A Capacitive Backscatter System for Intra-Body Identification

In this paper, we present a new intra-body communication technology that uses capacitive backscatter. The main goal of this technology is to allow for the transmission of binary IDs between a skin-coupled transceiver and a batteryless tag by utilizing finite conductivity of skin and air coupling capacitance. The intra-body identification (IBID) hardware system consists of two pairs of skin-coupled 50 ohm galvanically isolated electrodes: the interrogator(fixed size: 30 cm × 40 cm) and the tag (arbitrary shape and size). The flexibility of electrode shape enables the IBID tag to be easily deployed on various everyday objects. The interrogator is connected to a battery-powered wearable transceiver. The study investigated the capacitive backscatter phenomenon using two everyday object models: a remote control model and a rectangular single switch panel. The experimental results demonstrate the hardware system's ability to interrogate binary IDs seamlessly using 40 MHz pulsed radio frequency (RF) carrier with 33% duty cycle. However, the variable dimensions of the tag electrode lead to varying path gain within a short body channel, resulting in low available power for the tag. To address this challenge, we developed an ultra-low powered IBID tag that can sustain its operation at -11 dBm peak RF power and transmit multiple bursts of 16-bit binary packets.