A magnetic field variable circuit using permanent magnets

Abstract

The permanent magnet type variable magnetic circuit currently used in some accelerators has several drawbacks, such as requiring a large amount of movable space outside the circuit to move the short-circuiting member, and requiring a large amount of force to change the position of the short-circuiting member. [Solution] The magnetic field variable magnetic circuit of the present invention includes an external fixing plate and an internal fixing plate, which are constructed by arranging a plurality of magnetic material pieces in a stripe pattern in combination with a plurality of non-magnetic material pieces; a magnet plate, which is placed between these fixing plates and includes two or more rows of magnets in which a plurality of permanent magnets are aligned in a left-right direction perpendicular to the stripe pattern of the external and internal fixing plates; and an upper magnetic field application yoke and a lower magnetic field application yoke coupled to the internal fixing plate. One end of the upper magnetic field application yoke and the lower magnetic field application yoke is coupled to the internal fixing plate, and the other end is separated to form an air gap that becomes a magnetic field generating section.

Description

Technical Field

[0001] The present invention relates to a magnetic field variable magnetic circuit using a permanent magnet, in which the magnetic field intensity of a magnetic field generation part varies due to the sliding movement of the permanent magnet.

Background Art

[0002] An accelerator is a device that accelerates charged particles such as electrons and protons in an electric field to create a high-energy beam, and is used in various systems ranging from relatively small systems such as medical linacs used in cancer treatment and electron microscopes to large-scale systems such as heavy particle beam treatment facilities, synchrotron radiation facilities, and large-scale collider accelerators.

[0003] Since charged particle beams travel straight while diverging, control of the direction and divergence of the beam is necessary for transporting charged particle beams. In accelerators, a large number of magnets are used for beam control (deflection), and generally electromagnets are used. Electromagnets have the advantage that the magnetic field intensity can be easily and quickly controlled by adjusting the current flowing through the coil, and the design is also easy. On the other hand, there are demerits that a large current continues to flow during operation, auxiliary equipment for power supply and cooling is required, and regular repair and replacement for water leakage and corrosion are necessary, so the operation and maintenance costs become extremely high, especially in large-scale systems.

[0004] Various magnetic field variable magnetic circuits using permanent magnets that can be used as beam deflectors for accelerators are also known (as known examples of circuits that vary the magnetic field intensity by sliding movement of a permanent magnet or other members, Patent Documents 1 to 11, etc.). Even in large-scale systems such as synchrotron radiation facilities, attempts have been made to reduce costs by replacing part of the accelerator electromagnets with such permanent magnet type magnetic field variable magnetic circuits.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The permanent magnet type variable magnetic field circuits currently used in some accelerators have several drawbacks, such as requiring a large movable space outside the circuit to move the short-circuiting member that controls the magnetic field strength, and requiring a large force to change the position of the short-circuiting member. The present invention aims to provide a permanent magnet type variable magnetic field circuit that can solve these problems. [Means for solving the problem]

[0007] The inventors of this application conducted intensive research to solve the above problems and found that the above problems can be solved by a magnetic circuit having the following configuration, and that a magnetic field tunable magnetic circuit can be used not only as a beam deflector for accelerators but also in laboratory devices or systems such as magneto-optical measuring devices, and thus completed the present invention described below.

