# Frequency magnetics converting to tesla?

1. Jul 2, 2013

### Erik88

Hello,

For the last 2 months I've been trying to find a relation between a frequency magnetic field and the amount of tesla a coil has to induce. When I found this forum and I thought if somebody can help me it would be you guys.

I'm a student at the TU in Delft the Netherlands and I'm trying to make a device using geophysics to find saline groundwater and then pump up the water and desaline it.

This device uses electro magnetics to induce eddy currents in the soil which a receiver coil then measures and gives certain data. This magnetic field is a field with a frequency of 150, 500, 1000 and 2500 Hz. The depth I want to reach is minimum of 60 meters (180 feet) and the least inductive ground that we can have has a conductivity of 1 mS. Now to design the coil that needs to take care of this magnetic field we need the amount of tesla we need to calculate the current that flows through the coil.

I would be so happy if somebody knows how to do this!
Thanks!
Erik

2. Jul 2, 2013

### Staff: Mentor

There is no relation between the frequency of the oscillation of the magnetic field and the magnetic field strength. A stronger magnetic field will just give a stronger signal, and require a higher voltage and larger currents to drive the coil.

3. Jul 2, 2013

### marcusl

I'm afraid that your question is not very well formulated, suggesting that your knowledge of electromagnetics is somewhat cursory. (Forgive me if I'm wrong here.) Unfortunately, success at your task is best guaranteed by a mastery of that field. Understanding eddy currents at a level sufficient to answer your question, and others that you will need to answer but perhaps have not yet thought of, involves Maxwell's equations and advanced mathematical functions. After you have analyzed fields and eddy currents, and have designed your apparatus, you still have the challenging practical problem of detecting the miniscule phase shift caused by eddy currents in saline at a significant depth. I encourage you to increase your E&M skills and/or partner with someone who has them.

4. Jul 2, 2013

### Erik88

Oke thanks!

I've had some courses on electromagnetics but they were somewhat simpler than this problem. But mfb, if I'm correct I just need to know what the minimum change in phase shift needs to be for the receiver coil so I know the minimum strength of the magnetic field at a certain depth and then calculate the corresponding amount of tesla needed?

5. Jul 2, 2013

### Staff: Mentor

I would not expect a field strength-dependent frequency shift. I think a stronger field just makes the detection easier/more precise.

6. Jul 3, 2013

### Erik88

Okay thanks! I think this makes my job already a lot easier!