Home / Examples / Electric Analysis [Coulomb] / Example 4: Floating Electrode's Potential

The model consists of four plate electrodes arranged in parallel. Electric potential is applied
between the top and bottom electrodes. Intermediate electrodes are floating.
The capacitances across the electrodes, the electric field, and the equipotential map are solved.
Unless specified in the list below, the default conditions will be applied.
Results will vary depending on Femtet version and the PC environment.
Item |
Settings |
Analysis Space |
3D |
Model Unit |
mm |
Select [Static analysis] as the electric potential is static.
Item |
Settings |
Solver |
Electric Analysis [Coulomb] |
Analysis Type |
Static Analysis (Capacitance) |
Options |
N/A |
The electric field exists outside the analysis region. Therefore the open boundary condition below is applied initially.
Tabs |
Setting Item |
Settings |
Open Boundary Tab |
Type |
Absorbing Boundary |
Order of Absorbing Boundary |
1st-order |
Create 4 sheet bodies for electrodes. Then, specify the electric potential on each as boundary condition.

Two sheet bodies are used to imprint the electric potential-specified boundary condition.
The other two are used to imprint the floating electrode boundary condition.
They are called "imprinting body".
You don't need to set the body attribute or the material property on them.
Body Number/Type |
Body Attribute Name |
Material Name |
1/Sheet |
Imprinting body |
|
2/Sheet |
Imprinting body |
|
3/Sheet |
Imprinting body |
|
4/Sheet |
Imprinting body |
|
* Available from the material DB
Boundary Condition Name/Topology |
Tab |
Boundary Condition Type |
Specifications |
Electrode1/Face |
Electric |
Electric Wall |
Electric Potential Specified -1 [V] |
Electrode2/Face |
Electric |
Electric Wall |
Electric Potential Specified +1 [V] |
Floating1/Face |
Electric |
Electric Wall |
Floating Electrode |
Floating2/Face |
Electric |
Electric Wall |
Floating Electrode |
Outer Boundary Condition * |
Electric |
Open Boundary |
|
To set Outer Boundary Condition, go to the [Model] tab

and click [Outer Boundary Condition]
.
To view the calculation results, go to the [Results] tab

and click [Table]
.
The capacitances of floating electrodes are as follows.

The capacitances of fixed electrodes are as follows.

The vectors of the electric field are shown below.

The gradation contour of the voltage on the XZ section is shown below.

You can visually grasp the distributed electric potential in the space around the electrodes.