[0008] [1] A variable magnetic field circuit comprising an external fixing plate and an internal fixing plate, which are constructed by arranging a plurality of magnetic pieces in a stripe pattern in combination with a plurality of non-magnetic pieces; a magnet plate disposed between these fixing plates, which includes a plurality of permanent magnets arranged in two or more rows of magnets aligned in a left-right direction perpendicular to the stripe pattern of the external and internal fixing plates; and an upper magnetic field application yoke and a lower magnetic field application yoke coupled to the internal fixing plate, The upper magnetic field application yoke and the lower magnetic field application yoke have one end connected to an internal fixing plate, and the other end is separated to form a gap that becomes a magnetic field generation section. The aforementioned magnet plate includes a movable magnet plate that is slidable in the left-right direction and includes at least one row of magnets. Within each of the aforementioned arrays of magnets, one or m permanent magnets (where m means any number of up to a few; the same applies hereinafter) are arranged alternately at regular intervals with different magnetic pole faces facing inward and outward, and the intervals are approximately the same as the intervals between the stripes of non-magnetic material pieces on the external and internal fixing plates. The external fixing plate includes a first external magnetic piece positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but does not reach the lower end of the plate, a second external magnetic piece positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but does not reach the upper end of the plate, and an external non-magnetic piece that is longer than the first and second external magnetic pieces, and the first external magnetic piece and the second external magnetic piece are arranged alternately in sets of one or m pieces in the left-right direction with the external non-magnetic piece in between to form a stripe-like pattern on the external fixing plate. The internal fixing plate includes a first internal magnetic piece positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but not the lower end of the plate, a second internal magnetic piece positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but not the upper end of the plate, an internal non-magnetic piece longer than the first and second internal magnetic pieces, a first yoke piece positioned on the lower end of the plate and aligned with the first internal magnetic piece in the stripe direction, and a second yoke piece positioned on the upper end of the plate and aligned with the second internal magnetic piece in the stripe direction, wherein the first and second yoke pieces protrude from the surface of the internal fixing plate toward the external fixing plate and contact the second external magnetic piece and the first external magnetic piece, respectively, and the first and second internal magnetic pieces are arranged alternately in sets of one or m pieces in the left-right direction with the internal non-magnetic piece in between, forming a stripe-like pattern on the internal fixing plate. A variable magnetic field circuit is provided in which the arrangement of permanent magnets can be changed by sliding a movable magnet plate, between an ON state in which permanent magnets facing the same magnetic poles are arranged adjacently in the vertical direction and connected to external and internal magnetic material pieces, and an OFF state in which permanent magnets facing different magnetic poles are arranged adjacently in the vertical direction and connected to external and internal magnetic material pieces, thereby changing the magnetic field strength of the magnetic field generating section. [2] The magnetic plate includes a movable magnetic plate that is slidable in the left-right direction and includes at least one row of magnets, and a fixed magnetic plate that is in a fixed position and includes at least one row of magnets. The variable magnetic field circuit according to [1], wherein, in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of one or one set of magnetic material pieces, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of one or one set of magnetic material pieces. [3] In the external fixing plate, one first external magnetic piece and one second external magnetic piece are arranged alternately, and in the internal fixing plate, one first internal magnetic piece and one second internal magnetic piece are arranged alternately. The width of each permanent magnet is approximately the same as the width of the stripes of the external and internal magnetic material pieces. In each magnet array, one permanent magnet is arranged alternately with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to [2], wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a magnetic material piece, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of a magnetic material piece. [4] In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately, The width of each permanent magnet is approximately the same as the width of the stripes of the external and internal magnetic material pieces. In each magnet array, m permanent magnets are arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to [2], wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a magnetic material piece, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of a magnetic material piece. [5] In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately, The width of each permanent magnet is approximately the same as the width of a set of m external magnetic pieces with an external non-magnetic piece in between, and the width of a set of m internal magnetic pieces with an internal non-magnetic piece in between. In each magnet array, one permanent magnet is arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to [2], wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a set of magnetic material pieces, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a set of magnetic material pieces. [6] The stripe width of the magnetic body piece and the left - right width of the permanent magnet are larger than the stripe width of the non - magnetic body piece. The magnet plate includes two movable magnet plates each including at least one row of magnet rows, and switching between the on - state and the off - state is performed by the sliding movement of the two movable magnet plates. The variable - magnetic - field magnetic circuit according to [1]. [7] In the external fixed plate, the first external magnetic body piece and the second external magnetic body piece are alternately arranged one by one, and in the internal fixed plate, the first internal magnetic body piece and the second internal magnetic body piece are alternately arranged one by one. The left - right width of each permanent magnet is substantially the same as the stripe width of the external and internal magnetic body pieces. In each magnet row, the permanent magnets are alternately arranged at regular intervals with different pole faces facing the inside - outside direction one by one. In the on - state, a plurality of permanent magnets are arranged vertically with the same pole face connected to the stripe of one magnetic body piece. In the off - state, the magnets with different pole faces are arranged adjacent to each other vertically, and one permanent magnet connects two magnetic body pieces across one non - magnetic body piece. The variable - magnetic - field magnetic circuit according to [6]. [8] In the external fixed plate, the first external magnetic body piece and the second external magnetic body piece are alternately arranged in sets of m each, and in the internal fixed plate, the first internal magnetic body piece and the second internal magnetic body piece are alternately arranged in sets of m each. The left - right width of each permanent magnet is substantially the same as the stripe width of the external and internal magnetic body pieces. In each magnet row, m permanent magnets are alternately arranged at regular intervals with different pole faces facing the inside - outside direction. In the on - state, a plurality of permanent magnets are arranged vertically with the same pole face connected to the stripe of one magnetic body piece. In the off - state, the magnets with different pole faces are arranged adjacent to each other vertically, and one permanent magnet connects two magnetic body pieces across one non - magnetic body piece. The variable - magnetic - field magnetic circuit according to [6]. [9] In the external fixing plate, m pieces of the first external magnetic body pieces and m pieces of the second external magnetic body pieces are alternately arranged in sets, and in the internal fixing plate, m pieces of the first internal magnetic body pieces and m pieces of the second internal magnetic body pieces are alternately arranged in sets. The left and right widths of each permanent magnet are substantially the same as the left and right widths of the set of m external magnetic body pieces sandwiching the external non-magnetic body piece and the left and right widths of the set of m internal magnetic body pieces sandwiching the internal non-magnetic body piece. In each magnet row, the permanent magnets are arranged alternately at a certain interval with different magnetic pole faces facing the inside and outside directions one by one. In the on state, a plurality of permanent magnets are arranged vertically with the same magnetic pole face connected to a stripe of a set of magnetic body pieces, and in the off state, the magnets with different magnetic pole faces are arranged adjacent to each other vertically, and one permanent magnet straddles m non-magnetic body pieces and connects to (m + 1) magnetic body pieces. The magnetic field variable magnetic circuit according to [6].

Advantages of the Invention

[0009] According to the magnetic circuit of the present invention, it is not necessary to provide a large movable space outside the circuit for moving the short-circuit member. Also, compared with the position conversion of the short-circuit member in the conventional permanent magnet type magnetic field variable magnetic circuit, the magnets can be position-converted with a smaller force. Due to these features, it is possible to make the device or system using the magnetic field variable magnetic circuit more compact and miniaturize the switching motor, so that the operating cost can be further reduced and the degree of freedom in the design of the entire device or system can be increased.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic diagram showing the overall structure of an example of the slide type magnetic field variable magnetic circuit according to the present invention. [Figure 2] It is a schematic diagram showing the internal structure of an example of the slide type magnetic field variable magnetic circuit according to the present invention. [Figure 3] It is a schematic diagram showing the internal structure (the stripe structure of the internal fixing plate and the positional relationship of the permanent magnets) of an example of the slide type magnetic field variable magnetic circuit according to the present invention. [Figure 4] This diagram illustrates the magnetic flux flowing through the magnetic material pieces of the external and internal fixing plates when the device is in the ON state. [Figure 5] This diagram illustrates the magnetic flux flowing through the magnetic material pieces of the external and internal fixing plates when the device is in the off state. [Figure 6] This is a schematic diagram illustrating the change in the position of a magnet by sliding a movable magnet plate. It shows an example of a magnet plate configuration that includes a fixed magnet plate and a movable magnet plate. [Figure 7] This is a schematic diagram illustrating the change in the position of a magnet by sliding a movable magnet plate. It is an example of a magnet plate configuration in which the magnet plate includes two movable magnet plates, and a master-slave relationship is established between the movable magnet plates with respect to sliding movement. [Figure 8] This is a schematic diagram illustrating the change in the position of a magnet by the sliding movement of a movable magnet plate. It also shows a further example of a magnet plate configuration in which the magnet plate includes two movable magnet plates, and a master-slave relationship is established between the movable magnet plates with respect to sliding movement. [Figure 9] These are examples of stripe patterns for magnetic material pieces on an external fixing plate that can be adopted by the magnetic field variable magnetic circuit of the present invention. A: An example in which magnetic and non-magnetic stripes are arranged alternately, one at a time. B: An example in which magnetic stripes are arranged in sets of two (m=2). C: An example in which magnetic stripes are arranged in sets of three (m=3). [Figure 10] Figure 9 is a schematic diagram showing the arrangement of magnets in the ON and OFF states for each stripe pattern shown, in a variable magnetic field circuit where the stripe width of the magnetic material, the stripe width of the non-magnetic material, and the left-right width of the magnets are all the same, and the magnet array includes a fixed magnet array and a movable magnet array. In each figure, the upper of the two magnet arrays is the fixed magnet array, and the lower of the two is the movable magnet array. [Figure 11]Figures 9B and 9C show schematic diagrams illustrating the arrangement of magnets in the ON and OFF states for a variable magnetic field circuit where the stripe width of the magnetic material and the stripe width of the non-magnetic material are the same, the left-right width of the magnet is the same as the left-right width of one set of magnetic strips with a non-magnetic piece in between, and the magnet array includes a fixed magnet array and a movable magnet array. In each figure, the upper row of magnet arrays is the fixed magnet array, and the lower row is the movable magnet array. [Figure 12] This is a schematic diagram illustrating the change in the position of the magnets when switching between on and off in a variable magnetic field circuit where the stripe width of the magnetic material is larger than the stripe width of the non-magnetic material, the left-right width of the magnet is the same as the stripe width of the magnetic material, and the magnet array includes two movable magnet arrays, with the stripe pattern shown in Figure 9A. [Figure 13] This is a schematic diagram illustrating the positional change of the magnets during on / off switching in a variable magnetic field circuit where the stripe width of the magnetic material is greater than the stripe width of the non-magnetic material, the left-right width of the magnet is the same as the stripe width of the magnetic material, and the magnet array includes two movable magnet arrays, with the stripe pattern shown in Figure 9B. [Figure 14] This is a schematic diagram illustrating the change in the position of the magnets when switching between on and off in a variable magnetic field circuit where the stripe width of the magnetic material is greater than the stripe width of the non-magnetic material, the left-right width of the magnet is the same as the stripe width of the magnetic material, and the magnet array includes two movable magnet arrays, with the stripe pattern shown in Figure 9C. [Figure 15] This schematic diagram illustrates the change in the position of the magnets when switching between on and off in a variable magnetic field circuit, where the stripe width of the magnetic material is greater than the stripe width of the non-magnetic material, the left-right width of the magnet is the same as the left-right width of one set of magnetic stripes with a non-magnetic piece in between, and the magnet array includes two movable magnet arrays, as shown in Figure 9B. [Figure 16]This schematic diagram illustrates the change in the position of the magnets when switching between on and off in a variable magnetic field circuit, where the stripe width of the magnetic material is greater than the stripe width of the non-magnetic material, the left-right width of the magnet is the same as the left-right width of one set of magnetic stripes with a non-magnetic piece in between, and the magnet array includes two movable magnet arrays, as shown in Figure 9C. [Figure 17] Simulation data showing the flow of magnetic flux in the ON state (upper panel) and OFF state (lower panel) in circuit cross-sectional diagrams. [Figure 18] Simulation data of the magnetic force generated in the magnetic field generation section when a movable magnet is moved in stages (results of a 3D magnetic field simulation). [Figure 19] The data from Figure 18 is plotted for each magnet position. [Modes for carrying out the invention]

