Wearable Deformation Sensor With Ambient Interference Rejection Using Differential Backscattered RFID Signal

RFID technology not only enables wireless identification, it also provides the platform for batteryless 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 interferences, any ambient impacts, such as distance variation and noises in the transmission path can cause the amplitude and phase changes of the receiving 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 apparels using conductive yarns. Experiments show that differential sensing signals can effectively eliminate the impact from ambient interferences, while tracking the body gesture even under constant distant variations.