Reversal of transmission and reflection based on acoustic metagratings with integer parity design

Abstract

Phase gradient metagratings (PGMs) have provided unprecedented opportunities for wavefront manipulation. However, this approach suffers from fundamental limits on conversion efficiency; in some cases, higher order diffraction caused by the periodicity can be observed distinctly, while the working mechanism still is not fully understood, especially in refractive-type metagratings. Here we show, analytically and experimentally, a refractive-type metagrating which can enable anomalous reflection and refraction with almost unity efficiency over a wide incident range. A simple physical picture is presented to reveal the underlying diffraction mechanism. Interestingly, it is found that the anomalous transmission and reflection through higher order diffraction can be completely reversed by changing the integer parity of the PGM design, and such phenomenon is very robust. Two refractive acoustic metagratings are designed and fabricated based on this principle and the experimental results verify the theory.

Polarization-dependent asymmetric transmission using a bifacial metasurface

“…In this condition, the lattice vector of the periodic structure replaces the phase gradient; this reveals various interesting phenomena, such as high order diffraction, asymmetric transmission and retroreflection. [35][36][37][38] However, while the inherited physics has been theoretically revealed in past studies, devices utilizing the relevant content is still rare. 39,40 Because the current research framework of metasurfaces which modulate full space lacks polarization response, the combination of the phase gradient for asymmetric transmission and a conventional polarization multiplexing scheme may pave the way to achieve novel polarization-selective full-space control in the electromagnetic regime.…”

“…39,40 Because the current research framework of metasurfaces which modulate full space lacks polarization response, the combination of the phase gradient for asymmetric transmission and a conventional polarization multiplexing scheme may pave the way to achieve novel polarization-selective full-space control in the electromagnetic regime. 14,15,35 In this article, a metasurface platform is proposed which achieves asymmetric transmission according to the polarization states of incident light and conveys two independent phase profiles to each space at the same time. We utilize a birefringent nanopillar as a unit to impart different phase profiles at two arbitrary orthogonal polarizations.…”

“…Next, we show that the transmissive metasurface possessing a specific phase gradient can be utilized to reflection-type using the critical angle condition. 35 As a result, control of the transmission and reflection can be realized by polarization of the incident light, and at the same time, their phases can be determined independently. The fabrication and measurements of the proposed scheme are also conducted with two examples (beam steering and holographic image generation) and verified with three different polarization pairs.…”

Reflective Focusing Based on Few-Layer Gradient Metasurface Element Array

“…Fermat's principle [8] points out that the wavefront of a light beam can be modified by controlling the phase of the light wave [9,10]. A metasurface exhibits peculiar optical properties in controlling electromagnetic waves [11,12]; it is also widely used in the terahertz band [13]. Traditional metal-based metasurfaces can effectively reduce losses during electromagnetic wave propagation [14,15], but the interaction intensity decreases as the distance between the metasurface and the electromagnetic beam increases [16,17].…”

Acoustic levitation with optimized reflective metamaterials

“…geometries 47 to achieve control even at oblique incidence, including using only two types of unit cells 48 and Archimedean spiral structures 49 . To the author's best knowledge, however, Melde et al 20 were the only ones to use a reflecting metamaterial for acoustic levitation, managing to suspend two lines of water droplets, with vertical distances of λ/2 between the droplets in each line and a horizontal distance of 2λ between the lines.…”