Estimating potential drops within multi-media capacitors

In summary, the author is trying to estimate the potential drop across a capacitor containing three distinct media between the electrode plates. The system is as follows: Vo-(+) air gap | binary electrolyte phase | plastic phase (-) The lengths of the air gap is approximately that of the electrolyte phase, with the length of the plastic phase being much smaller. I'm trying to figure out a way to consider the the electric field at the interfaces due to the electrical double layer that should be generated by the potential difference across the capacitor. However, I'm having trouble with the solution I came up with which violates conservation of charge. Any ideas?
  • #1
Sancor
7
0
I was wondering if anyone had any insights on how to estimate or discern the potential drops across a capacitor containing three distinct media between the electrode plates. The system is as follows

Vo-(+) air gap | binary electrolyte phase | plastic phase (-)The lengths of the air gap is approximately that of the electrolyte phase, with the length of the plastic phase being much smaller. I'm trying to figure out a way to consider the the electric field at the interfaces due to the electrical double layer that should be generated by the potential difference across the capacitor.

Solving Laplace in one dimension gives

I1 = Ax+B
I2 = Cx+D
I3 = Ex+F

Applying boundary conditions I get

I1(x=0)=Vo=B
I3(x=2L)=0=2EL+F => F = -2EL

I1(x=L)=I2(x=L)
AL + Vo = CL + D

I2(x=2L)=I3(x=2L)
2CL + D = EL - 2EL
2CL + D = -EL

from conservation of charge
n*(σ1E12E2) = 0
σ of air and plastic = 0 thus
E2=0

C=0

leaving me with 3 unknowns and only two equations

AL + Vo = D
D = -EL

Which is why I am trying to see if I can estimate the approximate potential drop due to the air gap, which would allow me eliminate one of my unknowns. Still though, this is only good for determining the potential everywhere within my capacitor, and I am still no closer to determining the electric field due to the double layer at my interfaces. Any ideas?
 
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  • #2
So after working on this some more I decided to try and model the system as capacitors in series... and I decided to neglect the plastic layer for this... Anyhow what I ended up doing was to draw my system as a simple circuit with two capacitors in series connected to a power source.
C1=air phase
C2=electrolyte phase
CT=total system capacitance
L = length of phase
κ= dielectric constant
Vo = battery voltage

C=[itex]\frac{κ*ε*A}{d}[/itex]


C1=[itex]\frac{ε*A}{L}[/itex]

C2=[itex]\frac{κ*ε*A}{L}[/itex]


CT=[itex]\frac{C1*C2}{C1+C2}[/itex]=[itex]\frac{κ*ε*A}{(1+κ)*L}[/itex]

Q=CT*Vo=[itex]\frac{κ*ε*A*Vo}{(1+κ)*L}[/itex]

Q is conserved in series capacitors so

V1=Q/C1=[itex]\frac{κ*Vo}{(1+κ)}[/itex]

V2=Q/C2=[itex]\frac{Vo}{(1+κ)}[/itex]

The voltage drop across the electrolyte phase should therefore be from V2 to zero

Based on this, I rederived the potential function using Laplace's Eqn

I1=Bx+C
I2=Dx+P

Considering the system from 0<x<2L where x=0 corresponds to ground and x=2L is the positive terminal facing the air phase...

I1=Bx-2BL+Vo
I2=Dx

Both these functions must equal the potential at their interface, e.g. V2 found above. After a bit of algebra you end up with

I1=[itex]\frac{κ*Vo}{(1+κ)*L}[/itex]*(x-2L)+Vo

I2=[itex]\frac{Vo}{(1+κ)*L}[/itex]*x

But I'm uncomfortable with this solution as it violates the BC stipulated by conservation of charge that I describe in the original post. E2 should be equal to zero, but this is clearly not the case if we take the derivative of I2...

[itex]\nabla[/itex]I2=[itex]\frac{Vo}{(1+κ)*L}[/itex]=/=0

So... does anyone know where this discrepancy arises from? Is it fundamentally flawed to model this as a series of capacitors? Or does the E found in this way reflect the E in the double layer?

Any help would be greatly appreciated.
 

1. What is a multi-media capacitor?

A multi-media capacitor is an electronic device used for energy storage in electrical circuits. It is made up of multiple layers of different types of materials, such as metal foils and insulating materials, to increase its capacitance and energy density.

2. How is the potential drop calculated in a multi-media capacitor?

The potential drop, or voltage, in a multi-media capacitor can be calculated using the formula V = Q/C, where V is the voltage, Q is the charge stored in the capacitor, and C is the capacitance.

3. What factors affect the potential drop in a multi-media capacitor?

The potential drop in a multi-media capacitor is affected by several factors, including the number and type of layers, the thickness of the layers, and the dielectric constant of the materials used. The distance between the layers and the surface area of the layers also play a role in determining the potential drop.

4. How can the potential drop be estimated in a multi-media capacitor?

The potential drop in a multi-media capacitor can be estimated using computer simulations or analytical models. These methods take into account the various factors that affect the potential drop and provide an accurate estimation of the voltage across the capacitor.

5. What are some applications of multi-media capacitors?

Multi-media capacitors have a wide range of applications, including energy storage in electronic devices, power factor correction in electrical systems, and high voltage applications such as in medical equipment and particle accelerators. They are also used in renewable energy systems, such as solar panels and wind turbines, to store energy for later use.

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