SENSOR FOR A NUCLEAR RESONANCE DEVICE

Description

[0001] The invention relates to a sensor for a nuclear magnetic resonance device having a magnetic field generating device comprising a planar magnet arrangement and a measuring device. The invention further comprises a nuclear magnetic resonance device having at least one such sensor.

[0002] Magnetic field generating devices with a planar magnet arrangement are already known, for example from WO 2006 / 061618 A1, US 2010 / 244828 A1, DE 10 2014 218375 A1 and DE 20 2006 002074 U1.

[0003] Ashvin Bashyam et al, Proc. ISMRM, 2676, 2017, XP40690244, discloses a single-sided NMR device for portable diagnosis of disorder in liquids.

[0004] Nuclear magnetic resonance (NMR) is used in various technical applications to measure material properties. The measurement principle is based on a physical effect in which the material sample under investigation is exposed to external magnetic fields, and the change in the magnetization of the atomic nuclei within the material sample is measured in response to the external magnetic fields. Specifically, the atomic nuclei in the material sample are first aligned using a first magnetic field (B0 field). In this arrangement, the nuclear spins of the atomic nuclei are in resonance with the first magnetic field, with the spins of the atomic nuclei precessing around the magnetic field lines at the so-called Larmor frequency (Larmor precession).If the material sample is subsequently exposed to a second magnetic field (B1 field) that is orthogonal to the first magnetic field, the atomic nuclei in the first nuclear spin state can change the orientation of their spin by absorbing energy from the second magnetic field. If the second magnetic field is switched off again, while the material sample remains exposed to the first magnetic field, the atomic nuclei with the previously deflected nuclear spins enter an excited nuclear spin state. From this excited state, they return in a relaxation process to the lower-energy first nuclear spin state, in which their nuclear spins are aligned with the

[0005] Magnetic field lines of the first magnetic field are aligned. The relaxation process occurs with the emission of electromagnetic radiation, which is noticeable as a change in the magnetic field. This change in the magnetic field can be recorded as a response signal using a suitable detection or measuring device in the form of an antenna or coil. With a suitable choice of the operating parameters of the nuclear magnetic resonance device, the relaxation times of the nuclear spins and thus the amount or concentration of certain atoms in the material sample can be determined by evaluating the amplitude and the temporal course of the response signal. Since hydrogen atoms in particular can be detected using nuclear magnetic resonance, this measurement method is ideally suited for determining the amount or distribution of water in the material sample.

[0006] In particular, a static magnetic field with defined properties is used as the first magnetic field and an alternating electromagnetic field, such as a pulsed magnetic field, is used as the second magnetic field.

[0007] To achieve optimal nuclear magnetic resonance measurements, particularly precise and homogeneous magnetic fields are required in the volume or slice to be measured. In particular, the orthogonality of the magnetic fields within the useful volume must be ensured. For this reason, nuclear magnetic resonance devices are typically designed in the form of a closed cylinder. This design limits the use of the device, as only those material samples that fit within the cylinder can be measured.

[0008] The object of the invention is therefore to provide a method for measuring larger or flat material samples using nuclear magnetic resonance. This object is achieved by a sensor according to claim 1 and by a nuclear magnetic resonance device according to claim 18.

[0009] Further advantageous embodiments are specified in the dependent claims.

[0010] According to the invention, a sensor for a nuclear magnetic resonance device for determining at least one material property of a material sample arranged in a useful volume is provided according to claim 1. The nuclear magnetic resonance device comprises a magnetic field generating device comprising a planar magnet arrangement for generating a static magnetic field in the useful volume, wherein the planar magnet arrangement has, on a front side facing the useful volume, a plurality of magnetic poles arranged next to one another along a first extension direction of the planar magnet arrangement, each with an alternating orientation. The nuclear magnetic resonance device further comprises a measuring device for measuring a response signal based on nuclear magnetic resonance of the material sample arranged in the useful volume, comprising an electrical coil with at least one winding for generating an alternating magnetic field in the useful volume.The winding is arranged between two directly adjacent magnetic poles of the planar magnet arrangement, so that the alternating magnetic field of the electric coil overlaps the static magnetic field of the planar magnet arrangement essentially orthogonally in the useful volume. Due to the special arrangement of the magnetic poles of the two magnetic fields, with the magnetic poles of the alternating magnetic field each offset from the magnetic poles of the static magnetic field, an orthogonality between the field lines of the static magnetic field and the field lines of the alternating magnetic field automatically arises in the useful volume with a suitable choice of operating parameters. This defines a useful volume extending parallel to the nuclear magnetic resonance sensor, in which sufficiently good conditions exist for an NMR measurement. The useful volume is located outside the nuclear magnetic resonance device.Furthermore, the sensor has a flat design due to the planar magnet arrangement. Since such a sensor does not enclose the material sample, the size of the material sample to be measured is not limited. In particular, such a sensor can also be used to measure flat objects, such as a house wall. Due to its flat design, the sensor can also be designed as a portable device, for example, in the form of a handheld device.

[0011] Furthermore, the sensor is particularly compact due to its flat design.

[0012] This results in an extremely favorable ratio of sensor size to usable NMR-sensitive volume. The compactness also makes the sensor, or a nuclear magnetic resonance device equipped with such a sensor, easy to transport.

