Flat Sample Cell for DNP-NMR Signal Intensity
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Solution Overview
Problem
DNP-NMR measurements face challenges with low sensitivity, sample heating, and inhomogeneous excitation due to inefficient NMR coil placement and sample cell designs, leading to reproducibility issues and reduced signal intensity.
Innovation Solution
A sample cell with a flat, thin cavity for holding liquid samples, where the NMR coil is wound around the cavity and positioned close to the sample, minimizing MW electric field absorption and maximizing signal intensity, while maintaining a high q factor for the EPR microwave resonator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a classical sample tube is used for liquid samples, then the sample volume is sufficient, but the sample heating increases and excitation becomes inhomogeneous
Solution Approach 1:
The invention transitions from a conventional cylindrical sample tube to a planar sample cavity with dimensions L×W×H where H≤1/15·L and H≤1/15·W. This dimensional change allows the sample to be positioned in a plane perpendicular to the microwave magnetic field, achieving homogeneous excitation across the entire sample volume while minimizing exposure to the microwave electric field, thereby reducing sample heating.
Solution Approach 2:
The sample cavity is designed with specific dimensional ratios (H≤1/15·L and H≤1/15·W) to create optimal local conditions for DNP-NMR measurements. The thin profile (small H dimension) ensures that the entire sample volume lies within the homogeneous magnetic field region while minimizing dielectric heating, thus creating locally optimized conditions for both excitation uniformity and thermal management.
2Device complexity
If the NMR coil is wrapped around the EPR resonator, then the setup is simple, but the NMR signal intensity is low due to poor coupling
Solution Approach 1:
The invention merges the NMR coil and sample cavity into a single integrated unit where the NMR coil is wound directly around the sample cavity. This combination ensures optimal magnetic coupling between the coil and sample, maximizing NMR signal intensity. The integrated design maintains simplicity while achieving superior measurement sensitivity compared to separate coil and sample holder configurations.
3Quantity of substance
If the sample extends over the homogeneous range of the magnetic MW field, then the sample volume is maximized, but the excitation becomes inhomogeneous
Solution Approach 1:
The invention reorients the sample geometry from a conventional configuration to a planar cavity where the largest dimension (H) is perpendicular to the microwave magnetic field direction. This allows the sample to have sufficient volume (L×W area) while ensuring that the entire sample thickness (H≤1/15·L and H≤1/15·W) lies within the homogeneous field region, achieving both adequate sample volume and uniform excitation.
4Power
If MW electrical energy is absorbed by the liquid sample, then the DNP effect is achieved, but unwanted sample heating occurs leading to sample destruction
Solution Approach 1:
The sample cavity is designed with specific dimensional constraints (H≤1/15·L and H≤1/15·W) to create optimal local conditions that minimize dielectric heating. The thin profile ensures that the sample experiences minimal exposure to the microwave electric field while maintaining sufficient volume for effective DNP. This local optimization allows efficient spin polarization transfer without excessive heat generation that would lead to sample destruction.
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 enhances signal intensity, reduces sample heating, and improves measurement reproducibility by positioning the NMR coil close to the sample and aligning the sample with the MW magnetic field maximum and electric field minimum, resulting in more stable and comparable measurement results.
Implementation Method 1
an NMR coil wound around the flat sample cavity for generating an RF magnetic field B2
Implementation Method 2
The sample is then irradiated with a microwave (MW) magnetic field (near or at the EPR) B1 of appropriate direction and amplitude, wherein the sample is in an appropriate static background magnetic field B0, to saturate the electron spin transition
Implementation Method 3
In DNP the spin polarization from paramagnetic electrons is transferred to nuclei of the sample to be measured. The nuclear spins are aligned proportional to the extent that the electron spins are aligned, wherein the electron spin polarization is enhanced using microwave radiation
Data Source
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AI summary
The invention relates to a sample cell (1) for performing DNP-NMR measurements, for interchangeable use in an EPR microwave resonator (28), with the sample cell (1) comprising - a flat sample cavity (6) for holding a liquid (23) sample to be measured, wherein the flat sample cavity (6) extends with a maximum length L and a maximum width W in a sample cavity plane (19), and extends with a maximum height H perpendicular to the sample cavity plane (19), with H ≤ 1/15*L and H ≤ 1/15*W, and - an NMR coil (4) wound around the flat sample cavity (6) for generating an RF magnetic field B2, wherein a coil axis (4a) of the NMR coil (4) about which the NMR coil (4) is wound is oriented perpendicular to the sample cavity plane (19). The invention provides a sample cell which is easy to handle and improves the quality and the reproducibility of DNP-NMR measurements.