Absorption and scattering by a temporally switched lossy layer: Going beyond the Rozanov bound

TL;DR

This paper demonstrates that a temporally modulated lossy layer can absorb electromagnetic pulses beyond the traditional Rozanov bound, using numerical simulations and practical metamaterial designs with time-varying properties.

Contribution

It introduces a method to surpass the Rozanov bound by employing time-varying electromagnetic layers with abrupt or gradual switching of properties.

Findings

Time-varying layers can exceed Rozanov bound for broadband absorption.

Switching the layer's properties can be practically implemented with resistor-loaded metamaterials.

Gradual switching overcomes causality issues associated with abrupt changes.

Abstract

In this paper we study the electromagnetic scattering, absorption, and performance bounds for short time modulated pulses that impinge on a time-varying lossy layer that is sandwiched between vacuum and a perfect electric conductor. The electric characteristics of the layer, namely, the conductivity, permittivity, and permeability are assumed to change abruptly or gradually in time. We demonstrate numerically that a time-varying absorbing layer that undergoes temporal switching of its permittivity and conductance can absorb the power of a modulated, ultra-wideband, as well as a quasi-monochromatic, pulsed wave beyond what is dictated by the time invariant Rozanov bound when integrating over the whole frequency spectrum. We suggest and simulate a practical metamaterial realization that is constructed as a three-dimensional array of resistor loaded dipole. By switching only the dipole's load resistance, desired effective media properties are obtained. Furthermore, we show that Rozanov's bound can be bypassed with abrupt and a more practical gradual, soft, switching thus overcoming some possible causality issue in abrupt switching.