[0013] According to the invention, the planar magnet arrangement comprises a plurality of adjacent magnet segments along the first direction of extent and along a second direction of extent, which runs perpendicular to the first direction of extent, each with magnetization directions oriented orthogonally to the second direction of extent of the planar magnet arrangement. The magnet segments, which are arranged directly adjacent to one another along the first direction of extent of the planar magnet arrangement, each have magnetization directions rotated relative to one another, whereby a significantly stronger static magnetic field is generated on the front side of the planar magnet arrangement than on the back side of the planar magnet arrangement.By varying the magnetization directions of immediately adjacent magnet segments, the magnetic flux of the static magnetic field can be concentrated essentially on the front side of the planar magnet arrangement. This arrangement, which can be implemented, for example, in the form of a planar or rolled-up Halbach array, enables a significant increase in the field strength of the static magnetic field within the usable volume. The necessary high field strength can be achieved with relatively simple magnets, such as standard magnets.

[0014] This arrangement also allows for a particularly flexible design of the sensor, whereby the number of magnetic poles and their position along the first extension direction of the planar magnet arrangement can be adapted to the respective requirements.

[0015] In a further embodiment, magnet segments arranged directly adjacent to one another along the first extension direction of the planar magnet arrangement each have magnetization directions rotated by 45° relative to one another. This results in a relatively simple structure that allows for a sufficiently high concentration of the static magnetic field on the front side of the magnet arrangement. At the same time, compared to a magnet arrangement with magnet segments rotated by 90° relative to one another, a significantly finer gradation of the magnetic field and thus a more homogeneous field distribution in the usable volume can be achieved.

[0016] In a further embodiment, four magnetic poles, each with alternating orientations, are formed on the front side of the planar magnet arrangement. The electrical coil of the measuring device comprises three adjacent windings, each of whose magnetic poles is arranged between two immediately adjacent magnetic poles of the planar magnet arrangement. This design represents an optimized arrangement, with the aid of which a sufficiently homogeneous magnetic field can be generated in the usable volume. Furthermore, it allows for the realization of a relatively compact sensor module.

[0017] In a further embodiment, the electrical coil is further configured to measure a signal based on nuclear magnetic resonance of the material sample arranged in the usable volume. This simplifies the setup, as separate coils for excitation and detection are not required. However, separate coils for excitation and detection can also be used.

[0018] In a further embodiment, the electrical coil is arranged on the front side of the planar magnet arrangement. This increases the sensitivity of the electrical coil, particularly when detecting the response signal.

[0019] In a further embodiment, the electrical coil is designed in the form of a structured, electrically conductive layer. This enables a particularly flat design of the electrical coil, and thus of the entire sensor. The electrical coil can be produced, for example, using a photolithographic process, which enables particularly high precision.

[0020] In a further embodiment, at least one shim coil is formed in the electrically conductive layer to homogenize the static magnetic field generated by the planar magnet arrangement in the usable volume. Such shim coils enable particularly precise magnetic fields. The integration of the shim coil into the electrically conductive layer, however, enables a particularly flat design.

[0021] According to the invention, the electrical coil is designed as a multi-resonant coil. Using the multi-resonant coil, alternating fields with different frequencies can be generated or detected. Furthermore, the multi-resonant coil also makes it possible to measure different slices simultaneously, with the differentiation between the individual slices being achieved using a field-dependent contrast.

[0022] In a further embodiment, an inner shielding structure made of an electrically conductive material with high magnetic permeability is arranged between the electrical coil and the planar magnet arrangement. This inner shielding structure serves as a shield for the magnet segments against the alternating magnetic field of the electrical coil. The inner shielding structure can be used to shield the alternating magnetic field generated by the electrical coil in the area of ​​the permanent magnets. This prevents mechanical forces acting on the permanent magnets due to the alternating magnetic or electromagnetic field. Since such mechanical forces can distort the measurement signal, this measure can be used to increase the measurement accuracy of the sensor.

[0023] In a further embodiment, an outer shielding structure made of an electrically conductive material with high magnetic permeability is arranged between the electrical coil and the usable volume, which serves as a shield for the electrical coil against electromagnetic interference fields. The outer shielding structure prevents unwanted electromagnetic influences on the magnetic coil. This increases measurement accuracy. Using a material with high magnetic permeability can prevent unwanted attenuation of the static magnetic field in the usable volume.

[0024] In a further embodiment, the outer shielding structure comprises resonance structures that serve to specifically shield against electromagnetic interference fields with frequencies in the range of the mains frequency. Such resonance structures can be used to create a shielding structure that only shields interference signals of specific frequencies. This is particularly necessary for frequencies in the range of the mains frequency, as such interference fields frequently occur in technical applications. Thus, targeted shielding of mains frequencies can significantly increase measurement accuracy.

[0025] In a further embodiment, the magnetic field generating device comprises a carrier plate made of a non-magnetic material, wherein the magnet segments are inserted into at least one opening in the carrier plate. This arrangement enables a particularly simple and cost-effective design. The individual magnet segments can be installed and removed relatively easily. This makes it possible to remove the magnet segments from the carrier plate, for example, for transport. Furthermore, the static magnetic field can be dampened by rotating or swapping the magnet segments within the carrier plate for transport or storage of the sensor. Furthermore, the magnet segments can also be replaced individually, which makes it possible to adapt the static magnetic field to the respective application.

[0026] In a further embodiment, at least some of the magnet segments of the magnet arrangement are rotatable within the carrier plate. This makes it possible to adapt the static magnetic field to the respective specifications by rotating the individual magnet segments. In particular, by appropriately rotating certain magnet segments, the static magnetic field in the usable volume can be reduced, which is particularly advantageous for the storage and transport of the nuclear magnetic resonance device.

