On some constraints that limit the design of an invisibility cloak

TL;DR

This paper investigates the bandwidth limitations of invisibility cloaks based on transformation media, deriving a causality-based constraint and proposing a strategy to overcome it.

Contribution

It introduces a simple inequality constraint on bandwidth and suggests a method to bypass this causality-based limitation in cloak design.

Findings

Derived a causality-based bandwidth constraint

Proposed a strategy to circumvent the bandwidth limitation

Provided a theoretical framework for cloak bandwidth optimization

Abstract

Using the idea of transformation medium, a cloak can be designed to make a domain invisible for one target frequency. In this article, we examine the possibility to extend the bandwidth of such a cloak. We obtained a constraint of the band width, which is summarized as a simple inequality that states that limits the bandwidth of operation. The constraint originates from causality requirements. We suggest a simple strategy that can get around the constraint.