ScraTouch: Extending Touch Interaction Technique Using Fingernail on Capacitive Touch Surfaces

We present ScraTouch, an interaction technique using fingernails, as a new input modality for capacitive touch surfaces. We revealed the differences between the fingertip and the nail from the viewpoint of capacitance touch sensing. Differentiating between fingertip and fingernail touches requires only tens of milliseconds worth of shunt current data from the capacitive touch sensing mechanism, thus external sensors or other hardware are unnecessary. Owing to the small amount of friction generated when a nail touches the surface, not only tapping but also touch gestures by sliding a nail can be easily performed. In our initial investigation, we confirmed that setting a simple threshold on the measured shunt current for recognition works robustly.