Design and Realization of an Open EPR Resonator at ${X}$ -Band Frequencies

An open resonator compatible with $X$ -band commercial spectrometers for electron paramagnetic resonance was designed and built. In the design process, resonators with different shapes and dimensions were compared by using ad hoc defined cavity figures of merit. Three cylindrical cavities operating on TE X11 modes with $X = 1$ , 2, 3, were designed taking into account a coupling iris and a slit for microwave magnetic field leakage. The cavities were further improved toward the homogeneity of the 100 kHz modulation magnetic field. A cavity was then built, operating on TE 111 mode; the measured electromagnetic parameters were in a good agreement with simulations. Finally, the cavity was inserted in a commercial $X$ -band spectrometer, and measurements have been performed on three paramagnetic samples: 2, 2-diphenyl-1-picrylhydrazyl, and irradiated alanine and bone.