Sensor element, inspection device and method for inspecting data carrier having spin resonance characteristic

Abstract

The invention relates to a sensor element (30) for inspecting a flat data carrier (10) having a spin resonance feature (12), in particular a banknote. The sensor element comprises a magnetic core having an air gap into which a planar data carrier (10) can be introduced for inspection; a polarization device (34) for generating a static magnetic flux in the air gap; and a resonator device (40) for exciting a spin resonance characteristic of the data carrier to be inspected in the air gap. According to the invention, the resonator arrangement (40) comprises at least two stripline resonators (44, 46) arranged at different locations in the air gap (32). The polarization device (34) generates a non-uniform magnetic flux in the air gap (32) such that the static magnetic flux has a first field strength (B0, A) at the location of the first stripline resonator (44) and a different second field strength (B0, B) at the location of the second stripline resonator (46).

Description

[0001] The invention relates to a sensor element for authenticity checking of planar data carriers, in particular banknotes, having spin resonance properties, a checking device having such a sensor element and a method for authenticity checking by means of such a sensor element or such a checking device.

[0002] Data carriers, such as valuable documents or license documents, and other valuable items, such as branded goods are usually equipped with security elements, so as to achieve protection, and the security element realizes the verification of the authenticity of the data carrier and is used as protection for unallowed imitation at the same time. It is known to use security elements with spin resonance characteristics to protect files and other data carriers in machine-type authenticity checks. For this reason, security elements are provided with materials with spin resonance marks. Spin resonance marks that can be used for authenticity checks especially include nuclear magnetic resonance effect (NMR), electron spin resonance effect (ESR) and ferromagnetic resonance effect (FMR).

[0003] When checking banknotes, three different magnetic fields are usually generated in the measuring range of, for example, a banknote processing machine in order to detect spin resonance marks. Specifically, this is a quasi-static polarization field B0 extending parallel to the axial direction (z direction) of the magnetic circuit air gap. The second magnetic field is composed of a modulation field B mod The modulated field also extends parallel to the z-axis and typically has a frequency f in the kHz range. mod In order to excite the spin resonance marking transitions between the split spin energy levels of the material, an excitation field B1 is provided which is polarized perpendicularly to the direction B0. The excitation field oscillates at the resonance frequency of the material, which is also called the Larmor frequency and is proportional to the polarization field B0.

[0004] To generate the polarization field B0 , a magnetic circuit is usually used which conducts the magnetic flux of a permanent magnet and / or a coil to an air gap in which the flat data carrier is examined.

[0005] A high-frequency resonator, for example a stripline resonator, is used to generate an excitation field B1. This is a conductive structure with a characteristic length l, which is arranged on a carrier. If the wavelength λ of the high-frequency signal coupled in during the plausibility check is adapted to the dimension l of the conductive structure, a standing wave can form in the resonator and the stripline resonator resonates with respect to the excitation frequency associated with the wavelength λ. Since the extension of the stripline resonator in the plane of the carrier is significantly greater than perpendicular to this plane, the plane of the stripline resonator corresponding to the carrier plane is also referred to.

[0006] When checking a data carrier, for example within the scope of an authenticity check, a spin resonance spectrum of a spin resonance feature is usually determined and compared with an expected spectrum based on a characteristic mark. The spin resonance spectrum is usually recorded with a time-consuming B0 ramp method (also called a B0 scanning method). Here, the static polarization field B0 changes slowly around the resonance field strength at a fixed frequency of the excitation field B1 and passes through the field strength of the polarization field B0. Since the Larmor frequency of the spin resonance feature to be checked is proportional to the polarization field strength B0, the excitation frequency is effectively offset relative to the Larmor frequency, which allows the spectrum of the spin resonance feature to be recorded. Since the field strength of the polarization field B0 changes more slowly over time in the B0 ramp method than the modulation field B1, the excitation frequency is effectively offset relative to the Larmor frequency, which allows the spectrum of the spin resonance feature to be recorded. mod The excitation field B0 changes much more slowly over time, so that within the scope of the present application, B0 is preferably referred to as the static magnetic field or static magnetic flux even if a ramp field is present.

[0007] However, especially in fast-running banknote processing machines, the short measuring times required for the operation of the sensor are not sufficient to measure the complete spectrum of the spin resonance feature using a ramp (often also called a sweep). The spectrum can then only be recorded with a small number of measuring points, i.e. with a low resolution or over a narrow frequency band. However, for many applications, high-resolution, broadband measurements of the spectrum are desired, for example in order to be able to distinguish between characteristic materials with different Larmor frequencies. Spin resonance features with spectral codes can also be used with high spectral resolution, for example for different currencies or different denominations.

[0008] On this basis, the technical problem to be solved by the present invention is to provide a better device for checking data carriers with spin resonance characteristics, in particular to provide a sensor element which allows high-resolution and / or broadband measurement of the spin resonance spectrum of the data carrier to be checked in a short time.

[0009] This technical problem is solved by the features of the independent claim. Improvements of the invention are the subject matter of the dependent claims.

