Tach: An RFID Tag Based Touch Switch

Touch switches are the foundation of a smart automation system that provides us with a seamless and intuitive interaction between users and smart devices. Typical touch switches and recent gesture sensing solutions suffer from some limitations including low scalability, low robustness, hardware modifications, and long time delay. In this work, we propose an RFID tag based touch switch called Tach that provides users with a battery-free, low-latency, low-cost, and plug-n-play touch-based input primitive, with no need for any hardware modifications. In Tach, we turn a passive tag as a touch switch and use the principle of impedance mismatch to sense the touch action by users. More specifically, we observe that when the finger touches the tag, the impedance of tag antenna changes. This change gives rise to impedance mismatch between the tag antenna and the tag chip, which further causes a frequency shift and a specific signal pattern. We design a continue wavelet transform based segmentation scheme and a dynamic time warping approach to achieve accurate and reliable touch identification in real scenarios. Additionally, multi-tag switches are discussed to support more user inputs. We implement Tach with COTS RFID devices. Extensive experiments show that the sensing accuracy reaches 96.5% with a low latency of 300ms, regardless of different users and environmental changes. The promising results might open up a new avenue in the design of touch switches in the near future. Code and datasets will be made available.