What is an FTIR

FTIR stands for Frustrated Total Internal Reflection.

This is a term used among the multi-touch community. There are many different types of multi-touch methods, including capacitance screens, resistance screens, back lit IR screens, color tracking, and more. I chose FTIR because it is best suited for what I want to do, and it seems to have the best results. FTIR was originally thought up by a guy named Jeff Han in 2005 (Han).

refractive index

A refractive index is how much the speed of light is reduced when inside a certain material. Water has a refractive index of 1.3330 (Laven), and the acrylic glass used for the FTIR has a refractive index of 1.50 (Reed). If the refractive index is lower on the material the light is trying to pass through, the light will be reflected. So, at a certain angle, all light is reflected off of the surface of water. This is how fiber optic cables work. All of FTIR in the multi-touch community is based around this concept: Getting the light to reflect inside the screen.

Works Cited:

Han, Jefferson Y. “Low Cost Multi-Touch Sensing through Frustrated Total Internal Reflection.” Symposium on User Interface Software and Technology: Proceedings of the 18th annual ACM symposium on User interface software and technology. Seattle,WA, USA, 2005. 115-118.

Laven, Philip. "Refractive index." Mie scattering. 16 Aug. 2009. Web. 30 Dec. 2009.<http://www.philiplaven.com/p20.html>.

Reed, Rick. "Refraction - Snell's Law." Refraction of light. 28 May 2009. Web. 30 Dec. 2009.<http://interactagram.com/physics/optics/refraction/>.