[0010] The invention provides a sensor element for checking, in particular authenticity checking, a planar data carrier having a spin resonance characteristic. The planar data carrier can be, for example, a banknote. The sensor element comprises a magnetic core with an air gap, into which the planar data carrier can be introduced for checking, a polarization device for generating a static magnetic flux in the air gap, and a resonator device for exciting the spin resonance characteristic of the data carrier to be checked in the air gap.

[0011] The resonator device comprises at least two stripline resonators arranged at different positions in the air gap. In addition, the polarization device generates a non-uniform magnetic flux in the air gap of the magnetic core, so that the static magnetic flux has a first field strength at the position of the first stripline resonator and a different second field strength at the position of the second stripline resonator. The spin resonance characteristic is preferably an ESR characteristic.

[0012] As explained in more detail below, arranging multiple stripline resonators at different locations of the inhomogeneous polarization field enables simultaneous measurement of spin resonances at different polarization field strengths and thus allows higher spectral resolution and / or shorter measurement times. In addition, the requirements for the field slope for measuring the spectral lines are significantly reduced.

[0013] The stripline resonators used are characterized in particular by their very accessible sensitive region and by their very high filling factor for flat samples, such as banknotes to be checked. Stripline resonators are also sometimes referred to simply as resonators below.

[0014] In an advantageous embodiment, the stripline resonators of the resonator arrangement are arranged in the form of a one-dimensional array. The one-dimensional array is preferably arranged parallel to the gradient of the magnetic flux in the air gap.

[0015] In another equally preferred design, the stripline resonators of the resonator arrangement form a multi-line layout with a plurality of parallel lines, wherein each line is formed by a one-dimensional array of stripline resonators. Preferably, each one-dimensional array of lines is arranged parallel to the gradient of the magnetic flux in the air gap.

[0016] The resonator arrangement can in particular comprise two, three, four, five or six stripline resonators, wherein a greater number of stripline resonators, for example a multiline arrangement with two or three lines each with five stripline resonators, can also be advantageous. Increasing the number of stripline resonators has the advantage of better spectral resolution or shorter required measurement times.

[0017] Advantageously, provision is made for stripline resonators arranged at different positions in the air gap to be supplied in each case by different signal sources.

[0018] In an advantageous design, the air gap is defined by two pole faces of the magnetic core, wherein one or both pole faces are configured to be inclined and / or stepped. In particular, it can be provided that the two pole faces form an angle preferably between 1° and 10° relative to each other. Since the field strength of the polarization field in the air gap is inversely proportional to the local distance between the two pole faces, the desired inhomogeneous polarization field can be generated in the air gap by the inclination or stepped configuration of the pole faces. The magnetic core is preferably composed of a ferromagnetic material with a magnetic permeability μr>>1 on the pole faces, i.e., in particular, μr is greater than 1×10 2 .

[0019] In another equally advantageous design, the magnetic conductor of the magnetic core is provided with a flux guide, whose magnetic resistance is different from the magnetic resistance of the magnetic conductor. By shaping the flux guide, the strength of the polarization field in the air gap can be set and the desired inhomogeneous polarization field can be generated. The flux guide can be designed in particular in a wedge-shaped or stepped shape so as to produce a linearly or step-shaped increasing or linearly or step-shaped decreasing field strength in the air gap. If the flux guide is used to generate an inhomogeneous magnetic flux, the pole faces defining the air gap are advantageously parallel to each other. This makes it easier for the data carrier to be transported through the air gap without interference. In this case, the pole faces can also be formed from a paramagnetic material with μr≈1, i.e. in particular μr is at most 1+10 -2 .

[0020] The stripline resonators of the resonator arrangement advantageously have the same resonance frequency, for example the resonance frequencies of the stripline resonators deviate from one another by less than 1%, preferably by less than 0.1%. Preferably, the stripline resonators of the resonator arrangement are even designed and arranged to operate in the same spatial mode. Furthermore, it is advantageously provided that the stripline resonators of the resonator arrangement have the same geometric shape, for example a square, rectangular or ring shape.

[0021] The first field strength advantageously differs from the second field strength by at least 2%, preferably by at least 5%, in particular by at least 10%. The polarization device can in particular generate a throughflow that increases or decreases linearly over the air gap or a throughflow that increases or decreases in a stepped manner.

[0022] In an advantageous embodiment, the sensor element further comprises a modulation device for generating a time-varying magnetic modulation field in the air gap, wherein the modulation frequency is preferably equally high in all stripline resonators of the resonator device. For example, the modulation frequencies at the location of two stripline resonators in each case differ by a maximum of 2%. The modulation device is advantageously formed by a single modulation coil, in particular a single planar coil, arranged in the air gap.

[0023] Advantageously, the stripline resonator is designed in a planar manner with a main extension plane, which is perpendicular to the direction of the static magnetic flux generated by the polarization device. In the context of this description, the direction of the static magnetic flux is also referred to as the z-direction. The main extension plane of the stripline resonator extends in the xy plane perpendicular to the z-direction.

