Abstract: A nuclear magnetic resonance (NMR) probe circuit is used with a sample coil tuned to a primary frequency f1. The circuit is arranged to have a plurality of points of electric field minima at the f1 frequency. One or more additional frequencies may be coupled to the circuit at these points, without interaction with f1. The probe circuit also uses an impedance coupled between two of the minima points that affects the frequency response at the additional frequency or frequencies, without affecting the frequency response at f1. The impedance may be made adjustable to allow tuning of the relative frequency resonances.

Abstract: A circuit for a nuclear magnetic resonance probe uses three resonators to create resonances intermediate to the resonator resonant frequencies. The circuit is particularly useful for creating magnetic fields for two closely spaced high frequencies, such as those used for the excitation of 1H and 19F. The resonators are arranged in a parallel combination, or the electrical equivalent thereof, with input ports connected to it for inputting the desired high frequency resonances. Admittance inverters may be used to provide isolation between the input ports. Some of the resonators and the admittance inverters may be transmission lines. The transmission lines may have additional ports for additional input signals of lower frequencies located at null points for the frequencies of the signals coupled to the primary input ports. Adjustable dielectric components in the resonator transmission lines may be used for tuning purposes.