Sensor element for testing a data carrier with spin resonance feature, disassembly method, assembly method and test method

Description

[0001] The invention relates to a sensor element for testing a flat data carrier, in particular a banknote, with a spin resonance feature. The invention also relates to a method for disassembling such a sensor element, a method for assembling such a sensor element, and a method for testing a flat data carrier with a spin resonance feature using such a sensor element.

[0002] Data storage media, such as valuables or identification documents, as well as other valuable items such as branded goods, are often provided with security elements for security purposes. These elements allow verification of the authenticity of the data storage media and also serve as protection against unauthorized reproduction. It is known that security elements with spin resonance features are used in machine authentication to protect documents and other data storage media. For this purpose, the security elements are provided with substances that exhibit a spin resonance signature. The spin resonance signatures that can be used for authentication include, in particular, nuclear magnetic resonance (NMR), electron spin resonance (ESR), and ferromagnetic or ferrimagnetic resonance (FMR).

[0003] When testing banknotes, three different magnetic fields are usually generated in the measuring range of a banknote processing machine, for example, to detect spin resonance signatures. Specifically, this involves a quasi-static polarization field B0 that runs parallel to the axial direction (z-direction) of the air gap of a magnetic circuit. A second magnetic field is formed by a modulation field Bmod, which also runs parallel to the z-axis and typically has a frequency fmod in the kHz range. To excite transitions between the split spin energy levels of the spin resonance signature substances, an excitation field B1 is provided that is polarized perpendicular to the B0 direction. The excitation field oscillates at the resonance frequency of the material, also known as the Larmor frequency, which is proportional to the polarization field B0.In NMR applications, the Larmor frequency is typically less than 100 MHz, whereas in ESR and FMR applications, the Larmor frequency is typically greater than 1 GHz.

[0004] To generate the polarization field B 0 , a magnetic circuit is often used to direct the magnetic flux from permanent magnets and / or coils to the air gap in which the banknote verification takes place. The measured spin resonance signal strength increases approximately quadratically with the field strength B 0 , so that the polarization field is advantageously maximized for the measurement. However, a larger polarization field B 0 also leads to larger forces and stray fields between the individual components of the magnetic circuit, which can be problematic, especially with permanent magnetic circuits. If the magnetic circuit has to be assembled or disassembled for assembly, maintenance, or installation tasks, for example, the large forces acting make the work more difficult and / or can pose a hazard.

[0005] A further hazard can arise if the magnetic circuit is disassembled into its individual components and stored. In this case, stray magnetic fields arise in the vicinity of the circuit components, the strength of which increases with increasing polarization field B 0 . Magnetizable parts are attracted to these stray fields, making storage difficult.

[0006] CN 203 931 702 U concerns an H-shaped permanent magnet device for teaching experiments for nuclear magnetic resonance. The device consists of a magnet frame, a pair of Helmholtz coils, a pole piece made of pure iron, magnetic neodymium-iron-boron steel, an adjustable magnetic yoke, a hexagon socket screw, an adjustable locking screw, and an adjustable outward ejector screw. Six adjustment screws on the magnetic yoke are used for fine adjustment of the magnetic field uniformity, and the field uniformization and regulation functions can be additionally achieved by two sets of Helmholtz coils. The neodymium-iron-boron magnetic steel is paired by a shield, and the magnetic yoke made of pure iron is finely ground, ensuring high uniformity of the magnetic device arrangement.The device is easy to install, has a high degree of uniformity and can be used in teaching for experimental devices for continuous magnetic resonance and pulsed magnetic resonance.

[0007] Based on this, the invention is based on the object of providing an improved sensor element for testing a flat data carrier with a spin resonance feature, which can be easily and safely assembled and disassembled and can be safely stored in the disassembled state.

[0008] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0009] The invention provides a sensor element for testing a flat data carrier with a spin resonance feature. The flat data carrier can be, for example, a banknote that is subjected to an authenticity test. The sensor element contains a magnetic core with an air gap into which the flat data carrier can be inserted for testing. The magnetic core also contains at least one disassembly gap along which the magnetic core can be disassembled into two or more parts. The sensor element further contains a polarization device for generating a static magnetic flux in the air gap.

[0010] As a special feature of the sensor element, the magnetic core has at least one magnetic potentiometer that can be switched between two states, wherein the magnetic potentiometer has a first magnetic resistance in a first state and the sensor element is configured in the first state of the magnetic potentiometer to measure a spin resonance feature of a data carrier inserted into the air gap, and the magnetic potentiometer has a second magnetic resistance different from the first magnetic resistance in a second state and the sensor element is configured in the second state of the magnetic potentiometer to decompose the magnetic core along the decomposition gap.

[0011] The at least one magnetic potentiometer is advantageously designed such that in the first state it has essentially no influence on the magnetic flux in the air gap.

[0012] Advantageously, the disassembly force for disassembling the magnetic core along the at least one disassembly gap in the second state is at least 20%, in particular at least 40%, smaller than the disassembly force in the first state.

[0013] In a preferred embodiment, it is provided that, in order to disassemble the magnetic core, a magnetic conductor with a magnetic resistance R ref is to be bridged by means of a magnetic potentiometer, wherein the magnetic potentiometer is connected in parallel to the conductor to be bridged.

