The invention relates to a system and a method for identifying and authenticating a tag applied on a variety of items as means of identification and authentication.

BACKGROUND OF THE INVENTION

The positive identification of products, their tracking and authentication are already applied and used in many fields of the industry and are continuously developed and improved. The marking of products for identification, authentication and tracking purposes is increasingly applied in many fields of the industry. Security markings of various degrees of complexity exist and are applied on items and products helping to answer the question whether a given product is genuine or counterfeit. Counterfeiting indeed is a worldwide problem resulting in huge economic losses and negatively impacting consumers and producers. To counteract this problem, anti-counterfeiting technology is constantly being developed including new security markings and adapted readers. Such security marking may have both spatial and spectral coding components.

WO2010012046 generally describes a code carrier having fluorescent markings. It mentions a reader engineered for reading a fluorescent code carrier in which the recorded information is encoded into visual features of a coded visual marking. This reader apparatus may include a combination of two reading apparatuses, one that reads the fluorescent properties of the fluorescent material in the coded fluorescent marking and the other which reads the visual features of the coded fluorescent marking. In this document, the fluorescent signal is read and decoded first and the visual shape properties are subsequently decoded.

US74 1704 describes a system and method for identifying a spatial code having one or multi-dimensional pattern applied to an object, where the spatial code includes a plurality of security tags or compositions having one or more characteristic emission spectral signatures. The system uses beam source to illuminate the code, a spectrometer to analyse its signature and a camera to identify the code. It also comprises a beam splitter for splitting the emitted light from the code to both an image detector and an optical spectrometer which induces a simultaneous acquisition of the information/data.

US7938331 describes a reader to authenticate a tag/marking/code (an automatic identification symbol e.g. a barcode) applied to an item and having specific spectral emission signatures. The specific spectral signature of the tag/code is applied in addition elsewhere on the item. If both spectral signatures are recognized and both match, the product validation is performed without accessing an external database. The system uses an illumination light to excite the fluorescent tag, a spectrometer to analyse its signature and a camera to identify the code.

All the above-mentioned systems use the spectral properties of a tag having a code carrier structure. The use of a spectrometer in addition to a camera offers the highest accuracy and thus, guarantees a high level security. However, even if certain systems make use of these two detectors, they do not allow a fully independent setting of their acquisition parameters such as integration time and excitation light intensity. Moreover, none of the above- mentioned methods fully benefits from the information available in the camera images as they do not analyse their spectral characteristics prior to analysing the information recorded by the spectrometer.

Therefore, it is desirable to provide further systems and methods for identifying and authenticating security codes/tags that have unique spatial and spectral properties via optimized identification and authentication means, such means allowing a fast and reliable authentication process. SUMMARY OF THE INVENTION

In this view the present invention is concerned with a system for identifying and authenticating a tag applied to an object, wherein the tag is defined by at least one luminescent spatial pattern and one spectral signature of optically active nanoparticles contained in said tag and defining said spatial pattern, the system comprising:

a reading module to acquire the tag information, said reading module comprising: a lighting unit comprising a light source driven in a pulse-mode, said light source being adapted to illuminate the tag with infrared excitation light so as to excite the nanoparticles of the tag, thus resulting in the emission of the luminescent spatial pattern by the tag,

an imaging unit adapted to record an image of said spatial pattern,

a spectral unit adapted to record the spectrum of said spectral signature, a timing control unit adapted to synchronize the actions of the other units of the reading module,

a processing module both in communication with the reading module and with a database containing the spatial patterns and spectral signatures of predetermined tags, said processing module comprising:

a decoding unit adapted to decode the image recorded by the imaging unit, provide a serial number corresponding to said image and compare said serial number with the corresponding serial numbers of the predetermined tags so as to identify the tag, a validation unit adapted to compare the spectrum recorded by the spectral unit with the spectra of the predetermined tags so as to authenticate the tag, and a read-out unit to disclose information about the tag once authenticated, characterised in that the imaging unit and the spectral unit record their respective signals in a sequential manner, their acquisition being synchronized onto different excitation light pulses.

Important features of this system are defined in the dependent claims 2 to 6.

