Frustrated Total Internal Reflection
Frustrated Total Internal Reflection (FTIR) is a name used by the multi-touch community to describe an optical multi-touch methodology developed by Jeff Han. Total Internal Reflection describes a condition present in certain materials when light enters one material from another material with a higher refractive index, at an angle of incidence greater than a specific angle. When this happens, no refraction occurs in the material, and the light beam is totally reflected. The FTIR method uses this principle of Total Internal Reflection to great effect, flooding the inside of a piece of acrylic with infrared light by trapping the light rays within the acrylic.
When the user comes into contact with the surface, the light rays are frustrated, since they can now pass through into the contact material (usually skin layer on top of the glass or acrylic plane), and the reflection is no longer total at that point. This frustrated light is scattered downwards towards an infrared webcam, capable of picking these ‘blobs’ up, and relaying them to tracking software. This principle is very useful for implementing multi-touch displays, since the light that is frustrated by the user is now able to exit the acrylic in a well defined area under the contact point and becomes clearly visible to the camera below.
Advantages
- Unlimited number of touch points
- With a compliant surface, it can be used with something as small as a pen tip
Disadvantages
- Sensitive to ambient light
- Required on site calibration
- Requires a compliant surface coating (silicone rubber), sensitive to wear and scratches - no glass surface
- Cannot recognize objects or markers
Touch functionality
- Multi-touch
Product types
- Special setup
Partners