[0014] The magnetic potentiometer advantageously has a magnetic resistance RP of at least 10* R ref in the first state. Preferably, the magnetic resistance RP in the first state is even greater than 20* R ref or 50* R ref . Alternatively or additionally, the magnetic potentiometer has a magnetic resistance RP of at most 3* R ref in the second state. Preferably, the magnetic resistance RP in the second state is even less than 2* R ref or 1*R ref .

[0015] In another, likewise preferred embodiment, it is provided that, for a disassembly of the magnetic core, a magnetic conductor with a magnetic resistance R ref is to be switched flux-free by means of a magnetic potentiometer, wherein the magnetic potentiometer is connected in series with the conductor to be switched flux-free.

[0016] In the first state, the magnetic potentiometer advantageously has a magnetic resistance RP of at most 1 / 3* R ref . Preferably, the magnetic resistance RP in the first state is even less than 1 / 5* R ref or 1 / 10* R ref . Alternatively or additionally, the magnetic potentiometer has a magnetic resistance RP of at least 3* R ref in the second state. Preferably, the magnetic resistance RP in the second state is even greater than 5* R ref or 10*R ref .

[0017] According to an advantageous embodiment, in the second state of the magnetic potentiometer, the magnetic flux through the air gap is changed by more than 5% compared to the magnetic flux in the first state, and / or the field homogeneity in the air gap is reduced by more than 10%. This allows for a particularly significant reduction in the disassembly force.

[0018] The sensor element advantageously incorporates two or more magnetic potentiometers, particularly magnetic potentiometers of different types. This allows for a significant reduction in disassembly force while simultaneously maintaining a small size and easy movement of the potentiometers. Magnetic potentiometers of the types described in more detail below are preferred.

[0019] According to an advantageous embodiment, at least one magnetic potentiometer of the magnetic core comprises two spaced-apart magnetic conductors and a magnetic flux guide piece, which extends with a variable length in the free space between the two conductors in order to generate a variable magnetic resistance depending on the length of the flux guide piece. The magnetic flux guide piece can, for example, be a magnetic cylinder and, in particular, be formed by a movable bolt or a threaded rod. The length of the flux guide piece in the free space can vary between zero and the distance between the magnetic conductors. The two aforementioned states of the magnetic potentiometer with different resistances can be formed by a position of minimum or maximum length of the flux guide piece in the free space. This embodiment allows a particularly significant reduction in the disassembly force.

[0020] According to another advantageous embodiment, at least one magnetic potentiometer of the magnetic core comprises two spaced-apart magnetic conductors and a flux guide extending between the conductors with an enclosed magnetic modification element that can be variably positioned in the flux guide to generate a variable magnetic resistance depending on the position of the modification element in the flux guide. The magnetic modification element can, for example, be a magnetic cylinder that can be inserted or screwed to a greater or lesser extent into a corresponding bore in the flux guide. The two aforementioned states of the magnetic potentiometer with different resistances can be formed by a minimally or maximally inserted position of the modification element in the flux guide. This embodiment is particularly mechanically stable.

[0021] According to a further advantageous embodiment, at least one magnetic potentiometer of the magnetic core comprises two spaced-apart magnetic conductors and a flux guide extending between the conductors, which can be combined with a magnetic modification plate to generate a variable magnetic resistance depending on the presence or absence of the modification plate. This embodiment is mechanically particularly simple.

[0022] The aforementioned elements of the magnetic potentiometers, in particular the magnetic flux guides, the modification element, or the modification plate, are advantageously formed from materials with a high relative permeability µ r . The materials preferably have a relative permeability ≥ 50, with particular preference given to materials with a relative permeability ≥ 200. Furthermore, the aforementioned elements are preferably formed from a material with a high saturation flux density, in particular BS ≥ 1.0 T or even BS ≥ 1.8, in order to avoid saturation and thus a decrease in permeability at high magnetic field strengths. Advantageous materials are soft magnetic materials such as SiFe and NiFe alloys, CoFe alloys, soft iron, or magnetic steels with a carbon content below 0.55%.

[0023] Magnetic potentiometers can advantageously be arranged next to a disassembly gap of the magnetic core; in particular, two magnetic potentiometers can be arranged on either side of a disassembly gap. This position is easily accessible for adjustment. Magnetic potentiometers can also advantageously be arranged such that they can create a shunt between the legs and / or yokes of the magnetic core and the pole pieces and / or permanent magnets of the magnetic core. This enables a particularly significant reduction in the disassembly force.

[0024] In an advantageous embodiment, the sensor element further comprises a modulation coil for generating a time-varying magnetic field in the air gap and a resonator for exciting the spin resonance feature of the data carrier to be tested. The resonator is also designed, in particular, to detect the signal response of the spin resonance feature and can advantageously record the signal response of the spin resonance feature and output it to a detector.

[0025] The sensor element preferably further comprises an evaluation unit configured to generate a test result based on the signal response of the spin resonance feature detected by the resonator. For this purpose, a characteristic property derived from the signal response is preferably compared with a reference value or a reference interval. If the match is sufficiently high, a positive test result is output, indicating, for example, the authenticity or class affiliation of the verified value document. Characteristic properties that can be used include, for example, the resonance frequency of the spin resonance, its line width or amplitude, a relaxation time of the spin resonance, or the spatial distribution of the spin resonance feature.

[0026] The spin resonances can be determined, for example, using a continuous wave (CW) method, a pulsed method or a rapid scan method.

