Give me a Sign: Passive Pose-Time Coded Handshaking

This paper presents a device based on UHF RFID technology that operates in the UHF band and transmits a backscattered response that is dependent on the previous physical orientations of the tag. This is analogous to a physical “secret handshake” for UHF-RFID based devices. While similar to gesture recognition, this method which we call “pose-time coding” is a low-power technique that requires minimal processing capability and is independent of the reader. Furthermore, no active components such as accelerometers are needed and instead this system operates with a linearly polarized reader and two tag rectennas with orthogonal linear polarizations. The backscattered response is generated using the Zeroscatter technique that enables simple backscatter radios for existing microcontrollers using general purpose digital I/O pins. Although this approach is feasible for fully-passive systems, the example semi-passive device we present uses a commodity microcontroller with an external supply and consumes an average of 144.6 μA at 3.3 V.