CA1187551A - Capacitively shortened coaxial resonators for nuclear resonance signal reception - Google Patents
Capacitively shortened coaxial resonators for nuclear resonance signal receptionInfo
- Publication number
- CA1187551A CA1187551A CA000423134A CA423134A CA1187551A CA 1187551 A CA1187551 A CA 1187551A CA 000423134 A CA000423134 A CA 000423134A CA 423134 A CA423134 A CA 423134A CA 1187551 A CA1187551 A CA 1187551A
- Authority
- CA
- Canada
- Prior art keywords
- cylinders
- capacitor means
- coaxial resonator
- capacitor
- sample region
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- 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
- G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
-
- 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
-
- 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
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3628—Tuning/matching of the transmit/receive coil
-
- 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
- G01R33/30—Sample handling arrangements, e.g. sample cells, spinning mechanisms
- G01R33/307—Sample handling arrangements, e.g. sample cells, spinning mechanisms specially adapted for moving the sample relative to the MR system, e.g. spinning mechanisms, flow cells or means for positioning the sample inside a spectrometer
-
- 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
- G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
-
- 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
- G01R33/34092—RF coils specially adapted for NMR spectrometers
-
- 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
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56536—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to magnetic susceptibility variations
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S505/00—Superconductor technology: apparatus, material, process
- Y10S505/825—Apparatus per se, device per se, or process of making or operating same
- Y10S505/842—Measuring and testing
- Y10S505/843—Electrical
- Y10S505/844—Nuclear magnetic resonance, NMR, system or device
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S505/00—Superconductor technology: apparatus, material, process
- Y10S505/825—Apparatus per se, device per se, or process of making or operating same
- Y10S505/866—Wave transmission line, network, waveguide, or microwave storage device
Abstract
ABSTRACT
A capacitively shortened coaxial resonator for making nuclear magnetic resonance measurements includes inner and outer concentrically arranged metal cylinders.
The cylinders define therebetween a sample region and are shorted electrically by a conductive cap which closes one end of the inner and outer cylinders. A capacitor is connected across the cylinders at the opposite open end and functions to resonate with the inductance of a coaxial conductor formed by the short circuited cylinders.
Samples placed in the sample region are mounted on an air bearing and rotated by means of air holes formed in the inner and outer cylinders.
A capacitively shortened coaxial resonator for making nuclear magnetic resonance measurements includes inner and outer concentrically arranged metal cylinders.
The cylinders define therebetween a sample region and are shorted electrically by a conductive cap which closes one end of the inner and outer cylinders. A capacitor is connected across the cylinders at the opposite open end and functions to resonate with the inductance of a coaxial conductor formed by the short circuited cylinders.
Samples placed in the sample region are mounted on an air bearing and rotated by means of air holes formed in the inner and outer cylinders.
Description
755~
Nuclear magnetic resonance (N~R) is a well-~nown and widely used -technique for obtaining detailed structural information about materials. The usual technique consists of placing a sample of the material to be analyzed in a radio fre~uency resona-tor that is located in an intense, uniform static magnetic field; often that of a supercon-ducting solenoid. A radio frequency (rf) pulse is applied to the resonator to induce precessing transverse magnetiza-tion in an ensemble of nuclear spins. The signal then induced in the resonator by the precessing transverse magnetization in an ensemble of nuclear spins following the application of the rf pulse permits a detailed struc-tural analysis of the sample material.
This invention pertains to improving the sensi-tivity of nuclear magnetic resonance measurements by means of a novel, highly sensitive capacitively shortened coa~ial resonator. Heretofore, capacitively shortened coaxial resonators have been described in the articles appearing in the Journal of Scientific Instruments (Journal of Physics) Series 2, Volume 2, 1036 (1969) and the Review of Scientific Instruments, Volume 42, No. 4 (April, 1971).
Also, attempts have been made to use such resonators as NMR cavities, but, in general, little attention has been paid to them.
The present invention provides a capacitively shortened coaxial resonator for inducing transverse magne-tization in an ensemble of nuclear spins, the resonator comprises open-ended inner and outer concentrically ar-ranged metal cylinders which define therebetween a sample region for containing the ensemble of nuclear spins, wherein the ratio of the outer diameter of the inner cy-linder to the inner diameter of the ou-ter cylinder is be~
tween about 0~5 and O.B, removable annular metallic cap means for closing one end oi the inner and outer cylinders and providing an electrical short circuit therebetween, and at least one ring like capacitor means connected across the inner and outer cylinders at the other end of the cy-.~ ~
i~8~5S~
linders for resonating with the inductance of the coaxialconductor formed by -the shorted-together cylinders.
