Multi touch surface system

Abstract

This project is a design of MULTI_TOUCH SURFACE SYSTEM by FTIR (Frustrated Total Internal Reflection). An FTIR setup involves three vital components: a sheet of transparent acrylic, a chain of infrared LEDs, camera with an IR filter, and a projector. The LEDs are arranged around the outside of the sheet of acrylic so that they shine directly into the thin side surfaces. The foundation of the screen is the sheet of acrylic which serves as the medium for the infrared light. Acrylic has several properties that make it a good fit for our project. First, it has the right optical properties, allowing for an excellent FTIR effect. Additionally, it’s lightweight, strong, and very clear (more so than glass). Once the IR light is inside the acrylic, it strikes the top and bottom surfaces of the acrylic at a near-parallel angle, and is subject to the effect known as total internal reflection. This causes it to be wholly maintained in the acrylic. The net effect of the setup described above is a sheet of acrylic full of internally reflecting infrared light. When a finger is pressed against the acrylic, it causes some of the light to be reflected down, through the acrylic and into the cabinet, where it is detected by the webcam. This effect, called frustrated total internal reflection is a little complicated, and involves something called an evanescent wave. The webcam, which has been modified to detect only infrared light. Software running on a nearby computer extracts a map of where fingers have been pressed on the screen, and uses that data to control multi-touch applications. Finally there’s the cabinet—the structure that holds everything else together. The cabinet really only needs to do one thing: support the screen (including the acrylic, the lights, and the vellum surface) in such a location that's accessible to both the projector and camera. In an FTIR setup, the cabinet doesn’t even need to be closed.