[0024] The air gap advantageously has a height, ie a dimension in the z direction, of less than 10 mm, preferably less than 5 mm. As a result, a particularly strong polarization field, ie a strong static magnetic flux, can be generated in the air gap.

[0025] In an advantageous development of the invention, in order to increase the signal-to-noise ratio, at least a portion of the stripline resonators arranged at different positions in different magnetic flux field strengths are respectively replaced by an NxM array of stripline resonators, wherein N and M are natural numbers and at least one of the values ​​of N and M is greater than 1, wherein the stripline resonators of the NxM array are respectively all supplied by the same signal source and are electrically connected in parallel and / or in series.

[0026] In a particularly advantageous embodiment, the sensor element also has a ramp coil for generating a ramp function of the static magnetic flux.

[0027] The resonator arrangement is advantageously designed to excite a spin resonance signal with a frequency above 1 GHz, in particular between 1 GHz and 10 GHz. This enables a higher spectral resolution and a stronger measurement signal compared to lower frequencies.

[0028] The resonator device is also particularly designed to detect a spin resonance signal characteristic of a spin resonance. The resonator device can particularly receive a response signal characteristic of a spin resonance and output it to a detector. Spin resonance can be determined, for example, by a continuous wave (CW) method, a pulse method or a fast scanning method.

[0029] Stripline resonators can be operated both in reflection and in transmission when checking data carriers. The latter has the advantage that no elements such as circulators are required in the signal path, which separate the forward and return signals relative to the resonator.

[0030] Advantageously, the resonator arrangement comprises a planar carrier on which the stripline resonator is applied. The carrier is expediently formed by a printed circuit board, which allows reproducible and cost-effective production. However, it is also advantageous to use a carrier based on ceramic, Teflon or hydrocarbon, in particular in order to reduce the dielectric losses in the carrier material.

[0031] The invention also comprises an inspection device for inspecting planar data carriers, in particular banknotes, having spin resonance properties, the inspection device comprising a sensor element of the above-described type and having one or more signal sources, to which the stripline resonators of the resonator arrangement arranged at different positions in the air gap are supplied.

[0032] In an advantageous embodiment, a plurality of signal sources are provided, by which one of the stripline resonators of the resonator arrangement arranged at different positions in the air gap is supplied in each case. However, operating the resonators with independent signal sources also requires that the resonators be connected to independent signal branches. In particular, in the case of a large number of resonators, a large amount of installation space is required for implementing the circuit. Preferably, the plurality of signal sources are operated at the same excitation frequency, for example with a frequency deviation of less than 1%, preferably less than 0.1%.

[0033] It is therefore also advantageously possible that the stripline resonators arranged at different positions in the air gap are supplied by only one single signal source via a multiplexer. In this case, there is only one signal branch and all resonators are connected to it. The required installation space is therefore significantly smaller in this design and it is easy to ensure that all resonators operate at the same excitation frequency. Since in this method only one resonator can be measured simultaneously, the switching time τ of the multiplexer is preferably matched to the distance d of the resonators arranged one after the other, so that in the case of a data carrier moving at a speed v, the individual spectral components are always measured at the same position on the data carrier, i.e. τ=d / v. Viewed in the transport direction, in this method, gaps are generated between the positions on the data carrier where the spin resonances are measured, so that there are also positions at which no measurement is performed.

[0034] Alternatively, the switching time of the multiplexer can be reduced to a value τ<<d / v. Although this results in a lower signal-to-noise ratio due to the shorter measurement time per resonator, the spectral signature of the banknote can be detected over a larger range and essentially without gaps.

[0035] Advantageously, the inspection device further comprises a transport device which guides the flat data carrier to be inspected along a transport path through the air gap of the magnetic core, wherein the transport path is advantageously parallel to the gradient of the magnetic flux in the air gap.

[0036] - or the stripline resonators of the resonator device are arranged in parallel to the transport path in the form of a one-dimensional array in the manner described above,

[0037] - or the stripline resonators form a multi-line layout of the type described above, where each line is parallel to the transmission path.

[0038] The transport device is designed and arranged in particular for fast transport of the flat data carrier to be checked along the transport path, for example between 1 m / s and 12 m / s.

[0039] The invention also includes a method for checking a planar data carrier, in particular a banknote, having a spin resonance characteristic by means of a sensor element of the type described or a checking device of the type described, wherein in the method

[0040] - guiding the flat data carrier to be checked along a transport path through the air gap of the magnetic core of the sensor element, wherein a plurality of stripline resonators of the resonator arrangement are arranged one behind the other parallel to the transport path,

[0041] - generating an inhomogeneous magnetic flux in the air gap of the magnetic core by means of the polarization means and preferably generating a time-varying magnetic modulation field in the air gap by means of the modulation means,

[0042] - Exciting a spin resonance feature of the data carrier to be checked by means of a resonator device.

