AU735446B2

AU735446B2 - Anticounterfeiting method

Info

Publication number: AU735446B2
Application number: AU61317/96A
Authority: AU
Inventors: Keith Loder Lewis
Original assignee: UK Secretary of State for Defence
Current assignee: Qinetiq Ltd
Priority date: 1995-06-22
Filing date: 1996-06-19
Publication date: 2001-07-05
Anticipated expiration: 2016-06-19
Also published as: CA2224731A1; AU6131796A; GB9512698D0; EP0834159A1; WO1997001156A1; JPH11508073A; TW331616B

Description

P:\OPER\DI61317-9 rsl.doc-1605/01 -1- ANTICOUNTERFEITING METHOD This invention provides a means of identifying genuine and counterfeit articles and lends itself to covert operation. It has particular (although not exclusive) relevance to the retail trade.

Counterfeiting of articles is a long standing international problem in, for example, the retail trade and credit card industry and the need for an effective means of combating counterfeiting has attracted considerable attention. One technique for indicating the authenticity of a particular article is by the use of a trademark. Such trademarks are becoming increasingly complex in design incorporating, for example, optical effects such as holograms and diffraction patterns.

S However, large scale counterfeiting organisations have access to considerable resources and are 10 becoming increasingly successful at copying even the most complex marks.

The use of infrared technology in anticounterfeiting systems has already been established. For example, GB2284292 relates to a covert marking system in which genuine articles are endowed with a label whose appearance is very different when scanned using equipment which is sensitive to radiation in the near infrared region of the electromagnetic spectrum. In another example (patent application WO 91/08556) the presence of infrared absorptive materials can be detected by illumination at wavelengths close to the absorption peak and processing the detected signals to derive a signal characteristic of the absorbing species. Similarly, GB 2190996A relates to a S technique for authenticating articles by determining the characteristics of the envelope of single fluorescence, phosphorescence or absorption bands.

Another example of a covert anticounterfeiting system, UK patent application GB9409128.7, relates to a system for distinguishing between genuine and counterfeit articles where the apparatus comprises of a first optical filter which is applied to the genuine article and a second optical filter which is used for scanning purposes. The scanning of the genuine articles with the aid of the second optical filter gives rise to optical effects which would not otherwise be apparent.

The present invention extends these concepts to the use of an optical filter and a radiation source.

When observed under normal lighting conditions the filter has a neutral appearance, but when illuminated with radiation of selected wavelength components, gives rise to optical effects which m P:kOPE R\DM61317-9 rs I .do- 160501 -2would not be present in the absence of the filter or without use of the correct illuminating radiation. The system is effective under normal lighting conditions and has the advantage that it may be operated covertly. It has the advantage that although the counterfeiter may be aware of its use, the labels applied to the genuine articles may be changed regularly or used in association with barcodes.

Throughout this specification, the use of the word "article" or "articles" should be taken to relate to the said article or articles or the associated packaging or wrapping.

According to one aspect of the invention, a method for covertly marking an article and checking its authenticity comprises the steps of; applying an optical filter to the genuine article, (ii) illuminating the article to be authenticated with electromagnetic radiation at two or more angles of incidence, wherein said radiation comprises components of at least one wavelength, (iii) upon said illumination, detecting :radiation reflected or transmitted by the article to be authenticated at each angle of incident radiation and 15 (iv) comparing properties of the reflected or transmitted radiation at each angle of incident radiation with known properties of radiation reflected or transmitted by the filter at said angles of •oooo S• incident radiation.

In a preferred embodiment, the filter may be a multi layer interference filter, having at least one maximum and at least one minimum in the spectral characteristic and having a neutral appearance when observed under normal lighting conditions, wherein the multi layer interference filter comprises at least two materials having a selected thickness and refractive indices such that when illuminated with the electromagnetic radiation the filter gives rise to characteristic interference effects.

Preferably, the spectral characteristic of the optical filter has a plurality of maxima and minima.

The spatial distribution of reflected or transmitted radiation may be compared with a known i,",-.patial distribution of radiation reflected or transmitted by the filter at said angles of incident P:\OPER\DH\61317-.96 r I do-.1605i01 -3radiation. Alternatively, the intensity of the reflected or transmitted radiation at said angles of incident radiation may be compared with the known intensity of radiation reflected or transmitted by the filter at said angles of incident radiation.

