CN106257602A - A kind of radial direction adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field - Google Patents

Abstract

The invention relates to a portable NMR detection permanent magnet for radially adjusting a uniform field, which mainly includes a radially adjusting permanent magnet and a base plate. The radially adjusted permanent magnet provides the main magnetic field of the magnet, which is composed of M-layer sub-magnetic ring arrays stacked layer by layer. The inner and outer diameters of each layer of sub-magnetic rings are different, and the magnetic field distribution in the center of the magnet is controlled by adjusting the ratio of inner and outer diameters; the base plate includes upper and lower cover plates and the middle M-1-layer substrate, the upper and lower cover plates are placed at both ends of the magnet, grooves are processed on both sides of the middle substrate, and the magnetic blocks are embedded to form a sub-magnetic ring. The distance between each layer is determined by the substrate; Layers are stacked, and finally the entire magnet structure is fixed with screws. The portable NMR detection permanent magnet provided by the present invention adopts a radial adjustment method to improve the uniformity of the magnetic field, effectively solves the impact of the end effect caused by the limited height of the cylindrical magnet, and realizes the generation of a high uniformity magnetic field in a small volume, which is in line with the future The requirement of portability and miniaturization of NMR system.

Description

A Portable Permanent Magnet for Radial Adjustment of Uniform Field for NMR Detection

technical field

The invention relates to a nuclear magnetic resonance permanent magnet structure design, which can generate a uniform static magnetic field for NMR detection in a magnet structure with a small volume.

Background technique

Nuclear magnetic resonance (Nuclear Magnetic Resonance, NMR) technology has developed rapidly in recent years, and is widely used in physics, chemistry, life medicine, agricultural food safety, geological exploration, surveying, etc. Wells and other fields. However, the NMR magnets currently used increase the amount of magnetic materials used in order to increase the magnetic field strength and uniformity, resulting in a bulky and bulky body that does not meet the future development needs of portability and miniaturization. The Halbach array structure permanent magnet (magic ring magnet) has received extensive attention since it was proposed. The characteristic of this structure is that the magnetic field strength on one side of the magnetic ring is increased while the other side is smaller. This magnetic concentration effect can reduce the magnetic flux leakage around the magnet, thereby It can realize small-volume magnets to obtain high magnetic field strength, and provides a new method for the miniaturization of nuclear magnetic resonance magnets.

Permanent magnets with Halbach array structure have performance advantages such as high magnetic field strength, less flux leakage, and no need for iron yokes, which has attracted widespread attention from many scholars at home and abroad. During the research process, it was found that when the height of the traditional magnet is reduced, the end effect has a significant impact on the central magnetic field, resulting in a serious deterioration of the uniformity of the magnetic field, which needs to be solved urgently. Patent CN 100568016C discloses a permanent magnet for a portable nuclear magnetic resonance instrument, using a semi-cylindrical permanent magnet to compensate the axial magnetic field at the end of the cylindrical permanent magnet, but the magnetic fields at both ends of the semi-cylindrical permanent magnet diverge in space Distributed, large magnetic flux leakage and heavy structure; patent CN100568017C improved the magnet structure disclosed in patent CN 100568016C, changed the bottom semi-cylindrical permanent magnet into a hemispherical permanent magnet, and reduced the end effect of the cylindrical permanent magnet while compensating Peripheral magnetic flux leakage. Internationally, the Blümler laboratory team has done a lot of research on the Halbach structure. Raich et al. (Raich H, Blümler P. Design and construction of a dipolar Halbach array with a homogeneous field from identical bar magnets: NMR Mandhalas[J]. BMagnetic Resonance Engineering, 2004, 23B (23B): 16-25.) has designed a kind of NMR Mandhalas (Magnet Arrangements for Novel Discrete Halbach Layout) permanent magnet structure, adopts exactly the same rectangular magnetic piece to form Halbach array and multi-layer stacking, reduces Difficulty in processing and assembly and reduce the end effect to a certain extent; Soltner et al. (Soltner H, P. Blümler. Dipolar Halbach magnet stacks made from identically shaped permanent magnets for magnetic resonance [J]. ):211–222.) On this basis, he continued to explore the properties of Mandhalas magnets with different cross-sections such as circular and polygonal shapes, and showed that adjusting the layer spacing when stacking multilayer magnetic rings can improve the uniformity of the central magnetic field.

In summary, the use of additional devices such as hemispherical magnet structures to compensate the axial magnetic field of the magnets will lead to more complex permanent magnet structures and increase the volume of the magnets, which is not conducive to the miniaturization of the magnet structure; the Mandhalas multilayer array structure adjusts the layer spacing to improve the uniformity of the magnetic field However, as the gap increases, the flux leakage increases, and the height of the magnet is still too large, resulting in a larger magnet volume.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a portable NMR detection permanent magnet with a radially adjusted uniform field, which realizes the generation of a high-uniform magnetic field by a small-volume magnet, has a simple structure and good openness, and is useful in portable nuclear magnetic resonance systems. Wide application prospects.

