Transmodal Fabry-Pérot Resonance: Theory and Realization with Elastic Metamaterials

Abstract

We discovered a new transmodal Fabry-Pérot resonance where one elastic-wave mode is maximally transmitted to another. It occurs when the phase difference of two dissimilar modes through an anisotropic layer becomes odd multiples of π under the reflection-free and weak mode-coupling assumptions. Unlike the well-established Fabry-Pérot resonance, the transmodal resonance must involve two coupled elastic waves between longitudinal and shear modes. The investigation into the origin of wiggly transmodal transmission spectra suggests that efficient broadband mode conversion can be achieved if the media satisfy the structural stability condition to some degree. The new resonance mechanism, also experimentally characterized, opens up new possibilities for manipulating elastic wave modes as an effective alternative to generating shear-mode ultrasound.

Off-centered Double-slit Metamaterial for Elastic Wave Polarization Anomaly

“…As a novel application of the polarization anomaly, we will create a wave mode converting wedge that can transform an incident pure longitudinal wave into a pure shear wave. In the engineering view point, this longitudinal-to-shear converter has critical applications for nondestructive evaluation, sound/vibration reduction, medical diagnosis, and more 20 , 21 . Especially in the nondestructive evaluation area, converting wedges have been by far most commonly utilized for angle beam inspection 2 .…”

“…Almost all the conventional converters are built based on the critical angle scheme 2 , 22 – 24 , but they usually suffer from issues like low transduction efficiency and performance instability. Several recent studies 20 , 21 , 25 have paid attention to metamaterials to develop a new type of converter, but pure conversion between the dissimilar elastic wave modes still remains a challenge.…”

Theory for Perfect Transmodal Fabry-Perot Interferometer

“…Although complete mode conversion might be theoretically possible with double negative metamaterials 18 , 19 , their use is very restrictive and no actual realization is attempted. Recently, a mode conversion phenomenon through anisotropic slabs has been reported and the observed phenomenon was called the TFPR (transmodal Fabry-Perot resonance) 20 . On the assumption that the slabs are weekly-coupled and the background mediums are low-reflective, the pattern of local peaks in the mode conversion transmission was observed.…”

Controlling the effective bending stiffness via out-of-plane rotational resonances in elastic metamaterial thin plates

“…For acoustic and elastic metamaterials, exotic parameters have been widely investigated, such as negative mass density [1][2][3][4][5], negative bulk modulus [6][7][8], negative shear modulus [9], extreme anisotropy [10][11][12][13], hybrid properties [14][15][16], etc. These unprecedented properties give rise to novel phenomena and applications such as low-frequency blocking [17,18], negative refraction [19][20][21], cloaking [22][23][24][25][26][27][28], perfect absorption [29][30][31][32][33][34], acoustic impedance matching effect [35], mode conversion [9,36] and topological effects [37][38][39][40], etc. The development in acoustic and elastic metamaterials significantly enriches the physics and may have important implications in acoustics, structural mechanics, architecture, seismology and other disciplines in the future.…”