Bipolar adjustable permanent magnet assembly and adjusting method thereof

Abstract

The invention discloses a bipolar adjustable permanent magnet assembly and an adjusting method thereof, the assembly comprises a yoke, a permanent magnet and a pole head, and the permanent magnet can rotate around the symmetry axis of the permanent magnet; the number of the pole heads is two, the permanent magnet rotates to change the magnetic field intensity between the pole heads, a magnetic field vector between the pole heads only generates an available component in a specific one-dimensional direction, the value of the available component is not lower than 99% of a magnetic field vector module, and the maximum value of the magnetic field component in the direction perpendicular to the specific one-dimensional direction is smaller than 1% of the magnetic field vector module; and the yoke is arranged outside the permanent magnet and the pole head. The permanent magnet is adopted to provide magnetic flux potential for a magnetic circuit, a magnetic field with high uniformity and good direction consistency is generated, and continuous adjustment of magnetic field intensity and zero-crossing switching of magnetic field polarity are achieved through rotation of the permanent magnet. Components such as a coil, a high-power adjustable power supply and a high-power water chilling unit are omitted, so that the size, the weight, the manufacturing cost and the energy consumption of a magnetic field part are greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetism, and in particular relates to a bipolar adjustable permanent magnet component and an adjustment method thereof. Background Art

[0002] The study of magnetic properties such as magnetization curve, magnetoresistance, Hall, magneto-optical Kerr effect, etc. of materials cannot be separated from a bipolar magnetic field generating system with continuously adjustable intensity and high uniformity. Traditional electromagnetic schemes usually use DC power supply to drive electromagnets, Helmholtz coils, solenoids and other devices, control the intensity of the magnetic field by adjusting the magnitude of the current, and change the polarity of the magnetic field by switching the direction of the current. Some magnetic measurement equipment, such as vibrating sample magnetometers and BH loop meters, not only have high requirements for the directionality and uniformity of the magnetic field, but also require that the magnetic field intensity can be continuously reduced to zero and gradually increased from zero with opposite polarity, that is, the polarity of the magnetic field is switched at zero magnetic field intensity to avoid discontinuous jumps near the zero point. Therefore, the above equipment is usually driven by a high-power, high-precision and low-noise bipolar current-stabilized power supply. In order to prevent the heat generated by the power supply and electromagnetic coil during operation from affecting the magnetic field stability, measurement accuracy and equipment life, a high-power water cooling or air cooling system is usually required. The above-mentioned magnetic field generating systems are often complex in structure, large in size, and expensive to build. They place high demands on site space, ground load-bearing capacity, power supply lines, maintenance and overhaul, etc. Their high energy consumption also increases the long-term cost of use.

[0003] There is a permanent magnet assembly in the prior art, which is designed based on the Halbach theory. The assembly can generate a large magnetic field component in a specific one-dimensional direction, while the components in other perpendicular directions are very small. However, this design cannot continuously adjust the magnetic field intensity to zero and switch the polarity at the zero point, and cannot be used for vibrating sample magnetometers and BH loop meters.

[0004] The prior art also has a modular flux switching permanent magnet rotary transformer. Although it uses permanent magnets and silicon steel rotors, its purpose is to further reduce the number of stator teeth of the rotary transformer while reducing the volume of the rotary transformer, ensuring its measurement accuracy, and improving system integration. It does not involve how to generate a one-dimensional magnetic field with continuously adjustable intensity and capable of switching polarity at zero point. Summary of the invention

[0005] In view of the above problems, the present invention proposes a bipolar adjustable permanent magnet assembly, which can be used to replace the electromagnet assembly in the magnetic measuring instrument. Compared with the traditional electromagnet assembly, the present invention greatly reduces the volume, weight, cost and energy consumption of the magnetic field system. The present invention provides a bipolar adjustable permanent magnet assembly, including a yoke, a permanent magnet and a pole head, wherein: The permanent magnet is cylindrical and can rotate around its symmetry axis; Two poles are provided, and the permanent magnet rotates to change the magnetic field strength between the poles, and the magnetic field vector between the poles only generates an available component in a specific one-dimensional direction, the value of the available component is not less than 99% of the magnetic field vector modulus, and the maximum value of the magnetic field component along the direction perpendicular to the specific one-dimensional direction is less than 1% of the magnetic field vector modulus; The yoke is arranged outside the permanent magnet and the pole head.