The filter may be illuminated by electromagnetic radiation having wavelength components corresponding to spectral bands in the spectral characteristic of the filter.

Radiation having wavelength components corresponding to spectral bands in the spectral characteristic of the filter may be generated by placing a second filter in front of a radiation source, wherein said second filter has the spectral characteristic of the filter applied to the S genuine article.

The invention will now be described, by example only, with reference to the accompanying Sdrawings in which; Figure 1 illustrates, schematically, the use of the current invention in reflection mode and (b) in transmission mode and Figures 2, 3 and 4 show the spectral characteristics of three typical filters which may be incorporated in the invention.

S" Referring to Figure 1 the article to be authenticated 1 is marked with label 2 incorporating an optical filter with a known spectral characteristic. During operation, label 2 is irradiated with radiation 3a from an electromagnetic radiation source 4 and the intensity of reflected radiation 3b, at two or more wavelengths, is measured by detector 5. Radiation source 3 might comprise of a laser array, a light emitting diode array or a filtered lamp and is such that the radiation incident on the label comprises two or more component wavelengths. For example, a tungsten lamp with a filter mounted in front to transmit only certain wavelength components may be used.

The optical filter incorporated in the label 2 operates on the basis of interference effects. The filter may therefore be constructed on a transparent substrate, or constructed directly on a transparent article 1, thus enabling operation in transmission as well as reflection. For example, referring to Figure the article 1 to be authenticated may transmit incoming radiation, for P.\OPER\DIf-61317-96 r I.do-1605/01 -4example a glass bottle or container and radiation transmitted by the label 2 may therefore be detected by placing the detector 5 on the opposite of the article from the radiation source 3.

Detector 5 is a detection system or a camera sensitive to the range of wavelength components corresponding to the wavelengths of the reflected (or transmitted) radiation. For example, a suitable detection means would be a CCD detector array. A lens 6 is also required in this arrangement to focus the radiation 3b onto the detector In any of the following examples, the methods described may apply to either the measurement of radiation reflected or transmitted by the filter.

i: Referring to Figure 2 the spectral characteristic (reflectance versus wavelength curve) shown corresponds to a filter incorporated beneath a polychromatic black dye with an absorption edge at 700 nm. When the filter is viewed under normal lighting conditions it has a neutral appearance and appears black. The filter may also be designed to appear, for example, white, grey or silver.

The filter has a reflectance peak 5, providing a narrow reflection band in the infrared wavelength 1 region. If a monochromatic light source, with a wavelength corresponding to that of peak 7, is 15 used to irradiate the filter, the reflected radiation can be measured by an observer by means of an infrared detector, sensitive to 850 nm. No visible optical effect would be observed by the eye and so the system may be operated covertly.

000 If a second source is used, emitting radiation with a wavelength corresponding to a minimum 8 in the spectral characteristic, and a second detector is used which is sensitive to this radiation, the ratio of the respective intensities of the two detector outputs provides a unique signature for the filter. Such a concept could be extended to include a multiple number of incident wavelengths or a multiple number of detectors, each sensitive to radiation at a different incident wavelength. The intensity at one or more maximum and minimum in the spectral characteristic may then be measured.

Referring to Figure 3, the spectral characteristic shown corresponds to a transmission or interference filter a Fabry Perot etalon) of the type (HL) 2

HH(LH)

2 where H and L indicate materials of high and low refractive index respectively and each layer is a quarter-wave thick at design wavelength. In this example, the design wavelength is the wavelength at the minimum P:\OPER\D 61317.96 rsl.do-1605t01 in the spectral characteristic. The materials H and L might be TiO 2 and SiO 2 respectively. The materials incorporated in the filters and the thicknesses of the layers are selected such that the filter gives rise to characteristic interference effects. The construction of such filters would be conventional to one skilled in the art.

In this example, the filter is formed on top of a broadband absorber carbon based ink) and covered by a polychromatic black dye, as in the previous example. Under normal lighting conditions the filter would therefore have a neutral appearance and appears black. When illuminated with radiation having selected wavelength components, corresponding to the wavelength region of interest in the spectral characteristic, the filter gives rise to optical o10 interference effects which may be used as a means of identification.

The spectral characteristic has a maximum 9 at 800 nm, a minimum 10 at 850 nm and has an absorption band 11 extending throughout the lower wavelength region. By illuminating the filter with radiation comprising wavelengths at 800 nm and 850 nm, and using detectors sensitive to said wavelengths, a comparison of the respective intensities of the two detector outputs provides a ratio characteristic of the filter. This can be compared to the known standard ratio for the filter S to check the authenticity of the article.

