Crossed TM110 bimodal cavity for measurement of dispersion electron paramagnetic resonance and saturation transfer electron paramagnetic resonance signals for biological materials

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Abstract
When commercial reflection cavities are utilized for electron paramagnetic resonance (EPR) experiments at high‐microwave field intensities or for saturation transfer–electron paramagnetic resonance (ST–EPR) measurements, dispersion signals exhibit substantially worse signal‐to‐noise than absorption signals due to the increased sensitivity of the former to source frequency modulation noise. The development and testing of a TM110×TM110 bimodal cavity which completely eliminates the source noise problem is described. This cavity is used to obtain EPR and ST–EPR spectra of a variety of commonly encountered spin‐labeled biological samples. When samples are contained in capillary tubes, this TM110×TM110 cavity often permits the realization of better signal‐to‐noise than can be obtained with commercial reflection cavities.