Elastic Metasurface Design And Its Manipulation Of Flexural Wave

The structural vibration of major equipment,such as large-scale Aerospace/aircraft,underwater vehicle,high-speed train,and precision machine tool,is the macroscopic manifestation of the propagation and superposition of elastic wave in the exciting equipment structure.The research of manipulating elastic waves,based on metasurface,can help understand the complex structural vibration and provide solutions for vibration control and vibration utilization in a new perspective.Therefore,it is of high academic and engineering significance.This paper focuses on flexural wave manipulation,which is widely used in engineering.Firstly,we introduce a general method of designing the metasurface suitable for flexural waves.Then,we propose the metasurfaces with subunit coupling and disorder effect,respectively,and reveal the corresponding physical mechanisms.They solve some defects of the metasurface structures existing in most research,such as low transmittance,weak stiffness,and large thickness.Further,we extend the mode coupling method in acoustics to that in flexural waves and study the high-order diffraction of elastic waves in metasurface for the first time,which enriches the theoretical basis of elastic wave manipulation.Last,we realize the asymmetric transmission and absorption of flexural wave energy by the designed metasurface.The main work and innovative achievements of this paper are as follows:(1)We propose a universal method of adjusting the phase shift of transmission wave by multiple pillared resonators in series and reveal its intrinsic physical mechanism.The analytical model of multiple pillared resonators with the coupling between flexural waves and longitudinal waves is established,and the phase shift and transmission coefficient of transmission waves are analytically solved.According to the generalized Snell’s law,the pillared elastic metasurface is designed.The experimental results verify that the pillared elastic metasurface can effectively manipulate the vertically and obliquely incident flexural waves.(2)We propose a conceptual design of elastic metasurface with subunit coupling and reveal the physical mechanism of the coupling interference between the adjacent subunits.By using analytical and numerical methods,we study flexural wave manipulation based on the metasurface.The experimental results verify that the designed metasurface can deflect and focus the flexural wave under the condition of ensuring the host plate integrity.(3)We propose the disordered elastic metasurface composed of the same pillared resonators and reveal the physical mechanism of the disorder effect of pillared resonators in the subunits.The experimental results verify that the disordered elastic metasurface can deflect and focus the flexural wave effectively independent of the arrangement of pillared resonators in subunits.It broadens the application of the interaction between elastic waves and disordered artificial media.(4)We propose and design a type of double-layer elastic metasurface to realize asymmetric transmission of the flexural wave,without taking advantage of traditional methods,such as transmission mode conversion or internal loss.We explain the working mechanism in detail and obtain geometric conditions to be satisfied for the double-layer structure design.The experimental results verify that the double-layer metasurface structure has obvious asymmetric transmission characteristics in a wide frequency range.(5)We propose a kind of lossy gradient elastic metasurface to realize the low-frequency broadband absorption of flexural waves and reveal the mechanism of its high-efficiency absorption.The experimental results verify that in the frequency range of 343-1000 Hz(larger than 1.5 octaves),the average absorption coefficient of lossy gradient elastic metasurface is greater than 0.9.The main reasons for the low-efficiency absorption of lossy gradient elastic metasurface are also analyzed.Last,we propose the design method of reducing the thickness of the metasurface while maintaining the function,which provides a new idea for the smallscale structure to manipulate the low-frequency elastic wave.In summary,this paper designs the elastic wave metasurface through theory,simulation,and experimental methods to realize the effective manipulation of directional transmission,asymmetric transmission,focusing,and absorption of bending waves.The research results promote the application of metasurface in the field of engineering vibration control.