IMPACT OF HIGH-DIELECTRIC-LOSS MATERIALS ON THE MICROWAVE FIELD IN EPR EXPERIMENTS

A dielectric material distorts the microwave held inside an EPR resona tor, which results in distortion of the EPR signal from spins inside t he material. In this paper, the effects of a spherical bulb filled wit h a dielectric liquid such as water dr a water-ethanol mixture were ex amined. EPR spectra were recorded for small samples inside and outside of the sphere. The studies include CW and ESE experiments at two micr owave frequencies, X band (9.2 GHz) and L band (1.03 GHz). The double integral (area) of an EPR signal depends on B-1(2) at the position of the sample, causing a large difference in EPR signal intensities betwe en samples in regions of different dielectrics. The phase of the EPR s ignal also is affected by the presence of the dielectric. These result s were compared with three methods of calculating electromagnetic fiel ds (quasi-static method, plane-wave-superposition method, and numerica l analysis). Good agreement was found between experimental and calcula ted results. (C) 1996 Academic Press, Inc.