Equivalent magnetic dipole method used to design gradient coil for unilateral magnetic resonance imaging

The conventional magnetic resonance imaging(MRI) equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure. In order to realize the mobile MRI, this study focuses on the design of gradient coil of unilateral magnet. The unilateral MRI system is used to image the local area above the magnet. The current density distribution of the gradient coil cannot be used as a series of superconducting nuclear magnetic resonance gradient coils, because the region of interest(ROI) and the wiring area of the unilateral magnet are both cylindrical side arc surfaces. Therefore, the equivalent magnetic dipole method is used to design the gradient coil, and the algorithm is improved for the special case of the wiring area and the ROI, so the X and Y gradient coils are designed.Finally, a flexible printed circuit board(PCB) is used to fabricate the gradient coil, and the magnetic field distribution of the ROI is measured by a Gauss meter, and the measured results match with the simulation results. The gradient linearities of x and y coils are 2.82% and 3.56%, respectively, less than 5% of the commercial gradient coil requirement.     

欧洲FAIR中超导二极磁体样机的初步设计与分析

介绍了欧洲FAIR超导二极磁体样机设计的背景及设计要求,以及磁体样机的几个大部件及其作用。用有限元分析软件ANSYS进行了线圈电磁性能分析,得到其磁场、电感、储能随电流的变化曲线,并对其中的一个部件线圈盒进行了结构分析,为下一步的设计提供参考。     

GSI超导二极磁体的电磁分析

主要介绍超导二级磁体的结构,用有限元分析软件ANSYS对磁体在工作电流下进行了电磁分析,结果符合物理设计要求,同时为下一步的结构分析提供了电动力。     

FAIR超导二极磁体实验失超保护系统设计与分析

阐述了超导磁体线圈实验过程中采用的平衡桥路电压失超检测及保护方案,对超导磁体电压失超检测电路进行了分析,提出了平衡桥路失超电压检测法选取原则。     

Calculation of magnetic field for 4 T fast cycling superconducting dipole magnet

The problem of optimization of the two-dimensional magnetic field distribution of a dipole magnet with a field of 4 T and aperture diameter of 100–110 mm for a fast cycling synchrotron is considered. A singlelayer winding with a small number of turns is made from a hollow NbTi superconducting cable with an operating current up to 30 kA. The mathematical method providing optimization of the higher harmonics amplitude of the magnetic field by varying the position of current windings is described. The results of calculation of two-dimensional magnetic fields of the superconducting magnet are given.     

The correspondence between a current-carrying coil and a magnetic dipole

The difficulties associated with the correspondence between the electric vectors E and D and the magnetic vectors B and H, when a current-carrying coil is considered as a magnetic dipole, are eliminated if it is considered, not as a simple dipole, but as a ‘dipotential’ or dipole with a constant potential difference.     

An Efficacious Target-Field Approach to Design Shim Coils for Halbach Magnet of Mobile NMR Sensors

The main magnetic fields of mobile nuclear magnetic resonance (NMR) magnets differ from those of conventional NMR and magnetic resonance imaging (MRI) magnets. In the Halbach magnet, the main field B ₀ is perpendicular to the longitudinal axis, the symmetry of the current distribution with respect to the symmetry of the magnetic field differs from that in conventional target-field applications, and the current distribution on the coil surface cannot be expressed in terms of periodic basis functions. To obtain the winding pattern of the coil, an efficacious target-field approach. The surface of a coil is divided into small discrete elements, where each element is represented by a magnetic dipole. From the stream function of the elements, the resultant magnetic field is calculated. The optimization strategy follows an objective function defined by the power dissipation or efficiency of the coil. This leads to the optimum stream function on the coil surface, whose contour lines define the winding patterns of the coil. This paper shows winding patterns designed of shim coils for Halbach magnet and illustrates the craft of a shim coil using flexible printed circuit board. The performance of the coils is verified by simulating the fields they produce over the sensitive volume.     

开放式线圈屏蔽高场超导MRI磁体的优化设计

提出了开放式高场线圈屏蔽超导MRI磁体的混合优化设计方法,所设计的开放式MRI磁体仅有2对超导线圈。首先采用ISIGHT集成有限元分析软件ANSYS,构成协同式集成优化设计平台,设计磁体的主线圈和屏蔽线圈;然后提出改进的电磁场形状优化方法,设计磁体的匀场铁环,最后通过MATLAB运行遗传算法调用ANSYS进一步优化成像区域(Diameter of Spherical Volume,DSV)的磁场不均匀度,以达到高质量成像的要求。通过一个1.2T的开放式MRI磁体的设计实例清楚地展示了这种优化方法。     

A low-field, low-cost Halbach magnet array for open-access NMR

A working prototype of a novel low-cost Halbach-array-based NMR system is described. The new design provides open access to the sample relative to conventional NMR magnet designs and this facilitates the simultaneous use of multi-sensor techniques on the same sample, in which NMR/MRI can potentially be combined with other spectroscopies such as impedance spectroscopy, laser scattering and rheological experiments.     

