Pattern Reconfigurable Metasurface Antenna for Electromagnetic Torso Imaging

Abstract

A pattern reconfigurable metasurface antenna for an electromagnetic torso imaging system operating at the ultrahigh frequency (UHF) band is presented. To meet the requirements of electromagnetic torso imaging, the antenna can scan the human chest with steerable unidirectional radiation patterns. The designed antenna consists of three rectangular microstrip-fed slot radiators illuminating a metasurface layer with $7\times 5$ unit cells to cover the whole chest. Six p-i-n diodes are used to switch the radiating slots creating different beams. The unit cell dimensions are $0.125\lambda _{0}\times 0.125\lambda _{0}$ and the antenna has a low profile of $0.9\lambda _{0}\times 0.7\lambda _{0}\times 0.06\lambda _{0}$ ( $\lambda _{0}$ is the wavelength of the lowest operating frequency of the antenna). The antenna creates three distinct beams with a peak gain of 8 dBi at 1 GHz and 2 dBi gain variations across different beams over its measured wide operating frequency bandwidth of 27% at 0.8–1.05 GHz. A complete electromagnetic torso imaging system, which utilizes the designed antenna, is built and is successfully tested to detect 20 mL of fluid (water) inside the torso, thus differentiating between healthy and unhealthy cases.