Varian Associates, Inc.

Varian, Inc.

James Patrick Finnigan

Knut G Mehr

Robert G Rice

Andrew W Munsell

A 1/4 wave circuit switch for use in an NMR probe has a housing with a stepped cavity for precisely locating switch components inside. The 1/4 wave circuit switch cooperates with a 1/4 wave tube and is designed to receive either an external capacitor on a capacitor stick for single tune operations or a 1/4 wave center conductor with a threaded tip on a 1/4 wave stick for double tune operations. For single tune operations, the external capacitor comes into contact at one end with a resiliently supported, movable electrical contact and at the other end with a spring clip inside the housing cavity to orient the external capacitor in parallel with the NMR coil. The movable electrical contact is resiliently biased by a pair of crescent washers supported by an insert plug which serves as a positive stop for the travel of the electrical contact. For double tune operations, the threaded tip of the 1/4 wave center conductor simultaneously contacts a pair of threaded contacts provided inside the housing cavity and spaced by an insulating spacer. The simultaneous contact creates a current path which grounds the NMR circuit through the 1/4 wave tube, so that the NMR circuit may resonate at two separate frequencies. The two frequencies can be easily adjusted by employing an extension tube that effectively changes the length of the 1/4 wave tube and grounds the NMR circuit through the 1/4 wave tube to resonate at different frequencies.

NMR circuit-switch

A symmetric RF coil for use in a probe for NMR apparatus comprises an odd number of turns having generally straight portions and arc-shaped portions wound alternately in series on the curved surface of a cylindrical sample region. An additional pair of arc-shaped segments connect to the outermost turn to form continuous end rings, and to split the current on the outermost turn to the continuous end rings. Such an RF probe coil possesses material symmetry provided by the additional arc-shaped segments and RF symmetry as a result of the symmetry in current flow generated by the split in current of the outermost turn to the continuous end rings. The symmetric odd-turn RF coil achieves NMR performance at the same level of even-turn coils with high RF homogeneity, and is suitable for high resolution NMR applications. The coil inductance of the present invention bridges the gap between even-turn coils, and facilitates improved optimization of the resonance circuits over the entire operating range.

Saddle-shaped multiturn RF coils for NMR probe

A variable external capacitor produces greater functionality for NMR probes by reducing the size of components and efficiently arranging the components. The variable external capacity has a cavity that allows adjustment tools to be extended through the variable external capacitor to adjust additional components that may be stacked above the variable external capacitor. The cavity may be used to house reactance such as a fixed capacitor or inductor connected in parallel with the variable external capacitor. The variable external capacitor includes a polytetrafluoroethylene housing configured to minimize its size and reduce lead lengths of the NMR circuit. A silver deposit plate on the polytetrafluoroethylene housing constitutes a stationary capacitor plate. A drum disposed inside the cavity and movably spaced from the stationary capacitor plate functions as a movable capacitor plate. An anti-rotation rail supports the drum to prevent rotation. The drum includes internal threads that cooperates with threads provided in a plunger for adjustment of the drum in a translational direction. The plunger is supported by the rail and extends outside the cavity of the polytetrafluoroethylene housing for rotational adjustment. An insulator spaces the plunger and the drum from the stationary capacitor plate. The insulator and plunger provide a through passageway for an adjustment tool to extend therethrough. Alternatively, the space inside the insulator and plunger may be used to house a capacitor or inductor electrically supported by a current-conducting stick and connected in parallel with the variable external capacitor. A capacitor stick shifts the capacitance of the variable external capacitor, while an inductor stick forms a parallel LC resonant circuit. The structure provides the flexibility of choosing a stick to form a desirable circuit element for increased functionality of the NMR probe.

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Santa Clara, CA, United States of America

James Patrick Finnigan