Double resonance probes for close frequencies

A new double resonance probe design for NMR experiments for systems with close resonance frequencies is introduced. The design is based on two coupled resonators and was extensively tested on magnetically aligned powders of several high temperature superconductors by performing double resonance experiments between the (CU)-C-65 and (CU)-C-63 isotopes as well as between transitions of different magnetic quantum number of the same spin. The probe's performance approaches that of a single resonance circuit and it has only 4 variable tuning/matching elements. (C) 1998 Academic Press.