NMR Probe Coil Geometry for Reduced Sample Electric Fields
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Solution Overview
Problem
Existing NMR probe heads face challenges in reducing electric fields generated in samples, which lead to performance losses such as reduced signal-to-noise ratio, limited excitation bandwidth, and heating of temperature-sensitive samples, especially at frequencies other than proton frequencies.
Innovation Solution
The NMR probe head features a coil geometry with forward and return turns arranged on a common cylindrical surface, intersecting only at crossover regions, where the return turns have opposite pitch signs to the forward turns, and are connected via a matching network to ensure balanced potentials, minimizing electric fields and performance losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional coil designs are used, then the NMR probe head can operate at multiple frequencies, but electric fields are generated in conductive samples causing performance losses and heating
Solution Approach 1:
The coil is divided into forward and reverse winding sections with opposite pitch signs, creating a segmented structure where each section contributes to reducing the overall electric field while maintaining the magnetic field generation capability across multiple frequencies
Solution Approach 2:
The pitch parameter of the windings is changed to have opposite signs in different sections, which fundamentally alters the electric field distribution characteristics while preserving the inductive coupling and magnetic field generation properties needed for multi-frequency operation
2Loss of energy
If low-inductance coils are used to reduce electric fields, then electric field losses are minimized, but the inductance decreases reducing multi-core circuit efficiency
Solution Approach 1:
The coil is segmented into forward and reverse winding sections that are inductively coupled, allowing the structure to achieve low electric field losses while maintaining sufficient inductance through the coupled configuration rather than requiring a single low-inductance design
Solution Approach 2:
Inductive coupling acts as an intermediary mechanism between the forward and reverse winding sections, enabling energy transfer and maintaining circuit efficiency without requiring direct electrical connection that would increase inductance and electric field losses
3Loss of energy
If cross-coil configuration is used, then electric fields are reduced for proton frequencies, but losses at other frequencies (X-nuclei) are not addressed
Solution Approach 1:
The pitch sign parameter is inverted in different sections, creating a configuration that reduces electric fields across a broader frequency range including X-nuclei frequencies, not just proton frequencies, by fundamentally changing the field distribution characteristics
Solution Approach 2:
The coil design achieves universal applicability across multiple frequency ranges and nuclear types by incorporating forward and reverse windings with opposite pitches, making it effective for both proton and X-nuclei measurements rather than being optimized for a single frequency
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 design significantly reduces electric fields in the sample, maintaining high signal-to-noise ratio and efficiency across multiple frequencies, even with lossy or temperature-sensitive samples, particularly benefiting cryogenically cooled probes.
Implementation Method 1
at least one transmitting-receiving coil for generating an RF B1 magnetic field
Implementation Method 2
the windings of the reverse winding section have a pitch with an opposite sign to those of the forward winding section
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3
AI summary
An NMR probe head with a transmit-receive coil arrangement comprising at least one transmit-receive coil (1) for generating an RF B1 magnetic field, wherein the transmit-receive coil (1) comprises at least one electrical conductor section (2a, 2b) and a connection section (4), wherein the electrical conductor section (2a, 2b) comprises a forward winding section and a reverse winding section, wherein the forward winding section comprises forward turns (3a, 3b) and leads from the connection section (4) in a predetermined winding direction to an axial end (5a, 5b) of the transmit-receive coil (1), wherein the reverse winding section comprises reverse turns (6a, 6b) and leads from the axial end (5a, 5b) of the transmit-receive coil (1) in the same winding direction to the connection section (4), wherein the turns of the reverse winding section have a pitch P with opposite exhibiting signs in relation to those of the winding section, is characterized in that forward and reverse windings (3a, 3b, 6a,6b) of the electrical conductor section (2a, 2b), with the exception of crossing regions (8) where the forward and return windings (3a, 3b, 6a, 6b) intersect, are arranged on a common cylindrical surface around a longitudinal axis Z'. The invention provides a coil geometry for the NMR probe head that reduces the electric fields visible to the sample while simultaneously minimizing other performance losses.