A magnet pole plate for a nuclear magnetic resonance device, a manufacturing method and a magnet system

Abstract

The application relates to the technical field of medical imaging equipment, and discloses a magnet pole plate for a nuclear magnetic resonance device, a manufacturing method and a magnet system. The magnet pole plate comprises a substrate layer, a first insulating layer and a core layer made of soft magnetic composite material and arranged on the first insulating layer. The soft magnetic composite material is formed by pressing and solidifying iron-based powder coated with an insulating coating on the surface, and has a magnetic permeability sufficient to maintain main magnetic flux and a volume resistivity sufficient to inhibit eddy current generation. The magnet pole plate further comprises a guide layer and a shim ring. The core layer is segmented into multiple independent units, and an insulating gap is arranged between adjacent independent units. The soft magnetic composite material of the core layer is formed by pressing and solidifying, and the high volume resistivity of the material can inhibit eddy current from the intrinsic layer, and the core layer is segmented and provided with the insulating gap, so that the closed eddy current loop in the pole plate can be directly dispersed, the eddy current forming path is blocked, near-zero eddy current under a gradient pulse is realized, and the image quality is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical imaging equipment, in particular to a magnet pole plate for a nuclear magnetic resonance (NMR) device, a manufacturing method and a magnet system. BACKGROUND

[0002] The magnet pole plate is a key component in a NMR device for optimizing magnetic field distribution and suppressing eddy current interference. Through the collaborative design of the magnetic conduction layer and the insulation structure, it ensures the stable conduction of the main magnetic flux and weakens the eddy current induced by the gradient pulse, directly determining the imaging accuracy and long-term operation stability of the NMR device. With the widespread application of high-field and high-resolution NMR devices, higher requirements are placed on the eddy current suppression capability, magnetic field uniformity and structural reliability of the magnet pole plate.

[0003] In related technologies, the traditional magnet pole plate often needs to repeatedly trade off between magnetic flux continuity, eddy current suppression and mechanical strength, and under fast imaging sequences, perceptible residual eddy current and temperature rise may still occur. Therefore, how to achieve near-zero eddy current under the action of the gradient pulse while maintaining high magnetic conduction capability and mechanical robustness, thereby significantly improving image quality, reducing temperature rise and energy consumption, has become a problem to be solved. SUMMARY

[0004] Therefore, the present application provides a magnet pole plate for a NMR device, a manufacturing method and a magnet system to solve the problem of how to achieve near-zero eddy current under the action of the gradient pulse while maintaining high magnetic conduction capability and mechanical robustness, thereby significantly improving image quality, reducing temperature rise and energy consumption.

[0005] In a first aspect, the present application provides a magnet pole plate for a NMR device, the magnet pole plate comprising:

[0006] a substrate layer made of a magnetically conductive metal material;

[0007] a first insulation layer made of a material with electrical insulation and higher magnetic resistance than the substrate layer, disposed on the substrate layer;

[0008] a core layer made of a soft magnetic composite material, disposed on the first insulation layer; wherein the soft magnetic composite material is pressed and solidified from iron-based powder coated with an insulating coating on the surface, and has a magnetic permeability sufficient to maintain the passage of the main magnetic flux and a volume resistivity sufficient to suppress the generation of eddy current;

[0009] a guide layer made of a magnetically conductive material with higher electrical resistivity than the substrate layer and lower magnetic resistance than air, disposed around the outer periphery of the core layer;

[0010] a shim ring disposed on the side of the core layer close to the imaging space;

[0011] The core layer is segmented into multiple independent units along the radial and / or radial directions, and an insulating gap is arranged between adjacent independent units.

[0012] In a second aspect, the application provides a manufacturing method of a magnet pole plate, for manufacturing the magnet pole plate of the first aspect, the method comprising:

[0013] The iron-based powder is coated with an insulating coating to obtain an insulating coated powder; the insulating coated powder is pressed into a predetermined shape in a mold under a predetermined pressure, and then heat treated to solidify the insulating coating between the powders and eliminate internal stress, thereby forming a soft magnetic composite core blank;

[0014] The soft magnetic composite core blank is machined and segmented along the radial and / or radial directions to form multiple independent units; an electrically insulating material is arranged in the cutting gap between adjacent independent units to form a core layer with an insulating gap;

[0015] The substrate layer, the first insulating layer, and the core layer with an insulating gap are sequentially stacked and aligned, the guide layer is assembled around the outer periphery of the core layer, and the shim is directionally assembled on the side of the core layer close to the imaging space, to complete the fixed assembly of the components;

[0016] The stacked components are coated or frame-fixed with a non-magnetic shell or skeleton, and a pre-tightening force is applied for overall fixation, thereby completing the manufacturing of the magnet pole plate.

[0017] In a third aspect, the application provides a magnet system, which comprises a main magnet, a gradient coil, and the magnet pole plate of the first aspect, the gradient coil and the magnet pole plate being arranged adjacent to and parallel to each other, and the magnet pole plate comprising a core layer made of a soft magnetic composite material and an insulating segmented structure, which suppresses the eddy current induced by the gradient pulse.

[0018] In the magnet pole plate, the manufacturing method, and the magnet system for a nuclear magnetic resonance device according to the above-mentioned embodiments of the application, the core layer is made of a soft magnetic composite material obtained by pressing and solidifying iron-based powder coated with an insulating coating, which can suppress the eddy current from the intrinsic layer of the material due to its high volume resistivity; at the same time, the core layer is segmented along the radial and / or radial directions and provided with an insulating gap, which can directly break the closed eddy current loop inside the pole plate and block the path of the eddy current; in addition, the guide layer with a higher resistivity than the substrate layer and a lower magnetic resistance than air is arranged around the outer periphery of the core layer, which can guide the gradient magnetic flux to preferentially close along the high-resistance path and avoid the magnetic flux entering the low-resistance substrate layer to induce the eddy current. The above-mentioned three factors work together to solve the problem of residual eddy current in the traditional pole plate under the fast imaging sequence, realize near-zero eddy current under the gradient pulse, and thus significantly improve the image quality.

[0019] The substrate layer is made of a magnetically conductive metal material, which not only provides reliable mechanical support for the pole plate, but also serves as a basic path for the main magnetic flux conduction; the soft magnetic composite (SMC) of the core layer has a magnetic permeability sufficient to maintain the main magnetic flux passing through, can efficiently accept and conduct the main magnetic flux, and ensures the continuity of the magnetic flux; the first insulating layer only blocks the electrical coupling (suppresses eddy current), and does not affect the magnetic flux transmission. The overall structure does not need to compromise between magnetic flux, eddy current suppression and mechanical strength, and can meet the core performance requirements of the pole plate of the high-field MRI device, thereby balancing the high magnetic flux continuity and mechanical robustness.

[0020] In addition, due to the near-zero eddy current design, the eddy current loss is greatly reduced, the temperature rise during the operation of the pole plate can be significantly reduced, and the risk of structural deformation caused by temperature rise can be avoided; at the same time, the reduction of eddy current loss directly reduces the energy consumption of the equipment, and improves the long-term operation stability of the equipment. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the description of the specific embodiments or prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is a hierarchical structure sectional view of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0023] Figure 2 is a schematic diagram of a local asymmetric segmented implementation of a micro-shim function of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0024] Figure 3 is a core layer segmentation schematic diagram of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0025] Figure 4 is a detail schematic diagram of an insulating gap of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0026] Figure 5 is a schematic diagram of a guide layer and a shim ring arrangement of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0027] Figure 6 is a second hierarchical structure sectional view of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0028] Figure 7is a third hierarchical sectional view of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0029] Figure 8 is a shell / skeleton and fastener layout schematic of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0030] Figure 9 is a flow of a manufacturing method of a magnet pole plate according to an embodiment of the present application;

[0031] Figure 10 is an architecture schematic of a magnet system according to an embodiment of the present application;

[0032] Figure 11 is a whole magnetic circuit diagram and equipotential line schematic of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0033] Figure 12 is a thermal-structural co-design schematic of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application;

[0034] Figure 13 is a test evaluation flow and key index schematic of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0036] It can be understood that, before using the technical solutions disclosed in the embodiments of the present application, the type, use range, use scenario and the like of personal information involved in the present application should be informed to the user and the authorization of the user should be obtained through appropriate means according to relevant laws and regulations.

[0037] The terms "first", "second", "third", etc. are used only for the purpose of description and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0038] In the field of MRI system technology, the main magnet is used to establish a high uniformity and high stability static magnetic field in the imaging space, and the gradient coil is used to perform spatial encoding by applying a fast switching time-varying gradient field. In order to ensure the efficiency and uniformity of the magnetic field, the gradient coil is usually arranged close to the magnet pole plate. When the gradient coil passes through a pulse current in the kilohertz (kHz) frequency range, according to Faraday's law of electromagnetic induction, the rapidly changing magnetic field generated thereby will induce eddy currents in the adjacent conductive structures (especially the magnetically conductive pole plate).

[0039] Such eddy currents will generate additional and unexpected transient magnetic fields, which are superimposed on the main static magnetic field and the gradient field, and will cause a series of problems that seriously affect the performance of the system, mainly including:

[0040] 1. Image quality degradation, the eddy current field causes distortion of the gradient field waveform, causing k-space phase errors and geometric distortion, resulting in image artifacts such as ghosting, stretching or compression;

[0041] 2. Signal-to-noise ratio reduction and measurement error, the residual field generated by the eddy current decay process will interfere with the echo signal, reduce the signal-to-noise ratio, and affect the accuracy of quantitative measurement;

[0042] 3. Thermal management and energy consumption problems, eddy current loss is released in the form of Joule heat, causing local or overall temperature rise of the pole plate, which brings the risk of thermal deformation and increases the cooling load of the system;

[0043] 4. System complexity and control cost increase, in order to compensate for the eddy current effect, complex pre-distortion algorithms, active shielding technology and extended sequence design waiting time need to be introduced, which increases the control complexity and development cost of the system.

[0044] In order to suppress eddy currents, the industry has developed a variety of related technical solutions, and the mainstream path focuses on blocking or lengthening the eddy current path to increase resistance, mainly including: segmented pole plate combined with insulation, cutting the overall pole plate into multiple electrically isolated segments to physically block the formation of large-scale closed current loops; laminated magnetic conductive layer, using high resistivity silicon steel sheets and insulating layers to be stacked alternately, and using interlayer insulation to limit the flow of eddy currents in the sheet plane; guide ring or magnetic flux guiding layer, additional magnetic conductive structures are arranged on the outer periphery of the pole plate or specific paths, which are designed to guide the time-varying magnetic flux to preferentially pass through the high resistance path, and reduce the magnetic flux capture of the main pole plate; non-magnetic shell enhancement, using non-magnetic high-strength materials such as carbon fiber as a supporting framework to provide mechanical strength while avoiding the introduction of new eddy current sources.

[0045] However, the above-mentioned related solutions generally face a core contradiction when dealing with high-performance MRI (especially echo planar imaging (EPI), diffusion-weighted imaging (DWI) and other sequences that require fast switching of gradient fields): it is difficult to achieve an ideal balance between "high magnetic flux continuity", "intrinsic eddy current suppression" and "mechanical structure robustness". The specific pain points are as follows:

[0046] 1. Trade-off between magnetic performance and electrical performance. The segmented design blocks the eddy current while also dividing the magnetic circuit, which may degrade the uniformity and strength of the static magnetic field. The lamination structure has a short board in the normal magnetic permeability, which affects the efficiency of the main magnetic flux conduction.

[0047] 2. Limitations of suppression depth and frequency response. Traditional segmentation and lamination have some effect on low-frequency eddy currents, but in the presence of kHz-level gradient pulses, their size and insulation gaps may not be sufficient to completely break all eddy current loops, leaving a perceptible eddy current field and temperature rise.

[0048] 3. Increasing complexity of structure and manufacturing cost. Fine segmentation, multi-layer lamination or composite guide structure significantly increases the difficulty of manufacturing, assembling and debugging of the pole plate, leading to an increase in cost and possibly introducing new mechanical vibration or reliability risks.

[0049] 4. Poor adaptability of the solution. For different field strengths (such as 0.5T, 1.0T, 1.5T), different magnet types (permanent magnet / electromagnet) or different gradient performance of MRI systems, the parameters of the related solution (such as the number of segments, the thickness of the lamination) need to be re-designed and debugged empirically, and there is a lack of an intrinsic material solution with high electrical resistivity and high magnetic permeability as a universal foundation.

[0050] To solve the above problems, a magnet pole plate for a nuclear magnetic resonance device is provided in various embodiments of the present application. The magnet pole plate includes: a substrate layer made of a magnetically conductive metal material; a first insulating layer made of a material with electrical insulation and higher magnetic resistance than the substrate layer, disposed on the substrate layer; a core layer made of a soft magnetic composite material, disposed on the first insulating layer; wherein the soft magnetic composite material is formed by pressing and solidifying iron-based powder coated with an insulating coating on the surface, and has a magnetic permeability sufficient to maintain the main magnetic flux and a volume resistivity sufficient to suppress the generation of eddy currents; a guide layer made of a magnetically conductive material with higher electrical resistivity than the substrate layer and lower magnetic resistance than air, disposed around the outer periphery of the core layer; a shim ring disposed on one side of the core layer close to the imaging space; wherein the core layer is segmented into multiple independent units in the radial and / or radial directions, and an insulating gap is provided between adjacent independent units.

[0051] Figure 1is a hierarchical sectional view of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application, as shown in Figure 1 The magnet pole plate comprises:

[0052] A substrate layer 101 made of a magnetically conductive metal material.

[0053] In this embodiment, the magnetically conductive metal material is not all metals with magnetic conductivity, but a specific material that meets the dual requirements of main magnetic flux conduction and mechanical manufacturing of the MRI magnet pole plate (hereinafter referred to as the pole plate). That is, the magnetically conductive metal material can be used to conduct the static magnetic field magnetic flux generated by the main magnet with low loss, while having a certain mechanical strength. For example, the magnetically conductive metal material can include but is not limited to pure iron, low carbon steel.