[0006] Preferably, the permanent magnet rotates so that when the magnetic field strength at the center between the pole heads is zero, the magnetic flux of the permanent magnet is shielded by the yoke, or is shielded by both the yoke and the pole heads.

[0007] Preferably, two permanent magnets are provided, the permanent magnets are cylindrical, and the two pole heads are opposite and respectively arranged on the sides of the two cylindrical permanent magnets. The two permanent magnets rotate in opposite directions, have the same rotation speed, and have the same absolute value of the rotation angle.

[0008] Preferably, one permanent magnet is provided, the permanent magnet is columnar, and two poles are opposite to each other and are both arranged above the top surface of the columnar permanent magnet.

[0009] Preferably, the yoke and the pole head are both made of soft magnetic materials, including carbon steel, silicon steel, iron-cobalt alloy, Permalloy or pure iron.

[0010] Based on the above purpose, the present invention also provides an adjustment method for a bipolar adjustable permanent magnet assembly, using the above bipolar adjustable permanent magnet assembly, two permanent magnets are set, the symmetry axis direction of the permanent magnet is defined as the Y axis, the positive half axis direction of the X axis is defined as the initial magnetization direction, and the sample is set between the two poles. When the rotation angle of the two permanent magnets is 0°, the magnetization directions of the two permanent magnets are both along the positive half axis direction of the X axis, and the magnetic field near the sample is also along the positive half axis direction of the X axis and has the highest intensity; when the rotation angle of the two permanent magnets is 90°, that is, the magnetization directions of the two permanent magnets are The directions are respectively along the positive and negative directions of the Z-axis. The magnetic flux generated by the two permanent magnets is short-circuited by the yokes and poles on both sides. The magnetic field leaked to the vicinity of the sample will also be offset due to the opposite magnetization directions of the two permanent magnets, so the magnetic field strength is zero; when the rotation angle of the two permanent magnets is 180°, the magnetization directions of the two permanent magnets are both along the negative half-axis direction of the X-axis, and the magnetic field near the sample is also along the negative half-axis direction of the X-axis and has the highest intensity; by changing the rotation angle of the two permanent magnets, a uniform magnetic field with continuously adjustable intensity and variable polarity is generated between the two poles along the X-axis direction.

[0011] Based on the above purpose, the present invention also provides an adjustment method for a bipolar adjustable permanent magnet assembly, using the above bipolar adjustable permanent magnet assembly, a permanent magnet is set, the symmetry axis direction of the permanent magnet is defined as the Z axis, the negative half axis direction of the X axis is defined as the initial magnetization direction, and the sample is set between two pole heads. When the permanent magnet rotates at an angle of 0°, the magnetization direction of the permanent magnet is along the negative half axis direction of the X axis, and the magnetic field near the sample is along the positive half axis direction of the X axis and has the highest intensity; when the permanent magnet rotates at an angle of 90°, that is, the magnetization direction of the permanent magnet is along the negative direction of the Y axis, the magnetic flux generated by the permanent magnet is short-circuited by the yokes on both sides thereof, and the magnetic field intensity is zero; when the permanent magnet rotates at an angle of 180°, the magnetization direction of the permanent magnet is along the positive half axis direction of the X axis, and the magnetic field near the sample is along the negative half axis direction of the X axis and has the highest intensity; by changing the rotation angle of the permanent magnet, a uniform magnetic field with continuously adjustable intensity and variable polarity is generated along the X axis direction between the two pole heads.

