Physical bounds on electromagnetic invisibility and the potential of superconducting cloaks

• Published in: Photonics and nanostructures Vol. 12; no. 4; pp. 330 - 339
• Main Authors: Monticone, Francesco, Alù, Andrea
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Tokyo Elsevier B.V 01.08.2014; Elsevier
• Subjects: Applied classical electromagnetism; Cloaking; Diffraction and scattering; Electromagnetic wave propagation, radiowave propagation; Electromagnetism; electron and ion optics; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Metamaterials; Optics; Physics; Superconductors; Wave optics; Cloaking; Superconductors; Metamaterials; Electromagnetic wave scattering; Electrodynamics; Invisibility cloaks; Plasmonics; Metamaterial; Cross sections
• ISSN: 1569-4410; 1569-4429
• DOI: 10.1016/j.photonics.2014.05.008

•Physical bounds on cloaking imply more scattering than expected when integrated over frequency.•Superconductors may help reducing the scattering, both globally and locally.•The unique physics of superconductors appears ideally suited for plasmonic and mantle cloaking.•We discuss how these bounds may be extended to local bounds for selected frequency ranges. The possibility of suppressing the scattering cross section of an object is subject to fundamental physical bounds imposed by causality and passivity. Global cloaking limitations have been recently derived, which imply that any linear, causal and passive cloak necessarily increases the global scattering, integrated over the whole electromagnetic spectrum, compared to the uncloaked object. Here, we expand on this topic, discussing in detail an interesting exception to this limit represented by cloaks with static diamagnetism. In this context, we explore the potential of superconducting materials to realize global and local reduction of the scattering cross section. The concepts of plasmonic and mantle cloaking are extended to superconductors, realizing strong and tunable invisibility, with some unique properties stemming from the peculiar electrodynamics of superconductors. We conclude by qualitatively discussing a possible method to derive more stringent local bounds on cloaking.