[0054] Therefore, the substrate layer 101 made of the magnetically conductive metal material with the above characteristics can be used as a basic functional bearing unit of the pole plate, and becomes the main magnetic flux conduction hub and mechanical support carrier between the main magnet and the core layer of the pole plate.

[0055] Specifically, on the one hand, the substrate layer 101 becomes the main magnetic flux conduction hub between the main magnet and the core layer of the pole plate due to the low-loss magnetic conduction characteristics of the magnetically conductive metal material, that is, it can smoothly accept the static magnetic field magnetic flux (hereinafter referred to as main magnetic flux ) output by the main magnet and conduct the magnetic flux to the core layer in a low hysteresis loss and low leakage magnetic manner.

[0056] On the other hand, the substrate layer 101 can constitute the mechanical support skeleton of the overall structure of the pole plate due to its certain mechanical strength, that is, the substrate layer 101 can bear the weight of each functional layer level of the core layer 104, the first insulating layer 102, the guide layer 103, the shim ring 106, etc. resist the pre-tightening force applied during assembly, and the electromagnetic force generated between the gradient coil and the pole plate during MRI operation, prevent the pole plate from causing misalignment of each level due to structural deformation, and thus ensure the structural stability and performance consistency of the pole plate during long-term operation.

[0057] The first insulating layer 102 is made of a material with high electrical resistance and higher magnetic resistance than the substrate layer, and is arranged on the substrate layer 101.

[0058] In this embodiment, since the substrate layer 101 is made of metal, it is easy to form a cross-layer eddy current loop with the core layer 104, so the first insulating layer 102 with high electrical resistance and high magnetic resistance is needed between the substrate layer 101 and the core layer 104 to block the eddy current.

[0059] Here, the first insulating layer 102 can be a magnetic and electrical isolation functional layer between the substrate layer 101 and the core layer 104 in the pole plate, used to achieve the dual goals of blocking cross-layer eddy current and ensuring main magnetic flux conduction.

[0060] Further, the material that makes up the first insulating layer 102, which is electrically insulating and has a higher magnetic resistance than the substrate layer 101, can be a functional insulating material designed specifically to achieve the above-mentioned dual goals for the pole plate.

[0061] Therefore, the above-mentioned material needs to have the following characteristics:

[0062] 1. It needs to have high volume resistivity and high dielectric strength, which can completely block the conduction path between the substrate layer 101 and the core layer 104, so as to avoid cross-layer leakage current caused by electric field coupling (which will form a closed eddy current loop, which will offset the eddy current suppression effect of the segmented insulation of the core layer 104);

[0063] 2. It needs to satisfy the condition that the magnetic resistance is higher than that of the substrate layer 101, but does not significantly hinder the conduction of the main magnetic flux;

[0064] 3. It needs to have low hysteresis loss and compatibility with adjacent layers, i.e. no hysteresis loss to avoid additional heat generated by the material itself due to changes in the main magnetic flux, and good surface adhesion with the substrate layer 101 and the core layer 104, so as to avoid air gaps between the layers.

[0065] The core layer 104 is made of soft magnetic composite material and is arranged on the first insulating layer 102. The soft magnetic composite material is formed by pressing and solidifying iron-based powder coated with an insulating coating on the surface, and has a magnetic permeability sufficient to maintain the passage of the main magnetic flux and a volume resistivity sufficient to suppress the generation of eddy current.

[0066] In this embodiment, the core layer 104 can be the core functional layer of the pole plate for magnetic flux conduction and eddy current suppression on the first insulating layer 102.

[0067] Specifically, the SMC that makes up the core layer 104 takes iron-based powder as the matrix, each iron-based powder is coated with an electrically insulating coating on the surface, is pressed into a three-dimensional isotropic magnetic circuit part, and is solidified by low-temperature heat treatment to cure the coating and eliminate stress, while avoiding metal sintering between particles to maintain high volume resistivity, thereby significantly suppressing eddy current loss.

[0068] The core layer 104 has the functions of main magnetic flux conduction and eddy current suppression. On the one hand, the core layer 104 can serve as the main conduction path of the main magnetic flux in the pole plate, and needs to receive the main magnetic flux transmitted from the substrate layer 101 (through the first insulating layer 102) through its high magnetic permeability characteristic, uniformly diffuse the magnetic flux to the vicinity of the imaging space, and provide a magnetic flux basis for the magnetic field shaping of the shimming ring 106. On the other hand, the core layer 104 can serve as the main suppression barrier for gradient pulse eddy current, which blocks the closed eddy current loop inside the pole plate through the intrinsic high resistivity of the material and the segmented insulation of the structure.

[0069] Here, the material intrinsic high resistivity can refer to the inherent high resistivity characteristic of the SMC, which is obtained from the microstructure design and preparation process of the SMC itself, and does not depend on external auxiliary structures.

[0070] That is, each iron-based powder in the SMC is coated with an independent electrically insulating coating, which completely isolates the iron-based powder; at the same time, after compression and curing, the above-mentioned iron powder units wrapped in the insulating coating only form a block structure through physical contact (without metal sintering), and there is no free electron conduction metal path between the particles. The above two aspects can be the fundamental source of the high resistivity of the SMC, without relying on external additional insulating components.

[0071] Here, metal sintering refers to a process of making metal powder particles adhere to each other by atomic diffusion, bonding, reducing the porosity between particles and forming a more compact metallurgical bond at a temperature lower than the melting point of the metal material by applying heat and pressure.

[0072] If the iron-based powder is sintered, the iron powder particles will form a metal bond connection due to atomic diffusion, thereby directly destroying the insulating coating on the surface of the particles; in addition, the iron powder particles originally isolated by the insulating layer will form a free electron conduction metal path through metal sintering, which is easy to induce eddy current under gradient pulse, which counteracts the eddy current suppression effect of the intrinsic high resistivity of the SMC, and cannot meet the demand of near-zero eddy current of the MRI pole plate.

[0073] Therefore, by using compression and curing, the material can obtain sufficient mechanical strength without sintering, meeting the mechanical requirements of the pole plate assembly and operation.

[0074] Further, the core layer 104 is segmented into multiple independent units along the radial and / or radial directions, and an insulating gap 108 is provided between adjacent independent units.

[0075] Here, the independent unit can refer to a substructure formed by cutting the SMC in the core layer 104, which has independent magnetic conduction and electrical isolation characteristics, and the independent units are not directly connected by metal or conductive connection, but are only separated by the insulating gap 108. The shape of the independent unit can include but is not limited to a fan-shaped unit, a ring-shaped unit, or a spoke-shaped unit.

[0076] Further, the segmentation pattern of the core layer 104 can be pre-set according to the MRI magnetic field uniformity requirement, and the segmentation pattern can adopt symmetric segmentation or asymmetric segmentation.

[0077] When the segmentation pattern adopts symmetric segmentation, the segmentation pattern of the independent unit is mirror-symmetric relative to the magnetic pole center axis, so as to take into account the uniformity and mechanical symmetry.

[0078] When the segmentation pattern adopts asymmetric segmentation, the passive micro-shim function can be realized.

[0079] As an example, please refer to Figure 2 , Figure 2 is a schematic diagram of local asymmetric segmentation of a magnet pole plate for a nuclear magnetic resonance device to implement a micro-shim function according to an embodiment of the present application, as shown in Figure 2 The left side of the figure is labeled as a symmetric segmentation design (uniform magnetic field), and the area shown has been labeled as 201, indicating that the core layer 104 is uniformly divided into a structure of multiple mirror-symmetric independent units, which provides a basic uniform magnetic field for the imaging space.

[0080] Here, by symmetric unit segmentation, the main magnetic flux is uniformly diffused in the core layer 104, avoiding magnetic field distortion caused by structural asymmetry, and providing a basic uniform magnetic field environment for the imaging space, while cooperating with the segmented + insulation gap 108 to suppress eddy current.

[0081] Figure 2 The right side of the figure is labeled as an asymmetric segmentation design (micro-shim adjustment), and presents a structure in which the circular core layer 104 is divided into independent units of different sizes and shapes. The right side of the figure is labeled as an asymmetric segmentation design (micro-shim adjustment), and the area shown has been labeled as 202, indicating that the core layer 104 is divided into a structure of independent units of different sizes and shapes by asymmetric segmentation.

[0082] Here, the magnetic field of the main magnet often has slight non-uniformity (such as deviation of the second-order magnetic field component, local unevenness caused by edge magnetic flux leakage), and symmetric segmentation alone cannot correct these deviations. Therefore, by asymmetric design as shown in 202, the shape, size or distribution of the local unit is adjusted, and the magnetic flux of a specific area is guided or compensated by using the magnetic conductivity characteristics of the soft magnetic composite material, thereby realizing a passive micro-shim function, and the specific effects include:

[0083] Second-order term compensation: correcting the deviation of the second-order polynomial component in the main magnetic field to make the magnetic field closer to the ideal uniform distribution; edge effect correction: improving the unevenness of the magnetic field in the edge region of the magnet caused by magnetic flux leakage and structural mutation; local non-uniformity improvement: fine-tuning the local slight magnetic field fluctuations near the imaging space; shim ring cooperation optimization: working with the shim ring 106 to reduce the compensation pressure of the shim ring and improve the efficiency of the overall magnetic field uniformity control.

[0084] Further, when symmetric segmentation is used as the segmentation pattern, as an example, please refer to Figure 3 , Figure 3 is a schematic diagram of core layer segmentation for a magnet pole plate of a nuclear magnetic resonance device according to an embodiment of the present application, as shown in Figure 3As shown, the left annular segmentation design 301 can represent segmenting the core layer 104 into multiple independent units (e.g. 4 concentric rings) in an annular manner, and the right radial segmentation design 302 can represent segmenting the core layer 104 into multiple independent units (e.g. 12 sectors) in a radial manner.

[0085] The adjacent independent units after segmentation are provided with an insulating gap 108 for realizing electrical isolation and magnetic flux adaptation.

[0086] Preferably, the width of the independent unit is 5-50 mm, and the width of the insulating gap 108 between adjacent independent units is 0.2-2 mm.

[0087] Here, if the width of the insulating gap 108 is too narrow, the independent units may be in contact due to processing errors, thus causing insulation failure, and if the width is too wide, the magnetic resistance of the magnetic circuit may be increased, thus affecting the main magnetic flux conduction.

[0088] In one possible implementation, the insulating material of the insulating gap 108 can include but is not limited to polyimide sheet, epoxy glass plate, alumina ceramic sheet, and insulating tape.

[0089] As an example, please refer to Figure 4 , Figure 4 is a detailed schematic view of the insulating gap of the magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application, as Figure 4 shown, the width of the independent unit after segmentation in the core layer 104 is 5-50 mm, the width of the insulating gap 108 between adjacent two independent units is 0.2-2 mm, and the height of the insulating gap 108 is consistent with the height of each independent unit.

[0090] In summary, the SMC formed by pressing and solidifying the iron-based powder coated with an insulating coating on the surface in the core layer 104 can realize the intrinsic high resistivity of the core layer 104, and can weaken the small eddy current inside the independent unit from the microscopic level; at the same time, the segmentation + insulating gap 108 setting blocks the large loop eddy current between the independent units from the macroscopic level, and together realizes near-zero eddy current.

[0091] In addition, the core layer 104 can also form a full-dimensional electrical isolation in the longitudinal (interlayer) + transverse (between independent units) direction with the first insulating layer 102, that is, the first insulating layer 102 can block the cross-layer eddy current between the substrate layer 101 and the core layer 104, and the core layer 104 can block the transverse eddy current between the independent units inside, thus cutting off all possible closed eddy current paths inside the pole plate.

[0092] The guide layer 103 is made of a magnetic conductive material with a higher resistivity than the substrate layer 101 and a lower magnetic resistance than air, and is arranged around the outer periphery of the core layer 104.

[0093] In this embodiment, the guiding layer 103 may be a functional layer disposed on the outer periphery of the core layer 104, used to guide the magnetic flux path of the gradient magnetic field and suppress eddy currents.

[0094] The magnetically conductive material that forms the guiding layer 103, has a resistivity higher than that of the substrate layer 101 and a magnetic resistance lower than that of air, can be a type of functional material that combines weak conductivity and strong magnetic permeability.

[0095] Specifically, the aforementioned functional materials must simultaneously meet the following conditions: their resistivity is significantly higher than that of the substrate layer 101 material to reduce their own eddy current generation; their magnetic resistance is lower than that of air to ensure that magnetic flux is more easily conducted inside the material rather than leaking into the air; and they have compatibility with structures such as the core layer 104.

[0096] The resistivity of the guiding layer 103 needs to be at least one order of magnitude higher than that of the substrate layer 101 material.

[0097] Furthermore, the guiding layer 103 is arranged around the outside of the core layer 104 in a spatial layout, forming a circumferentially enclosed structure, thereby directionally guiding the magnetic flux around the core layer 104 to avoid the magnetic flux from needing to diffuse.

[0098] Specifically, the core layer 104 can be used for high permeability magnetic conduction of the main magnetic flux and suppression of intrinsic eddy currents, while the guiding layer 103 can be used for gradient magnetic flux guidance and low eddy current loss. The two can form a division of magnetic circuits between the main magnetic flux and the gradient magnetic flux, without interfering with each other, thereby jointly ensuring the purity of the magnetic field.

[0099] The guiding layer 103 can also block the conduction of gradient magnetic flux to the substrate layer 101 through the resistivity difference, so as to prevent the substrate layer 101 from generating strong eddy currents due to its low resistance characteristics, thereby assisting the first insulating layer 102 in achieving longitudinal synergy in blocking interlayer eddy currents.

[0100] The shimming ring 106 is located on the side of the core layer 104 near the imaging space.

[0101] In this embodiment, the shimming ring 106 is a functional ring component in the electrode plate used to compensate for magnetic field non-uniformity and shape the spatial magnetic field distribution for imaging.

