Study On Reflection Coefficient Measurement For Anechoic Coating At Low Frequency In Limited Space

Acoustic coverings have a wide range of applications in the field of vibration and noise reduction for underwater vehicles.Evaluating the sound absorption performance of various acoustic coverings scientifically is of great significance to their design and application.And the reflection coefficient is an important sound absorption index of the acoustic cover layer.Measuring the reflection coefficient in a limited space(such as a pressure tank)environment is an important part of the evaluation.In recent years,with the application of acoustic focusing technology in acoustic measurement,the measurement technology of acoustic cover reflection coefficient in limited space has made great progress and has solved the problem of reverberation interference in mid and high frequency range.But low frequency reflection Coefficient measurement is still a problem to be solved,facing the problem of strong reverberation interference and low resolution at frequencies below 1 k Hz.Based on the existing multi-channel inverse filtering and time-reverse focusing technology and reflection wave reconstruction method,a low-frequency reflection coefficient measurement of acoustic coverings is presented.The technology uses multi-channel inverse filtering technology to form the sound field focus,and the reflected wave reconstruction technology reconstructs the reflected wave on the sample surface and refocuses it on the sample surface,and effectively reduces the low frequency reverberation on the incident wave and reflected wave.The main research work is as follows:(1)For the problem that the reflected wave cannot be received on the surface of the sample,the reflected wave of the sample surface is reconstructed by Kirchhoff integration using the idea of sound wave shift,and then the reconstructed reflected wave is re-focused the surface of the sample for suppressing reverberation.(2)Simulation of the entire measurement process,using COMSOL numerical calculation software to simulate multi-channel transmission,reconstruct the sample surface reflected wave and numerical time recersal.Reflection coefficient of the sample is compared with the theoretical value to verify the effectiveness of the method.(3)Under the environment of a large pressure muffler water tank,measurement of the reflection coefficient is carried out and the measurement results are compared with the theoretical value to verify the effectiveness of the method in the actual measurement application.