We use particle swarm algorithms to devise subwavelength waveguide array structures that serve, for example, as transmissive walls (transmittance > 88%) for microwaves with incidence angles between -80 and +80 deg or spatial filters that refract microwaves with incidence angles smaller than +/-20 deg at a refraction angle of 0 deg in the forward direction. Furthermore, we optimized radar cross section reducing (RCSR) metasurfaces by use of stimulated annealing and applied machine learning to implement an RIS, whose backward deflection angle of a normally incident wave is electrically tuned between 5 deg and 65 deg for microwaves at 31 GHz.
Advanced technology, such as sensing and communication equipment, has recently begun to combine optically sensitive nano-scale structures with customizable semiconductor material systems. Included within this broad field of study is the aptly named frequency-selective surface; which is unique in that it can be artificially designed to produce a specific electromagnetic or optical response. With the inherent utility of a frequency-selective surface, there has been an increased interest in the area of dynamic frequency-selective surfaces, which can be altered through optical or electrical tuning. This area has had exciting break throughs as tuning methods have evolved; however, these methods are typically energy intensive (optical tuning) or have met with limited success (electrical tuning). As such, this work investigates multiple structures and processes which implement semiconductor electrical biasing and/or optical tuning. Within this study are surfaces ranging from transmission meta-structures to metamaterial surface-waves and the associated coupling schemes. This work shows the utility of each design, while highlighting potential methods for optimizing dynamic meta-surfaces. As an added constraint, the structures were also designed to operate in unison with a state-of-the-art Ti:Sapphire Spitfire Ace and Spitfire Ace PA dual system (12 Watt) with pulse front matching THz generation and an EOS detection system. Additionally, the Ti:Sapphire laser system would provide the means for optical tunablity, while electrical tuning can be obtained through external power supplies.
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