Pole shoe

Abstract

A pole shoe assembly for use in a Halbach-type magnet configuration, a magnetic resonance apparatus comprising the pole shoe assembly and a method for shimming a magnetic field using the pole shoe assembly are described. The pole shoe includes a back face, a front face S and ends spaced apart by a first distance defining a length of the pole shoe assembly along a first axis extending between the ends, the pole shoe assembly being configured for insertion along the first axis into an interior of a Halbach-type magnet configuration, where a surface of the front face S is curved and a surface of the back face S is curved. And wherein the curvature of the front face is mathematically defined for shimming the magnetic field generated by the magnet configuration.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 407,483, filed on September 16, 2022, the specification of which is incorporated herein by reference in its entirety. Technical Field

[0003] The disclosed subject matter generally relates to pole pieces and uses thereof. Background Art

[0004] Related background literature includes:

[0005] —Ernst R. R., Bodenhausen G. and Wokaun A., Principles of Nuclear Magnetic Resonance in One and Two Dimensions, International Series of Monographs on Chemistry (Vol. 14), Oxford University Press, 1990.

[0006] —Halbach K., “Design of Permanent Multipole Magnets—with Oriented Rare Earth Cobalt Material,” Nuclear Instruments and Methods 169, 1–10, 1980.

[0007] —Moresi G. and Magin R., “Miniature Permanent Magnet for Tabletop NMR,” Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, Vol. 19B, No. 1, pp. 35-43, 2003.

[0008] —Rose NE, “Magnetic Field Correction in the Cyclotron,” Physical Review 53, 715-719, 1938.

[0009] —Hamermesh, M. Group Theory and its Application to Physical Problems. Reading, Mass.: Addison-Wesley, 1962.

[0010] —Bloch. F. et al., “Innovating Approaches to the Generation of Intense Magnetic Fields: Design and Optimization of a 4 Tesla Permanent Magnetic Flux Source,” IEEE Transactions on Magnetics, vol. 34, p. 2465, 1998.

[0011] — U.S. Patent Application Publication No. US2011 / 0137589A1 and PCT Application Publication No. WO2011 / 066652, filed on December 1, 2010, both owned by the present applicant and entitled “METHOD AND APPARATUS FOR PRODUCING HOMOGENEOUS MAGNETIC FIELDS”.

[0012] —U.S. Patent 3,611,223, issued to Utsumi on October 5, 1971.

[0013] —U.S. Patent 4,093,912, issued June 6, 1978 to Double et al.

[0014] —U.S. Patent 4,580,098, issued April 1, 1986 to Gluckstern et al.

[0015] —U.S. Patent 4,673,882, issued to Buford on June 16, 1987.

[0016] —U.S. Patent 4,758,813, issued July 19, 1988 to Holsinger et al.

[0017] —U.S. Patent 5,003,276, issued March 26, 1991 to Sarwinski et al.

[0018] —U.S. Patent 6,275,128, issued to Aoki and Hashimoto on August 4, 2001.

[0019] —U.S. Patent 6,566,991, issued May 20, 2003 to Rimkunas and Wahl.

[0020] —U.S. Patent 6,768,407, issued July 27, 2004 to Kohda and Kumuda.

[0021] —U.S. Patent 7,199,689, issued to Abele on April 3, 2007.

[0022] —U.S. Patent Application Publication No. 2002 / 0179830A1 “HALBACH DIPOLE MAGNET SHIM SYSTEM”, published on December 5, 2002.

[0023] — U.S. Patent Application Publication 2009 / 0128272A1, “HALBACH MAGNET ARRAY FOR NMR ESTIGATIONS,” published May 21, 2009.

[0024] — U.S. Patent Application Publication No. 2010 / 0244828A1, “ADJUSTABLE PERMANENT MAGNET ASSEMBLY FOR NMR AND MRI,” published on September 30, 2010.

[0025] — U.S. Patent Application Publication No. 2011 / 0057655A1, Ando et al., “SOFTWARE FOR ADJUSTING MAGNETIC HOMOGENEITY, METHOD FOR ADJUSTING MAGNETIC HOMOGENEITY, MAGNET DEVICE, AND MAGNETIC RESONANCE IMAGING APPARATUS,” published on Mar. 10, 2011.

[0026] —Jointly owned and jointly invented international patent entitled “Pole Piece” with application number PCT / CA2021 / 051793.

[0027] Where permitted by law, all references cited herein are hereby incorporated by reference in their entirety.

[0028] In many technical fields, it is desirable to carefully control the spatial distribution of a magnetic field. Well-controlled magnetic fields are particularly important in nuclear magnetic resonance (NMR) spectroscopy and other magnetic resonance (MR) applications. In many NMR spectroscopy experiments, a strong static magnetic field is applied to a region of space containing the sample being studied, and it is desirable that the field be as uniform as possible in space in order to observe important but subtle changes in the magnetic response of the sample. In many NMR applications, it is also desirable to have as strong a static magnetic field as practicable.

[0029] At least three types of magnets have been used to provide strong static magnetic fields in NMR devices: superconducting electromagnets, resistive electromagnets, and permanent magnets. Permanent magnets or arrays thereof may be advantageous in applications where low cost, low maintenance, or portability are desired. A particularly useful design for compact applications is a permanent magnet assembly based on a Halbach cylinder, which includes assembly magnets oriented and arranged around a central bore.

[0030] In practice, static field magnets (including permanent magnets) are often accompanied by pole shoes. The term "pole shoe" is more fully defined herein, but generally refers to a piece of magnetically permeable material placed near a magnet in order to enhance the magnetic field or shape the magnetic field. In some cases, additional equipment or devices including magnetic materials are provided in order to shape the magnetic field for an application. Shaping the magnetic field often includes making it more spatially consistent or "uniform."

[0031] The pole shoe device of the prior art sometimes includes an auxiliary shimming element. For example, a shimming tray (magnetic field uniformity regulator) is disclosed in U.S. patent application 2011 / 0057655A1 by Ando et al. The shimming tray is a non-magnetic material, such as plastic or aluminum. The shimming tray has a disc or similar shape and is provided with a plurality of threaded screw holes passing therethrough. A threaded shimming bolt made of a magnetically permeable material is provided. In the magnetic field uniformity adjustment, the shimming bolt is screwed into the screw hole according to the position data provided by the software program. The shimming tray is arranged in a magnetic device designed to generate a uniform magnetic field using a superconducting coil.

[0032] In U.S. Pat. No. 6,275,128 to Aoki and Hashimoto, an MRI magnetic field generator is disclosed, wherein after the MRI magnetic field generator has been provided with a gradient coil already mounted on a pair of magnetic pole pieces, the MRI magnetic field generator can be used to adjust the magnetic field uniformity within the imaging field of view of the air gap without removing the gradient coil. Magnetic material particles or permanent magnetic particles for adjusting the magnetic field uniformity are inserted into the desired pits arranged in a certain pattern to adjust the field uniformity.

[0033] These prior art configurations of shimming elements are described in the context of large open magnet devices having large pole structures, such as those used in magnetic resonance imaging (MRI) devices. Pole shoes found in imaging devices used in open magnet configurations tend to exhibit a rounded overall shape with a flat front surface. There remains a need for improvements in pole shoes, pole shoe production methods, and pole shoe implementation methods, particularly when shimming magnetic fields generated by much smaller permanent magnet arrangements in the confined space of a Halbach cylinder used in compact NMR applications. Summary of the invention

[0034] The present embodiment addresses these needs.

[0035] According to one aspect of the present invention, there is provided a pole shoe assembly for use in a Halbach-type magnet construction, the pole shoe assembly comprising a back face, a front face S, and ends separated by a first distance, the first distance defining a length of the pole shoe assembly along a first axis extending between the ends, the pole shoe assembly being configured to be inserted into the interior of the Halbach-type magnet construction along the first axis, wherein the surface of the front face S is curved, and wherein the curvature of the front face is mathematically defined for uniforming the magnetic field generated by the magnet construction.

[0036] In one embodiment, the pole shoe assembly is elongated along a first axis.

[0037] In one embodiment, the pole shoe assembly further comprises: a reference plane P, including an origin O, the reference plane being in a three-dimensional volume occupied by and surrounding the pole shoe assembly; a Cartesian reference system, fixed at O, including a length axis, a width axis, and a height axis ( and ) and the corresponding Cartesian coordinates x, y and z along said axes, respectively; and a rectangular region R of length l, width w, located in the reference plane P and centered at the origin O, the rectangular region having sides parallel to the x-axis and y-axis of the Cartesian reference system and containing and , wherein the point located on the front surface S is described by a smooth depth function z(x,y) of Cartesian coordinates defined on R, the depth function quantifies the vertical distance z from R to the corresponding point on S; and wherein the depth function takes z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient.

[0038] In one embodiment, reference plane P coincides with a physically flat surface on the body of the pole piece assembly.

[0039] In another embodiment, reference plane P is an abstract plane in the three-dimensional volume occupied by and surrounding the pole shoe assembly.

[0040] In one embodiment, the main body of the pole piece assembly is made of a magnetically permeable material.

[0041] In one embodiment, the body of the pole piece assembly acquires a magnetic polarization when placed in a magnetic field.

[0042] In one embodiment, the basis function set Ω x and Ω y is a set of orthogonal, Jacobi, Legendre, Laguerre, Chebyshev, hypergeometric, trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, Bessel, Gaussian, rational, Padé approximation, or related Legendre functions, or a sum, product, quotient, or composite of these.

[0043] The pole piece may further include a shim hole adapted to receive at least one cooperating shim rod inserted therein.

[0044] In one embodiment, the shim holes include internal threads, and the shim rods include matching external threads, so that the shim rods can be screwed into the pole piece assembly.

