# Electromagnet offset between applied voltage and magnetic field intensity

1. Aug 10, 2011

### Mekatorque

I'm trying to find a mathematical formula between applied tension and resulted magnetic field intensity on an electromagnet.

I know that between the voltage and the electric current there is a pi/2 offset, but in practice there is a bit more than actually pi/2 offset probably something that has to do with the core material of the electromagnet.

Any ideas are welcomed.

2. Aug 14, 2011

### Bob S

There are three main sources of offsets of the pure imaginary relationship between current and voltage in an electromagnet. In all 3 cases, the phase shift in the frequency domain is θ = atan[ωL/R]:

1) coil resistance R (independent of frequency)

2) eddy currents (like in a laminated electromagnet). Use standard equations for transformer laminations, and coatings. R goes as frequency squared.

3) Hysteresis losses. There is a specific energy loss per cycle, depending on magnetic material, and excitation. You need to multiply the energy loss per cycle by the number of cycles per second, so is linear in frequency. See

http://www.electronics-tutorials.ws/electromagnetism/magnetic-hysteresis.html

Bob S