Preferably, the inner and outer cylinders each have axially spaced sets of circumferentially spaced open-ings forming a cylindrical air bearing and further com-prising a thrust air bearing mounted between the capaci-tor and the sample region for supporting and spinning a coaxial sample container positioned in the sample region.
One, two, or three additional axially spaced capacitor discs may be connected between the cylinders to permit double, triple, or quadruple resonance experi-ments. In order to match the rf power to separate constant-impedance lines at each fre~uency of resonance, appropria-te coupling links and/or coupling capacitors are provided.
In operation, a sealed, coaxial sample container is inserted in the sample region between the cap means and the ring-like capacitor means. Typically, the length of the sample region ranges from one to two times the dia-meter of the outside cylinder.
Embodiments of the invention are shown in the drawings in which:-Figure 1 is a vertical section of a single-tuned capacitively shortened coaxial resonator embodying the present invention;
2S Figure 2 is a sectional view of the Figure 1 embodiment taken along line 2-2 and looking in the di-rection of the arrows;
Figure 3 is a schematic drawing of the Figure 1 embodiment;
Figure 4 is a cross-section view of a ring-li]ce capacitor disc used in -the Figure 1 embodiment;
Figure 5 is a cross-section view of an alternate embodiment of a capacitor disc;
Figure 6 is a schematic drawing of a double-tuned capacitively shortened coaxial resonator; and Figure 7 is a schematic drawing of a -triple-tuned capacitively shortened coaxial resonator.
~7S5~
In the capacitively shortened coaxial resona-tor 10, as shown in Figures 1-3, the resonator comprises inner and outer concentrically arranged cylinders 12 and 14, respectively. The cylinders are formed of a me-tal, such as copper, and define therebetween a sample region 150 Preferably, the diameter of the inner cylinder 12 ranges from about 0.5 to about 0.8 times th~ diameter of -the outer cylinder 14. Although smaller rati.os would result in both higher inductance and higher Q, both of which are desirable, it is more desirable to maintain uniform rf magnetic fields over the ensemble of nuclear spins constituting the sample and to maintain a high rf filling factor. Bo-th oE these latter objectives are better realized with somewhat larger values of this ratio.
Coaxial alignment of the inner metal cylinder 12 and the outer metal cylinder 14 is maintained by means of a ring-like capacitor disc 16 soldered in place at the lower end and an annular press-fit copper cap 18 at the top end, with means such as a knob 19 provided to facili-tate removal of the cap~ A coaxial sample container 20 with a ring-like press-fit lid 22 is provided for contain~
ing the sample to be analyzed.
Two sets of circumferentially spaced air bearing holes 24 are formed on the inner cylinder 12 and two sets of circumferentially spaced air exhaust holes 26 are pro~
vided Oll the outer metal cylinder 1~ to form a cylindrical air bearing. A ring-like air thrust bearing 28 con-taining spaced and obliquely drilled air holes 29 is cemented in place as shown above the capacitor disc 16 to provide both vertical support and torque to the sample container 20 for NMR line narrowing via slow spinning. Air is supplied to the interior of the inner cylinder 12 through the open end of the resonator and to the thrust bearing 28 through an opening 30. A description of an NMR sample spinner including air bearings is given in our United States Patent 4,456,882, corresponding to Canadian Patent Applica-tion No. 418,877.
~8~55~
The cylinders 12 and 14 are thin-walled, hard-drawn, oxygen free, high conductivity copper and may contain up to about 0.1% silver for improved dimensional stability and creep resistance. In addition, the copper is plated with a corrosion resistant metal. The plating thickness on the exterior of the inner cylinder 12 and on the in-terior of the outer cylinder 14 mus-t be sufficiently thin so as not to degrade the quality factor, Q, of the resona-tor. Typically, thus, a gold plate .0002 mm thick is ap-plied, except that the plating thickness is increasedat the top of the cylinders to allow extended wear where the cylinders 12 and 14 engage the cap 18. The paramagnetic susceptibility of the copper cylinders and cap may be cancelled by plating the exterior of the outer cylinder 14, the interior of the inner cylinder 12, and the top surface of the cap 18 with the appropriate thickness as determined by the ratio of the susceptibilities of a cor-rosion resistant diamagnetic material such as rhodium or iridium. Aco-lstic ringing of the cap 18 may be reduced by plating its lower surface with platinum to a thickness of several rf skin depths.