[0102] Specifically, the shim ring 106 is designed for the main magnetic flux. To address edge attenuation and local distortion issues, the magnetic flux in specific areas can be enhanced or weakened through its own magnetic permeability, thereby optimizing the uniformity of the imaging spatial magnetic field.

[0103] Here, the shim ring 106 can be used to correct the main magnetic flux. The attenuation gradient at the edge of the imaging space (caused by the magnetic flux leakage of the core layer edge) makes the magnetic field strength of the edge region consistent with that of the center region, which can be used to offset the local slight magnetic field fluctuation caused by the core layer segmentation gap, guide layer magnetic flux leakage, etc., and ensure the uniform distribution of the magnetic field in the imaging space.

[0104] The shim ring 106 is arranged between the core layer 104 and the imaging space, which can ensure that the magnetic field compensation effect thereof directly acts on the imaging region, and avoid the compensation accuracy from being attenuated due to the too far distance between the layers.

[0105] In the magnet pole plate for the nuclear magnetic resonance device, the manufacturing method and the magnet system in the above-mentioned embodiments of the present application, the core layer is made of a soft magnetic composite material formed by pressing and curing an iron-based powder coated with an insulating coating, and the high volume resistivity thereof can inhibit eddy current from the material intrinsic layer; meanwhile, the core layer is segmented along the radial and / or radial directions and provided with an insulating gap, which can directly break the closed eddy current loop inside the pole plate and block the eddy current forming path; in combination with the guide layer with the resistivity higher than that of the substrate layer and the magnetic resistance lower than that of air and arranged around the outer periphery of the core layer, the gradient magnetic flux can be guided to be closed along the high-resistance path preferentially, and the magnetic flux from entering the low-resistance substrate layer to induce eddy current can be avoided. The above-mentioned three aspects can work together to solve the residual eddy current problem of the traditional pole plate under the fast imaging sequence, realize near-zero eddy current under the gradient pulse, and thus significantly improve the image quality. The substrate layer is made of a magnetically conductive metal material, which not only provides reliable mechanical support for the pole plate, but also serves as the basic path for the main magnetic flux conduction; the SMC of the core layer has sufficient magnetic permeability to maintain the continuity of the main magnetic flux, and the first insulating layer only blocks the electrical coupling (inhibits eddy current) without affecting the magnetic flux transmission. The overall structure does not need to compromise between the magnetic flux, eddy current inhibition and mechanical strength, and can meet the core performance requirements of the pole plate for the high-field MRI device, so as to balance the high magnetic flux continuity and mechanical robustness. Due to the near-zero eddy current design, the eddy current loss is greatly reduced, the temperature rise during the operation of the pole plate is significantly reduced, the risk of structural deformation caused by temperature rise is avoided, and the energy consumption of the device is directly reduced, which improves the long-term operation stability of the device. By the near-zero eddy current design, the eddy current loss is greatly reduced, the temperature rise during the operation of the pole plate is significantly reduced, the risk of structural deformation caused by temperature rise is avoided, and the energy consumption of the device is directly reduced, which improves the long-term operation stability of the device.

[0106] In one possible implementation of the above-mentioned embodiments, the material of the first insulating layer 102 is selected from an epoxy glass fiber plate, a polyimide composite sheet or a stack of the two.

[0107] In the present embodiment, the epoxy glass fiber plate can be a rigid insulating plate formed by impregnating an epoxy resin into an alkali-free glass fiber cloth as a reinforcing framework and then heat pressing and curing. The dielectric strength of the epoxy glass fiber plate is preferably not less than 20 MV / m, which meets the safety standards of medical devices, and the high rigidity thereof helps to maintain the overall structure flatness of the pole plate.

[0108] ​​​Polyimide composite sheets can be flexible / semi-rigid insulating sheets made of polyimide resin as the base material and reinforced with glass fiber or inorganic fillers. A key advantage of polyimide composite sheets is their wide operating temperature range (e.g., -20°C to over 200°C), easily covering the typical operating temperature range of MRI equipment (-20°C to 80°C), and providing stable insulation performance.

[0109] The laminated epoxy fiberglass board and polyimide composite sheet can refer to a two-layer composite structure with epoxy fiberglass board as the base layer and polyimide composite sheet as the bonding layer.

[0110] Here, the laminated structure can combine the advantages of two materials: the base layer provides mechanical support to ensure the overall rigidity of the first insulating layer 102 and avoid bending deformation during assembly; the bonding layer utilizes its flexibility and high insulation to fill and bond the micro-irregularities on the surfaces of the substrate layer 101 and the core layer 104 under assembly pressure, achieving near-zero air gap interface contact, thereby minimizing the risk of cross-layer leakage current and partial discharge.

[0111] In addition, the coefficient of thermal expansion of the selected materials in the laminated structure should be between that of the substrate layer 101 (metal) and the core layer 104 (SMC) as a transition to reduce the internal thermal stress caused by the large difference in thermal expansion and contraction of the materials in each layer during temperature changes, and to prevent delamination or deformation.

[0112] In the magnet electrode plate, manufacturing method, and magnet system for nuclear magnetic resonance equipment according to the above embodiments of the present invention, the high dielectric strength of the epoxy fiberglass board ensures medical-grade insulation safety and completely blocks translayer eddy currents. The high rigidity of the epoxy fiberglass board maintains the structural flatness of itself and the electrode plate as a whole, ensuring a tight fit with the substrate layer 101 and the core layer 104, eliminating air gaps caused by assembly deformation, and directly preventing the main magnetic flux caused by air gaps. Leakage, ensuring main magnetic flux Low-loss conduction from substrate layer 101 to core layer 104. The operating temperature range of the polyimide composite sheet not only fully covers the conventional temperature range of MRI, but also has significant temperature redundancy, avoiding insulation failure caused by temperature changes in traditional insulating materials. The stacking of the two materials can simultaneously provide rigid support and flexible bonding, balancing assembly stability and interface insulation reliability.

[0113] In one possible implementation of the above embodiments, the iron-based powder of the soft magnetic composite material in the core layer is selected from high-purity water-atomized pure iron powder or alloyed iron powder, and the alloyed iron powder is Fe-Si-based iron powder or Fe-Si-Cr-based iron powder; the insulating coating of the soft magnetic composite material is selected from phosphate layer, silane / oxide coating or organic-inorganic composite coating.

[0114] In this embodiment, SMC is formed by pressing and curing iron-based powder with the aforementioned insulating coating on its surface. Its core feature is that it simultaneously possesses high magnetic permeability and high volume resistivity.

[0115] Iron-based powders constitute the magnetic matrix of SMC. High-purity water-atomized pure iron powder (e.g., purity not less than 99.8%) provides the basis for obtaining high magnetic permeability and low coercivity. Fe-Si or Fe-Si-Cr alloyed iron powders, through the solid solution effect of elements such as silicon (Si) and chromium (Cr), help optimize the resistivity, magnetostrictive properties, and high-temperature stability of the material.

[0116] The insulating coating achieves the encapsulation and electrical isolation of each iron-based powder particle, which is key to imparting high resistivity to the material. Phosphate layers, as a mature inorganic insulating layer, provide basic and stable heat-resistant electrical insulation properties; silane / oxide coatings (such as nano-silica) can effectively enhance the continuity and density of the insulating layer; organic-inorganic composite coatings combine the good adhesion and flexibility of organic materials with the heat resistance advantages of inorganic materials.

[0117] By combining the above material systems, the resulting SMC can maintain high permeability ( To ensure efficient conduction of magnetic flux in the static magnetic field (B0 field), while possessing a significantly higher volume resistivity than traditional magnetic metals. This greatly suppresses the eddy current induced by the gradient pulse from the intrinsic properties of the material, thus achieving near-zero eddy current in the electrode.

[0118] in, Relative permeability is a core indicator for measuring the magnetic permeability of a material; The minimum threshold for relative permeability is 600; This indicates the test conditions under which the permeability value was measured, i.e., under an applied magnetic field strength of 10 millitalas (mT). This means that SMC can control the main magnetic flux Low-loss conduction.

[0119] Volume resistivity is a core electrical performance indicator that measures a material's ability to impede the conduction of electric current; its unit is 1000 volts (V / V). ( ); The minimum threshold for representing volume resistivity is .

[0120] Here, compared to traditional magnetic metals (such as pure iron), SMC's... This means that the resistivity has increased by at least three orders of magnitude, which can fundamentally cut off the eddy current conduction path and achieve the goal of near-zero eddy current on the plate.

[0121] In the magnet pole plate for a nuclear magnetic resonance device, the manufacturing method and the magnet system of the above-mentioned embodiments of the present application, the closed vortex loop in the pole plate is systematically dispersed through the synergy of the intrinsic high resistivity of the SMC, the segmented insulation design and the guide layer. Under the action of the gradient pulse, the residual eddy current and the additional magnetic field generated thereby are greatly suppressed, thereby effectively reducing the image artifacts, geometric distortion and signal-to-noise ratio reduction problem, and improving the accuracy and consistency of the MRI imaging. Due to the high resistance characteristics of the SMC material and the significant reduction of the eddy current loss, the temperature rise of the pole plate in operation is greatly reduced, which is beneficial to the long-term stable operation of the MRI system. The high magnetic permeability of the SMC and the design of the field-homogenizing ring and the guide layer ensure the efficient conduction and uniformity of the static magnetic field, and on the premise of maintaining the magnetic flux capacity and mechanical robustness, better imaging uniformity and reliability are achieved.

[0122] In one possible implementation of the above-mentioned embodiments, the material of the guide layer 103 is selected from a ferrite ring, an insulating coated silicon steel arc segment or a spliced structure of the two.

[0123] In this embodiment, the guide layer 103 can be an auxiliary layer for gradient magnetic flux guidance and eddy current suppression in the pole plate.

[0124] The ferrite ring can be a ring-shaped structure made of soft magnetic ferrite materials such as manganese-zinc ferrite and nickel-zinc ferrite; the insulating coated silicon steel arc segment can be an arc-shaped segment cut from a high-resistivity silicon steel sheet after being coated with an insulating layer (such as an epoxy coating or a phosphate coating) on the surface; and the spliced structure of the two can be a combined structure of the ferrite ring as the main magnetic conductive segment and the insulating coated silicon steel arc segment as the locally adaptive segment.

[0125] The volume resistivity of the above-mentioned material is significantly higher than that of the substrate layer 101, which can greatly reduce the eddy current loss, and the magnetic resistance is much lower than that of air, which can efficiently accept and guide the gradient magnetic flux to close in the ring direction.

[0126] Specifically, the guide layer 103 is specifically used to preferentially capture the gradient magnetic flux outside the core layer 104 by the characteristic of the magnetic resistance lower than that of air, guide it to close in the guide layer 103 itself, rather than enter the low-resistance substrate layer 101, thereby blocking the path of the gradient magnetic flux diffusion to the substrate layer 101 to induce strong eddy current from the magnetic flux source.

[0127] In the magnet pole plate, manufacturing method, and magnet system for nuclear magnetic resonance (NMR) equipment according to the above embodiments of the present invention, the guiding layer 103, as a preset magnetic flux discharge path, actively attracts and accommodates time-varying gradient magnetic flux that would otherwise intrude into the substrate layer 101 and core layer 104, suppressing eddy current generation at the source. The guiding layer 103 itself is made of high-resistivity materials such as ferrite or insulating silicon steel; even if magnetic flux passes through, the resulting eddy current loss and thermal effect are extremely low, avoiding additional temperature rise problems caused by introducing a new structure. By confining the destructive time-varying magnetic flux within the guiding layer 103 around the pole plate, the main static magnetic path formed by the core layer 104 and substrate layer 101 is protected from interference. This helps maintain the stability of the static magnetic field, reduces interference with the gradient magnetic field, and thus directly contributes to reducing image artifacts and geometric distortion, improving the signal-to-noise ratio, and enhancing imaging quality.

[0128] In one possible implementation of the above embodiments, the shimming ring 106 is made of a soft magnetic material selected from Fe-Ni alloys, ferrites, or insulating coated silicon steel; the structure of the shimming ring 106 is configured to compensate for the edge effects of the static magnetic field through local variations in geometry.

[0129] In this embodiment, the shimming ring 106 is used to compensate for the main magnetic flux. Edge attenuation and local distortion provide a highly uniform magnetic field for the imaging space. Therefore, the soft magnetic material constituting the shimming ring 106 must meet the requirements of high magnetic permeability and low interference characteristics.

[0130] High permeability refers to having a sufficiently high relative permeability to efficiently receive the main magnetic flux transmitted from the core layer. It enhances / weakens magnetic flux in specific areas through its own magnetic permeability, achieving a compensation effect. Low-interference characteristics refer to avoiding the impact of its own eddy currents or magnetic losses on magnetic field stability.

[0131] Based on this, soft magnetic materials can be selected from Fe-Ni alloys, ferrites, or insulating coated silicon steel.

[0132] As an example, please refer to Figure 5 , Figure 5 This is a schematic diagram of the arrangement of the guiding layer and shimming ring of the magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present invention, as shown below. Figure 5 As shown, the shimming ring 106 is disposed on the side of the core layer 104 near the imaging space 501, forming a spatial relationship with the guiding layer 103 (taking a ferrite ring as an example) disposed around the outer periphery of the core layer 104; the imaging space 501 is located in the central region of the core layer 104, and the main magnetic flux... It can be transmitted to the uniform ring 106 through the core layer 104, while the gradient magnetic flux 502 is guided by the guiding layer 103 on the outer periphery of the core layer 104.

