A nonradiative approach to single-mode dielectric resonators

The development of a single-mode dielectric resonator specifically designed for high-frequency paramagnetic resonance applications is discussed. The use of dielectric resonators is expected to give better performances in comparison to metallic cavities, as well established at low frequency. The relatively low dielectric constant of the common good-quality materials at high frequency requires the presence of a metallic shielding in order to obtain an efficient single-mode operation. The configuration proposed in this paper concerns a partially open structure in which the confinement of the radiation is guaranteed by the forbidden propagation around the dielectric region. By this way a single-mode resonator can be obtained for arbitrary values of the employed dielectric constant. The complex resonance frequencies and the field distributions and intensity can then be obtained even in the presence of a lossy sample. An efficient excitation scheme, fully compatible with the common electron paramagnetic resonance setups, has been developed exploiting the nonradiative nature of the proposed device. Preliminary measurements around 90 and 186 GHz have been then successfully realized. Finally, the specific benefits of the proposed resonator have been discussed and compared with the performances of a conventional metallic cavity.