A method of designing a room temperature shimming coil

Abstract

The application relates to a room temperature shimming coil design method. The shimming coil design method uses the contour line of a flow function as a center line of a coil conductor, draws a circle with a point on the contour line as a center to determine a boundary line of the conductor, adjusts the width of the transformed conductor while keeping the width cutting line, and can keep the wiring precision of the conductor. The method significantly improves the magnetic field precision of the shimming coil and helps to improve the magnetic field uniformity of a superconducting magnet.

Description

Technical Field

[0001] This invention belongs to the field of magnetic resonance, specifically relating to a room temperature shimming coil design method. Background Technology

[0002] Extremely high-field magnetic resonance imaging (MRI) offers significant advantages in imaging and material detection. The extremely high field can substantially improve the signal-to-noise ratio (SNR) of the MRI system, thereby enhancing the sensitivity for detecting minute materials. However, realizing these advantages requires a highly homogeneous magnetic field. Magnetic field inhomogeneity reduces the SNR of the MRI equipment and causes magnetic field spatial distortion, leading to signal loss and image artifacts. Although the magnetic field homogeneity of the target region is considered during the design of superconducting magnets, new magnetic field errors are introduced during the actual manufacturing and installation processes, compromising the homogeneity. In the extremely high magnetic fields generated by superconducting magnets, the corresponding non-uniform magnetic field components are also substantial, necessitating high-performance shimming techniques. In the design of active shimming coils, the contour plots of the stream function can be obtained using the target field method and the stream function method. In existing technologies, one coil structure uses thin wires directly along the contour lines of the stream function. This results in coils with excessively high resistance, unable to handle large currents, leading to high power loss, heat generation, and low sensitivity, thus limiting shimming performance. Another traditional coil structure uses a copper plate cutting method that directly cuts along the contour lines of the stream function. The resulting coil current trend differs significantly from the contour lines of the stream function, resulting in low magnetic field fidelity and reduced field uniformity accuracy.

[0003] Chinese patent application CN1536594A discloses a method for manufacturing a shimming coil, which forms the shimming coil by cutting or stamping the desired coil pattern in a sheet of conductive material, and proposes that the pattern can be stamped using a CNC punch or a stamping machine. The coils used are transverse saddle-shaped shimming coils and axial shimming coils, and the coil pattern design differs from the shimming coil pattern design of this invention. US patent US6311389B1 discloses a method for manufacturing a coil, in which a bent metal plate is attached to a fixture, the metal plate is cut along the contour of the coil winding, and the excess plate portion other than the coil winding is removed from the metal plate, leaving the coil winding on the fixture, thus manufacturing a saddle-shaped coil that fixes the helical coil inside a bent cylindrical insulating sheet. The helical coil used differs from the coil structure of this invention, and the spacing between the conductors is not equal. Chinese patent application CN106782998A discloses a planar fingerprint shimming coil group, which improves the magnetic field uniformity of the target area by applying current to each group of fingerprint coils to generate a corresponding magnetic field to compensate for the magnetic field in the central region. The coil used therein is wound with superconducting tape, and the manufacturing method is different from the coil manufacturing method of the present invention. Summary of the Invention

[0004] This invention aims to address the problems of insufficient shimming capability, high power loss, and low magnetic field fidelity in the design of shimming coils for ultra-high field superconducting magnets, which are difficult to meet the shimming performance requirements of ultra-high field superconducting magnets. To this end, this invention proposes a room-temperature shimming coil design method, which uses the stream function line as the center line of the coil conductor and maintains a uniform width cutting line. This method reduces the coil resistance and facilitates processing, improves the coil current carrying capacity and reduces power loss, optimizes the current density distribution of the coil, and improves the magnetic field accuracy, thereby improving the shimming performance of the coil.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first step is to use the contour lines of the stream function unfolded from the cylindrical plane as the center lines of the coil conductor. The boundary lines of the conductor are determined using the common tangents between circles centered on points on the stream function contour lines. The shortest distances from the stream function contour lines to the two boundary lines of the conductor are consistent. First, determine one side boundary line of the outer coil conductor as the known boundary. Then, using points on the stream function contour lines as centers and the shortest distance from those points to the known boundary as the radius, draw circles. Draw the common tangents between adjacent circles in sequence. Next, use straight lines to approximate the arcs between adjacent common tangents, and connect the adjacent common tangents with straight lines to form the other boundary line of the conductor.