[0027] The invention also includes a method for disassembling a sensor element of the described type, in which the at least one magnetic potentiometer of the magnetic core is brought into the second state, and the magnetic core is disassembled along the at least one disassembly gap. If the sensor element contains multiple magnetic potentiometers, all potentiometers are advantageously brought into the second state to achieve the greatest possible reduction in the disassembly force.

[0028] The invention further includes a method for assembling a sensor element of the type described. In the method, a first section of the magnetic core is provided, which has at least part of the aforementioned polarization device for generating the static magnetic flux, and which has at least one magnetic potentiometer switchable between two states, which is in the second state or is brought into the second state. Furthermore, a second section of the magnetic core is provided. The magnetic core of the sensor element is assembled from the first and second sections, so that, on the one hand, an air gap is formed in the magnetic core, in which a static magnetic flux is generated by the polarization device, and, on the other hand, at least one separation gap is formed between the sections.After the magnetic core has been mounted, the at least one magnetic potentiometer is brought into the first state in order to set up the sensor element for a measurement of a spin resonance feature of a data carrier inserted into the air gap.

[0029] If the sensor element contains multiple magnetic potentiometers, the specified steps are advantageously performed for all magnetic potentiometers. The second section of the magnetic core can also have part of the aforementioned polarization device for generating the static magnetic flux and can have at least one magnetic potentiometer switchable between two states. In this case, the specified steps are advantageously also performed for the magnetic potentiometers of the second section. For example, the sensor element is only configured for a spin resonance measurement when all magnetic potentiometers of the magnetic core are in the first state.

[0030] Finally, the invention also includes a method for testing a flat data carrier, in particular a banknote, with a spin resonance feature using a sensor element of the type described. The method checks whether the at least one magnetic potentiometer of the magnetic core is in the first state. If this is not the case, the at least one magnetic potentiometer is set to the first state. A flat data carrier to be tested is then inserted into the air gap of the magnetic core, and a spin resonance measurement is performed on the data carrier.

[0031] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0032] They show: Fig. 1 schematically shows the sensor element of a checking device according to the invention of a banknote processing system in normal operation with the magnetic potentiometers switched to the first state, Fig. 2 the sensor element of the Fig. 1 with the magnetic potentiometers switched to the second state for assembly, maintenance or installation tasks, Fig. 3 the structure and operation of some magnetic potentiometers used according to the invention, Fig. 4 magnetic equivalent circuit diagrams for the sensor element of the Figures 1 and 2 , where (a) shows the complete magnetic equivalent circuit, and (b) for R p » RZ the idealized equivalent circuit in normal operation of the Fig. 1 shows, Fig. 5 schematically a sensor element according to a further embodiment of the invention in control operation, wherein (a) shows the side view of the sensor element in the xz plane and (b) the side view in the yz plane, Fig. 6 in (a) and (b) the sensor element of the Fig. 5with the same views in the inoperable state, Fig. 7 the complete magnetic equivalent circuit diagram of the sensor element of Figures 5 and 6, Fig. 8 the amount of the calculated stray fields of the upper circular half of the sensor element along the central perpendicular line of the pole piece in the two configurations of the Figures 1 and 2 , and Fig. 9 the relative decomposition force FZ,rel of a magnetic circuit according to Figures 1 and 2 depending on the bolt diameter d (upper x-axis), or the ratio between the reference resistance R ref in the magnetic circuit and the potentiometer resistance RP of the potentiometer (lower x-axis).

[0033] The invention will now be explained using the example of sensor elements for the authentication of banknotes. Figures 1 and 2show schematically the sensor element 10 of a testing device of a banknote processing system. The banknote test pieces (not shown) contain a spin resonance feature in a feature area, the characteristic properties of which serve in particular to prove the authenticity of the banknote. The test pieces are guided along a transport path 12 through an air gap 24 of the sensor element 10, which in the illustration of the Figures 1 and 2 is perpendicular to the plane of the paper.

[0034] The sensor element 10 of the Figures 1 and 2Contains a magnetic circuit, referred to as an H-type circuit due to its geometry. The magnetic circuit comprises a magnetic core 20, which conducts the magnetic flux of two permanent magnets 22 and, as a rule, additional coil elements (not shown in the figure for the sake of simplicity), to an air gap 24 extending axially between the pole pieces 26 of the magnetic circuit and in which the spin resonance measurement of the banknotes under test takes place.

[0035] The magnetic core 20 forms a magnetic return path for the magnetic flux 14 of the permanent magnets 22, which Fig. 1 is shown in the left half of the sensor element for illustration purposes. The vertical return elements of the magnetic core 20 are referred to as legs, and the horizontal return elements are referred to as yokes.

[0036] The magnetic core 20 further comprises two disassembly gaps 30 at which the magnetic circuit can be separated and disassembled into two circuit halves 16, 18 for assembly, maintenance or installation tasks.

[0037] As described above, a high field strength of the polarization field B 0 in the air gap 24 is desired to achieve a high signal strength during banknote verification. However, as the permanent magnetic polarization field increases, the forces and stray fields between the individual components of the magnetic circuit also increase, which, on the one hand, make it difficult to disassemble the sensor element and, on the other hand, can also lead to a hazard when storing a magnetic circuit disassembled into its individual components.

[0038] To overcome these problems, four magnetic potentiometers 32 are provided in the magnetic core 20, which do not influence the control operation of the sensor element during banknote verification, but which enable a significant reduction of the disintegration forces and stray fields.