[0045] The pole shoe assembly may also include: a main pole shoe body having a front side and a back side; a shim plug-in body having a front side and a back side, the shim plug-in body being adapted to receive the main pole shoe body and / or be received by the main pole shoe body to form a pole shoe assembly, so that when in the assembled position, the back side of the main pole shoe body faces the front side of the shim plug-in body; a recess formed in at least one of the back side of the main pole shoe body and the front side of the shim plug-in body, so that when the main pole shoe body and the shim plug-in body are in the assembled position, a gap-filling shim cavity is formed by the recess; and a gap-filling shim layer is arranged in the gap-filling shim cavity.

[0046] In one embodiment, the shim card body defines a shim card aperture adapted to receive one or more shim cards inserted therein.

[0047] In another embodiment, the one or more shim plugs are threaded and engage with cooperating reciprocal threads on the inner surface of the shim plug-receiving hole so that the shim plug can be screwed into the pole piece assembly.

[0048] In yet another embodiment, the depth of the recess is greater than the thickness of the interstitial shim layer to allow insertion of materials with the same or different magnetic properties above or below the interstitial shim layer for shimming the magnetic field generated by the Halbach type magnet configuration.

[0049] On the other hand, there is provided a magnetic resonance device comprising a pole shoe assembly for use in a Halbach-type magnet construction, the pole shoe assembly comprising a back surface, a front surface S, and ends separated by a first distance, the first distance defining a length of the pole shoe assembly along a first axis extending between the ends, the pole shoe assembly being configured for insertion into the interior of the Halbach-type magnet construction along the first axis, wherein the surface of the front surface S is curved, and wherein the curvature of the front surface is mathematically defined for shimming the magnetic field generated by the magnet construction.

[0050] In another aspect, there is provided a method for shimming a magnetic field generated by a Halbach-type magnet configuration at least partially surrounding a sample volume, the method comprising:

[0051] - identifying magnetic field inhomogeneities in a sample volume of a Halbach-type magnet configuration, said inhomogeneities being generated by magnetic field gradients;

[0052] -Provide a pole shoe assembly, the pole shoe assembly comprising a main pole shoe body, the main pole shoe body comprising:

[0053] ○ curved front surface S;

[0054] ○ Reference plane P, which contains the origin O;

[0055] ○ Cartesian reference system, which is fixed at O ​​and includes the length axis Width axis and height axis and the corresponding Cartesian coordinates x, y, and z;

[0056] o A rectangular region R of length l, width w, located in the reference plane P and centered at the origin O, having sides parallel to the x-axis and y-axis of the Cartesian reference system and containing and The Cartesian coordinates (x, y) of a point,

[0057] wherein a point on the front surface S is described by a smoothed depth function z(x,y) of Cartesian coordinates defined on R, said depth function quantifying the perpendicular distance z from R to the corresponding point on S; and

[0058] The depth function takes z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient;

[0059] - forming an improved main pole shoe body by performing one or more of the following: removing material from the main pole shoe body or adding material to the main pole shoe body based on the identified magnetic field inhomogeneities; and

[0060] - Inserting an improved pole shoe assembly including an improved main pole shoe body into a Halbach type magnet configuration to shim the magnetic field.

[0061] In one embodiment, the method may further include: identifying one or more additional magnetic field inhomogeneities generated by the one or more additional magnetic field gradients; and repeating the identifying to inserting steps for each of the one or more additional magnetic field inhomogeneities.

[0062] In another embodiment, the method may further include identifying magnetic field inhomogeneities by simulating a magnetic field by adjusting a coefficient c defining the front surface S in the depth function. ij Generated by modifying the front surface of the main pole shoe body.

[0063] In one embodiment, the method may further include measuring the coefficient c of the front surface S defined in the depth function ij The magnetic field generated by modifying the front surface of the main pole shoe body by adjustment and using a magnetic field mapping device to record the changes in the field configuration corresponding to the adjustment to identify magnetic field inhomogeneities.

[0064] In one embodiment, the basis function set Ω x and Ω y is a set of orthogonal, Jacobi, Legendre, Laguerre, Chebyshev, hypergeometric, trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, Bessel, Gaussian, rational, Padé approximation, or related Legendre functions, or a sum, product, quotient, or composite of these.

[0065] In one embodiment, the method may further include assembling the two improved pole piece assemblies and the positioner into the central cavity assembly before inserting the two improved pole piece assemblies into the Halbach-type magnet configuration.

[0066] Features and advantages of the disclosed subject matter will become more apparent in view of the following detailed description of selected embodiments, as illustrated in the accompanying drawings. As will be appreciated, the disclosed and claimed subject matter is capable of modifications in various respects, all without departing from the scope of the claims. Accordingly, the drawings and description are to be regarded as illustrative in nature, rather than restrictive, and the full scope of the subject matter is set forth in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Other features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0068] Figure 1A is a perspective front view of an assembled pole piece assembly according to one embodiment;

[0069] Figure 1B is based on Figure 1A A perspective rear view of an assembled pole shoe assembly of an embodiment of;

[0070] Figure 2 is based on Figure 1A A perspective elevation view of an assembled pole piece assembly of an embodiment of the invention showing a reference plane, coordinate axes, and a rectangular region in the reference plane;

[0071] Figure 3A is based on Figure 1A An exploded front view of a pole shoe assembly of an embodiment of the present invention;

[0072] Figure 3B is based on Figure 1AAn exploded rear view of a pole shoe assembly of an embodiment of the present invention;

[0073] Figure 4A is based on Figure 1A A front view of an assembled pole shoe assembly of an embodiment of;

[0074] Figure 4B is based on Figure 1A A rear view of an assembled pole shoe assembly of an embodiment of;

[0075] Figure 4C is based on Figure 1A A side view of an assembled pole shoe assembly of an embodiment of;

[0076] Figure 4D is based on Figure 1A An end view of an assembled pole piece assembly of an embodiment of;

[0077] Figure 5A is based on Figure 1A An exploded perspective view of a central cavity assembly including a first pole piece assembly and a second pole piece assembly of an embodiment of the present invention;

[0078] Figure 5B is based on Figure 5A A perspective view of a central cavity assembly including a first pole piece assembly and a second pole piece assembly of an embodiment of;

[0079] Figure 5C yes Figure 5B A perspective view of a central cavity assembly of the embodiment of the present invention, the central cavity assembly including shimming rods;

[0080] Figure 6 is a block diagram of a magnetic resonance device including a pole piece assembly according to one embodiment of the present disclosure;

[0081] Fig. 7A is a schematic cross-sectional view of a magnet array (assembly) including two pole shoe assemblies according to one embodiment; and

[0082] Figure 7B is a schematic cross-sectional view of a magnet array (assembly) including two pole shoe assemblies according to another embodiment.

[0083] It should be noted that throughout the drawings, like features are identified by like reference numerals. DETAILED DESCRIPTION

[0084] A pole shoe assembly is described, the pole shoe assembly comprising a main pole shoe body having a curved front surface. The main pole shoe body is made of a magnetically permeable material. Accordingly, the main pole shoe body acquires magnetic polarization when placed in a magnetic field. The main pole shoe body comprises:

[0085] · a curved front surface S;

[0086] The reference plane P contains the origin O.

[0087] A Cartesian reference system, fixed at O, consisting of the length axis Width axis and height axis and the corresponding Cartesian coordinates x, y, and z;

[0088] A rectangular region R of length l and width w, located in the reference plane P and centered at the origin O, having sides parallel to the x-axis and y-axis of the Cartesian reference system and containing and The Cartesian coordinates (x, y) of a point,

[0089] where a point on the frontal surface S is described by a smoothed depth function z(x,y) of Cartesian coordinates defined on R, which quantifies the vertical distance z from R to the corresponding point on S,

[0090] · and where the depth function takes z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient.

[0091] The reference plane P does not necessarily coincide with a physical flat surface on the main pole shoe body. Rather, it is an abstract plane in the three-dimensional volume occupied by and surrounding the pole shoe assembly, used to define the surface S mathematically.

[0092] In one embodiment, a pole shoe assembly is adapted or configured for use in a Halbach-type magnet configuration, the pole shoe having an elongated body adapted for insertion into a Halbach-type magnet configuration. In one embodiment, the pole shoe assembly includes a main pole shoe body formed from a single piece of material. In another embodiment, the pole shoe assembly may include at least two parts that are operably and removably connected to each other. The at least two parts of the pole shoe may include: a main pole shoe body having a front face and a back face; a shim plug body having a front face and a back face; and a gap-filling shim layer adapted to be inserted into a shim cavity defined by a recess formed in at least one of the back face of the main pole shoe body and the front face of the shim plug body. The shim plug body may also be adapted to be inserted into a shim cavity located on the back face of the main pole shoe body. A method for shimming is also disclosed, the method comprising: modifying the material content of the shim cavity; and inserting the pole shoe assembly into a central cavity of a Halbach-type magnet configuration for shimming the generated magnetic field.

[0093] In the present disclosure, the term "pole shoe" refers to at least one magnetically permeable material that is placed near the primary magnet for enhancing the primary magnetic field or shaping the primary magnetic field, or is planned to be placed near the primary magnet for enhancing the primary magnetic field or shaping the primary magnetic field. In some embodiments, the pole shoe and the assembly including the pole shoe are suitable for confined spaces, for example, but not limited to, in some embodiments, the pole shoe and the assembly including the pole shoe are suitable for the central space or central cavity of the magnet array, wherein the magnet array is a Halbach array in some embodiments, and is a magnetic resonance device in some embodiments. In other embodiments, the magnet array includes a first plurality of magnets arranged in a Halbach cylinder configuration and a second plurality of magnets arranged in a non-Halbach cylinder configuration. In other embodiments, such a plurality of magnets may be accompanied by a part made of a soft magnetic material, and such a part is different from the main pole shoe body or the pole shoe assembly. Such a part may be located outside the main magnet assembly, within the inner bore of the magnet assembly, or within the extended inner bore, and may provide one or more functions of shaping, strengthening, shielding or constraining the local magnetic field.

