LC Repeater-Inspired Battery-Free, Chipless, Flexible Body Sensor Network With Lightweight Reader

Body sensor network (BSN) is rapidly evolving in mobile health (m-health), enabling the monitoring of multiple physiological sites through interconnected wireless wearable devices for efficient health management. However, the extensive use of devices on the body often requires substantial batteries and IC chips, increasing system complexity, weight, and cost, thus limiting practical applications. We present a battery-free, chipless physiological sensor employing an on-body passive LC repeater to enhance magnetic coupling between a sensor reader and the biomedical target. The passive LC repeater, encapsulated in flexible thermoplastic polyurethane (TPU), integrates seamlessly with skin or clothing to capture contact and noncontact physiological signals, including heart, lung, carotid, radial, and even femoral signals using an external coil connected to a compact $2.1 \times 2.3$ cm, lightweight 7.8 g sensor reader, simplifying signal acquisition, and reducing the complexity of readout techniques compared to cumbersome vector network analyzers (VNAs). To demonstrate its robust performance, the skin-attached passive LC repeater was sprayed with water and fully immersed, yet the sensor reader, positioned 2 cm away, continued to successfully capture physiological signals. In conclusion, this study presents a battery-free, chipless BSN solution utilizing on-body passive LC circuitry characterized by a simple structure, lightweight design, and low cost, ideal for disposable skin electronics and smart clothing, offering superior wearable, unobtrusive, and long-term health monitoring solutions.