Low profile linear sensing modules are based on high resolution CMOS sensors. A typical sensor implementation would include a 2048 pixel sensor die and a wide angle lens to image over a 90 degree field of view. Using sub-pixel interpolation this is sufficient to provide sub millimeter resolution over panels up to 100 inches in size. The sensor die, PCB, lens, optical filter and connector are incorporated into a thin housing structure as shown in the attached figure.
The Active Barrier® illumination module is comprised of a customized, edge emitting plastic optical light guide that runs along the edge of the screen. These light guides are illuminated from the ends with infra-red LEDs and emit a thin, planar beam of light that completely fills the sensing region. The patented light guide is designed to extract light uniformly along the length of the light guide and focus into a highly parallel planar beam. It is the position of this plane of light, which taken with the sensing modules, determines the precise height of the sensing plane. For small sensing regions we use illuminators as thin as 1 mm, whereas for larger screens light guides of 2 to 3 mm thick are typically used. In either case the finger or object must be brought essentially into contact with the surface to break the beam as with an ordinary touch screen. The light guides and LEDs are inserted into a thin plastic housing that is bonded directly to the touch panel surface. An optional rear reflector and cover can also be added to seal the module as shown in the figure.
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