[0011] In this specification, when describing the configuration of a magnetic circuit, the X direction of the three-dimensional axis shown in Figures 1 to 3 is expressed as "depth" or "inside-out direction," the Y direction as "height" or "up-down direction," and the Z direction as "width" or "left-right direction." Unless otherwise specified, left and right refer to the left and right when viewed from the surface side of the external fixing plate. These terms are for convenience only and do not limit the use of the magnetic circuit of the present invention to a state in which the Y direction is vertical.

[0012] In this specification, the term "approximately identical" with respect to size (dimensions) means that there may be a size difference of 5% or less, for example, 3% or less, or 1% or less. The term "identical" means that the size difference is less than 1%, for example, less than 0.5% or less than 0.1%.

[0013] The configuration of the variable magnetic field circuit (sometimes called a sliding-type variable magnetic field circuit) of the present invention will be described below with reference to the drawings as appropriate.

[0014] As shown in Figures 1 to 3, the variable magnetic field circuit 1 of the present invention includes an external fixing plate 10 and an internal fixing plate 20, which are constructed by arranging a plurality of magnetic material pieces in a stripe pattern in combination with a plurality of non-magnetic material pieces; a magnet plate 30, which is placed between these fixing plates and includes a plurality of permanent magnets 330, 340 arranged in two or more rows of magnets in a left-right direction perpendicular to the stripe pattern of the external and internal fixing plates; and an upper magnetic field application yoke 40 and a lower magnetic field application yoke 50 coupled to the internal fixing plate 20. One end of the upper magnetic field application yoke 40 and the lower magnetic field application yoke 50 is coupled to the internal fixing plate, while the other end is separated to form a gap that becomes a magnetic field generating section 60.

[0015] The external fixing plate 10 is constructed by alternately combining external magnetic pieces 101, 102 and external non-magnetic pieces 111. The internal fixing plate 20 is constructed by alternately combining internal magnetic pieces 201, 202 and internal non-magnetic pieces 211. The external magnetic pieces 101, 102 and the internal magnetic pieces 201, 202 all have the same width. The external non-magnetic pieces 111 and the internal non-magnetic pieces 211 all have the same width. The widths of the external and internal magnetic pieces and the external and internal non-magnetic pieces may be such that the former is larger than the latter, or they may all be the same.

[0016] The magnetic plate includes a movable magnetic plate 32 that is slidable in the left-right direction and contains at least one row of magnets. In one embodiment, the magnetic plate includes a movable magnetic plate 32 that is slidable in the left-right direction and contains at least one row of magnets, and a fixed magnetic plate 31 that is in a fixed position and contains at least one row of magnets. That is, two or more rows of magnets include at least one row of movable magnetic plates 34 and at least one row of fixed magnetic plates 33. In another embodiment, the magnetic plate includes two movable magnetic plates 32, 32' each containing at least one row of magnets. That is, two or more rows of magnets include at least two rows of movable magnetic plates 34, 34', for example, all of which are movable magnetic plates. The permanent magnets that make up the movable magnetic plates on the movable magnetic plate 32 are called movable magnets 340, and the permanent magnets that make up the fixed magnetic plates on the fixed magnetic plate 31 are called fixed magnets 330. Hereinafter, permanent magnets may be simply abbreviated as magnets.

[0017] Within each magnet row, permanent magnets (fixed magnets 330, movable magnets 340) are arranged alternately at regular intervals, with one or m permanent magnets (m means any number of magnets, such as up to five, four, or three, or two; the same applies hereinafter), each with different magnetic pole faces in the inward and outward directions. The spacing between permanent magnets in a magnet row (distance in the left-right direction) is approximately the same as the spacing between the stripes of magnetic material pieces on the external and internal fixed plates, i.e., the width of the non-magnetic material pieces 111, 211 (stripe width of the non-magnetic material pieces). For example, in the configuration examples shown in Figures 1-3, in the fixed magnet row 33, fixed magnets 330N with their N pole faces towards the external plate and fixed magnets 330S with their S pole faces towards the external plate are arranged alternately at regular intervals, and in the movable magnet row 34, movable magnets 340N with their N pole faces towards the external plate and movable magnets 340S with their S pole faces towards the external plate are arranged alternately at regular intervals. In other diagrams as well, magnets with their north pole facing the external fixing plate are shown in black to dark gray, and magnets with their south pole facing the external fixing plate are shown in light gray.

