What is a NON-LINEAR Capacitor?

[pese]

What is a NON-LINEAR Capacitor? I have heard about it in the internet, and I asked some people but no body knows what it is.

Possibele the mening was, that the capancity change  (exampöe degrease) if the voltage charges up.

So the capacitance of this device in not fixed in one value.

Ifyou ned this:
take an varicap diode

i worked with some type that varyi up to 500pf.

(Its possible to decreas also capavitance electronically, try to "google" out this knowledges)
G.P.

[Magnethos]

Thanks to all,. very interesting information and very helpfull.

I have found the answer in a book:
"Think of a really good conductor such as copper as an essentially LINEAR material. Linear means energy conservative. Overunity can only be done with a highly NONLINEAR effect. So your "conductors" have to be made of nonlinear materials. In fact, they have to be made of degenerate semiconductor material (...)"

So, nonlinear means a mixed/doped material, that isn't energy conservative.

[DrSimon]

Most capacitors are nonlinear.
A capacitor charges to 2/3 the input voltage in the first time constant.
Then to 2/3 of the remaining voltage in each additional time constant.
For all intensive purposes a capacitor is considered charged within 5 time constants.
But in reality a capacitor will never become fully charged with the input voltage.

A linear capacitor is one that would charge at a steady rate throughout the charge cycle.
I personally have never seen a linear capacitor and have no idea how one would  be constructed.
Here is one method of obtaining one.
http://invent.ucsd.edu/technology/cases/2005/SD2005-117.shtml
My guess is to use a variable input voltage that increases at the same rate as the capacitor charge increases.
In any case not a simple thing to construct.

@AbbaRue

Actually its very simple to charge a capacitor in a linear mode. Text books are convenient in the so called 67% in 1T, yet a capacitor is just a big bucket and you can fill it however you wish.  See an example by Dr. Stiffler --- http://www.youtube.com/watch?v=zehYlCWGyII

[pese]

@AbbaRue

Actually its very simple to charge a capacitor in a linear mode. Text books are convenient in the so called 67% in 1T, yet a capacitor is just a big bucket and you can fill it however you wish.  See an example by Dr. Stiffler --- http://www.youtube.com/watch?v=zehYlCWGyII

If you charge the cap with an constant current , than the cap will charge
-in any way- LINEAR .
In most schematics that i seen here , the cap is charged with an simple resistpr up.  this way the current (over resistor) is un-linear the time of pull up
the condensor.. So you find an unlinear charging offcause unlinear loding the cap.
Pese

For Overunity, you can use "Varicap Diodes" in milliwatt range (used for RF amplifiers.
also Tunnel-diodes , ,vor higher power , unlinearities in Magnetfield hysteresis and other materials
G.Pese

[Magnethos]

I saw these 2 videos, and in the second one you can read in the comments the nonlinear cap.

http://uk.youtube.com/watch?v=2cUS03yNl40&feature=channel_page

http://uk.youtube.com/watch?v=Y9irQJ6mivs&feature=channel

Any capacitor is ok to replicate the experiment? or we need a special nonlinear cap?
The main question is that.