[0039] The magnetic potentiometers 32 can each be switched between two states, each of which is in the Figures 1 and 2 are illustrated. In the Fig. 1 In the first state of the potentiometers 32 shown, the sensor element 10 is in normal operation and is set up to measure a spin resonance feature of a banknote test specimen in the air gap 24. In the second state of the potentiometers 32, which is shown in Fig. 2As illustrated, a substantial part of the magnetic flux flows through the potentiometers 32 and thereby reduces not only the flux in the air gap 24 but also, in particular, the flux in the separation gaps 30. The separation forces of the two circuit halves 16, 18 are thereby significantly reduced and allow easier assembly and disassembly of the magnetic circuit.

[0040] To explain in more detail how the magnetic flux is deliberately redirected using the magnetic potentiometers 32, first of all with reference to Fig. 3 the structure and operation of some magnetic potentiometers used in the invention are described in more detail.

[0041] Figure 3(a)shows a first embodiment of a magnetic potentiometer 40, in which a magnetically conductive cylinder 44 with variable length l 2 and cross-sectional area A extends between two magnetic conductors 42 arranged at a distance l. The length l 2 of the cylinder 44 can generally be between 0 and l, so that between the conductors 42, in addition to the magnetic cylinder 44, there is also a free space 48 of length l 1 = ll 2. If the relative permeability of the material of the cylinder 44 is µ 2 and the relative permeability of the free space 48 is denoted by µ 1, the total magnetic resistance of the potentiometer 40 formed between the outer conductors 42 is approximately given by R = l 1 / μ 0 μ 1 A + l 2 / μ 0 μ 2 A = l − l 2 / μ 0 μ 1 A + l 2 / μ 0 μ 2 A , with the permeability of the vacuum µ0.

[0042] The magnetic resistance of the potentiometer 40 can thus be adjusted via the length l 2 of the magnetically conductive cylinder 44. Since µ 2 > µ 1 applies to magnetic materials, a maximum magnetic resistance of the potentiometer 40 results for l 2 = 0 and a minimum magnetic resistance for l 2 = l. In a sensor element, these two extreme values and the associated positions of the cylinder 44 can represent the two aforementioned states of different magnetic resistance of the magnetic potentiometer 40.

[0043] A second embodiment of a magnetic potentiometer 50 is shown in Fig. 3(b)shown in front and side views. In the potentiometer 50, a magnetic flux guide 54 establishes a connection between an upper and a lower magnetic conductor 52. The flux guide 54 is made of a material with a relative permeability µ 2 and encloses a longitudinally displaceable cylinder 56 with a permeability µ 3 > µ 1 . The flux guide 54 and the cylinder 56 are located in a free space 58 with a relative permeability µ 1 , which in particular also fills the bore in the flux guide 54. The magnetic resistance of the potentiometer 50 can be adjusted by the position l of the cylinder 56 within the flux guide 54. In particular, a maximum magnetic resistance of the potentiometer 50 results for l = l max , i.e. a cylinder 56 pushed out as far as possible, and a minimum magnetic resistance for l = 0, i.e. a cylinder 56 pushed completely into the flux guide piece 54.In a sensor element, these two extreme values and the associated positions of the cylinder 56 relative to the flux guide 54 can be used as the two above-mentioned states of different magnetic resistance of the potentiometer 50.

[0044] Figure 3(c) shows a further embodiment of a magnetic potentiometer 60. A flux guide 64 with a relative permeability of µ 2 connects two external magnetic conductors 62. The relative permeability of the free space 68 is again designated µ 1. By adding a modification plate 66 with a relative permeability of µ 3 > µ 1, the magnetic resistance between the two external conductors 62 can be reduced. Therefore, in a first state with the added modification plate 66, the resistance of the magnetic potentiometer 60 is low, and in a second state without the modification plate 66, it is high.

[0045] At twoIn order to obtain states with the greatest possible difference in magnetic resistance with a small cross section of the potentiometer elements, the potentiometers 40, 50, 60 are advantageously formed with materials of high relative permeability µ 2 or µ 3. The relative permeability is preferably ≥ 50. A relative permeability ≥ 200 is particularly preferred. In order to avoid saturation and thus a decrease in permeability at high magnetic field strengths, a material with a high saturation flux density is advantageously selected, for example soft magnetic materials with BS ≥ 1.0 T, such as SiFe or NiFe alloys, or soft magnetic materials with even BS ≥ 1.8 T, such as CoFe alloys, soft iron or magnetic steels with a carbon content below 0.55%.

[0046] Returning to the presentation of the Figures 1 and 2In the sensor element 10, in each of the two halves of the magnetic circuit 16, 18, two magnetic potentiometers 32 of the type of potentiometer 40 of the Fig. 3(a) The magnetically conductive cylinders of the potentiometers are each formed by soft magnetic threaded rods 34, which in the first state of the Fig. 1 unscrewed outwards and in the second state the Fig. 2 are screwed into the magnetic circuit. As in connection with Fig. 3(a) As explained, the magnetic resistance of the potentiometer 32 in the first state ( Fig. 1 ) maximum and in the second state ( Fig. 2 ) is minimal. The potentiometers therefore form the second state of the Fig. 2 a shunt within the magnetic circuit which reduces the flux in the air gap 24 and the separation gaps 30.

[0047] The reduction of the magnetic flux using the potentiometer 32 can be illustrated using magnetic equivalent circuits. Figure 4 shows in Fig. 4(a) the complete magnetic equivalent circuit diagram of the sensor element 10 of the Figures 1 and 2 , in which the permanent magnets 22 are considered as voltage sources P and the magnetic elements of the magnetic circuit are shown as yoke resistances RJ , as leg resistances RS , as resistances of the conductor elements at the separation gap RZ , and as air gap resistance RL . The variable resistances of the four potentiometers 32 are designated RP . The pole pieces and any coil elements are neglected for simplicity.

