Activation and deactivation detection for a passive wearable metasurface using a segmented ground plane

Abstract

The technology described herein is directed towards a wearable device that includes a passive metasurface of unit cells with a segmented ground plane of electrically separated segments. When the wearable device is worn, e.g., as a ring or wristband that contacts the wearer's skin, the wearer's skin conductivity electrically connects the separated segments to provide a ground plane. With a complete ground plane, the metasurface's unit cells resonate when exposed to a transmitted signal and reflect a distinct signature corresponding to a physical radiation pattern of signals reflected by the activated metasurface. When not worn, the metasurface is deactivated because of the electrically disconnected ground plane segments. Thus, when a transceiver transmits a wireless radio frequency signal towards an activated metasurface, the radiation pattern of the reflected signal is distinct per metasurface, providing a signature of that particular metasurface, which can be used for proximity detection and/or authentication, for example.