# Help Generating magnetic field

Discussion in 'General Electronics Chat' started by jayhawk, Oct 4, 2010.

1. ### jayhawk Thread Starter New Member

Oct 4, 2010
3
0
Hi guys,

We are making a robot that must be able to detect certain magnetic fields. We need to simulate these fields to test our robot. The two fields that we need to generate are:

A 33 kHz approximately sinusoidal 10 mA-turns coil

and

A 44 kHz " "

Can somebody help with the best way to simulate these fields?

Thank you.

2. ### PRS Well-Known Member

Aug 24, 2008
989
35
When you say magnetic field, are you really just saying "electromagnetic field?" If so it is a matter of building an oscillator having a frequency of 33KHz and 44KHz respectively. Am on track here, or am I missing something?

What exactly is a 10 mA turns coil?

If you were more specific, you'd get more help from the folks in this forum. It seems you're mixing up terms but hang me if I'm wrong.

3. ### jayhawk Thread Starter New Member

Oct 4, 2010
3
0
Yes I mean EM field. There are coils that are generating these fields. There is sinusoidal current of 10 mA-turns in the coil. I need to make these coils to generate the correct fields for simulation. I assume this means that we can use any combination of current/turns that multiplies to 10 mA-turns, ex. 1 mA current into a coil with 10 turns. One is at 33 kHz and one is at 44 kHz and I'm not sure how to generate these frequencies. When you say oscillator do you mean a Wein Bridge oscillator?

4. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
The whole termnology of mA-turns is confusing.

You can make almost any oscillator as far as that goes, you could even use 555 timer ICs as oscillators to drive coils if they have enough impedance at those frequencies.

5. ### Jaguarjoe Active Member

Apr 7, 2010
770
90
Build a wein bridge oscillator.
Make a 10ma-turn coil out of 100 turns of #30 wire.
Use a 10k ohm current sense resistor in series with the coil.
Adjust amplitude for 1 volt across the resistor.
100 turns at 100uA is 10ma-turns.
1 volt across 10k ohms is 100uA.

6. ### russ_hensel Distinguished Member

Jan 11, 2009
820
47
Try Helmholtz coil - Wikipedia, the free encyclopedia and then use one of the oscc. above.

7. ### PRS Well-Known Member

Aug 24, 2008
989
35
Hello again, Jayhawk. Your project sounds interesting and I'd like to help you with it. Could you tell us a little more about the purpose of the 33kHz and 44kHz signals? If you need to distinguish between those signals do you realize you need filters? I'm guessing your antenna feeds a tuned amplifier. Is your signal modulated?

As for providing the test signals, I would simply make an antenna out of a long wire and feed it with my function generator. But if you don't have one of those, you'll have to make an oscillator and amplify and/or match it to an antenna.

8. ### jayhawk Thread Starter New Member

Oct 4, 2010
3
0
Ok, I will explain more because I think it might help clear some things up.

Our robot is looking for victims in rooms. All victims emit a low frequency electromagnetic field. This will be generated by a coil with a current of 10 mA-turns RMS at a frequency of 33 kHz with an approximately sinusoidal waveform.

In one of the four rooms, there is a EMF hazard at 44 kHz and 10 mA-turns in the whole room (mounted under floor in center) presumably to interfere with the EMF of the victims.

We want to use these signals to find victims and we also must identify the room that has the hazard.

One important note is that the coil beneath the floor (the hazard) is positioned vertically (looks like it is standing), and the coils for the victims are horizontal.

At the moment we are intending to use hall-effect sensors but are still not certain how to implement them.