Rutile dielectric loop-gap resonator for X-band EPR spectroscopy of small aqueous samples

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• Microwave resonator performance is influenced by dielectric-metal surface separation.
• Previous studies focused on X-band TE011 cylindrical cavity resonators with axial dielectric tubes.
• Loop-gap resonators (LGRs) offer advantages for X-band electron paramagnetic resonance (EPR) due to small sample size and high sensitivity (Λ).

Purpose of the Study:

• To investigate the performance of a rutile dielectric tube inserted into an X-band loop-gap resonator (dLGR).
• To develop the theory and present experimental results for this dielectric LGR (dLGR).
• To compare different dLGR configurations and assess their suitability for ultra-small sample analysis.

Main Methods:

• Theoretical development for a dielectric LGR (dLGR) with a short rutile dielectric tube at X-band.
• Experimental validation of the dLGR performance.
• Comparison of 5-loop-4-gap and 3-loop-2-gap configurations.
• Evaluation of performance at constant Λ (B1/Pl) and constant incident power.

Main Results:

• A 5-loop-4-gap configuration (central sample loop with four flux-return loops) is superior to a 3-loop-2-gap configuration.
• The rutile dLGR demonstrates preference over a standard LGR for samples smaller than 1 µL.
• Performance advantages are observed at both constant Λ and constant incident power.
• The dLGR enables EPR measurements with sample volumes as small as 50 nL.

Conclusions:

• The rutile dielectric LGR (dLGR) represents a significant advancement for X-band EPR spectroscopy.
• This technology further extends the capability of LGRs for site-directed spin labeling with ultra-small sample volumes.
• The dLGR facilitates high-performance EPR measurements on samples down to 50 nL, crucial for applications requiring minimal sample quantities.