[0027] In a further embodiment, the magnetic field generating device is modularly expandable by arranging several support plates side by side in at least one of the two extension directions of the planar magnet arrangement. This modular design allows for flexible adjustment of the sensor size along both extension directions. Thus, even larger objects can be measured.

[0028] In a further embodiment, magnet segments in an edge region of the planar magnet arrangement are designed to generate a static magnetic field with a higher magnetic field strength than magnet segments in a central region of the planar magnet arrangement. This counteracts a weakening of the magnetic field strength, which typically occurs in the edge regions of the magnet arrangement. By compensating for field inhomogeneities toward the edge, a homogeneous field strength can be achieved across the entire usable volume.

[0029] In a further embodiment, the higher magnetic field strength in the edge region of the planar magnet arrangement is achieved by magnet segments that have a higher magnetization and / or a larger vertical extent than magnet segments in the central region of the planar magnet arrangement. By using magnet segments with a higher magnetization in the edge region of the magnet arrangement, a particularly flat design of the sensor can be achieved. Conversely, when using magnet segments with a larger vertical extent, magnet segments with the maximum magnetization can also be used in the central region of the magnet arrangement. This makes it possible to achieve a significantly higher field strength overall across the entire usable volume.

[0030] In a further embodiment, several superimposed magnet segments are provided in the edge region of the planar magnet arrangement to achieve the higher magnetic field strength. With this arrangement, field strength compensation in the edge region of the planar magnet arrangement can be achieved using standard magnets. This allows the magnetic field generation device to be constructed particularly simply and cost-effectively.

[0031] In a further embodiment, at least some of the magnet segments of the planar magnet arrangement are coated with a plastic material. By carefully selecting the thickness of the plastic coating on each side of the magnet segment, the position of each magnet segment within the planar magnet arrangement can be defined. Particularly when multiple magnet segments are arranged within an opening in the carrier plate, the thickness of the plastic coating can be used to precisely adjust the distance between the individual magnet segments. Furthermore, the plastic coating enables better handling of the magnet segments during installation, removal, and transport of the sensor.

[0032] Furthermore, a nuclear magnetic resonance device according to the invention comprising a corresponding sensor is provided. The nuclear magnetic resonance device is designed to determine at least one material property of a material sample arranged in a useful volume for several measurement slices independently of one another.

[0033] In one embodiment, the magnetic resonance device comprises a lifting device for adjusting the distance between the sensor and a material sample arranged in the usable volume. The lifting device comprises at least one electrically and / or manually driven actuator. With the aid of such a lifting device, depth-dependent measured values ​​can be easily generated. This allows a precise depth profile of the measured material sample to be created.

[0034] In a further embodiment, the actuator comprises a first actuator part carrying the sensor and a second actuator part movably arranged thereto, with a support surface for placement on a support surface arranged stationary relative to the material sample. This achieves a particularly simple design.

[0035] In a further embodiment, the first actuator part is designed in the form of an electric motor, while the second actuator part is designed in the form of a spindle driven by the electric motor. Such a spindle drive allows for particularly precise adjustment of the sensor height.

[0036] In a further embodiment, the lifting device comprises several actuators distributed along the circumference of the sensor. This enables particularly stable and precise height adjustment.

[0037] The invention is described in more detail below with reference to the figures. These show: Fig. 1 a sensor for a nuclear magnetic resonance device comprising a magnetic field generating device with a planar magnet arrangement and a measuring device in a schematic cross-sectional representation; Fig. 2 a plan view of the magnetic field generating device of the sensor with the planar magnet arrangement of Figure 1 ; Fig. 3 a schematic side view of the planar magnet arrangement with eleven adjacent magnet segments, each with magnetization directions rotated by 45°; Fig. 4 a side view of a planar magnet arrangement with a magnetic field arranged substantially on the front side; Fig. 5 a schematic plan view of the planar magnet arrangement with four magnetic poles and an electrical coil comprising three windings; Fig. 6a plan view of an electrical coil with three developments produced by structuring an electrically conductive layer; Fig. 7 a side view of the planar magnet arrangement from Figure 4 and the electrical coil formed in the electrically conductive layer to illustrate the alternating magnetic field generated by the electrical coil; Fig. 8 a side view of the planar magnet arrangement from Figure 4 and the electric coil Figure 7 to illustrate the superposition of the magnetic fields generated by the planar magnet arrangement and the electric coil; Fig. 9 a plan view of a sensor with a planar magnet arrangement having three adjacent magnetic poles and an electrical coil having two adjacent windings; Fig. 10a plan view of a sensor with a planar magnet arrangement having four adjacent magnetic poles and an electrical coil having three adjacent windings; Fig. 11 schematically shows a plan view of a planar magnet arrangement comprising separate magnet segments arranged in the form of an 11x11 matrix; Fig. 12 schematically a top view of a planar magnet arrangement comprising a total of eleven prism-shaped magnet segments; Fig. 13 schematically a side view of a planar magnet arrangement comprising a magnet segment extending over the entire width, which has regions with differently oriented magnetization; Fig. 14 schematically a cross-sectional view through a planar magnet arrangement with carrier plates with magnet segments arranged one above the other in two planes; Fig. 15schematically a top view of the lower support plate to illustrate the special arrangement of the magnet segments in the lower support plate; and Fig. 16 schematically a side view of a nuclear magnetic resonance device comprising a sensor and a lifting device for adjusting the distance between the sensor and a material sample arranged in the useful volume.

