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Variable capacitor

Variable air capacitor consists of fixed stator plates and movable rotor. Capacitance between the stator plates depends on the position of the rotor.

Problem Type: electrostatics.

Geometry: 3D extrusion.

variable capacitor 3D model

Relative permittivity of air ε = 1,
Potential difference ΔU = 1000 V

Find the mutual capacitance between two stators as a function of the rotor position.

QuickField simulation gives energy W and electric potential U distribution. The capacitance then can be calculated as C = 2W / ΔU2.


Rotating angle α

Energy W

Capacitance C

1.29e-6 J

2.58e-12 C


2.25e-6 J

4.50e-12 C


2.97e-6 J

5.94e-12 C


3.22e-6 J

6.44e-12 C

variable capacitor simulation

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