US3757204A - Long the sample cavity resonator structure for an epr spectrometer employing dielectric material for improving rf electric and magnetic field uniformity a - Google Patents

Long the sample cavity resonator structure for an epr spectrometer employing dielectric material for improving rf electric and magnetic field uniformity a Download PDF

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Publication number
US3757204A
US3757204A US00229788A US3757204DA US3757204A US 3757204 A US3757204 A US 3757204A US 00229788 A US00229788 A US 00229788A US 3757204D A US3757204D A US 3757204DA US 3757204 A US3757204 A US 3757204A
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magnetic field
dielectric material
sample
sample cell
cavity
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US00229788A
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J Hyde
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Varian Medical Systems Inc
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Varian Associates Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/345—Constructional details, e.g. resonators, specially adapted to MR of waveguide type

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  • ABSTRACT In an electron paramagnetic resonance cavity resonator having a line sample therein, a dielectric material positioned near the sample and along at least a portion of its length, and extending into the RF electric field region near the sample, changes the gradient of the electric field intensity and, as a result, the RF magnetic field intensity along the line sample so as to make both the RF electric and magnetic field intensities more uniform along the sample length.
  • the dielectric material may take the form of a shaped sleeve surrounding the sample, or two shorter sleeves extending over the sample from either end and spaced apart at the center region, or parallel plates on either side of the sample,
  • the two most widely used cavity resonators in electron paramagnetic resonance spectrometers are the rectangular TE mode and the cylindrical TE mode cavities, while the cylindrical TM mode cavity is used to a much lesser extent. These cavity resonators form one arm of a microwave bridge and are positioned in the magnetic field gap of the polarizing magnet with the elongated sample cell extending down into the cavity along a line vertically through the center of the cavity and parallel to the magnet pole faces.
  • the radio frequency power delivered to the cavity resonator at the electron resonance frequency produces the driving RF magnetic field along the sample length, this RF magnetic field intensity varying as sin (X'rr/L), where L is the length of the cavity along the sample and x is the position of a point along the sample length measured from the bottom of the cavity, for the rectangular TE mode cavity and the cylindrical TE mode; a somewhat similar function exists for the RF magnetic field intensity in a cylindrical TM, mode cavity.
  • the RF magnetic field intensity is therefore stronger at the central region of the sample length than at the two regions on either end of the central region.
  • that part of the sample at the central region (x L/2) experiences microwave power saturation first, and, if the power continues to increase, the parts of the sample removed from the central region saturate.
  • a dielectric material is positioned in the RF electric field near the sample so as to change the RF electric and magnetic field intensities and to make them more uniform along the sample length, so as to minimize spatial variation of the RF magnetic field intensity along the sample length, minimize thermal gradients along the sample, and/or minimize bridge inbalance while optimizing the magnetic resonance signal output.
  • the dielectric material is in the form of a cylinder surrounding the sample and extending into the electric field region in the cavity, the wall of the cylinder being concave with its thinnest portion in the central region of the sample.
  • the cylinder is replaced with a pair of dielectric plates, one on each side of the sample, the plates being concave.
  • the dielectric is in the form of two hollow cylindrical members extending over the sample regions on either side of the central region, with the central region clear of the dielectric.
  • each separate cylinder is replaced by a pair of plates positioned on opposite sides of the sample and in planes normal to the broad sides of the cavity resonator.
  • FIGS. 1 and 2 are perspective diagramatic views of a rectangular TE mode EPR cavity resonator and a cylindrical TE, mode EPR cavity resonator, respectively, incorporating one embodiment of the present invention.
  • FIG. 3 is a plot of RF magnetic field obtained with and without the use of the present invention, illustrating the increase in uniformity of the RF magnetic field along the sample with the present invention.
  • FIG. 4 is a diagramatic view of another rectangular cavity resonator incorporating another embodiment of the present invention.
  • FIGS. 5 and 6 illustrate still another embodiment of the present invention.
  • FIG. 7 is another structural form of the invention as utilized in a cylindrical TM, mode cavity resonator.
  • FIG. 1 there is shown a typical form of rectangular TE mode cavity resonator which is placed in the gap of a strong magnet in an EPR spectrometer such that the two broad sidewalls 11 and 12 are parallel to the magnetic pole faces and normal to the direction of the magnetic field lines in the gap.
  • Means are provided (not shown) for supplying RF power to the cavity resonator at the magnetic resonance frequency of the electrons in the sample held in the cylindrical sample cell 13 extending vertically in the center of the resonator.
  • the electric field lines E in the cavity resonator extend normal to the two sidewalls 11 and 12 in a sinusoidal function with zero electric field strength at the center of the cavity where the sample is positioned, and maximum electric fields, in opposite and alternating directions, midway between the sample l3 and the two end walls 14 and 15.
  • the RF magnetic field lines extend in an alternating manner parallel to the elongated sample, with the maximum field strength in the center of the cavity at the sample position.
  • the RF magnetic field intensity along the sample varies approximately as sin (x'rr/L where L is the length of the cavity along the sample, as illustrated by thesolid line curve A in FIG. 3.
  • the ordinate in FIG. 3 represents distance from the center of the sample to either end of the sample, and the abscissa represents RF field intensity in arbitrary units. It can be seen that the RF field intensity is maximum at the center region of the sample and decreases in the regions along the sample on either side of the center region.
