Uniform field loop-gap resonator and rectangular TE_U02 for aqueous sample EPR at 94GHz.

Area of Science:

• Spectroscopy
• Resonator Design
• Biophysics

Background:

• Electron paramagnetic resonance (EPR) spectroscopy requires uniform microwave magnetic fields for accurate quantitative analysis.
• Existing resonator designs often struggle to achieve sufficient field homogeneity, particularly for aqueous samples.

Purpose of the Study:

• To design and implement two novel uniform-field resonators for 94GHz EPR spectroscopy of aqueous samples.
• To improve field homogeneity and accommodate specific sample geometries for enhanced EPR measurements.

Main Methods:

• Design and simulation of a seven-loop-six-gap loop-gap resonator (LGR) with Rexolite end-sections.
• Design and simulation of a rectangular TE_U02 cavity resonator with oversized end-sections and sample shielding.
• Experimental validation using lithium phthalocyanine (LiPC) and light-irradiated rose bengal.

Main Results:

• The LGR achieved 90% uniform field over a 3mm sample region using low-loss Rexolite end-sections.
• The TE_U02 cavity achieved 87% uniform field for a 0.1×2×6mm³ sample, with an evanescent slotted window for light access.
• Simulations were confirmed through experiments measuring microwave magnetic field and 100kHz field modulation uniformity.

Conclusions:

• The developed LGR and TE_U02 cavity resonators offer practical designs for uniform fields in EPR spectroscopy.
• These resonators advance the capabilities for quantitative EPR analysis, especially for aqueous samples and light-irradiation experiments.