[0012] The beneficial effect of the above arrangement of the present invention is that the present invention adopts permanent magnets to replace electromagnetic coils to provide magnetic flux potential for the magnetic circuit, and utilizes the rotation of the permanent magnets to achieve a magnetic field with continuously adjustable intensity, smooth polarity switching, high uniformity, and good directional consistency. When the magnetic field needs to change continuously, the motor drives the reduction mechanism to drive the permanent magnet to rotate slowly, and the energy consumption is low. When the magnetic field is constant, the permanent magnet is stationary and the theoretical energy consumption is zero. Compared with the traditional magnetic field generating system based on electromagnetic coils, the present invention omits components such as electromagnetic coils, high-power bipolar adjustable power supplies, and high-power water cooling units, and the volume, weight, cost, and energy consumption of the system are greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of a bipolar adjustable permanent magnet assembly of a dual permanent magnet embodiment of the present invention; Figure 2 A diagram showing the relationship between the magnitude and direction of the XZ cross-sectional magnetic flux density of a bipolar adjustable permanent magnet assembly and the rotation angle of the permanent magnets in a dual permanent magnet embodiment of the present invention; Figure 3 A relationship diagram between the three-axis magnetic flux density at the center point between the poles of a bipolar adjustable permanent magnet assembly and the rotation angle of the permanent magnet in a dual permanent magnet embodiment of the present invention; Figure 4 A relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnets along the X-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a dual permanent magnet embodiment of the present invention; Figure 5 A relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnets along the Y-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a dual permanent magnet embodiment of the present invention; Figure 6A relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnets along the Z-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a dual permanent magnet embodiment of the present invention; Figure 7 It is a structural schematic diagram of a bipolar adjustable permanent magnet assembly of a single permanent magnet embodiment of the present invention; Figure 8 A diagram showing the relationship between the magnitude and direction of the XZ cross-sectional magnetic flux density of a bipolar adjustable permanent magnet assembly and the rotation angle of the permanent magnet in a single permanent magnet embodiment of the present invention; Fig. 9 A relationship diagram between the three-axis magnetic flux density at the center point between the poles of a bipolar adjustable permanent magnet assembly and the rotation angle of the permanent magnet in a single permanent magnet embodiment of the present invention; Fig.10 A relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnet in the X-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a single permanent magnet embodiment of the present invention; Fig.11 A relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnet in the Y-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a single permanent magnet embodiment of the present invention; Fig.12 This is a relationship diagram between the magnetic field uniformity and the rotation angle of the permanent magnet along the Z-axis direction near the magnetic field center point of a bipolar adjustable permanent magnet assembly of a single permanent magnet embodiment of the present invention. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0017] Dual permanent magnet embodiment See also Figure 1 The figure shows a schematic diagram of the structure of a bipolar adjustable permanent magnet assembly of this embodiment. A bipolar adjustable permanent magnet assembly includes a yoke 1, a permanent magnet 2 and a pole head 3, wherein: The two permanent magnets 2 are cylindrical and can rotate around their symmetry axes; two pole heads 3 are provided, and the rotation of the two permanent magnets 2 changes the magnetic field strength between the pole heads 3, and the magnetic field vector between the pole heads 3 only generates an available component in a specific one-dimensional direction, and the value of the available component is not less than 99% of the magnetic field vector modulus, and the maximum value of the magnetic field component along the direction perpendicular to the specific one-dimensional direction is less than 1% of the magnetic field vector modulus; the yoke 1 is provided outside the permanent magnet 2 and the pole head 3. The yoke 1 and the pole head 3 are both soft magnetic materials, including carbon steel, silicon steel, iron-cobalt alloy, Permalloy or pure iron.

[0018] When the two permanent magnets 2 rotate so that the magnetic field intensity at the center between the pole heads 3 is zero, the magnetic flux of the permanent magnet 2 is shielded by the yoke 1, or shielded by the yoke 1 and the pole heads 3. The two pole heads 3 are opposite to each other and are respectively arranged on the cylindrical surface of the permanent magnet 2. The two permanent magnets 2 rotate in opposite directions, at the same rotation speed, and at the same absolute value of the rotation angle.