[0094] The present disclosure contemplates the use of pole shoes within the confined space of a magnetic field generating device. In the present disclosure, the term "Halbach-type" magnet array (magnet configuration, magnet assembly) refers to a magnet array comprising component magnets arranged in a Halbach configuration. All places where the term "Halbach-type magnet array (or assembly)" is used in the present disclosure, such a Halbach-type magnet array may also include other magnetic components besides those in the Halbach configuration, and the present disclosure is contemplated to include all such modifications.

[0095] In certain embodiments, the pole piece is composed of or includes any suitable material or substance, including but not limited to iron, cobalt, nickel, other chemical elements and alloys thereof, and can have any suitable shape and size.

[0096] In a particular embodiment, a pole shoe assembly used in a Halbach-type magnet configuration includes a back face, a front face, and ends separated by a first distance, the first distance defining a length of the pole shoe assembly along a first axis extending between the ends of the pole shoe assembly. The pole shoe assembly is configured for insertion into the interior of the Halbach-type magnet configuration along the first axis. The surface of the front face of the pole shoe assembly is curved, and the curvature of the front face is mathematically defined for shimming a magnetic field generated by the magnet configuration.

[0097] In certain embodiments, the pole shoe or pole shoe assembly is substantially elongated in one dimension and has a front or back side, or a front side and a back side, or a front side, a back side, an end, and a length. The pole shoe or pole shoe assembly may be elongated along the length or first axis of the pole shoe assembly. It should be understood that, in use, the front side of the pole shoe is or includes the surface of the pole shoe facing or approaching a defined volume or sample volume or sample, and the surface is away from the associated magnet or magnet assembly (the pole shoe is intended to affect its magnetic field). In contrast, the back side of the pole shoe refers to the surface or surface portion of the pole shoe that is close to one or more magnets (the pole shoe is intended to affect its magnetic field), and the surface or surface portion is away from the defined volume or sample volume in which the sample will be positioned.

[0098] In an exemplary but non-limiting embodiment, the pole shoe or pole shoe assembly can be substantially elongated, meaning that the length of the pole shoe can be 10% longer than the width of the pole shoe. In other embodiments, the length can be 50% longer than the width or any value between 10% and 50%. In other embodiments, the length can be any value between 50% longer than the width and 100% longer than the width. In other embodiments, the length can be any value between 100% longer than the width and 200% longer than the width. In other embodiments, the length can be significantly longer, for example, 200% or more longer than the width of the pole shoe or pole shoe assembly.

[0099] In the present disclosure, the term "main pole shoe body" refers to a segment or part or portion of a pole shoe or pole shoe assembly whose front face is close to a specified sample volume. In various aspects of the present disclosure, the front face surface is generally curved, and in some embodiments, the surface curvature can be described according to a mathematical formula.

[0100] In the present disclosure, the term "pole shoe assembly" refers to a pole shoe comprising a main pole shoe body and an auxiliary structure (magnetic or non-magnetic or partially magnetic), wherein the main pole shoe body is directly attached / connected to the auxiliary structure. Such structure may include shim plugs (or shim plug bodies), shim plug screws, shim screws, mounting screws or interstitial shim layers, etc.

[0101] In the present disclosure, a "magnet array" into which a pole shoe or pole shoe assembly is inserted refers to a magnet arrangement configured to generate a desired magnetic field, and may include Halbach cylinders, Halbach spheres, other Halbach arrays, or arrays including magnets arranged in Halbach and non-Halbach configurations. In some embodiments, pole shoes are included in or used in association with any form of magnet array, wherein any form of magnet array includes, but is not limited to, an array in which one or more primary magnets may be placed outside each pole shoe, and wherein magnetically permeable material may be placed further outside the primary magnets to confine or shield magnetic flux.

[0102] In the present disclosure, the term "shimming" refers to any method for suppressing magnetic field inhomogeneities (including, but not limited to, inhomogeneities in the primary field generated by the magnet array). For greater certainty, it should be understood that the term "shimming" includes both active shimming, which can achieve shimming effects by applying current to generate induced and user-determined magnetic field shimming, and passive shimming, which achieves shimming effects by simply positioning ferromagnetic or other objects with predetermined magnetic properties.

[0103] In the present disclosure, "suppressing" non-uniformity refers to any adjustment of a geometric or functional component of a magnetic field to correct or smooth or otherwise adjust, overcome or modify an undesirable irregularity or distortion in the field. Suppression according to embodiments includes complete suppression or partial suppression, and in some embodiments affects one or more geometric or functional components of the field. In certain embodiments, suppression is actuated so that the magnetic field adopts a predetermined desired degree of uniformity.

[0104] When characterizing magnetic fields it is convenient to consider the spatial correlation of the field, that is, to consider the field is expressed as a function of spatial coordinates, such as Cartesian coordinates (x, y, z) defined relative to an origin. For analytical purposes, the coordinate function itself can be further described or estimated as a sum or expansion of a set of basis functions:

[0105]

[0106] in represents the unit vector along the z-axis, where represents the basis function, and where B 0and a i Represents the coefficient.

[0107] In this disclosure, a "functional component" of a magnetic field is defined by its corresponding coefficient a i The quantized basis functions given in the expansion of this type are The strength of the magnetic field portion characterized by . Moreover, suppressing the inhomogeneity corresponding to such a functional component means reducing the value of the corresponding coefficient. In the present disclosure, these individual functional components are sometimes referred to as "gradients" or "magnetic field gradients".

[0108] In embodiments of the present disclosure, the magnetic field is a primary magnetic field, which is generated or maintained within a magnetic resonance device, wherein the magnetic resonance device is a nuclear magnetic resonance (NMR) machine in some embodiments, a spectrometer (instrument) in some embodiments, and a compact NMR machine in some embodiments.

[0109] In the present disclosure, the term "magnetic resonance" or "MR" means the resonant reorientation of the magnetic moment of a sample in one or more magnetic fields, and includes nuclear magnetic resonance (NMR), electron spin resonance (ESR), magnetic resonance imaging (MRI), and ferromagnetic resonance (FMR). Since the present disclosure relates to methods and apparatus for making a generally static magnetic field more uniform, in some embodiments, the present disclosure is also generally applicable to ion cyclotron resonance (ICR) or ion trap or particle beam technology. For simplicity of description, the term "magnetic resonance or MR" used herein will be understood to include all of these alternative applications. In specific applications and embodiments, the disclosed apparatus and methods are applied to NMR, and in some embodiments, they are applied to NMR spectrometers or NMR imagers. Materials that exhibit magnetic resonance when exposed to a magnetic field are referred to as magnetic resonance or MR active nuclides or materials.

[0110] In the present disclosure, the term "sample" has the broadest possible meaning consistent with the present disclosure, and means any article or material that can or may be expected to be examined or tested using a magnetic field, or any article or material in which it may be expected to induce or measure or detect magnetic resonance, or any article or material that may be expected to be examined using embodiments of the subject matter disclosed herein. In specific embodiments, the sample includes or contains solid and non-solid objects and materials, living, non-living or dead materials, chemicals, structures, equipment, gases, liquids and solids, or any combination of any of the foregoing (such as solutions, colloids, slurries, gels, foams or pastes, etc.), or consists of them. In specific embodiments, without limitation, the sample includes one or more organisms or tissues, and such organisms or tissues are or include plants, animals and microorganisms, and include human subjects and animal subjects or parts thereof. Without limitation, the term "sample" includes any kind of experimental subjects or medical subjects, whether living, dead or non-living.

[0111] In the present disclosure, the term "sample volume" refers to a volume of space in which a sample can be placed and in which the sample is exposed to a main magnetic field or a primary magnetic field for the purpose of detecting the magnetic resonance properties of the sample (including determining the presence, absence or characteristics of magnetic resonance in the sample). The sample volume has any suitable size, and in some embodiments is closed or partially closed, and can be in a vacuum or partial vacuum or in an atmosphere controlled or temperature controlled state. In some embodiments, the sample volume is a region in the central space or central cavity of the magnet array. In some embodiments, the sample volume has a pole shoe assembly, a shim path, a shim panel, and other devices that may be necessary or desired for applying magnetic resonance to the sample and analyzing the sample, which are arranged around it. In a specific embodiment, the sample volume is or includes a hexagonal or cylindrical or other shaped cavity, or is in a hexagonal or cylindrical or other shaped cavity, and in some embodiments, is defined by one or more of a plurality of magnets, pole shoe surfaces, glass tubes or other physical constraints, or is defined by an abstract geometric surface relative to a point in space. In some embodiments, the sample volume includes or defines a space for (multiple) devices suitable for rotating, turning or otherwise moving or positioning the sample.

[0112] In this disclosure, the term "channel" when used with reference to the pole shoe body means any form of channel, groove, recess or concave surface in the surface of the pole shoe, and any adjustment made to the volume or part of the pole shoe to reduce or change the magnetic permeability in that volume or part of the pole shoe.

[0113] In some embodiments, the channel is filled with any desired material having the desired magnetic or non-magnetic properties, or the desired material is selected to strengthen, mitigate, enhance, weaken or otherwise modify or adjust the physical properties and magnetic properties of the pole piece in a manner desired by the user.

[0114] In some embodiments, the channel extends over the entire length or substantially the entire length of the pole shoe, and in some embodiments, the channel extends over a portion of the length of the pole shoe, wherein the portion of the length may be much less than the length of the pole shoe, and may be approximately 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the length of the pole shoe, more or less. In some embodiments, the material used to fill the shaped channel in the main pole shoe body, interstitial shim layer or front iron may include holes, recesses or other shaped features, and the holes may be threaded and remain open, or provided with a correspondingly threaded helical insert to allow movement of the insert.

