Is Plate Capacitor Gap a "Non-linear" Medium?

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Discussion Overview

The discussion revolves around whether the air gap between two DC charged parallel plates in a capacitor can be considered a "non-linear" medium, particularly in relation to an electromagnetic field (EMF) radiated by a coil placed within that space. The scope includes theoretical considerations, practical applications, and the properties of dielectric materials.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the air gap could be considered non-linear only if the potential difference is near the breakdown potential, suggesting that air is generally more likely to behave linearly than solid dielectrics.
  • One participant notes that in high voltage applications, the surfaces of capacitor plates are often covered with materials like mylar or kapton, which could introduce non-linearity due to molecular distortion from the electric field.
  • Another participant mentions that the charge distribution in non-flat geometries, such as spherical or cylindrical capacitors, is inherently non-linear.
  • There is a claim that an ideal capacitor is linear by definition, and any observed non-linearity is considered a defect in the capacitor.
  • One participant points out that the charge/discharge curves of capacitors are exponential, indicating a lack of a straight-line relationship between voltage and current unless plotted together.
  • Questions are raised about the effects of inserting an EMF radiating coil within the capacitor and whether this could simulate a ferroelectric dielectric.
  • A clarification is made regarding terminology, suggesting that "EMF radiating coil" is not appropriate and should be referred to as "EM radiating coil."

Areas of Agreement / Disagreement

Participants express differing views on the linearity of capacitors and the implications of inserting coils within them. There is no consensus on whether the air gap can be classified as a non-linear medium, and multiple competing perspectives remain on the nature of the dielectric materials and their effects.

Contextual Notes

Limitations in the discussion include assumptions about the behavior of dielectric materials under different conditions, the dependence on specific configurations, and the unresolved nature of the effects of AC versus DC applications.

Fluxation
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Could the space (air gap) between two DC charged parallel plates be considered to be a "non-linear" medium with respect to an EMF radiated by a coil contained within that space?
 
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Fluxation said:
Could the space (air gap) between two DC charged parallel plates be considered to be a "non-linear" medium with respect to an EMF radiated by a coil contained within that space?
Only if the PD were very near the breakdown potential. Superposition applies over a huge range of Field Strengths and Air is more likely to be linear (in the limit) than any solid dielectric, I think.
 
In practical HV applications, the inner surfaces of the flat capacitor plates would probably be covered in a material such as mylar or kapton sheet. As I understand its molecules would be distorted by the superposed ES field gradient.

Would this of itself not give rise to some form of non-linearity with respect to intersecting EMF's?

Although not germaine to the OP, it might also be pointed out that in a spherical or cylindrical cap the charge distribution itself is non-linear.

All this no doubt becomes more complex if AC instead of DC is applied.

Comments?
 
An ideal capacitor is linear, by definition. Any nonlinearity is a defect in the capacitor.

Most real capacitors are pretty close to linear if operated within their designed parameters.
 
There appears to be a difference of opinion on this since the charge/discharge curves of a cap are exponential. There is no straight line relationship between V and I unless plotted together.

The dielectric material also needs to be factored in. Does it have ferroelectric properties?

http://www.eecg.toronto.edu/~ali/ferro/model.html

Here is a thought. What would happen if I sandwitched a flat spiral coil of insulated wire between two oppositely charged disks and fed it with a non-repetitive signal?

Could such a configuration be used to simulate a ferroelectric dielectric?
 
Fluxation said:
There is no straight line relationship between V and I unless plotted together
The defining equation ##i=C\frac{d}{dt}v## is a linear differential equation. As I said above, a capacitor is linear by definition
 
I did not mean to disagree with you, but was rather inquiring about any predictable effect upon the ideal linearity of a plate cap that might be caused by insertion within it of an EMF radiating coil.
 
Fluxation said:
an EMF radiating coil.
I think you mean an EM radiating coil. It's not appropriate terminology to talk of radiating an EMF.
 

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