Small wearable devices—such as smartwatches and digital jewelry—are fast becoming viable computing platforms. However, their small size severely limits the user experience. In response, we created a novel sensing approach that appropriates the skin as an interactive, touch-tracking surface.
Our system, SkinTrack, has two key components. First is a ring that emits an imperceptible and harmless 80MHz, 1.2Vpp AC signal into the finger on which it is worn. The second component is a wristband, worn on the opposite arm, and instrumented with a structured electrode pattern. When the user’s finger touches the skin, the electrical signal propagates into the arm tissue and radiates outwards. The signal takes time to propagate, which means electrodes located at different places around the wrist will observe characteristic phase shifts. By measuring these phase differences across several electrode pairs, SkinTrack can compute the location of the signal source (i.e., the finger), enabling real-time touch tracking on the skin.
Compared to prior work, our approach requires no direct instrumentation of the touch area (i.e., a skin overlay) or sensor line-of-sight (i.e., cameras). It also has a high signal-to-noise ratio (SNR), is unaffected by lighting conditions, and even works through clothing. Results from our user study demonstrate high reliability and accuracy with a mean distance error of 7.6mm. We also ran several supplemental and targeted experiments to further quantify performance and feasibility, which reveal similar promising results.
Zhang, Y., Zhou, J., Laput, G. and Harrison, C. 2016. SkinTrack: Using the Body as an Electrical Waveguide for Continuous Finger Tracking on the Skin. In Proceedings of the 34th Annual SIGCHI Conference on Human Factors in Computing Systems (San Jose, California, USA, May 7 - 12, 2016). CHI '16. ACM, New York, NY. 1491-1503.