Low-cost chipless sensor tags for wearable user interfaces

This paper addresses the design, the fabrication, and the experimental characterization of two fully-textile chipless tags used, for the first time, as wearable touch sensors. The first device is a multi-resonator chipless tag, wherein the information encoding relies on the presence/absence of resonance peaks. The second device consists of a hairpin resonator slotted on the ground plane and acting as a loading impedance of a microstrip line; in this case, the encoding mechanism is based on the variation of the resonance frequency. Prototypes for both devices were fabricated and characterized. Experimental tests performed on the prototypes exploiting two different measurement setups demonstrate that, when used as touch sensors, both the devices are able to encode four configurations corresponding to distinct relative positions between the sensor and the hand. The proposed devices are fully-textile solutions suitable for wearable applications in which low cost and a seamless integration with garments take priority over accuracy.