Inverse Design of Perfectly-Matched Metamaterials Via Circuit-Based Surrogate Models and the Adjoint Method

In this work, perfectly-matched metamaterials (PMMs) are described and combined with inverse design to realize broadband devices. PMMs are discretized metamaterials with anisotropic unit cells selected from a constrained design space, referred to as perfectly-matched media. PMMs exhibit the unique property that all their unit cells are impedance-matched to each other as well as to the host medium in which they are embedded under all excitations. As a result, PMM devices rely on reflectionless refractive effects to achieve a prescribed function. This property enables true time delay performance and promises broadband capabilities. Two design examples are presented to demonstrate the potential of inverse-designed PMMs: a compact, broadband beam-collimator with a prescribed amplitude taper and a multi-input multi-output beamformer exhibiting zero scan loss.