Multifunction Tunable Piezoelectric-Actuated Metasurface at Millimeter-Waves

Free space (also termed quasi-optical) metasurfaces have recently been designed and proposed as new types of polarizers that allow polarization control of an impinging wave in ways that are not possible with conventional designs. However, existing methods for tunable metasurface polarizers are not able to fully control the polarization dynamically; additionally, at mm-wave and submillimeter bands, they typically suffer from high losses, which are predominantly produced by the inherent limitations of the tuning elements or materials. An electromechanically tunable reflection polariser that has the ability to fully control the polarization of an impinging wave has been designed, fabricated, and experimentally tested in a frequency band centered at 57 GHz. The proposed technique utilizes a variable air cavity between a periodic metasurface array and a ground plane, controlled by a piezoelectric actuator. The periodic metasurface element consists of two slightly different cross-shaped metallic elements arranged in a periodic triangular lattice. Full-wave simulations are presented and experimentally validated with measurements. The proposed approach is scalable from microwave up to THz frequencies with low-loss performance due to the nature of the tuning technology whereby the tuning element is not interfering with the electromagnetic waves in the structure.