Axially uniform resonant cavity modes for potential use in electron paramagnetic resonance spectroscopy

This article is concerned with cylindrical transverse electric TE011 and re ctangular TE102 microwave cavity resonators commonly used in electron param agnetic resonance (EPR) spectroscopy. In the cylindrical mode geometry cons idered here, the sample is along the z axis of the cylinder, dielectric dis ks of 1/4 wavelength thickness are placed at each end wall, and the diamete r of the cylinder is set at the cutoff condition for propagation of microwa ve energy in a cylindrical waveguide at the desired microwave frequency. Th e microwave magnetic field is exactly uniform along the sample in the regio n between the dielectric disks and the resonant frequency is independent of the length of the cylinder without limit. The rectangular TE102 geometry i s analogous, but here the microwave magnetic field is exactly uniform in a plane. A uniform microwave field along a line sample is highly advantageous in EPR spectroscopy compared with the usual sinusoidal variation, and thes e geometries are called "uniform field" modes. Extensive theoretical analys is as well as finite element calculation of field patterns are presented. T he perturbation of field patterns caused by sample insertion as functions o f the overall length of the resonator and diameter of the sample is analyze d. The article is intended to provide a basis for design of practical struc tures in the range of 10 to 100 GHz. (C) 2001 American Institute of Physics .