Magnet structure with internal pores and design method

Abstract

The invention belongs to the technical field of nuclear magnetic resonance, and provides a magnet structure with internal pores and a design method, and the magnet structure comprises a hard magnetic material magnet, a pore array located in the hard magnetic material magnet, and a pore array optimization method. A certain magnetic conduction channel is formed in the magnet by adjusting the shape and the position of the hole in the magnet and the inclination angle of the hole relative to the axial direction of the magnet, so that the surface of the magnetic pole presents specific magnetic flux density distribution, and the peripheral magnetic field intensity, the magnetic field uniformity and the magnetic field gradient of the magnet are optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear magnetic resonance magnet systems, and in particular relates to a magnet structure with internal pores and a design method thereof. Background Art

[0002] The magnet system is the core part of magnetic resonance imaging (MRI) technology. It provides the basis for the generation and detection of nuclear magnetic resonance signals by generating a strong and stable magnetic field. The performance of the magnet system directly affects the resolution, sensitivity and imaging quality of the nuclear magnetic resonance equipment. The design of the magnet system needs to meet the following requirements: nuclear magnetic resonance usually requires a magnetic field with a gradient (that is, the magnetic field strength varies with the spatial position) to achieve lateral resolution and depth detection capabilities; within the detection area, the magnetic field needs to have a certain uniformity to ensure the stability and accuracy of the nuclear magnetic resonance signal; the magnetic field strength determines the nuclear magnetic resonance frequency (Larmor frequency), which affects the signal strength and measurement sensitivity; the magnet design needs to take into account the detection depth and resolution to ensure that the target formation range can be covered.

[0003] Hard magnetic material is a commonly used magnet material, for example, permanent magnets made of rare earth materials (such as neodymium iron boron and samarium cobalt). Its characteristics are low magnetic field strength (usually below 0.2T); no power supply or cooling system is required, and the operating cost is low; the magnet is large in size and heavy in weight. Common application areas include: miniaturized or portable NMR equipment; industrial testing (such as food, petroleum, material analysis); open MRI equipment (nuclear magnetic resonance logging equipment). The advantages of hard magnetic material magnets are: low cost, simple maintenance; suitable for portable and field applications. The disadvantages are also obvious: low magnetic field strength, limited sensitivity and resolution; poor magnetic field uniformity.

[0004] In the existing magnet design using hard magnetic materials, the main focus is on magnet arrangement technology. The main magnet, small magnet and pre-polarized magnet are arranged in a reasonable space to achieve a specific magnetic field distribution. The core of magnet arrangement technology is to control the distribution characteristics of the magnetic field by adjusting the spatial position, direction and polarity of the magnet. The main defects of this magnet design are: due to the limitations of magnet volume and weight, the existing magnet structure may not be able to provide a sufficiently high magnetic field strength; the existing magnet structure may not be able to provide a stable and controllable magnetic field gradient, reducing the measurement resolution. These defects limit the performance and applicability of nuclear magnetic resonance equipment. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a magnet structure with internal pores and a design method to solve the problems in the prior art. The technical solution adopted by the present invention is:

[0006] A magnet structure with internal pores comprises a hard magnetic material magnet and a pore array located inside the hard magnetic material magnet.

[0007] Furthermore, the hard magnetic material magnet has a fixed long cylindrical design to maximize the overall magnetic energy product within the space limit of the nuclear magnetic resonance device.

[0008] Furthermore, the aperture array is symmetrically distributed about the axial direction of the hard magnetic material magnet.

[0009] Furthermore, the number of pores in the pore array is m.

[0010] Furthermore, the pores in the pore array are long spindle-shaped, and their axial length is L i m, the radius of curvature is r i Meters, the angle between the hard magnetic material and the axial direction is θ i Spend.

[0011] Furthermore, the aperture array can be designed separately on the main magnet, the small magnet or the prepolarization magnet of the NMR magnet system.

