mu metal

[scrungy_doolittle]

Mu metal is a special type of material that essentially blocks magnetic fields. I've been wondering of taking a 1/2 inch wide piece long enough to wrap around the circumference of a coil, and gluing it to the edge of the coil, would provide shielding that would allow you to work up close to steel support pipe in tot lots. I recently managed to find a 51 wheatie at the base of a slide, that obviously got missed over the years. About 4 inches away, barely discernible in the noise from the steel pipe. Got me to thinking about the possibility with mu metal. We used to use it to shield floppy drives from magnetic fields....

[Chet]

I used to work with Mu metal shielding in radar and sonar equipment, it is most effective when it completely encloses the magnetic field. In this use with only a band around the edge of the coil would allow many of the magnetic lines of force to go outside of the band. Since Mu metal can conduct electricity it would be detected by the coil in the form of a permanent target. It would have a loading effect on both inductance and capacitance of the coil. I have had some success on shallow targets by using my pen pointer around the pipes and along metal fences.

[Gwil]

You may already have considered this, but if you're using an IB machine a coaxial stacked coil is less sensitive to metal fences etc.
They're described in the "Coil Basics" article here:

http://www.geotech1.com/cgi-bin/page...&file=info.dat

Gwil

[Carl-NC]

I've been wondering of taking a 1/2 inch wide piece long enough to wrap around the circumference of a coil, and gluing it to the edge of the coil, would provide shielding that would allow you to work up close to steel support pipe in tot lots.

In that position it would have no effect. And in any other position, it still wouldn't work. As Gwil said, get a coaxial coil.

[scrungy_doolittle]

it was just a thought. On a different topic, I found a nice cheap pinpointer harbor freight tools 97245. 17.99 Since it has a range of 1/2 inch or so, I may try that up close. several days ago I found a wheatie at the base of a slide in a tot lot. almost masked by the signal from the steel post. The 5900 found it. I'm liking the 5900 more and more.

[Carl-NC]

You're in luck... a coaxial coil was made for the 5900, by Applied Creativity (also made the Bigfoot coil). They are long out of business, so you'll have to poke around or watch eBay to get one. Come to think of it, a Bigfoot coil might work well close to pipes, and they're easier to find.