Device for authenticity checking of data carriers with zero field NMR features

Abstract

The invention relates to a device for authenticity checking of a planar data carrier (10) having zero-field nuclear magnetic resonance (NMR) features (12, 14), having one or more excitation coils (30) for generating excitation pulses for the zero-field NMR features (12; 14), an array (40) of a plurality of receiving coils (42) which are independent of the excitation coils (30) and are arranged at least partially adjacent to one another for position-resolved detection of the signal response of the zero-field NMR features (12; 14), wherein the number (N) of the receiving coils (42) of the array (40) of receiving coils is greater than the number (M) of the excitation coils (30) and the area (F A ) covered by the excitation coils (30) at least partially covers the area (F E ) covered by the receiving coils (42) of the array (40) of receiving coils and exceeds the size of the area (F E ).

Description

Technical Field

[0001] This invention relates to an apparatus for verifying the authenticity of planar data carriers with zero-field nuclear magnetic resonance (NMR) characteristics. Background Technology

[0002] Data carriers such as valuable documents or certificates, as well as other valuable items such as brand-name goods, are usually equipped with security elements to provide security. These security elements can verify the authenticity of the data carrier and also serve as protection against unauthorized copying.

[0003] To enable automated authenticity checks and, when necessary, further sensing and processing of the associated data carriers, security elements are typically designed to be machine-readable. For this purpose, security elements with machine-readable magnetic regions have long been used, whose information content can be detected and evaluated by the magnetic sensors of the processing system during authenticity checks.

[0004] For some time, as described, for example, in publication EP 2 778 705 A1, security elements with nuclear magnetic resonance characteristics have also been used for the security of documents and other data carriers.

[0005] Nuclear magnetic resonance (NMR) describes a physical effect in which the atomic nuclei of a sample absorb and emit alternating electromagnetic fields in a constant magnetic field B0. The nuclear spin here occurs at a Larmor frequency ω, which is proportional to the magnetic field strength B0. L The sample precesses around the axis of a constant magnetic field. By applying a suitable resonant excitation pulse to the excitation coil, the macroscopic magnetization of the sample can be tilted from the z-direction of the constant magnetic field to the xy-plane.

[0006] Deflection magnetization M xy Then, it rotates about the z-axis at a Larmor frequency, inducing a measurable voltage in a receiving coil, which can be the same as the excitation coil. Due to the inhomogeneity in the B0 field, the macroscopically measurable voltage varies with a certain time constant (T2). * The decrease in magnetization is known as free-induction decay (FID). However, under certain constraints, the potential dephase of the magnetic moment of a single nucleus is reversible. If a 180° pulse is applied at time TE / 2, i.e., an excitation pulse chosen to rotate the magnetization by 180°, a so-called spin echo is generated at echo time TE, which can be measured by an electromagnetic pulse in the receiving coil.

[0007] A series of spin echoes are generated by the successive switching of multiple 180° pulses separated by TE, the amplitude of which decreases with time constant T2 due to spin-spin interactions. In parallel, equilibrium magnetization is re-established along the z-axis with characteristic time constant T1.

[0008] NMR has long been widely used in medical imaging and chemical structure analysis, but it usually requires a strong static magnetic field B0 in order to induce measurable magnetization.

[0009] For applications related to document security, so-called zero-field nuclear magnetic resonance techniques, such as nuclear quadrupole resonance (NQR) or nuclear magnetic resonance in ferromagnetism (NMR-FM), are of particular interest. This zero-field NMR technique does not require an external magnetic field B0; instead, the field is already present in the crystal due to inherent effects. This allows for a significant simplification of the measurement structure and also makes zero-field NMR materials attractive as security features in valuable documents such as banknotes, cards, passports, or stickers.

[0010] The publication mentioned, EP 2 778 705 A1, discloses a security mark for banknotes with zero-field NMR signatures, and a related handheld sensor device without an external magnetic field.

