Gordon Coupler with Inductive or Capacitive Iris for Small EPR Resonators for Aqueous Samples

Area of Science:

• Physics
• Spectroscopy
• Materials Science

Background:

• The Gordon coupler, initially for Electron Paramagnetic Resonance (EPR) at liquid helium temperatures, couples microwave power to resonators via an evanescent wave.
• Previous extensions adapted the coupler for cavity and loop-gap resonators, using low-dielectric plastics like Teflon for aqueous samples.
• Microphonics from helium bubbling were a challenge in early applications.

Purpose of the Study:

• To extend the Gordon coupler's application to X-band five-loop-four-gap resonators.
• To investigate the use of fused quartz, sapphire, and rutile as dielectric materials.
• To optimize power matching and minimize resonant frequency shifts using a capacitive iris.

Main Methods:

• Adaptation of the Gordon coupler design for X-band dielectric resonators.
• Utilization of fused quartz, sapphire, and rutile dielectrics.
• Finite element modeling (FEM) for electromagnetic field analysis.
• Integration of a capacitive iris for improved resonator matching.

Main Results:

• The Gordon coupler was successfully adapted for X-band five-loop-four-gap resonators with new dielectric materials.
• FEM confirmed the electromagnetic field behavior and the coupler's scalability with dielectric resonator dimensions.
• The capacitive iris effectively reduced resonant frequency pulling during power matching.

Conclusions:

• The extended Gordon coupler provides a versatile and efficient method for microwave power delivery in advanced EPR resonator systems.
• The use of robust dielectric materials like quartz, sapphire, and rutile expands the operational temperature and sample compatibility.
• This advancement facilitates high-performance EPR spectroscopy with improved signal-to-noise ratios and stability.