Referring to Figure 4, the spectral characteristic 12 of the filter comprises a series of maxima 13 and minima 14 distributed throughout the visible wavelength region. The spacing of the maxima and minima (reflection bands) is chosen such that the filter has a neutral appearance when viewed in reflection under normal lighting conditions. For example, the filter may appear grey, white or black, depending on the design. The characteristic shown in Figure 4 corresponds to a Bragg reflector with the multi layer stack structure (20LH) 6 i.e. 20 layers of L material and 1 layer of H material arranged in a 6-period stack. Each layer is a quarter-wave thick at the design wavelength. In this example, the design wavelength would be considerably greater than the range covered in Figure 4 greater than 700 nm).

As in the previous example (Figure the filter operates on the basis of thin film interference effects and is preferably constructed such that its spectral features are sharp. For example, referring to Figure 4, the reflection bands have a bandwidth of approximately 20 nm. The ASqnstruction of such reflectors would be conventional to one skilled in the art. Other variations of P.OPER\DH61317-96 rs I .do- 1605,01 -6this reflector may also be used, particularly those based on a metallic-dielectric design. As in the previous examples, a measure of the reflected (or transmitted) intensities at wavelengths corresponding to one or more maximum and minimum in the spectral characteristic 12 provides an authenticating signature for this particular filter.

Such a concept could also be extended to include a multiple number of incident wavelengths or a multiple number of detectors, each sensitive to radiation at a different incident wavelength. For example, the filter may first be illuminated with a series of wavelengths corresponding to the maxima 13 in the spectral characteristic 7 and then with a series of wavelengths corresponding to the minima 14. The integrated intensities measured when the filter is illuminated with the *o:10 maxima wavelengths are then compared with the integrated intensities measured when the filter is illuminated with the minima wavelengths to give a characteristic ratio for the filter. If the i required ratio is not measured, the article does not have the authenticating filter applied.

The intensity measurements may be made, for example, using a CCD detector array having a linear variable filter bonded to the front surface of the array to measure the intensities at each individual wavelength of interest. Alternatively, a multiple number of detectors, each sensitive to radiation at a different wavelength, could be used.

The wavelength components of the incident radiation need not correspond exactly to a maximum or minimum in the spectral characteristic, although preferably they correspond to spectral bands in the reflectance-wavelength curve (see Figure For example, referring to Figure 2, the incident radiation might comprise wavelength components corresponding to 15 and 16. In this case, the detection system used would be sensitive to these wavelength components. A measure of the respective intensities at wavelengths 15 and 16 provides a characteristic ratio for the filter, even though the maximum and minimum reflectance is not detected.

In any of the examples, the radiation source (or sources) need not emit only discrete wavelengths, but a source may be used which emits radiation over a range of wavelengths such that the range encompasses the wavelength region of interest in the spectral characteristic.

The variation of the reflected intensity with the angle of incidence of the illuminating radiation /i/,ONrl. .also be used as a distinguishing feature. For example, referring to the spectral characteristic

-I

P:AOPER\DID61317-96 rsi.doc-1605i01 -7shown in Figure 4, when interrogated using a source at 532 nm (corresponding to a maximum 13 in the spectral characteristic 12), the reflectance will decrease as the angle of incidence is changed. This effect would be visible to the eye as the article to be protected is tilted before the observer. If a second source at, for example, 633 nm was used (corresponding to a minimum 14 in the spectral characteristic 12), the reverse effect would be seen and the reflected intensity would increase as the object was tilted.

The effect can be quantified by the use of suitable detectors. A comparison of the measured intensities at the selected angles with the known intensities at these angles for the filter may then be used to provide a further means of checking the authenticity of the filter.

Alternatively, the spatial distribution of the reflected (or transmitted) radiation, as modified by the filter, may be used as a signature of authenticity. In a preferred arrangement, a radiation source having a plurality of wavelength components may be used, for example a filtered tungsten lamp, where radiation emitted from the lamp passes through a filter having the construction of that of the example in Figure 4 20(HL) 6 Only selected wavelength components are :15 therefore incident on the optical filter, in this case corresponding to the maxima and minima in the spectral characteristic. Upon tilting the filter (or the article to which the filter is applied) the change in reflectance will be observed by the human eye. When the article is illuminated with radiation from the lamp and filter combination, an informed operator aware of the authenticating S optical effect may use the observed optical effect as a means of verifying the authenticity of the article.

