Abstract: A multilayer surface comprising at least two layers, said layers having different refractive indexes such that selective wavelengths/colours are transmitted and or reflected. The layers are preferably laid onto a transparent substrate. The surface can be used as an anti-counterfeit device. A method of determining whether an article is counterfeit comprising: providing such a surface; determining its transmission/absorption characteristics of particular colour(s); matching these up with the expected characteristics to determine whether the surface is counterfeit. This may comprise observing the reflected or transmitted colour at two different angles of incidence or detecting changes in the polarisation state of transmitted light.

Abstract: A grating comprising a plurality of substantially parallel members having a conducting surface of depth L, separated by a dielectric layer gap, and having of pitch &lgr;g and where L>16&lgr;g. The members are preferably metallic or comprise metallic foil covered plastic. The gap may be filled wholly or partially with dielectric material including liquid crystal whose refractive index can be controlled by suitable application of voltage across the gap.

Abstract: A radiation absorber comprising a substrate having free charges capable of being driven to form resonance charge density oscillators and a dielectric layer coated onto said surface wherein the dielectric layer has a textured/patterned surface. The substrate is preferably metallic and the dielectric layer is waveform.

Abstract: A grating comprising a plurality of substantially parallel members having a conducting surface of depth L, separated by a dielectric layer gap, and having of pitch &lgr;g and where L>16&lgr;g. The members are preferably metallic or comprise metallic foil covered plastic. The gap may be filled wholly or partially with dielectric material including liquid crystal whose refractive index can be controlled by suitable application of voltage across the gap.

Abstract: A signature recognition system for identifying an article with a distinctive diffraction element (or elements) and verifying the presence of that element or elements comprising: an article with one or more diffraction gratings impressed thereon, the grating(s) exhibiting periodic wave surface profiles having a depth-to-pitch ratio &dgr; of between 0.1 and 0.5, a source of polarized electromagnetic radiation of wavelength &lgr; 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, a device for directing the source of polarized 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° azimuth to the alignment of the grooves on the surface, and a device for detecting radiation reflected from the grating(s) surface which is oppositely polarized to the incident radiation.