A new class of bimodal loop-gap resonators for EPR spectroscopy was developed using the Hewlett Packard 85180A high-frequency structure simulator software. These resonators contain two axially placed one-loop one-gap resonators. In mode I, the axial magnetic components of the microwave field of both resonators are parallel. In mode II, these fields are opposite. The resonant frequency of mode II can be adjusted independently of the resonant frequency of mode I by changing the capacitance between the two one-loop one-gap resonators. The isolation between these two modes for a prototype S-band resonator was measured to be better than 60 dB for either equal or different resonant frequencies of the two modes. The resonators have a very high filling factor close to unity when used in the reflection configuration of the microwave bridge and 0.5 for transmission. The resonator was tested in regular EPR experiments as well as in CW ELDOR and multiquantum EPR experiments. As a consequence of the microwave field distribution, the new resonator cancels the unwanted FID signal in saturation-recovery EPR experiments. Construction of an X-band bimodal resonator has begun.
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