Broadband suppression of backscattering at optical frequencies using low permittivity dielectric spheres

TL;DR

This paper demonstrates that low permittivity dielectric spheres can achieve broadband backscattering suppression at optical frequencies by exploiting approximate duality, resulting in highly directive radiation patterns over an octave bandwidth.

Contribution

It introduces a novel approach using large, low permittivity spheres for broadband backscattering suppression, expanding design possibilities at optical frequencies.

Findings

Broadband backscattering suppression achieved with low permittivity spheres.

Highly directive radiation patterns across an octave bandwidth.

Analytical and numerical validation using Mie theory.

Abstract

The exact suppression of backscattering from rotationally symmetric objects requires dual symmetric materials where ${\epsilon_r} = {\mu_r}$. This prevents their design at many frequency bands, including the optical one, because magnetic materials are not available. Electromagnetically small non-magnetic spheres of large permittivity offer an alternative. They can be tailored to exhibit balanced electric and magnetic dipole polarizabilities, which result in approximate zero backscattering. In this case, the effect is inherently narrowband. Here, we put forward a different alternative that allows broadband functionality: Electromagnetically large spheres made from low permittivity materials. The effect occurs in a parameter regime that approaches the trivial ${\epsilon_r} \to {\mu_r} =1$ case, where approximate duality is met in a weakly wavelength dependence fashion. Despite the low permittivity, the overall scattering response of the spheres is still significant. Radiation patterns from these spheres are shown to be highly directive across an octave spanning band. The effect is analytically and numerically shown using the Mie coefficients.