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

Abstract

In this paper we study the electromagnetic scattering, absorption, and 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 in time. The analysis is carried out using the equivalent transmission line (TL) model of the actual electromagnetic system. Thus, it naturally take into account the effect of polarization (TE and TM) as well as the effect of the angle of incidence, by simply introducing the proper TL characteristics. After formulating the onedimensional TL problem in the complex temporal frequency variable s, we apply the inverse Laplace transform to find the signals in time. Specifically, we show that the spectral Green's function in the s plane possesses no branch point singularities but exhibits only simple pole singularities, and thus we use this fact to substantially accelerate the calculation of the inverse Laplace transform.As an important application we demonstrate numerically that a time-varying absorbing layer that undergoes temporal switching of its conductance only can absorb the power of a modulated, ultrawideband, as well as a quasi-monochromatic, pulsed wave beyond what is dictated by the Rozanov bound when integrating over the whole frequency spectrum.