FLUORESCENT MULTILAYER AUTHENTICATION DEVICE

Field of the Invention

The present invention relates to an authentication device, in particular for use in combating counterfeiting, and to a method of authenticating an article.

Background of the Invention

It is known to provide an authentication device for use in anti-counterfeiting protection techniques wherein the authentication device is applied to an article desired to be protected against counterfeiting and known properties of the authentication device are compared with subsequently detected properties to determine whether the article is genuine.

In one such arrangement, a complex mixture of fluorescent materials is printed in a layer on an article and when the layer is stimulated with exciting light a spectral signature is produced and recorded. The spectral signature may vary with the frequency of the exciting light. A determination is subsequently made as to whether the article is genuine by scanning the layer so as to derive a spectral signature and comparing the spectral signature with the recorded spectral signature.

However, this authentication technique has a significant limitation in that it is possible for a sophisticated counterfeiter to replicate the layer by separating the materials, for example by chromatographic separation, and subsequently identifying the materials, for example using mass spectroscopy or by analysis of the individual spectral signatures of the fluorescent materials.

Summary of the Invention

In accordance with a first aspect of the present invention, there is provided an authentication device comprising: a first layer of material; and a second layer of material, the second layer being disposed over the first layer,- wherein the electromagnetic response characteristics of the first and second layers are selected such that when illuminated with specific electromagnetic radiation the spectral signature produced by the device is dependent on the respective materials present in the first and second layers and the respective positions of the first and second layers .

Preferably, one layer of the first and second layers is arranged so as to absorb or reflect a portion of incident electromagnetic radiation and the other layer of the first and second layers is arranged so as to transmit electromagnetic radiation in response to illumination by said portion of electromagnetic radiation.

In this way, the "apparent" spectral signature of the device is altered, for example by the presence of absorbers which may be fluorescent or non- fluorescent in either layer, and the response spectral signature of the device is unable to be reproduced by any combination of the same fluorescent and/or absorbent materials in a single layer.

Thus, in order to counterfeit the authentication device, knowledge of the individual arrangement of materials in each layer must be known.

In one embodiment, at least one of the first and second layers is arranged so as to absorb at least some

electromagnetic radiation emitted by another layer of the first and second layers.

In one embodiment, at least one of the first and second layers is arranged so as to reflect at least some illuminating electromagnetic radiation.

In one embodiment, one of the first and second layers is arranged so as to reflect at least some electromagnetic radiation emitted by another of the first and second layers .

In one arrangement, the first layer includes at least one fluorescent material. In one example, two fluorescent materials are provided in the first layer.

In one arrangement, the second layer includes at least one fluorescent material having different fluorescent properties to the fluorescent materials in the first layer. In one example, two fluorescent materials are provided in the second layer.

The absorptive and/or reflective properties of the first and/or second layer may be obtained by appropriate selection of fluorescent materials in the first and second layers. Alternatively, the absorptive and/or reflective properties of the first and/or second layer may be obtained by addition of non- fluorescent absorptive and/or reflective materials.

The first and/or the second layer may be formed so as to be relatively thin, for example of the order of 0.1-100μm.

The article may be a pharmaceutical prescription; a lottery ticket; a contract; a document such as a letter, a deed or will; a Bill of Exchange; a Certificate of Deposit; perfume; or an item of clothing.

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The first and/or second layer may be a printable material.

In accordance with a second aspect of the present invention, there is provided a method of authenticating an article, said method comprising: providing an authentication device by forming a first layer of a first material on an article and forming a second layer of a second material over the first layer,- selecting electromagnetic response characteristics of the first and second layers such that when illuminated with specific electromagnetic radiation the spectral signature produced by the device is dependent on the respective materials present in the first and second layers and the respective positions of the first and second layers; obtaining first and second spectral signatures from the device using first and second illumination conditions respectively; recording the first and second spectral signatures; obtaining third and fourth spectral signature from the device using the first and second illumination conditions respectively; and comparing the first and second spectral signatures with the respective third and fourth spectral signatures.

In one embodiment, the method comprises obtaining the first and second spectral signatures and the third and fourth spectral signatures by illuminating the device using different frequencies.

In one embodiment, the method comprises obtaining the first, second, third and fourth spectral signatures by illuminating the device from substantially the same direction.

In one embodiment, the method comprises obtaining the first and third spectral signatures and obtaining the second and fourth spectral signatures by illuminating the device from substantially opposite directions.

In one embodiment, the method comprises obtaining the first and second spectral signatures by illuminating the device with electromagnetic radiation directed at one side of the device, and separately capturing electromagnetic radiation emitted from opposite sides of the device.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation of an article provided with an authentication device in accordance with an embodiment of the present invention; Figure 2 is a diagrammatic cross-sectional view of the authentication device shown in Figure 1 ;

Figure 3 is a schematic diagram of an authentication system for authenticating articles in accordance with an embodiment of the present invention; and Figure 4 is a flow diagram illustrating a method of authenticating an article in accordance with an embodiment of the present invention.

