Objects scattered on a capacitive multi-touch surface are usually detected only while the user is touching them. As soon as he lets go off such a tangible, the system cannot distinguish whether the user just released it, or picked it up and removed it from the surface. Persistent capacitive tangibles detect whether they are currently laying on a capacitive touch surface or not. This is achieved by adding a small field sensor to the tangible to detect the touch screen’s own, weak electromagnetic touch detection probing signal.
 

The Elektor Lab participates in the hardware design and production of the tangible objects for the Tabula project. We provide a technical overview of the theory behind PERCs and our prototype construction, and we evaluate detection rates, timing performance, and positional and angular accuracy for PERCs on a variety of unmodified, commercially available multi-touch devices.