Varian Associates, Inc.

John R Laudermilch

Howard D Hill

An NMR system for obtaining high resolution spectroscopic measurements at a selected temperature includes gradient correcting means disposed in proximity to an NMR probe, for imposing desired gradients on the volume occupied by the sample within the probe. A heat exchange gas is impelled through a heat exchanger and then surrounds the sample to bring the sample to the desired temperature. A thermal barrier, inocuous to RF excitation and of relatively low magnetic susceptibility protects the gradient correcting means from drift due to heat exchange with the heat exchanging gas.

Thermal barrier for variable temperature NMR

In a nuclear magnetic resonance spectrometer a gate is employed for time share multiplexing of the resonance and transmitter signals. An improved gate circuit is connected in series between the receiver and the resonance detecting circuit employed for picking up resonance of the sample. The improved gate circuit includes a pair of parallel connected branches of PIN diodes connected between the input and output terminals of the gate. The diodes in each parallel branch are poled toward an intermediate control node in such a manner so that a positive control potential applied to the control of one branch node turns that branch on and conversely a negative control potential applied to the other control node turns on the other branch. Equal magnitude and opposite sign control pulses are applied to the control nodes so that transient switching signals, tending to leak through the gate, cancel on the output line to the RF receiver.

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Foster City, CA, United States of America

John R Laudermilch