[0018] The external fixing plate 10 includes a first external magnetic piece 101 positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but does not reach the lower end of the plate, a second external magnetic piece 102 positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but does not reach the upper end of the plate, and an external non-magnetic piece 111 that is longer than the first and second external magnetic pieces. The first external magnetic piece 101 and the second external magnetic piece 102 are arranged alternately in sets of one or m pieces in the left-right direction with the external non-magnetic piece 111 in between, forming a stripe-like pattern on the external fixing plate 10. The external fixing plate 10 may further include a first external non-magnetic piece 112 aligned in the stripe direction with the first external magnetic piece 101 and having a length extending from the lower end of the magnetic piece to the lower end of the plate, and a second external non-magnetic piece 113 aligned in the stripe direction with the second external magnetic piece 102 and having a length extending from the upper end of the magnetic piece to the upper end of the plate.

[0019] Figure 9 shows an example of a stripe pattern for an external fixing plate. In Figure 9, for convenience, the widths of the magnetic pieces and non-magnetic pieces are all the same, but the width setting is not limited to this embodiment. A is a stripe pattern when the first external magnetic piece 101 and the second external magnetic piece 102 are arranged alternately one by one with an external non-magnetic piece 111 in between. B and C are examples of stripe patterns when the first external magnetic piece 101 and the second external magnetic piece 102 are arranged alternately in sets of m with an external non-magnetic piece 111 in between, with B being the example where m=2 and C being the example where m=3. The lengths of the first external magnetic piece 101 and the second external magnetic piece 102 may be the same as shown on the left side of Figure 9, or one may be longer than the other as shown on the right side. The magnetic piece 101 may be longer, or the magnetic piece 102 may be longer. In Figures 10 to 16, the lengths of the magnetic material pieces 101 and 102 are made the same for convenience, but the embodiment is not limited to this.

[0020] When the stripe pattern shown in Figure 9A is adopted, the magnets in each magnet row are arranged alternately at regular intervals (= the stripe width of the non-magnetic material pieces), with different magnetic pole faces facing inward and outward (Figure 10 upper panel, Figure 12).

[0021] When a stripe pattern is adopted in which external magnetic pieces are arranged alternately in sets of m, as shown in Figures 9B and 9C, two configurations are possible: one using magnets whose left-right width is approximately the same as the width of the magnetic pieces, and another using magnets whose left-right width is approximately the same as the left-right width of a set of m external magnetic pieces 101 or 102 with an external non-magnetic piece 111 in between (the length indicated by * in Figure 9; hereafter, this may be simply referred to as "the left-right width of one set of magnetic stripes"). In the former configuration, within each magnet row, m magnets are arranged alternately at regular intervals with different magnetic pole faces facing inward and outward (Figures 10 middle and lower, 13, and 14). In the latter configuration, within each magnet row, one magnet is arranged alternately at regular intervals with different magnetic pole faces facing inward and outward (Figures 11, 15, and 16).

[0022] The internal fixing plate 20 includes a first internal magnetic piece 201 positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but not the lower end of the plate; a second internal magnetic piece 202 positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but not the upper end of the plate; an internal non-magnetic piece 211 that is longer than the first and second internal magnetic pieces; a first yoke piece 203 positioned on the lower end of the plate and aligned with the first internal magnetic piece 201 in the stripe direction; and a second yoke piece 204 positioned on the upper end of the plate and aligned with the second internal magnetic piece 202 in the stripe direction. The first yoke piece 203 and the second yoke piece 204 protrude from the surface of the internal fixing plate toward the external fixing plate and contact the second external magnetic piece 102 and the first external magnetic piece 101, respectively. The first internal magnetic material piece 201 and the second internal magnetic material piece 202 are arranged alternately in sets of one or m pieces in the left-right direction, with an internal non-magnetic material piece 211 in between, to form a stripe-like pattern on the internal fixing plate 20. If the yoke pieces 203 and 204 are omitted, the magnetic material pieces of the internal fixing plate will have a stripe pattern that is an inverted version of the stripe pattern of the external fixing plate, as shown in Figure 2. The internal fixing plate 20 may further include a first internal non-magnetic material piece 212 filling the space between the first internal magnetic material piece 201 and the first yoke piece 203, and a second internal non-magnetic material piece 213 filling the space between the second internal magnetic material piece 202 and the second yoke piece 204.

[0023] The on / off switching of the variable magnetic field circuit is performed by sliding a movable magnet plate contained within the magnet plate. In the on state, permanent magnets facing the same magnetic poles are arranged adjacently in the vertical direction and connected to the external and internal magnetic material pieces 101, 102, 201, and 202. In the on state magnet arrangement, magnetic flux flows in the direction indicated by the arrows in Figure 4, and the magnetic field strength of the magnetic field generating section is maximized. In the off state, permanent magnets facing different magnetic poles are arranged adjacently in the vertical direction and connected to the external and internal magnetic material pieces 101, 102, 201, and 202. In the off state magnet arrangement, as shown in Figure 5, the magnetic flux is contained within the magnetic material pieces, so the magnetic field strength of the magnetic field generating section is minimized.

[0024] There are two main types of off-state configurations. One is a configuration in which the magnetic flux is contained within a single magnetic stripe in the vertical direction (off-state in Figures 10 and 11), and the other is a configuration in which the magnetic flux is contained within a single magnetic stripe in both the vertical and horizontal directions (off-state in Figures 12 to 16). Figure 5 shows only the containment of the magnetic flux in the vertical direction. In the former configuration, a portion of the magnet array can be fixed, so the magnet plate 30 may include a fixed magnet plate 31. In the latter configuration, all magnet arrays need to be slidable, so the magnet plate 30 includes two movable magnet plates, each containing at least one magnet array.

[0025] The sliding movement of the movable magnet plate 32 is controlled by a feed mechanism (not shown) that controls the sliding movement from outside the variable magnetic field circuit 1. The operating part (not shown) of the feed mechanism can be appropriately selected according to the purpose and environment of use of the variable magnetic field circuit, such as a nut operated with a wrench, a lever, or a feed screw. If operation from a remote location is required, electrical wiring connected to a switch at the remote location or a remote control signal receiver can be provided in the variable magnetic field circuit, and the left and right movement of the movable magnet plate 32 can be controlled by electricity or radio waves. The mechanism that transmits the operation of the operating part to the movable magnet plate 32 can be easily designed by a person skilled in the art.

[0026] Figures 6 to 8 are schematic diagrams illustrating the change in the position of the magnets by sliding the movable magnet plate.

