Extended Passive Shims for NMR Magnet Field Homogenization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing magnetic field homogenization techniques, such as passive shimming, face challenges in achieving high fidelity corrections with minimal spatial impact and avoiding the creation of high-order error fields, especially in small magnets with limited space and strong field requirements.
Innovation Solution
The development of passive shims with spatially extended structures and materials, such as thin magnetic ink or metal foils, that produce correction fields with nearly continuous values, reducing high-order field errors and allowing for precise, automated, and cost-effective field corrections without the need for electrical currents or complex calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional passive shimming with discrete buttons is used, then field correction can be achieved, but high-order error fields are created and spatial space is excessively occupied
Solution Approach 1:
The patent segments the correction field into multiple harmonic components (e.g., Z0, Z1, Z2, etc.) and addresses each component separately using specifically designed shim elements. This segmentation allows precise control over each harmonic term while minimizing unwanted high-order errors, as each segment can be optimized independently for its target harmonic content.
Solution Approach 2:
The patent applies local quality by designing shim elements with spatially varying magnetic moment densities tailored to correct specific local field inhomogeneities. Each region of the shim structure has optimized properties (magnetic moment density, geometry) matched to the local field error characteristics, enabling precise correction without introducing widespread high-order errors.
2Manufacturing precision
If discrete button shims are used for field correction, then field homogeneity can be improved, but the number of components and assembly complexity increase
Solution Approach 1:
The patent merges multiple discrete button shims into continuous or semi-continuous shim structures (such as shim sheets or shim blocks) that provide the same field correction functionality. This merging reduces the total number of components, simplifies assembly, and maintains field homogeneity by creating a more uniform magnetic moment distribution across the shim structure.
Solution Approach 2:
The patent designs universal shim structures that can correct multiple harmonic components simultaneously or that can be adapted to correct different field inhomogeneities. These multi-functional shim elements replace numerous specialized discrete buttons, reducing component count while maintaining comprehensive field correction capability across different spatial harmonics.
3Manufacturing precision
If conventional passive shimming materials are used, then field correction is possible, but the materials occupy excessive space within the magnet structure
Solution Approach 1:
The patent employs thin-film shim materials (such as thin magnetic sheets or deposited magnetic layers) instead of bulky conventional shim materials. These thin films provide the necessary magnetic moment density for field correction while occupying minimal volume within the magnet structure, thereby preserving space for other magnet components and improving the overall compactness of the system.
Solution Approach 2:
The patent uses composite shim materials that combine magnetic particles or layers with non-magnetic substrates or binders. These composite structures provide high magnetic moment density in a thin profile, enabling effective field correction with minimal material volume. The composite formulation allows optimization of magnetic properties while maintaining structural integrity and minimizing space occupation.
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
This approach enables efficient and precise correction of magnetic fields in small magnets with minimal spatial compromise, reducing the need for complex calculations and high-precision adjustments, while avoiding high-order field errors, thus improving field homogeneity and reducing production costs.
Implementation Method 1
the passive shims are designed and constructed in a manner that creates correction fields that can have nearly continuously-valued field strength
Implementation Method 2
Passive shimming is frequently achieved through the careful placement of small pieces (known as 'buttons') of highly magnetizeable materials (low-carbon steel, nickel, or similarly magnetically responsive materials) or of permanent magnet materials
Data Source
AI summary
Methods and apparatuses for homogenizing or correcting the magnetic fields of magnets, particularly the magnetic fields employed in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications. There are disclosed passive shims for making such homogenizations or corrections, methods for making such shims, and a method and apparatus for creating desirable correction fields in which the correction field strength has limited harmonic content, near continuous value of field strength, and occupies minimal space in the magnet.