[SI-LIST] Re: Determination of relative permittivity
- From: Xin Wu <xwu_umd@xxxxxxxxx>
- To: kalevi@xxxxxxxxxx, matthias-bergmann@xxxxxx, si-list@xxxxxxxxxxxxx
- Date: Thu, 26 May 2005 07:55:55 -0700 (PDT)
Hi Kai and Matthias,
This technique is based on cavity perturbation. The
cavity perturbed by a change in the permittivity will
result in a shift of resonance. The change of
resonance frequency is given by
delta_omega/omega_original ~=
stored_engergy_variation/stored_energy_original;
where, omega is the angular frequency. Stored_energy
can be calculated by integrating both the electrical
energy and magnetic energy.
Stored_energy = Volume_integration(eps*|E|^2+u*|H|^2);
stored_energy_variation=volume_integration(delta_eps*|E|^2+delta_u*|H|^2);
Please be advised that a well designed cavity at a
specific mode, the field can be theoretically
calculated and at each mode the field is different.
However, the perturbation method assumes the field
distribution will not change, if the dielectric slab
is thin comparing to the cavity height.
Hope this is helpful.
Xin
--- Kai Keskinen <kalevi@xxxxxxxxxx> wrote:
> I've lost the reference to an old microwave book
> that explained the cavity
> resonance method. One method was to make a disk of
> the material of a certain
> thickness that was the same radius as a cylindrical
> microwave cavity. You
> measured the resonant frequency and cavity Q before
> the disk was inserted
> and after the disk was inserted into the bottom of
> the cavity. The change in
> f gave you the dielectric constant and the change in
> Q gave you your loss
> tangent. I can't remember the equations to relate
> delta fr and delta Q to Dk
> and tan delta. Does anyone else remember this
> technique? The cavity was
> cylindrical with a side launch from rectangular
> waveguide.
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
> Matthias Bergmann
> Sent: Wednesday, May 25, 2005 7:32 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Determination of relative
> permittivity
>
>
> Hello,
>
> quite a lot of discussions deal about the
> (effective) permittivity, but how
> do I determine it ?
> I would like to measure the complex permittivity of
> synthetic materials in
> a frequency range between 1 till 500 MHz. I know
> there are methods like
> Parallel plate,
> Reflection wave, S Parameters or Cavity to measure
> it, but, it's sort of
> weird,
> I didn't find any paper which explains how to
> construct a measurement
> system.
> So, are there any basic papers or books you can
> recommend me ?
>
> Best regards, Matthias Bergmann
>
>
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Xin Wu, Ph.D
Special Operations Engineer,
ICE Electronics Design Solution Division,
Fluent Inc.--The Right Answer in Fluid..and Wave...
http://www.icepak.com
http://www.wam.umd.edu/~xwu
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