Patent ID: 10365768

Abstract:
A touch-sensitive apparatus operates by light frustration (FTIR) and comprises a light transmissive panel (1) that defines a front surface (5) and a rear surface (6), light emitters optically connected to the panel (1) so as to generate light that propagates by total internal reflection inside the panel, and light detectors (3) optically connected to the panel (1) so as to define a grid of propagation paths inside the panel (1) between pairs of light emitters and light detectors (3). Each light detector (3) is optically connected to the panel (1) via an angular filter (20). The filter (20) is applied to an outcoupling region on at least one of the front and rear surfaces (5, 6) and is configured to transmit light only within a confined range of angles with respect to the normal of the outcoupling region. The confined range extends from a lower angle limit θmin to an upper angle limit θmax. The lower angle limit θmin is equal to or larger than a critical angle θC, which is given by θC=arcsin(1/npanel), with npanel being the refractive index of the light transmissive panel (1) at the outcoupling region.