Modal and excitation asymmetries in magneto-dielectric particle chains

TL;DR

This paper investigates wave propagation in magneto-dielectric particle chains, revealing the coexistence of right- and left-handed modes, their unique dispersion properties, and how asymmetries can be exploited to reduce reflections.

Contribution

It introduces the existence of simultaneous RHM and LHM in isotropic particle chains with independent electric and magnetic responses, highlighting the role of structural bi-isotropy and excitation asymmetries.

Findings

LHM can exist even with positive polarizabilities and no bi-isotropy in particles.

LHM have smaller spatial width than RHM.

Asymmetries in excitation can eliminate reflections at chain terminations.

Abstract

We study the properties of dipolar wave propagation in linear chains of isotropic particles with independent electric and magnetic response, embedded in vacuum. It is shown that the chain can support simultaneously right-handed modes (RHM) and left-handed modes (LHM) of transverse-polarization. The LHM are supported by the structure even if the chain's particles possess positive polarizabilities and no Bi-isotropy; the needed structural Bi-isotropy is provided by the propagator instead of by the particle's local properties. In contrast to the transverse modes in chains that consist of purely electric particles that are inherently RHM, the LHM dispersion lacks the light-line branch since their dipolar features are not aligned with the electric and magnetic fields of a right-handed plane-wave solution in free space. Furthermore, it is shown that the spatial width of the LHM is significantly smaller than that of the RHM. Excitation theory is developed, and it is shown that the chain possesses modal and excitation asymmetries that can be used to eliminate reflections from chain's termination.