Internal-multiport-model-based fast inverse design of an antireflective artificial metastructure in a waveguide system

In practical applications, achieving perfect transmission of electromagnetic waves despite reflections from a complex medium segment in waveguide systems is of great significance. Using a preinstalled antireflective artificial metastructure (ARAMS) to mitigate reflections caused by the presence of a complex medium is an effective solution. The inverse design of ARAMS in waveguide systems is an optimization process. Recent applications of the topology optimization method in designing ARAMS have demonstrated attractive performances [Nature 607, 281 (2022)]. Topology optimization necessitates frequent utilization of full-wave electromagnetic simulations, while designing from scratch for different functional devices incurs exceedingly high computational costs. To address this problem, we introduce a fast inverse design method for ARAMS based on the internal multiport model (IMPM). Based on a single full-wave electromagnetic simulation dataset, IMPM abstracts the ARAMS electromagnetic field model into a microwave network, analytically establishing connections between actual excitation ports and fictitious internal ports while greatly reducing computational costs in optimization design. Furthermore, once IMPM is established, it can be reused for the rapid optimization design of various functional ARAMS devices in the same complex medium-filled waveguide environment. The cases presented in the paper validate the efficiency of this method in providing effective solutions for the perfect transmission of electromagnetic waves in waveguide systems filled with complex medium.