A coaxial microwave cavity for improved electron paramagnetic resonance sensitivity with lossy solvents

Abstract A design for a coaxial TE 011 -mode microwave cavity to optimize EPR sensitivity for measurements involving lossy samples is presented. A prototype cavity has been constructed and its sensitivity compared to the sensitivities of commercial rectangular TE 102 - and cylindrical TM 110 -mode cavities under a variety of experimental conditions. For saturable samples, the TE 011 and TM 110 cavities are approximately equivalent in sensitivity and twice as sensitive as the TE 102 cavity. For nonsaturable samples the sensitivity ratio is approximately 3 : 2 : 1 for TM 110 : TE 011 : TE 102 . The magnetic field modulation available from the TE 102 cavity is roughly double that available from the other two, so when broad lines are studied, all three cavities are equivalent. If the experiment requires temperature control deviating from ambient temperature by more than 25°C, the TE 011 coaxial cavity is two to three times more sensitive than the other two. It is concluded that the strength of the coaxial design is not only its sensitivity, but the ease with which its novel sample geometry permits the experimenter to modify the sample during an EPR experiment without adversely affecting the EPR sensitivity.