RFTouchPads: Batteryless and Wireless Modular Touch Sensor Pads Based on RFID

This paper presents RFTouchPads, a system of battery-less wireless modular hardware designs of 2D touch sensor pads based on ultra-high frequency (UHF) radio-frequency identification (RFID) technology. We connect an antenna to multiple touch-sensing ID modules in parallel to provide 2D touch input with a single antenna. Each touch-sensing RFID module connects only one of its endpoints to the antenna, so it is normally off as it gets insufficient energy to operate. When a finger touches the circuit trace that is attached to an endpoint of a chip, the finger functions as another half of the antenna that triggers the connected chip on, and then the presence of its ID indicates the finger touch location. We proposed two hardware designs, StickerPad and TilePad, based on this principle. StickerPad is a flexible 3 × 3 touch sensing pad that allows for the applications on curved surfaces, such as the human body. TilePad is a modular 3 × 3 touch sensing pad that supports modular area expansion by tiling and provides more flexible deployment as its antenna is folded. Our implementation of this design allows 2D touch input to be reliability detected from 2 m away from a remote antenna of an RFID reader. The proposed battery-less, wireless and extensible modular hardware design provides fine-grained, less constrained 2D touch inputs in various ubiquitous computing applications