[0048] At maximum magnetic resistance of the potentiometer 32, i.e. in the control operating state of the Fig. 1, R p » RZ , so that practically no magnetic flux flows through the potentiometers 32. This condition can therefore be described by the idealized equivalent circuit of the Fig. 4(b) described, and it becomes clear that the magnetic flux in the air gap 24 is not disturbed by the magnetic potentiometers 32 during control operation of the sensor element 10.

[0049] For assembly or disassembly work, the threaded rods 34 are screwed into the magnetic circuit, thereby minimizing the magnetic resistance of the potentiometers 32, and the resulting shunt reduces the magnetic flux in the air gap 24 and the disassembly gaps 30. Surprisingly, it has been shown that a potentiometer resistance of RP ≈ 3*RZ is sufficient to significantly reduce the disassembly force. A substantial portion of the magnetic flux then flows through the magnetic potentiometers 32, while simultaneously reducing the flux in the air gap 24 and the disassembly gaps 30.

[0050] In addition to reducing the disassembly forces, which facilitate assembly and disassembly of the magnetic circuit, the shifting of the magnetic flux from the air gap 24 or the disassembly gaps 30 into the potentiometer elements 32 also advantageously leads to lower stray fields in the vicinity of the circuit elements, as described in detail below.

[0051] A further embodiment of the invention will now be described with reference to the Figures 5 to 7 explained. The Figures 5 and 6 show a sensor element 70 according to the invention in (a) in a side view in the xz plane and in (b) in a side view in the yz plane. The sensor element 70 is in Fig. 5 in regular operation and in Fig. 6 shown in an inoperable state, ready for disassembly. Figure 7 shows the complete magnetic equivalent circuit of the sensor element 70.

[0052] The magnetic circuit of the sensor element 70 is also of the H-type and contains, like the design of the Figures 1 and 2 a magnetic core 20 with permanent magnets 22, a magnetic return path, and an air gap 24 extending between two pole pieces 26, in which the spin resonance measurement takes place. The magnetic circuit contains disassembly gaps 72, which in the sensor element 70 are arranged such that the original H-type circuit can be disassembled into a C-type circuit by removing the left circular leg 74. This is a frequently occurring task, especially during maintenance work on banknote processing machines. If, for example, a banknote jam occurs in the machine, the transport path 12 in the air gap 24 becomes accessible by disassembling the circular leg 74, and the banknote jam can be cleared more easily.

[0053] The magnetic core 20 of the sensor element 70 contains two different types of magnetic potentiometers 80, 84. On the one hand, in the immediate vicinity of the two disassembly gaps 72, two potentiometers 80 of the Fig. 3(b) described type, which are connected in series in the magnetic circuit. The movable cylinders of these potentiometers are formed in the sensor element 70 by soft magnetic threaded rods 82, which are screwed into the magnetic circuit ( Fig. 5 ) or largely unscrewed ( Fig. 6 ) can be. As in connection with Fig. 3(b) As explained, the magnetic resistance of the potentiometer 80 in the first, screwed-in state of the Fig. 5 small, in the second, unscrewed state of the Fig. 6 however, is much larger.

[0054] The series connection of the potentiometers 80 is particularly well represented in the magnetic equivalent circuit of the Fig. 7 to recognize, in which, in addition to the already Fig. 4 known elements P, RJ and RS , the potentiometers 80 arranged at the cutting gaps as variable Magnetic resistances R p (1)< are shown. The magnetic resistance of the disassembly gap is not shown for simplicity. The magnetic resistance R s of leg 74, which must be removed during disassembly, naturally forms a suitable reference resistance for the value of the potentiometer resistances R p (1)< .

[0055] On the right leg of the magnetic core 20 is a magnetic potentiometer 84 of the Fig. 3(c) described type, wherein the right leg 76 of the magnetic core plays the role of the flux guide and a removable soft magnetic plate 86 ( Fig. 6 ) takes over the role of the modification plate. As in Fig. 7 As shown, the potentiometer 84 with magnetic resistance R p (2)< is connected in parallel to the magnetic circuit.

[0056] In regular operation of the Fig. 5The threaded rods 82 of the potentiometers 80 are fully screwed in, so their series-connected magnetic resistance R p (1)< is small. On the other hand, the soft magnetic plate 86 of the potentiometer 84 is removed, so that the parallel-connected magnetic resistance R p (2)< of the potentiometer 84 is high, as in connection with Fig. 3(c) explained. During normal operation of the sensor element 70, the magnetic flux in the air gap 24 is therefore not disturbed by the magnetic potentiometers 80, 84.

[0057] In disassembled state of the Fig. 6The threaded rods 82 of the potentiometers 80 of the first type are unscrewed; their series-connected magnetic resistance R p (1)< is therefore high, so that they largely decouple the left circular leg 74 with magnetic resistance R s from the magnetic flux. The soft magnetic plate 86 is now mounted in the potentiometer 84 of the second type, so that the parallel-connected magnetic resistance R p (2)< of the potentiometer 84 is low and the magnetic flux is diverted away from the air gap 24 and the left circular leg 74. The left circular leg 74 can therefore be easily removed for maintenance work.