[0115] In some embodiments, where multiple channels are provided, the multiple channels have substantially the same size, and in alternative embodiments, the channels have different sizes. In some embodiments, one or more inner surfaces of the channel are optionally textured in various ways, and are partially or entirely substantially smooth, ridged, corrugated, grooved, dimpled and / or scratched in some embodiments, and have protrusions or recesses or both protrusions and recesses in some embodiments, and in some embodiments any grooves, ridges, corrugations, dimples, scratches and other surface features are oriented in any desired direction. It should be understood that the ridges can have a range of geometric shapes, whether in the channel or on the front or other surfaces of the pole shoe, and in specific embodiments, the ridges have uniform cross-sections, uniform heights, uniform spacings, uniform lengths and uniform orientations. In alternative embodiments, the ridges have uneven cross-sections, uneven heights, uneven spacings, uneven lengths and uneven orientations, and are notched in some embodiments.

[0116] In alternative embodiments, the channels are created in the pole piece by cutting, preforming, compression or any other suitable means. Where multiple channels are provided, these channels may be sized, shaped and filled in the same way or in different ways according to the needs of the user.

[0117] In some embodiments, the pole shoe includes one channel, and in alternative embodiments includes two, three, four, five, six, seven, eight, nine, ten, eleven, twelve or more channels. Where multiple channels are provided, in some embodiments, they extend to cover part or all of the length of the pole shoe, or are arranged symmetrically, or are arranged asymmetrically, or are oriented longitudinally, or are oriented transversely, or have the same or different lengths, depths, widths, or otherwise have the same or different geometries or properties. In embodiments including more than one channel, the channels may have equal or different lengths, and may be spaced equidistantly or unequally from each other. In alternative embodiments, the channel may be straight or curved, and may be continuous or discontinuous along the length or width of the channel.

[0118] In this document, the term "shimming rod" or "shimming plug" means a body for adjusting the magnetic field close to the pole shoe, and the term "shimming hole" means a hole in the pole shoe or shimming plug body adapted to (including shaping and changing the size) receive a matching shimming rod inserted therein. In some embodiments, the shimming rod is made of a magnetically permeable material having a magnetic permeability similar to or the same as the magnetic permeability of the pole shoe itself, or in an alternative embodiment, the magnetic permeability of the shimming rod is different from the magnetic permeability of the pole shoe. According to specific embodiments, the shimming rod or shimming plug and shimming hole are cylindrical or polygonal in shape and boundaries, or have any other cross-section. The shimming rod and shimming hole are optionally shaped in various ways to allow the degree of freedom required to adjust the position of the shimming rod relative to the pole shoe. In certain embodiments, without limitation, the cross-section of the shim rods and shim holes is substantially regular or irregular, and / or substantially circular, elliptical, triangular, rectangular, square, diamond, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, decagonal, or has 3, 4, 5, 6, 7, 8, 9, 10 or more sides. It should be understood that the shim holes do not need to be closed on all sides, so in some embodiments, the shim holes are open along one side.

[0119] It will also be appreciated that in some embodiments, one or more shim rods are positioned relative to the pole piece but are not inserted therein, or are only partially inserted into shim holes, or partially inserted into channels in a face or portion of a pole piece.

[0120] It should also be understood that in the case where the shimming rod or shimming plug is to be rotated, or is to be threadedly engaged with a matching shimming hole or shimming plug hole by reciprocal threads, the geometry of the rod or plug and the shimming hole or shimming plug hole will be adjusted to facilitate such use. It should be understood that the descriptor "by thread" can be used alternatively to describe such reciprocal thread engagement. The shimming hole or shimming plug hole can include an internal thread, and the shimming rod or shimming plug can include a matching external thread so that the shimming rod or shimming plug can be screwed into a pole shoe or pole shoe assembly. It should be understood that in the case of a shimming rod associated with a pole shoe mentioned herein, it is meant that such a shimming rod is close to such a pole shoe, and is inserted into such a pole shoe in some embodiments, and is only located outside such a pole shoe but at a certain distance from such a pole shoe in other embodiments.

[0121] In some embodiments, the shim rod or shim insert is threaded and engages with cooperating reciprocal threads on the inner surface of the receiving shim hole. In some embodiments, this threaded engagement is used to locate the rod or insert and secure the rod or insert in the hole, and the geometry of the rod or insert and the rod receiving hole or insert receiving hole will be selected to allow the necessary rotation.

[0122] In magnetic resonance and other technical fields, one way to generate a magnetic field within a specified volume is to place permanent magnets near or around the volume. A relatively efficient design for generating fairly strong fields in a small volume is a Halbach cylinder or sphere, in which the permanent magnet material is oriented in a well-defined manner and arranged around a central cavity. In order to increase the magnetic field strength in a magnet array, the presented embodiments describe the use of a specific type of pole shoe assembly. The pole shoes can acquire a magnetic polarization when placed in a magnetic field. This polarization can increase the magnetic field strength in the region of space near the pole shoes to a value greater than when the pole shoes are not present. Sometimes in applications, it is desirable to use pole shoes or pole shoe assemblies in pairs, rather than individually.

[0123] The present disclosure will be more readily understood by referring to the following examples which are given for the purpose of illustrating the invention rather than limiting the scope thereof.

[0124] Figure 1A and Figure 1B 1 and 2 are front and rear perspective views, respectively, of a pole piece assembly 100 according to one embodiment. Figure 2 is based on Figure 1A and Figure 1B 1 is a front perspective view of an assembled pole piece assembly 100 of an embodiment of FIG. 1 , showing a reference plane 200 and a Cartesian coordinate system 220 . Figure 3A and Figure 3B According to Figure 1A and Figure 1B 1 is a front exploded view and a rear exploded view of a pole piece assembly 100 of an embodiment of the present invention.

[0125] exist Figure 1A , a pole shoe assembly 100 is shown including a main pole shoe body 102, and the main pole shoe body 102 exhibits a substantially curved front surface 110. The main pole shoe body 102 is made of a magnetically permeable material such as iron, cobalt, nickel, other chemical elements or alloys thereof. Accordingly, when placed in a magnetic field in an application, the main pole shoe body acquires magnetic polarization. Figure 2 , the front surface 110 can be described mathematically.

[0126] exist Figure 2 , the pole piece assembly 100 is shown as having a reference plane 200 including an origin 210. A Cartesian reference system 220 fixed at the origin 210 is also shown. The Cartesian reference system 220 includes a length axis Width axis and height axis and corresponding Cartesian coordinates x, y, and z. A rectangular region 230 located in reference plane 200 is also shown as being centered at origin 210 and having sides parallel to the x-axis and y-axis of Cartesian reference system 220. Rectangular region 230 has a length l along the x-axis and a width w along the y-axis, and accordingly contains within rectangular region 230 a region having a shape satisfying and The Cartesian coordinates (x,y) of a point.

[0127] A real-valued function z(x,y) may be defined on the points (x,y) in the rectangular region 230. In one aspect of the present disclosure, a subset of points located on the front surface 110 of the main pole shoe body 102 is described by a smoothed depth function z(x,y) of the Cartesian coordinates (x,y) of the points located in the rectangular region 230, the depth function quantifying the vertical distance z(x,y) from a point 240 located on the plane 200 with Cartesian coordinates (x,y,0) to a corresponding point 250 located on the front surface 110 with Cartesian coordinates (x,y,z(x,y)).

[0128] In another aspect of the present invention, the depth function takes z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient.

[0129] The reference plane 200 does not necessarily coincide with a physical flat surface on the main pole shoe body. Rather, it is an abstract plane in the three-dimensional volume occupied by and surrounding the pole shoe assembly that is used to mathematically define the front surface 110. For clarity, in some embodiments, the function z(x,y) in combination with the rectangular area 230 may describe the entire front surface 110, and in other embodiments may describe only a portion of the front surface.

[0130] refer to Figure 3A and Figure 3B , shows a pole shoe assembly 100 , which includes a main pole shoe body 102 , a shim plug-in body 104 , and a gap-filling shim layer 106 disposed between the main pole shoe body 102 and the shim plug-in body 104 .

[0131] The main pole shoe body 102 includes Figure 3B The back side 108 shown and Figure 3A The front side 110 is shown. The shim plug body 104 has Figure 3B The back side 112 shown and Figure 3A The front side 114 is shown. Once assembled, as Figure 1A and Figure 1B As shown, the pole shoe assembly 100 has a back side formed by the back side 108 of the main pole shoe body 102 and the back side 112 of the shim plug body 104. In some embodiments, a channel (not shown) can be provided on the back side of the pole shoe 100. Figure 1B and Figure 3B As shown, in some embodiments, the back side 112 of the shim plug body may include an aperture pattern (shim plug holes) 140 already formed in the surface.

[0132] In some embodiments, the back surface 108 of the main pole shoe body 102 and the back surface 112 of the shim plug body 104 are located in the same plane, and in alternative embodiments, they are not located in the same plane and are at different heights when the pole shoe assembly is assembled. In other alternative embodiments, each of the surfaces can be substantially flat, and in other alternative embodiments, either surface can exhibit curvature.

[0133] exist Figure 3B In the embodiment of the present invention, the back side 108 of the main pole shoe body 102 includes a recess (hollow space or hollow cavity) 107, which is adapted to be when the main pole shoe body 102 and the shim plug body 104 are as shown in FIG. Figure 1B When assembled as shown it receives the interstitial shim layer 106. In some embodiments, shim insert mounting screws 105 may be provided to secure the shim insert body 104 into the main pole shoe body 102.

