Researchers from the National Taiwan University and the Eindhoven University of Technology have published a paper on wireless touch interfaces with a difference: their RFTouchPads require no batteries or microcontroller to operate.
"Touch inputs are direct and intuitive," the researchers explain in the paper detailing the technology. "However, the deployment of touch sensors usually requires a signal processing unit (i.e., microcontroller) and a power supply. These extra hardware requirements limit the scalability and flexibility of the touch input deployment in ubiquitous computing applications.
"Solutions that leverage computer vision or radio-frequency identification (RFID) can reduce their hardware requirements. Vision-based solutions use one or more camera(s) to track touch events on a surface. However, such a tracking easily fails in the cases of occlusion. RFID-based solutions use a wireless ultra-high frequency (UHF) reader to track touch events on UHF RFID tags, with the tracking being more resilient to the line-of-sight problems.
"Multiple RFID tags can be placed nearby each other to enable expressive gesture inputs such as swiping. However, the size of the antenna required for the signal transmission limits the number of possible ways of the deployment of such a solution. For example, the tags cannot be deployed as a two-dimensional (2D) grid that is large and dense enough for capturing fine-grained, less-constrained touch inputs we normally perform on a touchscreen. Hence, the following question arises: how can we enable fine-grained 2D touch inputs on RFID tags so that the scalability and flexibility of the solution remain uncompromised?"
The solution: RFTouchPads, a system of modular hardware designs which require no battery or external power source. The trick: multiple RFID chips connected to an antenna in parallel, but with only one of the endpoints linked. When a finger touches the other endpoint, the antenna circuit is completed and the chip activates — with enough harvested power, the researchers claim, for the touch to be detected on an RFID reader up to two meters (around 6'6") away.
The team's efforts have resulted in two implementations: StickerPad, a flexible 3x3-zone surface which can confirm to curved surfaces including the human body; and TilePad, which allows multiple 3x3 tiles to be connected to expand the sensing area. Neither include a battery, any external wiring, or a microcontroller — the latter differentiating it in cost and simplicity from earlier microcontroller-powered RFID-based touch detection systems.
The team presented its work, which does not yet have a direct path to commercialization, at the 32nd Annual ACM Symposium on User Interface Software and Technology (UIST '19); the paper is available to download via the ACM Digital Library.