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Rare Earth MRI Magnet Assembly

MRI with MagNet for Solidworks

Magnetic Resonance Imaging [MRI] is a non-invasive mechanism for assessing the nature of materials. Whether one desires to monitor the fat content in a cookie mixture, or review potential structural damage to a human joint, MRI equipment is readily available.

In this example we use MagNet for SOLIDWORKS to examine the use of rare-earth permanent magnets for generating an uniform field of 0.5 Tesla. Solution results show that the fields which are generated in the bore of the assembly are suitable for potential use in a medical MRI.

Three phase induction motor in 2D

METHODS and RESULTS

APPLYING STATIC & RADIO FREQUENCY MAGNETIC FIELDS CAUSES RESONANCE

MRI requires that two magnetic fields interact; one is uniform and the other is varying in time oriented perpendicular to the first. In 1980 Klaus Halbach invented the Halbach array. K. Halbach (1980). "Design of permanent multipole magnets with oriented rare earth cobalt material". Nuclear Instruments and Methods 169 (1): 1–10. Using a Halbach array one can generate the uniform field component for MRI using an array of permanent magnets.

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MRI ASSEMBLY: 3 CONCENTRIC ARRAYS of PERMANENT MAGNETS

A 0.5 Tesla MRI assembly is created with 3 concentric arrays of rare earth permanent magnets. Each array consists of 16 magnets working together to produce the fields.

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ASSIGNING NdFeB to the INNER ARRAY of MAGNETS

MagNet for SolidWorks allows one to click and assign a material to either a single Component or a group of Components. In this case an entire array of magnets is assigned to be of the Neodymium Iron Boron magnet type [NdFeB]. The required Halbach orientation for each magnet is assigned with a vector definition using a system angle called "Theta".

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ASSIGNING "MESH CONTROLS" to the MAGNET ARRAY

MagNet for SolidWorks allows one to assign a variety of mesh controls to the Components. Here both a Maximum Overall Element Size and a Curvature Refinement Angle are assigned to an array of magnet Components simultaneously.

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RESULTING MESH DISTRIBUTION

The chosen "mesh controls" result in an even distribution of tetrahedra throughout the volumes of the magnets and the bore Component.

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ANGULAR PERSPECTIVE of MESH

Viewing the mesh along each Component from an angle gives confidence in the choice for each of the "mesh control" parameters.

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FLUX DENSITY on COMPONENT SURFACE

MagNet for SolidWorks allows one to review the flux density solution on the surface of components, within a range of 0.0 - 1.8 Tesla, in the form of a shade plot using the vector magnitude filter.

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FLUX DENSITY VIEW on an ANGLE

MagNet for SolidWorks allows one to review the Flux Density solution from alternate perspectives. By rotating the assembly to the side the Shade Plot is shown from an angular perspective.

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UNIFORM FIELD in the BORE of the ASSEMBLY

MagNet for SolidWorks allows one to review the flux density solution as a function of a vector plot using the glyph filter. The distribution within the Bore of the assembly shows the resulting uniform field in the Y-direction.

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HALBACH REQUIRED ORIENTATION of EACH MAGNET

With a few changes to the Glyph filter's control parameters and some modifications to the viewing window, the vector plot clearly shows the resulting orientation of the magnets as required by the Halbach array.

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3D SHADE PLOT of BORE

MagNet for SolidWorks allows one to review the flux distribution in a volume of interest. Thresholds can be set to customize the solution. Here we see a 3D Shade Plot which reveals the nature of the flux in the Bore which has a value of 0.5 Tesla.

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FLUX DISTRIBUTION THROUGHOUT the ENTIRE MRI ASSEMBLY

MagNet for SolidWorks allows one to review the solution within the interior of the Components by reviewing a single plane using the Clip Mesh filter. This animation shows the solution as the plane propagates through the MRI assembly from the back to the front of the entire assembly.

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