[0011] However, several difficulties must be overcome to reliably verify the authenticity of zero-field NMR safety features. Therefore, the signal-to-noise ratio (SNR) is a critical parameter for every zero-field NMR measurement and should be as large as possible. The so-called dead time τ describes a time constant such that the energy stored in the resonant circuit of the sensor decreases with the excitation pulse. The dead time can be related to the time constant T2. * The same order of magnitude suppresses the detection of the dense initial portion of free induction decay under long dead times. Furthermore, unwanted artifacts may appear, especially when determining the time constant, due to the influence of moving samples entering or leaving the sensor region; these artifacts must be minimized for reliable measurements. Finally, interference with the measured signal intensity that is unrelated to the feature set being examined must be kept as low as possible or completely avoided. Summary of the Invention

[0012] Therefore, the technical problem to be solved by the present invention is to provide a device that allows for simple and reliable authenticity checks on data carriers with zero-field NMR safety features.

[0013] This technical problem is solved by the features of the independent claim. The extended embodiments of the invention are the subject of the dependent claims.

[0014] According to the invention, such devices include one or more excitation coils for generating excitation pulses for zero-field NMR characteristics and an array of multiple receiving coils arranged independently of the excitation coils and at least partially adjacent to each other, the receiving coils being used for position-resolved detection of the signal response of the zero-field NMR characteristics.

[0015] The number N of the receiving coil array is greater than the number M of the excitation coils, and the area F covered by the excitation coils is... A At least partially, and especially completely, covering the area F covered by the receiving coils of the receiving coil array. E And it exceeds the area F E Size.

[0016] The area F covered by the excitation coil A It can exceed the area F covered by the receiving coil by more than 10%, more than 20%, or even more than 50%. E If it is stipulated that the planar data carrier be transported through the device for authenticity verification, then the area F covered by the excitation coil... A In addition to the area F covered by the receiving coil E In addition, it is advantageous to detect the area F covered in the direction of transport. E The area in front and / or behind.

[0017] The area covered by a surface coil or surface coil array corresponds, for example, to a region in which a significant magnetic field appears above the coil plane during operation, i.e., a magnetic field with a field strength exceeding 50% of the maximum value in space. Alternatively, the area covered by a surface coil or surface coil array can be defined by the envelope of its geometry, i.e., as, for example, as the minimum square area containing all the printed conductors of the coil / coil array.

[0018] The receiving coils of the receiving coil array are advantageously formed by surface coils, particularly in the form of conductor loops or helical coils. The excitation coils can also be formed by surface coils, particularly by conductor loops or helical coils.

[0019] In an advantageous design, the receiving coils of the receiving coil array each have a coil radius of 500 μm or less. This makes the device particularly well-suited for verifying the thickness of thin samples of approximately 100 μm. One or more excitation coils advantageously have significantly larger diameters, for example, approximately 5 mm.

[0020] The receiving coil array is advantageously formed as a one-dimensional or two-dimensional array. In particular, the receiving coil array can be formed as a linear (one-dimensional) N×1 array, or a rectangular n×m array, where N = n*m. However, the receiving coils can also be arranged at grid positions of other grid types (e.g., hexagonal grids), or can have an irregular arrangement. In an advantageous configuration, the number of receiving coils N is 2 to 10.

[0021] To better decouple them from each other, it can be specified that the receiving coils of the receiving coil array are arranged to overlap each other at least partially.

[0022] In a suitable design, the device contains only a single excitation coil.

[0023] In an advantageous design, the receiving coil array comprises two or more subarrays, each of which has receiving coils designed to receive at a fixed frequency. Preferably, the receiving coils of each subarray are arranged concentrically with each other. If the receiving coil array comprises multiple subarrays, it is advantageous to provide a corresponding number of excitation coils that correspond to the number of subarrays.

[0024] The subarrays advantageously have different receiving frequencies, which enables multi-spectral measurements. The resonant frequencies of the associated excitation coils advantageously correspond to the corresponding receiving frequencies of the subarrays.

[0025] The receiving coil and / or excitation coil are advantageously equipped with active decoupling devices for mutual decoupling.

[0026] Advantageously, the area F covered by the receiving coil is specified. E The size is consistent with the zero-field NMR feature to be examined, so that the covered area F E Covering the entire width or even the entire area of ​​zero-field NMR features.

[0027] In a preferred design, the receiving coil of the device is equipped with a directional coupler in the receiving circuit and / or the excitation coil is equipped with a directional coupler in the transmitting circuit, especially for compensating for interference effects such as amplifier drift or pulse defects.

