Registers – Coded record sensors – Particular sensor structure
Patent
1986-10-30
1988-08-02
Pitts, Harold I.
Registers
Coded record sensors
Particular sensor structure
235485, G06K 710
Patent
active
047615435
DESCRIPTION:
BRIEF SUMMARY
This invention relates to security devices incorporating security information in a hologram, to security systems employing such devices to release a lock, operate a switch or perform some other security function, and to a method for making a hologram for use in such a device.
It is known to employ key cards provided with an operating code incorporated in a magnetic "stripe" or in a visual bar code. The code carried by such cards is "read" by a magnetic or optical decoder forming part of a security system, but for use in certain environments, for example in petrol filling stations, a magnetic-code-bearing key card has proved unsuitable, and the scanning system necessary with a key card having a bar code has proved to be too expensive.
It is also known to provide coded information in holographic form but the holograms and readers used to date necessitate the reconstruction of entire holographic images and their focusing on appropriate detectors and are complex and expensive.
An object of the present invention is to provide a security device and a security system for checking, or incorporating, such a device, which combine high security with the advantages of a non-contact reading or scanning arrangement and which are simpler and cheaper to manufacture than comparable known systems.
Accordingly, the present invention provides an identifiable security device comprising a carrier supporting holographically-applied identifying information, characterised in that said information is provided in a thick holographic film, as herein defined, and includes at least one discrete reflective region adapted to be read directionally and optically according to at least one optical parameter comprising intensity, wave length and polarisation of light reflected from the reflective region.
A further aspect of the invention provides a security system in which a security device as just defined is read by a reader arranged to perform a security function such as release of a lock or operation of a switch upon detecting the at least one discrete reflective region of the security device, the reader having a reading position for the carrier, means for illuminating the at least one reflective region when the carrier is at the reading position and reading means for optically and directionally detecting light reflected from each reflective region according to at least one optical parameter comprising intensity, wave length and polarisation of light and for discriminating against non-holographic reflections therefrom.
In the present invention, the holographic information is provided in a "thick-film" reflection hologram, a type generally known in the art, in which interference fringes are stored within the 3-dimensional volume of a thick photographic emulsion. The interference fringes are arranged to provide discrete reflective regions, these regions reflecting strongly light of the wave length of the laser light which created the fringes: the emulsion is transparent to or opaque to light of other wavelengths, this light being absorbed or scattered at the surface of the emulsion or of an underlying support but not being reflected strongly in a specific, predetermined direction.
The radiation currently usable lies in the U.V.--visible light--I.R. band of the spectrum but, for simplicity, will be termed "light" in the following specification. Similarly terms such as "light detector" and "light source" will be used to include U.V. and I.R. detectors and sources.
The use of a thick-film hologram, as opposed to a thin-film hologram, facilitates the reading of the holographic information in that a non-coherent light source rather than a laser may be used to illuminate the hologram for it to be read in a security system of the invention. The light source, preferably incorporated in the system, may emit white light or a more limited range of wave lengths, including that reflected by the reflection regions and may illuminate all or part of the hologram.
The photographic emulsion is normally supported on a thin transparent substrate such as a cellu
REFERENCES:
patent: 4108367 (1978-08-01), Hannan
patent: 4171766 (1979-10-01), Ruell
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