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 (32) having an air gap into which the 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 feature (12) of the data carrier to be inspected in the air gap (32). According to the invention, the resonator arrangement (40) comprises a plurality of stripline resonators (46-1, 46-2) which are designed and arranged to operate independently of one another at the same excitation frequency. The polarization device (34) generates a uniform magnetic flux in the air gap (32) such that, for each two stripline resonators (46-1, 46-2) of the resonator device, the static magnetic flux at the location of the first stripline resonator (46-1) has substantially the same field strength as at the location of the second stripline resonator (46-2).

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] By means of a sensor element with a stripline resonator, a spatial resolution in the scanning direction can be achieved when checking a data carrier by scanning, which spatial resolution is proportional to the size of the resonator. With a typical edge length of about 10 mm for a stripline resonator, a spatial resolution in the range of several millimeters is obtained accordingly.

[0007] On this basis, the object of the present invention is to provide an improved device for checking a data carrier having a spin resonance characteristic, in particular to provide a sensor element which even allows checking a data carrier having a complex spin resonance characteristic.

[0008] This technical problem is solved by the features of the independent claim. Improvements of the invention are the subject matter of the dependent claims.

[0009] 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. The spin resonance characteristic is preferably an ESR characteristic.

[0010] The resonator arrangement comprises a plurality of stripline resonators which are designed and arranged to be operated independently of one another at the same excitation frequency, for example with a frequency deviation of less than 1%, preferably less than 0.1%. Furthermore, the polarization arrangement generates a uniform magnetic flux in the air gap, so that for each of two stripline resonators of the resonator arrangement, the static magnetic flux at the location of the first stripline resonator has essentially the same field strength as at the location of the second stripline resonator.

[0011] As will be described in more detail below, by means of such a design of the resonator device and such a tuning of the polarization device, very wide-ranging requirements for the automatic checking of data carriers, in particular banknotes, can be met. For example, the integrity of the data carrier can be checked by means of the spatial resolution achieved in the case of a planar introduction of a spin resonance feature of the data carrier. Even in the case of a localized spin resonance feature, the design according to the invention can be used to perform a spatially resolved measurement of the feature and thereby check the predetermined, specific geometry and position of the feature.

[0012] 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.

[0013] Advantageously, in the sensor element according to the invention, provision is made for the static magnetic flux at each of two stripline resonator locations of the resonator arrangement to have a maximum deviation of 2%.

[0014] In an advantageous design, the stripline resonators of the resonator arrangement are arranged in the form of a one-dimensional array.

[0015] 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 multi-track arrangement with two or three tracks with five stripline resonators each, can also be advantageous. A one-dimensional array enables spatially resolved measurements on a moving data carrier, while a multi-track arrangement also enables spatially resolved measurements on a stationary data carrier.

[0016] Each stripline resonator of the resonator arrangement is advantageously supplied by a different signal source. Alternatively, the stripline resonators can also be supplied by a single signal source via a multiplexer. A hybrid design is also possible, in which the stripline resonators of the resonator arrangement are divided into a plurality of groups and the resonators of each group are supplied by a single signal source via a multiplexer, while different groups are supplied by different signal sources.

[0017] Advantageously, a plurality of stripline resonators covers an area that includes the entire width of the data carrier to be checked, in particular a banknote. The data carrier can then be checked for integrity by a linear scan along its length, since during the scan every position on the data carrier is detected by a stripline resonator. If the check is provided on a stationary test sample, a plurality of stripline resonators advantageously covers an area that includes the entire area of ​​the data carrier to be checked, in particular a banknote.

[0018] The stripline resonators of the resonator arrangement advantageously have the same resonance frequency, for example the resonance frequencies deviate from one another by less than 1%, preferably by less than 0.1%. It is also preferred that the stripline resonators are designed and arranged to detect spin resonance features in the same spatial mode of the excitation field, and particularly preferably the stripline resonators have the same geometric shape, for example a square, rectangular or ring shape.

