Microwave Coupler for NMR Probe HE11 Mode Focusing
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Solution Overview
Problem
Current NMR DNP-MAS systems face inefficiencies in microwave irradiation due to beam divergence and scattering, leading to reduced energy density and the need for high-power sources to achieve sufficient field strength for homogeneous sample polarization.
Innovation Solution
A conically tapered hollow microwave waveguide with a rod-shaped dielectric coupler positioned at a radial distance from the waveguide opening, optimized for HE 11 mode coupling, focuses the microwave beam onto the sample, increasing energy density and allowing for more efficient polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If microwave radiation is fed through an open end of the waveguide directly onto the rotor, then the beam can reach the sample, but the beam divergence and scattering reduce energy density at the sample location
Solution Approach 1:
A dielectric rod coupler is introduced as an intermediary component between the waveguide opening and the sample. The coupler projects into the waveguide opening at a radial distance, acting as a mediator that focuses and directs the microwave beam onto the sample, thereby reducing beam divergence and increasing energy density at the sample location without requiring high-power sources
Solution Approach 2:
The microwave coupler is positioned at a radial distance from the waveguide opening rather than flush with it, utilizing the radial dimension to optimize HE11 mode coupling. This dimensional adjustment allows the coupler to effectively focus the beam while maintaining proper mode coupling, resolving the contradiction between direct beam delivery and energy density maintenance
2Power
If a complex high-power microwave source is used to compensate for beam divergence, then sufficient field strength can be achieved, but the device complexity and power requirements increase
Solution Approach 1:
The dielectric rod coupler serves as a focusing intermediary that concentrates the microwave energy onto the sample. This simple passive component achieves the desired field strength through geometric focusing rather than requiring complex high-power microwave sources, thereby reducing both device complexity and power requirements while maintaining sufficient polarization field strength
Solution Approach 2:
The invention changes the geometric parameters of the microwave delivery system by introducing a coupler with specific dimensions and positioning at an optimal radial distance. This parameter optimization enables efficient HE11 mode coupling and focuses the beam to achieve the required field strength with lower power sources, avoiding the need for complex high-power systems
3Productivity
If the microwave coupler is flush with the waveguide walls, then TE modes can be coupled, but HE11 mode coupling is not optimized
Solution Approach 1:
The coupler is positioned at a radial distance from the waveguide opening rather than flush with the walls, utilizing the radial dimension to optimize HE11 mode coupling. This dimensional change allows the electromagnetic fields to couple more effectively into the HE11 mode, improving both coupling efficiency and mode coupling accuracy for the desired polarization mode
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 the energy density of the magnetic microwave field, enabling more efficient and homogeneous sample polarization with lower required microwave power, particularly suitable for small or elongated samples, and allows the use of compact solid-state sources.
Implementation Method 1
a conically tapered hollow microwave waveguide with a rod-shaped dielectric coupler positioned at a radial distance from the waveguide opening, optimized for HE 11 mode coupling, focuses the microwave beam onto the sample, increasing energy density
Implementation Method 2
an axially expanded rod-shaped microwave coupler made of dielectric material and located in the opening of the microwave waveguide
Implementation Method 3
an axially expanded rod-shaped microwave coupler made of dielectric material
Implementation Method 4
This method requires simultaneous irradiation of a magnetic microwave field for polarization of electron spins at a frequency that is higher by a factor of 660 than the Larmor frequency of the 1 H nuclear spins
Data Source
AI summary
An NMR DNP-MAS probe head (10) has an MAS stator (2) for receiving an MAS rotor (3) having a sample substance in a sample volume (4), and a hollow microwave waveguide (5)′ for feeding microwave radiation through an opening (5a) of the microwave waveguide into the sample volume, an axially expanded rod-shaped microwave coupler (6) located in the opening made of dielectric material, characterized in that the microwave waveguide has a conically tapered hollow transition piece for coupling in an HE 11 mode, into which the microwave coupler projects at an all-round radial distance to the opening of the microwave waveguide. It is thus possible, in a surprisingly simple manner and by means of readily available technical means, to irradiate a considerably higher microwave energy in the HE 11 mode into the NMR measuring sample than by means of the known arrangements.