Acoustic Scattering Strength Control Study Of Underwater Targets B Ased On Metamaterial

With the rapid development of underwater acoustic technology,the sonar range and directional accuracy have been continuously improved,which puts forward higher requirements for the anti-detection and acoustic stealth capability of underwater vehicle.Because of its good acoustic-absorbing performance in medium and high frequency band,the anechoic tile can effectively reduce the Target Strength of underwater vehicle,and has been widely used in underwater acoustic countermeasure technology.However,with the decrease of sonar detection frequency,the traditional acoustic absorption material needs a larger size to meet acoustic-absorbing performance of low frequency wave,which not only increases the weight of vehicle,but also affects other performances.Therefore,Researching on the topic of new underwater low-frequency stealth technology is advanced,and has very important theoretical value and engineering practical value.The emergence of acoustic metamaterials provides a new idea for controling of low-frequency waves.Metamaterials are composed of sub-wavelength scale acoustic structural units arranged in an orderly manner.Its unique "sub-wavelength" structural units can effectively control the transmission process of low-frequency acoustic waves.With the introduction of sound generalized Snell's law,a method of controlling acoustic waves by wavefront phase has emerged,but its application in underwater acoustic stealth has not yet been seen.In this paper,the low-frequency scattering characteristics of underwater targets are studied based on this kind of acoustic metamaterials.Firstly,the Helmholtz-like resonator structure is used to form sub-wavelength elements with phase mutation,and the calculation model of metamaterial phase control is established to realize the numerical simulation of metamaterial phase control.The reflection phase of the incident acoustic wave is of 0~2? range by designing the geometric size of elements.Acoustic metamaterial plates are composed of structural elements with different reflection phases which are randomly distributed on the plates according to certain rules.The effect of phase distribution on the underwater acoustic scattering intensity of the plates is analyzed.Secondly,the underwater scattering acoustic field of metamaterial plates are simulated by Boundary Element Method,and the simulation results are compared with those of a rigid plate.It is verified that the frequency of metamaterial plates with phase gradient can significantly reduce the Target Strngth and backscattering intensity within 1.5 kHz~3.2 kHz.Different phase distributions have different control over scattered acoustic waves.Unidirectional phase gradient metamaterial plate can deflect backscattering while multidirectional phase gradient metamaterial plates can transfer scattering energy to other angles to effectively reduce backscattering intensity.Based on metamaterial plates,the effects of phase distribution on acoustic scattering intensity of metamaterial curved plates are studied.The simulation results show that the control effect of phase gradient distribution on acoustic scattering intensity of curved plates is consistent with that of metamaterial plates.Finally,the underwater Target Strength of designed metamaterial plate is measured by direct method in the anechoic tank.The experimental results show that the Target Strength of acoustic metamaterial plate at 15 kHz ~ 35 kHz is 7-11 dB lower than that of ordinary plate,which proves that metamaterial plate with phase gradient can effectively reduce its underwater acoustic scattering strength..