[0027] Figure 6 is a schematic diagram showing a case where the magnet plate 30 includes a fixed magnet plate 31 and a movable magnet plate 32. In both the ON and OFF states, the magnets are positioned along the stripes of the magnetic material. In the OFF state, the magnetic flux is contained within a single stripe of magnetic material in the vertical direction.

[0028] Figures 7 and 8 show an example of the configuration of a magnet plate when the magnet plate 30 includes two movable magnet plates 32 and 32', and a master-slave relationship is established between the movable magnet plates with respect to sliding movement. The movable magnet plate 32 is the master plate that is directly connected to the feeding means, and the sliding movement of the master plate controls the sliding movement of the slave plate, the movable magnet plate 32'. In the off state, one magnet with the same width as the stripe width of the magnetic material connects to two magnetic material stripes, straddling one non-magnetic material stripe. As a result, two magnets with different orientations of their magnetic poles adjacent to each other within the same magnet row are simultaneously connected to one magnetic material stripe, so that the magnetic flux is completed in the left-right direction within one magnetic material stripe. Note that the sliding movement mechanism itself, in which two movable magnet plates have a master-slave relationship, is publicly known as disclosed in Japanese Patent No. 5716232. While establishing a master-slave relationship between the movable magnet plates simplifies the feeding mechanism, it is also possible to configure each movable magnet plate to have its own independent feeding mechanism, allowing for individual plate sliding operation.

[0029] Figures 10 to 16 show the positional relationship between the magnets and the stripe pattern in the ON and OFF states, using the case where there are two rows of magnets as an example, for each of the three types of stripe patterns shown in Figure 9.

[0030] Figures 10 and 11 show an embodiment in which the magnetic plate includes a fixed magnetic plate and a movable magnetic plate. Of the two rows of magnets, the upper row is a row of solid magnets and the lower row is a row of movable magnets. In the fixed magnetic plate, each magnet is fixed on a strip of magnetic material (in the three-dimensional structure of the magnetic circuit, it is positioned between an outer magnetic material piece and an inner magnetic material piece). In the off state, the movable magnets, with their magnetic pole faces different from those of the fixed magnets, are arranged on the strip of magnetic material, and the magnetic flux is completed in the vertical direction within a single strip of magnetic material.

[0031] Figure 10 shows the positional relationship between the magnet and the magnetic stripe in the ON and OFF states, in a configuration where the left-right width of the magnet is the same as the width of the magnetic stripe and the non-magnetic stripe.

[0032] The upper part of Figure 10 shows an example where the stripe pattern is the pattern shown in Figure 9A, that is, in the external fixing plate 10, one first external magnetic piece 101 and one second external magnetic piece 102 are arranged alternately, and in the internal fixing plate 20, one first internal magnetic piece 201 and one second internal magnetic piece 202 are arranged alternately. In each magnet row, one magnet is arranged alternately with different magnetic pole faces facing inward and outward. In the ON state, multiple magnets (two in the illustrated example) belonging to different magnet rows connect the same magnetic pole face to a single magnetic stripe and are aligned vertically along the magnetic stripe. In the OFF state, multiple magnets (two in the illustrated example) belonging to different magnet rows connect different magnetic pole faces to a single magnetic stripe and are aligned vertically along the magnetic stripe.

[0033] The middle and lower sections of Figure 10 show an example where the stripe pattern is the pattern shown in Figures 9B and C, i.e., in the external fixing plate 10, the first external magnetic material pieces 101 and the second external magnetic material pieces 102 are arranged alternately in sets of two or three, and in the internal fixing plate 20, the first internal magnetic material pieces 201 and the second internal magnetic material pieces 202 are arranged alternately in sets of two or three. In each magnet row, two or three magnets are arranged alternately with different magnetic pole faces facing inward and outward. In the ON state, multiple magnets (two in the illustrated example) belonging to different magnet rows are connected to the same magnetic pole face to a single magnetic material stripe and are arranged vertically along the magnetic material stripe, just as in the upper section of Figure 10. In the OFF state, multiple magnets (two in the illustrated example) belonging to different magnet rows are connected to different magnetic pole faces to a single magnetic material stripe and are arranged vertically along the magnetic material stripe. Because the magnets need to be slid into an arrangement of two or three, the sliding distance when switching between on and off is usually larger than that shown in the upper part of Figure 10, depending on the settings for the stripe width and magnet width.

[0034] Figure 11 shows an example where the stripe width of the magnetic material and the stripe width of the non-magnetic material are the same, the stripe pattern is the pattern shown in Figures 9B and 9C (a pattern in which magnetic material pieces are arranged alternately in sets of two or three), and the left-right width of the magnets is the same as the left-right width of one set of magnetic material stripes. In each magnet row, one magnet is arranged alternately with different magnetic pole faces facing inward and outward. In the ON state, multiple magnets belonging to different magnet rows (two in the illustrated example) are aligned vertically with the same magnetic pole faces connected to one set of magnetic material stripes. In the OFF state, multiple magnets belonging to different magnet rows (two in the illustrated example) are aligned vertically with different magnetic pole faces connected to one set of magnetic material stripes. If one set of magnetic material stripes is viewed as one large stripe, the magnets are aligned along the large stripe in both the ON and OFF states.

[0035] When the stripe width of the magnetic material is greater than the stripe width of the non-magnetic material, in addition to the circuit configurations in Figures 10 and 11 which include fixed magnet rows, it is also possible to make all magnet rows movable and, in the off state, arrange the magnets vertically at a position offset from the magnetic material stripe, thereby enabling a circuit configuration in which the magnetic flux can be completed not only vertically but also horizontally within a single magnetic material piece. Figures 12 to 16 show schematic diagrams of an example of a circuit configuration in which all magnet rows are movable and, through a two-stage sliding movement as shown in Figure 7, magnets facing different magnetic poles are arranged vertically at a position offset from the magnetic material stripe in the off state. The magnet arrangements shown in Figures 12 to 16 correspond to the movement of the movable magnet plate shown in Figure 7.

