Research On Wave Mode Conversion Characteristics By Tunable Phase Metasurface

The metasurface is an artificial composite structure that can change the elastic wave or acoustic wave propagation characteristics.This special structure can produce extraordinary physical phenomena and greatly expand the design and application prospects of structural functional materials.Its application area includes nondestructive testing,medical imaging,acoustic lenses,and so on.In this paper,a phasetunable piezoelectric metasurface is designed based on piezoelectric shunt technology.The incident longitudinal wave of wide frequency band can be converted into transverse wave without changing the original topology.Its great advantages include a wide range of incident angles(0~45°)and extremely high mode conversion efficiency(up to 90%).This paper expounds its physical properties and anomalous reflection phenomena through theoretical analysis,numerical simulation and experimental verification.The main research contents are as follows:Firstly,according to the theory of equivalent parameters and the propagation characteristics of elastic waves,a theoretical analysis model of one-dimensional piezoelectric shunt that can adjust the phase of elastic wave have been established.Therefore,the author explored the mechanism of phase transition of piezoelectric shunt unit.It is designed that one-dimensional piezoelectric shunt structure can be able to adjust the phase of elastic wave by this mechanism.Secondly,combined with piezoelectric shunt array technology,the onedimensional piezoelectric shunt structure is extended to two-dimensional piezoelectric metasurface.Generally,based on the generalized reflection law and Fermat's theorem,it is proved that the two-dimensional metasurface has the characteristic of wave-mode conversion.The piezoelectric metasurface is imported into the finite element software for simulation calculation.It is verified that the mode conversion can occur at different incident angles and frequencies by changing the circuit parameters of metasurface.Finally,to verifying the correctness of theoretical analysis and numerical simulation,the author has fabricated piezoelectric metasurface sample and built the experimental test system.The designed piezoelectric metasurface sample was prepared.And the measurement system of longitudinal wave field and transverse wave field is built.Combined with the result of numerical simulation,an experimental method for piezoelectric super-surface is designed.The experiment result show that the piezoelectric metasurface can realize the function of converting the longitudinal wave into the shear wave by changing the inductance parameter in the circuit.According to the adjustable characteristics of piezoelectric shunt unit,this piezoelectric metasurface has great application potential in the field of intelligent structure.