[0028] According to an advantageous extension, the device includes an additional single calibration coil with a reference sample, the single calibration coil being arranged to at least partially overlap with the excitation field of one or more excitation coils.

[0029] The device may comprise two or more sub-arrangements of excitation coils and receiving coils, wherein each sub-arrangement contains a unique excitation coil and an associated, overlapping array of multiple receiving coils independent of the respective excitation coil. In the sub-arrangement, the area covered by the excitation coil (F...) A,i) is greater than the area covered by the receiving coils of the associated receiving coil array (F) E,i The sub-arrangements are preferably constructed identically to each other, that is, each sub-arrangement contains the same configuration consisting of an excitation coil and a receiving coil.

[0030] In one advantageous design, the device defines an inspection surface for the planar data carrier to be inspected, wherein the excitation coil and the receiving coil array of the receiving coil are arranged on the same side of the inspection surface.

[0031] In an alternative, equally advantageous design, the device defines an inspection surface for the planar data carrier to be inspected, wherein the excitation coil and the receiving coil of the receiving coil array are arranged at a small distance on opposite sides of the inspection surface.

[0032] The device is advantageously designed and configured for verifying the authenticity of nuclear quadrupole resonance (NQR) features or NMR features in ferromagnetism. Attached Figure Description

[0033] Other embodiments and advantages of the present invention are described below with reference to the accompanying drawings. For the sake of clarity, reproduction by size and scale has been omitted in the illustration.

[0034] In the attached diagram:

[0035] Figure 1 A schematic diagram of an inspection device for verifying the authenticity of banknotes according to the present invention is shown.

[0036] Figure 2 Two specific configurations of the sensor front end of the inspection device according to the present invention are shown in (a) and (b).

[0037] Figure 3 Examples (a) through (c) show some advantageous specific arrangements in the inspection device according to the invention, which have M excitation coils and an array of N receiving coils.

[0038] Figure 4 This demonstrates an application for verifying the integrity of banknotes with uniform, full-surface zero-field NMR features.

[0039] Figure 5 Static, position-resolved measurements of structured zero-field NMR features are shown, as well as

[0040] Figure 6 A schematic block diagram of the transmitting circuit and receiving circuit of the device according to the present invention is shown. Detailed Implementation

[0041] The invention will now be illustrated using the verification of the authenticity of banknote 10 as an example. (See references.) Figure 1 The banknote 10 to be inspected has a zero-field NMR feature, which may be a feature 12 occupying the entire area of ​​the banknote, or it may exist only in a specific feature region 14. The zero-field NMR feature may be an NQR feature or an NMR-FM feature.

[0042] To perform an authenticity check, the banknote sample 10 is guided along transport path 22 through an inspection device, which... Figure 1 The sensor front end 20 is shown only schematically. In order to generate excitation pulses for zero-field NMR features 12, 14, the sensor front end 20 includes a single excitation coil 30 and an array 40 consisting of multiple receiving coils 42 independent of the excitation coil 30, which allows the signal response of features 12, 14 to be detected in a position-resolved manner.

[0043] In this embodiment, the receiving coil 42 passes through a coil radius R of 500 μm. E A planar micro-coil is formed, thereby optimizing the inspection of thin banknote samples. The excitation coil 30 can, for example, have a coil radius R of 5 mm. A .

[0044] The figure also shows the area F covered by the excitation coil 30. A and the area F covered by the array 40 of the receiving coil 42 E The area F covered by the excitation coil 30 A This covers the area F covered by the array 40 of the receiving coil 42. E And especially in the entry and exit regions of sample 10, it significantly exceeds this area F. E Size.

[0045] The transmitting circuit of the excitation coil 30 and the receiving circuit of the receiving coil 42 are respectively equipped with directional couplers. Figure 6 This is to compensate for interference effects such as amplifier drift or defects in the transmit pulse. The receiving coil 42 and, if necessary, the excitation coil 30 are also equipped with active decoupling devices (not shown) for mutual decoupling, which may be based, for example, on PIN diodes, capacitor diodes, or high-frequency switches.

