E-Textile Battery-Less Displacement and Strain Sensor for Human Activities Tracking

Wearable sensors demand flexible and concealable devices that can be seamlessly integrated with apparels and clothes. E-textile sensors and devices, built from specially functionalized fibers and yarns and constructed with embroidery and woven processes, provide an ideal solution for different wearable applications. In this article, we propose a textile-based, embroidered passive strain and displacement sensor functioned as a UHF RFID antenna that can be aesthetically integrated with garment fabrics. The antenna structure consists of a dipole arm and a coupling loop mounted with an RFID chip. The displacement between the loop and dipole arm will alter the impedance of the antenna and consequently modulate the backscattered signals from the RFID chip to the reader. The sensor is passive, i.e., no battery is needed on the sensor and the sensing information can be wirelessly retrieved by the reader from a few meters away. The structure is sensitive to strains and displacement caused by body movement. Our experiments demonstrate different applications for this sensor, i.e., when the sensor is embroidered on different locations on human body, such as breast, knees, and elbows, it can be used as a respiration monitor, gesture indicator, etc. to conveniently track and log various forms of body movements.