[0038] The inventive nuclear magnetic resonance sensor is characterized by a flat design, which allows for an open-ended measuring system that can be expanded as required by connecting several sensors in series. The flat design of the sensor is achieved by a special arrangement of permanent magnets for generating a B0 field and a special arrangement of at least one electrical coil for generating a B1 field. The Figure 1schematically a cross section through such a nuclear magnetic resonance sensor 100. The sensor 100 comprises a magnetic field generating device 101 for generating a static magnetic field (B0 field) in a useful volume and a measuring device 102 arranged between the magnetic field generating device 101 and the useful volume 200 for generating an excitation signal (B1 field) in the useful volume 200 and for measuring the subsequent response signal.

[0039] The magnetic field generating device 101 comprises a planar arrangement 120 of a plurality of magnet segments 121 1 , 121 2 , 121 3 arranged next to one another in a plane. These are permanent magnets which, in the present exemplary embodiment, are cube-shaped or cuboid-shaped and thus have square cross-sections. In principle, however, the magnet segments 121 1 , 121 2 , 121 3 can also have other suitable shapes, for example cylindrical or round. The magnetic field generating device 101 further comprises a carrier plate 110 which serves as a matrix for receiving the magnet segments 121 1 , 121 2 , 121 3 . For this purpose, the carrier plate 110 has a plurality of openings 111, in each of which a magnet segment 121 1 , 121 2 , 121 3 is arranged. The openings 111 define the position and alignment of the magnet segments 121 1 , 121 2 , 121 3 to one another.Alternatively, it is also possible to arrange multiple magnet segments within a common opening. In this case, the position and alignment of the magnet segments relative to one another can be determined by suitable spacer structures arranged between the magnet segments. If the magnet segments have a plastic coating, the mutual spacing of the magnet segments within the magnet arrangement can also be determined by the thickness of the plastic coating. It is also possible to arrange the magnet segments directly next to one another without any spacing.

[0040] The special arrangement of the magnet segments within the magnet arrangement 120 generates a magnetic field with defined properties within a specific spatial area 200, which in the Figure 1is arranged directly above the sensor 100. The spatial region 200 defines a useful volume characterized by particularly high NMR sensitivity. In particular, the magnetic fields generated by the sensor 100 exhibit particularly high homogeneity in the useful volume 200 with a suitable selection of the operating parameters.

[0041] As the Figure 1As further shown, the measuring device 102 is designed in the form of a layer stack comprising several layers 161, 162, 163, 164, 165, 166, 167, 168. The layer stack comprises an electrically conductive layer 164, which is preferably arranged on a carrier substrate 165, preferably a printed circuit board, such as a PCB. The electrically conductive layer 164 contains an electrical coil 140 with one or more adjacently arranged turns (not shown here). The electrical coil 140, which in the present exemplary embodiment was produced by structuring the electrically conductive layer 164, forms an essential component of the measuring device 102.During operation of the sensor 100, the electrical coil 140 generates an alternating magnetic field (B1 field), which is essentially orthogonally superimposed on the magnetic field of the planar magnet arrangement 120 in the useful volume 200 and serves as an excitation signal for the nuclear magnetic resonance measurement. The electrical coil 140 preferably also simultaneously forms an antenna for detecting the response signal following the excitation signal. A pulsed magnetic field, for example, can serve as the alternating field 150. Depending on the application, however, other time-varying electromagnetic fields can also be used as the excitation signal (B1 field).

[0042] In addition to the electrical coil 140, the electrically conductive layer 164 can also contain at least one further electrical coil, in particular a shim coil, for correcting the alternating magnetic field generated by the electrical coil 140. Furthermore, other passive and active components can also be arranged on the carrier substrate 165, preferably in the edge regions.

[0043] To prevent the measurement from being undesirably influenced by external alternating electromagnetic fields, the measuring device 102 may further comprise an external shielding structure. The shielding structure may have special structures that serve as resonance structures for filtering out electromagnetic radiation of certain frequencies, such as the mains frequency (50 Hz). Figure 1The outer shielding structure is in the form of a structured metallic layer 161, which consists, for example, of copper or another non-magnetic metal. The outer shielding structure 161 is arranged on its own carrier substrate 162. The carrier substrate 162 can, for example, be in the form of a circuit board and have a relatively small layer thickness, for example 1 mm. In order to adjust the distance between the electrical coil 140 and the outer shielding structure 161, a first separating layer 163 with a defined layer thickness is further provided between the electrically conductive layer 164 and the carrier substrate 162. The layer thickness is far preferably a few millimeters, for example 2 mm. Any suitable non-magnetic material can be used as the material for the first separating layer 163, for example an acrylic plate.

[0044] The measuring device 102 may further comprise an internal shielding structure that shields the magnet segments of the planar magnet arrangement 120 from the alternating magnetic field of the electrical coil 140. Such an internal shielding structure can prevent mechanical forces acting on the magnet segments due to the alternating magnetic field of the electrical coil 140, which could cause a falsification of the measurement signal. Figure 1The inner shielding structure is designed in the form of a thin metallic layer 168 arranged between the electrical coil 140 and the magnet segments of the magnet arrangement 120. Copper or another non-magnetic metal, for example, can be used as a material for the inner shielding structure 168. The inner shielding structure 168 can be arranged on a separate substrate layer 167, which preferably has a small layer thickness, for example 1 mm. The substrate layer 167 can be made of any suitable material, in particular a non-magnetic material, such as cardboard or laminated paper. Furthermore, a second separating layer 166 can be provided between the two electrically conductive layers 164, 168, with the aid of which separating layer 166 the exact distance between the electrical coil 140 and the inner shielding structure 168 can be determined.The thickness of this separating layer 166 is preferably a few millimeters, for example, 2 mm. The separating layer 166 can be formed from any suitable material, for example, a non-magnetic material.

