Open Permanent Magnet Research Articles

Proton Injector for Compact Neutron Source DARIA Systems Optimization

This paper is devoted to magnetic trap and extraction system upgrade of ECR ion source GISMO to utilize it as a proton injector for linear accelerator of compact neutron source DARIA. An open permanent magnet (Nd–Fe–B) trap was designed. It was adjusted to place the extraction system inside a part of magnet with larger inner diameter. Then, the three-electrode extractor optimization was made. It was shown that the use of additional magnetic lens allows to produce the proton beam with a low divergence angle. The use of the magnetic trap and the extraction system as a part of the proton injector for DARIA project possibility was shown using computer modeling. The following steps of the proton injector creation are discussed.

Influence of Magnetic Saturation and Rotor Eccentricity on Back EMF of Novel Hybrid-Excited Stator Slot Opening Permanent Magnet Machine

This paper introduces a novel hybrid-excited stator slot opening permanent magnet (PM) machine (HSSPMM). The operation principle of the machine is described and the effects of rotor eccentricity and magnetic saturation due to PMs on electromagnetic performance, with particular emphasis on back electromotive force (EMF), are analyzed by finite element method (FEM). It shows that different from the conventional PM machines, the open-circuit back EMF in this novel HSSPMM should be zero but may become non-zero if significant magnetic saturation exists, and furthermore, the rotor eccentricity has a detrimental effect on the waveforms, amplitudes, and symmetries of three-phase back EMFs, as confirmed by FEM and tests.

A permanent MRI magnet for magic angle imaging having its field parallel to the poles

A novel design of open permanent magnet is presented, in which the magnetic field is oriented parallel to the planes of its poles. The paper describes the methods whereby such a magnet can be designed with a field homogeneity suitable for Magnetic Resonance Imaging (MRI). Its primary purpose is to take advantage of the Magic Angle effect in MRI of human extremities, particularly the knee joint, by being capable of rotating the direction of the main magnetic field B0 about two orthogonal axes around a stationary subject and achieve all possible angulations. The magnet comprises a parallel pair of identical profiled arrays of permanent magnets backed by a flat steel yoke such that access in lateral directions is practical. The paper describes the detailed optimization procedure from a target 150mm DSV to the achievement of a measured uniform field over a 130mm DSV. Actual performance data of the manufactured magnet, including shimming and a sample image, is presented. The overall magnet system mounting mechanism is presented, including two orthogonal axes of rotation of the magnet about its isocentre.

Numerical Study on Magnetic Field Characteristics of Typical Permanent Magnet

Selecting a single piece of typical rectangular open planar magnet，with its axial magnetization, to build a finite element model. Based on ANSYS software, the article used NdFeB45 material properties, giving 100×100×10mm to fit the relationship of three-dimensional size. In the air zone as 10 times as model size, it adopted a static simulation analysis of the effect on relationship between axial magnetic distance and magnetic field strength. The magnetic field contours as simulation results, after the Origin software fitting process, obtained an equation is: ; Comparing with the formula: , which reflected the basic characteristics of permanent magnetic field, and with the numerical results by Jing-tian LI using equivalent magnetic charge method, they all appeared: the magnetic field strength exponentially decrease along with the magnetic distance increases, the magnetic field non-uniformity coefficient is of 4.628% deviation, the fitting correlation coefficient R is 0.99924; As a result of the numerical verification results, it also visually response to the magnetic field parameters of open permanent magnet.

Conductivity Image Reconstruction of Oblique Slice With C-Shaped Open Permanent Magnet MRI Systems

This work provides an improved image reconstruction technique, oblique slice magnetic resonance electrical impedance tomography (OS-MREIT), which can provide any cross-sectional conductivity distribution images with any type of MRI scanner. The OS-MREIT method can obtain conductivity distribution images using one component of magnetic field induced by injected currents with rotating subject once, and in the two-dimensional case, the conductivity distribution image can be reconstructed without rotating subject. The results of OS-MREIT studies performed with homemade C-shaped open permanent magnet MRI scanner are also presented in this work.

