Nonlocal homogenization theory in metamaterials: effective electromagnetic spatial dispersion and artificial chirality

TL;DR

This paper presents a first-principles formalism for predicting the electromagnetic response of metamaterials, including spatial dispersion and artificial chirality, using multiscale analysis and averaging techniques within the long wavelength limit.

Contribution

The authors develop a compact, general formalism for calculating effective permittivity and spatial dispersion tensors in metamaterials, incorporating second-order effects and symmetry-based chirality analysis.

Findings

Metamaterials can exhibit pseudo-chiral-omega chirality even if geometrically achiral.

A simple expression for the metamaterial chirality tensor is derived for negligible second-order dispersion.

One-dimensional metamaterials' chirality parameter is analytically related to their dielectric profile.

Abstract

We develop, from first principles, a general and compact formalism for predicting the electromagnetic response of a metamaterial with non-magnetic inclusions in the long wavelength limit, including spatial dispersion up to the second order. Specifically, by resorting to a suitable multiscale technique, we show that medium effective permittivity tensor and the first and second order tensors describing spatial dispersion can be evaluated by averaging suitable spatially rapidly-varying fields each satysifing electrostatic-like equations within the metamaterial unit cell. For metamaterials with negligible second-order spatial dispersion, we exploit the equivalence of first-order spatial dispersion and reciprocal bianisotropic electromagnetic response to deduce a simple expression for the metamaterial chirality tensor. Such an expression allows us to systematically analyze the effect of the composite spatial symmetry properties on electromagnetic chirality. We find that even if a metamaterial is geometrically achiral, i.e. it is indistinguishable from its mirror image, it shows pseudo-chiral-omega electromagnetic chirality if the rotation needed to restore the dielectric profile after the reflection is either a $0^\circ$ or $90^\circ$ rotation around an axis orthogonal to the reflection plane. These two symmetric situations encompass two-dimensional and one-dimensional metamaterials with chiral response. As an example admitting full analytical description, we discuss one-dimensional metamaterials whose single chirality parameter is shown to be directly related to the metamaterial dielectric profile by quadratures.