Mode conversions for elastic waves transmitted and reflected by ultrathin elastic metamaterial plates with anisotropic resonances

Abstract

In this work, we study the conversions between longitudinal and transverse modes by one layer of oblique anisotropic dipolar resonators, whose size can be orders smaller than the wavelength. The mode conversions are found for both transmitted and reflected waves by such small resonators with a normal incidence. A mass-spring model is proposed to depict analytically the mode conversion, giving simplified analytical expressions for the conversion rates. The reflected conversion will gradually increase to the maximum while the solid material behind resonators becomes soft, or vice versa. It may provide theoretical guidance for practical application.

Elastic metamaterials for guided waves: from fundamentals to applications

“…Accordingly, many types of mode conversion phenomena of guided waves have been reported. The most representative mode conversion phenomenon in guided waves in plates is the mode conversion between S0 and SH0 modes [73, 134,144,179,201,[203][204][205][206][207][208][209][210][211][212][213][214][215][216][217]. Unlike acoustic waves in fluids (which carry only longitudinal waves) and electromagnetic waves (which carry only transverse waves), an elastic solid medium can carry both longitudinal and transverse waves.…”

Complete mode conversion of elastic waves by utilizing hexapole resonances in a double-scatterers structure

“…The amplitude [9,10] and phase [10,11] of elastic waves can be manipulated by the elastic metamaterials. Very recently, the elastic-wave modes [12][13][14] have been also manipulated by the elastic metamaterials, and almost complete mode conversion under normal incidence is achieved [12,[14][15][16][17][18]].…”

Complete mode conversion between longitudinal and transverse waves by an elastic metamaterial slab with a double-scatterer structure

“…n recent years, the rise of elastic metamaterials has provided a new means for elastic wave manipulation, [1][2][3][4][5] which has attracted wide attention from researchers. The wave control of metamaterial mainly focuses on the amplitude, [6][7][8] phase [8][9][10][11][12][13] and polarization mode [14][15][16][17][18][19][20][21][22][23][24][25] of elastic wave. Among them, the conversion of the wave polarization mode is an interesting topic.…”

“…There has been found three ways to design an elastic metamaterial with the mode conversion function: design special anisotropic material parameters, [14][15][16][17][18][19] design phase gradient [20][21][22] (elastic metasurface), and design to generate oblique displacement. [23][24][25] Wang et al 24,25) shows that if a structure can generate oblique displacement relative to the incident waves, the oblique displacement will couple the P and S waves and consequently lead to mode conversions. In these works, the oblique displacement is induced by oblique anisotropic dipolar resonators.…”