[0133] In the above-mentioned embodiments of the magnet pole plate for a nuclear magnetic resonance device, the manufacturing method, and the magnet system, the one-time and permanent magnetic field optimization can be completed in the factory stage through the precisely processed and installed field-shimming ring. This passive field-shimming method reduces the dependence on a complex and expensive active field-shimming system or significantly reduces the burden of the active field-shimming when used in combination, thereby simplifying the system structure, reducing the manufacturing cost, and reducing the maintenance complexity. The field-shimming ring 106 is the front end of the pole plate assembly, which works in cooperation with the rear core layer 104 and the guide layer 103. The core layer 104 and the guide layer 103 ensure the low-loss conduction of the magnetic flux and the suppression of eddy currents, and provide a clean and stable magnetic field working background for the field-shimming ring 106. The field-shimming ring 106 further refines the magnetic field on this basis. The cooperative design ensures the best balance of the entire pole plate system in terms of magnetic field uniformity, stability, and rapid response, and finally realizes the goal of improving the imaging quality.

[0134] In one possible implementation of the above-mentioned embodiments, as shown in Figure 6 Figure 6 is a second hierarchical structure sectional view of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application, and the magnet pole plate further comprises a second insulating layer 105, which is arranged between the core layer 104 and the field-shimming ring 106, is made of a material with electrical insulation and higher magnetic resistance than the core layer, and is selected from an epoxy glass plate, a polyimide composite sheet, or a stack of the two, for avoiding the formation of an electrically conductive coupling or magnetic flux interference between the core layer 104 and the field-shimming ring 106.

[0135] In this embodiment, the second insulating layer 105 is configured to avoid the formation of an electrically conductive coupling or magnetic flux interference between the core layer 104 and the field-shimming ring 106, thereby suppressing the cross-layer eddy current and ensuring the directional conduction of the main magnetic flux and the gradient magnetic flux.

[0136] Therefore, the material for manufacturing the second insulating layer 105 needs to meet the requirements of electrical insulation and higher magnetic resistance than the core layer 104. The electrical insulation can block the electrically conductive path between the core layer 104 and the field-shimming ring 106 from the electrical perspective, and the higher magnetic resistance than the core layer 104 can regulate the transmission path and priority of the magnetic flux between the core layer 104 and the field-shimming ring 106 from the magnetic perspective.

[0137] Specifically, the electrical insulation of the second insulating layer 105 completely blocks the electronic migration path between the core layer 104 and the field-shimming ring 106, avoiding the induction of a cross-layer eddy current between the two layers by the gradient pulse. In combination with the internal eddy current suppression of the core layer 104 and the magnetic flux path eddy current suppression of the guide layer 103, the second insulating layer 105 further fills the gap in the eddy current prevention between the core layer 104 and the field-shimming ring 106 from the interlayer electrical isolation dimension, and finally strengthens the near-zero eddy current effect. ​​

[0138] The second insulation layer 105 has a higher magnetic resistance than the core layer, which can guide the main magnetic flux The main magnetic flux is preferentially conducted along the high magnetic conductive path inside the core layer 104 to the shim ring 106, avoiding the main magnetic flux The main magnetic flux is diffused in disorder at the interface between the core layer 104 and the shim ring 106, ensuring the main magnetic flux The efficiency and uniformity of the transmission; at the same time, it can isolate the local magnetic flux adjustment of the shim ring 106 due to the local change of the geometric shape to compensate for the edge effect, preventing it from interfering with the main magnetic flux of the core layer 104 Distribution, providing the shim ring 106 with an undisturbed magnetic flux input for precise correction of the magnetic field edge effect, ultimately improving the magnetic field uniformity of the imaging space.

[0139] Further, the epoxy glass plate and the polyimide composite sheet are both mature materials with high mechanical strength and excellent heat resistance, which can work stably for a long time in the magnetic field environment and temperature fluctuations (such as temperature rise during equipment operation) of the MRI equipment: They provide reliable structural support for the core layer 104 and the shim ring 106, ensuring the overall mechanical robustness of the pole plate.

[0140] In one possible implementation of the above embodiment, the magnetic pole plate further comprises an anti-eddy current lamination disc; the anti-eddy current lamination disc is arranged on the side of the substrate layer 101 away from the first insulation layer 102 and is made of multiple pieces of high-resistivity silicon steel sheets that have been electrically insulated and stacked in the thickness direction of the pole plate.

[0141] In this embodiment, the anti-eddy current lamination disc is arranged on the side of 101 away from the first insulation layer 102, opposite to the side where the core layer 104 is located.

[0142] The anti-eddy current lamination disc is made of multiple pieces of high-resistivity silicon steel sheets that have been electrically insulated and stacked in the thickness direction of the pole plate.

[0143] Among them, the high-resistivity silicon steel sheet (such as silicon steel containing more than 3% silicon) itself has a higher resistivity than pure iron, and the surface of each silicon steel sheet is electrically insulated by coating an insulating coating (such as an epoxy coating, a phosphate coating), and there is no direct conductive path between the pieces after stacking.

[0144] In the above embodiments of the present invention, the magnet electrode plate, manufacturing method, and magnet system for nuclear magnetic resonance equipment, the substrate layer 101 is made of magnetically conductive metal. Although it provides support for the magnetic circuit, its low resistivity makes it susceptible to strong eddy currents induced by gradient pulses. The anti-eddy current stack disk, through a design of high-resistivity silicon steel sheets and inter-sheet electrical insulation, utilizes the high resistivity of the silicon steel sheets to reduce the eddy current density within a single sheet. The inter-sheet insulating coating completely cuts off the longitudinal closed path of the eddy current along the thickness direction of the electrode plate, dividing the large-scale eddy currents that might otherwise form in and around the substrate layer 101 into tiny eddy currents within the silicon steel sheets. This significantly weakens the overall intensity and range of influence of the eddy currents, further enhancing the eddy current suppression effect from the back side of the electrode plate. The high-resistivity silicon steel sheets still possess the high magnetic permeability of soft magnetic materials; therefore, the anti-eddy current stack disk, while suppressing eddy currents, does not excessively obstruct the main magnetic flux. The longitudinal transmission, i.e., the main magnetic flux It can penetrate the stacked disk, continuing to provide a basic magnetic path for the magnetic field of the magnet system. This design achieves a balance between suppressing eddy currents and preserving magnetic flux, avoiding the loss of main magnetic flux due to excessive insulation. The conduction is blocked, ensuring the continuity of magnetic flux throughout the magnetic circuit.

[0145] In one possible implementation of the above embodiments, the iron-based powder of the soft magnetic composite material in the core layer has a particle size of 20 to 300 micrometers; the insulating coating covering the surface of the iron-based powder has a thickness of 0.1 to 5 micrometers; and the bulk density of the soft magnetic composite material after pressing and curing is not less than 95% of the theoretical density.

[0146] In this embodiment, preferably, the particle size of the fine powder in the iron-based powder can be 20-50 micrometers (μm), the particle size of the medium powder can be 50-150 μm, and the particle size of the coarse powder can be 150-300 μm. The particle packing efficiency can be optimized by combining bimodal or multimodal particles.

[0147] Here, the particle size of the iron-based powder is not a single fixed particle size, but can be flexibly adjusted according to the thickness and magnetic permeability requirements of the core layer 104. For example, the proportion of coarse powder can be appropriately increased for a thick core layer to improve pressing efficiency, while the proportion of fine powder needs to be increased for a thin core layer to ensure compactness.

[0148] The thickness of the insulating coating on the surface of iron-based powder refers to the thickness of the electrically insulating layer covering the surface of a single iron-based powder particle. The electrically insulating layer includes, but is not limited to, a phosphate layer, a silane / oxide coating, or an organic-inorganic composite coating.

[0149] Here, the thickness of the insulating coating is 0.1 to 5 μm. 0.1 μm is the lower limit to ensure the continuity of insulation (too thin and the insulation will fail due to particle collision), while 5 μm is the upper limit to avoid the decrease in magnetic permeability (too thick and the magnetic resistance between particles will increase, resulting in a decrease in the overall magnetic permeability of SMC).

[0150] The bulk density of SMC after compression curing refers to the percentage of the actual density of SMC after compression curing to the theoretical density of iron-based powder. The theoretical density specifically refers to the inherent density of the iron-based powder itself (e.g., the theoretical density of pure iron is approximately...). ).

[0151] Here, the bulk density of SMC after pressing and curing is the core standard for evaluating the quality of the SMC pressing process, and it is directly related to magnetic and electrical properties. That is, the higher the density, the closer the contact between the iron-based powder particles, the smoother the magnetic conduction path, and the less likely the insulating coating between the particles is to be damaged due to excessive gaps.

[0152] Taking the theoretical density of pure iron as an example, a density not less than 95% of the theoretical density corresponds to the actual density of SMC. .

[0153] In the magnet pole plate, manufacturing method, and magnet system for nuclear magnetic resonance (NMR) equipment described in the above embodiments of the present invention, selecting an iron-based powder particle size of 20-300 μm optimizes particle packing efficiency, balances packing properties and flowability, and ensures magnetic circuit continuity. An insulating coating thickness of 0.1-5 μm enables synergistic particle-level electrical isolation and permeability protection. (Bulk density...) Theoretical density can enhance magnetic properties and structural stability, ensuring long-term reliable operation. The selection of the above three parameters can achieve high permeability and high resistivity through optimized particle size packing, packing density assurance, and density-synergistic coating.

[0154] In one possible implementation of the above embodiments, such as Figure 7 As shown, Figure 7 This is a cross-sectional view of a third layered structure of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present invention. The magnet pole plate also includes a shell / framework 107. The shell / framework 107 is a non-magnetic high-strength composite material selected from carbon fiber composite material or glass fiber composite material. It covers the outer periphery of the assembly composed of substrate layer 101, first insulating layer 102, core layer 104, guiding layer 103 and shimming ring 106, and forms a pre-tight fit with core layer 104.

[0155] In this embodiment, the material used to make the shell / frame 107 must meet the requirements of being non-magnetic, having high strength, and being lightweight.

[0156] The non-magnetic nature of the housing / framework 107 ensures that it does not introduce additional magnetic resistance or magnetic field distortion into the magnetic circuit, thus avoiding interference with the main magnetic flux. Directional conduction of gradient magnetic flux; high strength ensures that the shell / frame 107 can withstand the weight of the electrode plate, assembly preload and electromagnetic force during MRI operation, avoiding overall structural deformation; lightweight design reduces the overall weight of the electrode plate and reduces the load on the magnet system.

[0157] Therefore, the material for making the shell / skeleton 107 can be selected as a carbon fiber reinforced polymer (CFRP) or a glass fiber reinforced polymer (GFRP).

[0158] The pre-tightening fit of the shell / skeleton 107 with the core layer 104 can be achieved based on the following steps:

[0159] The shell / skeleton 107 is formed by using a prepreg lay-up curing process, that is, before the core assembly is wrapped, carbon fiber / glass fiber prepreg is laid on the outer periphery of the core assembly at a designed angle, and is cured by vacuumizing and heating. During the curing process, the prepreg shrinks to generate a radial pre-tightening force, so that the shell / skeleton 107 is tightly attached to the core layer 104, the guide layer 103 and other layers. This not only avoids the generation of gaps between the layers due to vibration (the gaps will increase the magnetic resistance), but also constrains the thermal expansion and contraction deformation of each layer, thereby ensuring long-term structural stability.

[0160] In one possible implementation manner of the above embodiment, the shell / skeleton 107 is provided with a heat dissipation channel; the heat dissipation channel is a transverse cooling fluid channel (i.e., a liquid heat dissipation channel) or a longitudinal heat dissipation channel (i.e., an air heat dissipation channel), which is used to guide the heat generated during the operation of the pole plate out.

[0161] In this embodiment, preferably, the air heat dissipation channel can be a through hole reserved on the radial reinforcing ribs or the circumferentially wound layers of the shell / skeleton 107, and can be uniformly distributed along the circumferential direction of the shell. Part of the holes are in communication with the gap of the pole core assembly, so as to form an air convection path.

[0162] The liquid heat dissipation channel can be a closed loop type hose or a formed flow channel embedded in the shell / skeleton 107. The inlet / outlet of the flow channel extends to the outside of the shell, and can be connected to the liquid cooling loop of the MRI system.

[0163] Here, the heat dissipation channel is configured to guide the heat generated during the operation of the pole plate to the external environment, so as to adapt to the working conditions of different MRI devices. For example, the air heat dissipation channel can be preferentially used for a medium-low field strength MRI, which utilizes the natural convection or fan-assisted heat dissipation inside the device to meet the preset operation requirements; the liquid heat dissipation channel can be preferentially used for a high field strength or high power MRI, which quickly removes the heat through the circulation of the cooling liquid to cope with extreme fast sequences.

[0164] In one possible implementation manner of the above embodiment, the magnet pole plate further includes a non-magnetic fastener 803; the non-magnetic fastener 803 is made of titanium alloy and / or austenitic stainless steel, and is used to connect the shell / skeleton 107 with the substrate layer 101 and the core layer 104, so as to avoid the relative displacement of each layer.

[0165] In the present embodiment, the non-magnetic fastener 803 can serve as a connection core of the shell / skeleton 107 and the core assembly.

[0166] The non-magnetic fastener 803 can be divided into two types: pre-buried studs and through bolts.

[0167] As an example, the pre-buried studs can be embedded in the preset positions of the radial reinforcing ribs simultaneously when the shell / skeleton 107 is formed, with one end of the stud matched with the threaded hole of the substrate layer 101 to provide a basic pre-tightening force; the through bolts are austenitic stainless steel bolts, which pass through the reserved holes of the shell / skeleton 107 and the positioning holes of the core assembly, and apply a pre-tightening force through a nut to ensure that the shell and the core assembly are tightly attached and avoid air gaps between the layers.

[0168] Preferably, the non-magnetic fastener 803 can be uniformly distributed along the circumferential direction of the shell / skeleton 107.

[0169] As an example, please refer to Figure 8 , Figure 8 is a layout diagram of a shell / skeleton and a fastener for a magnet pole plate of a nuclear magnetic resonance device according to an embodiment of the present application, as Figure 8 shown, the CFRP shell 805 (i.e., the shell / skeleton 107) is an annular structure made of carbon fiber composite material, which is internally provided with a circumferential winding layer 801 and a radial reinforcing rib 802 for improving overall rigidity, and a heat dissipation hole 804 is reserved.