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阐述了FAIR收集环二极超导磁体电流引线的基本原理,给出了电流引线的主要参数及初步设计方案,提出了使用复合材料和通过结构优化以减小电流引线的漏热,并根据电流引线的传热特性进行了漏热的分析和计算,实验结果验证了概念设计的可行性。     

FAIR收集环二极超导磁体电流引线的概念设计

阐述了FAIR收集环二极超导磁体电流引线的基本原理,给出了电流引线的主要参数及初步设计方案,提出了使用复合材料和通过结构优化以减小电流引线的漏热,并根据电流引线的传热特性进行了漏热的分析和计算,实验结果验证了概念设计的可行性。     

Optimal Halbach permanent magnet designs for maximally pulling and pushing nanoparticles

Optimization methods are presented to design Halbach arrays to maximize the forces applied on magnetic nanoparticles at deep tissue locations. In magnetic drug targeting, where magnets are used to focus therapeutic nanoparticles to disease locations, the sharp fall off of magnetic fields and forces with distances from magnets has limited the depth of targeting. Creating stronger forces at a depth by optimally designed Halbach arrays would allow treatment of a wider class of patients, e.g. patients with deeper tumors. The presented optimization methods are based on semi-definite quadratic programming, yield provably globally optimal Halbach designs in 2 and 3-dimensions, for maximal pull or push magnetic forces (stronger pull forces can collect nanoparticles against blood forces in deeper vessels; push forces can be used to inject particles into precise locations, e.g. into the inner ear). These Halbach designs, here tested in simulations of Maxwell's equations, significantly outperform benchmark magnets of the same size and strength. For example, a 3-dimensional 36 element 2000 cm³ volume optimal Halbach design yields a 5× greater force at a 10 cm depth compared to a uniformly magnetized magnet of the same size and strength. The designed arrays should be feasible to construct, as they have a similar strength (≤1 T), size (≤2000 cm³), and number of elements (≤36) as previously demonstrated arrays, and retain good performance for reasonable manufacturing errors (element magnetization direction errors ≤5°), thus yielding practical designs to improve magnetic drug targeting treatment depths.     

磁记忆检测的力磁耦合型磁偶极子理论及解析解

磁偶极子理论在缺陷漏磁场解释中被成功广泛使用.由于磁荷密度等参数不易定量,磁偶极子理论在应用中常常进行归一化处理,被认为不适用于对应力相关的磁记忆信号做量化分析.本文通过建立力磁耦合型磁偶极子理论模型,以适用于分析磁记忆检测中应力对磁信号的影响.基于铁磁学理论确定应力和磁场联合作用下的等效场强度,基于弱磁化状态的一阶近...     

A design of novel type superconducting magnet for super—high field functional magnetic resonance imaging by using the harmonic analysis method of magnetic vector potentials

The approach of expanding the magnetic scalar potential in a series of Legendre polynomials is suitable for designing a conventional superconducting magnetic resonance imaging magnet of distributed solenoidal configuration. Whereas the approach of expanding the magnetic vector potential in associated Legendre harmonics is suitable for designing a single-solenoid magnet that has multiple tiers, in which each tier may have multiple layers with different winding lengths. A set of three equations to suppress some of the lowest higher-order harmonics is found. As an example, a 4T single-solenoid magnetic resonance imaging magnet with 4×6 layers of superconducting wires is designed. The degree of homogeneity in the 0.5m diameter sphere volume is better than 5.8 ppm. The same degree of homogeneity is retained after optimal integralization of turns in each correction layer. The ratio B_m/B₀ in the single-solenoid magnet is 30% lower than that in the conventional six-solenoid magnet. This tolerates higher rated superconducting current in the coil. The Lorentz force of the coil in the single-solenoid system is also much lower than in the six-solenoid system. This novel type of magnet possesses significant advantage over conventional magnets, especially when used as a super-high field functional magnetic resonance imaging magnet.     

FAIR收集环二极超导磁体外杜瓦泄放系统的概念设计

对FAIR(Facility for Antiproton and Ion Research)收集环-CR(Collector Ring)二极超导磁体外杜瓦的超压泄放系统进行了概念设计,给出了爆破片式的泄放系统结构,并基于ANSYS的结构分析初步确定了爆破片的结构参数;以及通过ANSYS对波纹管和外杜瓦进行了结构分析,分析结果表明波纹管和外杜瓦在超压状态下安全。文中的设计和分析研究,为外杜瓦的工程设计提供了有益的参考。