Bimodal inductors for ESR spectroscopy

Abstract

The results of extensive tests on three types of microwave bimodal X-band spin inductors are reported and discussed. The inductors examined were a square cross-section one, a cylindrical one, and a novel type designed around two orthogonal reentrant cavities. The tests made concerned important features such as the isolation between input and output ports far from spin resonance as function of the frequency, the effectiveness at very high decoupling levels of the rotary joints included in the cavity structures to work as decoupling devices and the effects of sample substitution and removal on coupling and tuning conditions. The results confirmed that the phenomenology of these inductors is now well understood and that, in agreement with the theory already developed, the square cross-section inductor is in many ways superior to the cylindrical one. Further, the limits of the rotating joint system of leakage reduction have been found to be about 80 dB of power attenuation. The tests made on the novel reentrant bimodal cavity (cloverleaf cavity) gave positive results about the independence of the coupling and tuning adjustments and about the small effect of sample insertion on mode coupling and tuning. Further the low electric energy density at the samples regions suggests use of this cavity for ESR of lossy samples while its smaller dimensions suggests its use at lower working frequencies (L, S bands).