Research On Abnormal Reflection Of Underwater Acoustic Wave From Acoustic Metasurface

Wave is a common form of motion in nature,and the research on wave regulation has extensive application value.In the past decade,more and more scholars have begun to pay attention to and study acoustic metamaterial.Different from natural materials,acoustic metamaterial achieve the purpose of controlling large wavelengths with small size by designing artificial structures with negative elastic modulus and negative mass density,but acoustic metamaterial have large volume,high processing cost The disadvantages such as high loss limit its application in practice,so acoustic metasurface emerges as the times require.Acoustic metasurface is a special form of acoustic metamaterial with low dimensions.It realizes the free control of sound waves through the sudden change of sound phase,and provides many methods to control sound waves,such as abnormal reflection/refraction of sound waves,sound focusing,sound absorption,sound stealth,asymmetric transmission of sound waves,etc.The research on acoustic metasurfaces is expected to have significant value in both theory and practice.The main content of the article is as follows:Chapter 1 introduces the research background,current research status,and current problems of acoustic metasurfaces.In Chapter 2,based on the generalized Snell’s law and the principle of sound wave propagation in layered media,a small-sized anomalous reflective metasurface with a unit structure of a double-layer uniform medium is constructed.The metasurface unit is equivalent to a uniform medium through equivalent parameter theory,explaining the reason for the decrease in metasurface thickness.The feasibility of the model is verified through COMSOL simulation.On the basis of the research content in Chapter 2,Chapter 3 reveals the influence of three factors: incident angle,unit reflection phase,and medium height within the unit on abnormal reflection phenomena.Based on this,the metasurface is further optimized to not only achieve thickness reduction,but also achieve abnormal reflection phenomena in the frequency range of4500Hz-7000 Hz.Then,it is compared with traditional metasurfaces in terms of thickness The comparison of reflection coefficient and working frequency band highlights the superiority of the metasurface designed in the article,which has good application prospects in the lowfrequency underwater acoustic field.In Chapter 4,based on the principle of coherent cancellation of sound waves,an acoustic focusing metasurface was constructed using only two units with a reflection phase difference of 180 °.The feasibility of the designed acoustic focusing metasurface was simulated and verified,and the focal point was numerically analyzed to evaluate its focusing performance.Factors affecting the acoustic focusing performance of the metasurface were studied,such as the number of units,the selection of focal length,and the width of the units,Then,it is proposed that the acoustic focusing hypersurface designed in this paper can be used in sonar systems to improve the signal strength received by the hydrophone instead of the acoustic baffle,which has a good application prospect.In Chapter 5,based on the principle of abnormal reflection on acoustic metasurfaces,experimental samples are prepared,and their abnormal reflection angles and acoustic characteristics when the incident wave deviates from the working frequency band are measured.Based on the experimental results,the designed acoustic metasurfaces can achieve broadband abnormal reflection phenomena,providing experimental basis for the application of acoustic metasurfaces.