[0019] The air gap is advantageously defined by two plane-parallel pole faces of the magnetic core. r >>1 Magnetic permeability, especially μ r Greater than 1×10 2 The pole surface can also be made of ferromagnetic material with μ r ≈1, that is, the maximum value is 1+10 -2 μ r Made of paramagnetic materials.

[0020] Advantageously, the stripline resonator is designed in a planar manner with a main extension plane, which is parallel to at least one pole face of the magnetic core that defines an air gap. The main extension plane is also advantageously 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.

[0021] 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.

[0022] 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.

[0023] The resonator arrangement is advantageously arranged in the air gap such that a planar data carrier introduced for examination is located in the near field of the excitation field generated by the stripline resonator.

[0024] In an advantageous development of the invention, in order to increase the signal-to-noise ratio, at least a portion of the stripline resonators are 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 each supplied by the same signal source and are electrically connected in parallel and / or in series.

[0025] In a particularly advantageous embodiment, the sensor element also has a ramp coil for generating a ramp function of the static magnetic flux.

[0026] 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.

[0027] The resonator arrangement is also designed in particular to detect a spin resonance signal characteristic of a spin resonance. The stripline resonator can in particular receive a response signal characteristic of a spin resonance and output it to a detector. The spin resonance can be determined, for example, by a continuous wave (CW) method, a pulse method or a fast scanning method.

[0028] 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.

[0029] 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.

[0030] The invention also includes a checking device for checking planar data carriers, in particular banknotes, having a spin resonance characteristic, the checking device having a sensor element of the above-described type. The checking device also comprises either a plurality of signal sources with the same excitation frequency, from which the stripline resonators of the resonator arrangement are supplied, or a single signal source, from which the stripline resonators are supplied via a multiplexer.

[0031] Advantageously, the testing device further comprises a transport device which introduces the planar data carrier to be tested into a testing position in the air gap and / or guides it along a transport path past the testing position in the air gap of the magnetic core, wherein the resonator arrangement is arranged in the air gap such that the testing position is located in the near field of the excitation field generated by the stripline resonator.

[0032] The transport device is designed and arranged in particular to transport the flat data carrier to be checked along the transport path at a high speed, for example between 1 m / s and 12 m / s.

[0033] 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

[0034] - introducing the flat data carrier to be checked into the air gap of the magnetic core of the sensor element,

[0035] - generating a static magnetic flux in the air gap 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,

[0036] - Exciting a spin resonance feature of the data carrier to be checked by means of a resonator device.

[0037] Advantageously, in the method, the flat data carrier to be checked is measured in a spatially resolved manner by exciting a spin resonance feature, in particular for the integrity check.

[0038] In an advantageous method, provision is made for the flat data carrier to be checked to be guided along a transport path through an air gap of a magnetic core of the sensor element and for a single-track or multi-track scanning of the data carrier to be performed by the stripline resonators of the resonator arrangement.

[0039] 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.

[0040] In the attached figure:

[0041] Figure 1 Schematically showing an inspection device of a banknote processing system for measuring the spin resonance of a banknote inspection sample,

[0042] Figure 2 a schematic top view of a resonator arrangement of a sensor element according to the invention,

[0043] Figure 3 Schematically showing the Figure 2 The structure of the resonator device when measuring the paper sample;

[0044] Figure 4 Shows the measurement Figure 3 The signal curve of the spin resonance characteristic of the paper sample, and

[0045] Figure 5 A circuit is shown for connecting the resonator arrangement of a sensor element according to the invention to only a single signal branch.

[0046] 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.

[0047] 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, as in the embodiment shown, or can also extend over the entire surface of the banknote inspection specimen.

[0048] The checking device 20 comprises a sensor element 30 with a magnetic core 35 having an air gap 32 delimited by two pole surfaces 38 , through which the banknote check specimen 10 is guided along the transport path 14 during the authenticity check.

[0049] 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 .

[0050] On the one hand, a uniform static magnetic flux parallel to the z-axis is generated in the measuring range by the polarization device 34. In order to generate a strong polarization field, the height of the air gap in the z-direction is advantageously less than 10 mm, in particular even less than 5 mm.

