Manual frequency tuning of a sapphire resonator

[yefj]

Hello, I have a wispering gallery mode at 10.24GHz, the resonator is a saphire cilinder which sits on a teflon.
I want to shift that mode to 14.5Ghz after that I need to do some tuning of the mode frequency.
I cannot change the saphire outer diameter as a way to do fine tuning for the modes frequency.
Is there some way giver the resonator structure where using some manual tuning of a screq or something I can tune the mode frequncy?
Thanks.

 

[Atmael]

Possible Solutions:

1. Metallic Tuning Screw

Place a brass or copper screw near (but not touching) the sapphire.

Adjust its distance to perturb the evanescent field, shifting frequency (~100–500 MHz/mm).

2. Dielectric Tuner

Use a movable high-ε dielectric (e.g., TiO₂, BaTiO₃) near the resonator.
Rotate or shift it to modify the effective permittivity.

3. Magnetic Tuning (if sapphire is doped)

Apply a DC magnetic field (Faraday effect) to slightly adjust ε.

4. Stress Tuning

Apply controlled pressure via a screw on the Teflon base to induce strain in sapphire (photoelastic effect).

Key Formula:

\[
\Delta f \approx f_0 \left( \sqrt{\frac{\varepsilon_{\text{eff}} + \Delta \varepsilon}{\varepsilon_{\text{eff}}}} - 1 \right)
\]

For large shifts (→14.5 GHz): Use a high-ε ring segment.

For fine-tuning: Use a screw or movable dielectric.

 

[yefj]

Hello, could you please draw in general, its hard to imagine your the exact location of the screw?
Thanks.
"1. Metallic Tuning Screw

Place a brass or copper screw near (but not touching) the sapphire.

Adjust its distance to perturb the evanescent field, shifting frequency (~100–500 MHz/mm)."