[0019] The symmetry axis is represented by the long straight dotted line and solid line in the figure. The arc-shaped arrow around the symmetry axis represents the rotation direction of the permanent magnet 2. The arrow on the permanent magnet 2 represents the magnetization direction of the magnet. For the convenience of description, the positive half axis direction of the X-axis is defined as the initial magnetization direction. The yoke 1 and the pole head 3 can guide the magnetic flux to converge in the space near the sample 4. The adjustment method of the component is as follows: two cylindrical permanent magnets 2 with the same volume and shape rotate synchronously along their respective symmetry axes, with the same rotation angle but opposite directions. See Figure 2 In order to more clearly show the change process of the magnetic field inside the component, the double permanent magnet component is cut along the XZ plane. The length of the arrow in the figure indicates the magnitude of the magnetic flux density, and the direction of the arrow indicates the direction of the magnetic flux density. When the two permanent magnets 2 rotate at an angle of 0°, the magnetization directions of the two permanent magnets 2 are along the positive half-axis direction of the X-axis, and the magnetic field near the sample 4 is also along the positive half-axis direction of the X-axis and has the highest intensity; when the two permanent magnets 2 rotate at an angle of 90°, that is, the magnetization directions of the two permanent magnets 2 are respectively along the positive and negative directions of the Z-axis, most of the magnetic flux generated by the two permanent magnets 2 can be short-circuited by the yoke 1 and the pole head 3 on both sides, and the very small amount of magnetic field leaked to the vicinity of the sample 4 will also be offset due to the opposite magnetization directions of the two cylindrical permanent magnets 2, so the magnetic field intensity is zero; when the two permanent magnets 2 rotate at an angle of 180°, the magnetization directions of the two permanent magnets 2 are along the negative half-axis direction of the X-axis, and the magnetic field near the sample 4 is also along the negative half-axis direction of the X-axis and has the highest intensity. By controlling the rotation angle of the two permanent magnets 2, a uniform magnetic field with continuously adjustable intensity and variable polarity can be generated along the X-axis direction between the planes of the two circular pole heads 3. The magnetic field system only requires extremely low power consumption to drive the permanent magnet 2 to rotate slowly. When the permanent magnet 2 is stationary and the magnetic field is constant, the theoretical power consumption is zero.

[0020] Finite element simulation can be used to simulate the magnetic field at the sample 4 when the permanent magnet 2 rotates to examine the magnetic field strength, direction consistency, and uniformity of the scheme. Figure 1 The bottom radius of the two cylindrical permanent magnets 2 is 25 mm and the height is 50 mm; the circular plane radius of the pole head 3 is 15 mm, and the distance between them is 10 mm; four yokes 1 surround the two permanent magnets 2 and the two pole heads 3, and the width of the yoke 1 in the Y-axis direction is 50 mm. The two yokes 1 parallel to the X-axis are 103 mm long and 40 mm high, and the two yokes 1 parallel to the Z-axis are 40 mm long and 216 mm high. In a specific embodiment, in order to save materials and reduce weight, the four vertex corners of the quadrilateral formed by the yoke 1 are provided with a chamfer angle of 28 mm from the vertex. A 1 mm air gap is provided between the permanent magnet 2 and the yoke 1 and the pole head 3.