[0170] At the preset positions of the radial reinforcing rib 802, the non-magnetic fastener 803 is assembled and uniformly distributed along the circumferential direction of the CFRP shell 805; part of the non-magnetic fastener 803 is in a local pre-buried form, and the other part of the non-magnetic fastener 803 is a through bolt for connecting the CFRP shell 805 and the pole core assembly to form an overall pre-tightening.

[0171] In the magnet pole plate, the manufacturing method and the magnet system for a nuclear magnetic resonance device in the above-mentioned embodiments of the present application, the shell / skeleton 107 avoids magnetic field interference through the non-magnetic properties of the material, which can guarantee the imaging uniformity. The material uses CFRP or GFRP, which has high strength and pre-tightening to strengthen the structure robustness and resist multi-working condition stress. By setting a heat dissipation channel, the loss heat can be accurately led out to guarantee the long-term performance stability of the pole plate. Through the non-magnetic fastener 803, the interlayer connection can be strengthened, and the structure and magnetic flux are guaranteed without interference.

[0172] Figure 9 is a flowchart of a manufacturing method of a magnet pole plate according to an embodiment of the present application, for manufacturing the magnet pole plate of any one of the above-mentioned embodiments, as Figure 9 shown, the method comprises the following steps:

[0173] Step S901, the iron-based powder is coated with an insulating coating to obtain an insulating coated powder; the insulating coated powder is pressed into a shape in a mold at a predetermined pressure, and then heat treated to solidify the insulating coating between the powders and eliminate internal stress, thereby forming a soft magnetic composite core blank.

[0174] In this embodiment, the manufacturing of SMC follows a specific material design and process flow to ensure that it has both high permeability and high volume resistivity , thereby significantly suppressing the eddy current induced by the gradient pulse while conducting the main magnetic flux .

[0175] Specifically, the iron-based powder, as the matrix of magnetic properties, can be selected from high-purity water-atomized pure iron powder or alloyed iron powder.

[0176] Exemplarily, the high-purity water-atomized pure iron powder can be selected from powder with ASC 100.29 brand, which has a purity of not less than 99.8% to ensure high permeability and low coercivity. The alloyed powder can be Fe–Si or Fe–Si–Cr iron powder, which can optimize the magnetostriction coefficient and resistivity of the material and improve the magnetic stability at high temperature through solid solution strengthening of alloying elements such as Si and Cr.

[0177] The particle size distribution of the iron-based powder can be designed as bimodal or multimodal to optimize the packing density.

[0178] Preferably, the median particle size D50 of the powder is about 80 μm, wherein D10 is about 45 μm and D90 is about 130 μm. The volume fraction of fine powder can be controlled between 18% and 22%, which helps to fill the voids between coarse particles, thereby obtaining higher green density and ultimate permeability.

[0179] The iron-based powder can be further controlled for impurities, with the content of impurities such as carbon (C), oxygen (O), nitrogen (N), and sulfur (S) being controlled at as low a level as possible, and in particular, the oxygen content should be less than 0.25‰ (by weight) to avoid the formation of non-magnetic inclusions and deterioration of magnetic properties.

[0180] Further, to achieve the purpose of insulating each particle, a continuous, dense, and firmly bonded electrically insulating layer is coated on the surface of the iron-based powder particles.

[0181] Preferably, the layer type of the electrically insulating layer includes but is not limited to phosphate layer, silane / oxide coating, organic-inorganic composite coating.

[0182] The phosphate layer, as the inorganic main insulation layer, has good heat resistance and electrical insulation, and the typical amount can account for 0.55% to 0.75% of the total weight of the powder; the silane / oxide coating can use silica sol with a particle size of 20-40 nanometers, and the amount can be 0.20% to 0.30%, which can fill the micro defects of the phosphate coating and enhance the continuity and density of the coating; the organic-inorganic composite coating combines the flexibility of organic matter and the heat resistance of inorganic matter, and a small amount (such as 0.05%-0.10%) of silane coupling agent, such as aminopropyl silane (type A1100), can be added to further improve the bonding force between the coating and the metal particles.

[0183] Here, the coating process of the iron-based powder on the electrical insulation layer can be carried out in the order of phosphate treatment → silica sol composite → low-temperature drying to ensure effective adhesion and coverage of each coating component, while avoiding significant reduction in magnetic permeability due to excessive coating thickness.

[0184] Preferably, the total weight of the coating is about 0.8% to 1.1% of the total weight of the powder.

[0185] Further, in order to balance the high green strength and the final magnetic properties, the iron-based powder also needs to be lubricated and pressed.

[0186] Preferably, the lubrication can mainly use mold wall lubrication, that is, the lubricant is applied to the inner wall of the mold by electrostatic spraying or oil mist.

[0187] Here, the amount of internal mixing lubricant can be reduced to 0.10%-0.15% (such as using amide wax), thereby reducing the negative impact of the lubricant occupying space or residual carbon on density, resistivity and magnetic permeability.

[0188] The pressing forming is preferably a warm die pressing process, in which the mold is heated to 75-85°C, and the powder is pressed at a unit pressure of 750-820MPa after being at room temperature or moderately preheated. Two-stage pressing and pressure holding for 10-20 seconds helps to control stress relaxation and springback, and obtain a compact with high density (green density up to 7.2-7.4g / cm3) and no microcracks. )and no microcracks.

[0189] Further, the powder is further heat treated and post-treated to solidify the coating, eliminate stress, and maintain electrical insulation between particles.

[0190] The heat treatment includes: in a typical heat treatment window, the compact is first kept in air at 180°C for 60 minutes to completely remove the mixed lubricant (dewaxing). Then, in a slightly wet steam atmosphere at 530°C for 30 minutes, the solidification of the coating such as phosphate is completed; then switch to dry nitrogen, keep at 530°C for another 30 minutes to further stabilize the coating and eliminate the pressing stress. The whole heat treatment process needs to be controlled cooling, the cooling rate is not more than 2K / min. The core control point is that the whole process temperature should not exceed 650°C, so as to prevent the formation of metal sintering neck between the particles and ensure the maintenance of high volume resistivity.

[0191] The post-processing includes: the heat-treated SMC compact is subjected to necessary machining (such as milling, grinding) to achieve the final size. In order to improve its long-term reliability in the internal environment of the MRI equipment, the SMC part can be subjected to impregnation sealing treatment, using epoxy resin or silicon-based impregnant to fill the open pores, so as to significantly improve its resistance to wet heat and corrosion resistance.

[0192] The SMC prepared by the above-mentioned material and process should achieve the following comprehensive performance indicators on a typical test sample (such as a φ25mm x h5mm ring sample) to meet the requirements of the MRI pole plate:

[0193] Physical properties: bulk density .

[0194] Electrical properties: volume resistivity Compared with pure iron (about ), the resistivity is increased by more than three orders of magnitude, which is the physical basis for realizing near-zero eddy current.

[0195] Magnetic properties: relative permeability under 10mT test conditions , ensuring efficient conduction of main magnetic flux Coercive force , ensuring low hysteresis loss. Iron loss under 1kHz, 0.1T conditions Saturation magnetic induction Permeability temperature stability .

[0196] In step S902, the soft magnetic composite material core compact is machined and cut into multiple independent units in the radial and / or radial directions; an electrically insulating material is arranged in the cutting gap between adjacent independent units to form a core layer with insulating gaps.

[0197] In this embodiment, the core target of this step can be to block the closed vortex loop inside the pole plate from the macroscopic structural level while ensuring that the magnetic properties of the SMC core compact are not damaged.

[0198] Specifically, the SMC core embryo prepared in step S901 is first machined to meet the dimensional accuracy and surface quality requirements of the core layer of the plate.

[0199] Here, the design size of the core blank before processing needs to be determined (such as a diameter of 500-1200 mm and a thickness of 20-50 mm, which can be determined by the MRI magnet field strength and the imaging space size), and the processing method preferably adopts a combination of milling and grinding.

[0200] Preferably, the upper and lower end faces of the blank are first coarsely milled using a numerical control vertical milling machine to remove the surface oxidation layer and warping deformation after heat treatment and to reserve a portion of the fine grinding allowance; then fine grinding is performed using a numerical control surface grinder to ensure that the flatness, upper and lower end face parallelism, and surface roughness of the core blank meet the preset accuracy requirements. The preset accuracy requirements can avoid air gaps due to uneven surfaces during subsequent layer assembly, prevent main magnetic flux leakage or partial discharge, and the like.

[0201] Preferably, diamond cutters can be used during processing, pure water-based emulsion can be used for cooling to prevent oily liquids from affecting insulation, and ultrasonic cleaning can be performed after processing to remove debris.

[0202] Further, the SMC core blank after machining is segmented and cut in the radial and / or radial directions to form a plurality of independent units, and the cutting process needs to strictly match the dual requirements of eddy current suppression and magnetic field uniformity.

[0203] Among them, the cutting method can be selected according to the magnetic field distribution requirements of the MRI magnet.

[0204] For example, if a basic uniform magnetic field is required, radial + radial direction combined cutting can be used to form fan-shaped independent units;

[0205] If edge magnetic field compensation is required, radial direction asymmetric cutting can be used to form independent units with different sizes / shapes, and passive micro-homogeneous field function is achieved through structural asymmetry (correcting the second-order component deviation of the main magnetic flux).

[0206] In addition, a numerical control laser cutting machine or a diamond disc saw cutting machine is preferably selected to ensure that the width tolerance of the cutting gap meets the preset processing requirements; the blank can be vacuum adsorbed and fixed during cutting to avoid cutting deviation caused by vibration; for fan-shaped unit cutting, the geometric center of the core blank is taken as the reference, the cutting angle deviation is set to be less than the preset deviation requirement through the numerical control system, and the splicing accuracy of adjacent units is ensured.

[0207] The width (the maximum size in the radial or radial direction) of the independent unit needs to be controlled within 5-50 mm, and the width that is too small will increase the assembly difficulty and magnetic resistance, and the width that is too large will not be able to effectively disperse large-scale eddy currents.​​

[0208] Preferably, the cut end face of the independent unit can also be deburred after cutting to prevent scratching the insulation material during subsequent assembly.

[0209] Further, an electrically insulating material is arranged in the cutting gap between adjacent independent units to achieve electrical isolation between units and fix the position of the units, forming a core layer 104 with an insulating gap 108.

[0210] The filling method can be flexibly selected according to the characteristics of the insulating material, the size of the cutting gap, and the assembly accuracy requirement, to achieve the goal of close fitting of the insulating material to the unit end face without air bubbles or loose core.

[0211] For example, when the gap size is small, the insulating material can be cut into a shape matching the cross section of the gap and then embedded. After embedding, pressure is applied through pressure means such as silicone roller, flat press, etc. The specific pressure value can be adjusted according to the pressure resistance of the material.

[0212] When the gap size is large, a combination of insulating material + insulating glue can be used for filling. First, a thin layer of insulating glue (such as epoxy insulating glue) is applied to the unit end face on both sides of the gap, then the insulating material is embedded and pressure is applied for curing. The type of insulating glue and the curing parameters can be determined according to the material compatibility.

[0213] The width of the insulating gap 108 between adjacent independent units needs to be set according to the comprehensive requirements of magnetic circuit design and processing accuracy, in order to prevent unit contact leading to insulation failure, and not significantly increase the magnetic resistance of the magnetic circuit.

[0214] For example, the gap width is 0.2-2mm. A too narrow gap is easy to cause unit contact due to processing errors or vibration, and a too wide gap may increase the main magnetic flux leakage. The specific value needs to be optimized in combination with the actual magnetic circuit.

[0215] After filling, the insulation effect and assembly accuracy need to be inspected. The inspection method can be selected according to actual requirements.

[0216] In step S903, the substrate layer, the first insulating layer, and the core layer with an insulating gap are sequentially stacked and aligned. The guide layer is assembled around the outer periphery of the core layer, and the field uniformity ring is directionally assembled on the side of the core layer close to the imaging space, to complete the fixed assembly of each component.

[0217] In this embodiment, the core goal of this step is to ensure magnetic flux continuity through precise stacking and alignment, ensure functional effectiveness through directional assembly, and strengthen structural stability through fixed assembly, so that each component forms a whole that works cooperatively, avoiding layer misalignment that interferes with the main magnetic flux ​Conduction, also ensures that the guide layer and the field uniform ring can accurately play the role of gradient magnetic flux guidance and magnetic field uniformization. All operations are carried out around the general needs of adapting to different specifications of the plate, and compatible with various magnetic circuit designs.

[0218] Specifically, the lamination and alignment of the substrate layer 101, the first insulating layer 102, and the core layer 104 (hereinafter referred to as the core layer 104) can include: lamination sequence confirmation, alignment reference setting and operation, and interlayer adhesion protection.

[0219] Among them, the lamination sequence confirmation can be realized based on the following steps: according to the magnetic circuit conduction logic, taking the substrate layer 101 as the mechanical basis, the first insulating layer 102 realizes the interlayer electrical isolation, and the core layer 104 accepts and conducts the main magnetic flux As a principle, the lamination sequence is determined as substrate layer 101→first insulating layer 102→core layer 104. Specifically, the interlayer adaptation relationship can be adjusted according to the overall structure design of the plate (such as whether it contains a second insulating layer 105), but it is necessary to ensure that the first insulating layer 102 is always located between the substrate layer 101 and the core layer 104, to avoid direct contact between the two to form a cross-layer eddy current loop.

[0220] The alignment reference setting and operation can be realized based on the following steps: taking the geometric center axis of the plate or the pre-set positioning mark as the unified alignment reference, using the appropriate positioning tooling (such as a support platform with a center positioning pin, an edge alignment clamp) to assist the alignment of each layer; first fix the substrate layer 101 on the positioning tooling, so that its reference coincides with the tooling reference; then cover the first insulating layer 102 on the substrate layer 101, and ensure that the edge deviation and center deviation of the two meet the assembly accuracy requirements through visual comparison or tooling limiting, for example, control the center deviation to be less than 0.5mm, and the edge misalignment to be less than 1.0mm (the two values are only examples, which can be adjusted according to the plate diameter and magnetic circuit precision requirements); finally, place the core layer 104 on the first insulating layer 102, adjust the position of the core layer 104, so that the center and edge positioning features (such as positioning holes, keyways) of the core layer 104 match the reference of the substrate layer 101 and the first insulating layer 102, for example, the positioning feature deviation is less than 0.1mm (the value is only an example, which needs to adapt to the positioning tooling accuracy), to ensure that the subsequent main magnetic flux Can be smoothly transmitted along the interlayer vertical direction.

