Capacitive touch screens have enabled compelling interfaces for displays [1]. Three-dimensional (3D) sensing, where user gestures can also be sensed in the out-of-plane dimension to distances of 20 to 30cm, represents new interfacing possibilities that could substantially enrich user experience. The challenge is achieving sensitivity at these distances when sensing the small capacitive perturbations caused by user interaction with sensing electrodes. Among capacitive-sensing approaches, self capacitance enables substantially greater distance than mutual capacitance (i.e., between electrodes), but can suffer from ghost effects during multi-touch. For gesture recognition, however, processing via classifiers can overcome such effects, enabling a rich dictionary of gestures [2]. Nonetheless, the sensing distance of such systems has been too limited for 3D sensing.
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