Calculating E-field Through Layers w/ Diff. Permittivities & Conductivities

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Discussion Overview

The discussion focuses on understanding how the total electric field behaves as it passes through multiple layers with differing electrical permittivities and conductivities. Participants explore the implications of these properties on the electric field profile, particularly in a steady-state scenario.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that the total normal component of the electric field will have a stepped pattern across the layers, with specific values derived from the relative permittivities.
  • Another participant raises the question of whether the system is in a steady state or if time-varying effects are considered.
  • A later reply suggests that in the presence of finite conductivities, charge migration will lead to a zero electric field inside the layers, which may not be a compelling scenario for analysis.
  • There is mention of the Displacement field D and its relationship to the electric field E and permittivity, indicating a potential approach to understanding the field behavior in the layers.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the behavior of the electric field, as there are differing views on the effects of conductivity and whether the system is in steady state or not.

Contextual Notes

The discussion does not resolve the implications of surface charge accumulation at the interfaces or how to calculate any secondary electric fields that may arise from this phenomenon.

ThomasAnderson
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I'm trying to understand how the total electric field changes as it passes through layers with different electrical permittivities and conductivities (as shown in the linked figure). The rectangular prism layers are assumed to be very thin. The conductivities ##\sigma## and relative permittivities ##\epsilon_r## for the 5 layers as well as the surrounding medium are labeled. The external field ##E_0## is uniform. I'm hoping to find the profile of the total normal component of the E-field along the line A-A'.

I assumed that the profile would have a stepped pattern as shown in the right panel. For example, the electric field normal component inside layer 2 would be ##E_{n,2}=E_0/\epsilon_{r,2}##, and similarly for the other layers.

However, I also recall learning that there is a surface charge accumulation that occurs at the interfaces between each layer, due to the difference in conductivities. If I understand correctly, these surface charges create a secondary electric field. I don't know if I need to find this secondary field, and I'm not sure how I would calculate it. I would appreciate some guidance on this problem!

https://i.stack.imgur.com/UHQ7L.png
 
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Do things vary with time or are you interested in steady state (after system settles)?
 
hutchphd said:
Do things vary with time or are you interested in steady state (after system settles)?

I was interested in the steady state
 
For any finite conductivities, the charge will migrate to the opposing surfaces and the field inside will be zero (ignoring edge effects). Not very interesting?

For all conductivities zero the Displacemant field D will be E0 and the local E will be εD rE0 in each slab. I think Griffiths does a nice job on this general subject.
 
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