Using a cross-coil to reduce RF heating by an order of magnitude in triple-resonance multinuclear MAS at high fields |
| |
Authors: | Doty F David Kulkarni Jatin Turner Christopher Entzminger George Bielecki Anthony |
| |
Institution: | Doty Scientific Inc., Columbia, SC, USA. david@dotynmr.com |
| |
Abstract: | Four different coil designs for use with MAS in triple-resonance multi-nuclear experiments at high fields are compared, using a combination of finite element analysis (FEA) software and NMR experiments, with respect to RF field strength per unit power and relative sample heating, as governed by mean E/B(1) within the sample region. A commercial FEA package, Microwave Studio 5.1 by Computer Simulation Technology (CST) is shown to obtain remarkably accurate agreement with the experiments in Q(L), L, B, E, and mode frequencies in all cases. A simplified treatment of RF heating in NMR MAS samples is derived and shown to agree with the NMR experimental results within about 10% for two representative stator designs. The coil types studied include: (1) a variable-pitch solenoid outside a ceramic coilform, (2) a conventional solenoid very closely spaced to the MAS rotor, (3) a scroll coil, and (4) a segmented saddle cross coil (XC) for (1)H with an additional solenoid over it for the two lower-frequency channels. The XC/solenoid is shown to offer substantial advantages in reduced decoupler heating, improved S/N, and improved compatibility with multinuclear tuning and high-power decoupling. This seems largely because the division of labor between two orthogonal coils allows them each, and their associated circuitry, to be separately optimized for their respective regimes. |
| |
Keywords: | MAS RF heating Cross-coil Electric fields Homogeneity Probe |
本文献已被 ScienceDirect PubMed 等数据库收录! |
|