Modified surface-coil-type resonators for EPR measurements of a thin membranelike sample
Surface-coil-type resonators (SCRs) equipped with a circular single-tum coil (conventional SCR), a circular spiral coil (spiral SCR), and a plate-type single-turn coil (plate-type SCR) were fabricated. By using these SCRs, the electron paramagnetic resonance (EPR) sensitivities of thin membranelike samples were investigated. For a non-dielectric-loss phantom, filter paper containing 1,1-diphenyl-2-picrylhydrazyl was used. For a high-dielectric-loss phantom, gauze containing an aqueous solution of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) was used. For a biological sample, a pea leaf impregnated with the carbamoyl-PROXYL solution was used. The sensitivity (signal-to-noise ratio) of the spiral and plate-type SCRs for the non-dielectric-loss phantom was significantly greater than that of the conventional SCR. Under these conditions, the sensitivity of the spiral SCR was relatively higher than that of the plate-type SCR. For the high-dielectric-loss phantom, the sensitivity of the plate-type SCRs was significantly greater than that of the conventional SCR, but there were no differences in sensitivity between the spiral and conventional SCRs. The sensitivity of the plate-type SCR in the EPR measurement of a pea leaf was significantly greater than that of the conventional SCR. These findings show that the spiral and plate-type SCRs are suitable for measuring EPR of thin membranelike samples, especially when the former is used for the non-dielectric-loss sample and the latter for high-dielectric-loss sample, including the leaf.