[0046] The inspection device according to the invention provides a number of particular advantages in the authenticity inspection of planar data carriers, which will now be described in detail.

[0047] The fundamental characteristic parameter of pulse NMR measurement is the signal-to-noise ratio (SNR), for which a proportional relationship between the fill factor η and the quality Q of the receiving coil applies:

[0048] SNR~η√Q

[0049] In the device according to the invention, the signal-to-noise ratio is optimized in particular by adjusting the fill factor η, which describes the ratio of the magnetic field energy present in the sample volume to the total magnetic field energy present in the space of the receiving coil.

[0050] The inventors have recognized that, in a thin sample having a thickness of approximately 100 μm, such as representing a banknote or other valuable document, by configuring the receiving coil 42 to have R E Surface coils with a coil radius of 500 μm or less can achieve a large fill factor η and therefore a high signal-to-noise ratio.

[0051] Therefore, in the inspection apparatus according to the invention, the array 40 of small receiving coils 42 provides a significantly better signal-to-noise ratio compared to a receiver composed of a larger single coil, in addition to the other advantages described, through this fill factor optimized in terms of the planar sample geometry of the banknote sample 10.

[0052] By dividing the sensor front end 20 into an excitation coil 30 and a separate receiving coil 42, the configuration according to the invention also allows for a reduction in the dead time τ. The dead time of the resonant circuit (here, the dead time of the receiving circuit) is given by the following formula having mass Q and resonant frequency ω:

[0053] τ=2Q / ω

[0054] Therefore, dead time can be reduced by decreasing the quality Q. However, this contradicts the equally desired high signal-to-noise ratio, which increases proportionally to √Q.

[0055] In the described device, these opposing requirements are considered through active decoupling of the excitation and receiving coils, which are separate from each other. For example, the resonant frequency ω of the receiving coil 42 can be shifted during the excitation pulse by means of a capacitor diode (varactor diode), so that the receiving coil circuit is not excited by the excitation pulse. The dead time τ of the receiving coil 42 is therefore a function of the dynamic behavior of the switch, and the receiver quality Q can be maximized independently of this.

[0056] Therefore, compared with the conventional structure that uses the same coil as both the transmitter and receiver, the structure according to the invention, which has separate coils 30 and 42 for the transmitter and receiver, achieves a reduced dead time and thus, in particular, higher measurement accuracy for free induction attenuation.

[0057] A particularly valuable advantage of using an array 40 consisting of receiving coils 42 is the achievable positional resolution of the signal response. The positional resolution of a single receiving coil 42, or the sensitive area of ​​the receiver coil 42 (i.e., in the present case, a single surface coil 42), in zero-field NMR is related to the coil radius R.E Inversely proportional. The small coil radius of 500 μm or less mentioned above therefore results in a correspondingly high position resolution, in which case the spatial resolution of the measurement point is, for example, less than 1 mm.

[0058] High positional resolution allows for the verification of security features of spatial coding (see...) Figure 5 However, high positional resolution is also advantageous when examining NMR features that are large and uniformly distributed, as it allows for verification of the integrity of sample 10 (see [reference]). Figure 4 ).

[0059] In order to measure the entire sample 10 in a position-resolved manner, an array 40 consisting of receiving coils 42 is designed such that the array can cover the entire sample. If... Figure 1 If the banknote sample 10 is transported through the inspection device 20 as described above, it may be sufficient to cover only the sample width with the receiving coil 42, since the entire sample is inspected within the operating time window. However, when using an array 40 consisting of receiving coils, spatial codes can also be identified and inspected in static measurements.

[0060] As described in more detail elsewhere, the receiving coils 42 can be advantageously overlapped to decouple from each other and equipped with low-impedance receiving amplifiers. Each receiving coil 42 is advantageously connected to an independent receiving branch.

[0061] Artifacts can occur when measuring moving samples, especially when determining time constants, due to the influence of the sample entering or leaving the sensitive area of ​​the sensor front end 20. In the proposed device, these motion artifacts are suppressed by a spatially uniform excitation field. (As shown from...) Figure 1 As can be seen from the diagram, the area F covered by the excitation coil 30 A Not only does it cover the area F covered by the receiving coil 42 of the receiving coil array E Furthermore, it covers the area of ​​the sample 10 that moves into or out of the sensitive receiving area during the measurement window.

