Patent ID: 6107798
Filing Date: 2000-08-22
Classification: H03H

Abstract:
A method for adjusting an impedance of a nuclear magnetic resonance probe in nuclear magnetic resonance experiments comprising:providing a source of a high frequency oscillating current suitable for use in the nuclear magnetic resonance experiments, the source having a required characteristic impedance;providing the nuclear magnetic resonance probe to be connected to the source for generating an electromagnetic field suitable for use in the nuclear magnetic resonance experiments in response to the current, the nuclear magnetic resonance probe having an impedance different from said required characteristic impedance;wherein the nuclear magnetic resonance probe comprises a transmitter inductor coil for generating the electromagnetic field connected in parallel with a variable capacitor, a subsidiary inductor coil arranged for variable mutual inductance between the transmitter inductor coil and the subsidiary inductor coil and a second capacitor connected in series with the subsidiary inductor, the current being connected from the source in series with the subsidiary inductor coil and the second capacitor;arranging the variable capacitor and the variable mutual inductance such that the adjustment of each causes adjustment of both a resistive component and a reactive component of the impedance and such that, over at least a part of a range of adjustment of the variable capacitor and the variable mutual inductance, adjustment of the variable capacitor while the variable mutual inductance remains constant generates a change in the impedance which is substantially orthogonal to a change in the impedance obtained by adjustment of the variable mutual inductance while the variable capacitor remains constant and such that adjustment of the variable capacitor to a first required adjustment position and adjustment of the variable mutual inductance to a second required adjustment position causes the impedance of the probe to be adjusted to said required characteristic impedance;providing a detection circuit responsive to the impedance of the probe and causing the detection circuit to provide first and second separate output values which are orthogonal to one another and which are indicative of a difference in the impedance of the probe from said required characteristic impedance;arranging the output values such that the first is indicative of a difference of the variable capacitor from the first required adjustment position and such that the second is indicative of a difference of the variable mutual inductance from the second required adjustment position;and using the first and second output values for controlling respectively the variable capacitor and the variable mutual inductance.