[0051] 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. ModFinally, the resonator device 40 generates an excitation field in the air gap, which induces energy transitions between spin energy levels in the spin resonance feature 12. The excitation field typically has a frequency above 1 GHz and is polarized perpendicular to the z direction.

[0052] The frequency of the excitation field 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.

[0053] In addition to the above-mentioned elements, the inspection device 20 also includes a detector diode 26 for measuring the high-frequency power reflected by the resonator device 40 and an evaluation unit 28 for evaluating and, if necessary, displaying the measurement results. If the spin resonance feature 12 resonates at the coupling frequency, the resonator quality changes and thus the power reflected by the stripline resonator also changes. 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.

[0054] Figure 2 The design of a resonator arrangement 40 of a sensor element 30 according to the invention is schematically shown according to a first exemplary embodiment of the invention. The resonator arrangement 40 comprises a planar carrier, for example a printed circuit board 42, on which a plurality of stripline resonators 46 are arranged for spatially resolved measurements, which are operated independently of one another at the same excitation frequency.

[0055] Specifically, in Figure 2 In the exemplary embodiment of the present invention, the resonator arrangement 40 comprises a 2x1 array of two stripline resonators 46-1, 46-2, which form a one-dimensional array extending perpendicularly to the transport direction 14. As explained in more detail below, the spin resonance intensity of the banknote inspection sample 10 can thereby be measured spatially resolved, i.e. along two spaced tracks parallel to the transport direction 14. Figure 2 Only a small array with only 2x1 stripline resonators is shown for the purpose of explaining the functional principle, but it is understood that in practice a one-dimensional array with more than two, for example 3, 4, 5, 6 or 10 resonators is also possible in order to achieve a higher spatial resolution. A two-dimensional array, for example with 2x2, 2x4 or 2x10 resonators is also possible and enables spatially resolved measurements even on stationary banknote inspection samples 10. Preferably, a plurality of stripline resonators are arranged in a linear array or two-dimensionally on grid points of a regular grid, for example in a rectangular, hexagonal or row-by-row offset arrangement.

[0056] The polarization device 34 generates a uniform static magnetic flux in the air gap 32, so that for each of the two stripline resonators 46-1, 46-2 of the resonator device 40, the static magnetic flux at the location of the first stripline resonator 46-1 has substantially the same field strength as at the location of the second stripline resonator 46-2. The term "substantially" the same field strength here means that the field strength at the location of the stripline resonators 46-1, 46-2 differs by at most 2%.

[0057] In order to demonstrate the function of the present invention, the simulation has the following characteristics in the spin resonance measurement: Figure 2 The resonator device 40 is in accordance with Figure 3 The structure of the sensor element according to the present invention has certain characteristics.

[0058] The resonator arrangement 40 here comprises two square λ / 2 stripline resonators 46-1, 46-2, which are constructed on a printed circuit board 42 with a thickness of 1.5 mm and a dielectric constant of 3.66. The resonators 46-1, 46-2 have an edge length of 7.1 mm, which corresponds to a resonance frequency of 9.8 GHz, and are arranged on the printed circuit board 42 at a distance of 50 mm from one another in the y direction perpendicular to the transport direction 14.

[0059] In order to couple to the signal source 22 via the circulator, the impedance of the resonators 46-1, 46-2 is converted to 50Ω by means of a λ / 4 converter. mod The positions of the two resonators 46 - 1 , 46 - 2 are identical.

[0060] Reference Figure 3 , a measurement on a suitably prepared paper sample 60 is simulated by means of such a resonator arrangement 40. For this purpose, a paper sample with a height of 100 mm is firstly loaded over its entire surface with spin resonance features 62. After the feature loading, a 35 mm x 35 mm large section is cut out in the upper region of the sample and replaced by a featureless paper section 64.