The present invention also concerns a method for identifying and authenticating a tag applied to an object according to claims 7 to 12 and claims 13 to 15.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become better understood with regard to the following detailed description, claims and drawings where: Figure 1 illustrates a tag and a reading module of a system according to a first embodiment of the present invention.

Figure 2 represents a block diagram illustrating the system according to a first embodiment of the present invention.

Figure 3 is a time-diagram illustrating the synchronization pattern of the units of the reading module used in the system of Figure 1

Figure 4 depicts a flow-chart of the method performed by the system of Figure 1.

Figure 5 represents a block diagram illustrating a system according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a system and method enabling the identification, authentication, tracing and the localization of tagged products with high-level security from any distance. The system comprises a reading module, a processing module and a database containing the stored tag identities. The identity of the tag is defined by two distinct signatures: a luminescent spatial pattern and a unique optical spectral signature. The tag contains or forms a spatial pattern, and is composed of luminescent material, i.e. fluorescent nanoparticles. By detecting the two signatures with the reading module, the information is processed and the tag identity validated against the information already contained in the database allowing thereby the authentication of the product. This overall procedure enables the identification and authentication of the product. Additionally, the system enables to reveal the accurate position of the tag through a combination of optical measurement and global positioning.

1. Definitions

The terms below have the following meaning unless indicated otherwise in the specification. A "tag" is an identity marking having two distinct signatures: a luminescent spatial pattern and a unique optical spectral signature. The tag may be affixed on a variety of products and items that need to be authenticated. Products bearing a tag are referred to as "tagged" or "marked" products

A "spatial pattern" or "luminescent spatial pattern", is a specific one- two- or three- dimensional structure that can be identified and related to a unique serial number. The structure may take any shape and/or form a one- two- or three-dimensional code. For example, it could be composed of multiple layers, offering a three-dimensional spatial extent.

The "spectral signature" refers to the distribution of the fluorescent light emitted by the tag along the wavelength axis. It can be measured with various instruments such as e.g. a spectrometer or a digital camera. When measured with a spectrometer, this signature is referred to as a spectrum or spectra. If recorded by a colour camera, the resulting colour of the image will be defined by said spectral signature.

"Nanoparticles" are metallic crystals or powders with a diameter in the nanometer range. When illuminated with infrared excitation light in the wavelength range from 800 to 2000 nm, these particles emit light with a specific spectral signature in a range from 450 to 900 nm. Each type of particle is characterized by a specific and unique spectral signature, depending on several parameters such as its chemical composition, size or shape. A mix of several types of particles will have a unique spectral signature, depending on the concentration of each type of particles contained into the mixed solution/powder. "Identification", "identify" as used herein refers to the step of decoding the first signature of the tag, i.e. spatial pattern, on the basis of a match against the data stored in a database. Each spatial pattern relates to a single serial number.

"Decoding" means reading the serial number coded into the spatial pattern and verifying its integrity. This process is uniquely based onto the spatial pattern signature of the tag. A successful decoding of a tag enables its "identification".

"Authentication", "authenticate" as used herein refers to the step of validating the second signature of the tag, i.e. spectral signature. This step comes after the identification step and thus, proves that a product is genuine. "Validation", "validate" means analysing the spectral signature of the tag via the information recorded by both a colour camera and a spectrometer. This process is performed after the decoding process. A successful validation of a tag enables its "authentication".

2. Tag

This section describes a tag that can be identified and authenticated with the system according to the invention. The identity of the tag is defined by two distinct signatures: a luminescent spatial pattern and a unique spectral signature specific to the luminescent particles contained into the spatial pattern. The tag contains or forms a spatial pattern representing some type of informatics code. It is composed of luminescent material, i.e. fluorescent nanoparticles. As illustrated in Figure 1 , when excited with infrared (IR) light (800- 2000 nm) emitted by a lighting unit 114, the nanoparticles present in the tag 101 emit light at shorter wavelengths (450-900 nm). This so-called optical upconversion is an anti-Stokes fluorescent process and results in a specific spectral signature for the emitted light. The emitted light is collected by the reader instrument containing the reading module 110 of the system 100 through two distinctive channels: the imaging unit 111 and the spectral unit 112. The imaging unit 111 records an image (e.g. , 102) of the optically activated spatial pattern when the excitation light is applied, while the spectral unit 111 records its detailed spectral distribution i.e. the spectrum (e.g. 103). The identity of a tag consists in both the spatial pattern and the spectral signature of optically active nanoparticles embedded into the tag. The spatial pattern is a one- or multi-dimensional structure created by the characteristic distribution of the nanoparticles in the tag. It arises due to the fact that fluorescent light is emitted only in the pre-defined areas of the tag 101 containing the luminescent nanoparticles while the other areas of the tag remain inactive. In order to create the tag, nanoparticles may be mixed into a polymer prior to its application to another material. The tag may be directly created onto the marked product or can form a full-assembly that is then attached or bonded to the marked product. It can be created onto (or attached to) any type of material.

