Stretchable Wearable RF Sensors

Abstract

Integration of flexible and soft materials into electric circuits has enabled a new generation of bio-medical and wearable devices for continuous health monitoring and health diagnosis. Such circuits are attractive due to their mechanical properties as they are lightweight and can conform to curved surfaces. Muscle strength monitoring and body motion recognition play an essential role in fatigue prevention for athletes, senior care, rehabilitation after an injury, cognitive diseases, smart prosthetics, and human-robot interactions. In this work, we present a wearable, lightweight, flexible, and stretchable RF sensor for muscle strength monitoring. The sensor is composed of two parts: the first part is an RF filter that stretches in accordance with the arm contractions and then reconfigures its frequencies based on the degree of stretching, and the second part is a flexible Back-End circuitry to detect and discern the generated frequency shift from the filter. Various fabrication techniques for stretchable circuits have been reported in the literature, however, they suffer from elevated complexity and high cost. In this work, we develop our own technique for a stretchable filter where different parts of the filter are fabricated separately and then joined together like a puzzle on a silicone sheet. Finally, the muscle strength sensor is fabricated and tested on 30 volunteers of different gender, ages, and arm fat content. It shows good reconfigurability for different stretching states, endurance, and reliability.