[0061] like Figure 3 As shown, the sample 60 prepared in this way is moved centrally in the transport direction 14 on the resonator arrangement 40 with two stripline resonators 46-1, 46-2, and the resulting spin resonance signal is recorded. At a given polarization field strength, the Larmor frequency of the spin resonance characteristic corresponds exactly to the resonance frequency of the two resonators 46-1, 46-2 of 9.8 GHz.

[0062] exist Figure 4In the diagram 70 of FIG. 7 , the simulated signal strength obtained thereby is shown as a function of position x for the upper resonator 46 - 1 as a signal curve 72 - 1 and for the lower resonator 46 - 2 as a signal curve 72 - 2 . The signal curves are normalized here to the average signal strength of the undisturbed signal curve 72 - 2 and are shown slightly offset for better illustration.

[0063] exist Figure 4 It is clearly seen in FIG. 4 that the featureless region 64 of the sample 60 can be detected without any problems with the aid of the signal disturbance 74 of the upper resonator 46 - 1 . This would not be possible with a single resonator on which the paper sample 60 is moved, for example centrally.

[0064] In this embodiment, the ordinate is marked with I and indicates the normalized intensity. In addition, the abscissa is marked with x and indicates the position in mm.

[0065] A plurality of stripline resonators of a resonator arrangement can advantageously be operated with independent signal sources. However, this also requires that the stripline resonators be connected to independent signal branches, for which, especially in the case of a plurality of resonators, a large amount of installation space is required for implementing the circuit.

[0066] Figure 5 An alternative circuit 80 is shown for connecting a resonator arrangement 40 of a sensor element according to the invention to only a single signal branch 82. All three stripline resonators 46-1, 46-2, 46-3 of the resonator arrangement 40 are connected to a circulator 86 of this signal branch via a multiplexer 84. Since only one signal branch 82 with only one signal source 22 is used, the required installation space is very small. Furthermore, without further measures it is ensured that the stripline resonators 46-1, 46-2, 46-3 are operated at the same excitation frequency. For the sake of simplicity, in Figure 5 Although three resonators are shown in the circuit 80 of FIG. 8 , a different number, in particular a larger number, of resonators can also be supplied by a single signal source 22 via a multiplexer.

[0067] But when using Figure 5 In the case of a circuit 80, at any point in time only a single resonator 46-1, 46-2 or 46-3 can be used for measurement. Thus, gaps are created in the transport direction between the positions at which the spin resonances are measured on the test sample, and therefore there are positions at which no measurement is performed. The measurement points in adjacent tracks are offset from one another in the transport direction.

[0068] Depending on the requirements of the application with regard to the required installation space and the spatial resolution of the measurement, a hybrid solution can also be chosen, in which the stripline resonators of the resonator arrangement are divided into a plurality of groups, the resonators of each group being connected to a single signal branch. For example, a resonator arrangement with nine stripline resonators can be divided into three groups with three resonators each, which are each connected to a single signal branch via a multiplexer. The required installation space can thus be reduced to approximately one third, while at the same time achieving a high measurement coverage of the test sample.

[0069] Reference numerals list

[0070] 10 Banknote Inspection Samples

[0071] 12 Spin resonance characteristics

[0072] 14 Conveying path

[0073] 20 Inspection device

[0074] 22 Signal Source

[0075] 24 Duplexer

[0076] 26 Detector diode

[0077] 28 evaluation units

[0078] 30 sensor element

[0079] 32 Air Gap

[0080] 34 Polarization device

[0081] 35 Magnetic core

[0082] 36 Modulation device

[0083] 38 Polar

[0084] 40 Resonator Device

[0085] 42 Carrier

[0086] 46-1, 46-2, 46-3 Stripline Resonators

[0087] 60 paper samples

[0088] 62 Spin resonance characteristics

[0089] 64 Non-characteristic paper part

[0090] 70 Charts

[0091] 72-1, 72-2 signal curve

[0092] 74 Signal Interference

[0093] 80 Circuit

[0094] 82 signal branch

[0095] 84 Multiplexer

[0096] 86 Circulator

Claims

1. A sensor element (30) for detecting 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, - a sensor element with 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 by: - the resonator device (40) comprises a plurality of stripline resonators (46-1, 46-2) designed and arranged to operate independently of each other at the same excitation frequency, and The polarization device (34) generates a uniform magnetic flux in the air gap (32), so that for each of the two stripline resonators (46-1, 46-2) of the resonator device (40), the static magnetic flux at the location of the first stripline resonator (46-1) has substantially the same field strength as at the location of the second stripline resonator (46-2).

