Fiber-reinforced composite metamaterials for mode conversion of elastic waves

Abstract

Metamaterials are a class of man-made composites that can realize extraordinary wave phenomena and can be designed through exploiting anisotropy of elastic media. Anisotropy, as is known, is also an inherent characteristic of classical composites. Therefore, there is a great potential that the anisotropy of classical composites can be utilized to achieve extraordinary manipulation of elastic waves. To this end, we propose a concept of fiber-reinforced composite metamaterials, which attains extraordinary wave properties with rationally designed ply angles. Specifically, we consider the phenomenon of transmodal Fabry-Perot interference. This phenomenon, which can transfer wave energy between longitudinal and transverse modes solely and maximally, requires that the interferometer should attain unique anisotropy. Based on the transmodal interference theory and the classical lamination theory, the composite metamaterials are designed and validated numerically and experimentally. We note that the base material properties of each layer can significantly affect the metamaterial design, and an anisotropy index is introduced to investigate the effects. Our work broadens the applications of classical composites and offers a new way to design metamaterials.

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

“…On the other hand, elastic metasurfaces are also used to convert elastic waves, where most of the inclined incident P waves can be converted to reflected S waves. [21][22][23] However, reliance on the Fabry-Pérot resonance [18][19][20]24,25) or phase gradient 22,26) makes the size of the conversion devices of the same order as the working wavelength. Very recently, Wang et al proposed a new method 27) that did not use the effective elastic parameters or phase gradient.…”

Total conversion between the longitudinal and transverse waves by ultrathin elastic metamaterials with anisotropic resonances

“…Recently, the emergence of elastic metamaterial that could manipulate the polarization of elastic waves provides new methods to achieve conversion. [19][20][21][22][23][24][25][26][27] Almost total mode conversions are achieved by utilizing the transmodal Fabry-Pérot resonance. [19][20][21] Fluid-like (pentamode) and solid-like metamaterials 22) are designed to carry only longitudinal or shear waves in a broad frequency range.…”

“…[19][20][21][22][23][24][25][26][27] Almost total mode conversions are achieved by utilizing the transmodal Fabry-Pérot resonance. [19][20][21] Fluid-like (pentamode) and solid-like metamaterials 22) are designed to carry only longitudinal or shear waves in a broad frequency range. The required abnormal elastic parameters 22) can be realized by metamaterials.…”

“…An elastic metasurface [23][24][25][26][27] with a phase gradient on the free boundary of a semi-infinite solid is proposed to convert reflected wave modes with a broad incident angle. In these designs, [19][20][21][22][23][24][25][26][27] the whole size of the conversion device is generally in the same order as the working wavelengths. Although some optimization can reduce the size, it is still challenging to fundamentally break the limitation.…”

“…In this work, we propose a method to achieve total conversion by utilizing local resonance. 6) Our design does not rely on effective elastic parameters [19][20][21][22] or phase gradient [23][24][25][26][27] but just requires a sufficiently strong oblique displacement that can be provided by dipolar resonances. We demonstrate that total conversion is achieved within an ultrathin elastic metamaterial plate (EMP) with thickness, two orders smaller than the wavelength.…”