The thin-walled coaxial sample container 20 is fabricated from a rigid, high strength, chemically inert and low loss dielectric material, such as borosilicate glass, alumina ceramic, or polyimide-amide plastic. The cap 22 is preferably made of a material, such as Teflon*
~polytetrafluoroethylene) or a silicone rubber, which facilitates sealing.
The essential electronic elements of the resona-~
tor, along with the elements of a coaxial cable coupledto the resonator, are illustrated schematically in Fig-ure 3. The resonator 10 possesses the inductance Ll of a shorted coaxial line since the two conducting cylinders 12 and 1~ are shorted together. The inductance Ll resona-tes with the capacitance Cl of the ring-like capacitor disc 16 and the capacitance Clm of the line matching capa-citor. The values of the inductance, capacitance, and *Registered Trade Mark 55~
resistance are determined by the well~known equa-tions of electromagnetism:
L = 2h ln ~ ) X 10 7 Henrys/me-ter C = (47r2 f2 L)-l C = ( _ ,C ) m 2~f Q Z
Q = 2~f L
where h is the distance between the cap 18 and the capacitor 16r rO is the inside radius of the outer cylinder 14, rl is the outside radius of the inner cylinder 12, f is the resonate frequency, Q is the resonance quality Eactor, R is the total effective series resistance (esr) of the inductor 1. and the capacitor C, RL is the esr of the in-ductor~ p is the mean bulk resistivity of the induc-tor surfaces, and ~O is the permeability of free space. All of the above equations are in standard MKS units.
The superioL performance of the resonator de-pends to a large extent on reducing the total eEfectiveseries resistance R to the minimum possible value. This is achieved by the metal plating applied to the surface of the copper cylinders 12 and 14 and to the underside of the cap 18, the la-tter effecting a short circuit between the cylinders. Also important is -the positioning and con-figuration of the ring-like capacitor disc 16.
The electric field within the resonator 10 is radial in direction and, because of the extremely low in-ductance of the resonator, the average field is much less than conventional coil designs of comparable volume and frequencyi Dielectric losses in the sample are reduced significantly and high voltage arcing problems are ef-5~ ' .~
~755~
fec-tively eliminated. The rE magnetic field within -the resonator is, obviously, perpendicuIar -to the electric ~ield.
Figure 4 illustrates a low loss ring-like ceramic disc capacitor 32 arranged according to the presen-t inven-tion which may be incorporated into the resonator of Fig-ure l. A low loss ceramic washer 34 is surrounded on all surEaces by metal 36. The metal may be applied to the ceramic by any o~ the well-known metalization techniques.
InsuIating rings 38 and 40 are then etched in the metal through to -the ceramic near the inner and outer edges of the ceramic washer 34. Larger values of capacitance may be achieved by stacking several such capacitors in parallel fashion, spaced apart with dielectric washers 42.
~nother preEerred ring-like capacitor disc 44 is shown in Figure 5. The disc 44 comprises an inner copper washer 46 and an outer copper washer 48, bo-th washers being supported by a dielectric substrate washer 50, typically made from conventional single-clad circuit board. Several conventional low loss ceramic chip capacitors 52 are soldered between the copper washers 46 and 48 in a sym-metrical fashion.
Figure 6 shows schema-tically a double-tuned co-axial resonator which is adapted to accommoda-te double resonance experiments. The area between the inner and outer cylinders is divided by a rin~-like capacitor disc C2, e.g. Figure 4, into an upper sample region Ll and a lower region L2. The latter region L2 may be filled par-tiallyiwith a solid dielectric to add to the struc-tural integrity of the system. Coupling to the high frequency line E2 is accomplished by means of an inductive link L2 m which intersects a portion of the high frequency flux in the lower region L2 in cooperation with a coupling capaci-tor C2m. For experiments requiring greater sensi-tivity at the lower frequency, L1 must be larger than L2 and vice ~ersa.
