Surpassing super-radiant scattering limit in a flat split-ring resonator

TL;DR

This paper demonstrates a 2D array of split-ring resonators that surpasses traditional scattering limits, using optimization and empirical criteria, with potential applications in radar visibility.

Contribution

Introduces a near-field coupled split-ring resonator array optimized via genetic algorithms that exceeds classical scattering bounds, and proposes a super-radiant empirical criterion for performance evaluation.

Findings

Experimental device surpasses single-channel limit by over 2 times.

Super-radiant criterion accurately predicts maximal scattering.

Monte-Carlo simulations verify empirical bounds.

Abstract

Electromagnetic scattering bounds on subwavelength structures play an important role in estimating performances of antennas, RFID tags, and other wireless communication devices. An appealing approach to increase a scattering cross-section is accommodating several spectrally overlapping resonances within a structure. However, numerous fundamental and practical restrictions have been found and led to the formulation of Chu-Harrington, Geyi, and other limits, which provide an upper bound to scattering efficiencies. Here we introduce a 2D array of near-field coupled split-ring resonators and optimize its scattering performances with the aid of a genetic algorithm, operating in 19th-dimensional space. Experimental realization of the device is demonstrated to surpass the theoretical single-channel limit by a factor of >2, motivating the development of tighter bounds of scattering performances. A super-radiant criterion is suggested to compare maximal scattering cross-sections versus the single-channel dipolar limit multiplied by the number of elements within the array. This new empirical criterion, which aims on addressing performances of subwavelength arrays formed by near-field coupled elements, was found to be rather accurate in application to the superscatterer, reported here. Furthermore, the super-radiant bound was empirically verified with a Monte-Carlo simulation, collecting statistics on scattering cross sections of a large set of randomly distributed dipoles. The demonstrated flat superscatterer can find use as a passive electromagnetic beacon, making miniature airborne and terrestrial targets to be radar visible.