[0062] exist Figure 1 The design scheme generates this uniform excitation field by using a single large excitation coil 30. Due to the separation of the transmitting and receiving coils according to the invention, it is possible to use only one or a few excitation coils, as there is no requirement for a fill factor for the excitation coils. Therefore, compared to conventional structures with coil arrays as the excitation source, Figure 1 The structure shown, with its unique large excitation coil 30, provides a significant advantage for the moving sample 10.

[0063] In the quantization of the measurement signal, the measured signal strength of the channel, i.e. the signal strength of a single receiving coil 42, is related to the feature set in the inspection features, but also depends on the strength and length of the excitation pulse and the characteristics of the receiving circuit.

[0064] To compensate for spatial variations in the excitation field, when the transmit power decreases or the receive amplification decreases, the excitation field amplitude is advantageously determined directly during continuous operation using the array 40 of the receiving coils 42. A compensation factor specific to the receiving coils can be calculated based on such measurements. The described configuration achieves this process because the excitation coil 30 and the receiving coil 42 are separate coils according to the invention.

[0065] Another possibility is to directly determine the coil's return loss and potential frequency drift, for example, using a directional coupler, so as to either determine a compensation factor, generate control signals for possible capacitor diodes for reverse control, or adjust the pulse length and amplitude of the excitation pulse. To compensate for temperature drift, a temperature sensor can be placed in the amplifier branch, or the actual amplification can be determined and adjusted using a sensing diode.

[0066] Furthermore, the receiving coil array can advantageously be equipped with an additional single calibration coil along with a static reference sample. Such a single calibration coil should not be located in the sample path 22; however, the sensitive region of the calibration coil must overlap with a portion of the excitation field. The signal strength measured in the calibration coil then allows compensation for interference effects on the strength measured at sample 10, such as temperature drift in the excitation branch.

[0067] In the case of an inspection device with a sensor front end constructed in this manner, a measurement time of less than 100 ms is sufficient for reliable authenticity verification of the sample, provided that the NMR characteristic material is suitable. Possible authenticity characteristics here include signal strength, relaxation time, spectral distribution of Larmor frequencies, i.e., the free induction decay (FID) or Fourier transform of the spin echo, and / or the spatial arrangement and formation of the characteristics.

[0068] Figure 2 Two specific possible configurations of the sensor front end are shown, in which different coils are exemplarily integrated into circuit board 50. Figure 2 (a) shows a configuration having a single excitation coil 30 and an array 40 consisting of nine receiving coils 42 arranged within the area covered by the excitation coil 30. The receiving coils 42 are integrated into the same circuit board 50 as the excitation coil 30, but may be constructed in a separate copper plane of the circuit board 50. The surface of the circuit board 50 defines an inspection surface 52 on which samples can be placed or transported short distances.

[0069] exist Figure 2 In the alternative configuration (b), in addition to the first circuit board 60 with an array 40 of nine receiving coils 42, the sensor front end also includes a barrier or clamping device 62 in a separate circuit board 64 that carries the excitation coil 30. Here, the nine receiving coils 42 are also arranged within the area of ​​the excitation coil 30 projected onto the plane of the receiving coils. The surface of the first circuit board 60 defines an inspection surface 66 on which the sample can be placed or transported short distances. Figure 2 (a) has the opposite configuration, in Figure 2 In configuration (b), the excitation coil 30 and the receiving coil 42 are not arranged on the same side of the inspection surface, but on opposite sides.

[0070] Figure 3 Some advantageous specific arrangements of an array of M excitation coils and N receiving coils in an inspection device according to the invention are shown. The coil configurations are shown in top views, wherein the excitation coils and receiving coils may be located in the same plane or in different planes, and in particular, as shown in… Figure 2 As shown in the figure, it is located on the same side or opposite side of the inspection surface used for the sample.

[0071] first, Figure 3 (a) shows in Figure 2 The coil configuration used in this design includes a single excitation coil 30 (M=1) and an array 40 consisting of nine receiving coils 42 (N=9) at the sensor front end. The receiving coils 42 are arranged within the area covered by the excitation coil 30 and cover an area smaller than that area.