[0043] In an advantageous method design it is provided that

[0044] - guiding the data carrier to be checked past the stripline resonators arranged in succession and recording from each of the stripline resonators a temporal measurement sequence of a response signal of a spin resonance characteristic generated after excitation,

[0045] - respectively identifying measurement data belonging to the same measurement position from the temporal measurement sequence of the stripline resonator,

[0046] - deriving spectral information about the spin resonance features from the identified measurement data

[0047] - evaluating the data carrier based on the derived spectral information, in particular with regard to authenticity and / or attribution to a class of data carrier.

[0048] The measured data are advantageously spatially resolved or spatially averaged.

[0049] According to the favorable improved design provisions of this method,

[0050] – superimposing a spatially uniform ramp field on the inhomogeneous static flux so that the total static flux in the air gap varies in time between a minimum and a maximum value,

[0051] - deriving spectral information from the identified measurement data taking into account the field strength of the static magnetic flux at the respective measurement time, and

[0052] - determining the authenticity of the checked data carrier and / or the affiliation of the checked data carrier to one of a plurality of data carrier categories having different spectral signatures based on the derived spectral information.

[0053] As described above, in a preferred design, the stripline resonators are arranged one after the other in the transport direction of the data carrier and the gradient of the polarization field is parallel to the transport direction. This has the advantage that all resonators measure the same line on the data carrier, i.e. the same measuring point with a certain time offset. This makes the evaluation and inspection of the data carrier easier.

[0054] A multi-line structure is also advantageous for generating spatial resolution transversely to the transport direction. For this purpose, a plurality of lines are each formed by a one-dimensional array of resonators for spectral resolution.

[0055] In another advantageous embodiment, it is provided that the gradient of the polarization field is transverse or oblique to the transport direction of the data carrier. The stripline resonators of the resonator arrangement can also be arranged adjacent to one another as seen in the transport direction. However, in all embodiments, it is preferred that the resonators are at least partially arranged on lines parallel to the polarization field gradient, since this achieves the maximum difference in the field strength B0. However, other arrangements are also possible in principle, provided that at least two resonators of the resonator arrangement are arranged at positions with different polarization field strengths.

[0056] Further embodiments and advantages of the present invention are described below with reference to the accompanying drawings, in which scales and ratios are not shown in order to improve readability.

[0057] In the attached figure:

[0058] Figure 1 Schematically showing an inspection device of a banknote processing system for measuring the spin resonance of a banknote inspection sample,

[0059] Figure 2 The top view schematically shows Figure 1 The resonator device of the inspection device and the transported banknote inspection sample, the direction of the inhomogeneous polarization field is schematically shown in the lower part,

[0060] Figure 3 shows a simplified spectrum of a spin resonance line as a function of the polarization field B0 at a fixed excitation frequency,

[0061] Figure 4 Shows the representation Figure 3 Graphs of recordings of spin resonance spectra of a spin resonance line of , in (a) by a conventional sensor element and in (b) by a sensor element according to the invention,

[0062] Figure 5 In (a) a conventional polarizing device is shown, and in (b) to (d) polarizing devices for generating non-uniform magnetic flux in an air gap of a magnetic circuit are shown,

[0063] Figure 6 Spectrum showing the spin resonance characteristics of a paper sample,

[0064] Figure 7 The sensor element according to the invention measures Figure 6 Signal curve of the spin resonance characteristic of the paper sample.

[0065] The invention will now be explained based on the example of authenticity checking of banknotes. Figure 1 For this purpose, a checking device 20 of a banknote processing system for measuring the spin resonance of a banknote checking specimen 10 is schematically shown.

[0066] The banknote inspection specimen 10 has a spin resonance feature 12 whose characteristic properties are used to verify the authenticity of the banknote. The spin resonance feature can be present only in a partial area of ​​the banknote or, as in the illustrated embodiment, can extend over the entire surface of the banknote inspection specimen.

[0067] The inspection device 20 comprises a sensor element 30 with a magnetic core 35 having an air gap 32 through which the banknote inspection sample 10 is guided during the authenticity check along the transport path 14. In order to detect the spin resonance signature of the spin resonance feature 12, the sensor element 30 generates three different magnetic fields within the measuring range of the air gap 32.

[0068] On the one hand, a static magnetic flux parallel to the z-axis is generated in the measuring range by the polarization device 34. As described in more detail below, the polarization device 34 generates an inhomogeneous magnetic flux in the air gap 32, so that the field strength of the polarization field B0 is different at different positions along the transmission path 14.

[0069] Secondly, the modulation device 36 generates a time-varying magnetic modulation field in the air gap, which also extends parallel to the z-axis and has a modulation frequency f in the range of 1 kHz to 1 MHz. Mod Finally, a resonator arrangement 40 arranged in the air gap 32 generates an excitation field B1 which induces an energy transition between the spin energy levels in the spin resonance feature 12. The resonator arrangement 40 here comprises at least two stripline resonators arranged at different positions in the air gap and which experience different field strengths due to the inhomogeneity of the magnetic flux.