~; It is frequently desirable to triple tune the ~8755~
sample resonator so as to permit observation of one nuclide while simultaneously decoupling the effec-ts of another nuclide and using a third nuclide for field stabilization.
In this case, high sensi-tivity is normally required a-t only one of the frequencies. Figure 7 illustrates schema-tically a triple tuned coaxial resonator arranged accord-ing to the present inven-tion. In Figure 7, a third ring-like disc capacitor C3 is added in such a way so as to maintain high sensitivi-ty at the middle frequency, f2.
The inductance in the sample region, L2, must be greater than the inductance of the high frequency tank, L3, and less than the inductance of the low frequency tank, Ll.
In an analogous way, a fourth annular capacitor disc may be added so as to define a fourth coaxial region and thus permit quadruple tuning.
Although the applicant's inven-tion has been described herein with reference to specific embodiments, it will be recognized that changes and modifications may be made without departing from the spirit of the present invention. All such changes and modifications are intended to be included within the scope of the following claims.
,.~
Nuclear magnetic resonance (N~R) is a well-~nown and widely used -technique for obtaining detailed structural information about materials. The usual technique consists of placing a sample of the material to be analyzed in a radio fre~uency resona-tor that is located in an intense, uniform static magnetic field; often that of a supercon-ducting solenoid. A radio frequency (rf) pulse is applied to the resonator to induce precessing transverse magnetiza-tion in an ensemble of nuclear spins. The signal then induced in the resonator by the precessing transverse magnetization in an ensemble of nuclear spins following the application of the rf pulse permits a detailed struc-tural analysis of the sample material.
This invention pertains to improving the sensi-tivity of nuclear magnetic resonance measurements by means of a novel, highly sensitive capacitively shortened coa~ial resonator. Heretofore, capacitively shortened coaxial resonators have been described in the articles appearing in the Journal of Scientific Instruments (Journal of Physics) Series 2, Volume 2, 1036 (1969) and the Review of Scientific Instruments, Volume 42, No. 4 (April, 1971).
Also, attempts have been made to use such resonators as NMR cavities, but, in general, little attention has been paid to them.
The present invention provides a capacitively shortened coaxial resonator for inducing transverse magne-tization in an ensemble of nuclear spins, the resonator comprises open-ended inner and outer concentrically ar-ranged metal cylinders which define therebetween a sample region for containing the ensemble of nuclear spins, wherein the ratio of the outer diameter of the inner cy-linder to the inner diameter of the ou-ter cylinder is be~
tween about 0~5 and O.B, removable annular metallic cap means for closing one end oi the inner and outer cylinders and providing an electrical short circuit therebetween, and at least one ring like capacitor means connected across the inner and outer cylinders at the other end of the cy-.~ ~
i~8~5S~
linders for resonating with the inductance of the coaxialconductor formed by -the shorted-together cylinders.
Preferably, the inner and outer cylinders each have axially spaced sets of circumferentially spaced open-ings forming a cylindrical air bearing and further com-prising a thrust air bearing mounted between the capaci-tor and the sample region for supporting and spinning a coaxial sample container positioned in the sample region.
One, two, or three additional axially spaced capacitor discs may be connected between the cylinders to permit double, triple, or quadruple resonance experi-ments. In order to match the rf power to separate constant-impedance lines at each fre~uency of resonance, appropria-te coupling links and/or coupling capacitors are provided.
In operation, a sealed, coaxial sample container is inserted in the sample region between the cap means and the ring-like capacitor means. Typically, the length of the sample region ranges from one to two times the dia-meter of the outside cylinder.
Embodiments of the invention are shown in the drawings in which:-Figure 1 is a vertical section of a single-tuned capacitively shortened coaxial resonator embodying the present invention;
2S Figure 2 is a sectional view of the Figure 1 embodiment taken along line 2-2 and looking in the di-rection of the arrows;
Figure 3 is a schematic drawing of the Figure 1 embodiment;
Figure 4 is a cross-section view of a ring-li]ce capacitor disc used in -the Figure 1 embodiment;
Figure 5 is a cross-section view of an alternate embodiment of a capacitor disc;
Figure 6 is a schematic drawing of a double-tuned capacitively shortened coaxial resonator; and Figure 7 is a schematic drawing of a -triple-tuned capacitively shortened coaxial resonator.