[0045] The Figure 1 The measuring device 102 shown comprises a total of eight layers 161-168. In principle, however, it is possible to reduce the number of layers and thus the necessary manufacturing steps by combining the substrate and separating layers. For example, the substrate layer 162 and the separating layer 163 can be formed as a single layer. The separating layer 166 can also form a single layer with the substrate layer 165 and / or with the substrate layer 167 (not shown here).

[0046] Due to the layered structure and the small layer thicknesses of the layers 161 - 168, the measuring device 102 has a relatively small overall height, for example 10 mm.

[0047] To establish a defined distance between the planar magnet arrangement 120 and the measuring device 102, an additional separating layer 170 can be provided between the two components. The separating layer 71 preferably consists of a non-magnetic material, such as an acrylic plate. In the present embodiment, the acrylic plate 170 has recesses that accommodate the portions of the magnet segments 121 1 , 121 2 , 121 3 that protrude from the carrier plate 110.

[0048] According to the invention, the planar magnet arrangement 120 comprises a plurality of magnet segments arranged next to one another in a plane, the number and spatial arrangement of which can vary depending on the respective application. Figure 2shows, by way of example, a plan view of a planar magnet arrangement 120 extending in the XY plane with a total of 121 magnet segments 121 1,1 - 121 11,11 arranged within the carrier plate 110. The magnet segments 121 1,1 - 121 11,11 are preferably evenly distributed over the carrier plate 110 and, in the present exemplary embodiment, form an 11x11 matrix with 11 rows and 11 columns. The magnet segments 121 1,j - 121 11,j (where j=1, 2, 3, ...11) arranged directly adjacent to one another in the first extension direction X of the magnet arrangement 120 each have different magnetization directions, resulting in a magnetic field with multiple magnetic poles that is concentrated essentially on the front side 103 of the planar magnet arrangement. In contrast, the magnet segments 121 i,1 - 121 i,11 (with i = 1, 2, 3, ...) arranged side by side along a second extension direction Y of the planar magnet arrangement 120 have11) of a column, according to the invention, have the same magnetization direction. In the present embodiment, the planar magnet arrangement 120 has a total of four magnetic poles 131, 132, 133, 134, each with alternating magnetic field directions, which are arranged in the . Figure 2 are indicated by dashed lines.

[0049] To illustrate, the Figure 3 a cross section through the planar magnet arrangement 120 from the Figure 2along the line 105, wherein the orientations of the magnetization of the magnet segments are shown by corresponding arrows. Here, it can be seen that the magnetization directions of immediately adjacent magnet segments 121 1.5 - 121 11.5 are each rotated by a certain angle to each other. By rotating the orientation of the magnetization of adjacent magnet segments, a special magnet arrangement is achieved, which essentially corresponds to a Halbach array. Such a configuration of permanent magnets allows the magnetic flux on a first side of the magnet arrangement to almost cancel out, while it is amplified on the second side opposite the first side. Thus, the magnetic field 130, which in the Figure 3is indicated schematically by means of the field lines, is mainly concentrated on the front side 103 of the planar magnet arrangement 120 facing the useful volume 200, while it is relatively weak on the back side 104 of the planar magnet arrangement 120.

[0050] In the present embodiment, the angle of rotation for the magnet segments 121 2.5 - 121 10.5 is 45° each. Only the two magnet segments 121 1.5 and 121 11.5 arranged at the outermost edge of the magnet arrangement are each rotated by 90° relative to their neighbors. This reduces possible distortions of the static magnetic field 130 in the edge region 127 of the magnet arrangement. The angle of rotation between adjacent magnet segments can generally vary depending on the respective application. In particular, when using a larger number of separate magnet segments, a smaller angle of rotation can be used than with a smaller number of magnet segments.

[0051] In order to compensate for a weakening of the static magnetic field 130 in the edge regions 127 of the planar magnet arrangement 120, stronger magnet segments can be used in the corresponding edge regions 127 than in a central region 128 of the magnet arrangement. Such an amplification of the magnetic field in the edge regions 127 can be eliminated, for example, by means of magnet segments that are larger or higher than the magnet segments from a central region 128 of the magnet arrangement. For this purpose, the Figure 4a corresponding planar magnet arrangement 120 with magnet segments of different heights 121 1.5 - 121 11.5 . By compensating for the magnetic field attenuation in the edge regions 127 of the magnet arrangement 120, the two outer sections 135, 137 of the static magnetic field 130 have a substantially equal strength to the central section 136 of the static magnetic field 130. This results in a substantially homogeneous field strength of the static magnetic field 130 in the various measuring layers of the useful volume 200. For reasons of clarity, Figure 4Only three of the measurement layers defining the useful volume 200 are indicated by lines 201, 202, and 203. As shown here, the measurement layers 201, 202, and 203 are preferably located above the electrical coil 140. The high homogeneity of the magnetic fields realized in the measurement layers makes it possible to measure different atomic nuclei simultaneously. Differentiation between the different atomic nuclei can be achieved using T1 / T2 relaxation.

[0052] An arrangement of the electrical coil 140 with respect to the planar magnet arrangement 120 is shown in the Figure 5 shown schematically. It can be seen that the electrical coil 140 in the present embodiment comprises a total of three windings 141, 142, 143. The windings, or the inner regions of the windings, are each arranged between two directly adjacent magnetic poles 131, 132, 133, 134.

