# Effect of electromagnetic damping with variable current

1. Apr 27, 2013

### Samlax

Hi guys, first time poster.

My question is; How would a constant damping provided by an electromagnet affect the damping ratio (and logarithmic decrement) amplitude? And how would increasing the current through the electromagnet affect the damping?

So far I've found Biot-Savart's Law which suggests the EMF will be directly proportional to the current.
However, my results suggest a curve between the Current and the logarithmic decrement.
I know that the logarithmic decrement to damping ratio relationship will be a straight line.

Am I reading the law wrong, or have I measured the results incorrectly?

Thanks,
Samlax

2. Apr 27, 2013

### rude man

You need to be more specific as to what you're doing.

3. Apr 27, 2013

### Samlax

I'm investigating the effect increasing the Current has on a particle that is freely oscillating between two springs, but is dampened by an electromagnetic dampener that is meant to model a linear viscous dampener.

From this I am finding the damping ratio, and need to find a relation between an increasing Current and the ratio. I predicted it would be linear as Current is a constant in Biot-Savart's Law, but my results have returned with a curved line.

Hope this is more accurate?

4. Apr 28, 2013

### rude man

The probable cause for the nonlinear relationship between damping and current is probably the tendency toward saturation of the "particle". Of course it could be other things, I don't know the details of your setup. The electromagnet could itself be saturating.

The relationship between B and H in paramagnetic materials (iron, nickel, alloys thereof etc.) is not linear. As H (current) increases, the B curve tends to flatten out.