Can I determine if my Electro magnetic field (EMF) measuring device is in very close proximity to the source of EMF?
I think what you are asking is "How can I improve my emitter so I can detect it unambiguously in the presence of background noise or interference"?

Ok, so your detector is a magnetic flux density measuring device hence it produces an output in gauss (these days magnetic flux density is measured in teslas or webers per sq metre). I am also presuming your source is something that is either a permanent magnet or something like a coil of wire excited with an AC signal.

If it's a permanent magnet I can't help you but if it is a coil of wire and it is producing an alternating magnetic field then it is detectable by using another coil and measuring the induced voltage. To avoid interference you can resonant tune the receiver coil to be mainly responsive to the frequency produced by the emitter. I don't think your sensor will help you in this respect - I'd use a coil of wire - It all depends what is more important to you; using your sensor or getting good results by a better technique.

So if you have a "send" coil and a "receive" coil, the basic maths is like this: -



Looking at the transmitter, if the distance from the loop/coil is small (Z a lot less than R) the flux density (B) is nearly constant but, as distance increases B reduces as the cube-root of Z.

On the receiver side, and assuming the received flux is constant across its area (not really too much of an approximation beyond certain distances), the induced voltage is proportional to the area of the loop, the peak flux density and the frequency of excitation.

Basic conclusion - up close the flux density can be almost constant and hence the induced voltage won't change too much but, further away you can use the induced voltage level to determine the distance.