Explicit bounds for the high-frequency time-harmonic Maxwell equations in heterogeneous media

TL;DR

This paper establishes explicit, frequency-dependent bounds for solutions to high-frequency time-harmonic Maxwell equations in heterogeneous media, covering new classes of coefficients and scattering scenarios with uniform estimates.

Contribution

It provides the first sharp, explicit bounds for high-frequency Maxwell problems in heterogeneous media, including cases with previously unproven well-posedness and scattering by penetrable obstacles.

Findings

Bounds valid for arbitrarily large frequency

Includes new classes of coefficients with proven well-posedness

Uniform bounds for scattering by penetrable obstacles

Abstract

We consider the time-harmonic Maxwell equations posed in $\mathbb{R}^3$. We prove a priori bounds on the solution for $L^\infty$ coefficients $\epsilon$ and $\mu$ satisfying certain monotonicity properties, with these bounds valid for arbitrarily-large frequency, and explicit in the frequency and properties of $\epsilon$ and $\mu$. The class of coefficients covered includes (i) certain $\epsilon$ and $\mu$ for which well-posedness of the time-harmonic Maxwell equations had not previously been proved, and (ii) scattering by a penetrable $C^0$ star-shaped obstacle where $\epsilon$ and $\mu$ are smaller inside the obstacle than outside. In this latter setting, the bounds are uniform across all such obstacles, and the first sharp frequency-explicit bounds for this problem at high-frequency.