High-power Low-Q RF ESR Resonator for Pulse Techniques

A new type RF ESR resonator for pulse techniques was developed. The resonator is an LC circuit that consists of a single turn coil (inner diameter, 45 mm) and ceramic capacitors. A two-turn coil-shaped polyethylene tube is located inside of the loop and an aqueous sodium chloride solution is perfused into the tube at a rate of 6 cm3/min. Its resonant frequency is approximately 300 MHz, with a Q of less than 70. Using this resonator, pulsed-longitudinally detected ESR measurements of a phantom (inner diameter, 20 mm) containing a triaryl methyl spin probe were performed. The Q value was sufficiently low for irradiation over wide frequency band in the pulsed radiowave where the pulse width was 200 ns. The apparatus can handle a sufficient high power (maximum, 100 W) adjusted according to the sample size.