Low-Expansion Shim Mounting for Stable NMR Field Homogeneity
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Solution Overview
Problem
NMR apparatuses face challenges in maintaining magnetic field homogeneity due to temperature fluctuations, which cause relative movement between the superconducting magnet and room temperature shims, leading to disruptions in NMR measurements.
Innovation Solution
Using materials with a low coefficient of thermal expansion (<5 ppm/K) for the mechanical connections between the magnet suspension and shim system, and employing temperature control mechanisms like heaters or TEC elements to minimize thermal expansion and maintain constant temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional materials are used for mechanical connections between the superconducting magnet and shim system, then the structure is simple and easy to manufacture, but thermal expansion causes relative movement between the magnet and shims, degrading magnetic field homogeneity
Solution Approach 1:
The patent changes the material parameter (coefficient of thermal expansion) from conventional values to less than 5 ppm/K by selecting specialized materials such as Invar, carbon fiber reinforced plastics, or titanium alloys for the mechanical connection components. This parameter change ensures that thermal expansion remains negligible across the operating temperature range, preventing relative movement between the superconducting magnet and shim system while maintaining magnetic field homogeneity.
Solution Approach 2:
The patent employs composite material structures combining materials with complementary properties. For example, using Invar (a nickel-iron alloy with low thermal expansion) for structural components, or combining carbon fiber reinforced plastics with metallic elements to achieve both low thermal expansion and mechanical strength. These composite approaches allow the mechanical connection structure to remain relatively simple while achieving the required thermal stability.
2Manufacturing precision
If materials with low thermal expansion coefficient are used in the mechanical connection path, then thermal expansion is reduced and magnetic field homogeneity is maintained, but the ease of manufacture decreases due to specialized material requirements
Solution Approach 1:
The patent specifies a clear material selection criterion (thermal expansion coefficient less than 5 ppm/K) that guides the choice of conventional low-expansion materials such as Invar, which is a well-established alloy with成熟的 manufacturing processes. This approach maintains ease of manufacture while achieving the required thermal stability for magnetic field homogeneity.
Solution Approach 2:
The patent applies low-expansion materials selectively only to the critical path components (suspension towers, positioning elements) rather than the entire NMR system. This targeted application minimizes the amount of specialized material needed, reducing overall manufacturing complexity and cost while effectively preventing thermal expansion in the critical mechanical connection path.
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 stabilizes the magnetic field homogeneity by reducing relative movements and fluctuations, ensuring consistent NMR measurements even with changing temperature conditions.
Implementation Method 1
einem magnetischen Auftriebselement, das einen magnetischen Auftrieb für die Lagerung des supraleitenden Magneten bereitstellt
Implementation Method 2
zweitem mechanischen Anschlusspunkt mit dem Vakuumgefäß über ein Positionierelement
Data Source
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AI summary
An NMR apparatus with a magnet coil system for generating a homogeneous magnetic field, comprising a superconducting magnet (1) arranged in the cold region of a cryostat within a vacuum vessel (8), and comprising a shim system (7) containing shim elements (6) arranged outside the vacuum vessel, wherein the magnet has a first mechanical connection point (11) with the vacuum vessel via a magnet suspension (3), and wherein the shim system has a second mechanical connection point (10) with the vacuum vessel via a positioning element (5);12) is characterized in that, on at least one section 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 section of a path along the positioning element from the second mechanical connection point to the shim system, only materials are used whose coefficient of thermal expansion at operating temperature is less than 5 ppm/K. This ensures that the magnetic field homogeneity can be kept largely stable and constant even under changing temperature conditions within and in the vicinity of the apparatus.