[0021] See also Figure 3 , the horizontal axis represents the rotation angle of the two permanent magnets 2. When the angle is 0°, the magnetization directions of the two permanent magnets 2 are as follows: Figure 1 As shown in the figure, along the positive half axis of the X-axis, when the angle is 90°, the magnetization directions of the two permanent magnets 2 are opposite, and when the angle is 180°, the magnetization directions of the two permanent magnets 2 are along the negative half axis of the X-axis. The ordinate represents the magnetic flux density at the spatial center point between the two circular pole heads 3 planes, that is, at the sample 4. When 0°, the magnetic flux density of this point along the positive half axis of the X-axis can reach a maximum of 1.04 T, which meets the saturation magnetization requirements of most magnetic materials; when 90°, the magnetic flux density of this point along the positive half axis of the X-axis is about 10 -5 T, close to zero; when 180°, the magnetic flux density at this point along the negative half axis of the X-axis can also reach 1.04 T, which is the same as the magnetic field strength at 0°, but with the opposite polarity. As can be seen from the figure, as the permanent magnet 2 rotates, the intensity of the magnetic field at this point can change continuously, and the magnetic field polarity flips at zero value, without discontinuous jumps. Regardless of how the rotation angle changes, the magnetic field vector between the poles 3 can only have a larger component in the X direction, while the components in the Y and Z directions are only one ten-thousandth of the maximum value of the X direction component, with good directional consistency.

[0022] See also Figure 4 , 5 , 6, the horizontal axis represents the point at different positions along the X, Y, and Z axes at the center of the space between the circular planes of the two pole heads 3, that is, at the sample 4; the vertical axis represents the magnetic flux density along the positive half axis direction at the point. When the rotation angles of the two permanent magnets 2 are 0° and 180°, the magnetic flux density deviations within the positive and negative 5 mm intervals in the X, Y, and Z axes are 1.1×10 - 3 T, 1.3×10 -3 T, 1.2×10-3 T, the deviation is the absolute value of the difference between the magnetic flux density at the center point of the space and the two end points; when the rotation angle of the two permanent magnets 2 is 90°, the deviation of the magnetic field in the range of plus or minus 5 mm in the Y-axis direction is 8.8×10 -3 T. In summary, at different angles, the gradient of the magnetic flux density along the X-axis direction within the range of positive and negative 5 mm in the X, Y, and Z-axis directions approaches 0, that is, the magnetic field along the X-axis direction at points at different positions in the three axis directions maintains good uniformity.

[0023] Single permanent magnet embodiment See also Figure 7 The figure shows a schematic diagram of the structure of a bipolar adjustable permanent magnet assembly of this embodiment. A bipolar adjustable permanent magnet assembly includes a yoke 1, a permanent magnet 2 and a pole head 3, wherein: The permanent magnet 2 is cylindrical and can rotate around its axis of symmetry; two pole heads 3 are provided, the two pole heads 3 are opposite to each other, and are both provided above the top surface of the cylinder of the permanent magnet 2. The rotation of the permanent magnet 2 changes the magnetic field intensity between the pole heads 3, and the magnetic field vector between the pole heads 3 only generates an available component in a specific one-dimensional direction, the value of the available component is not less than 99% of the magnetic field vector modulus, and the maximum value of the magnetic field component along the direction perpendicular to the specific one-dimensional direction is less than 1% of the magnetic field vector modulus; the yoke 1 is provided outside the permanent magnet 2 and the pole head 3. The yoke 1 and the pole head 3 are both soft magnetic materials, including carbon steel, silicon steel, iron-cobalt alloy, Permalloy or pure iron.

[0024] The circular arrow around the axis of symmetry indicates the rotation direction of the permanent magnet 2. For the convenience of description, the initial magnetization direction of the permanent magnet 2 is defined as along the negative half axis of the X axis. The yoke 1 and the pole head 3 can guide the magnetic flux to converge in the space near the sample 4. The adjustment method of this component is as follows: See Figure 8 In order to more clearly show the process of magnetic field change inside the component, the single permanent magnet component is cut along the XZ plane. The length of the arrow in the figure indicates the magnitude of the magnetic flux density, and the direction of the arrow indicates the direction of the magnetic flux density. When the rotation angle of the permanent magnet 2 is 0°, the magnetization direction of the permanent magnet 2 is along the negative half axis of the X axis, and the magnetic field near the sample 4 is along the positive half axis of the X axis and has the highest intensity; when the rotation angle of the permanent magnet 2 is 90°, that is, the magnetization direction of the permanent magnet 2 is along the negative direction of the Y axis, most of the magnetic flux generated by the permanent magnet 2 can be short-circuited by the yoke 1 on both sides, so the magnetic field intensity is zero; when the rotation angle of the permanent magnet 2 is 180°, the magnetization direction of the permanent magnet 2 is along the positive half axis of the X axis, and the magnetic field near the sample 4 is along the negative half axis of the X axis and has the highest intensity. By controlling the rotation angle of the cylindrical permanent magnet 2, a uniform magnetic field with continuously adjustable intensity and variable polarity can be generated along the X axis between the two circular pole heads 3 planes. The magnetic field system only needs extremely low power consumption to drive the permanent magnet 2 to rotate slowly. When the permanent magnet 2 is stationary and the magnetic field is constant, the theoretical power consumption is zero.

