# Permittivity of a Lossy Medium using Antennas

1. Sep 14, 2016

### Petrol Guy

First of all I will being with I'm not an electric engineer so I might be out of my wits, but I will give it a try.

So I have an instrument which reads relative permittivity using a transmitter and two receiver placed at different distances. The instrument is calibrated to read either in a vacumm or air and based on the phase and amplitude record at the antennas an value is outputed. In terms of a formula or how my eight variables are a function of each other I'm unsure. I know it should use some sort of wave equation using the reference wave vs the actual wave and solve the impedence caused by the medium.

Let me know if you have an idea how this may be formulated? Thanks

2. Sep 14, 2016

### Staff: Mentor

3. Sep 15, 2016

### Staff: Mentor

It sounds like you want to use a capacitive sensor to figure out the dielectric constant of a material, and use a reference set of plates with just air or vacuum between them to help you calibrate the measurement. Is that what you are wanting to do? Do you have a sketch of your setup? Do you know the equation that relates the capacitance and geometry of the plates to the permittivity of the material between the plates?

4. Sep 15, 2016

### Petrol Guy

That sounds to be what I'm after (not sure if the same principle as plates but using an attenna like receiver [circular bars]). As for a general geometery it is imaged below. I do have the permittivity values at set amplitudes and phases, the frequence of the wave and lots of data (amplitudes and phase vs permittivity) to build an empirical relationship. As for a the potential relationship I'm unsure since I'm not extensively familar with the wave equation and electromagnetics.

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5. Sep 15, 2016

### Staff: Mentor

Based on your username and you having a pipe in your drawing, are you wanting to measure the dielectric constant of some fluid flowing in the pipe?

What are the horizontal lines in the pipe drawing?

6. Sep 15, 2016

### Petrol Guy

Ya we measuring the dielectric constant, I just trying to figure out how it is done in order to troubleshoot or apply an offset if required.

The horizontal lines is a 1/4 inch thick piece of metal which divides the pipe in to two. On one side the permittivity is calculated and on the other side is a other sensor which determines the continuous phase.

7. Sep 15, 2016

### Baluncore

What RF frequency or range of frequencies is used by the instrument ?
Who is manufacturer and what model is the instrument ?

The relative permittivity is independent of the environment, vacuum or air.
It will be hard to detect the difference between a measurement made in vacuum versus air.

Relative amplitude and phase can be read with a two channel RF Vector Voltmeter such as the old HP8405.