3D evolutionarily designed metamaterials for scattering maximization.

Abstract

The rapid growth in drone air traffic calls for enhanced radar surveillance systems to ensure reliable detection in challenging conditions. Increasing radar scattering cross-section can greatly improve detection reliability in civilian applications. Here, we introduce a concept of evolutionarily designed metamaterials in the form of multilayer stacks of arrays, featuring strongly coupled electric and magnetic resonators. These structures demonstrate a broadband end-fire scattering cross-section exceeding 1 m² at 10 GHz and, despite their compact footprint, achieve over 10% fractional bandwidth, meeting essential radar requirements for high-range resolution. While scattering cross-section and bandwidth are typically contradictory in resonant structures, this trend is circumvented by applying the resonance cascading principle, wherein a series of closely spaced, spectrally aligned resonant multipoles create a coherent response. The resonance cascading is engineered with the aid of multi-objective optimization, implemented on top of a genetic algorithm, operating in a large search space, encompassing over 100 independent variables. Experimentally realized parameters match typical scattering cross-sections of large airborne targets. Consequently, these performance characteristics enable the exploration of highly scattering structures as identifiers for small airborne targets, supporting effective radar-based air traffic monitoring in civilian applications, which we demonstrate through outdoor experiments using the DJI Mini 2 drone.