Dielectric Constants from solids to pellets

[tommyers]

Hi,

Could someone explain why when comparing a materials dielectric constant in solid form it is sometimes higher in pellet form and sometimes lower for other materials.

For example, Polypropylene has a dk = 1.5 when in a solid (lump) block. This then becomes dk ~ 1.5 - 1.8 when in pellet form. i.e higher.

However when comparing to polyethylene its block dk electric is reported to be = 2.25 but its pellet dk = 1.5 i.e lower.

An explanation to this would be great. I orginally thought it was something to do with the air between the pellets, but as air dk = 1 then this shouldn't be the case?

Finally, I am interested in the dk for polycarbonate pellet, I can only find a value for the block at 2.9. A value and the source would be great.

I look forward to hearing from you guys!

Regards

Tom

 

[lalbatros]

Hi Tom,

Could you explain how you know about this surprising behaviour?
Everybody would guess that the permitivity of a mix would be a monotone function of its composition.

Have a look at this paper:

http://soilphysics.usu.edu/Robinson/2004 3 VZJ Rob clay permittivity.pdf"​

You will find there various models and experiments that -at first reading- confirm this point of view.

Michel

Postscriptum

From your previous thread here I guess the following thread might interrest you:

https://www.physicsforums.com/showthread.php?t=125483"​

To my great surprise there is a rather simple formula for this.

 

[tommyers]

Hi Micheal,

Thank you for the link - I will study this.

You may like to have a look at the following:

www.blazelabs.com/dielectric_chart.pdf[/URL]

Regards

Tom

 

[lalbatros]

Tom,

I looked at the table, but I did not find data related to your question.
Could you tell me what I should look at?

Michel

PS: the rest of the blazelab site is funny but not reliable at all, many wrong statements, no science actually, totally misleading

 

[eeka chu]

My first guess would be that these are mistakes either in the measurements themselves or that perhaps they've mixed some of the numbers up whilst building the table.

If you could increase the dielectric constant of these materials by forming them into pellets, I would have expected the capacitor manufacturing industry to have been all over the idea - making films from compressed pellets and such.

Neither can I, like you, think of any immediate reason for why the dielectric value would go up with the introduction of air space. Surely capacitors would exploit this factor if it existed, especially with the present drive by companies like Maxwell to develop super farad capacitors and the degree of improvement suggested by those numbers - yet this is the first I've ever heard of it.

Whilst I don't want to sound too close minded, this table is from a site that uses the word "lifter", and I've seen that floating around with the words "free energy" and "anti-gravity" far too often for my liking.

 

[tommyers]

Hi,

I know that the website from which I recommended the document - was not the most reliable source! But the documents figures agreed with figures which I have seen previously, here are a couple more links:

http://www.clippercontrols.com/info/dielectric_constants.html#P

http://www.flowmeterdirectory.com/dielectric_constant_03.html

I have being desparatly trying to find an official standards website i.e NIST or something similar!

Any recommendations?

Regards

Tom