[0058] Instead of the soft magnetic threaded rods and soft magnetic plates shown for illustration in the embodiments, other magnetic elements with high relative permeability can also be used, in particular soft magnetic bolts, soft magnetic cone elements and soft magnetic wing elements.

[0059] Some advantageous properties of the sensor elements according to the invention will now be explained in more detail using simulations and comparative calculations.

[0060] First, the magnetic circuit of the sensor element 10 of the Figures 1 and 2simulated. The magnetic circuit contains two NdFeB permanent magnets, as well as a magnetic return path and two pole pieces made of soft magnetic steel with a carbon content of < 0.19% and a saturation magnetization of 2.05 T. The permanent magnets have a remanence of 1.29 T and dimensions of 30 mm x 60 mm x 20 mm. Their magnetization is parallel to the z-axis. Without the magnetic potentiometers, the magnetic circuit has outer contours of 30 mm x 140 mm x 140 mm. The yokes and legs have a cross-section of 20 mm x 30 mm. In the center of the magnetic circuit, along the z-axis, there is an air gap with a height of 20 mm.

[0061] The magnetic circuit also contains two separation gaps 30, which allow the circuit to be separated in the xy plane. Two magnetic potentiometers 32 are located in each of the two circular legs. Each potentiometer 32 contains a soft magnetic bolt as a cylindrical element, made of the same material as the magnetic return. The diameter of the soft magnetic bolts is 15 mm each, and their usable length is 20 mm.

[0062] For this magnetic circuit, the separation force FZ was calculated, i.e. the minimum force required to pull the upper half of the circle 16 away from the lower half of the circle 18 in the z-direction. Furthermore, the B 0 flux density in the center of the air gap 24 was also determined. This flux density is directly proportional to the resonance frequency of the spin resonance feature and therefore crucial for the operability of the sensor element 10. All calculations were carried out for the two Figures 1 and 2 shown states of the potentiometer 32.

[0063] Configuration 1 or first state is the configuration of the Fig. 1 in which the magnetic circuit is in control mode and the potentiometers 32 are fully extended.

[0064] Configuration 2 or second state is the configuration of the Fig. 2 In this state, the magnetic circuit is in a non-operational but easily disassembled state. In the second state, the potentiometers 32 generate a shunt between the circular legs and the pole pieces, or between the circular legs and the permanent magnets. In principle, however, it is also possible to generate a shunt only between the circular legs and the pole pieces, or only between the circular legs and the permanent magnets, or to generate a shunt using the circular yoke.

[0065] The following Table I shows the results of the calculation of the decomposition force FZ and the flux density B 0 in the center of the air gap in the two configurations. Table I: configuration FZ (N) B 0 (mT) 1 - Regular operation, Fig. 1 450 330 2 - dismantable, Fig. 2 230 250

[0066] Table I shows that the disassembly force FZ is reduced by almost 50% through the use of the magnetic potentiometers 32. This halving of the force FZ required allows for significantly more comfortable and safer work during assembly and maintenance tasks.

[0067] At the same time, the decrease in the separation force FZ is accompanied by a decrease in the flux density B 0 in the air gap. This reduction in the flux density is equivalent to a reduction in the resonance frequency of the spin feature, in this case by 24%. Since the bandwidth within which, for example, a stripline resonator of a sensor element is capable of measurement is typically less than 1% of the fundamental frequency, the combination of magnetic circuit and resonator in configuration 2 is no longer capable of measuring a given spin resonance security feature due to the sharp decrease in the polarization field B 0. This is not problematic, however, since spin resonance measurements should only be performed with the sensor element in configuration 1.

[0068] In addition to reducing the disassembly forces, the use of the potentiometers 32 according to the invention also reduces the stray fields occurring in a disassembled magnetic circuit.

[0069] For illustration, diagram 90 shows the Fig. 8 the amount of the calculated stray fields of the upper half of the circle 16 of the sensor element 10 along the central vertical line of the pole piece 26. The field pattern in configuration 1 ( Fig. 1 ) is shown as curve 92, the field curve in configuration 2 ( Fig. 2 ) is shown as curve 94. The display runs in the negative z-direction (in the Figures 1 or 2, i.e. from top to bottom) and begins in the center of the air gap 24 at z=0. In both configurations, the lower half of the circle 18 was removed.

[0070] As from Fig. 8As can be seen, the stray fields in configuration 2 (curve 94) are lower than the stray fields in configuration 1 (curve 92) at all z values. For example, in the center of the air gap 24 at z=0, the stray field in configuration 2 is 24% lower than the stray field in configuration 1 with high potentiometer resistances due to the low magnetic resistance of the potentiometers 32.

[0071] In a further simulation calculation, the sensor element 10 was Figures 1 and 2 the influence of the thread or bolt diameter and thus the influence of the magnetic potentiometer resistance on the disassembly force was examined in more detail.

[0072] For this purpose, the magnetic potentiometers 32 of the sensor element 10 were simulated with bolts with diameters d ranging between 2 mm and 20 mm, and the disassembly force in the z-direction was determined. The holes in the circular legs were dimensioned so that they are completely filled by the respective bolts.

[0073] The calculation results are shown in diagram 95 of the Fig. 9 summarized and illustrated. For each selected bolt diameter d, shown on the upper x-axis, the disassembly force was calculated, both for fully screwed-in bolts ( Fig. 2 , minimum value of the potentiometer resistance RP ) as well as for maximum unscrewed bolts ( Fig. 1 , maximum value of the potentiometer resistance RP ).

