Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-10-03
2003-08-12
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S315000, C324S309000
Reexamination Certificate
active
06605945
ABSTRACT:
This application claims Paris Convention priority of DE 101 50 131.5 filed Oct. 11, 2001 the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns an NMR (nuclear magnetic resonance) resonator device with at least one RF (radio frequency) resonator for emitting and/or receiving RF signals at one or more desired resonance frequencies to and/or from a measuring sample in an investigational volume, disposed about a coordinate origin (x,y,z=0), of an NMR apparatus with a means for producing a homogeneous magnetic field B
0
in the direction of a z axis, wherein superconducting conductor structures of the RF resonator, which act inductively and partially also capacitively, are disposed between z=−|z
1
| and z=+|z
2
| substantially on a surface which is translation-invariant (=z-invariant) in the z direction at a radial (x,y) separation from the measuring sample.
An arrangement of this type is known from U.S. Pat. No. 5,585,723.
The present invention concerns the field of high-resolution nuclear magnetic resonance (NMR), in particular a configuration of superconducting resonators for receiving the NMR signal from the NMR measuring sample.
Although NMR is a very useful method for structure analysis of chemical compounds, it is not very sensitive. To increase the sensitivity, according to current prior art, cooled normally conducting and in particular superconducting resonators are used which considerably increase the S/N ratio. [1] describes e.g. such resonators.
The main problem with the use of superconductors for the production of NMR resonators is their static magnetization. In a superconductor of type II, this magnetization is produced by induced currents which flow in closed paths within the superconductor and which depend on the history of the superconductor [2]. These currents can produce strong disturbances in the homogeneous field of the active region of the measuring sample which cause distortion of the resonance lines in the NMR spectrum. As long as the external conditions remain unchanged, these currents continue to flow for a nearly unlimited length of time due to the zero resistance of the superconductor.
Methods ([2], [3], [4]) for minimizing this magnetization have been published. They are all complicated and have further disadvantages which are described below. Superconducting coil arrangements have also been described [5] which minimize their disturbing fields through limitation of the active measuring region using normally conducting connecting elements. These coil arrangements [5] are superior to the above-mentioned solutions of methods [1-3] with respect to fill factor and attainable RF field strengths, but have the disadvantage that the Q-value of the RF resonator is significantly reduced by the normally conducting components which must be used.
The known measures for minimizing the influence of magnetization are:
1. Division of the width of the superconductor into n individual longitudinal strips ([1], [5]), wherein n should be as large as possible. This reduces the maximum currents which can flow in these longitudinal strips and therefore also the maximum possible magnetization of the superconductor by the factor n.
2. Prevent magnetization completely by first cooling the superconductor when it is positioned in the static field of the magnet. Patent [4] additionally recommends slow cooling.
3. Largely eliminate existing magnetization by means of a demagnetization process ([2], [3]). This is achieved by a sequence of decreasing transverse magnetic fields which act on the superconductor. A current structure with opposite current regions is thereby induced in the superconductor, with the sum of the individual magnetic field contributions cancelling to a good approximation.
These known methods have significant disadvantages:
1. Although the measure described in 1 considerably reduces magnetization, the remaining residual magnetization is generally still too high for adequate performance in high-resolution NMR applications.
2. The methods described in 2 and 3 can function satisfactorily only when the position of the superconductor with respect to the static magnetic field remains exactly the same during the entire measuring process and when the static magnetic field itself also remains unchanged during this period. The principal problem is the constancy of the angular position which is usually insufficient in practice. A tilting of merely 0.1 degrees relative to the static magnetic field can produce shielding currents in the superconductor of such a strength that the field homogeneity is deteriorated to an unacceptable degree.
Tilting causes an additional transverse magnetic flux to be directed from the static magnetic field onto the surface of the superconductor, and since the superconductor tries to maintain the previously existing flux, it counteracts with additional surface currents such that the total flux through the superconductor once more corresponds to the original value. These surface currents produce an inhomogeneous field at the location of the measuring sample thereby unduly deteriorating the required spectral resolution.
3. The methods ([2], [3], [4]) are difficult to carry out and require additional devices in the critical region of the NMR resonator.
In contrast thereto, it is the object of the present invention to present a new type of superconducting NMR resonator having additional superconducting conductor structures which are optimally decoupled from the actual RF resonator and which optimally compensate for the disturbing influence produced by magnetization of the superconductor.
SUMMARY OF THE INVENTION
This objective is achieved in accordance with the invention in an NMR resonator having the above-described features in that an additional compensation arrangement is provided on the z-invariant surface, which extends to values of at least z<−|z
1
|−0.5|r| and z>+|z
2
|+0.5|r|, wherein |r| is the minimum separation between the measuring sample and the compensation arrangement, with the compensation arrangement comprising further superconducting conductor structures which are largely RF-decoupled from the RF resonator, wherein the conductor structures of the compensation arrangement and of the RF resonator are composed of individual surface sections (“Z-structures”) which comprise superconducting structures and which are disposed in the z-invariant surface to each extend across the entire length in the z direction of the conductor structures of the compensation arrangement and of the RF resonator and whose superconducting structures are disposed such that, with suitable conceptual decomposition of the surface of the Z structures into a plurality of small equally sized surface elements and with conceptual application of a homogeneous test magnetic field along the surface normal of each surface element, a magnetic dipole moment of essentially the same strength would be induced in all surface elements which differ only with respect to their z position.
The inventive resonators have many advantages:
the complicated methods ([2], [3], [4]) for demagnetisation of the superconductor are no longer required.
external disturbing fields and mechanical motion of the resonator relative to the static magnetic field produce a magnetization in the superconductor which has only minimal influence on the homogeneity of the static magnetic field in the active region of the measuring sample due to the above-mentioned compensation. This is also true when the superconductor is highly magnetized.
known coil structures [5] can be designed much more freely and therefore more effectively.
In the inventive resonator, the individual superconducting cond
Bruker Biospin AG
Shrivastav Brij B.
Vincent Paul
LandOfFree
Superconducting NMR resonators with macroscopically... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Superconducting NMR resonators with macroscopically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Superconducting NMR resonators with macroscopically... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3114173