Nonlinear, Active, and Tunable Metasurfaces for Advanced Electromagnetics Applications

We demonstrate a series of nonlinear, active, and tunable metasurfaces for a variety of electromagnetic applications. The metasurfaces have achieved a range of exotic properties by populating nonlinear or active circuit components on a periodically patterned metallic surface. The circuit components such as diodes, varactors, transistors, and other devices can be controlled manually, actively, or self-adaptively. This allows nonlinear metasurfaces to have active tuning, power-dependent behavior, self-focusing, reconfigurable surface topology, or frequency self-tuning capabilities. The power-dependent metasurfaces can be applied to active RF absorbers that only absorb high-power surface waves to prevent malfunction or damages to sensitive devices. The rectifier-based waveform-dependent metasurface absorber can be specifically designed to absorb either high power pulsed waves or continuous waves. The transistor based surface wave metasurface absorber provides another degree of freedom in that it can be manually switched to tune the absorber, or it can be tuned using computer controlled feedback. The self-focusing effect has been demonstrated for the first time at RF frequencies to automatically collimate high-power surface waves. The reconfigurable and self-tuning metamaterial surfaces can be implemented to support a broadband reconfigurable antenna system or to adapt to a wide range of incoming frequencies. In this paper, the concepts of nonlinear and active tunable metasurfaces are discussed, including results of full-wave simulation analysis, EM/circuit co-simulation, and experimental results in waveguides, using a near-field scanner, as well as far-field measurements in an anechoic chamber.