CN110706877A - Low-cost miniature Halbach magnet with adjustable magnetic field uniformity - Google Patents
Low-cost miniature Halbach magnet with adjustable magnetic field uniformity Download PDFInfo
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- CN110706877A CN110706877A CN201910897980.2A CN201910897980A CN110706877A CN 110706877 A CN110706877 A CN 110706877A CN 201910897980 A CN201910897980 A CN 201910897980A CN 110706877 A CN110706877 A CN 110706877A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/02—Permanent magnets [PM]
- H01F7/0205—Magnetic circuits with PM in general
- H01F7/021—Construction of PM
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/02—Permanent magnets [PM]
- H01F7/0205—Magnetic circuits with PM in general
- H01F7/0221—Mounting means for PM, supporting, coating, encapsulating PM
Abstract
The invention discloses a low-cost miniature Halbach magnet with adjustable magnetic field uniformity, which comprises a main magnet, a shimming structure and a magnet structure supporting piece, wherein the main magnet comprises 8 magnets with trapezoidal sections and 8 samarium-cobalt magnets with rectangular sections, and the magnets in the two shapes are closely arranged at intervals to form a circular ring; the shimming structure is divided into end shimming and center shimming according to different functions; the magnet structure support is used for general assembly of a magnet and comprises an upper sealing cover, a lower sealing cover, a guide opening and a shell; the invention can realize the magnetic field intensity of 1T, and the total mass of the magnet is lower than 3kg, thereby being beneficial to the portable development of the low-field nuclear magnetic resonance spectrometer and meeting the requirement of immediate detection of scientific researchers.
Description
Technical Field
The invention relates to a low-cost miniature Halbach magnet with adjustable magnetic field uniformity, belonging to the field of permanent magnet design, processing, assembly and the like.
Background
As low-field nmr techniques mature, more and more fields begin to use low-field nmr instruments. Unlike high-field nuclear magnetic resonance which uses a superconducting magnet with large volume and high price, low-field nuclear magnetic resonance mainly uses a rare earth permanent magnet with relatively low cost, although the magnetic field performance of the permanent magnet is weaker than that of the superconducting magnet, the magnetic field performance of the permanent magnet is greatly improved along with the application of novel materials and the improvement of processing technology, and the use of a low-field nuclear magnetic resonance instrument can be completely met.
At present, the type of permanent magnet used by the low-field nuclear magnetic resonance instrument is mainly a bipolar plate type magnet, the bipolar plate type permanent magnet has good processing performance, but because an additional soft magnetic material is needed to guide a magnetic field and support and fix, the mass of the permanent magnet cannot meet the requirement of portability, and the permanent magnet can only be used for a desk-top nuclear magnetic resonance instrument with heavier mass. With the maturity of the structure of the Halbach magnet, the magnet with the maximum field intensity-mass ratio can realize the magnetic field intensity and the magnetic field uniformity which are far larger than those of a bipolar plate type magnet under the condition of small volume and mass due to the fact that the magnet can realize the effect of magnetic concentration on one side of the magnet array, and is becoming a research object of numerous scholars. While Halbach magnets have excellent magnetic field properties, their complexity of construction and the requirement for machining accuracy limit their use. The current processing technology can only lead the magnetic field uniformity of the Halbach magnet to reach
Order of magnitude, but for a magnet to be used in a low-field NMR spectrometer, the magnetic field homogeneity needs to be achieved
Magnitude. Therefore, in order to promote the application of the Halbach magnet and the development of the portable low-field nuclear magnetic resonance instrument, the research on the miniature Halbach magnet with adjustable magnetic field uniformity and low cost has very important research significance and economic significance.
The portable nuclear magnetic resonance instrument is the development direction of low-field nuclear magnetic resonance, and has good application prospects in the aspects of environmental monitoring, biological detection, organic chemistry and medicine and pharmacology. However, the conventional table-type low-field nuclear magnetic resonance apparatus has a heavy mass, so that the apparatus can only be used in a fixed laboratory, and cannot meet the requirement of immediate detection of scientific researchers. Therefore, in order to improve the portability of the low-field nuclear magnetic resonance instrument and overcome the limitation of the current processing, a low-cost miniature Halbach magnet with adjustable magnetic field uniformity is needed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a low-cost miniature Halbach magnet with adjustable magnetic field uniformity aiming at the defects of the prior art.
