Re-entrant resonators for ESR spectroscopy between 2 and 10 GHz

Abstract

Presents the design equations and the physical construction of re-entrant resonators of square symmetry and circular shape of the enlarged section which are suited for ESR spectroscopy of aqueous samples. Four prototypes of frequencies 2.1, 3.4, 6.4 and 9.4 GHz have been constructed showing that this resonator design can be used in a very broad range of frequencies. The performances of the 9.4 GHz resonator have been experimentally compared with that of a rectangular TE₁₀₂ cavity in a laboratory-made ESR spectrometer showing that for aqueous samples an improvement in the spectrometer sensitivity by a factor of ten can be obtained. This improvement is due both to the higher filling factor and to the larger volume of the usable samples.