Halbach Magnet Notch for Field Homogeneity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Halbach magnet configurations for magnetic resonance applications face challenges in achieving high field homogeneity, particularly in compact and lightweight designs, due to inherent inhomogeneities caused by finite magnet segment lengths and material inhomogeneities, which complicate the generation of a homogeneous magnetic field and increase the weight and size of the magnet arrangement.
Innovation Solution
Incorporating a groove-shaped, hollow cylindrical recess around the z-axis in the annular magnetic element, symmetrically arranged relative to the plane z=0, with specific radial depth and axial length, to minimize remaining inhomogeneities of the magnetic field within a predetermined measurement volume, allowing for a more compact and lightweight magnet design without the need for additional correction mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a Halbach magnet configuration is used to generate a homogeneous magnetic field, then the field homogeneity is improved, but the device complexity increases due to the need for correction mechanisms to compensate for tolerances
Solution Approach 1:
The patent extracts and removes the need for complex correction mechanisms by introducing a groove-shaped recess in the annular magnetic element. This recess is strategically designed to compensate for field inhomogeneities caused by manufacturing tolerances and material variations, thereby achieving high field homogeneity (10ppm) without requiring additional correction devices.
Solution Approach 2:
The groove-shaped recess introduces a localized structural feature with specific geometric parameters (radial depth and axial length) that creates a controlled magnetic field modification in a specific region. This local modification compensates for global field inhomogeneities, allowing the majority of the magnet structure to remain simple while achieving overall field homogeneity.
2Manufacturing precision
If correction mechanisms are added to achieve high field homogeneity, then the manufacturing precision is improved, but the device complexity and weight increase
Solution Approach 1:
The patent eliminates the need for separate correction mechanisms by integrating the field compensation function directly into the annular magnetic element through the groove-shaped recess. This extraction of the correction function from separate components reduces the overall weight while maintaining the required 10ppm field homogeneity.
3Length of moving object
If the axial length of the magnet is reduced for a compact design, then the device size is reduced, but the field homogeneity deteriorates
Solution Approach 1:
The groove-shaped recess with specifically optimized axial length creates a localized field modification that compensates for the reduced overall axial length of the magnet. This local structural feature ensures that the shortened magnet maintains the required 10ppm field homogeneity in the measurement volume despite its compact dimensions.
4Power
If individual magnet segments with varying magnetization directions are joined to create a Halbach dipole, then the magnetic field generation is improved, but the manufacturing precision deteriorates due to tolerance accumulation
Solution Approach 1:
The patent removes the problematic joint interfaces between multiple magnet segments by designing the annular magnetic element as a single piece with an integrated groove-shaped recess. This eliminates tolerance accumulation at joints while maintaining the Halbach dipole field generation capability, achieving both strong magnetic field and high field homogeneity.
Solution Approach 2:
The groove-shaped recess is divided into multiple segments along the axial direction, with each segment having a specific magnetization direction. This segmentation allows the maintenance of Halbach configuration benefits while reducing the overall number of joints compared to traditional multi-segment designs, thereby reducing tolerance accumulation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves a homogeneous magnetic field with inhomogeneities limited to 10ppm in the measurement volume, reducing the weight and size of the magnet arrangement while maintaining high field homogeneity, and allows for the suppression of double-periodic field orders, eliminating the need for additional correction mechanisms.
Implementation Method 1
the annular magnetic element is constructed from individual magnet segments and is arranged so that it has a Halbach magnetization that generates a magnetic dipole field
Implementation Method 2
arranged so that it has a Halbach magnetization that generates a magnetic dipole field
Implementation Method 3
the circumferential groove-shaped recess of the annular magnetic element having a radial depth T=TA and an axial length Lz,A
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
A magnetic arrangement (1) with a hollow cylindrical magnetic element (2a; 2b; 2c) constructed from magnetic segments and arranged concentrically around the z-axis, having axial length Lz,M and inner radius Rin, and exhibiting Halbach magnetization, is characterized in that at least one annular magnetic element has a groove-shaped, hollow cylindrical recess (3a; 3b) circumferentially around the z-axis, symmetrically to the plane z=0, the axial extent Lz,A of which is less than the axial length Lz,M of the magnetic element, wherein the recess has a radial depth T=TA and an axial length Lz,A < Lz,M between the z-positions z=-zA to z=+zA, and that the radial depth TA and the axial length Lz,A of the recess are selected such that the remaining inhomogeneity of the homogeneous magnetic field B0 in a predetermined measuring volume (0) with an axial plateau length The LP level in the center of the magnet arrangement does not exceed 10 ppm.This provides an unusually compact and lightweight Halbach arrangement for an MR device which, at a given field strength, generates an area with a particularly homogeneous field distribution over an axial plateau length Lp, with the external dimensions of the arrangement and its weight being significantly reduced compared to known Halbach arrangements.