Physics of surface vibrational resonances: pillared phononic crystals, metamaterials, and metasurfaces

Abstract

The introduction of engineered resonance phenomena on surfaces has opened a new frontier in surface science and technology. Pillared phononic crystals, metamaterials, and metasurfaces are an emerging class of artificial structured materials, featuring surfaces, that consist of pillars-or branching substructures-standing on a substrate or a plate. A pillared phononic crystal exhibits Bragg band gaps while a pillared metamaterial may feature both Bragg gaps and local-resonance hybridization gaps. These two band-gap phenomena, along with other unique wave dispersion characteristics, have been exploited for a variety of applications spanning a range of length scales and covering multipe disciplines in applied physics and engineering. The placement of pillars on a semi-infinite surface has similarly provided new avenues for the control and manipulation of wave propagation, including Rayleigh and Love waves along the surface of substrates, as well as Lamb waves in plates-for frequencies ranging from Hz to several GHz. Even a finite placement of pillars along specific directions on a surface has been shown to offer unique functionality, such as steering a wavefront in the subwavelength regime. At the nanoscale, pillared membranes have been investigated and it was shown that atomic-scale resonances-stemming from the nanopillars-alter the fundamental nature of conductive thermal transport by reducing the group velocities and generating mode localization across the entire spectrum well into the THz regime. In this article, we first overview the history and development of pillared materials, then provide a detailed synopsis of a selection of key research topics that involve the utilization of pillars in different contexts. The following sections present a review of different configurations, properties, and 2 characteristics, namely: (i) fundamental vibrational and propagation properties of pillared plates; (ii) metamaterial phenomena in pillared plates including the opening of low and wide hybridization band gaps as well as super-resolution focusing; (iii) pillared metasurfaces and their wave steering functions;(iv) topologically protected phononic edge states in pillared plates; and (v) nanophononic metamaterials in the form of pillared membranes exhibiting exceptionally low in-plane thermal conductivity. Finally, we conclude by providing a short summary on the salient properties of pillared materials and structures and outlining some perspectives on the state of the field and its promise for further future development.

Rayleigh wave propagation in nonlinear metasurfaces

“…The presence of nonlinear forces can enable and enhance a variety of unique functionalities such as tunable [24] and asymmetric [25] propagation of waves. Although nonlinearity has been utilized to expand the available design space in metamaterials [1,26], its application in metasurfaces remains rare [3,27,28]. The most relevant studies, to the best of our knowledge, are those that involve nonlinear resonators attached to a one-dimensional substrate [29][30][31][32][33].…”

Topological surface wave metamaterials for robust vibration attenuation and energy harvesting

“…Mechanical metamaterials [3] whose configurations can be artificially fabricated and modulated have been proven to manipulate the propagation of mechanical waves with new effects such as wave isolation [4][5][6][7][8][9], topological insulator [10][11][12][13][14][15][16][17][18][19], Fano resonance [20][21][22][23], chirality [24], focusing and imaging [25], among others. Especially, surface wave metamaterials [1,[26][27][28][29][30][31][32][33][34][35][36] are designed mainly for transmission suppression of low-frequency surface wave in certain frequency ranges based on the conception of hybridized bandgaps.…”

Brillouin-zone characterization of piezoelectric material intrinsic energy-harvesting availability

“…In parallel to energy-harvesting research, the study of wave propagation in artificially structured materials has been an explosive area of research over the past three decades [25][26][27][28]. In this domain, two key classes of engineered materials emerged, namely phononic crystals (PnCs) [29][30][31][32][33][34][35] and locally resonant acoustic/elastic metamaterials [36][37][38][39][40].…”