A bridged loop-gap S-band surface resonator for topical EPR spectroscopy

The design and structure of a bridged loop-gap surface resonator developed for topical EPR spectroscopy and imaging of the distribution and metabolism of spin labels in in vivo skin is reported. The resonator is a one-loop, o ne-gap bridged structure. A pivoting single loop-coupling coil was used to couple the microwave power to the loop-gap resonant structure. A symmetric coupling circuit was used to achieve better shielding and minimize radiatio n. The frequency of the resonator can be easily adjusted by trimming the ar ea of the capacitive foil bridge, which overlaps the gap in the cylindrical loop. The working frequency set was 2.2 GHz and the unloaded Q was 720. Th e B-1 field of this resonator was measured and spatially mapped by three-di mensional EPR imaging. The resonator is well suited to topical measurements of large biological subjects and is readily applicable for in vivo measure ments of free radicals in human skin. (C) 2001 Academic Press.