NMR Sample Holder Using Anisotropic Conductive Tube
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Solution Overview
Problem
Existing NMR sample holders face challenges in maintaining pressure while minimizing eddy currents and maximizing signal-to-noise ratio, particularly when dealing with high-pressure rock cores and liquid samples, due to the need for materials that can withstand magnetic fields and radio-frequency energy without inducing unwanted electrical conductivity.
Innovation Solution
A pressurizable sample holder featuring a non-magnetic, electrically insulating pressure retaining tube made from materials like ceramic or carbon fiber reinforced composites, which surrounds the radio-frequency coils and inhibits eddy currents by providing anisotropic conductivity, allowing for a high coil filling factor and effective pressure containment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a non-magnetic metal tube is used to retain pressure, then the sample can be contained under pressure, but eddy currents are induced in the tube when gradient coils are switched on and off
Solution Approach 1:
The patent removes the pressure-containing function from the radio-frequency coil assembly and places it in a separate non-conductive pressure-containing tube. This extraction eliminates the source of eddy currents (the conductive material) while preserving the necessary pressure containment capability through a non-conductive tube that does not interact with the magnetic field gradients.
2Object-generated harmful factors
If the radio-frequency coil is placed outside the pressure retaining tube, then eddy currents are minimized, but the coil filling factor decreases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent introduces a non-conductive pressure-containing tube as an intermediary element between the sample and the external environment. This mediator allows the radio-frequency coil to be positioned inside the pressure-containing region while preventing eddy current induction, because the non-conductive tube does not form closed loops that would generate eddy currents in the magnetic field gradient.
3Strength
If a conductive material is used for the pressure retaining tube, then structural strength is improved, but eddy currents are induced and NMR signal quality deteriorates
Solution Approach 1:
The patent changes the electrical conductivity parameter of the pressure-containing tube from conductive to non-conductive. By selecting materials with appropriate electrical insulation properties, the tube can contain pressure effectively while preventing the formation of eddy currents that would otherwise degrade the NMR signal quality.
4Stress or pressure
If the pressure retaining tube wall thickness is increased to contain internal pressure, then pressure containment capability is improved, but the coil filling factor is reduced
Solution Approach 1:
The patent employs composite material structures for the pressure-containing tube that provide high strength-to-weight ratios and adequate pressure containment with minimal wall thickness. By using advanced composite materials, the tube can withstand internal pressures while maintaining a small outer diameter that allows the radio-frequency coil to achieve a high filling factor.
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 solution effectively maintains sample pressure, reduces eddy currents, and enhances signal-to-noise ratio by using non-metallic materials that are robust enough to contain internal pressure without compromising the coil filling factor, thereby improving NMR measurement accuracy.
Implementation Method 1
A tube which does not provide isotropic electrical conductivity may be electrically insulating or may provide conductivity which is anisotropic. Both possibilities will inhibit the induction of eddy currents when there is a change in the magnetic field to which the sample holder is subjected, as happens when gradient coils which impose a magnetic field gradient are switched on and off.
Implementation Method 2
Tests which have been carried out include examination by nuclear magnetic resonance (NMR) also referred to as magnetic resonance imaging (MRI) which entails placing the core within a magnetic field and using one or more radio-frequency coils to apply radio-frequency energy to the core and receive radio-frequency signals from it.
Implementation Method 3
nuclear magnetic resonance (NMR) also referred to as magnetic resonance imaging (MRI). There are circumstances where a sample is examined under pressure, thus requiring a sample holder which can contain the sample under pressure while it is in the magnetic field of an NMR spectrometer.
Data Source
AI summary
A pressurizable holder for a sample to be examined by NMR, comprises a pressure retaining nonmagnetic tube surrounding a radio-frequency coil which in turn surrounds a space for the sample. The pressure retaining tube is formed of (i) nonmetallic electrically insulating material such as a ceramic or (ii) nonmetallic electrically insulating matrix material reinforced with electrically insulating filaments such as glass fiber, or (iii) non-metallic electrically insulating matrix material reinforced with electrically conductive filaments configured so that conductivity is anisotropic. There is good coil filling factor without constraint on wall thickness of the pressure retaining tube. Avoidance of isotropically conductive material inhibits eddy currents when an NMR spectrometer's magnetic field gradient coils are switched on and off. The tube resists hoop stress from internal pressure. Longitudinal stress is resisted by structure connecting end pieces at the ends of the pressure retaining tube.