Spectrospin Ag

Anton Kuster

Arne Kasten

Daniel Marek

Dirk D Laukien

Tschopp Werner

Roland Kappeli

In an apparatus having at least one detection coil (1) for the detection of nuclear magnetic resonance (NMR) from a sensitivity region of the detection coil (1) in the ground, whereby nuclear spins within the sensitivity region are excited by repeated coherent excitation, in each case, to precess in the earth's field and produce a small NMR induction voltage in the detection coil (1) which is introduced to a first amplifier (7), the detection coil (1) consists of at least two oppositely wound partial coils (2, 3) having parallel coil axes which are connected electrically in series and at least one compensation coil (8, 9, 10) is provided for additional compensation of spatially inhomogeneous interfering fields whose induction signal is introduced to a second amplifier (18, 19, 20) having adjustable amplification. In this fashion, in addition to the homogeneous portion, an inhomogeneous portion due to distant disturbances can be eliminated from the measured signal.

Compensation of interfering fields in NMR measurements in the earth's

The present invention relates to a method and a device for compensating undesirable side bands in nuclear magnetic resonance spectrometers. The frequency (.omega..sub.m) and the phase of rotation of the sample (10) are detected by means of a light sensor (12) and supplied to a compensation generator (18). The latter generates modulation signals (44 and 43) for modulating the amplitude and the phase of the detected nuclear magnetic signal of the sample, using an amplitude modulator (13) and a phase modulator (14), the modulation frequency being equal to an integral multiple, including the simple value, of the frequency of rotation (.omega..sub.m) of the sample. The additional frequency components heterodyne with the side bands provoked by the rotation of the sample (10) in the static magnetic field (B.sub.O), whereby the said side bands are eliminated.

Method and device for compensating undesirable side bands in nuclear

Method for reducing the content of spurious signals in the output signal of a mixer and mixer designed for carrying out the method according to the invention. When using quadrature mixtures as generators for tunable rf signals it has been found to be a disadvantage that differences in the two channels of the quadrature mixers lead to a high content of undesirable mixture signals. The content of disturbing mixture signals in the output signals of such mixers is reduced according to the invention by feeding the ring modulators of the quadrature mixer with signals differing from pure sine oscillations, which are phase-shifted relative to each other by 90.degree. and which have been determined in such a manner that all pairs of d.c. signals supplied to the two ring modulators result in output signals which have all the same amplitude and each of which has a phase position conforming exactly to the phase position to which the respective pair of d.c. signals is assigned. By supplying these signals in a cyclical sequence one obtains a modulation signal of predetermined frequency supplying an output signal which is substantially free from undesirable mixture signals and whose frequency is displaced relative to the frequency of the supplied carrier signals by the frequency of the modulation signal.

Method for reducing the content of spurious signals in the output

In the case of NMR spectrometers comprising a cryomagnet with vertical axis, the sample to be examined is introduced into the measuring area of the magnet by means of a sample carrier which is arranged in a guide tube passing axially through a central space of the craymagnet, and can be moved therein by means of a flow of compressed air. For changing the sample, one switches on the compressed air flow so that the sample carrier is raised to the upper end of the guide tube where the sample can be changed. With increasing sizes of the cryomagnets, the upper end of the guide tube is no longer accessible without an aid (ladder or platform). The invention therefore provides that a direction switch is arranged at the upper end of the guide tube and that an inclined tube extends from the said direction switch to an easily accessible point, for inserting and removing the sample carrier at its end. By guiding the flow of compressed air in a suitable manner and switching over the direction switches as required, the sample can then be moved from the measuring area to the end of the inclined tube, and vice versa, so that the difficulties described before are no longer encountered.

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Greifensee, Switzerland

Anton Kuster