[0070] The frequency of the excitation field is usually above 1 GHz and is tuned to the Larmor frequency of the spin resonance feature 12 to be detected, so that its spin resonance signature can be measured and used for authenticity checking. For this purpose, the test device 20 comprises a signal source 22, whose excitation frequency f MW The excitation signal of the signal source 22 is supplied to the resonator device 40 via the duplexer 24 and generates there a frequency f MW of alternating magnetic field.

[0071] In addition to the above-mentioned elements, the test device 20 also comprises a detector diode 26 for measuring the high-frequency power reflected by the resonator arrangement 40 and an evaluation unit 28 for evaluating and, if necessary, displaying the measurement results. MW Due to the modulation of the static polarization field by the modulation device 36, the exact value of the Larmor frequency of the sample oscillates, so that the obtained measurement signal is amplitude modulated by the modulation frequency.

[0072] In order to explain the features of the present invention in more detail, Figure 2 In the upper part of the figure, a resonator arrangement 40 according to an embodiment of the invention is schematically shown in a top view, with a carrier 42 and a first and a second stripline resonator 44, 46 arranged on the carrier. The two stripline resonators 44, 46 are arranged one behind the other in the transport direction 14 and are therefore swept one after the other with a time shift by the spin resonance feature 12 of the banknote 10. The two stripline resonators 44, 46 are connected independently of one another, but have the same geometry and the same resonance frequency f.

[0073] Figure 2 The lower part of the diagram schematically shows the course 48 of the inhomogeneous polarization field B0 in the x direction, in particular at the location of the stripline resonators 44, 46. In the embodiment, the field strength of the polarization field B0 has a linear course in the transport direction 14. The first stripline resonator 44 is located at the location with the polarization field strength B0. 0,A The position x A , while the second stripline resonator 46 which is first scanned by the banknote 10 is located at a smaller polarization field strength B 0,B The position x B .

[0074] To further explain the function of the present invention, Figure 3 50 shows a simplified spectrum 52 of a spin resonance line, here for example a spin resonance feature 12 of a banknote 10, as a function of the polarization field B0 at a fixed excitation frequency f. Depending on the details of the electronic detection circuit, the maximum may be located to the left or to the right of the center.

[0075] Since the Larmor frequency of the spin resonance feature 12 is proportional to the polarization field B0, Figure 3 The curve 52 shown in FIG. 5 corresponds to the spectrum of the spin resonance line. The curve 52 shows the polarization field strength B at the position of the two resonators 44 or 46. 0,A Or B 0,B Two representative spectral components 54A, 54B at.

[0076] if Figure 2 If a banknote 10 with a spin resonance feature 12 is passed over the resonator device 40 at a certain field strength of the polarization field generated by the polarization device 34, each of the two stripline resonators 44, 46 detects a spectral component 54A or 54B of the spin resonance feature 12 belonging to its resonance frequency.

[0077] Specifically, at position x A The stripline resonator 44 at the measurement belongs to the field strength B 0,A The spectrum intensity Int(B 0,A ), and at position x BThe stripline resonator 46 at the location of the field strength B 0,B The spectrum intensity Int(B) of the spectrum component 54B 0,B ).

[0078] As already explained above in principle, in the actual plausibility check, the static magnetic field B0 of the polarization device 34 is additionally varied around the resonance field strength by means of a ramp coil and thereby passes through the field strength of the polarization field B0 at a fixed frequency f of the excitation field in order to allow the spectrum of the resonance of the feature 12 to be recorded.

[0079] Advantages of the design according to the invention Figure 4 The diagrams 60 , 70 of EMBODIMENT 3 are explained in more detail on the example of a spin resonance feature 12 having only one spin resonance line.

[0080] The spin resonance line 62 of the feature 12 shown in simplified form in the figure has a line width of, for example, 10 mT in the polarization field strength space, corresponding to the distance from the minimum to the maximum.

[0081] If a conventional single resonator is used to record the spin resonance spectrum, a field ramp 66 in the range of about 40 mT is required in order to fully detect the spectral signature at a line width of 10 mT, e.g. Figure 4 (a) shown.

[0082] In the comparative example shown, the spectrum was recorded in a uniformly polarized field by a single resonator with a resonance frequency f=8.41 GHz. In the case of a resonance field strength of 64, for example 300 mT, this frequency corresponds exactly to the Larmor frequency of the spin resonance feature 12. Figure 4 As shown in (a), a field ramp 66 with an amplitude of -20 mT to +20 mT must be passed around the resonance field strength 64 in order to be able to fully measure the spin resonance line 62 and its line width of 10 mT. Such a large field ramp involves a longer measurement time and a larger current requirement.

[0083] If, on the other hand, a spectrum is recorded using an inhomogeneous polarization field according to the invention and a resonator arrangement 40 having a plurality of stripline resonators arranged at a distance, significantly shorter measurement times and significantly lower current requirements can be achieved.