[0012] A method for designing a magnet structure with internal pores comprises the following steps:

[0013] Step 1: Clarify the design requirements, maintain the magnetic field distribution requirements of the specific detection area, the magnetic field strength is B, and the magnetic field gradient modulus is less than the given value

[0014] Step 2: Define and initialize the optimization design variables, including the shape parameters of the pore array, the inclination parameters of the pore array, and the distance parameters between the pore array and the magnetic pole surface; and set the allowable error;

[0015] Step 3: Calculate the magnetic field intensity and magnetic field gradient model in a specific detection area based on the pore array shape parameters, pore array inclination parameters, and the distance parameters between the pore array and the magnetic pole surface of the magnetic material.

[0016] Step 4: Determine whether the allowable error is met. If so, end the optimization; if not, adjust the pore array shape parameters, pore array inclination parameters, and pore array distance parameters from the magnetic pole surface, and proceed to step 3.

[0017] The present invention has the following beneficial effects:

[0018] (1) The magnet structure design with internal pores provided by the present invention forms a certain magnetic conductive structure inside the magnet by adjusting the shape of the internal pores, the position from the magnetic pole surface and the inclination angle relative to the axial direction of the magnet, so that the magnetic pole surface has a specific distribution of magnetic flux density, thereby achieving a magnetic field distribution around the magnet that meets the requirements; the present invention achieves the adjustment of the magnetic field distribution around the magnet by optimizing the internal pore structure, which is significantly different from the prior art;

[0019] (2) The magnet structure design with internal pores provided by the present invention has a simple magnet structure and is easy to assemble into the nuclear magnetic resonance equipment with the largest volume, maximizing the overall magnetic energy while meeting the assembly conditions;

[0020] (3) The magnet structure design with internal pores provided by the present invention can design different numbers of pores and a combination array structure as needed, so as to maximize the resolution, detection depth or multi-frequency detection while maintaining a certain overall magnetic energy product.

[0021] (4) The magnet structure design with internal pores provided by the present invention can be designed separately on the main magnet, small magnet or prepolarization magnet of the nuclear magnetic resonance magnet system, and the magnet design gap array can be selected according to needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a cross-sectional view of a hard magnetic material magnet along the axial direction;

[0023] Figure 2 A cross-sectional view of a magnet made of hard magnetic material along a radial direction and passing through an array of apertures;

[0024] Figure 3 The radial distribution law of magnetic flux density modulus, the starting point of the observation line segment is located on the radial section circle passing through the center of the magnet, and starts from the surface of the magnet;

[0025] Among them, 1. hard magnetic material magnet; 2. pore array; 3. S pole; 4. N pole DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention Figure 1-Figure 3 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0027] Reference Figure 1-3 A magnet structure with internal pores includes: a hard magnetic material magnet 1, a pore array 2 located inside the hard magnetic material magnet 1, an S pole 3 of the hard magnetic material magnet and an N pole 4 of the hard magnetic material magnet.

[0028] Furthermore, the pore array 2 located inside the hard magnetic material magnet 1 is a closed pore.

[0029] Preferably, the hard magnetic material magnet 1 is in the shape of an elongated cylinder, with a length of 300 mm and a radius of the upper and lower circular bottom surfaces of 60 mm.

[0030] Preferably, the hard magnetic material magnet 1 is made of neodymium iron boron NdFeB material.

[0031] Preferably, the upper bottom surface of the hard magnetic material magnet 1 is an S pole 3 and the lower bottom surface is an N pole 4 .

[0032] Preferably, in the pore array, the number of pores is m=2. Figure 2 It can be seen that the pore array consists of two annular pores, and the radial cross-section of each pore is a long shuttle shape. Figure 2 In the figure, the pore in the upper half is the first pore in the pore array, and the pore in the lower half is the second pore in the pore array.

[0033] Preferably, the pores in the pore array 2 are long spindle-shaped annular pores. (The pores here are annular, which can be understood as a spindle rotating around an axis to form a pore array)

[0034] Preferably, the pore arrays 2 are distributed in a centrally symmetrical manner with respect to the axial direction of the magnetic material magnet 1 .

[0035] Preferably, the pore array 2, viewed from an axial cross section, has a long shuttle-shaped axis length of L meters and a curvature radius of 10 mm.

[0036] Furthermore, from the radial cross section, Figure 3 , in this viewing angle, the aperture array 2 is a circular ring, and the inner and outer radii of the ring are 20 mm and 25 mm respectively.

