SIGNATURE MARK RECOGNITION SYSTEMS

摘要

A signature recognition system for identifying an article with a distinctive diffractive element (or elements) and verifying the presence of that element or elements comprising; an article with one or more diffraction gratings impressed thereon, the gratings) exhibiting periodic wave surface profiles having a depth-to-pitch ratio .delta. of between 0.1 and 0.5, a source of polarised electromagnetic radiation of wavelength .lambda., such that the pitch G of the periodic wave surface profile of the grating(s) is comparable to an integer multiple n of that wavelength means for directing the source of polarised electromagnetic radiation to the surface of the grating(s) at a plane of incidence substantially normal to the plane of the surface of the diffraction grating and at an angle of approximately 45 .degree. azimuth to the alignment of the grooves on the surface, and means for detecting radiation reflected from the grating(s) surface which is oppositely polarised to the incident radiation.