~7S5~
In the capacitively shortened coaxial resona-tor 10, as shown in Figures 1-3, the resonator comprises inner and outer concentrically arranged cylinders 12 and 14, respectively. The cylinders are formed of a me-tal, such as copper, and define therebetween a sample region 150 Preferably, the diameter of the inner cylinder 12 ranges from about 0.5 to about 0.8 times th~ diameter of -the outer cylinder 14. Although smaller rati.os would result in both higher inductance and higher Q, both of which are desirable, it is more desirable to maintain uniform rf magnetic fields over the ensemble of nuclear spins constituting the sample and to maintain a high rf filling factor. Bo-th oE these latter objectives are better realized with somewhat larger values of this ratio.
Coaxial alignment of the inner metal cylinder 12 and the outer metal cylinder 14 is maintained by means of a ring-like capacitor disc 16 soldered in place at the lower end and an annular press-fit copper cap 18 at the top end, with means such as a knob 19 provided to facili-tate removal of the cap~ A coaxial sample container 20 with a ring-like press-fit lid 22 is provided for contain~
ing the sample to be analyzed.
Two sets of circumferentially spaced air bearing holes 24 are formed on the inner cylinder 12 and two sets of circumferentially spaced air exhaust holes 26 are pro~
vided Oll the outer metal cylinder 1~ to form a cylindrical air bearing. A ring-like air thrust bearing 28 con-taining spaced and obliquely drilled air holes 29 is cemented in place as shown above the capacitor disc 16 to provide both vertical support and torque to the sample container 20 for NMR line narrowing via slow spinning. Air is supplied to the interior of the inner cylinder 12 through the open end of the resonator and to the thrust bearing 28 through an opening 30. A description of an NMR sample spinner including air bearings is given in our United States Patent 4,456,882, corresponding to Canadian Patent Applica-tion No. 418,877.
~8~55~
The cylinders 12 and 14 are thin-walled, hard-drawn, oxygen free, high conductivity copper and may contain up to about 0.1% silver for improved dimensional stability and creep resistance. In addition, the copper is plated with a corrosion resistant metal. The plating thickness on the exterior of the inner cylinder 12 and on the in-terior of the outer cylinder 14 mus-t be sufficiently thin so as not to degrade the quality factor, Q, of the resona-tor. Typically, thus, a gold plate .0002 mm thick is ap-plied, except that the plating thickness is increasedat the top of the cylinders to allow extended wear where the cylinders 12 and 14 engage the cap 18. The paramagnetic susceptibility of the copper cylinders and cap may be cancelled by plating the exterior of the outer cylinder 14, the interior of the inner cylinder 12, and the top surface of the cap 18 with the appropriate thickness as determined by the ratio of the susceptibilities of a cor-rosion resistant diamagnetic material such as rhodium or iridium. Aco-lstic ringing of the cap 18 may be reduced by plating its lower surface with platinum to a thickness of several rf skin depths.
The thin-walled coaxial sample container 20 is fabricated from a rigid, high strength, chemically inert and low loss dielectric material, such as borosilicate glass, alumina ceramic, or polyimide-amide plastic. The cap 22 is preferably made of a material, such as Teflon*
~polytetrafluoroethylene) or a silicone rubber, which facilitates sealing.
The essential electronic elements of the resona-~
tor, along with the elements of a coaxial cable coupledto the resonator, are illustrated schematically in Fig-ure 3. The resonator 10 possesses the inductance Ll of a shorted coaxial line since the two conducting cylinders 12 and 1~ are shorted together. The inductance Ll resona-tes with the capacitance Cl of the ring-like capacitor disc 16 and the capacitance Clm of the line matching capa-citor. The values of the inductance, capacitance, and *Registered Trade Mark 55~
resistance are determined by the well~known equa-tions of electromagnetism:
L = 2h ln ~ ) X 10 7 Henrys/me-ter C = (47r2 f2 L)-l C = ( _ ,C ) m 2~f Q Z
Q = 2~f L
where h is the distance between the cap 18 and the capacitor 16r rO is the inside radius of the outer cylinder 14, rl is the outside radius of the inner cylinder 12, f is the resonate frequency, Q is the resonance quality Eactor, R is the total effective series resistance (esr) of the inductor 1. and the capacitor C, RL is the esr of the in-ductor~ p is the mean bulk resistivity of the induc-tor surfaces, and ~O is the permeability of free space. All of the above equations are in standard MKS units.
