RU2808801C1 - Magnet - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: magnet consists of many individual magnets and includes arrays of fibre-reinforced insulating material. Each grid cell defines a socket large enough to accommodate a separate magnet. The magnet is assembled from two ferrite plates and several disk-layer frames assembled from magnetic elements arranged in accordance with the Halbach magnetic assembly principle. Each magnetic layer is assembled from three rings. Between the layers there are buffer layers of dielectric material. Each ring consists of an even number of cells in which magnetic elements based on NdFeB alloy are located.

EFFECT: simple design that can be easily adjusted to the desired parameters of the magnetic field, small dimensions and weight, while ensuring high uniformity of the magnetic field in the cylindrical gap along the magnet axis.

3 cl, 2 dwg

Description

The magnetic system is the main part of NMR relaxometers, which determines their dimensions and weight. To create small-sized relaxometers, small magnetic systems with sufficiently high values of intensity and uniformity of the magnetic field in the “working” region of space (in the area where the object under study is located) are required.

A small-sized magnetic system for an NMR spectrometer based on magnets made of an Nd-Fe-B alloy is known according to the article [1] Vasiliev P.A., Saikin K.S. Instruments and experimental techniques, 1993, No. 3, p. 211-214. The main design elements of the system are a yoke and liners made of soft magnetic steel, forming a closed magnetic circuit and located parallel to each other to form an air gap, magnetic plates (permanent magnets) made of Nd-Fe-B alloy with pole tips. Field shift coils are located on the outside of the magnetic circuit, and correction coils are located inside the system. The required field uniformity is achieved by passing current through them and using ring shims.

The disadvantage of this system is the relatively small area of field uniformity and the need to maintain it by passing a stable current through the correction coils, which makes it energy-dependent, and the technological difficulties of manufacturing, associated primarily with the difficulty of selecting a pair of identical magnetic plates based on the magnitude of the residual induction and the nature distribution of residual magnetization in the body of the plate.

The invention is known - Magnetic system according to RF patent [2] No. 2620579 C2, IPC H01F 7/02 (2006.01), G01R 33/38 (2006.01), N05N 1/16 (2006.01), authors N.V. Kudrevatykh, A. Maslov. N., Volegov A.S., Kozlov A.I. Application: 2015143578, 10/12/2015, (24). Start date of the patent term: 10/12/2015, (45). Published: 05/29/2017, Bulletin. No. 16. Patent holder(s): Federal State Educational Institution of Higher Education "Ural Federal University named after the first President of Russia B.N. Yeltsin", JSC "Research and Production Association of Automation named after Academician N.A. Semikhatov".

The objective of the above invention is to increase the efficiency of using the magnetic potential of the plate elements and increase the uniformity of the magnetic field in the working space without changing the dimensions and weight of the magnetic system itself while maintaining its energy independence.

This is achieved due to the fact that in a magnetic system containing enclosed in a closed magnetic circuit made of soft magnetic material, two magnetic plates installed parallel to each other are made of stacked individual magnets rigidly connected to each other, one side of which is equipped with pole pieces made of soft magnetic material and faces each other. each other with the formation of an air gap, and the opposite sides of the plates are connected to the magnetic circuit, the stacked individual magnets of the plates are divided into three concentric zones: central, the area of which is 10-20% of the total area of the plate, the peripheral area is 50-60% of the total area of the plate and the intermediate , equal in area to the difference between the total area of the plate and the areas of the central and peripheral zones, magnets identical in magnitude of the magnetic moment are installed in the central zone with the orientation of the residual magnetization vector of the magnets perpendicular to the plane of the plate, and the modulus of their residual magnetization vector is 0.6 relative to the magnitude of the residual magnetization vector modulus of peripheral magnets with a similar orientation of the residual magnetization vector; magnets are installed in the intermediate zone with a magnitude of the residual magnetization vector modulus of the magnets equal to the magnitude of the residual magnetization vector modulus of the peripheral magnets, with its orientation towards the center of the plate at an angle in the range 50÷60° relative to the normal to the plane of the plate. To make the design compact, the magnetic circuit is made in the form of two supporting square plates made of soft magnetic material, rigidly connected by four posts, forming a rigid frame, and the supporting square plates are located parallel to the magnetic plates, also made in the shape of a square, turned at an angle of 45° relative to them and rigidly connected with them. To correct the magnitude and degree of uniformity of the magnetic field, spacers made of soft magnetic material are placed between the posts and one of the supporting plates.

The disadvantage of the invention is the low uniformity of the magnetic field due to the difficult compatibility of the magnetic elements during gluing and the large weight and dimensions due to the use of a continuous closed magnetic circuit made of soft magnetic material.

The closest in terms of the achieved result, aimed at further reducing the dimensions and mass of the magnetic system and increasing the uniformity of its field, is the invention under RF patent [3] No. 2759 599 C2 MPK H02K 1/27 (2006.01) H01F 7/02 (2006.01) Magnetic structure with by a plurality of individual magnets inserted into a lattice structure by the authors MICHAILA, Vasile (FR), MEYER, Loic (FR), TIENYA, Huguette (FR), RAVAULT, Romain (FR), Application: 2019132966, 03/20/2018. Start date of the patent term: 03/20/2018. Registration date: 11/16/2021. Convention priority: 03/22/2017 FR 1700295; 09/11/2017 FR 1700915. Application publication date: 04/22/2021. Bull. No. 12, (45). Published: 11/16/2021. Bull. No. 32. Patentee(s): WHILOT SAS (FR).