In order to solve the technical problems, the invention adopts the technical scheme that:
a low-cost miniature Halbach magnet with adjustable magnetic field uniformity comprises an upper sealing cover, a lower sealing cover, a shell, a main magnet and a central shimming field, wherein the shell is of a hollow cylindrical structure, two ends of the shell are provided with openings, the main magnet is positioned in the shell, the central shimming field is positioned in the main magnet, and the upper sealing cover and the lower sealing cover are respectively arranged at two ends of the shell; the main magnet is a hollow columnar structure and comprises a plurality of first magnets with trapezoidal cross sections, the upper bottoms of the first magnets are opposite and annular, a second magnet is arranged between every two adjacent first magnets, and the second magnet is a longitudinally-arranged long-strip structure; the magnetic strip grooves are positioned on the upper radius position of the upper sealing cover or the lower sealing cover, magnetic strips are arranged in the magnetic strip grooves, and a gap is formed between the magnetic strips and the main magnet; the central shimming is of a tubular structure, a plurality of blind holes are distributed on the inner wall of the central shimming, and magnetic sheets are arranged in the blind holes.
As a further preferred scheme, 16 magnetic stripe grooves are respectively arranged on the upper sealing cover and the lower sealing cover, and a circle of magnetic stripe grooves are arranged at equal intervals.
As a further preferred scheme, 10 magnetic stripes are arranged in the magnetic stripe grooves, every 5 magnetic stripes are continuously arranged to form a fan-shaped structure, and the two fan-shaped structures are oppositely arranged.
As a further preferred scheme, an upper fixing cover is arranged on the inner side of the upper sealing cover and covers the magnetic strip, and a lower fixing cover is arranged on the inner side of the lower sealing cover and covers the magnetic strip.
As a further preferred solution, the main magnets comprise eight first magnets and eight second magnets.
Preferably, the magnetization direction of the magnetic stripe is the same as the magnetization direction of the corresponding main magnet end.
Compared with the prior art, the invention has the following beneficial effects: the magnetic field strength is high under the small volume and low mass, the influence of processing and positioning errors on the uniformity of the magnetic field is fully considered, and a structure for adjusting the uniformity of the magnetic field is added, so that the influence on the use of the magnet and the detection precision of a final instrument due to the fact that the actual performance of the magnet is greatly different from the theoretical performance is avoided. The Halbach magnet is favorable for promoting the use of the Halbach magnet in the low-field portable nuclear magnetic resonance instrument, thereby promoting the miniaturization and the portability of the nuclear magnetic resonance instrument on the basis of unchanged actual performance, and being favorable for improving the detection convenience of scientific research workers.
Drawings
FIG. 1 is a schematic view of the internal structure of the present invention;
FIG. 2 is an exploded view of the internal structure of the present invention;
FIG. 3 is a schematic view of the magnetization direction of the main magnet;
FIG. 4 is an exploded view of the upper seal cap structure; FIG. 5 is a schematic view of the housing construction;
FIG. 6 is a schematic diagram of a central shim structure;
FIG. 7 is a graph of magnetic field performance for different main magnet heights of the present invention;
FIG. 8 is a schematic illustration of the effect of a magnetic stripe on the performance of a main magnetic field;
FIG. 9 is an external schematic view of the present invention;
the magnetic field generator comprises a shell, an upper sealing cover, a lower sealing cover, a shell, a main magnet, a first magnet, a second magnet, a central shimming magnet, a magnetic strip groove, a magnetic strip, a magnetic sheet, an upper fixing cover and a lower fixing cover, wherein the upper sealing cover is 1-2-3-the shell, the main magnet is 4-41-the first magnet, the second magnet is 42-the central shimming magnet, the magnetic strip groove is 6-the magnetic strip groove.
Detailed Description
The preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
A low-cost miniature Halbach magnet with adjustable magnetic field uniformity comprises a main magnet 4, a central shimming 5, an end shimming (magnetic strip 7), an upper sealing cover 1, a lower sealing cover 2 and a shell 3 of a magnet structure supporting piece.
The main magnet 4, i.e. the main source of the static magnetic field, is one of the important parameters for measuring the detection performance of the low-field nuclear magnetic resonance instrument, and comprises 8 magnets (the first magnet 41) with trapezoidal cross sections and 8 samarium cobalt magnets (the second magnet 42) with plate shapes, wherein the magnets with the two shapes are closely arranged at intervals to form a circular ring, as shown in fig. 3, and the magnetic field generated by the main magnet is positioned in the circular ring.
The shimming structure is a novel structure provided according to the processing and manufacturing errors and the assembly errors of the magnet, can be used for making up the loss of the magnetic field uniformity caused by the errors, and is divided into end shimming and central shimming 5 according to different shimming functions.
