GhostID: Enabling Non-Persistent User Differentiation in Frequency-Division Capacitive Multi-Touch Sensors.

Current touch devices are adept at tracking finger touches, but cannot distinguish if multiple touches are caused by different fingers on a single hand, by fingers from both hands of a single user, or by different users. This limitation significantly reduces the possibilities for interaction techniques in touch interfaces. We present GhostID, a capacitive sensor that can differentiate the origins of multiple simultaneous touches. Our approach analyzes the signal ghosting, already present as an artifact in a frequency-division touch controller, to differentiate touches from the same hand or different hands of a single user (77% reliability at 60 fps) or from two different users (95% reliability at 60 fps). In addition to GhostID, we also develop a framework of user-differentiation capabilities for touch input devices, and illustrate a set of interaction techniques enabled by GhostID.