Cloaking a sensor via transformation optics

TL;DR

This paper reveals that transformation optics cloaks can allow wave coupling between cloaked and uncloaked regions, enabling sensors inside the cloak to measure external waves despite cloaking.

Contribution

It demonstrates the coupling between cloaked and uncloaked regions and proposes a method to hide sensors while still allowing wave measurement.

Findings

Cloaking does not fully shield the interior from wave coupling.

Interior resonances can amplify the coupling effect.

Sensors can be hidden yet effectively measure external waves.

Abstract

It is generally believed that transformation optics based cloaking, besides rendering the cloaked region invisible to detection by scattering of incident waves, also shields the region from those same waves. We demonstrate a coupling between the cloaked and uncloaked regions, exposing a difference between cloaking for rays and waves. Interior resonances allow this coupling to be amplified, and careful choice of parameters leads to effective cloaks with degraded shielding. As one application, we describe how to use transformation optics to hide sensors in the cloaked region and yet enable the sensors to efficiently measure waves incident on the exterior of the cloak, an effect similar to the plasmon based approach of Alu' and Engheta.