[0221] The interlayer bonding can be achieved based on the following steps: during the alignment of each layer, the close interlayer bonding can be ensured by auxiliary means (such as vacuum adsorption, light pressure positioning) without obvious air gap; if the first insulating layer 102 is a flexible material (such as a polyimide composite sheet), it can be bonded to the surface microtopography of the substrate layer 101 and the core layer 104 by uniform pressure; if it is a rigid material (such as an epoxy glass fiber plate), the surface flatness of each layer needs to be confirmed in advance to meet the assembly requirements, for example, the surface flatness is ≤0.03 mm / m (this value is only an example, and it is necessary to avoid the formation of interlayer gap due to protrusion), and finally ensure that the interlayer gap meets the magnetic circuit requirements, for example, the interlayer gap is less than 0.05 mm (this value is only an example, which can be adjusted according to the thickness of the insulating material and the allowed range of magnetic flux leakage).

[0222] Further, the guide layer 103 is assembled around the outer periphery of the core layer 104, which can include: surrounding position and attitude control, guide layer 103 fixation.

[0223] The surrounding position and attitude control can be achieved based on the following steps: according to the gradient magnetic flux guiding requirement, the guide layer 103 is assembled around the outer periphery of the core layer 104, and the inner side is adapted and bonded to the outer periphery wall of the core layer 104, to ensure that the guide layer can fully capture the gradient magnetic flux of the outer periphery of the core layer; if the guide layer 103 is a split structure (such as a multi-segment insulating coated silicon steel arc segment), each segmented guide layer needs to be arranged around the outer periphery of the core layer 104 in a predetermined order, and the butt joint gap of adjacent segments needs to be adjusted, for example, the butt joint gap is less than 0.2 mm (this value is only an example, which needs to avoid the leakage of gradient magnetic flux from the gap); if it is a one-piece structure (such as a ferrite ring), the guide layer 103 is directly sleeved from the outer periphery of the core layer 104, to ensure that the coaxiality and radial gap of the guide layer 103 and the core layer 104 meet the magnetic circuit design requirements, for example, the coaxiality error is less than 0.2 mm, and the radial gap is controlled within 0.1-0.3 mm (these two values are only examples, which need to adapt to the gradient magnetic flux guiding efficiency).

[0224] The guide layer 103 fixation can be achieved based on the following steps: the guide layer 103 is fixed to the outer periphery of the core layer by an appropriate fixing method, and the fixing process needs to avoid damaging the magnetic conductivity and insulation performance of the guide layer 103; if insulating glue is used, a type compatible with the material of the guide layer 103 and non-magnetic is selected, and coated on the contact area of the guide layer 103 and the core layer 104 or the support area of the guide layer 103 and the substrate layer 101, for example, the thickness of the glue layer is controlled within 50-100 μm (this value is only an example, which needs to avoid the influence of too thick glue layer on bonding), and the fixation is realized after the glue layer is solidified; if a mechanical clamp is used, it needs to ensure that the clamp is made of non-magnetic material, and the clamping force is moderate, for example, the clamping force is controlled within 50-100 N (this force value is only an example, which needs to be adjusted according to the strength of the guide layer material to avoid plastic deformation of the guide layer 103 and affect the magnetic flux guiding path.

[0225] Further, the shim ring 106 is directionally assembled on the side of the segmented core layer close to the imaging space, which can include: directional reference confirmation and assembly, and shim ring position fixation.

[0226] The directional reference confirmation and assembly can be implemented based on the following steps: the magnetic field compensation area of the shim ring 106 directly faces the imaging space and can directly act on the main magnetic flux distribution. The directional principle is to first determine the side of the core layer 104 close to the imaging space, and then place the shim ring 106 on the side of the core layer 104 in a predetermined posture (such as the ring surface being parallel to the end surface of the core layer 104, and the compensation structure of the shim ring 106 facing a specific area of the imaging space). If the shim ring 106 has positioning features (such as protrusions matching the edges of the core layer 104, and identifiers corresponding to the imaging space), the directional accuracy of the shim ring 106 needs to be ensured through these features, for example, the directional deviation is less than 0.3 mm (this value is only an example, and needs to adapt to the magnetic field compensation accuracy requirement), to avoid the magnetic field compensation effect deviating from the design target due to directional deviation. If the second insulating layer 105 needs to be arranged between the shim ring 106 and the core layer 104, the second insulating layer 105 is assembled first, and then the shim ring 106 is assembled according to the above directional requirements, and the fitting gap of the second insulating layer 105 and the shim ring 106, the core layer 104 is ensured to meet the requirements, for example, the fitting gap is less than 0.05 mm (this value is only an example, and needs to avoid affecting the main magnetic flux transmission).

[0227] Further, according to the strength of the pole plate structure and the operation condition requirement, an appropriate overall fixation mode is selected.

[0228] For example, non-magnetic fasteners 803 can be used to fix each layer in the assembly order, ensuring that the fasteners only act on the non-functional area of the pole plate and do not penetrate the independent unit of the core layer or the magnetic conduction area of the guide layer. The layers, guide layer, and shim ring can also be integrally bonded and fixed by insulating glue, or combined with tooling for auxiliary fixation, and the fixation effect can be further strengthened after the shell / skeleton 107 is assembled later.

[0229] After the fixation assembly is completed, the position and fitting state of each component are inspected.

[0230] For example, visual inspection can be used to confirm that each layer is not misaligned, the guide layer 103 is complete, and the shim ring 106 is correctly oriented. The interlayer electrical isolation performance can be verified by simple testing. The physical inspection (such as gently pushing each component to confirm that there is no looseness) can ensure the fixation reliability, and the overall function is not affected, and the subsequent main magnetic flux and gradient magnetic flux are stable.

[0231] Step S904, the stacked assembly is covered or fixed by a non-magnetic shell or skeleton, and a pre-tightening force is applied for overall fixation, and the manufacturing of the magnet pole plate is completed.

[0232] In the embodiment, the shell / skeleton 107 made of non-magnetic high-strength composite material (such as carbon fiber composite material or glass fiber composite material) is selected to ensure that the material is non-magnetic and can adapt to the outer peripheral size of the stacked assembly. The shell is covered on the outer periphery of the stacked assembly, or the skeleton is used to frame-fix the key stress part of the assembly to ensure that there is no exposed functional area of the assembly.

[0233] A radial or axial pre-tightening force is applied through a preset process (such as shell pre-impregnated material curing shrinkage and non-magnetic fastener 803 tightening), for example, the pre-tightening pressure is controlled at 5-10 MPa (this value is only an example, which can be adjusted according to the size of the assembly), so that the shell / skeleton 107 and the stacked assembly are tightly fitted without interlayer gap.

[0234] After checking whether the fitting state of the shell / skeleton 107 and the assembly and the pre-tightening force are uniform and confirming that there is no looseness, the manufacturing of the magnet pole plate is completed.

[0235] In the magnet pole plate for the nuclear magnetic resonance device, the manufacturing method and the magnet system of the above-mentioned embodiments of the application, the SMC core blank is successfully manufactured through the process path of “insulation covering-pressing forming-low temperature curing”. This process inherently realizes the unification of high magnetic permeability and high volume resistivity at the material level. Through the steps of segmented cutting and embedding insulating material, the manufacturing method can systematically and controllably introduce physical insulation barriers in the core layer, which completely disperses the macroscopic eddy current path in three-dimensional space. The assembly step integrates multiple structural units with different functions into an organic whole with high performance coordination of magnetic circuit and electric circuit, which can stably and repeatedly produce pole plates with near-zero eddy current, high magnetic field uniformity and structural robustness, can reduce the overall eddy current related cost and improve the image consistency and reliability, and has significant industrial value.

[0236] In one possible implementation of the above-mentioned embodiment, the segmented cutting adopts wire cutting or water jet cutting; when the electrically insulating material is arranged in the cutting gap between adjacent independent units, it is achieved by inserting an insulating sheet and gluing and curing the contact part of the insulating sheet and the independent unit; wherein the material of the insulating sheet is selected from epoxy glass fiber sheet, polyimide sheet or laminated sheet of the two.

[0237] In the present embodiment, the machined SMC core blank is fixed to a special tooling (such as a platform with positioning pins) to align with the geometric center of the pole plate or a pre-set mark as the reference; according to the segmentation design, linear cutting (adapt to fine gap, avoid damage to the powder insulation coating) or water jet (adapt to large size blank, reduce heat affected zone) is selected to cut along the radial and / or radial direction to form multiple independent units, ensuring that the cutting gap width meets the design requirements.

[0238] Select epoxy glass flakes, polyimide flakes, or laminated flakes of both, and cut them into shapes that match the size of the cutting gap; insert the insulating flakes into the cutting gap between adjacent independent units, ensuring that the flakes fit the end surface of the unit; apply non-magnetic epoxy insulation glue to the contact part of the flake and the independent unit, and cure it in a normal or low temperature environment (such as 25°C for 2-4 hours); after curing, check if the flake is stable and not loose, and complete the insulation gap 108 setting.

[0239] In the above-mentioned embodiments of the magnet pole plate for a nuclear magnetic resonance device, the manufacturing method, and the magnet system, by selecting precise machining techniques such as linear cutting or water jet, a controllable width and neat edge cutting gap can be formed on the brittle SMC blank, which can effectively avoid micro-cracks caused by mechanical stress and prevent damage to the powder insulation coating in the heat affected zone, thereby accurately realizing physical segmentation while maintaining the intrinsic high performance of SMC materials. By inserting insulating flakes and supplementing with glue curing, this technology not only establishes reliable permanent electrical insulation between adjacent units, but also provides additional mechanical support and connection through the cured glue layer and the flake. This allows multiple independent units to be completely isolated electrically to block the eddy current loop while still being able to bear structural stress as a whole mechanically.

[0240] Figure 10 is a schematic diagram of the architecture of a magnet system according to an embodiment of the present application, including a main magnet 1001, a gradient coil 1003, and any of the above-mentioned magnet pole plates 1002. The upper and lower main magnets 1001 (N and S poles respectively) are used to generate a longitudinal main magnetic flux B0, and the upper and lower magnet pole plates 1002 are arranged on the inner side surfaces of the upper and lower main magnets 1001 respectively. The upper and lower gradient coils 1003 are arranged adjacent to and parallel to the upper and lower magnet pole plates 1002 respectively. The magnet pole plate 1002, composed of a core layer of soft magnetic composite material and an insulation segmentation structure, suppresses the eddy current induced by the gradient pulse under the action of the gradient pulse.

[0241] In the present embodiment, the main magnet 1001 is used to provide a main magnetic flux In the present embodiment, the main magnet 1001 can include N-pole and S-pole main magnets arranged in an up-down distribution, which cooperate to form a longitudinal main magnetic flux path to provide a basic static magnetic field for the imaging space 501 (the space covered by the dashed circle in the figure).

[0242] The magnet pole plate 1002 is provided with two upper and lower plates, which are located between the main magnet 1001 (N pole, S pole) and the gradient coil 1003. The magnet pole plate 1002 is composed of a core layer of soft magnetic composite material and is segmented by an insulating segmented structure. When the gradient coil 1003 is connected with a gradient pulse current, the magnet pole plate 1002 can effectively suppress the eddy current induced by the gradient pulse by means of the low eddy current characteristic of the soft magnetic composite material and the blocking effect of the insulating segmented structure on the current, thereby avoiding the interference of the eddy current on the stability of the gradient magnetic field and the imaging quality.

[0243] The gradient coil 1003 and the magnet pole plate 1002 are arranged adjacently and in parallel (the upper and lower gradient coils 1003 are arranged on the upper and lower sides of the imaging area, respectively, corresponding to the upper and lower magnet pole plates 1002), which is used to superimpose a time-varying gradient magnetic field on the main magnetic flux to realize the spatial encoding of the magnetic resonance signal in the imaging area and meet the gradient field requirement of magnetic resonance imaging. Through the cooperation of the main magnet 1001, the gradient coil 1003 and the magnet pole plate 1002, the magnet system can stably provide the main magnetic field and the gradient magnetic field, and suppress the eddy current by means of the special structure of the magnet pole plate 1002, thereby guaranteeing the imaging performance.

[0244] Further, as an example, please refer to Figure 11 , Figure 11 The overall magnetic circuit diagram and equipotential line diagram of the magnet pole plate for the nuclear magnetic resonance device according to the embodiment of the present application are shown in Figure 11 , the upper part is a main magnet (N pole) 1101, and the lower part is a main magnet (S pole) 1105, which cooperate to generate a main magnetic flux , and the main magnetic flux forms a closed magnetic circuit along the path of the main magnet (N pole) 1101→magnet pole plate (upper) 1102→imaging space 501→magnet pole plate (lower) 1104→main magnet (S pole) 1105, thereby providing a basic static magnetic field for the imaging space 501.

[0245] The magnet pole plate (upper) 1102 and the magnet pole plate (lower) 1104 adopt SMC to form a core layer and are segmented by an insulating segmented structure, thereby guiding and uniformly distributing the main magnetic flux in the main magnetic circuit and providing support for the action of the gradient magnetic field 1106.

[0246] The imaging space 501 is located between the upper and lower magnet pole plates, and the gradient magnetic field 1106 is superimposed on the main magnetic field, which is used to spatially encode the magnetic resonance signal in the imaging space 501. Figure 11 The equipotential lines in the imaging space 501 area are regularly circularly distributed, which indicates that a uniform magnetic field area can be formed in this area, thereby meeting the requirement of nuclear magnetic resonance imaging on the uniformity of the magnetic field.