The three-dimensional magnetic structure consists of many individual magnets. The magnetic structure has a thickness that forms its smallest size. The magnetic structure includes at least one grid, each of the cells of which defines a slot for a corresponding individual magnet. The cells are made of fiber-reinforced insulating material. A space is left between the socket and the individual magnet and is filled with fiber-reinforced resin. The magnetic structure contains a layer of non-conductive composite covering the individual magnets and lattice structure. The invention finds its preferred, but not limited, application for an electromagnetic drive producing greater power at increased rotor speed, which is achieved through the use of one or more magnetic structures in accordance with the present invention.

This invention is taken as a prototype of the proposed invention.

The technical problem of the proposed invention is to create a simple design that can be easily adjusted to the desired parameters of the magnetic field, small dimensions and weight, but at the same time ensure high uniformity of the magnetic field in the cylindrical gap along the magnet axis. To overcome the phenomenon of magnetic field loss without using a bulky and heavy closed magnetic circuit, the Halbach magnetic circuit is selected [4]. With this structure, the magnetic field is concentrated in the gap, and the amount of loss outside the magnet is insignificant.

This invention is illustrated in Fig. 1, which shows the structure of the magnet layer, consisting of square magnetic elements arranged in accordance with the Halbach principle.

The numbers indicate:

1 - hole with a diameter of 6.6 mm for connecting and fixing layers;

2 - magnetic elements;

3 - ferrite plate (soft iron);

4 - buffer layer;

5 - magnetic frame;

6 - holes for positioning layers.

In FIG. Figure 2 shows the complete structure of a magnet consisting of 9 magnetic and 10 intermediate layers.

The numbers indicate:

1 - hole with a diameter of 6.6 mm for connecting and fixing layers;

2 - magnetic elements;

3 - ferrite plate (soft iron);

4 - buffer layer.

Each magnetic layer has 3 magnetic rings, each ring consisting of 16 elements arranged according to the Halbach principle. Magnetic elements 2 are NdFeB type magnets with dimensions 10×10×10 mm. These elements are installed in holes of the same size in magnetic frames 5, made of acrylic glass by laser cutting. 9 layers are stacked on top of each other, and between the layers a buffer layer 4 is added (see Fig. 2) with a thickness of 3 mm, made of the same acrylic material and in the same way as the magnet frame, only without square holes for installing magnetic elements. These buffer layers perform the function of optimizing the magnetic field strength. In addition, 8 holes 1 with a diameter of 6.6 mm are designed on these frames to connect and fix the magnetic and buffer layers together. 2 other holes 6 of the same diameter are used to position the layers during assembly. In the cylindrical gap in the center of the frames there are 2 grooves measuring 35x4 mm, designed to install two ferrite 3 plates with high permeability (μ = 10000-15000) measuring 120x35x4 mm (or soft iron plates) to increase the uniformity of the magnetic fields in the gap. In addition, 2 buffer layers 4 are located on the top and bottom.

The total weight of the magnet per sample diameter ∅35 mm is 4.3 kg, which is 4 times less than the weight of a magnet with a solid magnetic core made of soft iron (electrical steel). The magnet size is 120×140×140 mm. Measurements of the magnetic field in the cylindrical gap of the magnet showed the field induction value B _o =0.3068 T with an axial inhomogeneity of 1.6⋅10 ^-4 .

Literature Cited

1. Vasiliev P.A., Saikin K.S. Instruments and experimental techniques, 1993, No. 3, p. 211-214.

2. RF Patent No. 2620579 C2 Magnetic system Kudrevatykh N.V., Maslov A.N., Volegov A.S., Kozlov A.I. dated 10/12/2015.

3. RF Patent No. 2759599 C2 Magnetic structure with a plurality of individual magnets inserted into a lattice structure MIHAILA, Vasile (FR), MEYER, Loic (FR), TIENA, Huguette (FR), RAVO, Romain (FR), Application: from 20.03 .2018.

4. Mitchell J., Gladden L.F., Chandrasekera T.C., Fordham E.J. Low-field permanent magnets for industrial process and quality control // Progress in Nuclear Magnetic Resonance Spectroscopy, 76 (2014) 1-60 www.elsevier.com/locate/pnmrs

Claims (3)

1. A magnet consisting of a plurality of individual magnets and including a grid of fiber-reinforced insulating material, each of the cells of which defines a socket sufficient for the introduction of a separate magnet, characterized in that it is assembled from two ferrite plates and several disk-layer frames assembled of magnetic elements arranged in accordance with the Halbach magnetic assembly principle, each magnetic layer is assembled from three rings, between the layers there are buffer layers of dielectric material, and each ring consists of an even number of cells in which magnetic elements based on an NdFeB alloy are located. 2. The magnet according to claim 1, in which the frame used for installing the magnetic elements is made of a dielectric material, for example, acrylic glass. 3. A magnet according to claim 1, which has buffer layers, for example, made of acrylic glass.