[0053] The Figure 6shows a possible design of an electrical coil 140 with three adjacent windings 141, 142, 143, which was produced by structuring the electrically conductive layer 164. The adjacent windings 141, 142, 143 of the Figure 6The electrical coil 140 shown is designed in the form of partial coils, with each partial coil in the present case comprising two windings. In principle, the number of windings per partial coil can vary depending on the application. According to the invention, the electrical coil 140 is designed in the form of a multi-resonant coil, with the aid of which alternating fields of different frequencies can be emitted or detected simultaneously. With the aid of a multi-resonant coil, different layers of the useful volume 200 can be measured simultaneously. The differentiation of the different layers can be achieved by means of a field-dependent contrast. For this purpose, a magnetic field-dependent contrast agent can be used, for example.

[0054] The Figure 7 shows one of the arrangements, which corresponds to the configuration from the Figure 4, whereby only the alternating magnetic field 150 of the electrical coil 140 is shown here. As can be seen here, the alternating magnetic field 150 generated by the three partial coils 141, 142, 143 during operation has a total of three magnetic poles 151, 152, 153 on the upper side facing the useful volume 200.

[0055] The Figure 8 shows a superposition of the static magnetic field 130 from Figure 4 and the alternating magnetic field 150 Figure 7It can be seen that the two magnetic fields 130, 150 each have mutually offset magnetic poles, with one magnetic pole 151, 152, 153 of the alternating magnetic field 150 being arranged essentially centrally between two immediately adjacent magnetic poles 131, 132, 133, 134 of the static magnetic field 130. Due to this special arrangement, the field lines of the two magnetic fields 130, 150 run essentially orthogonally to one another in the usable volume 200 defined by the usable measuring layers 201, 202, 203. By appropriately adjusting the operating parameters or the configuration, a field distribution optimized for NMR measurement can be achieved in the usable volume 200.

[0056] In principle, the sensor 100 can also be manufactured in different sizes. The number of magnet segments used can vary depending on the number of partial coils. Figure 9a scaled-down version of the Sensor 100 from the Figure 5 The sensor 100 has a planar magnet arrangement 120 with a total of 41 magnet segments arranged in a 7x6 matrix. The magnetic field generated by the planar magnet arrangement 21 has only three magnetic poles 131, 132, 133 on the front side. Accordingly, the electrical coil 41 has only two windings or partial coils 141, 142.

[0057] In contrast, the Figure 10 an enlarged version of the sensor 100 from the Figure 5 The enlarged sensor 100 has a planar magnet arrangement 21 with a total of 150 magnet segments arranged in a 15x10 matrix. The static magnetic field on the front side of the planar magnet arrangement 120 has a total of five magnetic poles 131, 132, 133, 134, 135 with alternating field directions. Accordingly, the electrical coil 41 comprises a total of four windings or partial coils 141, 142, 143, 144.

[0058] In principle, the magnet segments of the planar magnet arrangement 120 can also be arranged next to each other without gaps. Figure 11 a correspondingly designed planar magnet arrangement 120.

[0059] In addition to a matrix-like arrangement of the magnet segments, which for example in Figure 2 As shown, the planar magnet arrangement can also be created by arranging elongated magnet segments. Figure 12 a corresponding planar magnet arrangement 21, which does not fall within the scope of the invention defined by the claims and comprises a total of eleven bar-shaped or rod-shaped magnet segments arranged next to one another in the first extension direction X. In principle, it is possible to use magnet segments which have a complex magnetization. For this purpose, the Figure 13a planar magnet arrangement 120 with a single magnet segment 121, which does not fall within the scope of the invention as defined by the claims and has sections with different magnetization directions. In particular, immediately adjacent sections of the magnet segment 121 each have magnetization directions rotated by a certain angle. Such a permanent magnet can be produced, for example, by sintering.

[0060] In order to achieve compensation of the magnetic field attenuation in the edge regions 127 of the planar magnet arrangement 120, as an alternative to the method described in connection with the Figure 4 As described above, a three-dimensional arrangement of magnet segments can also be used. Figure 14A cross-sectional view through a planar magnet arrangement 120 correspondingly extended in the Z direction. The magnet segments are arranged in two superimposed planes 122, 123. For this purpose, the magnetization device 101 comprises an additional carrier plate 112, which is fastened below the first carrier plate 110. The second carrier plate 112 has magnet segments 124 1.5 - 124 11.5 only in its edge regions 127. In contrast, no magnet segments are present in the central region 128 of the second carrier plate 112. The superposition of the magnetic fields of the magnet segments arranged one above the other in the edge regions 121 of the magnet arrangement results in the desired amplification of the static magnetic field 130 in the edge regions 127.

[0061] The Figure 15 shows a top view of the additional support plate 112 from Figure 14. It can be seen that the additional carrier plate 112 also has additional magnet segments 124 1,1 - 121 11,11 in a central region in the X direction. To better illustrate the distribution of the magnet segments 124 1,1 - 121 11,11 within the carrier plate 112, the openings 113 of the carrier plate 112 in which no corresponding magnet segment is located are shown with a dashed-dotted line.

[0062] In principle, the static magnetic field 130 of the magnetic field generating device 101 can be modified as desired by adding or removing magnet segments from the openings 113 of the lower support plate 112. Furthermore, it is also possible to arrange the magnet segments in more than two planes, one above the other.

[0063] The use of a carrier plate with removable magnets allows for relatively easy modification of the magnet arrangement. This allows the planar magnet arrangement to be fundamentally adapted to the specific application. Furthermore, the static magnetic field (B0 field) can be dampened or even almost completely compensated for by rotating individual magnet segments within the carrier plate for transport or storage of the sensor. A similar reduction in the magnetic field can be achieved by swapping the position of individual magnet segments within the carrier plate.