When the spatial pattern consists of repetitive structures, a large number of codes is created by varying the contrast of each individual structure. Data matrix code made out of square structures is a typical two-dimensional example of such patterns. The number of codes available can be further increased by tuning the spectral signature of the fluorescent light emitted by the tag.

3. System and method

This section describes a system 100 able to identify, authenticate and localize a tag. The identification and authentication are achieved by decoding the spatial pattern and validating the spectral signature contained into the tag. The localization of the reader instrument is performed by the use of a global positioning system. In combination with the optical localization provided by the system, the precise position of the tag is identified and recorded into the database 130.

The system 100 comprises a reading module 110 in communication with a processing module 120, which in turns communicates with the database 130 during decoding and validation processes as well as during the read-out. Figure 2 discloses a block diagram of the whole system and the interactions between the different units.

The system 100 is preferably constructed as part of a hand-held device. However, for applications where it is convenient to scan tags at fixed positions, the system can be designed and operated at a fixed unit. The reader instrument provides a user interface, enabling the user to control and communicate with the system 100. The reader instrument is driven by a software, embedded into a processing apparatus, such as a computer.

The reading module 110, may be composed of the following units:

A lighting unit 114 that provides a homogeneous illumination of the tag with at least one light source, at a wavelength corresponding to the excitation wavelength of the active nanoparticles contained into the tag, typically in the IR spectrum when using the upconversion effect. This light source is driven in a pulse-mode, triggered by the timing control unit 115. To create the illumination pattern, the output of the light source is redirected towards the tag through an optical system (composed of elements such as lenses, mirrors and optical fibres). For safety reasons, a lighting indicator may advantageously be placed externally onto the reader instrument, so as to indicate to the user if the light source emits light or not. Such a lighting indicator may be controlled by the timing control unit 115. In another embodiment, the lighting unit 114 contains at least one additional light source at any wavelength for the detection of other optical effects than upconversion that may be generated by the tag.

An imaging unit 111 that collects the image emitted by the tag 101 by the use of at least one sensor, such as a colour CMOS chip. In this unit, an optical filter discards the remaining excitation light. The sensor acquires and sends data to the processing module 121. The images correspond to visual representations of the spatial pattern. The imaging unit 111 may record images whilst the excitation light is on or off. The image recorded when the excitation light is on corresponds to the "signal" image whereas the one recorded whilst the excitation light is off is referred to as the "background" image. The background image can be recorded prior or after recording the signal image. A spectral unit 112 that collects the fluorescent light emitted by the tag and redirects it towards a spectrometer, for example by the use of an optical fibre. An optical filter discards the remaining excitation light. The spectrometer may be made out of a diffraction grating, an imaging lens and a CCD line array. In another embodiment, the spectrometer uses other optical components to record the spectrum, such as a prism and/or a CMOS detector. The spectrometer records the spectrum and sends data to the processing module 121.

The spectral unit 112 may record the spectrum whilst the excitation light is on or off. The spectrum recorded when the excitation light is on corresponds to the "signal" spectrum whereas the one recorded whilst the excitation light is off is referred to as the "background" spectrum. The background spectrum can be recorded prior or after recording the signal spectrum.

