Subwavelength Focusing by Engineered Power Flow-Conformal Metamirrors

TL;DR

This paper introduces lossless, power flow-conformal metamirrors capable of subwavelength focusing of incident waves into a point, enabling high-resolution focusing without undesired scattering for various practical applications.

Contribution

The work presents a novel method using power flow-conformal surfaces for lossless wave focusing, adaptable to different wave sources and configurations.

Findings

Achieved λ/20 resolution focusing of a point source.

Demonstrated focusing of plane waves with high precision.

Provided a practical design strategy for lossless, subwavelength focusing metasurfaces.

Abstract

Many advances in reflective metasurfaces have been made during the last few years, implementing efficient manipulations of wavefronts, especially for plane waves. Despite numerous solutions that have been developed throughout the years, a practical method to obtain subwavelength focusing without the generation of additional undesired scattering is a challenge to this day. In this paper, we introduce and discuss lossless reflectors for focusing incident waves into a point. The solution is based on the so-called power flow-conformal surfaces that allow theoretically arbitrary shaping of reflected waves. The metamirror shape is adapted to the power flow of the sum of the incident and reflected waves, allowing a local description of the reflector surface based on the surface impedance. In particular, we present a study of two scenarios. First, we study the scenario when the field is emitted by a point source and focused at an image point (in the considered example, with the {\lambda}/20 resolution). Second, we analyze a metasurface capable to focus the power of an illuminating plane wave. This work provides a feasible strategy for various applications, including detecting biological signals near the skin, sensitive power focusing for cancer therapy, and point-to-point power transfer.