  • the sample in the center region experiences microwave power saturation first, followed by saturation at the upper and lower regions as the power continues to increase.
  • Undesirable heating of the sample results from sample dielectric loss, and is concentrated in the center region. It is therefore desirable to make the RF magnetic field intensity more uniform along the central region so that saturation can occur over an increased sample length at the same power incident on the cavity, and it is desirable to reduce the spatial variation of the RF electric field intensity along the sample length so that the sample temperature will be more uniform.
  • the RF magnetic field intensity at a sample position can be increased by placing a sleeve of dielectric material, such as quartz, about the sample.
  • a simple increase or decrease of RF magnetic field in the present instance will not solve the problem caused by the RF magnetic field concentration at the cavity sample center; what is desired is control over the RF field distribution in the cavity to obtain more RF magnetic field intensity uniformity over greater sample length.
  • a sleeve 16 of dielectric material, such as quartz, having a concave outer surface is placed over the sample, the walls of the sleeve extending into the region of the electric field lines E on either side of the sample.
  • This dielectric material in the electric field changes the gradients of the electric field intensity which in turn give rise to changes in the intensity of the RF magnetic field.
  • the thinner walled section of the dielectric material at the center region of the sample causes very little change in the RF magnetic field intensity at that region whereas the thicker walled section of the sleeve in the regions on either side of the center sample region result in an increase in the intensity of the RF magnetic field in these regions, in comparison to the uncompensated resonator.
  • Saturation of the sample will also occur more uniformly along the length of the sample.
  • more uniform RF electric and magnetic field intensities along the sample length more sensitivity is obtained in experiments where the sample is near saturation and more faithful representation of the line shape in the region near saturation is obtained, more uniform sample temperature occurs, and more reliable measurements of saturation characteristics of lines results.
  • FIG. 2 A similar form of dielectric sleeve for controlling the relative intensity and orientation of the RF electromagnetic field vectors along the sample length in a cylindrical TE mode EPR cavity resonator 11 is illustrated in FIG. 2.
  • the dielectric cylinder of FIG. I is replaced with a structure approximating the cylinder and comprising a pair of dielectric plates 17, 18 extending on either side of the sample and in the electric field.
  • the outer surfaces of the two plates are concave so that the material is thinner at its center region than at the areas on either side of the center. This results in a more uniform RF magnetic field as represented by curve B in FIG. 3.
  • two cylindrical sleeve section 19 and 21 with uniform wall thickness may be employed to make the RF magnetic field intensity more uniform along the sample.
  • the sleeves extend over the sample from either end thereof, leaving the central region free from dielectric material. Further control over the field uniformity may be accomplished by increasing the thickness of the sleeve wall slightly at the inner ends of the sleeves, as by annular dielectric ring portions 22 affixed thereto as shown in FIG. 6.
  • FIG. 7 there is shown a diagrammatic view of a cylindrical TM mode cavity resonator with still another embodiment of the invention uti lized therein.
  • a typical form of such resonator for X- band has about a 1.5 inch diameter and is 0.17 inch wide.
  • Two pairs of plates 23, 24 and 25, 26 of dielectric material extend from the wall of the resonator along either side of the elongated sample 13 located in the center of the cavity. The plates extend about one-third of the way into the cavity from each side, leaving the middle third of the length along the sample free of dielectric.
  • With a sample cell diameter of about 0.16 inch good results were obtained with quartz plates about 0.04 inch thick and spaced about 0.20 inch from the axis through the sample.
  • the sizes and shapes of the dielectric material can be selected to accomplish the desired results, it has been found that if the dielectric extends too far into the RF electric field, there is a tendency for the change in the RF magnetic field intensity to be reversed in direction.
  • the dielectric material may be quartz, which has a low loss and a high dielectric constant or it may be of other suitable material such as polyethylene, tetlon or corundum.
  • Apparatus for use in testing samples in an electron paramagnetic resonsance spectrometer system compllSll'lg a cavity resonator having an aperture therethrough to receive an elongated sample cell and to apply a radio frequency magnetic field to said sample cell along a substantial portion of its length to produce electron paramagnetic resonance therein, and
  • a dielectric material positioned in the electric field near said sample cell aperture for controlling the relative intensity of the radio frequency magnetic field applied to a cell along the sample cell length wherein a greater thickness of dielectric material is present at regions of the sample cell length on opposite sides of the central region of the cell length than at the central region.
  • said dielectric material is a hollow cylindrical member surrounding the elongated sample cell and with a concave outer surface.
  • said dielectric material comprises at least two sections extending near the two end regions of the sample cell removed from the central region.
  • each of said sections comprises a hollow cylinder surrounding the sample cell.
  • said dielectric material at each side region comprises a pair of plates extending parallel to the sample cell and being positioned on opposite sides of the cell.
  • a cavity resonator for an EPR spectrometer including, means for sustaining electric and magnetic field intensity waves in said resonator, said resonator including an aperture defining an axis therethrough for receiving an elongated sample cell, said magnetic field intensity being non-uniform along said sample cell axis, the improvement comprising:
  • said means comprising a dielectric material being interposed between said sample cell and at least a pair of cavity walls, said dielectric material includes a surface wherein the cross section of the surface through said axis includes elongated elements parallel to said axis.

