NMR Shim Mount Materials for Temperature-Stable Field Homogeneity
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Solution Overview
Problem
The homogeneity of the magnetic field in NMR apparatuses is compromised due to temperature fluctuations, leading to relative movement between the superconducting magnet and the shim system, which affects the quality of magnetic resonance images and spectra.
Innovation Solution
The use of materials with low thermal expansion coefficients, such as carbon fiber-reinforced plastic (CFRP) and Invar, on the connecting paths between the magnet suspension and the shim system, along with temperature regulation using heating and cooling elements, minimizes strain changes and maintains field homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional materials with high thermal expansion coefficients are used in the connecting paths, then the mechanical connection is simple and easy to manufacture, but the relative movement between the superconducting magnet and the shim system increases due to thermal expansion, degrading magnetic field homogeneity
Solution Approach 1:
The patent applies parameter changes by selecting materials with specific thermal expansion coefficients (less than 5 ppm/K) for the connecting paths. This parameter selection (low thermal expansion) directly addresses the homogeneity problem by minimizing temperature-induced dimensional changes in the mechanical connection paths between the superconducting magnet and the shim system.
Solution Approach 2:
The patent employs composite materials, specifically mentioning carbon fiber-reinforced plastic (CFRP) and Invar, which combine structural integrity with low thermal expansion properties. These composite materials enable the connecting paths to maintain dimensional stability across temperature variations while providing the necessary mechanical strength.
2Manufacturing precision
If materials with low thermal expansion coefficients are used in the connecting paths, then magnetic field homogeneity is maintained under temperature fluctuations, but the availability and ease of manufacture may be reduced
Solution Approach 1:
The patent specifies a parameter threshold (thermal expansion coefficient less than 5 ppm/K) that balances manufacturing feasibility with performance requirements. This parameter-based approach allows manufacturers to select from a defined class of materials that meet both the homogeneity requirement and practical manufacturing considerations.
Solution Approach 2:
The patent applies local quality by using low thermal expansion materials specifically in the connecting paths where thermal stability is critical, while other parts of the system can use conventional materials. This localized application of special materials minimizes the overall complexity and cost while achieving the desired homogeneity.
3Strength
If the mechanical connection path is long, then the mechanical connection is more stable and supports larger components, but the cumulative thermal expansion effect increases, causing greater relative movement and field inhomogeneity
Solution Approach 1:
The patent addresses the length-thermal expansion relationship by changing the material parameter (thermal expansion coefficient) to compensate for the long connection path. By using materials with extremely low thermal expansion (less than 5 ppm/K), the cumulative expansion effect over long distances is minimized, maintaining homogeneity despite necessary long mechanical connections for structural stability.
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 configuration stabilizes the magnetic field homogeneity by reducing relative movements between the superconducting magnet and the shim system, ensuring consistent field quality even under changing temperature conditions.
Implementation Method 1
The latter part of the path follows the fluctuations of the ambient temperature and changes its length due to its thermal expansion
Implementation Method 2
temperature regulation using heating and cooling elements
Implementation Method 3
temperature regulation using heating and cooling elements
Data Source
AI summary
An NMR apparatus having a magnet coil system for generating a homogeneous magnetic field comprises a superconducting magnet within a vacuum vessel in the cold region of a cryostat and a shim system containing shim elements outside the vacuum vessel, wherein the magnet has a first mechanical connection point to the vacuum vessel via a magnet suspension, and the shim system has a second mechanical connection point to the vacuum vessel via a positioning element. On at least one portion of a path along the vacuum vessel from the first mechanical connection point to the second mechanical connection point and/or on at least one portion of a path along the positioning element from the second mechanical connection point to the shim system, only materials whose thermal expansion coefficient at operating temperature is less than 5 ppm/K are used. Magnetic field homogeneity can thus be kept largely stable and constant.