Gas/Fluid Dielectric: Seeking EE Help for Variable Dielectric Constant

[tekness]

Hi!

First time poster seeking some EE help.

I'm looking for a gas or a fluid that has a dielectric constant that can be varied by some sort of means(physical).
Something in the area of changing the pressure. I will be sending microwaves in the 10-20Ghz range through this gas/fluid, so as little absorption is preferred.Any help is greatly appreciated.

 

[berkeman]

Are you wanting this effect in order to control the delay? Are the microwaves linearly polarized? Are they confined to a wave guide, or are they in free space?

 

[tekness]

Thank you for your reply.
I would like as little attenuation as possible. They are linearly polarized, will be confined and will pass through to a tube-ish medium from one point to another. Vacuum space.

 

[berkeman]

I googled anisotropic dielectric constant microwave, and got some interesting hits. Here is a sample hit:

http://www.scientific.net/0-87849-947-4/207/

And here is the hit list:

http://www.google.com/search?source...ric+constant+microwave&btnG=Search&nochrome=1

You might be able to have a region in your waveguide where you have a cylinder of anisotropic dielectric material, with the long axis perpendicular to the tube. As you rotate the cylinder, that will change the effective dielectric constant as seen by the linearly polarized microwave EM as it propagates down the tube. Not sure if that will cause any rotation of the direction of polarization, though.

Not sure that's of much help, just thinking out loud.

 

[dlgoff]

You could make use of the Kerr Effect and change the dielectric constant with an external electrical field. You could do as Berkeman says and rotate it relative to your mircowaves polarization.