Resonant Lenz Lens for NMR B1 Field Focusing and Frequency Compensation
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Solution Overview
Problem
Existing NMR probes struggle to achieve a high signal-to-noise ratio (SNR) with small sample volumes due to limited focusing of the B1 field and frequency shifts caused by additional elements like the Lenz lens, which can exceed the tunable range of the probe's tuning device.
Innovation Solution
An additional element with a capacitively acting structure forms an electrical resonant circuit that focuses the B1 field into a smaller area while establishing a resonance splitting, allowing for a frequency shift compensation within the probe's tunable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an additional element (Lenz lens) is inserted to focus the B1 field, then the signal-to-noise ratio is improved, but the frequency shift exceeds the tunable range of the probe
Solution Approach 1:
The additional element is segmented into multiple conductive layers (first conductive layer, second conductive layer, third conductive layer) separated by dielectric layers. This segmentation allows independent optimization of field focusing and resonance frequency properties for each layer, enabling the B1 field to be focused while keeping frequency shifts within the probe's tunable range.
Solution Approach 2:
The additional element uses composite structures combining conductive materials (for field focusing) with dielectric materials (for resonance control). The dielectric layers between conductive layers create resonant circuits that generate beneficial frequency shifts, while the conductive layers focus the B1 field. This composite approach allows simultaneous optimization of both signal-to-noise ratio and frequency adaptability.
2Measurement precision
If the B1 field is focused into a smaller area, then the signal-to-noise ratio is enhanced, but the frequency shift increases beyond acceptable limits
Solution Approach 1:
The invention changes key parameters of the additional element including the conductivity distribution across layers, dielectric constant of insulating layers, thickness of each layer, and pattern of conductive regions. By optimizing these parameters, the B1 field is concentrated into a smaller focal area enhancing signal-to-noise ratio, while the resonant circuits control frequency shifts to remain within acceptable limits.
3Measurement precision
If a Lenz lens is used to focus magnetic flux, then measurement sensitivity is improved, but the device complexity increases due to frequency tuning limitations
Solution Approach 1:
The additional element incorporates resonant circuits that automatically generate frequency shifts to compensate for those caused by field focusing. The conductive and dielectric layers work together to create self-regulating resonant behavior, reducing the need for complex external tuning devices and simplifying the overall system while maintaining high measurement sensitivity.
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 significantly enhances the SNR by focusing the B1 field and compensating frequency shifts, enabling effective NMR measurements with small sample volumes without exceeding the probe's tunable frequency range.
Implementation Method 1
The induced current flow in the conductor loops is reversed on the inside around the passage window compared to the outside. The B1 field is expelled from the cover zone and at least partially focused into the passage window in the central region of the RF coil.
Implementation Method 2
Such an additional element is also referred to as a Lenz lens. The Lenz lens comprises one or more metal cover elements through which one or more closed conductor loops are formed.
Implementation Method 3
The additional element has one or more cover elements which are electrically conductive at least in the region of a part of their respective boundary curve or outer surface, wherein the totality of the cover elements forms one or more closed conductor loops which, in said top view, each enclose a conductor loop area
Implementation Method 4
an additional element with a capacitively acting structure forms an electrical resonant circuit that focuses the B1 field into a smaller area while establishing a resonance splitting, allowing for a frequency shift compensation within the probe's tunable range
Data Source
Figure 1(a)~1(f)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
An additional element (1) for focusing a time-varying magnetic flux (B1), for installation in a sample holder (51) of an NMR probe head (201), wherein the additional element (1) forms a cover zone (5) and a through window (2) at least with respect to a plan view along a basic direction (GR), wherein the cover zone (5) encloses the through window (2), wherein the additional element (1) has one or more cover elements (10; 10a, 10b; 20; 20a, 20b;30, 40) which are electrically conductive at least in the region of a part of their respective edge curve or outer surface, wherein the entirety of the cover elements forms one or more closed conductor loops (14, 24), wherein the entire coverage of the associated one or more conductor loop surfaces (14a, 24a) forms the cover zone (5) which has a surface area Acover, and wherein the through-window (2) has a surface area Awindow with Acover≥ 2*Awindow, and wherein the additional element (1) comprises at least one capacitively acting structure (60), so that the additional element (1) forms an electrical resonant circuit (208) comprising the one or more cover elements, with a natural resonance of a resonant frequency RF, with 5 MHz ≤ RF ≤ 3000 MHz. The additional element can be used to improve the signal-to-noise ratio with low-volume samples when measuring in an existing NMR probe head.