[0036] Figure 12 illustrates the change in the position of the magnets when switching between on and off, when the stripe pattern is the same as that shown in Figure 9A, and the width of the magnets is the same as the width of the magnetic stripe. In the on state, similar to the on state in the upper part of Figure 10, multiple magnets (two in the illustrated example) belonging to different magnet rows connect the same magnetic pole surface to a single magnetic stripe and are arranged vertically along the magnetic stripe. When switching from the on state to the off state, first the lower movable magnet row (movable magnet row on the main plate) slides one step, resulting in the upper center state where magnets with different magnetic pole surfaces are arranged vertically along the magnetic stripe. This state is the same as the off state in the configuration example of Figure 10, which uses a fixed magnet row. In the configuration where all magnet rows are movable, the magnet rows slide one more step from this state. By sliding both rows of magnets, the positional relationship between the magnets shown in the upper center is maintained, and each magnet crosses the non-magnetic stripe and connects to the magnetic stripe on either side, resulting in the off state (Figure 12 right). This arrangement results in two magnets with oppositely oriented magnetic poles being simultaneously connected to a single magnetic stripe within the same magnet row. As a result, the magnetic flux is contained not only vertically but also horizontally within a single magnetic stripe, creating an "off" state. This configuration is thought to further reduce the magnetic field strength generated in the magnetic field generating section when the device is off. In the example shown in Figure 12, the sliding movement from the first to the second stage is half the width of the magnetic stripe, but the movement is not limited to this example, as it is sufficient for one magnet to straddle a non-magnetic stripe and connect to the magnetic stripes on either side of it. The same applies to Figures 13-16. When switching from the off state to the on state, the lower movable magnet row first slides one stage, resulting in the lower center state where magnets with the same magnetic pole faces are aligned vertically. Then, the second stage of sliding causes both rows of magnets to slide, resulting in the on state magnet configuration.

[0037] Figure 13 illustrates the change in the position of the magnets when switching between on and off, when the stripe pattern is the same as that shown in Figure 9B, and the width of the magnets is the same as the width of the magnetic stripe. In the on state, similar to the on state in the middle of Figure 10, multiple magnets (two in the illustrated example) belonging to different magnet rows connect the same magnetic pole surface to a single magnetic stripe and are arranged vertically along the magnetic stripe. When switching from the on state to the off state, first the lower movable magnet row (movable magnet row on the main plate) slides one step, resulting in the upper center state (same state as the off state in the configuration example of Figure 10 which uses a fixed magnet row) where magnets with different magnetic pole surfaces are arranged vertically along the magnetic stripe. Next, with a second sliding movement, while maintaining the relative positions of the magnets shown in the upper center, each magnet crosses the non-magnetic stripe and connects to the magnetic stripe on either side, resulting in the off state (Figure 13 right). Unlike Figure 12, within each magnet row, magnets facing the same pole face are arranged alternately in pairs. This results in locations where two adjacent magnets facing the same pole face connect to a single magnetic stripe simultaneously, and locations where two adjacent magnets facing different pole faces connect to a single magnetic stripe simultaneously. In the latter cases, the magnetic flux is also completed in the left-right direction. Even with this configuration, it is thought that the magnetic field strength generated in the magnetic field generation section when off can be further reduced compared to the configuration using a fixed magnet row where the state at the top center of Figure 13 is the off state. When switching from the off state to the on state, first the lower movable magnet row slides one step, resulting in the state at the bottom center where magnets facing the same pole face are arranged vertically. Then, in the second step of sliding, both rows of magnets slide, resulting in the magnet arrangement for the on state.

[0038] Figure 14 illustrates the change in the position of the magnets when switching between on and off, when the stripe pattern is the same as that shown in Figure 9C, and the width of the magnets is the same as the width of the magnetic stripe. In the on state, similar to the on state in the lower part of Figure 10, multiple magnets (two in the illustrated example) belonging to different magnet rows connect the same magnetic pole surface to a single magnetic stripe and are arranged vertically along the magnetic stripe. When switching from the on state to the off state, first the lower movable magnet row (movable magnet row on the main plate) slides one step, resulting in the upper center state (same state as the off state in the configuration example of Figure 10 which uses a fixed magnet row) where magnets with different magnetic pole surfaces are arranged vertically along the magnetic stripe. Next, with a second sliding movement, while maintaining the relative positions of the magnets shown in the upper center, each magnet crosses the non-magnetic stripe and connects to the magnetic stripe on either side, resulting in the off state (Figure 14 right). Unlike Figure 12, within each magnet row, three magnets facing the same pole face are arranged alternately in sets of three. As a result, there are locations where two adjacent magnets facing the same pole face connect to a single magnetic stripe simultaneously, and locations where two adjacent magnets facing different pole faces connect to a single magnetic stripe simultaneously. In the latter case, the magnetic flux is also completed in the left-right direction. Even with this configuration, it is thought that the magnetic field strength generated in the magnetic field generating section when off can be further reduced compared to the configuration using a fixed magnet row where the state at the top center of Figure 14 is the off state. When switching from the off state to the on state, first the lower movable magnet row slides one step, resulting in the state at the bottom center where magnets facing the same pole face are arranged vertically. Then, in the second step of sliding, both rows of magnets slide, resulting in the magnet arrangement for the on state.

[0039] Figures 15 and 16 illustrate the positional changes of the magnets when switching between on and off in a stripe pattern where the first external magnetic material piece 101 and the second external magnetic material piece 102 are arranged alternately in sets of m pieces, with an external non-magnetic material piece 111 in between, and the left-right width of the magnets is the same as the left-right width of one set of magnetic stripes. Figure 15 is an explanatory diagram for the m=2 stripe pattern shown in Figure 9B, and Figure 16 is an explanatory diagram for the m=3 stripe pattern shown in Figure 9C. In this embodiment, in each magnet row, one magnet is arranged alternately with different magnetic pole faces facing inward and outward. In the off state, permanent magnets with different magnetic pole faces are lined up next to each other in the vertical direction and connected to the magnetic stripes (external and internal magnetic material pieces 101, 102, 201, 202), and one permanent magnet is connected to (m+1) magnetic stripes across m non-magnetic stripes. The following explanation describes the change in the magnet's position when switching between on and off modes, based on Figures 15 and 16.

[0040] In the m=2 configuration, as shown in Figure 15, in the ON state, multiple magnets (two in the illustrated example) belonging to different magnet rows are arranged vertically with the same magnetic pole faces connected to one set of magnetic stripes. When switching from the ON state to the OFF state, first the lower movable magnet row (movable magnet row on the main plate) slides one step, resulting in the upper center state (the same state as the OFF state in the configuration example in Figure 11, which uses a fixed magnet row), where magnets with different magnetic pole faces are arranged vertically along one set of magnetic stripes. Next, in the second step of sliding, the two rows of magnets slide while maintaining the relative positions of the magnets shown in the upper center, resulting in the OFF state where one permanent magnet spans two non-magnetic stripes and connects to (2+1) magnetic stripes (Figure 15 right). In some magnetic stripes, two adjacent magnets with different magnetic pole faces are simultaneously connected to one magnetic stripe, completing the magnetic flux in the left-right direction as well. Even with this configuration, it is thought that the magnetic field strength generated in the magnetic field generating section when off can be further reduced compared to a configuration using a fixed magnet array where the state at the top center of Figure 15 is the off state. When switching from the off state to the on state, first the lower movable magnet array slides one step, resulting in the state at the bottom center where magnets with the same magnetic pole faces are aligned vertically. Then, in a second sliding step, both rows of magnets slide, resulting in the magnet arrangement for the on state.