[0037] Preferably, the angle between the axis of the first pore in the pore array 2 and the axial direction of the magnet is θ degrees, and the angle between the axis of the second pore and the axial direction of the magnet is 180-θ degrees.

[0038] Preferably, the first pore of the pore array 2 is 6 mm away from the S-level magnet 3 , and the second pore is 6 mm away from the N-level magnet 4 .

[0039] A method for designing a magnet structure with internal pores, comprising the following steps:

[0040] Step 1: Clarify the design requirements: In the space area d = 50 mm away from the center of the magnet side, the magnetic field intensity requirement is B0 = 0.05 T, and the magnetic field gradient norm requirement is less than the given value of 0.001 T / m;

[0041] Step 2: Define the design variables and initialize them: The design variables are the shape parameters of the pore array, the length L and the angle θ of the long shuttle. Initialize these two variables to L = 30 mm, θ = 30 degrees; set the allowable error to 1%;

[0042] Step 3: According to the shape parameters of the pore array, the finite element method is used to calculate the magnetic field intensity and magnetic field gradient norm in the detection area. The solution area is a rectangular area with a side length of 1000 mm. The boundary is set to a magnetic shielding condition. It is divided by a free triangle mesh. The maximum side length of the triangle mesh is 0.01 mm. The remanence of the hard magnetic material is set to 1.4 Br. The other areas are air materials. The Coulomb norm equation satisfied by the discretized magnetic vector potential is After obtaining the numerical solution, calculate the magnetic scalar potential

[0043] Step 4: Determine whether the allowable error is met. If the allowable error is met, end the optimization; if the allowable error is not met, adjust the pore array shape parameters, the pore array inclination parameters, and the distance parameters between the pore array and the magnetic pole surface, and proceed to step 3;

[0044] Step 4 mainly determines whether the following two inequalities are satisfied at the same time

[0045] and

[0046] Here ||·|| represents the Euclidean distance. If they are satisfied at the same time, the optimization is terminated. If the allowable error is not satisfied, the shape parameters of the pore array, the length L and the angle θ of the long shuttle are given, random perturbations are added, and the process goes to step three.

[0047] The embodiments described above are only descriptions of the preferred modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A magnet structure having internal pores, characterized in that: The invention comprises a magnet (1) made of a hard magnetic material and a pore array (2) located inside the magnet (1) made of a hard magnetic material.

2. The magnet structure with internal pores according to claim 1, further characterized in that: The hard magnetic material magnet (1) has a fixed long columnar design so as to maximize the overall magnetic energy product within the space reserved inside the nuclear magnetic resonance device.

3. The magnet structure with internal pores according to claim 1, further characterized in that: The aperture array (2) is symmetrically distributed with respect to the axial direction of the hard magnetic material magnet (1).

4. The magnet structure with internal pores according to claim 1, characterized in that: The number of pores in the pore array (2) is m.

5. The magnet structure with internal pores according to claim 1, characterized in that: The pores in the pore array (2) are long spindle-shaped, with an axial length of L i m, the radius of curvature is r i m, and the angle between the axis of the hard magnetic material magnet (1) is θ i Spend.

6. The magnet structure with internal pores according to claim 1, characterized in that: The aperture array (2) can be designed separately on the main magnet, small magnet or pre-polarization magnet of the nuclear magnetic resonance magnet system.

7. A method for designing a magnet structure with internal pores, characterized in that: The following steps are involved: Step 1: Clarify the design requirements, maintain the magnetic field distribution requirements of the specific detection area, the magnetic field strength is B0, and the magnetic field gradient modulus is less than the given value Step 2: Define and initialize the optimization design variables, including the shape parameters of the pore array, the inclination parameters of the pore array, and the distance parameters between the pore array and the magnetic pole surface; and set the allowable error; Step 3: Calculate the magnetic field intensity and magnetic field gradient model of the specific detection area according to the pore array shape parameters, the pore array inclination parameters, and the distance parameters between the pore array and the magnetic pole surface of the magnetic material magnet (1). Step 4: Determine whether the allowable error is met. If so, end the optimization; if not, adjust the pore array shape parameters, pore array inclination parameters, and pore array distance parameters from the magnetic pole surface, and proceed to step 3.

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