Detecting a magnet... from a distance.

[Lenp]

And..
House trailers attract tornados
Pleasure boats attract 'friends'
Wills attract relatives.....

[Lenp]

Externet, I have been following this thread, and added a few comments, but the question now is...
Why do you want to measure this minuscule magnetic field?

I would think that the earth's much larger magnetic influence, and the clutter all else around this magnet's minor field, would swamp it completely, and if not, why would not a common compass point to it?
At first glance it would seem akin to hearing a whisper from across a rock concert venue without lip reading!

[dyarker]

In post 1 he said he wanted more posts on the forum.

[CeaSaR]

I'll say it one more time:
1200 dollars, eh?

[MrAl]

Hello,

I like the replies so far, very interesting. The 'rube' one was funny too thanks to Len for that one.

Detecting a magnet from a distance isnt that easy because it's a static field so you cant use radio methods like tuned circuits to detect some frequency. Here are a few lesser ideas though just to keep it interesting. BTW i have one of those 1200 dollar sensors but blew it out yesterday so today i claimed bankruptcy

Ok so first we have the rotating coil. With a rotating coil you can detect a static field. The current will vary as it is rotated.
Next up we have the Hall Effect Device. These can be used at no too large distances.

A DIY method would be to rotate a very strong magnet.that is suspended by a long sewing thread. When the fields attract, the push or pull will be greater so the magnet will swing slightly. If the magnet to be detected is also on a thread, it will rotate with the first magnet, so you can control the orientation of the magnet to be detected with the large magnet. This can work at distances of some 2 feet with rare earth magnets.

There are many sources of interference though so it gets sticky to get long distance.

The thing about magnetic fields is that the strength drops off quickly because it is a reciprocal power function. Even if just 1/r^2 at twice the distance you go down to 1/4 the signal for example, so we lose field strength fast as we move away.

BTW a magnet suspended by a long sewing thread is sensitive enough to align itself with the Earths magnetic field so it can function as a compass. A rare earth magnet will align itself pretty fast, possibly within a couple seconds.

[jwax]

FWIW, just saw on the science channel that our sun's magnetic field extends out to the Ort Cloud- way past Pluto.

[Externet]

Hi John.
So far I reached a 3 metre distance detection, with a 39000 turns coil. Ideal would be at least 50 metres. Perhaps am lacking mechanical dimensions (length) for the coil core bar.
And refuse to spend too much $ for experimenting. Whenever you find how they detected the sun's magnetism reach to Pluto, advise.

[jwax]

May have already seen this article: https://en.wikipedia.org/wiki/Spacecraft_magnetometer

[haklesup]

your signal is diminishing as the cube of the distance while your detector is gaining in sensitivity linearly with the number or turns. I'm impressed you go to this distance but incrementally increasing the distance will quickly result in a coil so big you couldn't lift or afford it. additional losses like coil resistivity and the sheer bulk of it self shielding inner turns will rob you of efficiency as you proceed.

Logically, the next step in increasing sensitivity is to further amplify and filter the signal you are getting from your present coil. you are probably already at a point where passive filtering is effective and to pick out a signal with lower amplitude than your noise will definitely need some DSP, look at Audio DSP apps that run on your phone as a start. Stochastic filtering (audio) should be able to pick a periodic signal from background white noise for at least some improvement.