We introduce a simple technique that enables robust multi-touch sensing at a
minimum of engineering effort and expense. It relies on frustrated total
internal reflection (FTIR), a technique familiar to the biometrics community
where it is used for fingerprint image acquisition. It acquires true touch information at high
spatial and temporal resolutions, and is scalable to very large installations.
Han, J. Y. 2005. Low-Cost Multi-Touch Sensing through Frustrated Total Internal Reflection. In Proceedings of the 18th Annual ACM Symposium on User Interface Software and Technology
Short video [13MB] (pretty old)