Control of the Scattering Properties of Complex Systems By Means of Tunable Metasurfaces

TL;DR

This paper demonstrates how tunable metasurfaces inside a microwave cavity can actively control scattering properties, enabling on-demand coherent perfect absorption with extremely low output power at specific frequencies.

Contribution

It introduces a method to manipulate scattering in wave-chaotic systems using voltage-tunable metasurfaces to achieve desired scattering states like CPA.

Findings

Achieved near-perfect absorption with a power ratio of 3.71e-8 at 8.54 GHz.

Controlled the scattering matrix poles and zeros via multiple voltage biases.

Demonstrated on-demand CPA at a specific frequency.

Abstract

We demonstrate the ability to control the scattering properties of a two-dimensional wave-chaotic microwave billiard through the use of tunable metasurfaces located on the interior walls of the billiard. The complex reflection coefficient of the metasurfaces can be varied by applying a DC voltage bias to varactor diodes on mushroom-shaped resonant patches, and this proves to be very effective at perturbing the eigenmodes of the cavity. Placing multiple metasurfaces inside the cavity allows us to engineer desired scattering conditions, such as coherent perfect absorption (CPA), by actively manipulating the poles and zeros of the scattering matrix through the application of multiple voltage biases. We demonstrate the ability to create on-demand CPA conditions at a specific frequency, and document the near-null of output power as a function of four independent parameters tuned through the CPA point. A remarkably low output-to-input power ratio of $\frac{P_{out}}{P_{in}} = 3.71 \times 10^{-8}$ is achieved near the CPA point at 8.54 GHz.