[0025] Finite element simulation can be used to simulate the magnetic field at the sample 4 when the permanent magnet 2 rotates to examine the magnetic field strength, directional consistency, and uniformity of the scheme. As an example, Figure 7 The bottom radius of the cylindrical permanent magnet 2 is 25 mm and the height is 50 mm. The circular plane spacing between the two pole heads 3 is 10 mm, the top radius is 15 mm, and the bottom radius is 23 mm. The thickness of the two yokes 1 extending beyond the permanent magnet 2 in the X-axis direction is 24 mm, the width in the Y-axis direction is 46 mm, and the height in the Z-axis direction is 133 mm. A 1 mm air gap is provided between the permanent magnet 2 and the yoke 1.

[0026] See also Fig. 9 , the horizontal axis is the rotation angle of the permanent magnet 2. When the angle is 0°, the magnetization direction of the permanent magnet 2 is along the negative half axis of the X axis. When the angle is 90°, the magnetization direction of the permanent magnet 2 is along the Y axis. When the angle is 180°, the magnetization direction of the permanent magnet 2 is along the positive half axis of the X axis. The vertical axis represents the magnetic flux density of the center point of the space between the two circular pole heads 3 planes. When 0°, the magnetic flux density of this point along the X axis can reach a maximum of 0.494 T; when 90°, the magnetic flux density of this point along the positive half axis of the X axis is about 4×10 -6 T, close to zero; when 180°, the magnetic flux density at this point along the negative half axis of the X-axis can also reach 0.494T, which is the same as the magnetic field intensity at 0°, but with the opposite polarity. Fig. 9 It can be seen that as the permanent magnet 2 rotates, the strength of the magnetic field at this point can change continuously, and the magnetic field polarity flips at zero value, and no discontinuous jump is observed. No matter how the rotation angle changes, the magnetic field vector between the poles 3 can only have a larger component in the X direction, and the components in the Y and Z directions are only one ten-thousandth of the maximum value of the X direction component, which has good directional consistency.

[0027] See also Fig.10 , 11 , 12, the horizontal axis represents the point at different positions along the X, Y, and Z axes at the center of the space between the circular planes of the two pole heads 3, that is, at the sample 4; the vertical axis represents the magnetic flux density along the positive half axis direction at the point. When 0° and 180°, the magnetic flux density deviation within the positive and negative 5 mm interval in the X, Y, and Z axes is 2×10 -4 T, 3×10 -4 T, 4×10 -4 T; when the angle is 90°, the deviation of the magnetic field is only 4.5×10 -6T. In summary, at different angles, the gradient of the magnetic flux density along the X-axis direction within the range of positive and negative 5 mm in the X, Y, and Z-axis directions approaches 0, that is, the magnetic field along the X-axis direction at points at different positions in the three axis directions maintains good uniformity.

[0028] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bipolar adjustable permanent magnet assembly, characterized in that: It includes yoke iron, permanent magnet and pole head, among which, The permanent magnet can rotate around its axis of symmetry; Two poles are provided, and the permanent magnet rotates to change the magnetic field strength between the poles, and the magnetic field vector between the poles only generates an available component in a specific one-dimensional direction, the value of the available component is not less than 99% of the magnetic field vector modulus, and the maximum value of the magnetic field component along the direction perpendicular to the specific one-dimensional direction is less than 1% of the magnetic field vector modulus; The yoke is arranged outside the permanent magnet and the pole head.

