capacitance of Coaxial Cable with a semi conductor

[JohnRizik]

I am looking for an information about the capacitance of Coaxial Cable, in which the inside part is made of a conductor and coated with a semi conductor, and the outside tube is made of a conductor material.

Do you have any explanation? or Formula ?

Attached a pic for the status.

[studiot]

From your diagram it is not clear whether the thickness and properties of the semiconductor are sufficient to significantly distort the normal coax equations, which assume a homogenous material (or lack of it) between the conductors.

 

BTW What is the purpose of the semiconductor?

 

Is it for instance connected to an earth or source of voltage?

[JohnRizik]

From your diagram it is not clear whether the thickness and properties of the semiconductor are sufficient to significantly distort the normal coax equations, which assume a homogenous material (or lack of it) between the conductors.

BTW What is the purpose of the semiconductor? Am Not sure of the semiconductor properties, but my purpose is to reduce the capacitance between the two conductors. and am not sure if there is a capacitance between the grey conductor and the saline..!!

Is it for instance connected to an earth or source of voltage? The saline is grounded, each one of the conductors are acting as an input for the system. and the semiconductor is connected to the black conductor.

Edited August 19, 2014 by JohnRizik

[studiot]

I'm sorry, I'm not following this.

 

How and why is the semiconductor connected to the outer electrode?

What do you think this will achieve, since connecting the semiconductor at one point says nothing about the potential anywhere else in the semiconductor?

 

What do you mean by saying that the electrolyte is earthed?

Again this has implications for the potential distribution and therefore the capacitance.

 

This is getting very complicated and a numerical mode as opposed to an analytical one, may be the only way forward.

There is capacitance between any two points in space that have a potential difference between them, governed by the intervening material.

 

You have asked about a coax cable, but show saline between the inner and out.

Please explain.

 

Finally please confirm this is not the beginning of some HHO or other crank generator device discussion.

[Enthalpy]

The setuop is globally complicated, possibly more than necessary, and the resulting answer as well.

 

If the saline liquid conducts well enough and is grounded, the capacitance between the grey and black conductors is very small. It would take several MHz upwards for a saline solution to be mainly capacitive. This depends on the concentration and frequency.

 

A semiconductor is a bizarre choice. Depending again on the dopant concentration, possibly the temperature, and the frequency, some semiconductors (like compensated GaAs) can be mainly capacitive, but if this one was deposited on the black metal (probable due to the shape) it's more likely resistive than capacitive. To reduce the capacitance, a metal would be better - or a good ceramic.

 

And if you want to make a good coaxial cable, water does nothing good there, and grounding it is even worse.

 

As it looks, you want a capacitance with materials not capacitive. What frequency, what resistivites...?

[John Cuthber]

 

I am looking for an information about the capacitance of Coaxial Cable, in which the inside part is made of a conductor and coated with a semi conductor, and the outside tube is made of a conductor material.

 

Why?