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
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US00229788A 1972-02-28 1972-02-28 Long the sample cavity resonator structure for an epr spectrometer employing dielectric material for improving rf electric and magnetic field uniformity a Expired - Lifetime US3757204A (en)

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AU (1) AU472073B2 (show.php)
CA (1) CA976613A (show.php)
CH (1) CH552809A (show.php)
DE (1) DE2307517C2 (show.php)
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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USD247432S (en) 1977-02-28 1978-03-07 The United States Of America As Represented By The Field Operations Bureau Of The Federal Communications Commission Fine and coarse tuning assembly for cavities
US4549136A (en) * 1983-04-07 1985-10-22 Varian Associates, Inc. Controlled susceptibility plugs
US4748427A (en) * 1985-11-20 1988-05-31 Gte Telecommunicazioni, S.P.A. Microwave resonating cavity with metallized dielectric
US5596276A (en) * 1992-06-09 1997-01-21 Nikkiso Co., Ltd. Cavity resonator for an electron spin resonator
US5698986A (en) * 1996-02-12 1997-12-16 Allen-Bradley Company, Inc. Cigarette density monitor
JP2003500133A (ja) * 1999-05-21 2003-01-07 ザ ゼネラル ホスピタル コーポレーション 撮像システム用ｒｆコイル
WO2003010849A1 (en) * 2001-07-25 2003-02-06 Mcw Research Foundation, Inc. Cavity for epr spectroscopy having axially uniform field
US20040027128A1 (en) * 2000-07-31 2004-02-12 Regents Of The University Of Minnesota Radio frequency magnetic field unit
US20050017720A1 (en) * 2003-07-25 2005-01-27 Mett Richard Raymond Aqueous sample holder for EPR and MR spectroscopy
US20080084210A1 (en) * 2004-05-07 2008-04-10 Regents Of The University Of Minnesota Multi-current elements for magnetic resonance radio frequency coils
US20090007692A1 (en) * 2007-07-06 2009-01-08 Airbus Uk Limited Method and apparatus for testing composite materials
US9190707B2 (en) * 2011-10-18 2015-11-17 Prism Microwave, Inc. Method for manufacturing an RF filter and an RF filter
EP3070488A1 (en) 2015-03-18 2016-09-21 Bruker BioSpin GmbH EPR microwave cavity for small magnet airgaps
CN112242599A (zh) * 2019-07-19 2021-01-19 布鲁克碧奥斯平有限公司 由可变流体体积引起的q-变化、m-变化和d-变化

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3559043A (en) * 1967-07-03 1971-01-26 Varian Associates Bimodal cavity resonator and microwave spectrometers using same