A timing control unit 115 that controls the sequence of the reading process. This unit triggers light pulses of the lighting unit 114 and synchronizes the acquisition of the imaging 111 and the spectral units 112. Each of these two units acquires data sequentially, synchronized on individual light pulses. The reading process can be continuously, automatically or manually enabled. In manual mode, a user operating the system presses on a physical trigger placed onto the reader instrument to enable the reading. While kept pushed, this trigger enables the repetitive output of light pulses, such as illustrated in Figure 3. In Figure 3, from top to bottom, the lines represent (a) the "trigger" (system enabled) and (b) the laser pulses of the lighting unit 114. A1 and A2 represent the amplitudes of the laser pulses (optical power); t1 and t2, the durations of pulse 1 and pulse 2 respectively. In this example, the enabling line allows the generation of one full cycle of two pulses and stops after the first light pulse of the second cycle. The use of sequential pulses, preferably two, for the camera (pulse 1 ) and the spectrometer (pulse 2) allows setting the amplitude and the duration of each pulse independently. As the imaging unit 111 and the spectral unit 112 have completely different sensitivities, the sequential acquisition allows maximizing the signal-to-noise ratio for each component independently. Another advantage of this synchronization pattern lies in the fact that the processing of the data acquired by the imaging unit 111 on the first pulse, can start while the spectral unit 114 is still acquiring. This enables a faster authentication process. The information acquired through the reading module 110 is delivered to the processing module 120 that may be composed of the following units:

A decoding unit 121 that allows identifying the tag using the images (background and signal) sent by the imaging unit 111 . The spatial pattern is decoded in order to get the tag serial number. The decoding may be performed by various known methods such as barcode or Quick Response (QR) code reading (see e.g. EP0672994 for QR code decoding). The decoding may also be performed by simple pattern recognition where each tag serial number is uniquely related to a specific pattern. A communication with the database 130 is then established in order to verify the existence of this number in the database 130. If this number already exists in the database 130, the tag 101 is considered as identified. A validation unit 122 that allows authenticating the tag using the spectra (background and signal) sent by the spectral unit 112. The spectrum is compared to the predetermined spectra of the "authentic" tags stored in the database 130. Mathematical criteria are used to perform an accurate comparison and thus conclude whether it is genuine or not.

The validation unit 122 may in addition use the images (background and signal) acquired by the imaging unit 111. In this case it proceeds to a validation process in two distinctive steps: the analysis of the image colours followed by the above-mentioned analysis of the spectrum. In the first step, the analysis of the image colours, after background subtraction, the image of the spatial pattern is decomposed into three colour channels: red, green and blue. This decomposition may be performed by known techniques such as the one described in US8313030. Indeed, with a colour camera, each pixel of an image is coded over three values corresponding to red, green and blue components of the light. While reading a tag, the intensity ratios between these three components are specific to the type of nanoparticles contained into the tag. Thus, it allows rapidly validating or invalidating the tag. In the second step, the spectrum acquired by the spectral unit 112 is compared to the predetermined spectra of the "authentic" tags stored in the database 130. This second validation procedure offers a greater precision than the first one and is therefore necessary to ensure high security level. However, the calculations required are time-consuming. Hence, this two-step method avoids initiating relatively long computations for a spectrum which obviously does have a correct match in the database 130 as it will be discarded by the first step. Moreover, this approach provides more robustness and security to the authentication.

A read-out unit 124 that discloses information about the tag once authenticated. This unit may be used as an interface by a user to record information about the local position and state of the product into the database 130. The user may also consult the database 130 to get further information about the product. A system configuration 125 unit that loads configuration files from the processing module 120 to the reading module 110, This configuration sets all the parameters that are necessary for the different units of the reading module 110, such as for example the integration times of the different sensors or the duration and amplitudes of the lighting unit 114 light pulses. These settings are loaded prior to any tag reading. A database 130 that contains predetermined spatial patterns and spectral signatures enabling the identification and authentication of each tag. It may contain a variety of information about marked products (e.g. description, picture, location), recorded by users. The user may also store current information about the marked products (e.g. location, state of the product). The database can be partly or fully stored into a remote electronic device. It can only be accessed by reader instruments that were formerly authorized.

In a preferred embodiment, as illustrated in Figure 5, the system 100 comprises two further units: a global positioning unit 113 in the reading module 110 and a localization unit 123 in the processing module. The global positioning unit 113 communicates with the localization unit 123 and the imaging unit 111 communicates with the decoding unit 121 , validation unit 122 and localization unit 123.

