Impact of High-Dielectric-Loss Materials on the Microwave Field in EPR Experiments

✍ Scribed by Minoru Sueki; George A. Rinard; Sandra S. Eaton; Gareth R. Eaton

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 283 KB
• Volume: 118
• Category: Article
• ISSN: 1064-1858
• DOI: 10.1006/jmra.1996.0025

✦ Synopsis

A dielectric material distorts the microwave field inside an EPR have been investigated thoroughly due to possible health resonator, which results in distortion of the EPR signal from spins hazards in MRI. The research has focused on the calculations inside the material. In this paper, the effects of a spherical bulb of heating caused by absorption of the radiofrequency energy filled with a dielectric liquid such as water or a water-ethanol . In MRI calculations of RF power deposition and/ mixture were examined. EPR spectra were recorded for small samor reduction of signal intensity, the human body has been ples inside and outside of the sphere. The studies include CW and approximated by a sphere, cylinder, or other geometries [ for ESE experiments at two microwave frequencies, X band (9.2 GHz) example, see ( )], and the RF field is represented by a and L band (1.03 GHz). The double integral (area) of an EPR plane wave propagating in one direction. In EPR, however, signal depends on B 2 1 at the position of the sample, causing a large the RF field inside the commonly used microwave resonators difference in EPR signal intensities between samples in regions of is a standing wave. Therefore, the theoretical approaches different dielectrics. The phase of the EPR signal also is affected used for NMR are not applicable for EPR. In this paper, we by the presence of the dielectric. These results were compared with

present a general theoretical description applicable to EPR, three methods of calculating electromagnetic fields (quasi-static method, plane-wave-superposition method, and numerical analy-seeking to communicate it in terms that are both precise for sis). Good agreement was found between experimental and calcuthe microwave engineer and also useful to researchers seeklated results.