[0007] The second step involves maintaining uniform cutting lines and designing each turn of the coil sequentially, starting with the outer turn and then moving to the inner turn. The inner boundary of the outer turn is offset inwards by a fixed cutting line width to obtain the outer boundary of the next turn. Similarly, the contour lines of the stream function are used as the center line of the next turn, and the method from the previous step is repeated to obtain the inner boundary of the next turn. This process is repeated, drawing each turn of the coil sequentially from the outside in, thus obtaining the coil's planar unfolded structure.

[0008] The third step involves using a cutting head to cut a planar copper coil, unfolded from a cylindrical surface, directly along a uniform cutting line on the copper plate. Finally, sheet metal processing is used to bend the cut planar copper coil into a three-dimensional cylindrical uniform field coil.

[0009] Beneficial effects:

[0010] The shimming coil of this invention is used to adjust the uniformity of the background magnetic field generated by an ultra-high field superconducting magnet. The ultra-high field places high demands on the performance of the shimming coil. Existing methods, such as directly arranging thin wires along the stream function contour lines, result in coils with excessively high resistance, limiting shimming performance. Traditional copper plate cutting methods, which involve cutting along the stream function contour lines, result in coils with significant magnetic field offsets. Therefore, this invention proposes a method using the stream function line as the centerline of the coil wire while maintaining a uniform cutting width. This method reduces coil resistance and facilitates manufacturing, improves the coil's current carrying capacity and reduces power loss, optimizes the current density distribution of the coil, and improves magnetic field accuracy, thereby enhancing the coil's shimming performance. Attached Figure Description

[0011] Figure 1 This is a flowchart of a room temperature uniform field coil design method according to the present invention;

[0012] Figure 2a , Figure 2b , Figure 2c This is a schematic diagram illustrating a specific implementation method of the room temperature shimming coil of the present invention, using the contour lines of the stream function as the center lines of the coil conductors; wherein, Figure 2a This is a schematic diagram showing the drawing of circles centered at points on the contour lines of the stream function and the common tangent between adjacent circles. Figure 2b This is a schematic diagram showing how adjacent common tangents are connected by straight lines to form another boundary line of a conductor. Figure 2c This is a schematic diagram of copper wires cut from a copper plate.

[0013] Figure 3a , Figure 3b This is a diagram of the room temperature shimming coil structure of the present invention, wherein... Figure 3a This is a planar development diagram of the shimming coil. Figure 3b This is a three-dimensional coil structure diagram of a shimming coil;

[0014] Explanation of the reference numerals in the attached figures: 1 is the contour line of the stream function, 2 is the known boundary line of the traverse, 3 is the common tangent, 4 is a straight line, 5 is the cut-off part, 6 is the remaining part after cutting, 7 is the first turn of the traverse, 8 is the second turn of the traverse, 9 is the third turn of the traverse, 10 is the fourth turn of the traverse, and 11 is the fifth turn of the traverse. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0016] like Figure 1As shown, the room temperature shimming coil design method of the present invention includes the following steps:

[0017] The first step is to use the contour lines of the stream function expanded from the cylindrical plane as the center lines of the coil conductors. The specific implementation method is as follows: Figure 2a , Figure 2b , Figure 2c As shown. The boundary line of the conductor is determined by the common tangent between circles centered at points on the contour line 1 of the stream function. The shortest distances from the contour line 1 of the stream function to the boundary lines on both sides of the conductor are the same. First, determine one side boundary line of the first turn conductor 7, which is the outermost turn of the coil, as the known boundary line 2 of the conductor. Then, draw circles centered at points on the contour line 1 of the stream function, with the shortest distance from that point to the known boundary as the radius. Draw the common tangent line 3 between adjacent circles in sequence, as shown. Figure 2a As shown. Next, a straight line is used to approximate the arc between adjacent common tangents 3. The adjacent common tangents 3 are connected by a straight line 4 to form another boundary line of the conductor, as shown. Figure 2b As shown. During final processing, the designed wires will be cut out on the copper plate. The remaining portion 6 after cutting is the required copper wire for the coil, as shown. Figure 2c As shown.