[0064] The Figure 16shows, by way of example, a magnetic resonance device 300 arranged on a base plate 400. The magnetic resonance device 300 comprises a sensor 100 arranged within a housing 180, a housing 180 accommodating the sensor 100, and a mechanical lifting device 310 arranged on the housing for adjusting the distance between the sensor 100 and a material sample arranged underneath. The essentially analogous to the sensor from the Figure 4The sensor 100 constructed in this way comprises a magnetic field generating device 101 with a magnet arrangement 120 for generating a static magnetic field 130 and a measuring device 102 with an electrical coil 140 for generating an alternating magnetic field 150. In the present example, however, the sensor 100 is arranged rotated by 180°, so that the static magnetic field 130 generated by the magnet arrangement 120 extends downwards into the base plate 400. Accordingly, the useful volume 200 and the measuring layers 201, 202, 203 contained therein are also arranged below the sensor 100. In this arrangement, the nuclear magnetic resonance device 300 can determine certain material properties of the base plate 400, which in the present example serves as a material sample. In principle, however, it can also be used to measure material samples that are arranged on or below the base plate 400 or within the base plate 400.

[0065] The mechanical lifting device 310 comprises one or more manually or electrically operated actuators 320, 330, which are preferably arranged distributed along the outer circumference of the housing 180. In particular, four actuators can be provided, each arranged at the corners of the housing 180. In the Figure 16A total of two actuators 320, 330 are shown, which are arranged on two opposite sides of the housing 180. In the present exemplary embodiment, the actuators 320, 330 are arranged on the outside of the housing 180. Alternatively, the actuators 320, 330 can also be arranged inside the housing 180 (not shown here). The actuators 320, 330 each comprise a first actuator part 321 connected to the housing 180 and a second actuator part 322, 332 that is movable relative to the housing 180 and rests with a support surface 323, 333 on the surface 410 of the base plate 400 serving as the material sample. In the present example, the actuators 320, 330 are designed in the form of electric drives. The second actuator part 322, 332 forms an electric motor while the first actuator part 321, 331 is designed in the form of a spindle driven by the electric motor.Such a design enables particularly fine and precise adjustment. During operation of the actuator device 300, the first actuator part 321, 331 is displaced relative to the respective second actuator part 322, 332. A coordinated movement of all actuators creates a desired lifting movement of the sensor 100 relative to the base plate 400. For this reason, depth-dependent measured values ​​can be generated relatively easily using the lifting device 300, with the aid of which a depth profile of the base plate 400 or of a material sample fixedly connected to the base plate 400 can be generated.

[0066] The lifting device is preferably controlled by a suitable control device. This control device can, for example, be an integral component of the control and evaluation device of the magnetic resonance device. However, a self-contained control device for controlling the lifting movement of the sensor 100 is also possible.

[0067] In addition to the electric motors with spindles shown here, any suitable mechanical device can be used as an actuator for adjusting the height of the sensor 100. Among other things, manually operated actuators can also be used, for example, with a manual locking mechanism at predefined intervals.

[0068] For reasons of clarity, the Figure 16 Further components of the nuclear magnetic resonance device 300, such as the control and evaluation device or the energy supply device, are not shown.

[0069] The nuclear magnetic resonance device may comprise one or more of the NMR sensors described here. A typical nuclear magnetic resonance device also comprises other components, such as a control and evaluation device and a power supply device.

[0070] Although the invention has been described primarily with reference to specific embodiments, it is by no means limited thereto. Those skilled in the art will thus be able to appropriately modify and combine the described features, provided the resulting subject matter falls within the scope of protection of the invention as defined by the claims. In particular, the methods described separately here for locally modifying the magnetic properties of the correction layer can also be combined with one another as desired.

Claims

1. Sensor (100) for a nuclear magnetic resonance apparatus (300) for determining at least one material property of a material sample arranged in a useful volume (200), comprising: - a magnetic field generating device (101) comprising a planar magnetic arrangement (120) for generating a static magnetic field (130, 135, 136, 137) in the useful volume (200), wherein the planar magnetic arrangement (120) on a front side (103) facing the useful volume (200) has a plurality of magnetic poles (131, 132, 133, 134) which are arranged next to each other with respectively alternating orientation along a first direction of extent (X) of the planar magnetic arrangement (120), and - a measuring device (102) for measuring a signal based on nuclear magnetic resonance of the material sample arranged in the useful volume (200), comprising an electric coil (140) having at least one winding (141, 142, 143, 144) for generating an alternating magnetic field (150, 154, 155) in the useful volume (200), wherein the winding (141, 142, 143, 144) is arranged between two directly adjacent magnetic poles (131, 132, 133, 134) of the planar magnetic arrangement (120) so that the alternating magnetic field (150, 154, 155) of the electric coil (140) overlaps with the static magnetic field (130, 135, 136, 137) of the planar magnetic arrangement (120) substantially orthogonally in the entire useful volume (200), wherein the planar magnetic arrangement (120), along the first direction of extent (X) and along a second direction of extent (Y) which runs perpendicular to the first direction of extent (X), in each case comprises a plurality of magnetic segments (121i,j) arranged next to each other and each having magnetization directions oriented orthogonal to the second direction of extent (Y) of the planar magnetic arrangement (120), and wherein magnetic segments (121i,j) which are arranged directly next to each other along the first direction of extent (X) of the planar magnetic arrangement (120) each have magnetization directions which are twisted relative to each other, as a result of which a substantially stronger static magnetic field (130) is generated on the front side (103) of the planar magnetic arrangement (120) than on the back side (104) of the planar magnetic arrangement (120), wherein the magnetic segments (121i,j) arranged next to each other along the second direction of extent (Y) of the planar magnetic arrangement (120) have the same magnetization direction, wherein the electric coil (140) is designed in the form of a multi-resonant coil.