2. The sensor element (30) according to claim 1, characterized in that The static magnetic flux at the positions of each of the two stripline resonators (46-1, 46-2) of the resonator device (40) has a maximum deviation of 2%.

3. The sensor element (30) according to claim 1 or 2, characterized in that The stripline resonators (46-1, 46-2) of the resonator device (40) are arranged in the form of a one-dimensional array.

4. The sensor element (30) according to at least one of claims 1 to 3, characterized in that Each stripline resonator (46-1, 46-2) of the resonator device (40) is supplied by a different signal source.

5. The sensor element (30) according to at least one of claims 1 to 4, characterized in that A plurality of stripline resonators (46-1, 46-2) covers a surface comprising the entire width of a data carrier (10) to be checked, in particular a banknote.

6. The sensor element (30) according to at least one of claims 1 to 5, characterized in that The stripline resonators (46-1, 46-2) of the resonator arrangement (40) have the same resonance frequency. The stripline resonators are preferably designed and arranged to detect spin resonance characteristics in the same spatial mode of the excitation field. The stripline resonators particularly preferably have the same geometry.

7. The sensor element (30) according to at least one of claims 1 to 6, characterized in that The air gap (32) is defined by two plane-parallel pole faces (38) of the magnetic core (35).

8. The sensor element (30) according to at least one of claims 1 to 7, characterized in that The stripline resonator (46-1, 46-2) is designed in a planar manner with a main extension plane which is parallel to at least one pole plane of the magnetic core that defines an air gap.

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

10. The sensor element (30) according to claim 9, characterized in that The modulation device 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, characterized in that The stripline resonators (46-1, 46-2) 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 (34).

12. The sensor element (30) according to at least one of claims 1 to 11, 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, characterized in that The resonator arrangement (40) is arranged in the air gap so that a planar data carrier (10) introduced for inspection is located in the near field of the excitation field generated by the stripline resonator.

14. An inspection device (20) for inspecting planar data carriers, in particular banknotes, having spin resonance characteristics. - a testing device having a sensor element (30) according to one of claims 1 to 13, and - an inspection device or a plurality of signal sources with the same excitation frequency, the stripline resonators of the resonator device being supplied by said signal sources, The test device either has a single signal source, from which the stripline resonators are supplied via a multiplexer.

15. The testing device (20) according to claim 14, comprising a transport device which introduces the flat data carrier (10) to be tested into a testing position in the air gap and / or guides it past the testing position in the air gap of the magnetic core along a transport path (14), wherein: The resonator arrangement is arranged in the air gap such that the test location is located in the near field of the excitation field generated by the stripline resonator.

16. The inspection device (20) according to claim 15, characterized in that The conveying device is designed and arranged to quickly convey the planar data carrier to be inspected along a conveying path (14).

17. 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 16, wherein: In the method - introducing the flat data carrier (10) to be checked into the air gap of the magnetic core of the sensor element (30), - generating a static magnetic flux in the air gap 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), and - Exciting a spin resonance feature (12) of the data carrier (10) to be checked by means of a resonator device.

18. The method according to claim 17, characterized in that A planar data carrier (10) to be checked is measured in a spatially resolved manner by exciting a spin resonance feature (12), in particular for an integrity check.

19. The method according to claim 17 or 18, characterized in that A flat data carrier (10) to be checked is guided along a transport path through the air gap of the magnetic core of the sensor element (30), and a single-track or multi-track scanning of the data carrier is performed by the stripline resonators of the resonator arrangement.

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