Electromagnetic energy stored in inhomogeneous scattering systems

TL;DR

This paper provides an analytical framework for calculating electromagnetic energy in inhomogeneous scatterers, revealing how inclusion properties influence energy storage and scattering behavior in disordered media.

Contribution

It derives a shape-independent energy-transport velocity expression and relates internal energy to absorption, advancing understanding of electromagnetic energy in complex media.

Findings

Energy-transport velocity is independent of scatterer shape.

Enhanced electromagnetic energy occurs with negative scattering asymmetry.

Disordered media with backscattering can have high quality factors.

Abstract

We analytically study the time-averaged electromagnetic energy stored inside scatterers containing inclusions of arbitrary shapes. Assuming the low density of inclusions, we derive the expression for the energy-transport velocity through disordered media without relying on the radiative transfer equation. Moreover, this expression is independent of the shape of scatterers. In addition, we obtain a relation between the dwell and absorption times associated with inclusions by considering the relationship between internal energy and absorption cross-section. An approximation for the electromagnetic energy stored inside a disordered medium in terms of the transport mean free path and the packing fraction is also derived. This expression suggests that the enhanced electromagnetic energy within the host medium is achieved for inclusions exhibiting negative scattering asymmetry parameters. As a result, disordered media with enhanced backscattering is expected to exhibit large quality factors.