[0134] In another embodiment (not shown), a recess may be provided in the front face 114 of the shim plug body 104, either replacing the recess 107 or as an extension thereof. In other words, a recess in the front face 114 may be provided instead of the recess 107 or may be provided in addition to the recess 107, wherein in this case the two recesses may face each other and preferably overlap each other (at least partially) to define a single hollow space in which the interstitial shim 106 may be located. In the present disclosure, this hollow space is referred to as an interstitial shim cavity.

[0135] The recess 107 is shaped and sized to receive the interstitial shim layer 106 therein when the main pole shoe body and the shim insert body are assembled together to form an interstitial shim cavity therebetween. In one embodiment, the recess (and likewise the interstitial shim cavity) may have a depth that exceeds the thickness of the interstitial shim layer 106, whereby (not shown) additional material having the same or different magnetic properties may be added on top of (or below) the interstitial shim layer 106 to shim the magnetic field and / or suppress field non-uniformities to achieve desired characteristics of the magnet assembly and / or magnetic resonance device in which the pole shoe assembly is assembled, inserted or implemented.

[0136] In some embodiments, the additional material added on top of or below the interstitial shim layer 106 can take the form of a flat plate of one or more shapes and have the same or different materials as the interstitial shim layer, the main pole shoe body, or the shim plug body. The additional material can be solid or patterned into other elevated or lowered areas with holes, slits, pits, channels, or additional materials. The additional material can be made of ferromagnetic material or non-ferromagnetic material or a combination of ferromagnetic and non-ferromagnetic materials. In some embodiments, a portion of the additional material can be made of a soft magnetic ferromagnetic material and can include flat buttons or plates of various sizes, shapes, and thicknesses that are positioned on top of or below the interstitial shim layer 106 by a user or machine.

[0137] The interstitial shim layer 106 comprises a substantially flat piece of magnetically permeable ferromagnetic metal. The interstitial shim layer 106 comprises a back side (oriented toward the shim plug body 104) and a front side (oriented toward the main pole shoe body 102). In operation, the interstitial shim layer may have material removed therefrom by various subtractive processes, including but not limited to chemical etching, machining, scraping, punching, laser cutting, water jet cutting, grinding and / or planing. Such material removal is performed in order to shim the magnetic field and / or suppress field non-uniformities so as to achieve the desired characteristics of the magnet assembly and / or magnetic resonance device in which the pole shoe is assembled, inserted or implemented. Such material removal may be performed in a manner that defines one or more apertures through the entire thickness of the interstitial shim layer. Alternatively, material removal may occur on the front side ( Figure 3Avisible surface) or the back surface ( Figure 3B surface visible in the image), or can occur on both surfaces where variable depth of material removal is under the control of the user, machine, or material removal process.

[0138] In one example, the thickness of the interstitial shim layer may be about 0.1 mm (about 0.004 inches). Figure 1A The corresponding depth of the interstitial shim cavity for receiving the interstitial shim layer formed by the main body 102 and the second body 104 when assembled, or formed and created by both, can be about 0.1 mm (about 0.004 inches) or more than about 0.1 mm (about 0.004 inches) to receive the interstitial shim layer. Alternatively, the depth of the recess in each of the main body or the second body can be about 0.1 mm to receive two interstitial shim layers stacked on each other. Various other alternatives are possible, including thicker or thinner interstitial shim layers, more than one interstitial shim layer stacked on each other, and recesses of different depths for receiving one or more interstitial shim layers in the main body, the second body, or both.

[0139] In another example, the thickness of the interstitial shim layer can be about 0.1 mm (about 0.004 inches), and the corresponding depth of the interstitial shim cavity formed by the recess in either the main body or the second body or both to receive the interstitial shim layer can be about 0.2 mm or 0.3 mm or deeper to receive the interstitial shim layer, wherein the interstitial shim layer is located in the interstitial shim cavity with an intermediate space above or below it in the interstitial shim cavity, which space is configured to receive a formed piece of ferromagnetic material or non-magnetic material.

[0140] In some embodiments, removal of material from the interstitial shim layer can be combined with adding or moving material into the interstitial shim cavity, and these modifications can also be combined with patterned removal of material from the front or back side of the main body and / or second body of the pole piece assembly by manual and / or automated processes, where the manual and / or automated processes include, but are not limited to, chemical etching, machining, scraping, punching, laser cutting, water jet cutting, grinding and / or planing.

[0141] The interstitial shim layer may be constructed of any magnetic material (e.g., mild steel or other types of steel, or nickel, or Hyperco alloy). The thickness of the interstitial shim layer may vary to allow fine tuning of the magnetic field. The interstitial shim layer may cover most of the surface of the recess in the body of the pole piece.

[0142] In some embodiments, the shim plug body 104 may include a threaded hole and a corresponding threaded insert (screw), and the movement of material within the interstitial shim cavity may include adjusting the threaded insert by screwing the threaded insert into or out of the threaded hole. In some embodiments, the shim plug body may include a formed portion of another material as a result of removing a portion of the shim plug body and replacing the portion with the other material.

[0143] In further embodiments, a cut-out region (not shown) may be defined in the shim plug body of the pole shoe assembly, and the cut-out region may be adapted to receive a center piece. The center piece may be constructed of magnetic or non-magnetic material(s) (e.g., aluminum, or any of a variety of ceramic or plastic materials such as Delrin or ABS (acrylonitrile butadiene styrene)), and a magnetically inert portion of a magnetically permeable ferromagnetic metal such as HiBoc may be provided within the shim plug body. The shape of the shim plug body having the cut-out region (and thus the overall shape of the pole shoe assembly) may provide improved magnetic field uniformity compared to a pole shoe assembly without the cut-out region in the shim plug body.

[0144] Positioning the non-magnetic center piece in the cut-out region of the shim plug-in body can allow the high spatial density of the shim plug-in holes in the shim plug-in body to continue into the cut-out region (not shown). This can allow the shimming function of the shim plug-in (e.g., shim plug-in screw) to be more diverse than without the center piece. The shape of the cut-out region and the center piece can be adjusted to improve the overall effectiveness of the pole shoe in a given magnet array or magnetic resonance device. When the pole shoe is produced and implemented in a magnet array or magnetic resonance device, it may be necessary to iterate the machining of the pole shoe to optimize the influence of the uniformity of the magnetic field generated by the magnet array. By selecting the shape of the cut-out region and the center piece in advance, production time can be saved while improving the quality of the magnetic field for sample analysis.

[0145] In the present disclosure, specific locations where material is removed from the main pole shoe body, the shim plug body, or the interstitial shim layer, or specific locations where material is added to the interstitial shim cavity above or below the interstitial shim layer, and the amount of material removed or added can be calculated by first estimating or measuring the magnetic field structure within the sample volume through field mapping or numerical simulation, and then estimating or measuring the amount of magnetic material to be added to or removed from the pole shoe assembly structure to modify the overall magnetic field structure within the sample volume.

[0146] In one embodiment, the body, shim insert body, and interstitial shim layers are made of soft (permeable) ferromagnetic metals. Examples include iron, cobalt, nickel, steel, or alloys such as Permanent Magnet, Hyperco, or other materials that acquire magnetic polarization when placed in a polarizing magnetic field. Hyperco is a class of soft magnetic alloys containing cobalt and other metals.

[0147] In some embodiments, the pole shoe assemblies may be used in pairs, with the front faces of the respective main pole shoe bodies positioned to face (oppose) each other across a gap. It should be understood that such a gap may be established and maintained by positioning the pair of pole shoe assemblies within a retaining structure or frame (sometimes referred to as a locator or locator assembly) to form another assembly (sometimes referred to as a central cavity assembly). The structure or frame may generally hold the pole shoe assemblies fixed in position, or alternatively may allow adjustment to the appropriate position by a user or an actuator. Such adjustment may be performed using one or more of a variety of actuators provided for this purpose, such as (but not limited to) screws, levers, slides, tilting devices, goniometers, or movable wedges, etc.

[0148] In applications where pole shoe assemblies are used in pairs, it may be useful to position the members of the pair so that their respective front faces are substantially parallel when in a nominal position (e.g., when the pair of pole shoe assemblies are initially positioned or placed in a magnet array). Because in some embodiments, the front face surfaces of the main pole shoe bodies are curved according to a mathematical formula, it is useful to clarify what is meant by two curved front faces being "substantially parallel." In this disclosure, two curved front faces are referred to as being substantially parallel when the reference planes defining the curvature of the respective front face surfaces are substantially parallel or coincident.

[0149] Also useful is to define a preferred volume that may exist between the two pole shoe assemblies, and a central abstract geometric feature such as an origin, a coordinate system, or a plane (such as a plane that may be substantially parallel to the two front faces of the pole shoe) defined relative to the volume. Similarly, a plane is substantially parallel to the curved front face surface if it is substantially parallel to a reference plane that defines the curved front face surface, or coincides with the reference plane. In some embodiments, the preferred volume may include a sample volume configured to receive a sample or sample tube. In some embodiments, the preferred volume may be a volume in which a user may expect a magnetic field with certain preferred features (such as a certain degree of spatial uniformity) to exist. In this case, it may be desirable to map or estimate the features within the preferred volume.

[0150] Figure 4A , Figure 4B , Figure 4C and Figure 4D According to the aforementioned Figures 1A to 3B The front view, rear view, side view and end view of the pole shoe assembly 100 of the embodiment of the present invention are shown. Figure 4A and Figure 4BAs shown, the main pole shoe body 102 defines a cutout portion 120 at each of the first and second ends of the main pole shoe body 102. Proximate the cutout portion 120 is a mounting tab 121, which in some embodiments may include a hole 123 or a groove or similar feature to accommodate a fastener (such as a mounting screw).

