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(Color online) Principle of a waveguide-based touch screen. L = light source, D = detector, θ = angle of interrogation.
(Color online) Top view of the touch module comprising a polymer waveguide with specially shaped edges, a light source V, and a linear detector array D.A. Cx , y are Fresnel-shaped collimating edges, Fx , y are Fresnel-shaped focusing edges, and T is a touch point. The two x- and y-parts of the detector array are dedicated to the x- and y-interrogating rays, respectively.
(Color online) The fact that both the collimated rays C and the diverging rays D are touch sensitive leads to unintended, multiple dark spots at the detector array, here illustrated by the two dark spots appearing on the x-part of the detector array. Similarly, two dark spots will appear on the y-part.
(Color online) Cross-sectional view at the reflection point R in Fig.3. The tilted edge at R alters the angle of interrogation of the reflected ray, making it touch sensitive.
(Color online) Photograph of the PMMA waveguide illustrating the effect of the tilted Fresnel-shaped edge: an in-the-plane ray originating from the lower left corner is transformed into a zig-zag ray with interrogation angle = 72°.
(Color online) (a) Realized touch module being tested. Laser light is being launched at the upper left corner; the camera is placed at the opposite corner. Note the “glow” at the tip of the finger, which is light being picked up from the waveguide. (b) Green curve (top curve) is the un-touched camera signal, red curve (middle curve) is the touched camera signal, black curve (bottom curve) is a result of a subtraction between the green and red curves. (c) Result of the peak finding algorithm that tells the touch location.
(Color online) Average, relative peak-height changes (in relation to reference signal) of the x and y peaks versus force applied by the finger.
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