[0018] The second step involves maximizing the wire width to reduce resistance, ensuring the spacing between each turn of wire is controlled to be the minimum machinable cutting edge width of 1mm, i.e., the cutting line width is 1mm. The turns of wire are designed sequentially, starting with the outer turns and then the inner turns. The inner boundary of the first turn of wire 7, obtained in the previous step, is offset inward by a cutting line width of 1mm to obtain the outer boundary of the second turn of wire 8. Similarly, the contour line of the corresponding stream function line is used as the center line of the second turn of wire, and the method from the previous step is repeated to obtain the inner boundary of the second turn of wire 8. Then, the inner boundary of the second turn of wire 8 is offset inward by a cutting line width of 1mm to obtain the outer boundary of the third turn of wire 9, and so on. The fourth turn of coil 10 and the fifth turn of coil 11 are then drawn sequentially from the outside in using the same method, resulting in one sub-coil of the shimming coil. The shimming coil includes four sub-coils, all of which are fingerprint-type coils with identical structures. The shimming coil consists of 20 turns of wire, with each sub-coil having 5 turns. First, design one sub-coil of the shimming coil using the method described above. Then, by translating and rotating this sub-coil, obtain three other sub-coils, thus obtaining the planar unfolded structure of the entire shimming coil, as shown below. Figure 3a As shown.

[0019] The third step involves using an X-type shimming coil, as shown in this example. Due to the spatial constraints of the superconducting magnet magnetic resonance system in which this shimming coil is located, the coil's radial thickness along the cylinder is 0.5 mm. Therefore, a 0.5 mm thick copper plate is used for cutting during coil fabrication. Based on the coil's planar unfolded structure diagram, a 1 mm wide cutting head is used to cut the cylindrical unfolded planar copper coil directly along the wire spacing, i.e., the equal-width cutting line, on the copper plate. Finally, using sheet metal processing, the cut planar copper coil is bent to a designed inner radius of 13.31 mm and an outer radius of 13.81 mm to create a three-dimensional shimming coil, as shown below. Figure 3b As shown.

[0020] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is 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 within the scope of protection of the present invention.

Claims

1. A method of designing a room temperature shimming coil, characterized in that, Using the stream function line as the center line of the coil conductor and keeping the cutting line with equal width, the method comprises the following steps: Firstly, using the contour line of the stream function as the center line of the coil conductor, the common tangent line between the circles with the points on the contour line of the stream function as the center is used to determine the boundary line of the conductor; the shortest distance from the contour line of the stream function to the two side boundary lines of the conductor is consistent; the side boundary line of the outer turn of the coil conductor is determined as the known boundary, then the circle with the point on the contour line of the stream function as the center and the shortest distance from the point to the known boundary as the radius is drawn, the common tangent line between the adjacent circles is drawn in turn, the straight line is used to approximate the circular arc between the adjacent common tangent lines, the other boundary line of the conductor is obtained by connecting the adjacent common tangent lines with the straight line; Secondly, keeping the cutting line with equal width, each turn of the conductor is designed in turn according to the order of the outer turn and the inner turn, and then the planar structure diagram of the coil is obtained; the interval between the turns of the coil is consistent, i.e. the cutting line is equal in width; The inner boundary of the outer turn of the conductor is offset inward by a fixed size cutting line width to obtain the outer boundary of the next turn of the conductor; then the contour line of the stream function is used as the center line of the next turn of the coil conductor, the method of the previous step is repeated to obtain the inner boundary of the next turn of the conductor, and the turns of the coil are drawn in turn from the outside to the inside; Thirdly, the cutting head is used to cut the planar copper coil after the cylindrical surface is unfolded along the cutting line with equal width; finally, the planar copper coil is bent into a three-dimensional cylindrical shimming coil by using the sheet metal process.

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