[0084] Reference Figure 4(b) The resonator device 40 of the sensor element 30 according to the invention comprises, for example, three stripline resonators arranged one after the other in the transport direction, each having a resonance frequency of f = 8.41 GHz. In the exemplary embodiment, the stripline resonators are arranged in the air gap and matched to the inhomogeneous magnetic flux generated by the polarization device 34 in such a way that a field strength 72 of 287 mT is present at the location of the first stripline resonator, a field strength 74 of 300 mT is present at the location of the second stripline resonator, and a field strength 76 of 313 mT is present at the location of the third stripline resonator.

[0085] The spin resonance signal of feature 12 can thus be measured simultaneously in three different polarization field strengths 72, 74, 76 at a fixed excitation frequency of, for example, f=8.41 GHz. Figure 4 (b) It can be seen that in order to fully detect the spectral signature of the spin resonance line 62, a significantly smaller field ramp 78 with an amplitude of only about -6.5 mT to 6.5 mT is sufficient, corresponding to Figure 4 Substantially one third of the amplitude of the conventionally required field ramp 66 of (a).

[0086] There are several possibilities for generating non-uniform magnetic flux in the air gap of the magnetic circuit, such as Figure 5 According to some advantageous designs, in the case of a conventional magnetic core 80, the pole faces 82 of the air gap 32 forming a uniform magnetic core are arranged in parallel, as shown in FIG. Figure 5 In the case of such a uniform magnetic core 80, the polarizing means generates a uniform magnetic field B0 in the air gap 32 which is not suitable for the present invention.

[0087] In the case of the magnetic core 84 according to the first embodiment of the present invention, one of the pole faces 86 of the magnetic core 84 is inclined at a defined angle, such as Figure 5 (b) As shown. The two pole faces 86, 88 of the magnetic core 84 may also be inclined, as shown in FIG. Figure 5 (b) is shown. The angle formed by the two pole faces is in particular between 1° and 10°, for example 5°. The magnetic core 84 with inclined pole faces 86 or 86, 88 can be realized mechanically in a convenient manner. The field strength B0 in the air gap 32 varies inversely with the local distance between the pole faces, for example the field strength of the polarization field B0 varies inversely with the local distance between the pole faces. Figure 5 The orientation in (b) decreases linearly from left to right.

[0088] In another embodiment, one or both pole surfaces of the magnetic core 90 may also be constructed in a stepped manner, such as Figure 5 (c) is shown in which the two pole surfaces 92, 94 are of stepped design. The field strength B0 in the air gap 32 has a stepped course and is, for example, Figure 5The step-wise progression of the polarization field B0 has the advantage that the stripline resonators can be arranged in regions with locally constant field strengths, so that the stripline resonators experience different polarization fields B0 that are constant over their surface area. 0,A , B 0,B wait.

[0089] According to another embodiment, the magnetic core 100 has Figure 5 (d) In this embodiment, the magnetic conductor 102 of the magnetic core 100 is provided with a wedge-shaped flux guide 104, whose magnetic resistance is greater than the magnetic resistance of the conductor 102 itself. The flux guide 104, due to its wedge shape, causes a position-dependent variation of the magnetic field generated in the air gap 32 and thus causes an inhomogeneous polarization field.

[0090] The desired course of the inhomogeneous polarization field can be set by shaping the magnetic flux guide 104. Figure 5 The wedge shape shown in (d) results in a linear increase or decrease of the polarization field in the air gap. A stepped orientation of the polarization field B0 can also be produced by a stepped flux guide. An advantage of the design with the flux guide 104 is that the pole faces 106 of the core 100 can themselves be parallel, which makes it easier to transport the banknote inspection sample through the air gap 32 without interference. The flux guide 104 can be located directly on the air gap 32, or as Figure 5 (d) is shown close to the air gap, but in which the pole face 106 is formed by another component, which can be made of the same material as the magnetic core 100, for example.

[0091] In order to demonstrate the mode of action of the present invention, a simulation was performed with two Figure 2 Characteristics of the sensor element of the square λ / 2 stripline resonator resonator device.

[0092] The stripline resonators 44, 46 are mounted here on a printed circuit board 42 with a thickness of 1.5 mm and a dielectric constant of 3.66. The resonators 44, 46 are spaced 15 mm apart in the banknote transport direction 14. The edge length of the resonators is 7.1 mm, which corresponds to a resonance frequency of 9.8 GHz.

[0093] The two resonators 44, 46 are operated via a circulator with an independent 50Ω signal source, which is operated at the resonant frequency in continuous wave (CW) mode with the same power. For coupling to the signal source, the resonators are connected via a through-hole connection in the circuit board 42. The through-hole connection has a distance of 2.2 mm to the edge of the resonator. The resonator impedance is 50Ω.

[0094] The resonator device 40 thus constructed is installed in the air gap of the magnetic circuit. The air gap is defined by the two pole faces of the magnetic core 84, wherein Figure 5(b) shows that one of the two pole faces is parallel to the plane of the banknote to be checked, while the second pole face 86 is inclined and extends at an angle of 5° to the plane of the banknote. With this design, a polarization field B0 with non-uniform magnetic flux density is generated in the air gap.