[0072] Figure 3 (b) illustrates a coil configuration in which the receiving coil array 40 comprises two subarrays, each consisting of nine receiving coils 42-A and 42-B, respectively, each receiving coil adapted to its own resonant frequency ω. A or ω B The first subarray is formed by nine receiving coils 42-A, and the second subarray is formed by nine receiving coils 42-B. The corresponding receiving coils 42-A and 42-B of the two subarrays are arranged concentrically and electrically decoupled from each other. Multi-spectral measurements can thus be performed through appropriate wiring. Correspondingly, two excitation coils 30-A and 30-B are also provided in the transmitting circuit at the front end of the sensor, such that in this embodiment, M=2 and N=18. The receiving coils 42-A and 42-B are arranged within the area covered by the excitation coils 30-A and 30-B and cover an area smaller than that area.

[0073] Another coil configuration is in Figure 3As shown in (c). In this embodiment, the sensor front end comprises a 2×2 grid of sub-arrangements 70-1, 70-2, 70-3, 70-4, wherein each sub-arrangement 70-i has a unique excitation coil 30-i and an associated array 40-i consisting of receiving coils 44 independent of the excitation coil 30-i. Here, i = 1,...4, where, for clarity, only the excitation coil 30-1 and the array 40-1 are explicitly shown in the figure.

[0074] The receiving coils 44 of each array 40-i overlap each other to decouple them. As shown, in each sub-arrangement 70-i, the area F covered by the excitation coils 30-i is... A,i The area F is larger than that covered by the receiving coil 44 of the associated receiving coil array 40-i. E,i Correspondingly, the total area covered by the excited coil 30-i is also greater than the total area covered by the receiving coil 44.

[0075] In the preceding embodiments, the excitation coil and the receiving coil are exemplarily shown as conductor loops; however, it should be understood that the coils can also be designed in a helical or rectangular shape. Different coils can be arranged on the same or different copper planes of a circuit board, or on different circuit boards. In principle, the outer contour shape of the receiving coil array can also be arbitrary.

[0076] Figure 4 This demonstrates an application for verifying the integrity of banknotes with uniform, full-surface zero-field NMR features 88. (Reference) Figure 4 (a) The sample 80 moves along the transport direction 82 past the sensor front end 90, which includes a linear array 94 of a single excitation coil 92 and nine receiving coils 96. In the example shown, the sample 80 represents a tampered banknote, wherein the area on the right edge of the banknote has been cut off and replaced with plain paper 84 without NMR characteristics.

[0077] From Figure 4 The measurement data from the sensor front end 90 shown in (b) immediately reveals any tampering. Here are the measurement curves 98-O, 98-M, and 98-U for the three measurement tracks 86-O, 86-M, and 86-U in the upper, middle, and lower parts of the sample 80. Figure 4 The measurement curve has been detected by three correspondingly arranged receiving coils 96-O, 96-M and 96-U at the front end of the sensor 90.

[0078] For clarity, measurement curves 98-O, 98-M, and 98-U are shown as vertically offset from each other by a constant value, and the relative signal intensity Sig is shown, depending on the position x of signal detection along the corresponding measurement tracks 86-O, 86-M, and 86-U on the sample. Due to the signal drop in measurement curve 98-M of the intermediate receiving coil 96-M, a local absence of NMR features in region 84 of sample 80 can be immediately inferred, and thus, banknote tampering can be deduced.

[0079] Figure 5 Static, position-resolved measurements of structured zero-field NMR features are shown. Figure 5 (a) For this purpose, a card-shaped data carrier 100 with a printed block 102 containing features is shown. The printed block is in the form of a rhombus with a central blank 104. The data carrier 100 is placed on the inspection surface of an inspection device according to the invention, the sensor front end 110 of which contains a 10×10 array 112 of a single excitation coil and a receiving coil 114. For clarity, only the array 112 with the receiving coil 114 indicated by the ring is shown in the figure.