[0041] In the m=3 configuration, as shown in Figure 16, in the ON state, multiple magnets (two in the illustrated example) belonging to different magnet rows are arranged vertically with the same pole faces connected to one set of magnetic stripes. When switching from the ON state to the OFF state, first the lower movable magnet row (movable magnet row on the main plate) slides one step, resulting in the upper center state (the same state as the OFF state in the configuration example in Figure 11, which uses a fixed magnet row), where magnets with different pole faces are arranged vertically along one set of magnetic stripes. Next, in the second sliding step, the two rows of magnets slide while maintaining the relative positions of the magnets shown in the upper center, resulting in the OFF state where one permanent magnet spans three non-magnetic stripes and connects to (3+1) magnetic stripes (Figure 16 right). In some magnetic stripes, two adjacent magnets with different pole faces are simultaneously connected to one magnetic stripe, completing the magnetic flux in the left-right direction as well. Even with this configuration, it is thought that the magnetic field strength generated in the magnetic field generating section when off can be further reduced compared to a configuration using a fixed magnet array where the state in the upper center of Figure 16 is the off state. When switching from the off state to the on state, first the lower movable magnet array slides one step, resulting in the state in the lower center where magnets with the same magnetic pole faces are arranged vertically. Then, in a second sliding step, both rows of magnets slide, resulting in the magnet arrangement for the on state.

[0042] The external and internal magnetic pieces, the upper and lower magnetic field application yokes, and the yoke pieces are formed from magnetic materials. Specific examples of magnetic materials include elemental iron, cobalt, nickel, and gadolinium, as well as compounds containing one or more of the following: iron, cobalt, nickel, gadolinium, chromium, and manganese, and martensitic stainless steel. All of the above parts may be formed from the same magnetic material, or some or all of the components may be formed from different magnetic materials.

[0043] The external and internal non-magnetic pieces, non-magnetic small pieces, and the main body of the magnet plate that holds the permanent magnet are made of non-magnetic material. "Non-magnetic material" does not mean a material that does not conduct magnetism at all, but rather a material that has a very large difference in permeability (for example, several hundred to several thousand times or more) compared to the magnetic material used. Specific examples of non-magnetic materials include non-magnetic metals such as copper, zinc, tin, lead, aluminum, magnesium, sulfur, and titanium, or compounds containing one or more of these (e.g., brass, bronze), and austenitic stainless steel; petroleum-based materials such as plastics, polyethylene, and vinyl; non-metallic and non-petroleum-based materials such as rubber and glass; and plant-derived materials such as natural fibers (cotton, etc.), natural resins, wood, and wood products (paper, etc.).

[0044] The tunable magnetic field circuit of the present invention can be used in various devices or systems that utilize a magnetic circuit capable of controlling the magnetic field. Specifically, the tunable magnetic field circuit of the present invention can be used as a beam deflector for accelerators, or as a uniform magnetic field generator used in magneto-optical measuring devices. Specific examples of devices or systems that can utilize the tunable magnetic field circuit of the present invention as a beam deflector include, for example, relatively small devices or systems such as medical linacs used in cancer treatment and electron microscopes, and for example, large devices or systems such as heavy ion beam therapy facilities, synchrotron radiation facilities, and large-scale colliders. In these devices or systems, the tunable magnetic field circuit of the present invention can be used as the entire beam deflector, or in combination with electromagnets as appropriate. Furthermore, the tunable magnetic field circuit of the present invention can also be used in devices or systems used in laboratories for magneto-optical measurements. When using the tunable magnetic field circuit of the present invention to generate a uniform magnetic field during magneto-optical measurements of optical crystals with sides ranging from several millimeters to several centimeters, it becomes possible to maintain a constant magnetic field strength without changing the temperature of the optical crystal. [Examples]

[0045] The present invention will be described more specifically below based on examples. However, the present invention is not limited to the following examples.

[0046] In the variable magnetic field circuit shown in Figures 1-3, where magnetic and non-magnetic stripes are arranged alternately, a three-dimensional static magnetic field analysis was performed using Ansys Maxwell software to simulate the magnetic flux distribution in the XY plane for two cases: when the magnetic poles of the magnet array are aligned in the same direction (on state) and when the magnetic poles of the magnet array are aligned in opposite directions (off state). As shown in the upper part of Figure 17, when the magnetic poles of the magnet array are aligned in the same direction, the magnetic flux makes a full circuit through all the yokes, and a uniformly uniform magnetic field of maximum strength is generated in the air gap. On the other hand, as shown in the lower part of Figure 17, when the magnetic poles of the magnet array are aligned in opposite directions, the magnetic flux circulates within the first external magnetic material piece and the second internal magnetic material piece, and the magnetic flux does not propagate to other yokes. Therefore, the magnetic flux does not propagate in the air gap, and the magnetic field strength is zero. As shown in Figure 18, when the pitch between magnets in the movable magnet array is L = 30 mm, a uniform zero magnetic field is generated in the Z direction at L = 0 mm (when the magnetic poles of the magnet array are aligned in opposite directions). As the movable magnet array is slid in the Z-axis direction, a magnetic field of 95.7 gauss can be generated at L = 10 mm, 192 gauss at L = 15 mm, 287 gauss at L = 20 mm, and a maximum intensity of 381 gauss can be generated at L = 30 mm (when the magnetic poles of the magnet array are aligned in the same direction). When this is displayed on a graph, it is possible to continuously vary the magnetic field as shown in Figure 19. [Explanation of Symbols]

[0047] 1. Variable Magnetic Circuit 10 External fixing plate 20 Internal fixing plate 30 Magnetic Plates 31 Fixed magnetic plate 32, 32' Movable Magnet Plate 33 Fixed magnet array 34 movable magnet array 40 Upper magnetic field applied yoke 50 Lower magnetic field Sanctuary York 60. Gap (magnetic field generation part) 101 First external magnetic piece 102 Second external magnetic piece 111 External non-magnetic piece 112 First external non-magnetic fragment 113 Second external non-magnetic fragment 201 First internal magnetic piece 202 Second internal magnetic material piece 203 First York Piece 204 Second York Piece 211 Internal non-magnetic piece 212 First internal non-magnetic fragment 213 Second internal nonmagnetic fragment 330 Fixed Magnets North pole surface of a 330N fixed magnet 330S Fixed Magnet's S Pole Surface 340 movable magnets North pole surface of a 340N movable magnet 340S movable magnet's south pole surface