The technical solution of the present invention is: the specific solution of the present invention is as follows: a portable nuclear magnetic resonance detection permanent magnet for radially adjusting the uniform field, including a radially adjusting permanent magnet and a base plate, and the radially adjusting permanent magnet is It is composed of M layers of sub-magnetic ring arrays with different ratios of inner and outer diameters, said M>2; each layer of sub-magnetic ring arrays is composed of N identical magnetic blocks arranged along a circular array and fixed on a base plate correspondingly, N =2n, n>2.

Further, there is a gap between adjacent magnetic blocks of the sub-magnetic ring array, so that the size and position of the magnets can be adjusted radially, while isolating the magnetic blocks reduces the difficulty of assembling the magnetic ring.

Further, the number of base plates is M+1, including an upper cover plate, a lower cover plate, and an intermediate substrate. Grooves are processed on the lower surface of the upper cover plate, the upper surface of the lower cover plate, and the upper and lower surfaces of the intermediate substrate. The sub-layer magnetic ring arrays are respectively embedded between the upper cover plate and the middle substrate, between two middle substrates, and between the middle base plate and the upper cover plate.

Further, the base plate material is selected from aluminum alloy or other non-magnetic materials.

Further, the cross-sectional shape of the magnetic blocks constituting the sub-magnetic ring array is trapezoidal, rectangular, circular, elliptical or regular polygonal.

Further, the magnetic block material of the sub-magnetic ring array is selected from neodymium iron boron, samarium cobalt permanent magnet materials or other permanent magnet materials.

Further, the magnetization direction rotates regularly with the position of the magnetic block, and the position deflection angle of the i-th magnetic block θ=i·2π/N corresponds to the magnetization deflection angle β of the magnetic block _i =2θ, i=0,1,..., N-1.

Further, the permanent magnet structure is composed of multiple layers of substrate plates embedded with magnetic blocks. The ratio of the inner and outer diameters of each sub-magnetic ring array is different. Finally, the entire magnet structure is fixed with copper screws and copper nuts.

Beneficial effects: the portable NMR detection permanent magnet with radially adjusted uniform field provided by the present invention, on the basis of traditional cylindrical magnets, adjusts the inner and outer diameters of the magnetic rings of each layer, and increases the compensation of the outer magnetic rings to the central magnetic field of the magnet , to homogenize the central magnetic field distribution, and effectively solve the end effect caused by the height reduction of traditional magnets. Moreover, this structure does not need to introduce an external magnetic field compensation device, the overall structure is simple, and the aluminum alloy substrate is used to position and fix the magnetic ring magnet, which greatly reduces the difficulty of assembling the magnet. Therefore, the present invention provides a permanent magnet that can generate a high-intensity and high-uniformity magnetic field in a small-volume structure, and is generally used in a portable and miniaturized nuclear magnetic resonance detection system.

Description of drawings

Figure 1 is a schematic diagram of the overall structure of the present invention.

FIG. 2 is a schematic diagram of the rotation of the magnetization direction of the single-layer magnetic ring structure of the present invention.

Fig. 3 is a partial schematic diagram of the single-layer magnetic ring structure of the present invention.

Fig. 4 is an axial sectional view of the present invention.

Fig. 5 is an exploded schematic diagram of the assembly of the single-layer magnetic ring structure of the present invention.

Fig. 6 is a contour diagram of the magnetic induction intensity B _z in the xz coordinate plane when the working air gap center y=0 according to the embodiment of the present invention.

7 is a contour diagram of the magnetic induction intensity B _z in the yz coordinate plane when the working air gap center x=0 according to the embodiment of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the invention provides a portable NMR detection permanent magnet for radially adjusting the uniform field. System screw rod (401) and nut (101). In this embodiment, the permanent magnet is formed by stacking M=11 layers of sub-magnetic ring arrays, and the ratio of the inner and outer diameters of each layer of sub-magnetic rings is optimized and adjusted. The sub-magnetic ring is composed of N=8 identical trapezoidal magnetic blocks (501,...,508) arranged in a circular array, embedded in the groove of the base plate (201,301...,310,601) and fixed with special glue, and then the base plate ( 201,301,...,310,601) are stacked layer by layer and then fixed with screw rods (401) and nuts (101).

As shown in Figure 2, it is a schematic diagram of the rotation of the magnetization direction of the single-layer magnetic ring structure of the present invention. N=8 trapezoidal magnetic blocks (501, ..., 508) are arranged in a circular array, and gaps are left between adjacent magnetic blocks. The magnetization direction of the magnetic block changes regularly with its position, and the specific law is shown in Figure 3. The permanent magnetic ring is evenly divided into N pieces of small magnetic blocks, which can theoretically generate a static magnetic field with a magnetic induction intensity of B ₀ in the central area.

