IBID: Intra-Body Identification Using Capacitive Backscatter

This study presents a novel intra-body identification (IBID) technology that uses capacitive backscatter for data transmission. The primary goal of IBID is to facilitate transmission of arbitrary data (e.g., IDs) between a battery-powered interrogator and a batteryless tag through physical interactions. Unlike traditional RFID, which relies on electromagnetic fields in the air for backscatter, IBID uniquely utilizes the finite conductivity of human skin and air-coupled capacitance to enable backscatter communication. In this study, we explore a configuration where the interrogator is worn on the body, and the tags are affixed to everyday objects for human activity monitoring. Specifically, we investigate capacitive backscatter performance when acquiring IDs from two object models: a cylindrical handle and a rectangular switch panel. Preliminary results demonstrate the successful implementation of intra-body capacitive backscatter and the system's ability to interrogate binary IDs. However, variations in the tag electrode dimensions result in fluctuating path gain, even over short distances, causing distortion in demodulated bits. To address this, we designed and implemented a proof-of-concept tag circuit on a PCB that transmits bursts of 16-bit binary values within one capacitor charge cycle and an interrogator that reliably demodulates and decodes an 8-bit binary ID.