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removed trailing spaces from ReadMe.txt input
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saurabh-s-sawant committed Aug 17, 2024
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###################################
#### parallel_plate_capacitor #####
###################################
-This example models a parallel plate capacitor such that
a voltage of 10 V is specified at Zmax boundary and 0 V

-This example models a parallel plate capacitor such that
a voltage of 10 V is specified at Zmax boundary and 0 V
is specified at Zmin boundary.

-First four examples provided in this folder show different ways
to specify these voltages.

1) inhomo_const_dirichlet:
1) inhomo_const_dirichlet:
This example specifies voltages directly through where
boundary conditions are specified, e.g. dir(10) or dir(0).

2) function_parsed_dirichlet:
This example specifies voltages through dirichlet function
This example specifies voltages through dirichlet function
parsers whose name is specified at the time of specifying boundaries,
e.g. dir(Zmin) or dir(Zmax). Function parsers are specified for
e.g. dir(Zmin) or dir(Zmax). Function parsers are specified for
Zmin and Zmax.

3) function_parsed_robin:
Expand All @@ -27,33 +27,33 @@
This example is similar to example 2 but voltage at the top plate
is applied as a cosine function 10*cos(2 pi x/(2Lx)).

-Fifth example, is for the case with two dielectrics, where in upper Lz/2 region there is air
-Fifth example, is for the case with two dielectrics, where in upper Lz/2 region there is air
and in the lower, SiO2, epsilon_2 = 3.8.

-On all lateral sides we can either specify Neumann boundaries
-On all lateral sides we can either specify Neumann boundaries
or periodic boundaries.

For verification:
-Check that voltage in the ghost cells is as specified.
-Note:
-Note:
Charge on the plate, Q = C V_0 (where V_0 = 10 V in our case)
Surface charge density, sigma = Q/A (A = 0.2**2 in our case)
Surface charge density, sigma = Q/A (A = 0.2**2 in our case)
From Gauss' law, sigma = D (D_z in our 1-D example)
For single dielectric, D_z = E_z / epsilon_0

From above equations, E_z = D_z/epsilon_0 = sigma/epsilon_0 = Q/(A*epsilon_0) = (C V_0)/(A*epsilon_0)
So, C = E_z *A*epsilon_0 / V_0
So, C = E_z *A*epsilon_0 / V_0

Now from solution, we can find that |E_z| = 200 V/m
By calculating, we obtain C = 7.04 pF (as expected from theory).

-For the two dielectric case:
potential phi at the interface is given by,
phi_int = epsilon_1 d_2 / (epsilon_2 d_1 + epsilon_1 d_2) V_0
phi_int = epsilon_1 d_2 / (epsilon_2 d_1 + epsilon_1 d_2) V_0

In our example, epsilon_1 = epsilon_0 and epsilon_2 = 3.8*epsilon_0, d_1 = d_2 = L_z/2
this gives, phi_int = 2.04 V

By probing cell-centered phi at the air-dielectric interface we find this phi_int = 2.07 V.

-E_z in the air and dielectric can also be easily estimated by taking the gradient, e.g.
Expand All @@ -62,4 +62,4 @@ For verification:
These values are close to what we see from the solution.



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