Cited By (34)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USD247432S (en) 1977-02-28 1978-03-07 The United States Of America As Represented By The Field Operations Bureau Of The Federal Communications Commission Fine and coarse tuning assembly for cavities
US4549136A (en) * 1983-04-07 1985-10-22 Varian Associates, Inc. Controlled susceptibility plugs
US4748427A (en) * 1985-11-20 1988-05-31 Gte Telecommunicazioni, S.P.A. Microwave resonating cavity with metallized dielectric
US5596276A (en) * 1992-06-09 1997-01-21 Nikkiso Co., Ltd. Cavity resonator for an electron spin resonator
US5698986A (en) * 1996-02-12 1997-12-16 Allen-Bradley Company, Inc. Cigarette density monitor
US20060033501A1 (en) * 1999-05-21 2006-02-16 The General Hospital Corporation D/B/A Massachusetts General Hospital RF coil for imaging system
JP2003500133A (ja) * 1999-05-21 2003-01-07 ザ ゼネラル ホスピタル コーポレーション 撮像システム用ｒｆコイル
US20070247160A1 (en) * 1999-05-21 2007-10-25 The General Hospital Corporation D/B/A Massachusetts General Hospital Rf coil for imaging system
US7268554B2 (en) * 1999-05-21 2007-09-11 The General Hospital Corporation RF coil for imaging system
US20030146750A1 (en) * 1999-05-21 2003-08-07 The General Hospital Corporation RF coil for imaging system
US20070007964A1 (en) * 1999-05-21 2007-01-11 The General Hospital Corporation D/B/A Massachusetts General Hospital RF coil for imaging system
US20060255806A1 (en) * 2000-07-31 2006-11-16 Regents Of The University Of Minnesota Assymetric radio frequency magnetic line array
US6958607B2 (en) 2000-07-31 2005-10-25 Regents Of The University Of Minnesota Assymetric radio frequency transmission line array
US20060001426A1 (en) * 2000-07-31 2006-01-05 Regents Of The University Of Minnesota Assymetric radio frequency magnetic line array
US20040027128A1 (en) * 2000-07-31 2004-02-12 Regents Of The University Of Minnesota Radio frequency magnetic field unit
US7893693B2 (en) 2000-07-31 2011-02-22 Regents Of The University Of Minnesota Assymetric radio frequency magnetic line array
US6828789B2 (en) 2001-07-25 2004-12-07 The Mcw Research Foundation, Inc. Cavity resonator for electron paramagnetic resonance spectroscopy having axially uniform field
US20030038633A1 (en) * 2001-07-25 2003-02-27 Hyde James S. Cavity resonator for electron paramagnetic resonance spectroscopy having axially uniform field
WO2003010849A1 (en) * 2001-07-25 2003-02-06 Mcw Research Foundation, Inc. Cavity for epr spectroscopy having axially uniform field
US20050017720A1 (en) * 2003-07-25 2005-01-27 Mett Richard Raymond Aqueous sample holder for EPR and MR spectroscopy
US7088101B2 (en) 2003-07-25 2006-08-08 Molecular Specialties, Inc. Aqueous sample holder for EPR and MR spectroscopy
US7710117B2 (en) 2004-05-07 2010-05-04 Regents Of The University Of Minnesota Multi-current elements for magnetic resonance radio frequency coils
US20080084210A1 (en) * 2004-05-07 2008-04-10 Regents Of The University Of Minnesota Multi-current elements for magnetic resonance radio frequency coils
US20090007692A1 (en) * 2007-07-06 2009-01-08 Airbus Uk Limited Method and apparatus for testing composite materials
US7798014B2 (en) * 2007-07-06 2010-09-21 Airbus Uk Limited Method and apparatus for testing composite materials
US9190707B2 (en) * 2011-10-18 2015-11-17 Prism Microwave, Inc. Method for manufacturing an RF filter and an RF filter
EP3070488A1 (en) 2015-03-18 2016-09-21 Bruker BioSpin GmbH EPR microwave cavity for small magnet airgaps
CN105990631A (zh) * 2015-03-18 2016-10-05 布鲁克碧奥斯平有限公司 用于小磁体气隙的epr微波腔体
US10353027B2 (en) 2015-03-18 2019-07-16 Bruker Biospin Gmbh EPR microwave cavity for small magnet airgaps
CN105990631B (zh) * 2015-03-18 2020-05-12 布鲁克碧奥斯平有限公司 用于小磁体气隙的epr微波腔体
CN112242599A (zh) * 2019-07-19 2021-01-19 布鲁克碧奥斯平有限公司 由可变流体体积引起的q-变化、m-变化和d-变化
EP3767318A1 (en) 2019-07-19 2021-01-20 Bruker BioSpin GmbH Q-,m- and d-variation by variable fluid volume
US11079457B2 (en) 2019-07-19 2021-08-03 Bruker Biospin Gmbh Microwave resonator for an EPR probehead providing Q-, M- and D-variation using a variable fluid volume
CN112242599B (zh) * 2019-07-19 2022-05-27 布鲁克碧奥斯平有限公司 含微波谐振器和修改剂容器的系统及电子顺磁谐振波谱仪

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AU5227173A (en) 1974-08-22
DE2307517C2 (de) 1985-01-31
CA976613A (en) 1975-10-21
DE2307517A1 (de) 1973-10-04
GB1366475A (en) 1974-09-11
CH552809A (de) 1974-08-15
AU472073B2 (en) 1976-05-13
FR2178570A5 (show.php) 1973-11-09

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