The superioL performance of the resonator de-pends to a large extent on reducing the total eEfectiveseries resistance R to the minimum possible value. This is achieved by the metal plating applied to the surface of the copper cylinders 12 and 14 and to the underside of the cap 18, the la-tter effecting a short circuit between the cylinders. Also important is -the positioning and con-figuration of the ring-like capacitor disc 16.
The electric field within the resonator 10 is radial in direction and, because of the extremely low in-ductance of the resonator, the average field is much less than conventional coil designs of comparable volume and frequencyi Dielectric losses in the sample are reduced significantly and high voltage arcing problems are ef-5~ ' .~
~755~
fec-tively eliminated. The rE magnetic field within -the resonator is, obviously, perpendicuIar -to the electric ~ield.
Figure 4 illustrates a low loss ring-like ceramic disc capacitor 32 arranged according to the presen-t inven-tion which may be incorporated into the resonator of Fig-ure l. A low loss ceramic washer 34 is surrounded on all surEaces by metal 36. The metal may be applied to the ceramic by any o~ the well-known metalization techniques.
InsuIating rings 38 and 40 are then etched in the metal through to -the ceramic near the inner and outer edges of the ceramic washer 34. Larger values of capacitance may be achieved by stacking several such capacitors in parallel fashion, spaced apart with dielectric washers 42.
~nother preEerred ring-like capacitor disc 44 is shown in Figure 5. The disc 44 comprises an inner copper washer 46 and an outer copper washer 48, bo-th washers being supported by a dielectric substrate washer 50, typically made from conventional single-clad circuit board. Several conventional low loss ceramic chip capacitors 52 are soldered between the copper washers 46 and 48 in a sym-metrical fashion.
Figure 6 shows schema-tically a double-tuned co-axial resonator which is adapted to accommoda-te double resonance experiments. The area between the inner and outer cylinders is divided by a rin~-like capacitor disc C2, e.g. Figure 4, into an upper sample region Ll and a lower region L2. The latter region L2 may be filled par-tiallyiwith a solid dielectric to add to the struc-tural integrity of the system. Coupling to the high frequency line E2 is accomplished by means of an inductive link L2 m which intersects a portion of the high frequency flux in the lower region L2 in cooperation with a coupling capaci-tor C2m. For experiments requiring greater sensi-tivity at the lower frequency, L1 must be larger than L2 and vice ~ersa.
~; It is frequently desirable to triple tune the ~8755~
sample resonator so as to permit observation of one nuclide while simultaneously decoupling the effec-ts of another nuclide and using a third nuclide for field stabilization.
In this case, high sensi-tivity is normally required a-t only one of the frequencies. Figure 7 illustrates schema-tically a triple tuned coaxial resonator arranged accord-ing to the present inven-tion. In Figure 7, a third ring-like disc capacitor C3 is added in such a way so as to maintain high sensitivi-ty at the middle frequency, f2.
The inductance in the sample region, L2, must be greater than the inductance of the high frequency tank, L3, and less than the inductance of the low frequency tank, Ll.
In an analogous way, a fourth annular capacitor disc may be added so as to define a fourth coaxial region and thus permit quadruple tuning.
Although the applicant's inven-tion has been described herein with reference to specific embodiments, it will be recognized that changes and modifications may be made without departing from the spirit of the present invention. All such changes and modifications are intended to be included within the scope of the following claims.
,.~
Claims (10)
1. A capacitively shortened coaxial resonator for inducing transverse magnetization in an ensemble of nuclear spins, said resonator comprising:
open-ended inner and outer concentrically ar-ranged metal cylinders which define therebetween a sample region for containing said ensemble of nuclear spins, wherein the ratio of the outer diameter of the inner cy-linder to the inner diameter of the outer cylinder is be-tween about 0.5 to 0.8;
removable annular metallic cap means for closing one end of the inner and outer cylinders and providing an electrical short circuit therebetween; and at least one ring-like capacitor means connected across the inner and outer cylinders at the other end of the cylinders for resonating with the inductance of the coaxial conductor formed by the shorted-together cylinders.
open-ended inner and outer concentrically ar-ranged metal cylinders which define therebetween a sample region for containing said ensemble of nuclear spins, wherein the ratio of the outer diameter of the inner cy-linder to the inner diameter of the outer cylinder is be-tween about 0.5 to 0.8;
removable annular metallic cap means for closing one end of the inner and outer cylinders and providing an electrical short circuit therebetween; and at least one ring-like capacitor means connected across the inner and outer cylinders at the other end of the cylinders for resonating with the inductance of the coaxial conductor formed by the shorted-together cylinders.
