Sliding Band Capacitor Tuning for Low-Temperature NMR Probes
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Solution Overview
Problem
Existing NMR probes face challenges in maintaining high signal-to-noise ratio (SNR) due to the presence of metallic objects and magnetic coupling loops, which degrade RF homogeneity and SNR, particularly in low temperature probes where variable capacitors with leads act as inductors, reducing the amplitude of the parent coil flux.
Innovation Solution
The use of a sliding band capacitor composed of materials with zero sum volume magnetic susceptibility, including a paramagnetic metal like titanium surrounded by a diamagnetic metal like copper, to adjust parent coil resonance without degrading the magnetic field, combined with a high conductance metal to ensure effective RF penetration and minimize inductive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable capacitors with leads are used to adjust parent coil resonance, then the resonance frequency can be tuned, but the leads act as inductors that reduce the amplitude of the parent coil flux and degrade SNR
Solution Approach 1:
The patent removes the leads from the variable capacitor assembly and integrates the capacitance adjustment directly into the capacitor body itself, eliminating the inductive interference that leads would cause while maintaining the frequency tuning function
Solution Approach 2:
The patent combines the variable capacitance element and the capacitor body into a single integrated component, eliminating the separate lead connections and reducing the number of inductive elements in the circuit
2Adaptability or versatility
If metallic objects and magnetic coupling loops are present in the probe, then coupling between coils can be achieved, but RF homogeneity is degraded and SNR is reduced
Solution Approach 1:
The patent removes magnetic coupling loops and other metallic objects from the probe design, achieving coil coupling through alternative means that do not interfere with RF homogeneity, thereby eliminating the source of SNR degradation
Solution Approach 2:
The patent introduces nonmagnetic materials as intermediaries to achieve the necessary coupling between coils without the harmful effects of metallic objects, using materials that transmit RF fields without creating inhomogeneities
3Adaptability or versatility
If more metallic objects are added to the probe, then coupling and tuning functions can be enhanced, but the number of inductive elements increases, diluting the SNR
Solution Approach 1:
The patent eliminates unnecessary metallic objects and inductive elements from the probe design, achieving the required coupling and tuning functions through a minimized set of components that do not interfere with SNR
Solution Approach 2:
The patent discards the conventional approach of adding more metallic elements to enhance coupling, instead recovering and optimizing the existing minimal set of components to achieve the same functions with better SNR performance
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 enhances the performance of low temperature NMR probes by maximizing the Q value and maintaining RF homogeneity, thereby improving the SNR by ensuring that most of the high frequency resonating nucleus current is in the parent coil, reducing inductive interference, and maintaining magnetic field integrity.
Implementation Method 1
The sliding band capacitor is adapted to physically move relative to the tapered inner conductance skirt to adjust a capacitance of the sliding band capacitor to allow the parent coil to detect the resonance
Implementation Method 2
the sliding band capacitor comprises a diamagnetic insulator with a first volume magnetic susceptibility, at least one paramagnetic metal with a second volume magnetic susceptibility and at least one diamagnetic metal with a third volume magnetic susceptibility, where a sum of the first volume magnetic susceptibility and the second volume magnetic susceptibility and the third volume magnetic susceptibility is approximately zero
Implementation Method 3
combined with a high conductance metal to ensure effective RF penetration and minimize inductive interference
Implementation Method 4
NMR generally uses induction to detect the oscillating magnetic moment from nuclei precessing in a magnetic field
Data Source
AI summary
In various embodiments of the invention, a cooled nuclear magnetic resonance (NMR) probe can utilize a sliding band capacitor which can be moved relative to a parent coil inner conductance tapered skirt to adjust the frequency of the parent coil to allow the parent coil to detect the resonance of at least two nuclei without requiring leads between the parent coil and a lock coil. In this manner a cooled NMR probe can be provided without the disadvantages of prior art cooled NMR probes. In an embodiment of the invention, the sliding band capacitor comprises a diamagnetic insulator with a first volume magnetic susceptibility, at least one paramagnetic metal with a second volume magnetic susceptibility and at least one diamagnetic metal with a third volume magnetic susceptibility, where the sum of the first volume magnetic susceptibility, the second volume magnetic susceptibility and the third volume magnetic susceptibility is approximately zero.