Description of an Embodiment of the Invention

Referring to Figures 1 and 2 of the drawings, there is shown an article 10 to which anti-counterfeit protection is desired to be applied. In this example, the article 10 is a bank cheque, although it will be understood that other articles are envisaged, the important aspect being that the article is of a type wherein a recipient of the article requires confirmation that the article is genuine.

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For example, the article may be a pharmaceutical prescription; a lottery ticket; a contract; a document such as a letter, a deed or will; a Bill of Exchange; a Certificate of Deposit; perfume; an item of clothing; and so on.

The article 10 shown in Figure 1 is provided with an authentication device 12 disposed adjacent a corner of the article 10 and of a relatively small size relative to the article 10.

As shown more particularly in Figure 2, in this example the authentication device 12 is applied to a substrate 14 of the article 10 by printing a first layer 16 of printable material onto the substrate 14 and subsequently printing a second layer 18 of printable material onto the first layer 16. The first and second layers 16, 18 are such that the first layer has an associated first response which varies with frequency of incident light, and the second layer has an associated second response which is different to the first response and which varies with frequency of incident light. The materials from which the first and second layers are formed are selected such that the first and second layers interfere with each other so that the electromagnetic response produced by the two layers at a particular wavelength is different to the electromagnetic response which would be produced by a device having the same materials in a single layer.

In this embodiment, one of the first and second layers 16,

18 is at least partially absorptive at a particular electromagnetic wavelength and the other of the layers is light emissive at the wavelength so that when the device 12 is illuminated with electromagnetic radiation including the electromagnetic wavelength, the spectral signature produced by the first and second layers is derived from

the first and second layers and is dependent on the respective positions of the first and second layers.

In the present example, the second layer 18 is arranged so as to be absorptive at at least one electromagnetic wavelength, although it will be understood that other variations are possible. For example, the first layer 16 may be arranged so as to be at least partially absorptive instead of the second layer, or both first and second layers 16, 18 may be arranged so as to be at least partially light absorptive at different wavelengths.

First and/or second layers which are at least partially light absorptive may be obtained by appropriate selection of fluorescent materials having the desired absorptive properties, or by adding appropriate non- fluorescent absorptive materials into the respective one or more desired layers.

It will be understood that in the present example the second layer 18 is partially light absorptive, as shown in Figure 2, and the arrangement is such that some of the light 20 incident on the device 12 is absorbed by the second layer 18, some light 24 is transmitted to the first layer 16, and some light 22 is emitted from the second layer 18 in response to the transmitted light 24. In addition, some light reflected from the substrate 14 and/or from the first layer 16 is also absorbed and/or reflected by the second layer 18, and some light 26 is emitted upwards from the first layer 16 through the second layer 18. As a consequence, the spectral signature produced by the device 12 is a function not only of the materials and amounts of materials used in the layers 16, 18, but also of the materials and material amounts in each layer 16, 18 and the relative positions of the layers 16, 18 in the device 12. As a consequence, a would be counterfeiter wishing to replicate the spectral signature

of the device 12 would not be able to achieve this by removing both layers 16, 18 and identifying the materials in the layers 16, 18, since knowledge of the materials and amounts in each layer 16, 18 and the respective locations of each layer would also be required.

In the present example, the second layer 18 may be configured, for example by appropriate choice of materials included in the second layer 18, so as to absorb, reflect or transmit light in varying amounts, either in relation to exciting light and/or in relation to emitted light.

In the present example, the first layer 16 comprises a complex mixture of two or more fluorescent materials and similarly the second layer 18 comprises a complex mixture of two or more fluorescent materials.

Each fluorescent material may be an organic or inorganic material which emits light when irradiated with electromagnetic radiation such as ultraviolet light. A fluorescent dye may be water-based or solvent-based, including diaminostilbene, coumarin, oxazol, pyrazoline, etc. Examples of fluorescent pigment that can be used as the fluorescer include sulphide pigment such as CaS=Bi, SrS: SM: Ce, ZnS: Ag, ZnS: Cu, ZnS: Cu: Co, and oxygen acid chloride such as Sr ₅ (PO ₄ ) ₃ C1 : Eu, 3 (Ba, Mg) .8Al ₂ O ₃ : Eu, ZnO:Zn, Zn ₂ SiO ₄ = Mn, Zn ₂ GeO ₄ : Mn, YVO ₄ = Eu, Y ₂ O ₂ S: Eu, 0.5MgF ₂ : 3.5MgO-GeO ₂ : Mn, or a fluorophore such as Green Fluorescent Protein (GFP) , fluorescein, Molecular Probes' Alexa Fluor 488 dye, a BODIPY dye, BCECF, carboxy SNARF-I, a hydroxycoumarin (umbelliferone) , or an aminonaphthalene such as prodab, badan, or dansyl . Any afterglowing pigment may also be used in the fluorescent dye.

In order to significantly reduce the likelihood of a would be counterfeiter being able to separate the layers and thereby obtain an indication as to the materials and the

material amounts in each of the layers, each layer 16, 18 in this example is relatively thin, for example of the order of lOμm.

It will be appreciated that because the spectral signature of the device is dependent on the positions of the layers, the emission spectral signature of a single layer including a complex mix of four materials will be different to the emission spectral signature of 2 layers each including 2 of the four complex materials.