[0151] exist Figure 5A , Figure 5B and Figure 5C 5 shows a central cavity assembly 525 including a locator 502. The locator 502 has protrusions 122 that correspond to the cutout portions 120 on each of the two pole shoe assemblies 100. Eight protrusions 122 are shown on the locator 502; however, Figure 5A , Figure 5B and Figure 5C In each of the , only two of the eight protrusions 122 are marked. The protrusions 122 are received in (matched with) the corresponding cutout portions 120, as shown in FIG. Figure 5B and Figure 5C , the central cavity assembly 525 is shown in its assembled configuration. In the assembled configuration, the screws 133 engage the holes 123 in the mounting tabs 121 of the pole piece assembly 100 and the corresponding holes 137 in the retainer 502 to secure the pole piece assembly 100 to the retainer 502. FIG. 5A to FIG. 5C The protrusions and cutout portions shown are examples and may have different shapes and sizes in other embodiments. When the pole piece assembly and retainer are assembled, the protrusions and cutout portions may together define a substantially flat surface. FIG. 5A to FIG. 5C In the illustrated embodiment, the positioner 502 is shown as a single piece; however, in alternative embodiments, the positioner may have multiple parts.

[0152] Although in Figure 5A and Figure 5B Not shown, but in Figure 5C 5 , the first shim holes 130 in the pole shoe assembly 100 and the protrusions 122 in the positioner 502 are oriented relative to each other (when the pole shoe assembly 100 and the positioner 502 are assembled together) to allow the shim rods 134 to travel within the first shim holes 130 and approach (or be guided by) the protrusions 122. Adjusting the shim rods 134 into and / or out of the first shim holes 130 modifies the magnetic field created by the magnet assembly into which the central cavity assembly 525 is (will be) inserted.

[0153] As shown in FIGS. 3-5 , each of the first shim holes 130 is adapted to receive a shim rod 134. As an alternative to the protrusions 122 on each of the first and second ends of the positioner 502 (which serve as physical guides for the shim rods 134), second shim holes (not shown) may instead be provided in the positioner. In such an alternative embodiment, when one or more pole shoe assemblies are assembled with the positioner, the first shim holes defined by the pole shoe assemblies and the second shim holes defined by the positioner are aligned with each other to allow the shim rods to travel (be adjusted) within the first and second shim holes until a desired change in the uniformity of the magnetic field is achieved.

[0154] Other modifications of the positioner are possible, and the configuration shown in FIG5 is shown by way of illustrative example, not limitation. For example, there may be fewer protrusions, such as four protrusions instead of eight, i.e., two protrusions instead of four protrusions on each of the first and second ends of the positioner. When the two pole shoe assemblies are assembled into the central cavity assembly with the positioner, each of the four protrusions may correspond to (match) one of the cutouts on the pole shoe assembly.

[0155] The locator can be composed of one or more parts, including a part that extends beyond the length of the pole shoe assembly when the pole shoe assembly is assembled with the locator into the central cavity assembly. Depending on the magnet assembly in which the locator and pole shoe assembly are utilized, the locator can have various functions. The functions of the locator can include, but are not limited to: (i) providing a structure for receiving the pole shoe assembly and inserting the pole shoe assembly into the central cavity (inner bore) of the central cavity assembly and the magnet assembly; (ii) providing a structure by which physical adjustment can be made to set or change the position or alignment of the pole shoe assembly relative to the locator and the inner bore; (iii) securing the central cavity assembly to the magnet assembly, for example, within the inner bore of the magnet assembly; and / or (iv) positioning the pole shoe assembly within the inner bore and magnetic field of the magnet assembly to a defined distance from the location where the sample will be located for analysis.

[0156] The embodiments of the present disclosure are not limited to the number of shimming holes, shimming rods, cutouts, and protrusions shown in the figures. In other embodiments, a single shimming hole or more than two shimming holes may be used in each or either of the first end and the second end of the pole piece assembly. In other embodiments, there may be no shimming holes.

[0157] like Figure 3B As shown, the shim plug body 104 of the pole piece assembly 100 defines a shim plug hole 140. The shim plug hole 140 is adapted to receive a shim plug screw 142 to achieve a change in magnetic field uniformity. Figure 3B61 shim plug holes 140 are shown in the shim plug body 104 of FIG; however, fewer or more shim plug holes may be defined in the shim plug body. The present disclosure contemplates varying the number, size, and pattern of shim plug holes (with corresponding shim plug screws) as required by the application. Figure 3B An embodiment is shown that includes two staggered rectangular shim hole configurations that coincide with a grid of points (one grid is 5×9 points, the other grid is 4×4 points, a total of 61 points). As an alternative embodiment, the present disclosure includes rectangular or hexagonal or triangular grids containing different numbers of points distributed on the surface of the shim plug body. The greater the number and density of grid points, the finer the control of magnetic field uniformity, but at the expense of increased manufacturing complexity.

[0158] The shim plug screws may be of the same length or of different lengths, and may be inserted into the shim plug holes to varying degrees to improve or optimize magnetic field uniformity. Depending on the characteristics of the magnetic field to be shimmed, any of the shim plug holes may be occupied or unoccupied by a shim plug screw, and any particular shim plug screw used may be inserted to varying degrees to shim the magnetic field. Other embodiments are also contemplated for optimizing magnetic field uniformity by inserting objects into the receiving apertures / holes, including, but not limited to, inserting round / square / rectangular / irregular shaped objects into the receiving apertures / holes to optimize magnetic field uniformity.

[0159] The magnetic field generated by one magnet array (in which the pole shoe assemblies are subsequently inserted) may be different from the magnetic field generated by another magnet array, depending on the specific construction of the component magnets or mechanical or magnetic tolerances associated with the materials or manufacturing methods used in the construction of the magnet arrays. There may be differences in the magnetic characteristics, material properties and / or shape of each component magnet and / or pole shoe (or pole shoe assembly) provided. These differences may result in different arrangements of shim plug screws (or alternatives) in shim plug holes (or other apertures) to improve or optimize the magnetic fields generated by different magnet arrays.

[0160] exist Figure 3A and Figure 3B In the embodiment of the present invention, the shim plug screw 142 is threaded and engages with matching reciprocal threads on the inner surface of the receiving shim plug hole 140. In some embodiments, this thread engagement is used to locate the shim plug screw and secure the shim plug screw into the shim plug hole. The geometry of the corresponding mating parts will be selected to allow the necessary rotation.

[0161] In one embodiment, the shim plug screw is screwed into the shim plug hole in the shim plug body of the pole piece assembly substantially along an axis that coincides with the main magnetic field that magnetically polarizes the magnetically permeable material of the pole piece (or pole piece assembly). Figure 3A and Figure 3BAs shown, in this embodiment, the shim plug screw 142 is screwed into or out of the shim plug hole 140 along the axis, wherein the axis is perpendicular to the axis along which the shim rod 134 is screwed into or out of the first shim hole 130 and the second shim hole 132.

[0162] For a given pole piece assembly, the shim rods can have different lengths, and / or the shim insert screws can have different lengths, thereby allowing different amounts of magnetic material to be positioned at different locations to improve or optimize the uniformity of the magnetic field. In some embodiments, the length of the shim insert screw can be in the range of 0.05 inches to 0.16 inches or longer, depending on the application requirements.

[0163] The multi-part nature of the pole shoe assembly of the disclosed embodiments allows for independent physical modification of each of the discrete parts of the pole shoe assembly prior to its application in a positioner, magnet array, or magnetic resonance device. Specifically, the back, front, and body of the main pole shoe body, the back, front, and body of the shim plug body, and the back, front, and body of the (multiple) interstitial shim layers can all be physically adjusted so that when assembled as a whole into the pole shoe assembly, the effect on the magnetic field of the magnet array is enhanced and / or refined, or more conveniently compared to a single-part pole shoe (a pole shoe without multiple parts).

[0164] In another aspect of the present disclosure, the presence, absence, and location of the shim plug screw 142 within the shim plug body 104 and the depth function z(x,y)=∑ i,j c ij f i (x)g j The exact functional content of (y) (particularly with respect to the chosen set of basis functions Ω x and Ω y The coefficient c ij ).

[0165] The physical adjustment may include removing ferromagnetic material using any subtractive process, such as, but not limited to, chemical etching, machining, scraping, punching, laser cutting, water jet cutting, drilling, tapping, grinding and / or planing. After the removal, the removed material may be replaced with a non-magnetic material of the same or similar shape to maintain the strength of the pole shoe part, which may otherwise be impaired in the absence of the replacement material. The replaced formed material may also be used to continue the purpose of the pattern of the recess, threaded hole or other features in the pole shoe part, which is impossible when the removed magnetic material is not replaced by a non-magnetic material. Moreover, each of these independent modifications may be combined with another independent modification, which is to insert a plurality of formed magnetic materials into the interstitial shim cavity above or below the interstitial shim layer (multiple) interstitial shim layers, into the main pole shoe body, and / or into the shim plug-in body of the pole shoe (or pole shoe assembly).

[0166] In one embodiment, the magnetic field in the preferred volume can have several functional components of magnetic field inhomogeneities, i.e., several separate gradients. In the present disclosure, multiple regions (the back, front, and body of one or more interstitial shim layers, the back and front of the main pole shoe body, the back and front of the shim plug body, and the space below and / or above the (multiple) interstitial shim layers within the interstitial shim cavity) where magnetic material can be removed or added to suppress multiple inhomogeneities of the magnetic field within the preferred volume. Specifically, different gradients can be addressed by modifying different ones of the multiple regions.

