PUCs: Detecting Transparent, Passive Untouched Capacitive Widgets on Unmodified Multi-touch Displays

Simon Voelker, Kosuke Nakajima, Christian Thoresen, Yuichi Itoh, Kjell Ivar Øvergård, and Jan Borchers
In Proceedings of ITS '13, ACM, 101 - 104

Capacitive multi-touch displays are not designed to detect passive objects placed on them-in fact, these systems usually contain filters to actively reject such touch data. We present a technical analysis of this problem and introduce Passive Untouched Capacitive Widgets (PUCs). Unlike previous approaches, PUCs do not require power, they can be made entirely transparent, they are detected reliably even when no user is touching them, and they do not require internal electrical or software modifications of the touch display or its driver. We show the results from testing PUCs on 17 different off-the-shelf capacitive touch display models, and provide initial technical design recommendations.