Abstract: A multiple-reader system for authentication of articles uses a first reader (400) which employs predetermined modulated illuminating light (20) and a multiplicity of discriminating variables, such as wavelengths (110), amplitudes (120), and time delays (140) relative to the modulated illuminating light (20) to characterize fluorescent light (70) detected from fluorescent indicia on the articles. The fluorescent indicia may also incorporate spatial distributions such as bar codes as discriminating features. Additional readers (410 and 420), which may be readers of fluorescent marks and/or readers of other indicia, are synchronized with the fluorescence reader by timing signals. The discriminating features may be re-programmed by the user of the authentication system. Thus the discriminating features define a user-determined and programmable encryption of the articles' authentic identity.

Abstract: Accessory apparatus for authenticating articles is used in conjunction with existing readers or scanners of articles bearing stored data, such as credit cards or identification cards. The accessory apparatus is disposed before, after, on, under, inside, or adjacent to existing reader apparatus, to have a view of the article whose data is to be read. Information in addition to the stored data is coded on the article in non-visible indicia and is detected by the accessory authenticating apparatus. This coded additional information may be related to identification data stored in the article by the article's normal storage mechanism, such as a magnetic stripe or an embedded memory IC chip. The additional information may be coded in various combinations of predetermined characteristics of light emitted by the article to be authenticated when the article is irradiated with non-visible light from the accessory apparatus.

Abstract: A system for authentication of articles uses a multiplicity of discriminating variables to characterize light detected from the articles after predetermined illumination. Articles are tested which have been marked with substances such as dye or ink that fluoresce in a region of the optical spectrum when illuminated with light in another region of the spectrum, such as the ultraviolet region. The authentication system illuminates the articles with light modulated at a frequency of more than about 50 kHz, and secondary fluorescent light returned from the articles is synchronously detected. A programmable microcomputer digitizes the synchronously detected signal and analyzes it to compare the signal with predetermined standard digital signals. The standard signals incorporate a number of discriminating features, for example the fluorescent light's wavelengths, amplitudes, and time delays relative to the modulated illuminating light.

Abstract: The response of a fluorescence detector is calibrated using apparatus and methods for both static and dynamic calibrations. The apparatus and methods are especially suited for portable use in field calibration of fluorescence detectors of authentication systems that use non-visible light. The calibration apparatus incorporates standard target elements (20) comprising predetermined fluorescent substances with known emission spectra, and either non-fluorescent substances or fluorescent substances with other known emission spectra. The substances are either mixed in predetermined proportions, or one substance is arranged in a predetermined pattern (170), such as a bar code, on the other substances. An aperture (30) exposes a predetermined surface area of a standard target element to the view of the fluorescence detector. The distance of the standard target element from the optical front end (70) of the fluorescence detector to be calibrated is adjustable (50).