Perfectly Reflectionless Omnidirectional Absorbers and Electromagnetic Horizons

TL;DR

This paper explores the fundamental limitations of perfectly reflectionless omnidirectional electromagnetic absorbers, introduces the concept of electromagnetic horizons, and proposes practical, effective alternative absorber designs that are robust to wave diversity.

Contribution

It identifies fundamental constraints on passive PR-OEMA devices, explains the emergence of electromagnetic horizons, and offers practical absorber blueprints that, while not perfectly reflectionless, are effective and robust.

Findings

Active media are required for perfect reflectionless absorption.

Electromagnetic horizons are a fundamental limitation in true PR-OEMA.

Practical absorber designs can be effective without being perfectly reflectionless.

Abstract

We demonstrate the existence of metamaterial blueprints describing, and fundamental limitations concerning, perfectly reflectionless omnidirectional electromagnetic absorbers (PR-OEMA). Previous attempts to define PR-OEMA blueprints have led to active (gain), rather than passive, media. We explain this fact and unveil new, distinct limitations of true PR-OEMA devices, including the appearance of an "electromagnetic horizon" on physical solutions. As practical alternatives we introduce alternative OEMA blueprints corresponding to media that, while not reflectionless, are nonetheless effective in absorbing incident waves in a manner robust to incident wave diversity.