Conveniently, a range of angles may be assessed by illuminating the article with a spatially extended radiation source and tilting it with respect to a fixed detector. Alternatively, the angular signature may be determined as the article (for example, a credit card) is passed through a reader, wherein the reader is fitted with the suitable radiation source and detectors in a fixed arrangement, giving a fixed geometrical relationship to the article.

The concept of using the tilting of the filter to provide the required authentication signature could also be extended outside the visible wavelength region using a suitable radiation source (or xS es) and suitable'-detection means, such as a camera.

O z~ Ij P:OPER\DHM61317-96 rsl.dm.16050,1 -8- The design of the filter can be adjusted to allow its use with any convenient wavelength of light by the definition of the design wavelength and the selection of the order parameter m in (mLH)" or In this case, the number of pairs of layers, n, in the Bragg reflector defines the contrast level achieved at the maximum of the reflection band. Furthermore, the filter may be constructed such that the reflection bands have a relatively narrow bandwidth.

The filter may be used on a surface, either alone or in conjunction with absorbing materials, to produce suitable reflection characteristics. The features of the filter (or label) applied to the article may be incorporated into various visible features of the article, for example a trademark, a S surface decoration or a bar code.

If the filter is distributed on the label in the form of a bar code, one or more different spectral characteristics can be used for different lines in the bar code pattern. The filters would be designed to be equivalent when viewed in daylight or tungsten light, so that all lines in the bar code would be equally intense to the observer or camera. When viewed with the correct i illuminating wavelengths, differences are seen by the observer or camera, therefore providing an :15 additional level of security in the bar code.

The filter to be incorporated into a label may be realised in the form of a paint, by incorporating flakes of the filter into a suitable binder, therefore allowing ease of application. Alternatively, the layers which make up the filter may be deposited on a polymer film which is then applied to the article. Filters with a small number of maxima and minima in the reflectance curve may be deposited on to a series of such films and then laminated together in different combinations. This provides a convenient means of continuously varying the characteristics of the filters used.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion pl -ny other integer or step or group of integers or steps.

0

Claims

1. A method for covertly marking an article and checking its authenticity comprising the steps of; applying an optical filter to the genuine article, (ii) illuminating the article to be authenticated with electromagnetic radiation at two or more angles of incidence, wherein said radiation comprises components of at least one wavelength, (iii) upon said illumination, detecting radiation reflected or transmitted by the article to be authenticated at each angle of incident radiation and (iv) comparing properties of the reflected or transmitted radiation at each angle of incident radiation with known properties of radiation reflected or transmitted by the filter at said angles of incident radiation.

2. The method of claim 1 wherein the filter is a multi layer interference filter, having at least one i maximum and at least one minimum in the spectral characteristic and having a neutral appearance when observed under normal lighting conditions, wherein the multi layer interference filter comprises at least two materials having a selected thickness and refractive indices such that when illuminated with the electromagnetic radiation the filter gives rise to characteristic S interference effects.

3. The method of claim 1 or 2 wherein the spectral characteristic of the filter has a plurality of maxima and minima.

4. The method of claim 3 wherein the spatial distribution of reflected or transmitted radiation at said angles of incident radiation is compared with the known spatial distribution of radiation reflected or transmitted by the filter at said angles of incident radiation. The method of claim 4 wherein the intensity of the reflected or transmitted radiation at said angles of incident radiation is compared with the known intensity of radiation reflected or transmitted by the filter at said angles of incident radiation.

P.OPER\DH61317-96 rsl.doc- 1605/01

6. The method of any of claims 1-5 wherein the filter is illuminated by electromagnetic radiation having wavelength components corresponding to spectral bands in the spectral characteristic of the filter.

7. The method of claim 6 wherein electromagnetic radiation having wavelength components corresponding to spectral bands in the spectral characteristic of the filter is generated by placing a second filter in front of a radiation source, wherein said second filter has the spectral characteristic of the filter applied to the genuine article.

8. A method for covertly marking an article and checking its authenticity, substantially as hereinbefore described with reference to the drawings. :10 DATED this 16th day of May, 2001 THE SECRETARY OF STATE FOR DEFENCE By DAVIES COLLISON CAVE Patent Attorneys for the applicant .4