Impedance Matching in NMR Probe with an Adjustable Segmented Transmission Line
The present invention describes the use of a pair of dielectric slugs in transmission line as impedance transformers for a wide range of load impedance. Impedance matching between the RF probe and the spectrometer is a standard requirement for NMR probes. Both lumped element and branched transmission line methods are in wide use. Here we propose to use a segmented transmission line structure. It relies upon reflections between transmission lines of different impedances that are serially connected to match the impedance of a coil or resonator to the characteristic impedance of the NMR spectrometer. Two quarter-wave length dielectric slugs are placed within a coaxial transmission line. Adjustment of the positions of the slugs allows the variable tuning and matching needed for NMR probes, eliminating the need for variable capacitors and inductors.
- A successful prototype demonstrates this approach outperforms existing technologies as it can match both capacitive and inductive impedance, as compared to matching only one of the two.