EPR Microwave Cavity for Small Magnet Airgaps

Patent metadata

Field	Value
Publication number	US-2016274200-A1
Application number	US-201615063536-A
Country	US
Kind code	A1
Filing date	Mar 8, 2016
Priority date	Mar 18, 2015
Publication date	Sep 22, 2016
Grant date	—

Abstract

A microwave resonator for an EPR probe head has a metal cavity body ( 1 ) supporting an electromagnetic microwave resonance mode. The metal cavity body ( 1 ) has an opening for inserting a sample tube ( 2 ) to a center position of the resonator. The center of the opening and the center position of the resonator define an x-axis. The cavity body also has an opening for transmitting microwave radiation into the resonator. Two dielectric elements ( 4 a , 4 b ) are located symmetrically to the E-field nodal plane containing the x-axis and a z-axis perpendicular to the x-axis. Each dielectric element is geometrically formed and positioned such that it provides an equal overlap with a local maximum of the microwave electric field energy. The microwave resonant cavity has a thin planar shape and the resonator is loaded with two dielectric elements, placed symmetrically relative to the central EPR sample.

First claim

We claim:

1 . A microwave resonator for an EPR (=“electron paramagnetic resonance”) probe head, the resonator comprising:
a metal cavity body structured for supporting an electromagnetic microwave resonance mode, said microwave resonance mode having an even number of local maxima of microwave electric field energy, said metal cavity body having at least one first opening for inserting a sample tube to a center position of the resonator, wherein a center of said first opening and a center position of the resonator define an x-axis, said metal cavity body also having at least one second opening for transmitting microwave radiation into the resonator; and
at least two substantially identical dielectric elements disposed symmetrically with respect to an E-field nodal plane, said E-field nodal plane containing said x-axis and a z-axis which is perpendicular to said x-axis, wherein each dielectric element is geometrically formed and positioned to provide an equal overlap with a local maximum of said microwave electric field energy.

2 . The resonator of claim 1 , wherein each of said dielectric elements is elongated along an axis parallel to said x-axis.

3 . The resonator of claim 1 , wherein a ratio of a thickness of said dielectric elements to a dimension of said first opening, both in a direction of said z-axis of the resonator, is in a range of 0.5 to 1.5.

4 . The resonator of claim 1 , wherein said equal overlap is such that at least 50% of said microwave electric field energy is confined within said dielectric elements.

5 . The resonator of claim 1 , wherein the resonator has a flat structure having a smallest internal extension along said z-axis substantially equal to a thickness of said first opening or of said dielectric elements, whichever is greater.

6 . The resonator of claim 1 , wherein said dielectric elements are adjustable in order to change a resonance frequency of said cavity body.

7 . The resonator of claim 1 , wherein the resonator is of cylindrical shape.

8 . The resonator of claim 1 , wherein the resonator is box-shaped.

9 . The resonator of claim 1 , further comprising at least one set of coils for creating a low frequency magnetic field traversing said cavity body and the sample tube, said coils being located at least partly inside the resonator, said coils having a connection to an outside of the cavity body via openings in the side walls of said cavity body which are perpendicular to said z-axis.

10 . The resonator of claim 9 , wherein windings of said coils are completely outside said cavity body.

11 . The resonator of claim 9 , wherein a section of windings of said coils inside said cavity body has a general orientation parallel to said x-axis.

12 . The resonator of claim 9 , wherein the resonator comprises metallized side plates having openings for providing access to said coils inside the resonator.

13 . The resonator of claim 1 , wherein said cavity body of the resonator operates in dielectric loaded rectangular TE102 or cylindrical TM110 resonance modes, and said dielectric elements are placed parallel to said x-axis centered to points of microwave E-field maxima.

14 . An EPR probe head comprising the microwave resonator of claim 1 , further comprising a housing for holding the resonator located in a static magnetic field along said z-axis.

15 . The EPR probe head of claim 14 , further comprising a cryostat within which said probe head is placed, wherein said cavity body of the resonator is spaced from innermost walls of said cryostat, and a space between said cryostat and the resonator is equipped with modules containing stacks of low frequency planar coils for creating main magnetic field modulation, gradient fields, and/or for fields for ENDOR or NMR excitation and detection.

Assignees

• Bruker Biospin Gmbh

Inventors

• Prisecaru Ion
• Hoefer Peter

Classifications

• G01R33/345 Primary

  of waveguide type (G01R33/343 takes precedence) · CPC title

• G01R33/60

  using electron paramagnetic resonance (G01R33/24, G01R33/62 take precedence) · CPC title

• G01R33/343 Primary

  of slotted-tube or loop-gap type · CPC title

• H01P1/207 Primary

  Hollow waveguide filters (H01P1/212, H01P1/213, H01P1/215, H01P1/219 take precedence) · CPC title

• H01P7/10

  Dielectric resonators · CPC title