2. Sensor (100) according to Claim 1, wherein magnetic segments (121i,j) arranged directly next to each other along the first direction of extent (X) of the planar magnetic arrangement (120) each have magnetization directions twisted by 45° to each other.

3. Sensor (100) according to either of Claims 1 and 2, wherein the electric coil (140) is further designed to measure a signal based on nuclear magnetic resonance of the material sample arranged in the useful volume (200).

4. Sensor (100) according to one of the preceding claims, wherein the electric coil (140) is arranged on the front side (103) of the planar magnetic arrangement (120).

5. Sensor (100) according to one of the preceding claims, wherein the electric coil (140) is designed in the form of a structured electrically conductive layer (164).

6. Sensor (100) according to Claim 5, wherein at least one shim coil for homogenizing the static magnetic field (130) generated by the planar magnetic arrangement (120) in the useful volume (200) is furthermore formed in the electrically conductive layer (164).

7. Sensor (100) according to one of the preceding claims, wherein four magnetic poles (131, 132, 133, 134) are formed with respectively alternating orientations on the front side (103) of the planar magnetic arrangement (120), and wherein the electric coil (140) of the measuring device (102) comprises three windings (151, 152, 153) arranged next to each other, the magnetic poles (151, 152, 153) of which are each arranged between two directly adjacent magnetic poles (131, 132, 133, 134) of the planar magnetic arrangement (120).

8. Sensor (100) according to one of the preceding claims, wherein an inner shielding structure (161) made of an electrically conductive material with a high magnetic permeability is arranged between the electric coil (140) and the planar magnetic arrangement (120) and acts as a shield for the magnetic segments (121i,j) against the alternating magnetic field (150, 154, 155) of the electric coil (140).

9. Sensor (100) according to one of the preceding claims, wherein an outer shielding structure (168) made of an electrically conductive material with a high magnetic permeability is arranged between the electric coil (140) and the useful volume (200) and acts as a shield for the electric coil (140) against electromagnetic interference fields.

10. Sensor (100) according to Claim 9, wherein the outer shielding structure (168) has resonance structures which serve for the targeted shielding against electromagnetic interference fields with frequencies in the range of the network frequency.

11. Sensor (100) according to one of the preceding claims, wherein the magnetic field generating device (101) comprises a carrier plate (130) made of a non-magnetic material, and wherein the magnetic segments (121i,j) are inserted into at least one opening (111) in the carrier plate (110).

12. Sensor (100) according to Claim 11, wherein at least some of the magnetic segments (121i,j) of the magnetic arrangement (120) are designed so as to be able to rotate within the carrier plate (110).

13. Sensor (100) according to Claim 11 or 12, wherein the magnetic field generating device (101) is modularly expandable by arranging a plurality of carrier plates (110, 112) next to each other in at least one of the two directions of extent (X, Y) of the planar magnetic arrangement (120).

14. Sensor (100) according to one of the preceding claims, wherein magnetic segments (121i,j) are formed in an edge region (127) of the planar magnetic arrangement (120) in order to generate a static magnetic field having a higher magnetic field strength than magnetic segments (121i,j) in a central region (128) of the planar magnetic arrangement (120).

15. Sensor (100) according to Claim 14, wherein the higher magnetic field strength in the edge region (127) of the planar magnetic arrangement (120) is achieved by magnetic segments (121i,j) which have a higher magnetization and / or a greater vertical extension than magnetic segments (121i,j) in the central region (128) of the planar magnetic arrangement (120).

16. Sensor (100) according to Claim 14 or 15, wherein a plurality of magnetic segments (121i,j, 124i,j) arranged on top of each other are provided in the edge region (127) of the planar magnetic arrangement (120) in order to achieve the higher magnetic field strength.

17. Sensor (100) according to one of the preceding claims, wherein at least some of the magnetic segments (121i,j) of the planar magnetic arrangement (120) have a coating made of a plastic.

18. Nuclear magnetic resonance apparatus (300) comprising a sensor (100) according to one of preceding Claims 1 to 17, wherein the nuclear magnetic resonance apparatus (300) is designed to determine at least one material property of a material sample arranged in a useful volume (200) for a plurality of measuring layers (201, 202, 203) independently of each other.

19. Nuclear magnetic resonance apparatus (300) according to Claim 18, wherein the nuclear magnetic resonance apparatus (200) comprises a lifting device (310) having at least one electrically and / or manually driven actuator (320, 330) for adjusting the distance between the sensor (100) and a material sample arranged in the useful volume (200).

20. Nuclear magnetic resonance apparatus (300) according to Claim 19, wherein the actuator (320, 330) comprises a first actuator part (321, 331) carrying the sensor (100) and a second actuator part (322, 332) which is arranged so as to be movable with respect to said first actuator part and which has a contact area (323, 333) for laying on a surface (410) which is fixedly arranged in relation to the material sample.

21. Nuclear magnetic resonance apparatus (300) according to Claim 20, wherein the first actuator part (321, 331) is designed in the form of an electric motor, and wherein the second actuator part (322, 332) is designed in the form of a spindle driven by the electric motor.

22. Nuclear magnetic resonance apparatus (300) according to Claim 20, wherein the lifting device (310) comprises a plurality of actuators (320, 330) arranged distributed along the circumference of the sensor (100).