[0095] Specifically, the polarization field B0 is generated by the tilting, which increases linearly in the transport direction and has a gradient of 3 mT / mm. The field intensity of the polarization field B0 at the position of the second stripline resonator 46 is B in the embodiment. 0,B =300mT, the field strength at the position of the first stripline resonator 44 is B 0,A =345mT. The inhomogeneous polarization field is modulated by a spatially constant modulation field B mod Overlay.

[0096] Then a paper sample with a length of 100 mm is loaded, and a spin resonance feature is uniformly applied on its surface, and its spectrum 112 is as follows: Figure 6 The polarization field strength B at the resonator 44 and 46 is also shown. 0,A and B 0,B And the related relative signal strength Int(B 0,A ) and Int(B 0,B ).

[0097] The paper sample having the spin resonance characteristic is conveyed through the resonator device 40 and the signal intensity of the spin resonance characteristic is recorded by the two resonators 44, 46. The obtained signal curves 122A (resonator 44) and 112B (resonator 46) are Figure 7 122A, which shows the measured signal strength as a function of position x. The signal curve is normalized here to the average signal strength of signal curve 122A.

[0098] By averaging the signal intensities in the plateau region of each signal curve 122A, 122B, the ratio of the signal intensity of the first resonator 44 to the signal intensity of the second resonator 46 is obtained, that is, 1.0 / -0.55, which is consistent with the ratio obtained from Figure 6 The resonance spectrum of the expected ratio Int(B 0,A ) / Int(B 0,B ) are very consistent.

[0099] In the arrangement described so far, the stripline resonators of the resonator arrangement are positioned and dimensioned in such a way that the field strength of the polarization field B0 at the resonator location lies essentially within the line width of the Larmor frequency to be measured, as a function of the resonator frequency. However, it is also possible to position the stripline resonators in such a way that the field strength present there does not correspond to the desired Larmor frequency.

[0100] With such a resonator, a negative proof can be carried out, ie for a genuine banknote no spin resonance signal is expected from this resonator.

[0101] Reference numerals list

[0102] 10 Banknote Inspection Samples

[0103] 12 Spin resonance characteristics

[0104] 14 Conveying path

[0105] 20 Inspection device

[0106] 22 Signal Source

[0107] 24 Duplexer

[0108] 26 Detector diode

[0109] 28 evaluation units

[0110] 30 sensor element

[0111] 32 Air Gap

[0112] 34 Polarization device

[0113] 35 Magnetic core

[0114] 36 Modulation device

[0115] 40 Resonator Device

[0116] 42 Carrier

[0117] 44, 46 Stripline Resonator

[0118] 48 Direction of inhomogeneous polarization field

[0119] 50 Charts

[0120] Spectrum of 52 spin resonance lines

[0121] 54A, 54B spectral components

[0122] 60 Charts

[0123] 62 Spin resonance lines

[0124] 64 Resonance Field Strength

[0125] 66 Slopes

[0126] 70 Charts

[0127] 72, 74, 76 polarization field strength

[0128] 78 Slopes

[0129] 80 Polarization device

[0130] 82 parallel polar planes

[0131] 84 Polarization device

[0132] 86, 88 tilted polar surface

[0133] 90 Polarization Device

[0134] 92, 94 Stepped pole face

[0135] 100 Polarization Device

[0136] 102 Magnetic Conductor

[0137] 104 Magnetic flux guide

[0138] 106 parallel polar planes

[0139] 110 Charts

[0140] 112 Spin resonance characteristic spectrum

[0141] 120 Charts

[0142] 122A, 122B signal curve

Claims

1. A sensor element (30) for checking a planar data carrier (10), in particular a banknote, having a spin resonance characteristic (12), - a sensor element having a magnetic core with an air gap (32) into which a planar data carrier (10) can be introduced for testing, - the sensor element has polarization means (34) for generating a static magnetic flux in the air gap (32), - a sensor element with a resonator device (40) for exciting a spin resonance feature (12) of a data carrier to be checked in the air gap, It is characterized in that - the resonator device (40) comprises at least two resonators arranged at different positions (x A 、x B ) at a stripline resonator (44, 46), and - the polarizing device (34) generates a non-uniform magnetic flux in the air gap (32) of the magnetic core, so that the static magnetic flux is at the position (x A ) has a first field strength and at a position (x B ) have different second field strengths.

2. The sensor element (30) according to claim 1, It is characterized in that The stripline resonators (44, 46) of the resonator device (40) are arranged in a one-dimensional array, preferably in parallel with the gradient of the magnetic flux in the air gap (32).

3. The sensor element (30) according to claim 1, It is characterized in that The stripline resonators of the resonator device (40) form a multi-line layout with a plurality of parallel lines, wherein each line is formed by a one-dimensional array of stripline resonators, wherein the one-dimensional array of each line is preferably arranged parallel to the gradient of the magnetic flux in the air gap.

4. The sensor element (30) according to at least one of claims 1 to 3, It is characterized in that Stripline resonators (44, 46) arranged at different positions in the air gap are supplied by different signal sources, respectively.

