Simple theoretical model for parity-time-symmetric metasurfaces

TL;DR

This paper introduces a simple analytical model based on acoustic circuit theory to identify exceptional points in PT-symmetric metasurfaces, enabling efficient design and analysis of wave manipulation effects like unidirectional antireflection.

Contribution

The authors develop a straightforward theoretical approach that directly finds EPs in PT-symmetric metasurfaces, simplifying the complex transfer matrix and parametric sweep methods used previously.

Findings

The model accurately predicts EPs in acoustic metasurfaces.

FEM simulations confirm the model's predictions across various conditions.

The approach facilitates the design of metasurfaces with tailored wave control effects.

Abstract

Many new possibilities to observe and use novel physical effects are discovered at so called exceptional points (EPs). This is done by using parity-time (PT) -symmetric non-Hermitian systems and balancing gains and losses. When combined with EP-physics, recently, metasurfaces have shown greater abilities for wave manipulation than conventional metasurface systems. However, the solving process for EPs usually requires the transfer matrix method (TMM) or a parametric sweep, which are both complex and time-consuming. In this Letter, we develop a simple theoretical model, which is based on acoustic equivalent-circuit theory and can find the analytic solutions for EPs directly. As a proof of concept, PT-symmetric acoustic metasurfaces are studied to test the theoretical model, which enables unidirectional antireflection effects at EPs. In addition, finite element method (FEM) simulations are performed to study these EP solutions using the theoretical model for different mediums, wavelengths, angles of incidence, and gain-loss ratios. Our work offers a simple and powerful theoretical tool for designing PT-symmetric metasurfaces at EPs and may also be used for other classical wave systems.