2. A capacitively shortened coaxial resonator according to claim 1, in which the inner and outer cy-linders each have axially spaced sets of circumferentially spaced openings forming a cylindrical air bearing and fur-ther comprising a thrust air bearing mounted between the capacitor and the sample region for supporting and spinning a coaxial sample container positioned in the sample region.
3. A capacitively shortened coaxial resonator according to claim 1, in which the surfaces of the cap means and the inner and outer cylinders are plated with thin layers of metal to minimize the paramagnetic suscepti-bility thereof.
4. A capacitively shortened coaxial resonator according to claim 1, 2 or 3, wherein the capacitor means comprises a ceramic washer, metal applied to and surrounding the surface of the washer and a pair of concentric insula-ting rings formed as cutouts in the metal surrounding the ceramic washer, one ring being formed on each flat surface of the washer, with one ring nearer the inside diameter and the other ring nearer the outside diameter.
5. A capacitively shortened coaxial resonator according to claim 1, further comprising a second capacitor means between the inner and outer cylinders and axially spaced from the at least one capacitor means for defining a second region between said second capacitor means and the cap means and for producing resonance at two different frequencies.
6. A capacitively shortened coaxial resonator according to claim 5, further comprising a third capacitor means between the inner and outer cylinders and axially spaced from the second capacitor means for defining a third region between the third capacitor means and the cap means and for producing resonance at three different frequencies.
7. A capacitively shortened coaxial resonator according to claim 1, wherein the cylinders are made from copper with up to 0.1% silver.
8. A capacitively shortened coaxial resonator according to claim 1, wherein the cap means includes a layer of platinum.
9. A capacitively shortened coaxial resonator for making nuclear magnetic resonance measurements com-prising open-ended inner and outer concentrically arranged metal cylinders which define therebetween a sample region, cap means for closing one end of the inner and outer cy-linders and providing an electrical short circuit there-between, and at least one capacitor means connected across the inner and outer cylinders at the other open end of the cylinders for resonating with the inductance of the coaxial conductor formed by the shorted-together cylinders, said capacitor means including a pair of concentric metal washers supported on a dielectric substrate and a plurality of ceramic chip capacitors symmetrically attached between the washers.
10. A capacitively shortened coaxial resonator for making nuclear magnetic resonance measurements com-prising open-ended inner and outer concentrically arranged metal cylinders which define therebetween a sample region, cap means for closing one end of the inner and outer cy-linders and providing an electrical short circuit there-between, at least one capacitor means connected across the inner and outer cylinders at the other open end of the cylinders for resonating with the inductance of the coaxial conductor formed by the shorted-together cylinders, said capacitor means having a ring-like form and being connected between the cylinders at the end thereof opposite from the short-circuited end, and an air bearing mounted between the capacitor means and the sample region for sup-plying air under pressure into the sample region.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/379,116 US4463328A (en) | 1982-05-17 | 1982-05-17 | Capacitively shortened coaxial resonators for nuclear magnetic resonance signal reception |
US379,116 | 1989-07-13 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1187551A true CA1187551A (en) | 1985-05-21 |
Family
ID=23495891
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000423134A Expired CA1187551A (en) | 1982-05-17 | 1983-03-08 | Capacitively shortened coaxial resonators for nuclear resonance signal reception |
