Wearable Deformation Sensor with Ambient Interference Rejection Using Differential Backscattered RFID Signals

RFID technology not only enables wireless identification, it also provides the platform for battery-less antenna sensing capabilities, i.e., the sensing information is modulated by the antenna impedance, and it can later be extracted from the backscattered signals by the readers. However, antenna sensing is prone to interference and ambient environment impacts, such as distance variation and noise in the transmission path. These factors can cause amplitude and phase changes of the received signals, and deteriorate the quality of the sensing information. In this paper, we propose a deformation sensor that consists of two adjacent-placed RFID antennas. The impedance of the two antennas will be modulated differently under the bending condition, and the deformation information can be extracted from the differential backscattered signals of the two antennas. To be deployed as a wearable body gesture sensor, the two antennas are embroidered on apparel using conductive yarns. Experiments show that differential sensing signals can effectively eliminate the impact from ambient interference, while tracking the body gesture even under varying reading distances.