Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2003-03-28
2004-05-25
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S450000
Reexamination Certificate
active
06741360
ABSTRACT:
INTRODUCTION
The present invention relates to a method for identifying an object.
STATE OF THE ART
In order to identify each of the objects of a series of objects with identical appearance, the most standard method consists of fixing an identification plate on each object, each of the identification plates bearing a distinctive mark. However, if the identification plates are exchanged between several objects of the series, it is no longer possible to identify a particular object of the series with certainty.
GB-A-2,221,870 relates to a security device for use in an optical method based on the speckle interferometry phenomenon, better known as the “speckle effect”. The security device comprises a substrate whereon or wherein there is a structure scattering the radiations. This radiation-scattering structure when it is illuminated by a coherent ray of radiations, causes random scattering; the scattered rays then interfering to generate an interference pattern. It should be noted that the radiation-scattering structure is formed by stamping with a die bearing a relief pattern. More specifically, a resin layer is stamped by means of said die so as to form the relief pattern therein, which is then covered with an aluminium reflecting layer. The radiation-scattering structure thereby formed, is then mounted on a support, thereby forming a security device, which in turn is irremovably mounted on an object for which a guarantee of authenticity is desired. The use of the stamping die has the advantage of allowing identical security devices to be manufactured, which will be fixed to objects of identical appearance in order to guarantee their authenticity.
Authentication of an object is performed by checking the security device which is associated with it. The interference pattern of the tested device is compared with the reference interference pattern, obtained under the same irradiation conditions, and the authenticity of the object is confirmed when the interference pattern of the tested device and the reference pattern are identical.
Such a security device provides relatively high security, as it is not conceivable that a potential counterfeiter may make a copy of the radiation-scattering structure capable of generating an interference pattern identical with the reference pattern. However, considering the high sensitivity of the involved physical phenomenon, the possibility of manufacturing by means of the die, a series of identical security devices which generate interference patterns identical with the reference interference pattern, is questionable. Further, if a counterfeiter would lay hold of the die, he would then be able to readily reproduce the radiation-scattering structure, and therefore also the security device.
Moreover, it should be noted that the security device, which forms an unforgeable identification plate, does not allow a particular object to be identified from a series of objects with an identical appearance. For this, a different security device must be made for each object of the series. However, the aforementioned problem would always remain, i.e. if the security devices were exchanged, it would no longer be possible to identify one object of the series, individually.
Finally, the requirement of fixing an identification plate to the object to be identified or authenticated, may prove to be a problem.
Indeed, it may not be possible to fix the identification plate in a sufficiently secure way. Furthermore, depending on how the object is used, the identification plate may be damaged.
OBJECT OF THE INVENTION (PROBLEM TO BE SOLVED BY THE INVENTION)
The object of the present invention is to provide a method for identifying an object which does not have the drawbacks of the method using identification plates, and which notably enables an object of a series of objects with identical appearance, to be identified individually. According to the invention, this object is achieved by a method according to claim 1.
General Description of the Claimed Invention with its Main Advantages
A method for identifying an object according to the invention comprises the following steps:
(a) selecting an intrinsic surface of an object to be recognized;
(b) illuminating at least one identification area in the intrinsic surface of the object to be recognized with coherent light and intercepting at least one portion of the light reflected by the identification area, in order to obtain an interference pattern under determined illumination and interception conditions;
(c) retaining this interference pattern as a reference interference pattern for the object to be recognized;
(d) placing a candidate object liable to be the object to be recognized under the same illumination and interception conditions as those used for obtaining the reference interference pattern and obtaining an interference pattern from this candidate object;
(e) comparing the reference interference pattern with the interference pattern of the candidate object; and
(f) evaluating the probability of identity between the object to be recognized and the candidate object according to the matching level between the reference interference pattern and the candidate object's interference pattern.
By “intrinsic surface” of the object to be recognized, it is meant a surface specific to the object, which is an integral part of it, as opposed to a surface which would belong to a device fixed on the object for an identification purpose.
The method according to the invention uses an optical interference phenomenon, known as “speckle interferometry”, for identifying an object.
When an object, which is not an ideal specular reflector is illuminated by a coherent light, microscopic variations on its surface shift the phase of the reflected and scattered light. If this light is intercepted, for example on a screen, an interference pattern may be observed, or a “speckle” pattern, produced by interferences between the phase-shifted components of this light. In the method according to the invention, an interference pattern obtained under determined illumination and interception conditions is considered as a unique imprint of the surface of the scanned object. Indeed, considering the complexity of the phenomenon involved, sensitive to surface variations on a micron scale, only the same object replaced under the same determined conditions will be able to produce a substantially identical interference pattern. Thus, in accordance with the method according to the invention, the interference pattern of an object to be recognized is retained as a reference interference pattern, a unique imprint allowing its identification. When it is subsequently desired to identify this object to be recognized, from a plurality of candidate objects liable to be the object to be recognized, it is sufficient to place each candidate object under the same illumination and interception conditions as those used for obtaining the reference interference pattern and obtain the interference pattern therefrom. A high matching level between an interference pattern obtained for a candidate object and the reference interference pattern will allow the identity of both objects to be confirmed with a high likelihood, i.e. the candidate object is actually the object to be recognized. A first advantage of the present method is its sensitivity, which makes it tamperproof. Indeed, the method is sensitive to surface variations on the micron scale, whereby it is therefore difficult to imagine a replacement of the object to be recognized, with a copy.
A second advantage of the method according to the invention, is that it does not require any labeling, any treatment, of the object to be recognized. Indeed, the natural surface state of the object to be recognized is preferably used. This means using the actual surface of the object which is therefore an integral part of the latter, and which has not undergone any specific treatment for standardizing the interference pattern which it is susceptible to produce. From the method according to the invention, it is sufficient to select a por
Causse D'Agraives Bertrand
Chiaramello Michel
European Community
Font Frank G.
Lee Andrew H.
Meyer Jerald L.
Nath Gary M.
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