[0247] The magnet pole plate, by virtue of the magnetic properties of the soft magnetic composite material and the insulation segmentation structure, not only efficiently conducts the main magnetic flux to ensure the uniformity of the main magnetic field, but also suppresses eddy current under the action of the gradient pulse to avoid the interference of the gradient magnetic field 1106 by the eddy current, thereby realizing stable and high-quality nuclear magnetic resonance imaging in cooperation with the main magnet and the gradient system.

[0248] Further, the magnet system further comprises a heat dissipation channel and a temperature sensor for temperature control to form a closed-loop temperature control.

[0249] In the present embodiment, the heat dissipation channel and the temperature sensor can cooperate with an externally connected temperature control control unit to form a closed-loop temperature control system to regulate the system temperature in real time, avoid overheating of components caused by the continuous action of the gradient pulse or the fluctuation of the ambient temperature, and ensure the magnetic field stability and long-term operation reliability of the magnet system.

[0250] The heat dissipation channel can be made of a non-magnetic, high-thermal-conductivity and insulating composite material (such as a polyimide-aluminum composite film or an epoxy glass-reinforced resin pipeline), the structure and arrangement of which can be adapted to the component layout of the magnet system and do not interfere with the distribution of the main magnetic flux B0 and the gradient magnetic field 1106.

[0251] Preferably, the cooling medium flowing in the heat dissipation channel can be deionized water or insulating coolant, which has high specific heat capacity and low electrical conductivity, ensuring heat exchange efficiency and avoiding the formation of additional eddy current due to the conductivity of the medium. The temperature sensor can be a fiber-optic temperature sensor with a FOP cavity, which has zero electromagnetic interference characteristics and can realize high-precision temperature measurement in a strong magnetic field environment.

[0252] As a possible implementation of the above embodiment, the closed-loop temperature control system takes the temperature control control unit as the core and can realize precise temperature control through the closed-loop process of temperature collection, signal processing, execution adjustment and feedback correction. The specific logic can be as follows:

[0253] The temperature sensor transmits the real-time monitored temperature data to the temperature control unit through an optical fiber. The unit is built-in with a signal filtering module to denoise and smooth the original data, eliminating signal interference in the magnetic field environment. The temperature control unit presets a normal working temperature range (e.g. 20-30℃). When the monitored temperature is lower than the lower threshold, the control flow regulating valve reduces the cooling liquid flow rate to reduce heat dissipation. When the temperature is higher than the upper threshold (e.g. more than 30℃), the temperature regulation is started. The temperature control system can use a fuzzy adaptive proportional-integral-differential (PID) control algorithm, which can automatically adjust the control parameters according to the gradient pulse frequency (dynamic change of heating power) under different imaging sequences, achieving fast response. When any sensor temperature exceeds the critical threshold (e.g. 45℃), the system immediately triggers an alarm and cuts off the power supply to the gradient coil to prevent component damage, while retaining the temperature anomaly data for subsequent fault diagnosis.

[0254] As an example, refer to Figure 12 , Figure 12 is a schematic diagram of a thermal-structural collaborative design of a magnet pole plate for a nuclear magnetic resonance device according to an embodiment of the present application. The key indicators of the thermal design are explicitly shown in the form of an example to provide design basis for the heat dissipation system.

[0255] The key indicators can include but are not limited to: maximum temperature rise thermal conductivity convective coefficient heat dissipation channel diameter 2-5mm. The maximum temperature rise can limit the temperature rise of components such as the core layer 104, avoiding the influence of high temperature on the magnetic performance of soft magnetic materials and the reliability of insulating structures; the thermal conductivity requires that the heat dissipation related materials have high thermal conductivity to ensure rapid heat conduction; the convective coefficient defines the convective heat exchange efficiency requirement of the cooling medium (air or liquid) in the heat dissipation channel (longitudinal heat dissipation channel 1203, transverse cooling fluid channel 1204) and the channel wall surface; the heat dissipation channel diameter 2-5mm can balance the key geometric dimensions of flow resistance and heat exchange area, ensuring the consideration of heat dissipation efficiency and fluid flow performance.

[0256] Further, through the cooperation of heat conduction and convective heat exchange, each component realizes efficient heat dissipation.

[0257] Specifically, the thermal interface material 1201 is arranged above the core layer 104 to eliminate contact thermal resistance and enhance the heat conduction efficiency of the core layer 104 and the upper structure (or heat dissipation channel), so that the heat generated by the SMC is more smoothly transferred to the heat dissipation system.

[0258] Figure 12The middle gray area is the core layer 104, which generates heat due to hysteresis loss, residual eddy current, etc. during operation, and is a main heat source, which needs to be promptly discharged through a heat dissipation system.

[0259] The heat dissipation channel can include a transverse cooling fluid channel 1204 and a longitudinal heat dissipation channel 1203.

[0260] The cooling medium (liquid) in the transverse cooling fluid channel 1204 flows along the cooling fluid flow direction (horizontal right arrow), directly conducts convective heat exchange with the channel wall surface (accepts the heat transferred by the core layer 104 and the heat-conducting interface 1201), and quickly takes out the heat;

[0261] The longitudinal heat dissipation channel 1203 transmits heat along the heat flow direction (vertical up and down arrow), which can be transmitted through air natural convection, and the transverse channel can assist in strengthening the overall heat dissipation capacity to realize multi-dimensional heat dissipation.

[0262] The temperature sensor monitoring point 1205 is arranged in the core layer 104 and is used for real-time monitoring of the temperature.

[0263] The following provides several specific embodiments for description. In a first embodiment, a magnet pole plate applied to a 0.5T open C-shaped permanent magnet MRI is taken as an example.

[0264] The magnet pole plate adopts a multi-level composite structure, and the components and key parameters of each layer are as follows: a substrate layer, which is made of pure iron material, has a thickness of 15mm, and provides basic support and initial magnetic induction capacity for the pole plate; a first insulation layer, which is made of epoxy glass plate, has a thickness of 2mm, and is arranged between the substrate layer and the core layer to realize electrical insulation between the two; the core layer is made of iron-based powder with an organic-inorganic composite insulation coating on the surface, has a diameter of 1000mm and a thickness of 30mm after forming; is equally angularly divided into 12 sector-shaped independent segments along the circumference, and has a gap of 0.5mm between adjacent segments, and a polyimide sheet is embedded in the gap to realize electrical insulation.

[0265] The guide layer is a ferrite ring structure with a cross-sectional size of 5mm (radial) x 30mm (axial), and is arranged continuously in a ring direction to guide the magnetic field distribution; the second insulation layer is made of polyester film and has a thickness of 0.2mm, and is arranged between the guide layer and the shim ring to ensure electrical insulation between the layers; the shim ring is a soft magnetic material ring belt with a thickness of 10mm, and is used to optimize the magnetic field uniformity; the outer shell / skeleton is a carbon fiber reinforced composite material formed by ring winding + radial reinforcing ribs, and has a local embedded non-magnetic stud to realize the cladding, fixation and structure reinforcement of the stacked components.

[0266] The above magnet pole plate can be manufactured by the following steps:

[0267] 1. SMC powder insulation coating: surface treatment is performed on the iron-based powder to apply an organic / inorganic composite insulation coating, so that the powder particles have electrical insulation;

[0268] 2. Molding and curing: After the insulation-coated iron-based powder is placed in a special mold, it is subjected to isothermal high-pressure pressing, followed by post-curing and stress relief treatment to ensure the stability of the structure and magnetic properties of the core layer;

[0269] 3. Machining and segmented cutting: The core layer is machined to have an outer circle, an end face, and positioning holes, and is cut into 12 equal-angle sector-shaped independent segments using wire cutting or water jet technology;

[0270] 4. Insulation gap treatment: After cleaning the segment gaps, polyimide sheets are embedded and glued to cure, achieving electrical insulation and structural fixation between segments;

[0271] 5. Layer assembly and pre-tightening: The layers are assembled in the order of substrate layer, first insulation layer, core layer, guide layer, second insulation layer, and shim, and a predetermined pre-tightening force is applied to the stacked assembly to ensure close fitting between layers;

[0272] 6. Shell curing and secondary positioning: CFRP prepreg is used to laminate and coat the stacked assembly, and after vacuum curing, the runout and concentricity are rechecked to ensure structural precision;

[0273] 7. Finished product inspection: Insulation withstand voltage, interlayer contact resistance, flatness, dynamic balance, and size review tests are carried out to ensure that the performance and precision meet the design requirements.

[0274] The test results of the pole plate of the embodiment show that under the gradient pulse with the steepest rising edge , the peak value of the eddy current response measured by the pickup coil on the surface of the pole plate is significantly lower than that of the pure iron whole pole plate control sample, and eddy current suppression can be achieved; after field shimming, the magnetic field uniformity in the Φ300mm imaging area (Diametral Spherical Volume, DSV) reaches 8 million parts per million (ppm) level, meeting the MRI imaging requirements and having magnetic field uniformity; after 30 minutes of continuous sequence operation, the temperature rise on the surface of the pole plate is significantly lower than that of the metal whole pole plate control sample, and it has thermal stability.

[0275] The magnet pole plate of the first embodiment realizes the synergistic optimization of eddy current suppression, magnetic field uniformity, and thermal stability through multi-level structure design and precise manufacturing, and meets the imaging performance requirements of 0.5T open C-type permanent magnet MRI equipment.

[0276] In the second embodiment, a magnet pole plate applied to a 1.0T closed electromagnetic / iron core MRI is taken as an example.

[0277] The magnet pole plate still has a basic framework of substrate layer-insulation layer-core layer-guide layer-function layer-outer shell. The core differentiation design focuses on high field strength adaptability, intense sequence anti eddy current and heat dissipation enhancement. The parameters and design purposes of each component are as follows:

[0278] The core layer (eddy current suppression enhancement) uses iron-based powder coated with organic-inorganic composite insulation coating on the surface (referring to the powder system of the first embodiment), with a pressing density Theoretical density, ensuring high magnetic permeability and high volume resistivity;

[0279] The thickness of the core layer is increased to 40mm (to adapt to the magnetic flux conduction requirements of 1.0T main magnetic field), and is cut into a composite segmented pattern of 8 rings and 8 spokes along the radial and radial directions. The rings are distributed at intervals along the circumference, and the spokes extend along the radial direction and penetrate the rings, forming a crisscross insulation boundary that can more efficiently block eddy current loops in different directions. The segmented gap is still 0.5mm, embedded with polyimide sheets to achieve electrical insulation.

[0280] The guide layer discards the ferrite ring of the first embodiment and uses an insulation-coated silicon steel arc segment (a single silicon steel sheet coated with an epoxy insulation layer on the surface). Three layers are stacked and assembled, and the adjacent two layers are arranged in a staggered joint along the ring direction (staggered joint width 5-8mm) to avoid interlayer eddy current conduction.

[0281] A 1.5mm wide annular heat dissipation channel is reserved on the outer periphery of the guide layer, and the inner wall of the channel is coated with a heat-conducting insulation coating (such as an aluminum oxide ceramic coating) to conduct the local heat generated by the guide layer due to the gradient magnetic flux induction.

[0282] An anti-eddy current lamination disc (intense sequence adaptation) is added between the second insulation layer and the shim ring, with a thickness of 8mm. It is made of multiple pieces of high resistivity silicon steel sheets (single thickness 0.35mm, surface coated with polyimide insulation film) that are stacked axially. After stacking, the whole is cured and shaped to absorb residual eddy current under EPI sequence (fast switching gradient pulse) and avoid interference with imaging signals.

[0283] The outer shell / skeleton (heat dissipation enhancement) continues to use carbon fiber reinforced composite material (CFRP) with ring winding + radial reinforcement structure.

[0284] In addition, a ring-shaped air cooling hole array is uniformly arranged on the circumference of the outer shell, with a hole diameter of 2-3mm and a hole spacing of 15-20mm. The hole extends through the outer shell in the radial direction, allowing cooling air to flow through the annular heat dissipation channel on the outer periphery of the guide layer, forming an air cooling convection-heat dissipation path to adapt to the continuous heat dissipation requirements under high field strength.

[0285] The substrate layer is a pure iron plate with a thickness of 18mm (thicker than the first embodiment, to adapt to the electromagnetic force bearing requirements of closed devices);

[0286] The first insulation layer is an epoxy glass fiber plate with a thickness of 2 mm, and the second insulation layer is a polyester film with a thickness of 0.2 mm.

[0287] The field-shaping ring is a soft magnetic material ring belt with a thickness of 12 mm (adapted to the uniformity compensation requirement of 1.0T magnetic field).

[0288] On the basis of the manufacturing process of the first embodiment, the following key steps are supplemented for the differentiated design of the second embodiment:

[0289] 1. Core layer composite segmented cutting: using a high-precision numerical control water jet (to avoid thermal effects), cutting the SMC preform according to the preset pattern of 8 ring belts + 8 spokes, and polishing the segmented edges after cutting to remove burrs and ensure uniform insulation gaps.

[0290] 2. Guiding layer stacking and heat dissipation channel reservation: stack 3 layers of insulating coated silicon steel arcs along the outer periphery of the core layer, and define the staggered position by positioning pins after each layer is stacked. After stacking is completed, reserve a 1.5mm annular gap between the outermost silicon steel arc and the shell as a heat dissipation channel.

[0291] 3. Anti-eddy current lamination disc assembly: after the second insulation layer is assembled, the pre-solidified anti-eddy current lamination disc is fixed to the side of the second insulation layer close to the imaging space through non-magnetic positioning pins, ensuring that the lamination disc and the core layer have the same coaxiality deviation .

[0292] 4. Shell air cooling hole processing: during the CFRP prepreg layering, insert the degradable core material according to the preset hole position, and remove the core material after the CFRP is cured and formed to form a through annular air cooling hole. The inner wall of the hole is polished and smoothed to reduce air resistance.