The end shimming aims at the problem that the central magnetic field of the Halbach magnet is uneven mainly due to the fact that the magnetic field intensity of the end part is reduced suddenly caused by the fact that two ends of the main magnet 4 are cut off, theoretically, if the magnetic field intensity of the end part of the Halbach magnet is equal to the magnetic field intensity of the central part, the uniformity of the magnetic field is greatly improved, but the magnetic field is limited by the types of magnetic materials, the neodymium iron boron material with the largest remanence is used at present, therefore, in order to form a stronger end magnetic field, the end shimming adopts a magnetic strip device which comprises 20 magnetic strips 7 with rectangular sections, the material of the magnetic strips is neodymium iron boron magnetic strips, the magnetic strips 7 are symmetrically distributed at two ends of the main magnet 4 and are arranged at the ends to form symmetrical fan-shaped, the effect is shown in fig. 8, as can be seen from the simulation result of fig. 8, the solid line is the end shimming magnetic strip 7, the dotted line is the end shimming magnetic strip 7, the effect of the shimming magnetic strips at the visible end part on improving the magnetic field at the end part is obvious, so that the uniformity of the magnetic field at the center of the magnet is improved.
The central shimming 4 is directly distributed around a target region by using a permanent magnet material array to change the magnetic field distribution of a local region and comprises a fixed structure and magnetic sheets 8.
The structural support comprises an upper sealing cover 1, a lower sealing cover 2 and a housing 3. The upper sealing cover 1 and the lower sealing cover 2 are respectively composed of the same aluminum alloy metal components.
The shell 3 has screw thread with size M3 on the wall for fixing the main magnet 4 and connecting with the upper sealing cover 1 and the lower sealing cover 2.
The main magnet 4 is made of SmCo32 material, the samarium cobalt material has excellent temperature coefficient, the magnetic field property has small change in the temperature fluctuation process, the remanence strength of the material can reach 1.11T, the height of the main magnet 4 is an important parameter in a Halbach magnet, the value directly influences the magnetic field property of a basic magnet, and the magnetic field properties corresponding to different magnet height sizes are different.
The height of the main magnet 4 is provided with 8 groups of parameters which are 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm and 140mm, the magnetic field intensity and uniformity of a target area are simulated, and the center of the magnet is selected
The region is a target region. The three curves in fig. 7 can be classified according to the line type, wherein the dotted line represents the magnitude of the central magnetic field strength value corresponding to different magnet heights, the thin solid line represents the magnitude of the central magnetic field uniformity value corresponding to different magnet heights, and the thick solid line represents the result of the first-order difference of the magnetic field uniformity values of different heights. According to simulation results, the magnetic field strength of the center of the Halbach magnet is enhanced along with the increase of the height of the magnet, the magnetic field uniformity value of a target area is firstly rapidly reduced along with the increase of the height of the magnet and then slowly reduced, a first-order difference result shows that the effect of improving the magnetic field uniformity is not obvious when the height of the magnet is 120mm, and the height of the Halbach magnet is set to be 120mm in consideration of the fact that the manufacturing cost of the magnet is obviously improved along with the increase of the height.
The magnetic strips 7 are arranged at the upper end and the lower end of the main magnet 4, and as can be seen from the above, the magnetic strips 7 have the function of improving the uniformity of the magnetic field, in order to maximize the effect, the magnetic strips 7 are made of N52 material, N52 is a material which can achieve the maximum residual magnetic strength of the prior neodymium iron boron material, and is an ideal end magnetic strip material.
According to the Halbach magnet strength calculation formula, the ratio of the magnet central magnetic field strength to the inner diameter and the outer diameter of the magnet is related, so that on the basis of the same outer diameter, the inner diameter of a sector formed by the magnetic strips 7 at the end part is smaller than the inner diameter of the main magnet 4, a higher magnetic field can be generated, and each sector is composed of 5 shimming magnetic strips.
The end magnetic strips 7 are used as a part of a magnetic field source, the magnetization direction of each magnetic strip 7 forming the sector shape must be the same as the magnetization direction of the SmCo32 main magnet 4 at the corresponding position, and the generated magnetic field can have a superposition effect with the magnetic field of the main magnet.
The fixed structure in the central shimming 5 is provided with blind holes which are uniformly distributed and have the same size and are used for installing the fixed magnetic sheets 8, and the number of the magnetic sheets 8 can be combined for use according to the requirement.
Since the magnetic sheet 8 for center shimming has a small distance from the target region, if the remanence and the coercive force are too large, the adjustment of the magnetic field distribution is also very large, and it is difficult to meet the demand, and therefore, the magnetic sheet 8 uses the SmCo18 material, and the coercive force and the remanence can be conveniently used for fine adjustment of the magnetic field.
The magnet structure can generate a magnetic field with the magnetic field intensity of up to 1T in the center of the magnet, and the overall size of the magnet is ∅ 64 multiplied by 132mm3The outer shape is shown in fig. 9.
A low-cost miniature Halbach magnet with adjustable magnetic field uniformity comprises the following installation steps:
and 5, fixing the main magnet 4 together with the upper sealing cover 1, the lower sealing cover 2, the guide opening and the shell through bolts.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the embodiments, and various equivalent modifications can be made within the technical spirit of the present invention, and the scope of the present invention is also within the scope of the present invention.
