# Force from a magnet passing through coils!

Mr Pudding
Hi there

I'm engineering a suspension system with the damper consisting of a magnet going through some coils.
As the energy produced from this is proportional to the velocity of the magnet, this would be ideal for an "energetic" damper.

To calculate the damping coefficient produced, I need the formulas to calculate the power generated dependant on the magnet strength, number of coils, velocity etc...

Anyone got it?

## Answers and Replies

Bob S
Using a coil with a series resistance is suitable for a variable damping rate system. Precision chemistry weighing scales (balances) use a damper system with a stationary permanent magnet and a moving vane of copper or aluminum.

For a coil, the voltage output (from Faraday's law) is proportional to -N·A·dB/dt, where N is number of turns, A is coil area, and B is the average magnetic field in the coil. The damping is accomplished by terminating the coil in a resistance R to create an opposing damping current (I = V/R) using Lenz's Law. It is difficult to write down the equations until the exact geometry is specified. Using a magnet and vane is easier.

Bob S