Hmmm?

That is basically what I did my MS thesis on:

"An Automated Microwave Network Analyzer
?and its Application in the Measurement
?of the Dielectric Properties of Materials"

I put together a 8410 system out of manually controlled
8410 network analyzer bits, and some this and that,
automated it, and then made tons of measurements on the
dielectric properties of water at microwave frequencies.

Probably a bit more than you were looking to do.

The test cells were gold plated stainless steel sections
of coaxial "air line", that I filled with the liquids being
sampled.? Distilled water, normal saline, and normal saline
with DNA.... Oh, and air.

I then wrote a function that computed the dielectric constant
of water according to the Debye equation to compare my results
to.

-Chuck Harris

peter bunge wrote:
> Has anyone made test fixtures for measuring liquids or solids (essentially a capacitor with the DUT as dielectric)
> I know they are available for their weight in gold but I would like to make some.
> The solids are a problem as there are boundary effects where electrons in the dielectric don't like getting close to the conductive plate.
> Amorphous solids (think talcum powder) are a problem for plate design and need compression forces. Other solids like sand or salt crystals are also a challenge.
> Transducers like Barium Titanate probably have metal evaporated on the surface.
> Anyone out there with experience?
> Anyone have something for sale? (contact offline)
>
>
>
>

On Fri, 8 Feb 2019, 22:21 peter bunge <bunge.pjp@... wrote:

Has anyone made test fixtures for measuring liquids or solids (essentially a capacitor with the DUT as dielectric)
I know they are available for their weight in gold but I would like to make some.
The solids are a problem as there are boundary effects where electrons in the dielectric don't like getting close to the conductive plate.
Amorphous solids (think talcum powder) are a problem for plate design and need compression forces. Other solids like sand or salt crystals are also a challenge.
Transducers like Barium Titanate probably have metal evaporated on the surface.
Anyone out there with experience?
Anyone have something for sale? (contact offline)

I have played with liquids.?

The frequency you want to make the measurement at is important, as is the loss, as they set what methods work and what will not.

Also is the liquid polar??

I have a document from NPL that lists about 50 ways of making such measurements!?

Andrew Gregory at NPL is very helpful

I managed to get a tour of the lab on the last NPL open day. The lab was not open to the public, but I arranged it in advance.?

I have used an air spaced Jackson capacitor and measured impedance on an LCR meter. It is not perfect as you get fringing fields with air, which are reduced with a dielectric.?

Polar liquids are a problem as they set up a boundary layer between the electrodes.?

I made an air-spaced 50 ohn transmission line, then filled the air with liquid. Unfortunately my design has no analytical solution, so I resorted to EM simulation, but a variation with stripline does?

I am told for low loss liquids like cyclohexane, the only method that works is a resonance method, looking for a reduction in Q with the dielectric.?

Dave

On Sat, 9 Feb 2019, 11:14 Tobias Pluess <tobias.pluess@... wrote:

This is a really interesting topic. I also wanted to do several measurements of (complex) permittivity and permeability. But some of the math is a bit cumbersome.

I also wonder what kind of test fixture could be home made (eg. using a ordinary lathe and/or mill).

I think a open end semirigid cable could be used for dielectric measurements of liquids. At least the photographs in some Keysight application note about this topic look like this.

Tobias

To get both permittivity & permeability you need two independent measurements, such as reflection & transmission.?

A lot depends on the frequency. Putting the material under test inside a waveguide is very practical at microwave frequencies, whereas it is not in the MHz range, where a parallel plate capacitor is much more practical.?

Dave.?

At work we have the Agilent liquid test fixture, use together with a LCR meter to measure the permittivity of different oil's

I remember that my company didn't want to buy? more than one, due to price....

Keysight also has one for solids as well

The price is way to high for these, but if you study the manuals, you will see that the construction isn't that advanced, so making one should not be a problem if you have access to some proper machining tools.

And the dimensions isn't that critical as you compare the dialectic of what you want to measure against the dialectic of air.

But of course you will? need a instrument to connect to the test fixture.

BR,

Askild

On Sat, Feb 9, 2019 at 12:47 PM Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...> wrote:

On Sat, 9 Feb 2019, 11:14 Tobias Pluess <tobias.pluess@... wrote:

This is a really interesting topic. I also wanted to do several measurements of (complex) permittivity and permeability. But some of the math is a bit cumbersome.

I also wonder what kind of test fixture could be home made (eg. using a ordinary lathe and/or mill).

I think a open end semirigid cable could be used for dielectric measurements of liquids. At least the photographs in some Keysight application note about this topic look like this.

Tobias

To get both permittivity & permeability you need two independent measurements, such as reflection & transmission.?

A lot depends on the frequency. Putting the material under test inside a waveguide is very practical at microwave frequencies, whereas it is not in the MHz range, where a parallel plate capacitor is much more practical.?

Dave.?

In the late 1980s I worked at E. I. DuPont Co at their Engineering Physics Lab in Delaware. We did a lot of dielectric measurements for the company, and also had an 8510 plus the 1970s 8409 automatic network analyzer, a two rack wide series of instruments controlled with a 9836 computer. The basis was the 8410 network analyzer.

One of the typical measurements we made was liquid dielectric measurements. We had a brass cell, with O rings, that looked like a vertical coaxial cylinder. It was filled a certain height with the liquid, and it fitted on top of the HP 4342A Q meter. We made empty and full measurements and plugged the dial setttings into a program that computers K' and K"". I think we had a heat tape around it, and could measure vs temperatur. Later I automated it with a swept measurement system and had the dielectric properties vs temperature.?

Keysight and an aftermarket Swiss? company make a surface probe that can measure flat materials and liquids. Damaskos in Pennsylvania also makes some devices.