[0167] As described in the present disclosure, the size, material, and location on the interstitial shim layer of the material selected to be removed and / or added are determined based on an understanding of the magnetic field gradients generated by the magnet array. Adding and removing material relative to the interstitial shim layer, the main pole shoe body, and the shim plug body in the pole shoe assembly allows for selective improvement of the magnetic field non-uniformity generated by different magnetic field gradients. In applications, improving, suppressing, adjusting, modifying, or shimming the magnetic field may result in improved performance of a magnetic resonance device including a magnet array and a pole shoe assembly for magnetic resonance sample analysis. Such improvements may include making the magnetic field more uniform in the sample volume.

[0168] In embodiments of the present disclosure, a magnet array may be included in a magnetic resonance device or apparatus. For example, Figure 6 FIG. 6 is an exemplary block diagram of a magnetic resonance device 650 according to an embodiment of the present disclosure. Figure 6The two pole shoe assemblies 600 are schematically shown as being located in a magnet array 660 having a central cavity 661 (sometimes referred to as the inner bore of the magnet array). The device 650 also includes a computer 651, which is operably connected to a sample rotation control module 652 for controlling the rotation of an optional sample rotator 654, which is used to rotate a sample 656 in a sample tube 657 within a sample channel 658 provided in the magnet array 660.

[0169] The computer 651 may also be operably connected to a pulsed magnetic field control and signal detection electronics module 662 for controlling the detection coils 663 and receiving signals therefrom. The apparatus 650 may also include a field uniformity control module 664 for controlling the magnetic field in a centrally located test volume 665. A temperature control module 667 may also be provided for controlling the temperature of the magnet array 660 and the temperature within the channel 658. In some embodiments, the pole shoe assembly 600 is supported by (assembled with) a positioner to produce a central cavity assembly; however, for clarity of illustration, Figure 6 Positioner and center cavity assembly are not included.

[0170] Fig. 7A is a cross-sectional view of a magnet array (assembly) 770 including two pole shoe assemblies 700 . Fig. 7A An example of how to position the pole piece assembly of the present disclosure in a magnet assembly (array) that can be configured to be used in a magnetic resonance device (e.g., Figure 6 1 and 2. In the embodiment shown in FIG.

[0171] from Fig. 7A As can be seen in the cross-sectional view of FIG, two pole shoe assemblies 700, each having a back side 708 and a front side 710, are arranged within a central cavity 771 of a hexagonal Halbach cylinder, Halbach-type, or other magnet array 770. The pole shoe assemblies are supported by positioners 702 such that the pole shoe assemblies and positioners together form a central cavity assembly 725. A central sample volume or sample space 756 for analysis (sometimes referred to as a central region containing a sample test volume) is shown in the central cavity and between the two pole shoe assemblies 700. Fig. 7A In the illustrated embodiment, the magnet array 770 includes six individual magnets 740, each having an individual magnetization direction 715, as shown. In an alternative embodiment, the six magnets shown are the center six magnets of a larger assembly that includes additional magnets.

[0172] In the cross-sectional view of the magnet array 780 Figure 7B A more general embodiment is shown in FIG. 7 , where the magnet array includes a Halbach cylinder, Halbach type or other magnet array portion 742, and relative to Fig. 7AThe extended inner portion 745 of the central cavity 771. The extended inner portion 745 can include magnetic and non-magnetic structures around the central cavity 781. Fig. 7A and Figure 7B As can be seen in both, the front face 710 of the main pole shoe body of each pole shoe assembly 700 is close to the central sample volume or sample space 756, and the back face 708 of the main pole shoe body of each pole shoe assembly 700 is close to the magnet array 780 ( Figure 7B 780 in, or Fig. 7A The pole shoe assembly 700 is assembled with the positioner 702 to form a central cavity assembly 725 within the central cavity 781. In alternative embodiments, the pole shoe (or pole shoe assembly) may be any other embodiment according to the subject matter of this document.

[0173] In some embodiments, the length of the shim rods 134 may be as long as 1.5 inches or longer, depending on the application needs of adjusting the magnetic field. Although the pole piece assembly may have additional shim holes and shim rods, Figures 1A to 5C In the non-limiting example shown, up to four shim rods are inserted into the shim holes of one pole shoe assembly; thus, up to eight shim rods can be used in a magnetic resonance apparatus having two pole shoe assemblies (e.g., Figure 6 ). Depending on the type and size of the magnet array or magnetic resonance device that contains the pole pieces, the maximum length of the shim rods may be shorter or longer.

[0174] When determining the pole piece assembly characteristics (including, but not limited to, shape, composition, size, number of parts) that are useful or desirable in an application, even slight variations in the pole piece in close proximity to the sample in the magnetic resonance device may have a significant impact on the magnetic field uniformity and sample analysis results. In order to improve or optimize the magnetic field uniformity and provide predictable and scalable production of magnet arrays including pole piece assemblies, pole piece manufacturing and adjustment requires the identification of one or more magnetic field non-uniformities by:

[0175] -Simulate the magnetic field generated by the magnet array, with or without contribution from the pole piece assembly;

[0176] - using a field mapping device to measure the magnetic field generated by the magnet array, with or without contribution from the pole piece assemblies; or

[0177] - A combination of these.

[0178] A method for shimming a magnetic field generated by a Halbach-type magnet configuration is disclosed herein. The method may be iterative and comprises:

[0179] - providing a pole shoe assembly, the pole shoe assembly comprising: a main pole shoe body having a front side and a back side; a shim plug body having a front side and a back side, the shim plug body being adapted to receive and / or be received by the main pole shoe body to form an assembled pole shoe assembly, such that the back side of the main pole shoe body faces the front side of the shim plug body; a recess formed in at least one of the back side of the main pole shoe body and the front side of the shim plug body, such that when the main pole shoe body and the shim plug body are in an assembled position, the recess forms an interstitial shim cavity; and an interstitial shim layer disposed in the interstitial shim cavity;

[0180] - identifying magnetic field inhomogeneities generated by magnetic field gradients by simulating (using field mapping equipment / devices) or measuring the magnetic field generated by a Halbach-type magnet configuration;

[0181] - modifying the material content of the interstitial shim cavity by one or more of: removing material from the interstitial shim layer; adding material above or below the interstitial shim layer in the interstitial shim cavity; and moving material within the interstitial shim layer; and

[0182] - Inserting a pole piece assembly into the central cavity of a Halbach type magnet configuration for shimming the magnetic field generated by the Halbach type magnet configuration to improve the magnetic field uniformity.

[0183] The method may further include:

[0184] - identifying one or more additional magnetic field inhomogeneities respectively generated by one or more additional magnetic field gradients; and

[0185] - Repeat any of the previous steps until the magnetic field homogeneity reaches the desired level allowing sample analysis.

[0186] The expected level of magnetic field homogeneity can be determined by comparing measurements of field deviation using magnetic field mapping equipment, or by observing characteristics (such as linewidth or decay time) of magnetic resonance signals obtained from a test sample placed within the magnet configuration.

[0187] A method for shimming a magnetic field generated by a Halbach-type magnet configuration at least partially surrounding a sample volume is disclosed. The method comprises:

[0188] - identifying magnetic field inhomogeneities in a sample volume of a Halbach-type magnet configuration, said inhomogeneities being generated by magnetic field gradients;

[0189] - providing a pole shoe assembly, the pole shoe assembly comprising a main pole shoe body, a shim plug body and a gap-filling shim layer, the main pole shoe body comprising a curved front surface;

[0190] - forming an improved pole piece assembly by performing one or more of: removing material from at least a portion of the pole piece assembly, adding material to at least a portion of the pole piece assembly, moving material within at least a portion of the pole piece assembly based on the identified magnetic field inhomogeneities; and

[0191] -Inserting an improved pole piece assembly into a Halbach magnet array to shim the magnetic field.

[0192] The method may further include:

[0193] - identifying one or more additional magnetic field inhomogeneities respectively generated by one or more additional magnetic field gradients; and

[0194] - Repeating any of the preceding steps for each of one or more additional magnetic field inhomogeneities.

[0195] The method may also include identifying magnetic field inhomogeneities by:

[0196] - simulate the magnetic field generated by a Halbach type magnet configuration; or

[0197] - Use magnetic field mapping equipment to measure the magnetic field generated by the Halbach type magnet configuration.

[0198] The step of moving material within at least a portion of the pole piece assembly may include:

[0199] - adjusting the position of at least one shim rod in at least one first shim hole or second shim hole defined by the main pole shoe or the positioner, respectively;

[0200] - adjusting the position of at least one shim plug screw in at least one shim plug hole defined in the shim plug body; or

[0201] - A combination of these.

[0202] The method may further include assembling the two modified pole piece assemblies and the positioner into the central cavity assembly prior to inserting the two modified pole piece assemblies into the Halbach-type magnet configuration.

[0203] In another aspect of the present disclosure, a method for shimming a magnetic field generated by a Halbach-type magnet configuration at least partially surrounding a sample volume is disclosed herein. The method comprises:

[0204] - identifying magnetic field inhomogeneities in a sample volume of a Halbach-type magnet configuration, said inhomogeneities being generated by magnetic field gradients;

[0205] -Provide a pole shoe assembly, the pole shoe assembly comprising a main pole shoe body, the main pole shoe body comprising:

[0206] ○ curved front surface S;

[0207] ○ Reference plane P, which contains the origin O;

[0208] ○ A Cartesian reference system fixed at O, the Cartesian reference system comprising a length axis Width axis and height axis and the corresponding Cartesian coordinates x, y, and z;

[0209] o A rectangular region R of length l, width w, located in the reference plane P and centered at the origin O, having sides parallel to the x-axis and y-axis of the Cartesian reference system and containing and The Cartesian coordinates (x, y) of a point,

[0210] ○ where a point on the frontal surface S is described by a smoothed depth function z(x,y) of Cartesian coordinates defined on R, which quantifies the perpendicular distance z from R to the corresponding point on S,

[0211] ○ and wherein the depth function takes z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ii Yes Expand

[0212] coefficient.