[0074] The Fig. 9 shows on the y-axis the relative disassembly force FZ,rel , i.e. for each bolt diameter d the disassembly force FZ,min at minimum potentiometer resistance (second state, easy to disassemble) relative to the disassembly force at maximum potentiometer resistance FZ,max (first state, control operation). A relative disassembly force FZ,rel of 100% corresponds to the disassembly force of the initial situation set up for the spin resonance measurement of the Fig. 1, a relative disassembly force of less than 100% indicates a corresponding reduction in disassembly force compared to the initial situation.

[0075] The lower x-axis shows the relationship between the relevant reference resistance R ref in the magnetic circuit and the minimum potentiometer resistance RP of the potentiometers 32 in the second, disassemblable state. The relevant reference resistance R ref is the total resistance of the bridged magnetic return between the two potentiometers in the upper and lower halves of the circuit.

[0076] From the presentation of the Fig. 9It can be seen that potentiometer elements with a resistance ratio of R Ref / RP = 0.33 (corresponding to RP = 3*R Ref ) reduce the disassembly force by approximately 20% (roughly corresponding to data point 96). As the magnetic resistance decreases further, i.e., as the bolt diameter d increases, the disassembly force continues to decrease. For bolts with a very large diameter d, especially with R Ref / RP ≥ 1, the disassembly force is reduced by approximately 60% and almost disappears with even larger bolt diameters.

[0077] With a further simulation calculation, the magnetic circuit of the sensor element 70 of the Figures 5 and 6 examined in more detail. In normal operation ( Fig. 5 ) the return, the pole pieces and the permanent magnets used are identical to the magnetic circuit of the Figures 1 and 2This configuration is referred to below as Configuration 1 or the first state. Unlike this configuration, however, the sensor element 70 has vertical disassembly gaps 72, with which the H-type circuit can be converted into a C-type circuit by disassembling a leg 74.

[0078] To facilitate disassembly, 72 soft magnetic threaded rods with a diameter of 10 mm each are located near the two disassembly gaps. During normal operation of the Fig. 5 The threaded rods are screwed into the return path. To disassemble the circular leg 74, the threaded rods can be turned halfway out of the return path, as shown in Fig. 6illustrated. Additionally, a soft magnetic plate 86, for example, with dimensions of 30 mm x 10 mm x 140 mm, can be attached to the right circular leg 76. For calculation purposes, both the potentiometer threaded rods 82 and the potentiometer plate 86 are made of the same soft magnetic steel as the pole pieces and the return path. This configuration is referred to below as Configuration 2 or the second state.

[0079] For this magnetic circuit, the separation force FZ was again calculated, whereby the separation force in this embodiment represents the minimum force required to separate the left circular leg 74 in the negative y-direction from the circle (in Fig. 5(b) and 6(b) i.e. to the left).

[0080] The calculation was made for the two Figures 5 or 6 shown configurations with the different states of the potentiometers 80, 84. Table II: configuration FZ (N) 1 - Regular operation, Fig. 5 756 2 - dismantable, Fig. 6 467

[0081] From Table II it can be seen that the potentiometers 80, 84 can reduce the disassembly force required to remove the circular leg 74 by almost 40%.

[0082] In addition, the magnetic circuit in the configuration of the Fig. 6 a strong asymmetry in the design. This asymmetry is also reflected in the distribution of the magnetic flux in the circuit and ultimately leads to an asymmetric B 0 distribution in the air gap. This is synonymous with poor field homogeneity, which complicates banknote measurements. However, this is not problematic, since spin resonance measurements should only be performed with the sensor element in configuration 1. List of reference symbols

[0083] 10 Sensor element 12 Transport path 16 Upper half of the circle 18 Lower half of the circle 20 Magnetic core 22 Permanent magnets 24 Air gap 26 Pole shoes 30 Disassembly gap 32 Magnetic potentiometers 34 Soft magnetic threaded rods 40 Magnetic potentiometer 42 Magnetic conductors 44 Magnetically conductive cylinder 48 Free space 50 Magnetic potentiometer 52 Magnetic conductors 54 Flux guide 56 Movable cylinder 58 Free space 60 Magnetic potentiometer 62 Magnetic conductors 64 Flux guide 66 Modification plate 68 Free space 70 Sensor element 72 Disassembly gap 74 Left circular leg 76 Right circular leg 80 Magnetic potentiometers (first type) 82 Soft magnetic threaded rods 84 Magnetic potentiometer (second type) 86Soft magnetic plate 90Diagram 92Field profile in configuration 1 94Field profile in configuration 2 95Diagram 96Data point R Ref / RP = 0.33

Claims

1. Sensor element (10) for the inspection of a planar data carrier, in particular a banknote, having a spin-resonance feature, comprising - a magnetic core (20) with an air gap (24), into which the planar data carrier is capable of being inserted for the purpose of inspection, and with at least one disassembly gap (30), along which the magnetic core (20) is capable of being disassembled into two or more parts, and - a polarization device (22) for generating a static magnetic flux in the air gap (24), characterized in that - the magnetic core (20) exhibits at least one magnetic potentiometer (32) capable of being switched between two states, wherein - in a first state the magnetic potentiometer (32) exhibits a first magnetic reluctance, and in the first state of the magnetic potentiometer (32) the sensor element (10) has been set up for a measurement in respect of a spin-resonance feature of a data carrier inserted into the air gap (24), and - in a second state the magnetic potentiometer (32) exhibits a second magnetic reluctance, different from the first magnetic reluctance, and in the second state of the magnetic potentiometer (32) the sensor element (10) has been set up for a disassembly of the magnetic core along the disassembly gap (30), with the result that a disassembly force for disassembling the magnetic core along the at least one disassembly gap (30) is smaller in the second state than the disassembly force in the first state.

