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# Magnetic field measurement

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## Magnetic field measurement

(OP)
Hi guys.  I have what I think is a basic question.  I'm not much of an electrical engineer, so I hope it does not sound too silly.  I have the basic equations that characterize the magnetic field on axis with a solenoid shell at a distance away from the solenoid.  However since the field falls away so quickly I wanted to concentrate the flux with a solenoid with some sort of core (probably ferrite).  I only need a magnetic field a few millimeters away from the electromagnet, but it will not make contact with the magnetic substrate.  I have tried to find equations to help characterize the field away from a solenoid with a core but have not been able to.  I also looked for commercial electromagnets that may have specific field equations for that particular electromagnet, but none I found have the formula, plus they are all contact electromagnets.

Any ideas on where I can get (or I guess make?) an electromagnet to attract a magnetic material from a distance of a few mm and its magnetic field equation so I can model it?

George

### RE: Magnetic field measurement

I think you mean to put the ferrite inside your second solenoid, the solenoid that is used to measure.  Thus you are not going to modify the first solenoid, the electromagnet solenoid.  If that is true, you could start with the equations, but that would be very difficult. I would experiment to calibrate your measurement device, which seems to be a loosely coupled transfomer.  You would do this with a know magnetic solenoid source that is not affected by your measuring device.

You asked for advice on if someone already has simplified equations for just this application.  I am sorry I do not know that, but someone in this forum might.  If you do not get an easy answer, then maybe measuring will have to suffice.  You might want to measure anyway, just to refine the calibration.  The equations can get you in the ballpark in your experimental stage.

### RE: Magnetic field measurement

A few years ago I had to calculate magnetic field near a solenoid.  The project didn't have much money, but I found a free finite element solver that did the trick.  Take a look at www.quickfield.com.  When I last used it, the free version was 2-D and limited to 200 nodes.  But that was enough to get an answer for my problem, it may be enough for yours.

Peter

### RE: Magnetic field measurement

Maxwell 2D (Maxwell SV) is available free of charge from Ansoft now.  It is a decent FEA solver.  The GUI is a bit clunky, but after you go through the tutorial you'll be able to set up a solution for a system.

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