[0213] - forming an improved main pole shoe body by performing one or more of the following: removing material from the main pole shoe body or adding material to the main pole shoe body based on the identified magnetic field inhomogeneities; and

[0214] - Inserting an improved pole shoe assembly including an improved main pole shoe body into a Halbach type magnet configuration to shim the magnetic field.

[0215] The method may further include:

[0216] - identifying one or more additional magnetic field inhomogeneities respectively generated by one or more additional magnetic field gradients; and

[0217] - Repeating any of the preceding steps for each of one or more additional magnetic field inhomogeneities.

[0218] The method may also include identifying magnetic field inhomogeneities by:

[0219] - simulated magnetic field, which is obtained by modulating (adjusting) the coefficient c defining the front surface S in the depth function ij Generated by modifying the front surface of the main pole shoe body; or

[0220] -Measured by defining the coefficient c of the front surface S in the depth function ij The magnetic field generated by the modulation (adjustment) to modify the front surface of the main pole shoe body, and the changes in the field configuration corresponding to the adjustment are recorded using a magnetic field mapping device.

[0221] In the foregoing disclosure of the method (and the related disclosure of the mathematical configuration of the front surface of the main pole shoe body), a depth function z(x, y) is defined for the front surface of the main pole shoe body, and the depth function takes z(x, y) = ∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient. Accordingly, the implementation of the disclosed main pole shoe body and shimming method includes selecting a suitable basis function set Ω x and Ω y . In the desired basis function set, each function is differentiable and, in some embodiments, smooth. In some embodiments, in a non-limiting example, examples of basis functions are: orthogonal polynomials (including Jacobi polynomials, Legendre polynomials, Laguerre polynomials, Chebyshev polynomials), hypergeometric functions, trigonometric functions, inverse trigonometric functions, hyperbolic functions, inverse hyperbolic functions, Bessel functions, Gaussian functions, rational functions, Padre approximations, and related Legendre functions. The present disclosure also contemplates the use of proportional sums, products, quotients, and composite forms of the aforementioned types of functions. The user can select a basis function set based on the needs of the application, and in some embodiments, the basis function set is selected based on a simulation of magnetic field changes associated with changes in the front surface caused by changing the corresponding expansion coefficients.

[0222] As described above, in one embodiment of the present disclosure, a pole shoe assembly is attached to a positioner to form a central cavity assembly. The positioner positions, for example, two pole shoe assemblies into a suitable arrangement for direct placement or implementation in the central cavity of a magnet array. In an exemplary embodiment, the two pole shoe assemblies are positioned so that the front faces of their respective main pole shoe bodies face each other and are parallel to each other across the spatial volume containing the sample volume, wherein their front faces (more precisely, the reference planes for mathematically defining their front faces) are substantially perpendicular to the main static magnetic field provided by the magnet array. In some embodiments, the pole shoe assembly extends the entire length of the magnet array or the central cavity therein. In alternative embodiments, the pole shoe assembly extends a distance longer than the magnet array or the cavity therein. In other embodiments, the pole shoe assembly extends only a portion of the length of the cavity or magnet array.

[0223] Although the preferred embodiment has been described above and shown in the drawings, it is obvious to those skilled in the art that modifications can be made without departing from the present disclosure. Such modifications are considered to be possible variations within the scope of the present disclosure.

Claims

1. A pole shoe assembly for use in a Halbach-type magnet structure, the pole shoe assembly comprising a back face, a front face S, and ends separated by a first distance, the first distance defining the length of the pole shoe assembly along a first axis extending between the ends, the pole shoe assembly being configured for insertion into the interior of the Halbach-type magnet structure along the first axis, wherein the surface of the front face S is curved, and wherein the curvature of the front face is mathematically defined for shimming the magnetic field generated by the magnet structure. 2 . The pole piece assembly of claim 1 , wherein the pole piece assembly is elongated along the first axis.

3. The pole shoe assembly according to claim 1, further comprising: include: - a reference plane P containing an origin O, said reference plane being in a three-dimensional volume occupied by and surrounding said pole shoe assembly; -Cartesian reference system, fixed at O, including length, width and height axes ( and ) and the corresponding Cartesian coordinates x, y and z along said axes, respectively; and a rectangular region R of length l and width w, located in the reference plane P and centered at the origin O, having sides parallel to the x-axis and the y-axis of the Cartesian reference system and containing and The Cartesian coordinates (x, y) of a point, wherein a point on the front surface S is described by a smoothed depth function z(x,y) of Cartesian coordinates defined on R, said depth function quantifying the vertical distance z from R to the corresponding point on S; and The depth function is z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient.

4. The pole piece assembly of claim 3, wherein the reference plane P coincides with a physically flat surface on the body of the pole piece assembly.

5. The pole piece assembly of claim 3, wherein the reference plane P is an abstract plane in a three-dimensional volume occupied by and surrounding the pole piece assembly.

6. The pole piece assembly of claim 1, wherein a body of the pole piece assembly is made of a magnetically permeable material.

7. The pole piece assembly of claim 1, wherein a body of the pole piece assembly acquires magnetic polarization when placed in a magnetic field.

8. The pole piece assembly according to claim 3, wherein the basis function set Ω x and Ω y is a set of orthogonal, Jacobi, Legendre, Laguerre, Chebyshev, hypergeometric, trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, Bessel, Gaussian, rational, Padé approximation, or related Legendre functions, or a sum, product, quotient, or composite of these.

9. The pole piece assembly of claim 1, further comprising a shim hole adapted to receive at least one mating shim rod inserted therein.

10. The pole piece assembly of claim 9, wherein the shim holes include internal threads and the shim rods include matching external threads such that the shim rods can be screwed into the pole piece assembly.

11. The pole shoe assembly according to claim 1, include: - a main pole shoe body having a front side and a back side; - a shim plug-in body having a front side and a back side, the shim plug-in body being adapted to receive the main pole shoe body and / or to be received by the main pole shoe body to form the pole shoe assembly, such that when in the assembled position, the back side of the main pole shoe body faces the front side of the shim plug-in body; a depression formed in at least one of the back side of the main pole shoe body and the front side of the shim plug body, so that when the main pole shoe body and the shim plug body are in an assembled position, a gap-filled shim cavity is formed by the depression; as well as - an interstitial shim layer, arranged in the interstitial shim cavity.

12. The pole piece assembly of claim 11, wherein the shim plug body defines a shim plug aperture adapted to receive one or more shim plugs inserted therein.

13. The pole piece assembly of claim 12, wherein the one or more shim plugs are threaded and engage with cooperating reciprocal threads on an inner surface of a shim plug receiving hole so that the shim plug can be screwed into the pole piece assembly.

14. The pole piece assembly of claim 11, wherein the depth of the recess is greater than the thickness of the interstitial shim layer to allow insertion of a material having the same or different magnetic properties above or below the interstitial shim layer for shimming the magnetic field generated by the Halbach-type magnet structure.

15. A magnetic resonance device comprising the pole piece assembly according to claim 1.

16. A method for shimming a magnetic field generated by a Halbach-type magnet configuration, the magnet configuration at least partially surrounding a sample volume, the method include: - identifying magnetic field inhomogeneities in a sample volume of said Halbach-type magnet configuration, said inhomogeneities being generated by magnetic field gradients; -Provide a pole shoe assembly, the pole shoe assembly comprising a main pole shoe body, the main pole shoe body comprising: ○ curved front surface S; ○ Reference plane P, which contains the origin O; ○ Cartesian reference system, which is fixed at O ​​and includes the length axis Width axis and height axis and the corresponding Cartesian coordinates x, y, and z; o A rectangular region R of length l, width w, located in the reference plane P and centered at the origin O, having sides parallel to the x-axis and y-axis of the Cartesian reference system and containing and wherein a point located on the front surface S is described by a smoothed depth function z(x,y) of Cartesian coordinates defined on R, the depth function quantifying the vertical distance z from R to the corresponding point on S; and The depth function is z(x,y)=∑ i,j c ij f i (x)g j (y) in the form of i and g j is from the basis function set Ω x and Ω y The smooth basis function selected in , and where c ij is the expansion coefficient; - forming an improved main pole shoe body by performing one or more of the following: removing material from the main pole shoe body or adding material to the main pole shoe body based on the identified magnetic field inhomogeneities; and - inserting the improved pole shoe assembly including the improved main pole shoe body into the Halbach type magnet structure to shim the magnetic field.

17. The method according to claim 16, further comprising: include: - identifying one or more additional magnetic field inhomogeneities generated by the one or more additional magnetic field gradients; as well as - Repeating the steps of identifying to inserting for each of said one or more additional magnetic field inhomogeneities.

18. The method of claim 16, further comprising identifying the magnetic field inhomogeneity by simulating a magnetic field by adjusting a coefficient c defining the front surface S in the depth function. ij Generated by modifying the front surface of the main pole shoe body.

19. The method according to claim 16, further comprising measuring the coefficient c of the front surface S defined in the depth function ij The magnetic field generated by modifying the front surface of the main pole shoe body by adjustment and using a magnetic field mapping device to record the changes in the field configuration corresponding to the adjustment to identify magnetic field inhomogeneities.

20. The method according to claim 16, wherein the basis function set Ω x and Ω y is a set of orthogonal, Jacobi, Legendre, Laguerre, Chebyshev, hypergeometric, trigonometric, inverse trigonometric, hyperbolic, inverse hyperbolic, Bessel, Gaussian, rational, Padé approximation, or related Legendre functions, or a sum, product, quotient, or composite of these.

21. The method according to claim 16, further comprising: include: The two modified pole piece assemblies and the positioner are assembled into the central cavity assembly before inserting the two modified pole piece assemblies into the Halbach type magnet configuration.

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