Claims (6)
1. The utility model provides a low-cost, miniature Halbach magnet of magnetic field degree of consistency adjustable which characterized in that: the magnetic field generator comprises an upper sealing cover (1), a lower sealing cover (2), a shell (3), a main magnet (4) and a central shimming field (5), wherein the shell (3) is of a hollow cylindrical structure, two ends of the shell are provided with openings, the main magnet (4) is positioned in the shell (3), the central shimming field (5) is positioned in the main magnet (4), and the upper sealing cover (1) and the lower sealing cover (2) are respectively arranged at two ends of the shell (3); the main magnet (4) is of a hollow columnar structure, the main magnet (4) comprises a plurality of first magnets (41) with trapezoidal cross sections, the upper bottoms of the first magnets (41) are opposite and annular, a second magnet (42) is arranged between every two adjacent first magnets (41), and the second magnets (42) are of a longitudinally-arranged long strip structure; one surfaces, facing the main magnet (4), of the upper sealing cover (1) and the lower sealing cover (2) are respectively provided with a circle of magnetic strip groove (6), the magnetic strip grooves (6) are located at the positions of the upper radius of the upper sealing cover (1) or the lower sealing cover (2), a magnetic strip (7) is installed in the magnetic strip grooves (6), and a gap is formed between the magnetic strip (7) and the main magnet (4); the central shimming (5) is of a tubular structure, a plurality of blind holes are distributed on the inner wall of the central shimming (5), and magnetic sheets (8) are arranged in the blind holes.
2. The low-cost miniature Halbach magnet of claim 1 having adjustable magnetic field uniformity, wherein: the upper sealing cover (1) and the lower sealing cover (2) are respectively provided with 16 magnetic stripe grooves (6), and a circle of magnetic stripe grooves (6) are arranged at equal intervals.
3. A low cost, miniature Halbach magnet of adjustable magnetic field homogeneity according to claim 2, characterized in that: 10 magnetic stripes (7) are arranged in the magnetic stripe grooves (6), every 5 magnetic stripes are continuously placed to form fan-shaped structures, and the two fan-shaped structures are placed oppositely.
4. The low-cost miniature Halbach magnet of claim 1 having adjustable magnetic field uniformity, wherein: the inner side of the upper sealing cover (1) is provided with an upper fixing cover (9), the upper fixing cover (9) covers the magnetic strip (7), the inner side of the lower sealing cover (2) is provided with a lower fixing cover (10), and the lower fixing cover (10) covers the magnetic strip (7).
5. The low-cost miniature Halbach magnet of claim 1 having adjustable magnetic field uniformity, wherein: the main magnet (4) comprises eight first magnets (41) and eight second magnets (42).
6. The low-cost miniature Halbach magnet of claim 1 having adjustable magnetic field uniformity, wherein: the magnetization direction of the magnetic strip (7) is the same as that of the end part of the main magnet (4) corresponding to the magnetic strip.
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| CN201910897980.2A CN110706877A (en) | 2019-09-23 | 2019-09-23 | Low-cost miniature Halbach magnet with adjustable magnetic field uniformity |
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| CN201910897980.2A CN110706877A (en) | 2019-09-23 | 2019-09-23 | Low-cost miniature Halbach magnet with adjustable magnetic field uniformity |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112068055A (en) * | 2020-08-27 | 2020-12-11 | 东南大学 | Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human finger |
| CN112211500A (en) * | 2020-09-22 | 2021-01-12 | 兰州万里航空机电有限责任公司 | Aviation bidirectional self-holding electromagnetic lock with magnetic conductive column |
| CN114200366A (en) * | 2021-12-16 | 2022-03-18 | 武汉联影生命科学仪器有限公司 | Shimming device, magnetic field assembly, magnetic resonance imaging system and shimming method |
| CN116256680A (en) * | 2023-05-16 | 2023-06-13 | 中国科学院精密测量科学与技术创新研究院 | Passive shimming structure and method of Halbach magnet for magnetic resonance |
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| JP2005101437A (en) * | 2003-09-26 | 2005-04-14 | Neomax Co Ltd | In-magnetic-field extrusion molding apparatus and manufacturing method of magnet |
| EP2144076A1 (en) * | 2008-07-07 | 2010-01-13 | RWTH Aachen | Segmented ring magnet arrangement for providing a magnetic field |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112068055A (en) * | 2020-08-27 | 2020-12-11 | 东南大学 | Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human finger |
| CN112211500A (en) * | 2020-09-22 | 2021-01-12 | 兰州万里航空机电有限责任公司 | Aviation bidirectional self-holding electromagnetic lock with magnetic conductive column |
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| CN116256680A (en) * | 2023-05-16 | 2023-06-13 | 中国科学院精密测量科学与技术创新研究院 | Passive shimming structure and method of Halbach magnet for magnetic resonance |
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