[0080] Figure 5 (b) shows the position-resolved results 120 of static measurements of signal strength in the region of printed block 102, wherein, in each measurement field 122, the signal strength detected by the associated receiving coil 114 after excitation is represented by the intensity of the shaded line. High position resolution can be achieved through miniaturization of the receiving coil 114, thereby making it easy to identify the shape of printed block 102, including its rhomboid orientation and the presence of the central blank 104. Therefore, various possibilities for encoding printed block 102 can be derived by modifying the print design.

[0081] Figure 6 A block diagram of the transmitting circuit 132 and receiving circuit 134 of the device 130 according to the invention is shown schematically. The entire circuit can be controlled by means of a microcontroller or FPGA 136. The single transmitting circuit includes a frequency source that is synchronized with the Larmor frequency during operation, a phase shifter for setting the correct pulse phase, and a pulse switch. Next is an adjustable power amplifier for setting the pulse amplitude. After the amplifier, for example, two directional couplers with associated detector diodes P1 and P2 are connected. Detector diode P1 determines the power supplied to the corresponding excitation coil, and detector diode P2 determines the power reflected by the excitation coil. The excitation coil itself enters resonance, for example, by means of a varactor diode.

[0082] In addition to NMR measurements, this circuit can be used to perform a frequency source sweep, and thus determine the frequency dependence of the return loss (RL) of the excitation coil using detectors P1 and P2. Based on this measurement, the resonant frequency of the excitation coil can be determined, and this resonant frequency can be matched to the Larmor frequency using a varactor diode. Furthermore, the quality Q of the excitation coil can be determined based on the return loss.

[0083] To generate a pulse with a defined pulse angle, that is, an angle defined by the nuclear spin deflection of the sample, the pulse length τ can be used as a parameter. Conversely, the field strength of the excitation field generated at the excitation coil is the sum of the mass Q and the power P in the coil. Spule The latter's power can be calculated, for example, using the power and RL determined in detector P1. Given the mass Q and the power P... Spule In this case, the pulse length can be flexibly adjusted according to the calibration table stored in the controller 136 or according to the analytical relationship, and thus the measurement results are stabilized. Alternatively, it is also conceivable to determine the excitation field channel-specifically using the receiver circuit.

[0084] Each in Figure 6 The receiver circuit 134 shown consists of an NMR coil, a receiver coil that has been brought into resonance by means of a varactor diode, a configurable low-noise amplifier, and a directional coupler with a detector diode P3. Finally, there is a bandpass filter, an IQ demodulator with an associated local oscillator (LO), and an A / D converter.

[0085] To avoid receiver circuit saturation, the receiver circuit is switched to resonance only during the measurement window using a varactor diode. If frequency scanning is performed in the transmitting circuit, the frequency correlation of the return loss of the receiving coil can be measured using diodes P1, P2, and P3. Here, for example, the measurement data of diodes P1 and P2 are used to calculate the characteristics of the transmitting circuit based on the frequency correlation measured using diode P3. The resonant frequency and quality Q of the receiving coil can then be determined from the measured curve. The value of the resonant frequency can then be used as an input parameter for adjusting the varactor diode, and the quality Q can be used to correct the signal amplitude.

