NMR probe head with integrated remote tuning

Details NMR probe head with integrated remote tuning NMR probe head with integrated remote tuning

1998-09-28

2001-03-20

Oda, Christine (Department: 2862)

Electricity: measuring and testing

Particle precession resonance

Spectrometer components

C324S321000

Reexamination Certificate

active

06204665

ABSTRACT:

This application claims Paris Convention priority of German patent application 197 44 763.5 filed Oct. 10, 1997, the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention a probe head having concerns an actuator for remote adjustment of electrical and/or mechanical units, e.g. trimming capacitors, variable resistors, adjustable inductors etc. in a probe head of a nuclear magnetic resonance (NMR) spectrometer having one or more drive units, one or more transmission units as well as one or more drive shafts which couple to probe head adjustment rods.
An actuator of this kind is e.g. known in the art from EP 0 518 100 B1.
Modern nuclear magnetic resonance (NMR) spectrometers normally have a powerful computer which controls all important adjustments and parameters of the spectrometer.
The spectrometer user sits at a console and issues instructions and optimization adjustments directly to the computer. This is done with the assistance of a monitor, a mouse, a computer key board as well as possible additional input apparatus having keys and nobs to transfer special requests. The computer then passes these directions in a suitable form to the corresponding electronic units of the spectrometer.
As long as the user carries out measurements on the same sample, this user-friendly function is available to him. However, if the user wants to use a new sample, it is necessary for him to leave his working area in order to introduce a new sample into the magnet. If this new sample has a dielectric constant or electric conductivity which is different than the previous one, then it is necessary for the user to manually readjust the resonance frequency as well as the impedance matching of the NMR receiver resonator at the probe head location, i.e. at the magnet. Impedance matching refers to electrical adjustment of the resonator to the RF cable and the downstream preamplifier so that maximum signal energy reaches the preamplifier.
In order to improve user friendliness, units have been developed, so-called sample changers, which facilitate a remote control changing of a large number of samples (e.g. 60 individual samples). Remote-controlled electromagnetic units, so-called actuators, have also been developed by means of which both the trimming capacitor as well as fixed capacitances in the probe head can be adjusted, added or switched-out (see EP 0 518 100 B1). In this manner, it is possible to also remotely control the resonance frequency and the impedance matching of the NMR resonator.
The use of sample changers and actuators allows for the full automatic operation of the spectrometer during long periods of time and using different samples. The computer then receives a schedule of requests which it transfers into directions for adjustment of the various hardware components. The computer instructs e.g. the sample changer to introduce a particular sample into the magnet. Towards this end, pressurized air must first be switched-on within the bore
30
(see
FIG. 4
) so that the sample can be transferred on an air cushion from the upper end of the bore
30
down into the region of the magnetic center
32
. The air pressure must thereby be regulated in such a fashion that the sample does not travel too rapidly in a downward direction, since otherwise it could be damaged. As soon as the sample has reached its end position, the pressurized air must once more be switched-off. The pressure from a second pressurized air lead which serves for driving the air turbine of the sample is subsequently regulated in such a fashion that the sample rotates at the desired frequency. All these processes proceed automatically. In addition, the computer instructs the actuator to change the capacitors in such a fashion that an optimum adjustment of the resonance frequency and impedance matching of the NMR resonator is effected. The prescribed measurement is subsequently started. This measurement can vary from sample to sample. Such a measurement procedure has the substantial advantage that a large number of samples (e.g. 60 samples) can be measured in one single measurement cycle without human monitoring. A measuring cycle can therefore easily be carried out overnight and during the weekend.
The conventional actuators
34
(see
FIG. 4
) each contain at least one drive unit which normally consists essentially of an electrical motor. The actuator is not positioned too close to the magnet, since the ferromagnetic and permanent magnetic components of the motor would negatively influence the homogeneity of the H
0
-field of the magnet. In addition, large electromagnetic forces can occur between the magnet coil and the motor which could critically load not only the magnet/dewar-system but also the motor. Not the least of all, these electric motors loose effectiveness in high fringe fields. For these reasons, the electric motors which are located in the conventional actuator
34
are disposed at a relatively large separation from the magnetic center
32
of the magnet and are connected to the adjustment rods,
8
a
,
8
b
,
8
c
of the probe head via long connection rods
33
consisting essentially of either individual jointed shafts or individual flexible mechanical shafts. A rather cumbersome assembly thereby results which blocks space in the region below the magnet i.e. in a region which, for technical reasons, is in any event limited and offers little freedom of motion to the user.
In contrast thereto it is the purpose of the present invention to improve a probe head having an actuator of the above mentioned kind in such a fashion that it provides more freedom of motion and comfort below the magnet to the user by minimizing space requirements for the actuator and optimizing access to the vicinity below the magnet. Another purpose of the invention is to simplify installation of the actuator. In conventional actuators, the user must recouple the actuator connection rods to the probe head after each probe head change. This should no longer be required with a probe head having actuators in accordance with the invention.
SUMMARY OF THE INVENTION
This purpose is achieved in accordance with the invention with the initially apparently unrealistic concept of integrating the actuator directly into the probe head of the NMR spectrometer, i.e. to place it directly proximate to the magnetic center. This would initially seem inappropriate, since the amount of room in the region of the probe head is very limited, since one or more electrical motors must work reliably in a relatively high fringe field of the NMR magnet, and since the H
0
-field of the magnet at the location of the sample may be excessively influenced. These are conditions which render realization of the concept in accordance with the invention unlikely when first examined by one of average skill in the art. It is therefore not surprising that up to this point in time, this concept has not been enacted, although actuators for NMR-probe heads have been known in the art for more than six years and miniaturized components, e.g. motors, transmissions, etc. for an even longer period of time.
The key concept for realizing the idea in accordance with the invention is a systematic miniaturization of the probe head actuator as well as an optimization of the performance of the drive unit in high fringe fields.
An embodiment of the actuator probe head in accordance with the invention is highly preferred with which the drive unit comprises one or more miniaturized DC-motors to produce torque.
An extreme miniaturization of the most troublesome components, namely the electric motor in the drive unit, facilitates a strong reduction of its influence on the H
0
-field. If the mass of the ferromagnetic and permanent magnetic material proximate the magnet is kept small then its influence on the homogeneity of the magnet is also small. Expressed in another way: if the entire mass of the ferromagnetic and permanent magnetic material is reduced then it is also possible for these materials to be closer to the magnet. An extremely small elect

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