DOUBLE-STACKED DIELECTRIC RESONATOR FOR SENSITIVE EPR MEASUREMENTS

A new approximate method for predicting the resonant frequencies and f or solving the held distribution problem of a cylindrical dielectric r esonator (DR) is developed. The model proposed in this paper bridges t he gap between rigorous and accurate finite-element or Green function- based numerical methods on the one hand and on the other hand, simple approximate solutions in which the held distribution can be described analytically, but the resulting frequency is accurate within a few per cent only. In the method described here, the approximate solution for the microwave field distribution is modified by substituting different values of the radial separation constants inside and outside of the d isk-shaped DR. The model is generalized for the double-stacked DR stru cture and enables one to introduce corrections that take into account the presence of the shielding walls and of the cylindrical sample hole . Good agreement is found between experimental and calculated results for both the single and double-stacked structures that are designed ar ound commercially available X-band DRs (9-10 GHz). For the resonant fr equency of the lowest transverse-electric TE(01 delta) mode that is co mmonly used for EPR measurements, the accuracy of the method is better than 1%. Experimentally measured resonator filling factors are also i n good agreement with those theoretically estimated. Both the theory a nd the experimental results suggest that the double-stacked DR structu re with finite spacing between the ceramic cylinders is the most suita ble for EPR measurements of long lossy samples. (C) 1997 Academic Pres s.