${\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>$

in:

B _r : remanence of permanent magnetic material;

r _out : the outer diameter of the permanent magnet ring;

r _in : the inner diameter of the permanent magnet ring;

In the present invention, the effect of the end effect of the finite height magnet and the gap between adjacent magnetic blocks will also be considered, so after correction,

${\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&rsqb;</span>$

in:

f: correction factor considering actual factors;

Fig. 3 is a partial schematic view of the single-layer magnetic ring structure of the present invention, the position deflection angle θ=i·2π/N of the i (i=0,1,...,N-1) magnetic block, then the magnetization of the magnetic block Deflection angle β _i =2θ.

As shown in Figure 4, the present invention provides a sectional view of the axial direction of the permanent magnet. The radial adjustment of the inner and outer diameters of each layer of the permanent magnet is optimized and adjusted. The first, second and third layers (L1, L2, L3) and the ninth The inner and outer diameter ratio (r _out / r _in ) of the tenth and eleventh layers (L9, L10, L11) is larger than that of the middle layer (L4, L5, L6, L7, L8), increasing the central magnetic field strength and compensating the magnet at the same time end effect. Then radially fine-tune the position of the magnetic block of the middle layer magnetic ring to improve the uniformity of the magnetic field. The sub-magnetic rings of each layer are nested in the grooves of the aluminum base plate, and the distance between layers is d _m . As shown in FIG. 5 , it is a schematic diagram of an assembly explosion of a single-layer magnetic ring structure of the present invention.

The number of magnetic ring layers in this embodiment is M=11, the number of trapezoidal magnetic blocks in each sub-magnetic ring is N=8, the height is 7.2 mm, the layer spacing d _m =2 mm, the complete assembly size is φ150×100 mm, and the middle aperture It is φ60mm. As shown in Figures 6-7, they are the contour map of the magnetic induction intensity B _z in the xz coordinate plane and the contour map of the magnetic induction intensity B _z in the yz coordinate plane when the working air gap center y=0 of the embodiment of the present invention Line diagram, the unit of magnetic induction is mT. Calculate the magnetic induction intensity in the z direction in the 20mm×20mm area of the central air gap plane. It can be seen from the diagram that the magnetic field intensity can reach 447mT, and the unevenness can be controlled at the order of 10 ^-2 .

The above is only a preferred embodiment of the present invention, it should be pointed out that: the sub-magnetic ring layer number, layer height and layer spacing of the permanent magnet in the present invention can be adjusted according to the design requirements, and the number of magnetic blocks forming the sub-magnetic ring is also not affected. Limitation, the cross-sectional shape does not have to be restricted to a trapezoid, and the inner and outer diameters of each sub-magnetic ring are determined according to the design. Therefore, without departing from the principle of the present invention, appropriate improvements and modifications can be made, but all the improvements and modifications are included in the protection scope of the present invention.

Claims (8)

1. the portable nuclear magnetic resonance detection permanent-magnet radially adjusting uniform field, it is characterised in that: include radially adjusting Permanent-magnet and substrate plate, it is to be stacked structure by the sub-magnet ring array of M shell difference internal-and external diameter ratio that described radial direction adjusts permanent-magnet Become, described M > 2；Every straton magnet ring array is fixed on a base by correspondence after N block identical magnetic piece circumferentially array arrangement On base plate, N=2n, n > 2.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: between the composition magnetic piece of described sub-magnet ring array is adjacent, leave gap, it is possible to radially adjust magnet sizes and position, with Time isolation magnetic piece reduce magnet ring assembly difficulty.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: described substrate plate is M+1, including upper cover plate, lower cover and Intermediate substrate, table on upper cover plate lower surface, lower cover The upper and lower surface of face and Intermediate substrate is all machined with groove, M every straton magnet ring array be respectively embedded into upper cover plate and Intermediate substrate it Between, between two Intermediate substrates and between Intermediate substrate and upper cover plate.

A kind of radial direction the most according to claim 3 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: described base sheet material aluminium alloy material or other non-magnet_conductible materials.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: the composition magnetic piece shape of cross section of described sub-magnet ring array be trapezoidal, rectangle, circle, ellipse or rule many Limit shape.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: composition magnetic piece material selection neodymium iron boron, samarium-cobalt permanent-magnetic material or other permanent magnet material of described sub-magnet ring array Material.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: the direction of magnetization rotates with magnetic piece position rule, the location deflection angle θ=i 2 π/N of i-th magnetic piece, then corresponding magnetic piece Magnetization deflection angle beta_i=2 θ, i=0,1 ..., N-1.

A kind of radial direction the most according to claim 1 adjusts the portable nuclear magnetic resonance detection permanent-magnet of uniform field, and it is special Levy and be: described permanent-magnet structure is had been inserted into the substrate plate stacking of magnetic piece and constitutes by multilamellar, every straton magnet ring array inside and outside Footpath ratio is different, finally coordinates copper screw rod and copper nut to fix whole magnet structure.