title: Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples.
abstract: This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3.5mm O.D. star shaped sample holder, named AquaStar. Simulations and experimental results at X-band show that the EPR signal intensity increases by factors of 1.43 and 3.87 in the DoubleDee and AquaStar respectively, over the current TPX 0.9mm O.D. sample tube in a two-loop-one-gap LGR. Finally, combining the insight gained from the constructed sample holders and finite-element solutions, a third multi-lumen sample holder for a cylindrical TE011cavity is optimized, named AquaSun, where simulations show an EPR signal intensity increase by a factor of 8.2 over a standard 1mm capillary.
authors.affiliation: Medical College of Wisconsin, Department of Biophysics, Milwaukee, WI 53226, USA. Electronic address: jason.sidabras@gmail.com.
authors.forename: Jason W
authors.initials: JW
authors.lastname: Sidabras
authors.affiliation: Medical College of Wisconsin, Department of Biophysics, Milwaukee, WI 53226, USA; Milwaukee School of Engineering, Department of Physics and Chemistry, Milwaukee, WI 53202, USA.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Mett
authors.affiliation: Medical College of Wisconsin, Department of Biophysics, Milwaukee, WI 53226, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Hyde
mesh_terms: D003198:Computer Simulation; D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D020342:Finite Element Analysis; D008872:Microwaves; D011138:Polytetrafluoroethylene; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D011138:Polytetrafluoroethylene
keywords: Aqueous samples; Cylindrical symmetry; Electron paramagnetic resonance; Loop-gap resonator; Multi-lumen sample holders