Claims

1. A variable magnetic field circuit comprising an external fixing plate and an internal fixing plate, which are constructed by arranging multiple magnetic pieces in a stripe pattern in combination with multiple non-magnetic pieces; a magnet plate, which is positioned between these fixing plates and includes two or more rows of magnets in which multiple permanent magnets are aligned in a left-right direction perpendicular to the stripe pattern of the external and internal fixing plates; and an upper magnetic field application yoke and a lower magnetic field application yoke coupled to the internal fixing plate, The upper magnetic field application yoke and the lower magnetic field application yoke have one end connected to an internal fixing plate, and the other end is separated to form a gap that becomes a magnetic field generation section. The aforementioned magnet plate includes a movable magnet plate that is slidable in the left-right direction and includes at least one row of magnets. Within each of the aforementioned arrays of magnets, one or m permanent magnets (where m means any number of magnets up to a few; the same applies hereinafter) are arranged alternately at regular intervals with different magnetic pole faces facing inward and outward, and the intervals are approximately the same as the intervals between the stripes of non-magnetic material pieces on the external and internal fixing plates. The external fixing plate includes a first external magnetic piece positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but does not reach the lower end of the plate, a second external magnetic piece positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but does not reach the upper end of the plate, and an external non-magnetic piece that is longer than the first and second external magnetic pieces, and the first external magnetic piece and the second external magnetic piece are arranged alternately in sets of one or m pieces in the left-right direction with the external non-magnetic piece in between to form a stripe-like pattern on the external fixing plate. The internal fixing plate includes a first internal magnetic piece positioned on the upper end of the plate and having a length that reaches the lowest row of magnets but not the lower end of the plate, a second internal magnetic piece positioned on the lower end of the plate and having a length that reaches the uppermost row of magnets but not the upper end of the plate, an internal non-magnetic piece longer than the first and second internal magnetic pieces, a first yoke piece positioned on the lower end of the plate and aligned with the first internal magnetic piece in the stripe direction, and a second yoke piece positioned on the upper end of the plate and aligned with the second internal magnetic piece in the stripe direction, wherein the first and second yoke pieces protrude from the surface of the internal fixing plate toward the external fixing plate and contact the second external magnetic piece and the first external magnetic piece, respectively, and the first and second internal magnetic pieces are arranged alternately in sets of one or m pieces in the left-right direction with the internal non-magnetic piece in between, forming a stripe-like pattern on the internal fixing plate. A variable magnetic field circuit is provided in which the arrangement of permanent magnets can be changed by sliding a movable magnet plate, between an ON state in which permanent magnets facing the same magnetic poles are arranged adjacently in the vertical direction and connected to external and internal magnetic material pieces, and an OFF state in which permanent magnets facing different magnetic poles are arranged adjacently in the vertical direction and connected to external and internal magnetic material pieces, thereby changing the magnetic field strength of the magnetic field generating section.

2. The magnetic plate includes a movable magnetic plate that can slide horizontally and includes at least one row of magnets, and a fixed magnetic plate that is in a fixed position and includes at least one row of magnets. The variable magnetic field circuit according to claim 1, wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of one or one set of magnetic material pieces, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of one or one set of magnetic material pieces.

3. In the external fixing plate, one first external magnetic piece and one second external magnetic piece are arranged alternately, and in the internal fixing plate, one first internal magnetic piece and one second internal magnetic piece are arranged alternately. The left-right width of each permanent magnet is approximately the same as the stripe width of the external and internal magnetic material pieces. In each magnet array, one permanent magnet is arranged alternately with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 2, wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a magnetic material piece, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of a magnetic material piece.

4. In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately. The left-right width of each permanent magnet is approximately the same as the stripe width of the external and internal magnetic material pieces. In each magnet array, m permanent magnets are arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 2, wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a magnetic material piece, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a stripe of a magnetic material piece.

5. In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately. The width of each permanent magnet is approximately the same as the width of a set of m external magnetic pieces with an external non-magnetic piece in between, and the width of a set of m internal magnetic pieces with an internal non-magnetic piece in between. In each magnet array, one permanent magnet is arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 2, wherein in the ON state, multiple permanent magnets are arranged vertically with the same pole faces connected to a stripe of a set of magnetic material pieces, and in the OFF state, multiple permanent magnets are arranged vertically with different pole faces connected to a set of magnetic material pieces.

6. The stripe width of the magnetic material and the left-right width of the permanent magnet are greater than the stripe width of the non-magnetic material. The variable magnetic field circuit according to claim 1, wherein the magnetic plate includes two movable magnetic plates, each containing at least one row of magnets, and the on and off states are switched by sliding the two movable magnetic plates.

7. In the external fixing plate, one first external magnetic piece and one second external magnetic piece are arranged alternately, and in the internal fixing plate, one first internal magnetic piece and one second internal magnetic piece are arranged alternately. The left-right width of each permanent magnet is approximately the same as the stripe width of the external and internal magnetic material pieces. In each magnet array, one permanent magnet is arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 6, wherein in the ON state, multiple permanent magnets are arranged vertically with the same magnetic pole faces connected to a stripe of a single magnetic material piece, and in the OFF state, magnets with different magnetic pole faces are arranged adjacent to each other vertically, and one permanent magnet connects to two magnetic material pieces across one non-magnetic material piece.

8. In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately. The left-right width of each permanent magnet is approximately the same as the stripe width of the external and internal magnetic material pieces. In each magnet array, m permanent magnets are arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 6, wherein in the ON state, multiple permanent magnets are arranged vertically with the same magnetic pole faces connected to a stripe of a single magnetic material piece, and in the OFF state, magnets with different magnetic pole faces are arranged adjacent to each other vertically, and one permanent magnet connects to two magnetic material pieces across one non-magnetic material piece.

9. In the external fixing plate, m sets of first external magnetic material pieces and second external magnetic material pieces are arranged alternately, and in the internal fixing plate, m sets of first internal magnetic material pieces and second internal magnetic material pieces are arranged alternately. The width of each permanent magnet is approximately the same as the width of a set of m external magnetic pieces with an external non-magnetic piece in between, and the width of a set of m internal magnetic pieces with an internal non-magnetic piece in between. In each magnet array, one permanent magnet is arranged alternately at regular intervals, with different magnetic pole faces oriented inward and outward. The variable magnetic field circuit according to claim 6, wherein in the ON state, multiple permanent magnets are arranged vertically with the same magnetic pole faces connected to a stripe of a set of magnetic material pieces, and in the OFF state, magnets with different magnetic pole faces are arranged adjacent to each other vertically, and one permanent magnet is connected to (m+1) magnetic material pieces across m non-magnetic material pieces.

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