Image correction during large and rapid B0 variations in an open MRI system with permanent magnets using navigator echoes and phase compensation

An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method.

A New Development of Fully Open MRI Magnet by a Hybrid FEM-NESM Computation

A fully open permanent magnet configuration for magnetic resonance imaging (MRI) system, which can produce lice imaging region with field homogeneity outside the magnet structure, is presented. It is a totally new problem about magnet design to build a slice imaging region with homogeneous magnetic field outside the magnet source. In order to satisfy the special design requirement for the fully open magnet structure of unilateral MRI devices, a new approach based on the combination of finite element and new-style equivalent source methods (FEM-NESM) is proposed in detail. To verify the effectiveness of the combined method, the calculated results are compared with those obtained by finite element method. Good agreement is obtained. The possibility of the existence of such a remote slice region and the location and size of the slice region are discussed.

3-D optimal shape design of ferromagnetic pole in MRI magnet of open permanent-magnet type

This paper presents 3-D optimal shape design method of ferromagnetic pole pieces for magnetic resonance imaging (MRI) devices of open permanent magnet type. The design method is based on a continuum sensitivity analysis in conjunction with the boundary integral equation method (BIEM). The magnetic poles of an open magnet assembly are designed by the proposed method and the conventional shimming method. Magnetic field strength, ppm order homogeneity and working space volume are compared between the proposed method and conventional one.

Double-cavity open permanent magnet for dedicated MRI

A new 0.2 T magnetic structure for dedicated (extremities) Magnetic Resonance Imaging is presented. The main features are: magnetic circuit based on rare-earth permanent magnet material and iron, ergonomic double-height cavity shape (optimized to allow shoulder, legs and joints examinations in a very compact magnet with respect to traditional whole body systems), special design of split pole plates to improve magnetic field homogeneity and reduce eddy current effects. The typical magnetic field homogeneity (a few parts per million inside the imaging volume) necessary for MRI is achieved with a special shimming procedure, also outlined in the paper. The presented magnet is part of a commercial scanner produced by Esaote S.p.A (E-SCAN/sup TM/).

Development of permanent magnet assembly for MRI devices

The properties of various permanent magnet configurations for producing a homogeneous field for magnetic resonance imaging (MRI) are reviewed. The most significant characteristics of these permanent magnet assemblies are compared. The configuration of a novel, open permanent magnet assembly is considered. It is an access permanent magnet MRT system with two pronounced poles open on four sides. It is shown that such a configuration keeping all the advantages of a usually open permanent magnet configuration provides an efficiency of permanent magnet material utilization such as a tunnel-like system.

5495222 Open permanent magnet structure for generating highly uniform field

5495222 Open permanent magnet structure for generating highly uniform field

MR imaging of excessively obese patients: The use of an open permanent magnet

Excessive obesity can pose a limitation to both clinical and radiographic evaluation. Although CT and MR have revolutionized head and body imaging, patients with weights above 300 lb present a restriction of these imaging modalities. Magnetic resonance imaging (MRI) is well suited for imaging excessively obese patients, because the RF used does not have difficulty in penetrating large amounts of adipose tissue as ionizing radiation or sound waves does. The limitations of conventional MR imaging in these obese patients are the gantry size and the table weight limit. The recent development of a new low field MR imager with a larger gantry size and greater weight capacity, has the potential for imaging obese patients that cannot be evaluated by standard CT or MR. In this paper, we report our experience in imaging nine excessively obese patients with weights between 350 and 490 lb using a permanent magnet operating at 0.064 T.

Operational Results and Development of the E.C.R. Sources and the Injector into Cyclone

A large superconducting ECR-source (ECREVIS) has been producing high charge state ions up to Xe27+ for injection into CYCLONE and as a stand alone source for atomic physics for over two years now. An improved analysing system has been installed increasing greatly the acceptance without harming the resolution. Operational results of transmission and realistic charge state distributions are reported. The design of a more compact ECR-source, to be called OCTOPUS and using water cooled copper solenoids, an open permanent magnet octupole structure and an iron yoke is presented. This source will replace ECREVIS and it is expected to have better performance and to be more reliable and economical to operate.