2. Sensor element (10) according to Claim 1, characterized in that the at least one magnetic potentiometer (32) has been designed in such a way that in the first state it has substantially no influence on the magnetic flux in the air gap.

3. Sensor element (10) according to at least one of Claims 1 and 2, characterized in that the disassembly force for disassembling the magnetic core along the at least one disassembly gap (30) is at least 20% smaller in the second state, in particular at least 40% smaller, than the disassembly force in the first state.

4. Sensor element (10) according to at least one of Claims 1 to 3, characterized in that for a disassembly of the magnetic core (20) a magnetic conductor with a magnetic reluctance Rref has to be bridged with the aid of a magnetic potentiometer (32), the magnetic potentiometer (32) being connected in parallel with the conductor to be bridged, and in that the magnetic potentiometer (32) in the first state preferably exhibits a magnetic reluctance RP of at least 10 * Rref.

5. Sensor element (10) according to Claim 4, characterized in that the magnetic potentiometer (32) in the second state exhibits a magnetic reluctance RP of at most 3 * Rref.

6. Sensor element (10) according to at least one of Claims 1 to 5, characterized in that for a disassembly of the magnetic core a magnetic conductor with a magnetic reluctance Rref has to be switched to be flux-free with the aid of a magnetic potentiometer (32), the magnetic potentiometer (32) being connected in series with the conductor to be switched to be flux-free, and in that the magnetic potentiometer (32) in the first state preferably exhibits a magnetic reluctance RP of at most 1 / 3 * Rref.

7. Sensor element (10) according to Claim 6, characterized in that the magnetic potentiometer (32) in the second state exhibits a magnetic reluctance RP of at least 3 * Rref.

8. Sensor element (10) according to at least one of Claims 1 to 7, characterized in that in the second state of the magnetic potentiometer (32) the magnetic flux through the air gap (24) has been changed by more than 5% in comparison with the magnetic flux in the first state, and / or in that the field homogeneity in the air gap has been diminished by more than 10%.

9. Sensor element (10) according to at least one of Claims 1 to 8, characterized in that two or more magnetic potentiometers (32), in particular at least two magnetic potentiometers of different types (80, 84), have been provided.

10. Sensor element (10) according to at least one of Claims 1 to 9, characterized in that at least one magnetic potentiometer (32) of the magnetic core (20) includes two spaced magnetic conductors and a magnetic flux-conducting part which extends with variable length within the free space between the two conductors in order to generate a variable magnetic reluctance, depending on the length of the flux-conducting part.

11. Sensor element (10) according to at least one of Claims 1 to 10, characterized in that at least one magnetic potentiometer (80) of the magnetic core (20) includes two spaced magnetic conductors and a flux-conducting part extending between the conductors with an enclosed magnetic modification element that is capable of being variably positioned in the flux-conducting part in order to generate a variable magnetic reluctance, depending on the position of the modification element in the flux-conducting part.

12. Sensor element (10) according to at least one of Claims 1 to 11, characterized in that at least one magnetic potentiometer (84) of the magnetic core (20) includes two spaced magnetic conductors and a flux-conducting part extending between the conductors that is capable of being combined with a magnetic modification plate in order to generate a variable magnetic reluctance, depending on the presence or absence of the modification plate.

13. Sensor element (10) according to at least one of Claims 1 to 12, characterized in that the sensor element (10) exhibits a modulation coil for generating a temporally varying magnetic field in the air gap, and a resonator for exciting the spin-resonance feature of the data carrier to be inspected.

14. Method for disassembling a sensor element (10) according to one of Claims 1 to 13, in which the at least one magnetic potentiometer (32) of the magnetic core is brought into the second state and the magnetic core is disassembled along the at least one disassembly gap (30).

15. Method for assembling a sensor element (10) according to one of Claims 1 to 13, in which - a first portion of the magnetic core (20) is made available that exhibits at least a part of the stated polarization device for generating the static magnetic flux and that exhibits at least one magnetic potentiometer (32) capable of being switched between two states, which is in the second state or is brought into the second state, - a second portion of the magnetic core (20) is made available, - the magnetic core (20) of the sensor element (10) is assembled from the first and second portions, so that, on the one hand, an air gap (24) is formed in the magnetic core (20), in which a static magnetic flux is generated by the polarization device, and, on the other hand, at least one disassembly gap (30) is formed between the portions, - after the assembly of the magnetic core (20), the at least one magnetic potentiometer (32) is brought into the first state in order to set up the sensor element (10) for a measurement in respect of a spin-resonance feature of a data carrier inserted into the air gap.

16. Method for inspecting a planar data carrier, in particular a banknote, having a spin-resonance feature by means of a sensor element (10) according to one of Claims 1 to 13, in which - an inspection is made as to whether the at least one magnetic potentiometer (32) of the magnetic core (20) is in the first state, and if this is not the case the magnetic potentiometer is brought into the first state, and - a planar data carrier to be inspected is inserted into the air gap (24) of the magnetic core (20), and a measurement of spin resonance is performed in respect of the data carrier.