Country Status (5)
Country | Link |
---|---|
US (1) | US4463328A (en) |
EP (1) | EP0094734B1 (en) |
JP (1) | JPS58223738A (en) |
CA (1) | CA1187551A (en) |
DE (1) | DE3369385D1 (en) |
Families Citing this family (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4641098A (en) * | 1985-03-15 | 1987-02-03 | Doty Scientific, Inc. | Parallel single turn saddle resonator for nuclear magnetic resonance signal reception |
US4841248A (en) * | 1985-08-14 | 1989-06-20 | Picker International, Inc. | Transverse field limited localized coil for magnetic resonance imaging |
EP0389868B1 (en) * | 1989-03-29 | 1995-09-13 | Siemens Aktiengesellschaft | Nuclear spin tomograph |
DE4107627C2 (en) * | 1991-03-09 | 1994-12-15 | Bruker Analytische Messtechnik | Resonator for electron spin resonance spectroscopy |
US5162739A (en) * | 1991-04-05 | 1992-11-10 | F. David Doty | Balanced multi-tuned high-power broadband coil for nmr |
US5424645A (en) * | 1993-11-18 | 1995-06-13 | Doty Scientific, Inc. | Doubly broadband triple resonance or quad resonance NMR probe circuit |
US6083883A (en) * | 1996-04-26 | 2000-07-04 | Illinois Superconductor Corporation | Method of forming a dielectric and superconductor resonant structure |
JP2003500133A (en) * | 1999-05-21 | 2003-01-07 | ザ ゼネラル ホスピタル コーポレーション | RF coil for imaging system |
US6788056B2 (en) * | 2000-07-31 | 2004-09-07 | Regents Of The University Of Minnesota | Radio frequency magnetic field unit with aperature |
US6894584B2 (en) | 2002-08-12 | 2005-05-17 | Isco International, Inc. | Thin film resonators |
EP1751571B1 (en) * | 2004-05-07 | 2020-07-15 | Regents Of The University Of Minnesota | Multi-current elements for magnetic resonance radio frequency coils |
US20120194194A1 (en) * | 2011-01-31 | 2012-08-02 | Norell, Inc. | NMR Sample Containers |
CN103000280B (en) * | 2011-09-15 | 2016-06-29 | 上海裕生特种线材有限公司 | Core rod wire and facture thereof is electrically run through for nuclear power generating equipment |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US934714A (en) * | 1908-05-23 | 1909-09-21 | Edouard Denieport | Electric condenser. |
US2201199A (en) * | 1934-04-02 | 1940-05-21 | Rca Corp | Ultra short wave apparatus |
US3242427A (en) * | 1962-09-11 | 1966-03-22 | Melpar Inc | Tunable microwave cavity |
US3434043A (en) * | 1966-02-14 | 1969-03-18 | Varian Associates | Nuclear magnetic resonance probe apparatus having double tuned coil systems for spectrometers employing an internal reference |
US3402346A (en) * | 1966-04-22 | 1968-09-17 | Varian Associates | Coaxial receiver coil and capacitor structure for probes of uhf gyromagnetic spectrometers |
DE1950184A1 (en) * | 1968-10-07 | 1970-10-08 | Erie Technological Prod Ltd | Capacitor and process for its manufacture |
US3681683A (en) * | 1970-09-14 | 1972-08-01 | Varian Associates | Gyromagnetic resonance spectrometer utilizing an improved sample spinning and ejecting structure |
FR2140744A5 (en) * | 1971-06-07 | 1973-01-19 | Thomson Csf | |
US3771055A (en) * | 1972-03-17 | 1973-11-06 | Varian Associates | Double nuclear magnetic resonance coil |
US3811101A (en) * | 1973-03-12 | 1974-05-14 | Stanford Research Inst | Electromagnetic resonator with electronic tuning |
US4275350A (en) * | 1979-05-29 | 1981-06-23 | Varian Associates, Inc. | Sample spinning mechanism for NMR probes |
DD144460B1 (en) * | 1979-06-20 | 1993-08-19 | Haubenreisser Uwe Dr Dipl Phys | SPIND TECTOR FOR HIGH-TEMPERATURE SOLID-STICKER NMR |
-
1982
- 1982-05-17 US US06/379,116 patent/US4463328A/en not_active Expired - Fee Related
-
1983
- 1983-03-04 DE DE8383301171T patent/DE3369385D1/en not_active Expired
- 1983-03-04 EP EP83301171A patent/EP0094734B1/en not_active Expired
- 1983-03-08 CA CA000423134A patent/CA1187551A/en not_active Expired
- 1983-03-29 JP JP58051757A patent/JPS58223738A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
DE3369385D1 (en) | 1987-02-26 |
EP0094734A1 (en) | 1983-11-23 |
US4463328A (en) | 1984-07-31 |
JPS58223738A (en) | 1983-12-26 |
EP0094734B1 (en) | 1987-01-21 |
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