Toffee is a sensing approach that extends touch interaction beyond the small confines of a mobile device and onto ad hoc adjacent surfaces, most notably tabletops. This is achieved using a novel application of acoustic time differences of arrival (TDOA) correlation. Previous time-of-arrival based systems have required semi-permanent instrumentation of the surface and were too large for use in mobile devices. Our approach requires only a hard tabletop and gravity – the latter acoustically couples mobile devices to surfaces. We conducted an evaluation, which shows that Toffee can accurately resolve the bearings of touch events (mean error of 4.3° with a laptop prototype). This enables radial interactions in an area many times larger than a mobile device; for example, virtual buttons that lie above, below and to the left and right.
Xiao, R., Lew, G., Marsanico, J., Hariharan, D., Hudson, S., and Harrison, C. 2014. Toffee: Enabling Ad Hoc, Around-Device Interaction with Acoustic Time-of-Arrival Correlation. In Proceedings of the 16th International Conference on Human-Computer Interaction with Mobile Devices and Services (Toronto, Canada, September 23 – 26, 2014). MobileHCI ’14. ACM, New York, NY. 67-76.