142 research outputs found
Do Cloaked Objects Really Scatter Less?
We discuss the global scattering response of invisibility cloaks over the
entire frequency spectrum, from static to very high frequencies. Based on
linearity, causality and energy conservation we show that the total extinction
and scattering, integrated over all wavelengths, of any linear, passive, causal
and non-diamagnetic cloak necessarily increases compared to the uncloaked case.
In light of this general principle, we provide a quantitative measure to
compare the global performance of different cloaking techniques and we discuss
solutions to minimize the global scattering signature of an object using thin,
superconducting shells. Our results provide important physical insights on how
invisibility cloaks operate and affect the global scattering of an object,
suggesting ways to defeat countermeasures aimed at detecting cloaked objects
using short impinging pulses.Comment: 29 pages, 4 figure
Invisibility and Cloaking: Origins, Present, and Future Perspectives
The development of metamaterials, i.e., artificially structured materials that interact with waves in unconventional ways, has revolutionized our ability to manipulate the propagation of electromagnetic waves and their interaction with matter. One of the most exciting applications of metamaterial science is related to the possibility of totally suppressing the scattering of an object using an invisibility cloak. Here, we review the available methods to make an object undetectable to electromagnetic waves, and we highlight the outstanding challenges that need to be addressed in order to obtain a fully functional coating capable of suppressing the total scattering of an object. Our outlook discusses how, while passive linear cloaks are fundamentally limited in terms of bandwidth of operation and overall scattering suppression, active and/or nonlinear cloaks hold the promise to overcome, at least partially, some of these limitations.AFOSR Award FA9550-13-1-0204NSF CAREER Award ECCS-0953311DTRA YIP Award HDTRA1-12-1-0022Electrical and Computer Engineerin
Multi-Layered Plasmonic Covers for Comb-Like Scattering Response and Optical Tagging
We discuss the potential of multilayered plasmonic particles to tailor the
optical scattering response. The interplay of plasmons localized in thin
stacked shells realizes peculiar degenerate cloaking and resonant states
occurring at arbitrarily close frequencies. These concepts are applied to
realize ultrasharp comb-like scattering responses and synthesize staggered,
ideally strong super-scattering states closely coupled to invisible states. We
demonstrate robustness to material losses and to variations in the background
medium, properties that make these structures ideal for optical tagging.Comment: 15 pages, 4 figure
Beyond the Rozanov Bound on Electromagnetic Absorption via Periodic Temporal Modulations
Incorporating time-varying elements into electromagnetic systems has shown to
be a powerful approach to challenge well-established performance limits, for
example bounds on absorption and impedance matching. So far, the majority of
these studies have concentrated on time-switched systems, where the material
undergoes instantaneous modulation in time while the input field is entirely
contained within it. This approach, however, necessitates accurate timing of
the switching event and limits how thin the system can ultimately be due to the
spatial width of the impinging pulse. To address these challenges, here we
investigate the periodic temporal modulation of highly lossy materials,
focusing on their relatively unexplored parametric absorption aspects. Our
results reveal that, by appropriately selecting the modulation parameters, the
absorption performance of a periodically modulated absorber can be greatly
improved compared to its time-invariant counterpart, and can even exceed the
theoretical bound for conventional electromagnetic absorbers, namely, the
"Rozanov bound". Our findings thus demonstrate the potential of periodic
temporal modulations to enable significant improvements in absorber performance
while circumventing the limitations imposed by precise timing and material
thickness in time-switched schemes, opening up new opportunities for the design
and optimization of advanced electromagnetic absorber systems for various
applications.Comment: 12 pages, 4 figure
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