Free-space scattering characterization of ultrathin reflective metasurfaces and high-Q-factor sensing methods for conductor-backed materials

Abstract

Metal-backed materials establish the bridge linking traveling and surface waves for beam manipulation. Based on S-parameters, extracting the constitutive effective parameters (CEPs) is significant for characterizing their electromagnetic (EM) properties. However, precisely measuring S-parameters is vulnerable in free space. Here, a free-space method of extracting the S-parameters located at the upper surfaces of the ultrathin reflective metasurfaces is proposed, which is expected to facilitate fast testing of EM properties. Using the proposed method, measuring the distance between antennas and samples is unnecessary. Besides, the disturbing noise, especially the self-reflection of the source-horn port can be sufficiently eliminated by calibrating the horns with a vector network analyzer. The experimental and simulation results (both amplitude and phase) match well for both normal and oblique incidences. Inspired by the measurement process, two wireless sensing methods (dielectric and thickness) aimed at conductor-backed materials are discussed. The proposed scenarios are beneficial for wireless sensors, retrieval of CEPs, non-destructive test, design of reflective metasurfaces.

Keywords

• Ultrathin metal-backed metasurfaces
• Free-space S-parameters
• Measurement and extraction
• Dielectric and thickness sensing
• Noise elimination