2. The bipolar adjustable permanent magnet assembly according to claim 1, characterized in that: The permanent magnet rotates so that when the magnetic field intensity at the center between the pole heads is zero, the magnetic flux of the permanent magnet is shielded by the yoke iron, or is shielded by the yoke iron and the pole heads.

3. The bipolar adjustable permanent magnet assembly according to claim 1, characterized in that: Two permanent magnets are provided, the permanent magnets are columnar, and the two pole heads are opposite and respectively arranged on the sides of the two columnar permanent magnets. The two permanent magnets rotate in opposite directions, have the same rotation speed, and have the same absolute value of the rotation angle.

4. The bipolar adjustable permanent magnet assembly according to claim 1, characterized in that: One permanent magnet is provided, the permanent magnet is columnar, and the two poles are opposite to each other and are both arranged above the top surface of the columnar permanent magnet.

5. The bipolar adjustable permanent magnet assembly according to claim 1, characterized in that: The yoke iron and the pole head are both made of soft magnetic materials, including carbon steel, silicon steel, iron-cobalt alloy, Permalloy or pure iron.

6. A method for adjusting a bipolar adjustable permanent magnet assembly, characterized in that: The bipolar adjustable permanent magnet assembly according to any one of claims 1 to 3 is adopted, two permanent magnets are arranged, the symmetry axis direction of the permanent magnet is defined as the Y axis, the positive half axis direction of the X axis is defined as the initial magnetization direction, and the sample is arranged between the two poles. When the rotation angle of the two permanent magnets is 0°, the magnetization directions of the two permanent magnets are both along the positive half axis direction of the X axis, and the magnetic field near the sample is also along the positive half axis direction of the X axis and has the highest intensity; when the rotation angle of the two permanent magnets is 90°, that is, the magnetization directions of the two permanent magnets are respectively along the positive direction of the Z axis and the positive half axis direction of the X axis. In the opposite direction, the magnetic flux generated by the two permanent magnets is short-circuited by the yokes and poles on both sides, and the magnetic field leaked to the vicinity of the sample will also be offset due to the opposite magnetization directions of the two permanent magnets, so the magnetic field strength is zero; when the two permanent magnets are rotated by 180°, the magnetization directions of the two permanent magnets are both along the negative half-axis direction of the X-axis, and the magnetic field near the sample is also along the negative half-axis direction of the X-axis and has the highest intensity; by changing the rotation angle of the two permanent magnets, a uniform magnetic field with continuously adjustable intensity and variable polarity is generated between the two poles along the X-axis direction.

7. A method for adjusting a bipolar adjustable permanent magnet assembly, characterized in that: A bipolar adjustable permanent magnet assembly as described in any one of claims 1 to 4 is used, one permanent magnet is set, the symmetry axis direction of the permanent magnet is defined as the Z axis, the negative half axis direction of the X axis is defined as the initial magnetization direction, and the sample is set between the two pole heads. When the permanent magnet is rotated at an angle of 0°, the magnetization direction of the permanent magnet is along the negative half axis direction of the X axis, and the magnetic field near the sample is along the positive half axis direction of the X axis and has the highest intensity; when the permanent magnet is rotated at an angle of 90°, that is, the magnetization direction of the permanent magnet is along the negative direction of the Y axis, the magnetic flux generated by the permanent magnet is short-circuited by the yokes on both sides thereof, and the magnetic field intensity is zero; when the permanent magnet is rotated at an angle of 180°, the magnetization direction of the permanent magnet is along the positive half axis direction of the X axis, and the magnetic field near the sample is along the negative half axis direction of the X axis and has the highest intensity; by changing the rotation angle of the permanent magnet, a uniform magnetic field with continuously adjustable intensity and variable polarity is generated along the X axis direction between the two pole heads.

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