[0086] List of reference numerals

[0087] 10 banknotes

[0088] 12, 14 Zero-field NMR characteristics

[0089] 20 Sensor front end

[0090] 22 Transportation routes

[0091] Excitation coils 30, 30-A, 30-B, 30-i

[0092] 40, 40-i array

[0093] 42, 42-A, 42-B receiving coils

[0094] 44 Receiving coil

[0095] 50 circuit boards

[0096] 52 Inspection Surface

[0097] 60 First Circuit Board

[0098] 62 Barrier or clamping device

[0099] 64 separate circuit boards

[0100] 66 Inspection Surfaces

[0101] Sub-arrangements 70-1, 70-2, 70-3, 70-4

[0102] 80 samples

[0103] 82. Transportation Direction

[0104] 84 Areas with ordinary paper

[0105] 86-O, 86-M, 86-U measuring tracks

[0106] 88 Zero-field NMR characteristics

[0107] 90 Sensor front end

[0108] 92 Excitation Coil

[0109] 94 Linear Arrays

[0110] 96, 96-O, 96-M, 96-U receiving coils

[0111] Measurement curves for 98-O, 98-M, and 98-U

[0112] 100-card-shaped data carrier

[0113] 102 Printed blocks containing features

[0114] 104. Middle blank area

[0115] 110 Sensor front end

[0116] 112 array

[0117] 114 Receiving Coil

[0118] 120 Measurement Results

[0119] 122 Measurement Field

[0120] 130 equipment

[0121] 132 Transmitting Circuit

[0122] 134 Receiver Circuit

[0123] 136 microcontroller / FPGA

Claims

1. An apparatus for verifying the authenticity of a planar data carrier exhibiting zero-field nuclear magnetic resonance (NMR) characteristics, said apparatus having - One or more excitation coils, said excitation coils being used to generate excitation pulses for said zero-field NMR characteristics, - An array of multiple receiving coils, the receiving coils being independent of the excitation coils and arranged at least partially adjacent to each other, the receiving coils being used for position-resolved detection of the signal response of the zero-field NMR feature, wherein... - The number of receiving coils (N) in the receiving coil array is greater than the number of excitation coils (M), and - The area covered by the excitation coil ( ) at least partially covers the area covered by the receiving coils of the receiving coil array. And it exceeds the area covered by the receiving coils of the receiving coil array. The size of ) Each receiving coil is connected to an independent receiving branch.

2. The device according to claim 1, characterized in that, The receiving coils of the receiving coil array are formed by surface coils.

3. The device according to claim 2, characterized in that, The surface coil is a surface coil in the form of a conductor circuit or a helical coil.

4. The device according to any one of claims 1 to 3, characterized in that, The receiving coils of the receiving coil array each have a coil radius of 500 μm or less.

5. The device according to any one of claims 1 to 3, characterized in that, The receiving coil array forms a one-dimensional or two-dimensional array.

6. The device according to any one of claims 1 to 3, characterized in that, The receiving coils of the receiving coil array are arranged to overlap each other at least partially.

7. The device according to any one of claims 1 to 3, characterized in that, The receiving coil array comprises two or more subarrays, each of which has a receiving coil designed to receive at a fixed frequency, wherein the receiving coils of the two or more subarrays are arranged concentrically with each other.

8. The device according to any one of claims 1 to 3, characterized in that, The receiving frequencies of the subarrays are different.

9. The device according to any one of claims 1 to 3, characterized in that, The receiving coil and / or the excitation coil are respectively equipped with active decoupling devices for mutual decoupling.

10. The device according to any one of claims 1 to 3, characterized in that, The area covered by the receiving coil ( The size of the zero-field NMR feature being examined is consistent with that of the area covered ( It covers the entire width or even the entire area of ​​the zero-field NMR feature.

11. The device according to any one of claims 1 to 3, characterized in that, The receiving coil of the device is equipped with a directional coupler in the receiving circuit and / or the excitation coil is equipped with a directional coupler in the transmitting circuit.

12. The device according to any one of claims 1 to 3, characterized in that, The device includes an additional single calibration coil with a reference sample, the single calibration coil being arranged to at least partially overlap with the excitation field of the one or more excitation coils.

13. The device according to any one of claims 1 to 3, characterized in that, The device comprises two or more sub-arrangements of the excitation coil and the receiving coil, wherein each sub-arrangement comprises a unique excitation coil and an associated overlapping array, the array consisting of a plurality of receiving coils independent of the respective excitation coil, and wherein, in the sub-arrangement, the area covered by the excitation coil ( () is greater than the area covered by the receiving coils of the associated receiving coil array. ).

14. The device according to any one of claims 1 to 3, characterized in that, The device defines an inspection surface for the planar data carrier to be inspected, and the excitation coil and the receiving coil of the receiving coil array are arranged on the same side of the inspection surface.

15. The device according to any one of claims 1 to 3, characterized in that, The device defines an inspection surface for the planar data carrier to be inspected, and the excitation coil and the receiving coil of the receiving coil array are arranged at a small distance on opposite sides of the inspection surface.

16. The device according to any one of claims 1 to 3, characterized in that, The device is designed and configured to perform authenticity checks on nuclear quadrupole resonance (NQR) features or NMR features in ferromagnetism.

Images