Quartz crystal temperature sensors (QCTS) were tested for the interference with electromagnetic fields (e.g., eddy curfirst time as wireless thermometers in NMR MAS rotors utilizing rents).
the NMR RF technique itself for exiting and receiving electro-
Temperature measurements in operating MAS rotors have mechanical quartz resonances. This new tool in MAS NMR has a been a challenge since the invention of magic angle spinning high sensitivity, linearity, and precision. When compared to the in NMR. This is due to a typically used separate temperature frequently used calibration of the variable temperature in the NMR calibration of the NMR system and moreover to a depensystem by a solid state NMR chemical shift thermometer (CST), dence of any output (e.g., from CST or solid phase transisuch as lead nitrate, QCTS shows a number of advantages. It is tion) on spinning speed (8, 9), rotor material (8), and saman inert thermometer in close contact with solid samples operating ple structure. This paper shows the first known test results parallel to the NMR experiment. QCTS can be manufactured for of QCTS under MAS conditions. Some comparisons are any frequency to be near a NMR frequency of interest (typically 1 to 2 MHz below or above). Due to the strong response of the made to lead nitrate, one of the most sensitive solid chemical crystal, signal detection is possible without changing the tuning shift thermometers (8, 9). As can be seen from the literature, of the MAS probe. The NMR signal is not influenced due to the calibrations for lead nitrate and also for other CST have relative sharp crystal resonance, restricted excitation by finite been made at spinning speeds above 1500 Hz, in order to pulses, high probe Q values, and commonly used audio filters. The derive high enough intensity for the isotropic line. According quadratic dependence of the temperature increase on spinning to (8, 9) and to experimental results shown here, spinning speed is the same for the QCTS and for the CST lead nitrate and affects temperature and creates gradients along the rotor in is discussed in terms of frictional heat in accordance with the several ways and differently at different temperatures. Static literature about lead nitrate and with the results of a simple rotor or nearly static measurements would be best and precise for speed jump experiment with differently radial located lead nitrate calibration purposes. A QCTS gives a sharp, intense line in the rotor. α§ 1997 Academic Press
with and without spinning and enables an accurate temperature calibration at the location of the small crystal plate. Since no commercial specification of the temperature coef-