Design of NMR RF Probe Constructed With High-Temperature Superconducting Elliptical-Coupled Resonators

A high-temperature superconducting (HTS) radio frequency (RF) probe has been designed for nuclear magnetic resonance spectroscopy that is constructed of two newly developed HTS elliptical-coupled resonators that are placed on either side of the sample. The probe has a higher quality factor and a more uniform magnetic field along the z-axis than one with square resonators. The measured unloaded quality factor (Qu) of a pair of elliptical-coupled resonators fabricated using YBa2Cu3Oy thin films on an Al2O3 substrate was about 30 000 at 15 K, which is about 82 times higher than the simulated Qu of a copper counterpart at room temperature. Measurement of the input power dependence of Qu showed that a Qu of over 20 000 was obtained up to 16 dBm. Measurement of the RF magnetic field profile along the z-axis showed that the RF magnetic field was more than 85% uniform around the sample region.