In one illustrative example, a first fluorescent chemical is added to the first layer 16 and a second fluorescent chemical is added to the second layer 18. The first fluorescent chemical added to the first layer 16 emits a red spectral signature (600nm) when excited with electromagnetic radiation of frequency X or frequency Y. The second fluorescent chemical added to the second layer 18 emits a blue spectral signature (450nm) when excited with electromagnetic radiation of frequency X only.

With this arrangement, top-down excitation of the device 10 with frequency Y produces a red spectral signature, and top-down excitation of the device 10 with exciting light of frequency X, produces a predominantly or completely blue spectral signature. This is because the exciting light of frequency X is predominantly or completely absorbed in the second layer 18 and is thus unable to excite the fluorescent material in the first layer 16 to produce an additional red spectral signature (as would be the case if both fluorescent materials were printed in one layer) .

Therefore, the top-down spectral signature of the device is dependant on the individual fluorescent and/or absorbent materials added, and also on the arrangement of the individual layers, and cannot be reproduced by any

combination of the same fluorescent and/or absorbent materials in a single layer.

It will be understood, therefore, that by separately exciting the device with light of two different frequencies or two different frequency bands, two different response spectral signatures can be reproduced which together characterize the device. The same two response spectral signatures cannot be reproduced using a single layer device.

In another example, an initial first layer 16 is printed containing a fluorescent material that absorbs at excitation frequency X and frequency Y and emits red light, and a non- fluorescent absorber that absorbs electromagnetic radiation at frequency Y. The second layer 18 contains a fluorescent material that also absorbs frequency X or frequency Y, and emits blue light.

In this example, the fluorescent material in the first layer 16 is independently affected by the presence of the absorber when using top-down irradiation by exciting light, while the fluorescent material in the second layer 18 is unaffected.

In one arrangement, the device may be characterised by obtaining electromagnetic spectra using stimulation of the device 10 by top-down exciting light and bottom-up exciting light. In this case, the substrate 14 must be clear or translucent to the exciting light, for example paper, plastics etc. The response spectra produced at one or both sides of the device when the device is illuminated with top-down or bottom-up radiation may be captured for subsequent comparison purposes.

In a further arrangement, the device may be characterised by illuminating the device with electromagnetic radiation

directed at one side of the device, and separately capturing electromagnetic radiation emitted from opposite sides of the device.

An authentication system 30 usable to create an authenticatable article 10 and carry out a method of authenticating the article 10 is shown in Figure 3 and illustrated in flow diagram 50 in Figure 4.

The system 30 comprises a first computing device 32 usable by an operator of the system 30 to control a printer 34 and a first scanner 36. The printer 34 is arranged to receive an article 10 to be provided with anti-counterfeit protection and according to a pre-determined printing scheme controlled by the first computing device 32, the printer 34 prints the first and second layers 16, 18 onto the article 10 using predetermined fluorescent materials in predetermined amounts so as to produce the authentication device 12, as indicated by method steps 52 and 54 in the flow diagram 50. The article 10 provided with the authentication device 12 is then passed through the first scanner 36 which illuminates the authentication device 12 with a first predetermined range of electromagnetic radiation and detects a first response spectral signature indicative of the specific materials and amounts in the layers 16, 18 of the authentication device 12, as indicated by method step 56. The first scanner 36 then illuminates the authentication device 12 with a second predetermined range of electromagnetic radiation and detects a second response spectral signature indicative of the specific materials and amounts in the layers 16, 18 of the authentication device 12, as indicated by method step 58.

In this example, the derived first and second response spectral signatures are forwarded through the Internet 38 to a remote computing device 40 for storage in a database

42 as an authentication record 44 associated with the article 10. The communications between the first scanner 36 and the database 42 may be encrypted so as to minimize the likelihood of interception by a would be counterfeiter.

In the present example, the article 10 is a bank cheque and, accordingly, the above described operations to create the authentication device 12 and store an authentication record 44 in the database 42 may be carried out by a person associated with a bank.

It will be understood that although the above example is described in relation to an authentication device which includes at least one layer arranged to at least partially absorb light, other variations are possible. For example, the second layer 18 may be arranged to at least partially reflect light of specific wavelengths, thereby affecting the ability of the first layer 16 to emit light in response to the reflected light.

It will be understood that in order to produce a spectral signature associated with the device 12 which depends on the composition of the layers themselves, one of the layers 16, 18 must be arranged so as to at least partially absorb or reflect at least some of the excitation light and/or at least some of the light emitted in response to the exciting light.

On receipt 60 of the bank cheque by the intended recipient, such as by a recipient bank, the bank cheque 10 is passed through a second scanner 46 which generates third and fourth response spectral signatures from the authentication device 12 under control of a second computing device 48 by separately illuminating the authentication device 12 with the first and second predetermined ranges of electromagnetic radiation, as

indicated by method steps 62 and 64. The detected spectral signatures are then forwarded through the Internet to the remote computing device 40 which compares the third and fourth response spectral signatures with the first and second response spectral signatures recorded in the authentication record 44. If the spectral signatures match, then an indication is provided 66 to the recipient that the article is genuine.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.