planar scatter detection (multitouch) (PSD)
Planar Scatter Detection(PSD) is a method used in touch-sensitive multi-touch screens for position determination. Like Frustrated Total Internal Reflection( FTIR), the PSD method works with diffuse infrared light that is fed into the display surface from the edges.
The infrared light is reflected in the substrate and scattered and refracted by an object, pen, glove or finger touching the surface. This affects the distribution in the substrate and less IR light arrives at the side-mounted light sensors. The incoming light is evaluated in terms of its strength and the coordinates of the point of contact are determined from this.
With the PSD process, no additional coating is required, which means that the brightness and contrast of the display are not affected. The substrate can be sealed so that the PSD technique works even under unfavorable environmental conditions. The process features extremely high resolution and is supported by drivers for Windows 7. It is also supported by Mac OS X, Windows Vista and Linux.
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The PSD technique is independent of ambient light, and can be used to simultaneously detect over twenty points of contact and determine the size of objects. The repetition rates are such that the user can follow the actions on the screen. The Planar Scatter Detection technology can be used equally with TFT displays, LCD and OLED displays.