Touch Sensing based on FTIR in the Presence of Ambient Light

Touch sensing based on the effect of frustrated total internal reflec- tion (FTIR) can be used to build low-cost, multi-touch capable pro- jection surfaces (Han 2005). An acrylic panel is illuminated from the shorter sides. The refractive index of acrylic relative to air leads to total internal reflection within the panel, similar to optical fibers. If an object come close enough to the surface the total reflection is frustrated, light dissipates, and the object is illuminated. Thus, a finger touching the panel will be illuminated. The resulting illumi- nated blob can be captured and tracked with a camera.