# Calculating magnetic field strength through objects.

1. Nov 21, 2013

### LordBerkley

If I have a magnetic field of say 5 Tesla which is 3m from a concrete wall 0.25m thick how would I go about calculating the strength of the magnetic field on the other side of the wall?

Any help/guidance much appreciated!

2. Nov 21, 2013

### Staff: Mentor

That depends on the size of your magnet and its field geometry. The concrete wall won't influence the field significantly if there is no steel inside, but the maximal field strength (5T) is not enough to describe a magnetic field.

3. Nov 21, 2013

### LordBerkley

Take the field to be generated by a long solenoid, with a coil diameter of 1m. Is there a specific equation to give the loss of magnetic stray field strength when passing through a material?

4. Nov 21, 2013

### nasu

The problem is that even without the wall the field may decrease dramatically over a distance of 25 cm. Do you know the field in the absence of the wall?

5. Nov 21, 2013

### Staff: Mentor

Then it will still depend on the length of the solenoid (as long as it is not >>10m).
And it will depend on everything (ferro-)magnetic nearby.

For solenoids, there are formulas for the field strength.
Not in general. You will need a simulation, but the effect will be small as concrete is not ferromagnetic.

6. Nov 25, 2013

### paujuan

Dear,
I have been working for long in the electromagnetic fields interaction with concrete. I would say that depending on the purpose of your test, you should carefully measure the characteristics of the concrete that you are using, as there are some concretes that use ferrous sands or gravels, which can affect your measurements.
Yours,