title: A rectangular loop-gap resonator for EPR studies of aqueous samples.
abstract: A new rectangular geometry of the loop-gap resonator for the use with a flat cell has been developed. Maxwell's equations for the resonators with two, four, six, and eight gaps have been solved assuming the existence of only the magnetic z-component. The formulas obtained were numerically solved for the electric and magnetic field distributions over the cross-sections of the resonators. The presence of a nodal plane for the electric field in the center of the resonator allows the use of a flat cell instead of a capillary for EPR measurements. Using the field distributions obtained, the quality factor and EPR signal amplitude for various shapes and gap numbers for the resonators containing a flat cell filled with water were examined numerically. This allowed finding the geometry that yields the maximum EPR signal intensity. Several X-band resonators were built in order to verify the results obtained theoretically. The experiments confirmed the ability of a novel resonant structure to accommodate a flat cell filled with an aqueous sample. It has been found that the optimum aqueous sample volume for the X-band rectangular loop-gap resonator equals 16 mm3. For a saturable aqueous sample this gives a fourfold improvement in the S/N ratio over the circular 1 mm i.d. loop-gap resonator equipped with 0.6 mm i.d. capillary.
authors.affiliation: Department of Biophysics, Institute of Molecular Biology, Jagiellonian University, Al. Mickiewicza 3, Kraków, 31-120, Poland.
authors.forename: W
authors.initials: W
authors.lastname: Piasecki
authors.forename: W
authors.initials: W
authors.lastname: Froncisz
authors.forename: W L
authors.initials: WL
authors.lastname: Hubbell
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical; D012996:Solutions; D014867:Water
chemical_list: D012996:Solutions; D014867:Water