[0293] Assemble the pole plate of the second embodiment into a 1.0T closed electromagnet / iron core MRI device and conduct targeted tests, with the following results:

[0294] The k-space distortion in the gradient-echo sequence is reduced; the time constant of the eddy current residual field is significantly shortened; the sound noise level and temperature rise control are better than the control structure.

[0295] The second embodiment effectively adapts to the high field strength and intense gradient sequence requirements of 1.0T closed electromagnet / iron core MRI devices through the cooperative design of composite segmented core layer + staggered guiding layer + anti-eddy current lamination disc + air cooling and heat dissipation, while considering eddy current suppression, imaging quality and long-term operation stability.

[0296] In the third embodiment, the magnet pole plate applied to portable / compact MRI is taken as an example.

[0297] For the core requirements of portable / compact MRI, such as small volume, light weight, controllable cost, and easy transportation and assembly, the first and second embodiments are further miniaturized and optimized in manufacturing process, as follows:

[0298] The magnet pole plate is designed with the principles of simplified structure, lightweight, and low cost. The core component parameters and miniaturization trade-offs are as follows:

[0299] Core layer diameter , thickness , adapt to the space limit of portable devices; adopt a finer segmentation method in the circumferential and radial directions, with a segmentation width of 5-15 mm. By reducing the size of the segmented units, the eddy current loop can still be effectively blocked in a small volume, ensuring the eddy current suppression effect; the segmentation gap is 0.3-0.5 mm (polyimide sheet insulation is used).

[0300] Shell / skeleton (abandon high-cost carbon fiber reinforced composite material (CFRP), replace with glass fiber reinforced composite material (GFRP), reduce material cost under the premise of meeting mechanical strength requirements; in the key areas of the installation interface, corners, and other parts of the shell that are prone to impact, embed non-magnetic metal inserts (such as titanium alloy inserts), which not only improve the local impact resistance but also provide a stable connection reference for the overall assembly of the device, adapting to the transportation and movement scenarios of portable devices.

[0301] No additional independent shim ring is set. Passive shimming is achieved by fine-tuning the segmentation gap of the core layer (such as adjusting the gap from 0.3 mm to 0.5 mm locally). The small difference in segmentation gap compensates for local magnetic field inhomogeneity, simplifying the structure while reducing the overall weight of the pole plate;

[0302] No anti-eddy current sheet is set. Relying on the high volume resistivity and fine segmentation structure of the core layer, the eddy current suppression requirements of the portable device for conventional imaging sequences are met, further simplifying the hierarchy, reducing the weight and cost.

[0303] The base plate layer is made of thin pure iron plate, which reduces the weight under the premise of ensuring basic support and magnetic conductivity;

[0304] The first insulation layer is made of epoxy glass plate, and there is no second insulation layer, simplifying the interlayer structure.

[0305] In the manufacturing process, prefabricated SMC "fan-shaped bricks" standard parts are used to reduce the investment in large-size molds, and on-site gluing + positioning pin rapid assembly is adopted.

[0306] Further, the testing aspects are as follows:

[0307] Eddy current response test: Orthogonal pickup coils are arranged in the near field of the pole plate, and bipolar square / triangular wave gradient pulses are applied to record the time domain of the induced voltage. The residual field amplitude and time constant are obtained by exponential superposition fitting.

[0308] Magnetic field uniformity test: Samples are taken within the DSV (200–300 mm in diameter) using an NMR probe or fluxmeter, and spherical harmonic expansion is used to calculate the uniformity at the ppm level.

[0309] Thermal performance testing: Infrared thermal imaging + embedded temperature sensing to record steady-state temperature rise and spatial temperature gradient under continuous sequence.

[0310] Mechanical and vibration testing: Acceleration / displacement monitoring under pulse loading to verify the dynamic stability of the shell and preload structure.

[0311] As an example, please refer to Figure 13 , Figure 13 This is a schematic diagram illustrating the testing and evaluation process and key indicators for magnet plates in a nuclear magnetic resonance (NMR) device according to an embodiment of the present invention. Figure 13 As shown in the figure, the test evaluation process includes the above-mentioned eddy current response test, magnetic field uniformity test, thermal performance test, and mechanical and vibration test.

[0312] Specifically, as shown in the upper left subfigure characterizing the eddy current response test, a pickup coil 1301 is arranged in the near-field region of the SMC electrode sample 1302, and a gradient pulse is applied using a gradient pulse generator 1303. Simultaneously, the time-domain response curves of the induced voltage of a conventional electrode (such as a pure iron electrode) and the SMC electrode 1302 are compared (the dashed line is the time-domain response curve 1304 of the induced voltage of the conventional electrode, and the solid line is the time-domain response curve 1305 of the induced voltage of the SMC electrode). The conventional electrode response is approximately 1.5 s, while the SMC electrode response is... It is evident that the SMC plate 1302 has a significantly smaller eddy current time constant, which indicates that it can effectively suppress gradient pulse-induced eddy currents, allowing residual eddy currents to decay more quickly and ensuring the accuracy of gradient field switching.

[0313] As shown in the upper right sub-figure of the magnetic field homogeneity test, magnetic field data are acquired using a nuclear magnetic resonance (NMR) probe or fluxmeter in a ring-shaped multi-point distribution within a 300mm diameter imaging space (DSV). The magnetic field homogeneity is then analyzed using methods such as spherical harmonic expansion. The homogeneity index can be defined as "within the DSV: ; 32 measurement points; spherical harmonic expansion: up to order 5; peak-to-peak value: This ensures that the electrode plates provide a uniform magnetic field that meets the requirements for the imaging area, supporting high-quality MRI imaging.

[0314] As shown in the lower left subgraph of the test for characterizing thermal performance, the temperature distribution of the pole plate is monitored using the infrared thermal imaging module 1306, and the temperature rise process is recorded in combination with the embedded temperature sensors (such as T1 measurement point 1307, T2 measurement point 1308, T3 measurement point 1309), and the temperature rise curve 1310 is drawn. The thermal performance index is "maximum temperature rise: ; static time: ; temperature uniformity: ; thermal cycle life: ", to verify the controllability and thermal stability of the pole plate during continuous operation, and to avoid the adverse effects of high temperature on magnetic performance and insulation structure reliability.

[0315] As shown in the lower right subgraph of the test for characterizing mechanical and vibration, the pole plate assembly 1313 is subjected to pulse excitation, and the acceleration, displacement and other responses are monitored through multiple sensors (such as sensor 1 (1311), sensor 2 (1312), sensor 3 (1314)), and the frequency response characteristic curve 1315 is analyzed. The mechanical performance index can be "natural frequency: ; damping ratio: ; dynamic displacement: ; fatigue life: ", to verify the structural stability and fatigue resistance of the pole plate under pulse load and vibration environment, and to ensure the reliability of long-term operation.

[0316] The third embodiment of the pole plate realizes the optimization of volume, weight and cost on the premise of meeting the core performance requirements of portable / compact MRI equipment, such as eddy current suppression and magnetic field uniformity, through miniaturized structure design, standardized prefabrication and on-site rapid assembly process, and has strong industrialization and application adaptability.

[0317] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A magnet pole plate for a nuclear magnetic resonance apparatus, characterized by, The magnet pole plate comprises: a substrate layer made of a magnetically conductive metal material; a first insulating layer made of a material that is electrically insulating and has a higher magnetic reluctance than the substrate layer, disposed on the substrate layer; A core layer made of soft magnetic composite material is disposed on the first insulating layer; wherein the soft magnetic composite material is formed by pressing and solidifying iron-based powder coated with an insulating coating on the surface, and has a magnetic permeability sufficient to maintain the main magnetic flux passing through and a volume resistivity sufficient to suppress the generation of eddy current; wherein the magnetic permeability of the soft magnetic composite material is not less than , the magnetic permeability is the relative magnetic permeability , The minimum threshold value of the relative magnetic permeability is 600, The test condition of the relative magnetic permeability is measured under an applied magnetic field of 10 millitesla; and the volume resistivity of the soft magnetic composite material is not less than ; a guide layer made of a magnetically conductive material that has a higher electrical resistivity than the substrate layer and a lower magnetic reluctance than air, disposed around the outer periphery of the core layer; a shim ring disposed on the side of the core layer close to the imaging space; wherein the core layer is segmented into multiple independent units in the radial and / or radial directions, and an insulating gap is provided between adjacent independent units; wherein the independent units are fan-shaped units, ring-shaped units, or spoke-shaped units; the width of the independent units is 5-50 mm, and the width of the insulating gap between adjacent independent units is 0.2-2 mm.

2. The magnet pole plate of claim 1, wherein, The material of the first insulating layer is selected from epoxy glass fiber board, polyimide composite sheet, or a laminate of the two.

3. The magnet pole plate of claim 1, wherein, The iron-based powder of the soft magnetic composite material in the core layer is selected from high-purity water atomized pure iron powder or alloyed iron powder, and the alloyed iron powder is Fe-Si-based iron powder or Fe-Si-Cr-based iron powder; the insulating coating of the soft magnetic composite material is selected from a phosphate layer, a silane / oxide coating, or an organic-inorganic composite coating.

4. The magnet pole plate of claim 1, wherein, The material of the guide layer is selected from a ferrite ring, an insulating coated silicon steel segment, or a spliced structure of the two.

5. The magnet pole plate of claim 1, wherein, The segmentation pattern of the independent units is mirror symmetric relative to the central axis of the magnetic poles.

6. The magnet pole plate of claim 1, wherein, The shim ring is made of a soft magnetic material selected from Fe-Ni alloy, ferrite, or insulating coated silicon steel; the structure of the shim ring is configured to compensate for the edge effect of the static magnetic field through local changes in geometry.

7. The magnet pole plate of claim 1, wherein, The magnet pole plate further comprises a second insulating layer disposed between the core layer and the shim ring, made of a material that is electrically insulating and has a higher magnetic reluctance than the core layer, selected from epoxy glass fiber board, polyimide composite sheet, or a laminate of the two, to avoid the formation of electrically conductive coupling or magnetic flux interference between the core layer and the shim ring.

8. The magnet pole plate of claim 1, wherein, The magnet pole plate further comprises an anti-eddy current lamination disc; the anti-eddy current lamination disc is disposed on the side of the substrate layer away from the first insulating layer, made of multiple pieces of high electrical resistivity silicon steel sheets that have been electrically insulated and stacked in the thickness direction of the pole plate.

9. The magnet pole plate of claim 3, wherein, The particle size of the iron-based powder of the soft magnetic composite material in the core layer is 20-300 microns; the insulating coating on the surface of the iron-based powder has a thickness of 0.1-5 microns; the volume density of the soft magnetic composite material after compression and curing is not less than 95% of the theoretical density.

10. The magnet pole plate of claim 1, wherein, The magnet pole plate further comprises an outer shell / skeleton; the outer shell / skeleton is a non-magnetic high-strength composite material selected from carbon fiber composite material or glass fiber composite material, and is wrapped around the outer periphery of the assembly consisting of the substrate layer, the first insulating layer, the core layer, the guide layer, and the shim ring, and forms a pre-tightening fit with the core layer.

11. The magnet pole plate of claim 10, wherein, The outer shell / skeleton is provided with a heat dissipation channel; the heat dissipation channel is an air or liquid heat dissipation channel, used to conduct heat generated during the operation of the pole plate outwards.

12. The magnet pole plate of claim 10, wherein, The magnet pole plate further comprises a non-magnetic fastener made of titanium alloy and / or austenitic stainless steel for connecting the shell / skeleton and the base plate layer and the core layer to avoid relative displacement of the layers.

13. A method of manufacturing a magnet pole plate, characterized by, A method for manufacturing the magnet pole plate according to any one of claims 1-12, the method comprising: The iron-based powder is coated with an insulating coating to obtain an insulating coated powder; the insulating coated powder is pressed into a predetermined shape in a mold under a predetermined pressure, and then heat treated to solidify the insulating coating between the powders and eliminate internal stress, thereby forming a soft magnetic composite core blank; wherein the magnetic permeability of the soft magnetic composite is not less than , the magnetic permeability being the relative magnetic permeability , , the minimum threshold of the relative magnetic permeability being 600, , the test condition of the relative magnetic permeability being measured under an applied magnetic field of 10 mT; and the volume resistivity of the soft magnetic composite not being less than ; The soft magnetic composite core blank is machined and segmented in the radial and / or radial direction to form a plurality of independent units; an electrically insulating material is arranged in the cutting gap between adjacent independent units to form a core layer with insulating gaps; wherein the independent units are fan-shaped units, ring-shaped units or spoke-shaped units; the width of the independent units is 5-50 mm, and the width of the insulating gap between adjacent independent units is 0.2-2 mm; The base plate layer, the first insulating layer and the core layer with insulating gaps are sequentially stacked and aligned, the guide layer is fitted around the outer periphery of the core layer, and the shimming ring is directionally fitted on the side of the core layer close to the imaging space to complete the fixed assembly of the components; The stacked components are covered or framed by a non-magnetic shell or skeleton, and a pre-tightening force is applied for overall fixation to complete the manufacturing of the magnet pole plate.

14. The method of claim 13, wherein, The segmented cutting uses wire cutting or water jet cutting; when the electrically insulating material is arranged in the cutting gap between adjacent independent units, the insulating sheet is inserted and the contact part of the insulating sheet and the independent unit is glued and solidified; wherein the material of the insulating sheet is selected from epoxy glass fiber sheet, polyimide sheet or laminated sheet of the two.

15. A magnet system, characterized by A magnet system comprising a main magnet, a gradient coil and a magnet pole plate according to any one of claims 1-12, the gradient coil and the magnet pole plate being arranged adjacent to and parallel to each other, the magnet pole plate comprising a core layer made of soft magnetic composite material and an insulating segmented structure, which suppresses gradient pulse-induced eddy currents under the action of gradient pulses.

16. The magnet system of claim 15, wherein, The magnet system further comprises a heat dissipation channel and a temperature sensor for temperature control to form a closed-loop temperature control.

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