5. The sensor element (30) according to at least one of claims 1 to 4, It is characterized in that The air gap (32) is bounded by two pole faces of the magnetic core, wherein one or both pole faces are configured to be inclined and / or stepped.

6. The sensor element (30) according to claim 5, It is characterized in that The two pole faces form an angle with respect to one another which is preferably between 1° and 10°.

7. The sensor element (30) according to at least one of claims 1 to 6, It is characterized in that The stripline resonators (44, 46) of the resonator arrangement (40) have the same resonance frequency. The stripline resonators (44, 46) are preferably designed and arranged to detect spin resonance characteristics in the same spatial mode of the excitation field. The stripline resonators (44, 46) particularly preferably have the same geometry.

8. The sensor element (30) according to at least one of claims 1 to 7, It is characterized in that The first field strength differs from the second field strength by at least 2%, preferably by at least 5%, in particular by at least 10%.

9. The sensor element (30) according to at least one of claims 1 to 8, It is characterized in that The sensor element also has a modulation device (36) for generating a time-varying magnetic modulation field in the air gap, wherein the modulation frequency is preferably equally high at the location of each stripline resonator of the resonator arrangement.

10. The sensor element (30) according to claim 9, It is characterized in that The modulation device (36) is formed by a single modulation coil, in particular a single planar coil, arranged in the air gap.

11. The sensor element (30) according to at least one of claims 1 to 10, It is characterized in that The stripline resonators (44, 46) are designed in a planar manner with a main extension plane which is perpendicular to the direction of the static magnetic flux generated by the polarization device.

12. The sensor element (30) according to at least one of claims 1 to 11, It is characterized in that The air gap (32) has a height of less than 10 mm, preferably less than 5 mm.

13. The sensor element (30) according to at least one of claims 1 to 12, It is characterized in that The sensor element has a ramp coil for generating a ramp function of the static magnetic flux.

14. A checking device (20) for checking planar data carriers, in particular banknotes, having spin resonance properties, - a testing device having a sensor element (30) according to one of claims 1 to 13, and The inspection device has one or more signal sources (22), by which the stripline resonators (44, 46) of the resonator device (40) arranged at different positions in the air gap are supplied.

15. The inspection device (20) according to claim 14, It is characterized in that A plurality of signal sources are provided, by which one of the stripline resonators (44, 46) of the resonator device (40) arranged at different positions in the air gap is respectively supplied.

16. The testing device (20) as claimed in claim 14 or 15, comprising a transport device which guides the flat data carrier (10) to be tested along a transport path (14) through the air gap of the magnetic core. in, The conveying path is advantageously parallel to the gradient of the magnetic flux in the air gap, and preferably - or the stripline resonators (44, 46) of the resonator arrangement (40) are arranged in parallel to the transport path (14) in the form of a one-dimensional array according to claim 2 or a claim dependent thereon, - or the stripline resonators form a multi-line arrangement according to claim 3 or a claim dependent thereon, wherein each line is parallel to the transmission path (14).

17. The inspection device (20) according to claim 16, It is characterized in that The transport device is designed and arranged to quickly transport the flat data carrier to be inspected along a transport path (14).

18. A method for checking a planar data carrier (10), in particular a banknote, having a spin resonance characteristic (12) by means of a sensor element (30) according to one of claims 1 to 13 or a checking device (20) according to one of claims 14 to 17, in, In the method - guiding the flat data carrier (10) to be checked along a transport path through the air gap of the magnetic core of the sensor element (30), wherein a plurality of stripline resonators (44, 46) of the resonator device (40) are arranged one behind the other parallel to the transport path, - generating an inhomogeneous magnetic flux in the air gap (32) of the magnetic core by means of the polarization means (34) and preferably generating a time-varying magnetic modulation field in the air gap by means of the modulation means (36), - Exciting a spin resonance feature (12) of the data carrier (10) to be checked by means of a resonator device (40).

19. The method according to claim 18, It is characterized in that - guiding the data carrier (10) to be checked past the stripline resonators (44, 46) arranged in succession and recording a time measurement sequence of a response signal of the spin resonance feature (12) generated after excitation by each of the stripline resonators, - respectively identifying measurement data belonging to the same measurement position from the temporal measurement sequence of the stripline resonator, - deriving spectral information about the spin resonance feature (12) from the identified measurement data, and - evaluating the data carrier (10) based on the derived spectral information, in particular with regard to authenticity and / or attribution to a data carrier class.

20. The method according to claim 18 or 19, It is characterized in that The measured data are either spatially resolved or spatially averaged.

21. The method according to at least one of claims 18 to 20, It is characterized in that - superimposing a spatially uniform ramp field on the inhomogeneous static magnetic flux so that the total static magnetic flux in the air gap (32) varies in time between a minimum value and a maximum value, - deriving spectral information from the identified measurement data taking into account the field strength of the static magnetic flux at the respective measurement time, and - determining the authenticity of the checked data carrier (10) and / or the affiliation of the checked data carrier (10) to one of a plurality of data carrier categories having different spectral signatures based on the derived spectral information.

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