design of absorber in cavity

[nasimgoli]

design of absorber in HFSS

Hi everybody
I want to design a cavity excited by a coaxial cable which has an absorber at the end ; the frequency of operation is 900MHz,but i don't know how to design the absorber in HFSS!
I would be thankfull if somebody help me.

 

[jiripolivka]

Your question lacks any sense or data.
To excite a cavity by a coaxial cable, I need to know what is the cavity type, coupling to the cable, etc.
Why you want to add an absorber at all?
A cavity resonator can be coupled as a rejection device which attenuates a signal at a resonant frequency. It can be coupled as the reflective resonator, to make standing waves on the feed cable.
What do you want to do at all?

 

[nasimgoli]

I'm so sorry for imperfect information.
well the cavity dimentions are: 44.5,20,9cm. the frequency of operation:900MHz
coaxial cable type:RG217
The goal is to meassure the electric field in the cavity and find the effect of such field on human's cells.so VSWR should be minimized.
my question is about design of the suitable absorber in HFSS.I mean type of material,shape of absorber and procedure of design.
Thank you so much

 

[jiripolivka]

Dear friend:

you again did not indicate what mode your resonator utilizes. In any case, the simplest way to increase the electric field component (and on the other resonator end, the magnetic component, I would use a coaxial resonator with TEM mode. It is easy to tune, by adjusting the length of the quarter-wave center conductor, or by a variable capacitor on the "live" end. Also, it is easy to use a coupling loop between the cable and the cavity.
In any case, connecting such resonator (or yours) to the coaxial line will inevitable cause a standing wave on the line. Using absorber will not help. You can, however, use an attenuator just where cable connects to the resonator, to reduce the SWR. If you insert an absorber in the resonator, in my opinion the resonator will be damped and field intensity in it reduced; the same effect you will get by reducing the power from the generator (usually adjustable).
In the end I do not understand why you want to use any absorber?

 

[FvM]

Referring to the original question, a commonly used method to generate defined electrical fields up to the lower UHF band, e.g. for EMC testing, is a TEM cell. http://www.schwarzbeck.de/Datenblatt/k5233.pdf They are terminated at the other end with a load resistor.

I wonder, if you can't design a similar (somewhat downscaled) cell for 900 MHz?