Determination of Quality Factor for Highly Overcoupled EPR Resonators

We reported determination of the loaded quality factor (Q) of highly overcoupled (dielectric, loop-gap, and cavity) resonators used in time-domain electron paramagnetic resonance. We introduced a microwave absorber into resonators and achieved critical-coupling. Due to the deep Q-dip of critical-coupling, we can easily determine the loaded Q as low as 10. The loaded Q of resonators with and without the microwave absorber was examined under various overcoupling conditions. We found that the radiation Q (Q (r)) can be calculated from the loaded Q of the resonator that contains the microwave absorber. We proposed a simple model that represents the loaded Q of the overcoupled resonator in terms of two parameters, Q (0) and Q (r). Q (0) is the effective unloaded Q of the resonator determined for the critically coupled resonator without the microwave absorber and is independent of a degree of coupling. The model can be applied to overcoupling in which the coupling parameter (Q (0)/Q (r)) is in the range of 1 to ca. 20.