Here you can see an instance how capacitances can be simulated and evaluated. A Rainsensor consist of an active primary planar aircoil and a passive secondary planar aircoil. Energy is transmitted from primary coil to the secondary coil. The system works on a resonance base. The self capacitance and therefore the resonance frequency change if the dielectrical environment varies. In this case it varies if water cover the aircoil.
The capacitance is a function of the water covering the coil and therefore it is a quantity for rain strength.
