US Patent 10161886 Detection of surface contamination

A device implements a method for detecting contamination of an FTIR-based panel. The apparatus generates projection signals representing detection lines that have propagated on a plurality of propagation paths by total internal reflection (TIR) inside a transmissive panel such that contamination on the panel surface causes attenuation (frustration) of at least one of the projection signals. The device generates a transmission value for each detection line in the transmissive panel, and determines the presence of contamination on the surface of the panel by comparing the transmission values according to at least one of the presented comparison techniques.