how to suppress the multipath effect in the measurement of underwater acoustic materials is an urgent problem to be solved.A method suppressing multipath effect when measuring the underwater acoustic materials is proposed,which is called “virtual end-fire array technology”.The method analyzes the received waveforms of the hydrophone by measuring the signals at different positions transmitting by a single transducer,which shows this method can suppress reflection interference by damaging the coherence of the same frequency reflection interference of each path.According to the moving method,the directivity function of the virtual end-fire array is deduced and the end-fire array is designed by the actual layout.Signals all at the above positions were superimposed to eliminate the clutter and the parameter of the material was finally calculated by the desired waveform.The reverberant pool with a geometry size of 5.5 m×3.5 m×3.5 m was used to measure the aluminum plate and the sound absorption wedges.The measurement results show that the technique can reduce and eliminate the interference of the boundary reflection wave and the sample diffraction wave in the low-frequency measurement range.The effective measurement frequency by the virtual end-fire method is lower than the conventional method.Compared with conventional method,virtual end-fire array method has smaller error and better suppression effect in the lower frequency.The measured effective frequency band is consistent with the theoretical derivation values,which indicate that the theoretical derivation is correct and this method can guide practical application.In addition,the test system according to the principle of virtual end-fire array method can save the cost and achieve the low-frequency measurement of the underwater acoustic material in a small reverberant pool.The implementation of virtual end-fire array method made up for the insufficiency that non-directional sound source cannot suppress sample edge-effect in traditional measurement method and provides a new idea for the low-frequency acoustic performance measurement of underwater materials.