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Uniformity of magnetic field is an important parameter of magnetic resonance system. Improving the uniformity of magnetic field is helpful for detecting the magnetic resonance time domain signal and improving the resolution of magnetic resonance frequency domain signal. Based on the idea of continuous current density distribution in an active shimming field, the shimming coil is designed by combining the target field point method with the current function method. That is to say, the relationship between magnetic field distribution and current density is determined by Biot-Savart law. After confining the coil radius and setting the constraint point, the current density distribution on the coil plane is inversely solved according to the target field distribution. Then the current density distribution is discretized by the current function, and the winding position distribution of the uniform field coil is obtained. According to the results of electromagnetic simulation, the first-order and second-order shimming coils are fabricated and applied to the magnetic resonance analyzer. The experimental results show that the shimming coils can effectively improve the magnetic field uniformity of the permanent magnet in nuclear magnetic resonance (NMR) system.
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阶次 次序 分量 系数 球坐标系 直角坐标系 ($r,\;\,\theta,\;\,\phi $) ($x,\;\,y,\;\,z$) 0 0 Z0 A01 1 1 1 0 Z 2A02 rcosθ z 1 1 X 3A12 rsinθcosϕ x 1 1 Y 3B12 rsinθsinϕ y 2 0 Z2 3A03 r2(3cos2θ–1)/2 z2–(x2+y2)/2 2 1 XZ 12A13 r2cos θsinθcosϕ xz 2 1 YZ 12B13 ${r^2}\cos \theta {\rm{sin}}\theta {\rm{sin}}\phi $ yz 2 2 X2–Y2 15A23 ${r^2}{\rm{si}}{{\rm{n}}^2}\theta {\rm{cos}}2\phi $ x2–y2 2 2 2XY 15B23 ${r^2}{\rm{si}}{{\rm{n}}^2}\theta {\rm{sin}}2\phi $ 2xy 3 0 Z3 4A04 ${r^3}\cos \theta (5{\cos ^2}\theta - 3)/2$ $z[{z^2} - 3\left( {{x^2} + {y^2}} \right)/2]$ 3 1 XZ2 15A14 ${r^3}\sin \theta \cos \phi (5{\cos ^2}\theta - 1)/2$ $x[4{z^2} - \left( {{x^2} + {y^2}} \right)]$ 3 1 YZ2 15B14 ${r^3}\sin \theta \sin \phi (5{\cos ^2}\theta - 1)/2$ $y[4{z^2} - \left( {{x^2} + {y^2}} \right)]$ 3 2 Z(X2–Y2) 90A24 ${r^3}{\rm{cos}}\theta {\rm{si}}{{\rm{n}}^2}\theta {\rm{cos}}2\phi $ z(x2–y2) 3 2 XYZ 90B24 ${r^3}{\rm{cos}}\theta {\rm{si}}{{\rm{n}}^2}\theta {\rm{sin}}2\phi $ 2xyz 3 3 X3 105A34 ${r^3}{\rm{si}}{{\rm{n}}^3}\theta {\rm{cos}}3\phi $ ${x^3} - 3x{y^2}$ 3 3 Y3 105B34 ${r^3}{\rm{si}}{{\rm{n}}^3}\theta {\rm{sin}}3\phi $ $3{x^2}y - {y^3}$ 4 0 Z4 5A05/8 ${r^4}(35{\cos ^4}\theta - 30{\rm{co}}{{\rm{s}}^2}\theta + 3)$ $8{z^4} - 24{z^2}\left( {{x^2} + {y^2}} \right) + 3{\left( {{x^2} + {y^2}} \right)^2}$ … … 
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有源匀场线圈 FID信号(积分区域) 频谱半高宽/Hz 磁场均匀性/ppm 匀场前 1270683 338 19.17 一阶线圈匀场 3937325 98 18.23 二阶线圈匀场 4866520 48 1.98 DownLoad:
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
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