The global positioning unit 113 gets an access to the local position of the reader instrument (for example by the use of a GPS or A-GPS module) and, depending on the application, it also monitors the direction in which the reader is pointing by the use of an electronic compass and inclinometer. After each successful validation, this information is sent to the processing module.

The localization unit 123 determines the exact global position of the tag. This position is calculated in three steps based on the information sent by the imaging 111 and the global positioning units 113. First, the distance between the reader instrument and the tag is optically measured based on the imaging unit 111 information. Second, the relative position of the tag in reference to the reader instrument is calculated by using the distance and the direction in which the reader instrument is pointing. Third, the relative position of the tag is added to the global position of the reader. The optical localization allows higher accuracy in determining the position of the tag in comparison to standard methods, such as radio systems. The optical distance measurement can be based on several techniques, depending on the working distance of the reader (distance between the reader and the tag). For distances up to several meters, either the distance is defined by the optical design (with fixed focal lenses) or it is be calculated by measuring the position of an auto-focussing lens. For longer distances, the distance is calculated by measuring the time of flight (time for the light to travel from the reader to the tag and return) or similarly, by phase shift methods. To implement such techniques, the imaging unit 111 may contain an additional dedicated sensor, such as a photodiode. This step may use a different timing scheme with a time modulation of the excitation light intensity.

The identification and authentication of the tag 101 is achieved by decoding and validating the spatial pattern and spectral signature contained into the tag using the system 100. Figure 4 shows a flow-chart representing the steps (S) and processes (P) of a method to identify and authenticate a tag 101 as shown in Figure 1 that can be performed by various units of the system 100 described above. Once the program starts S01 , the configuration files are loaded S03 and the program initialises S02 the reading process by the reading module 110. This process may start upon triggering S04. Upon triggering, the timing control unit 115 controls the sequence of the reading process and in turn triggers light pulses from the lighting unit 114 and synchronizes the acquisition of the imaging unit 111 and spectral unit 112. In step S05, the imaging unit 111 acquires a background image followed in step S06 by the acquisition of a signal image synchronised onto the emission of a first light pulse by the lighting unit 114. Next, the spectral unit 112 acquires a background spectrum S07 and acquires a signal spectrum S08 synchronised onto the emission of a second light pulse by the lighting unit 114.

The information recorded by the reading module units is delivered to the processing module 120. Then, the decoding process P01 takes place, meaning that the decoding unit 121 first identifies the tag by retrieving the tag serial number from the database 130. This decoding is based on the images of the spatial pattern recorded by the imaging unit 111.

Prior to the proper decoding step S11 , the decoding unit 121 may perform a pre-validation step S10 in order to ensure that the tag contains fluorescent particles excitable by the lighting unit 114. This pre-validation step S10, which could be optional, consists in subtracting the background image to the signal image. If the resulting image reveals the optically activated spatial pattern, the pre-validation S10 is successful and the decoding S11 starts.

After a successful identification of the tag by the decoding process, the validation process P02 takes place. The validation unit 122 validates the tag by comparing the spectrum acquired by the spectral unit 112, to predetermined spectra of the "authentic" tags stored in the database 130. The validation unit may in addition use the data acquired by the imaging unit 111. In this case it proceeds to a validation process in two distinctive steps: the analysis of the image colours followed by the analysis of the spectrum as detailed above in the paragraph describing the validation 122 unit. Finally, the read-out step S12, performed by the read-out unit 124, discloses information about the tag once authenticated.

In another embodiment, a third validation step is added to further increase the security level of the authentication. This step measures the fluorescence lifetime of the nanoparticles contained into the tag either by the use of the information recorded by the imaging unit 111 , possibly by the use of an additional dedicated sensor, such as a photodiode. This step may use a different timing scheme with a time modulation of the excitation light intensity. Again, the measured values are compared to the corresponding information recorded into the database.

A person skilled in the art will appreciate that the system design described here may vary but still remain in the scope of the current invention. For example, we propose to use independent optical paths for each unit of the reading module 1 10. Obviously, it is also possible to share some optical components for different units, such as lenses for the lighting unit 114 and the spectral units 112. In that case, the separation between the two paths would be performed by the use a dichroic mirror. Moreover, in special cases where the light emitted by the tag would be weak or for long-distance detection, dedicated schemes for low signal amplification are implemented.