Hideki Koike talked at the Symposium on Interaction with Smart Artifacts in Tokyo. One of the examples he showed is the PhotoelasticTouch technology. The idea is to use a transparent gel and the effect of photoelasticity to detect interaction on a surface, see  for details.  give a brief overview (the picture below is taken from this publication).
There is a nice youtube videp the shows the concept very well: http://www.youtube.com/watch?v=RJaEg0xB98E
 Toshiki Sato, Haruko Mamiya, Hideki Koike, and Kentaro Fukuchi. 2009. PhotoelasticTouch: transparent rubbery tangible interface using an LCD and photoelasticity. In Proceedings of the 22nd annual ACM symposium on User interface software and technology (UIST ’09). ACM, New York, NY, USA, 43-50. DOI=10.1145/1622176.1622185 http://doi.acm.org/10.1145/1622176.1622185
 One page abstract: http://www.vogue.is.uec.ac.jp/PET/photoelasticTouch1Page.pdf