Eddy currents / Metal Detectors

[ElectMan]

Hello everyone. I've just entered this forum, so I'm new here . I'am interested in knowing some basic info on metal detectors and basic principles, like the eddy currents. Can't seem to find this anywhere.

First thing:

• When and oscilating current is passed trough a coil, in the presence of a metal, how is this oscilation affected? In frequency, phase, amplitud? I'm expecting frequency, but heard some stuff about phase.

[mariush]

May I suggest reading up on some of the patents around metal detectors?  They're usually quite informative

http://www.google.com/?tbm=pts&hl=en#hl=en&tbm=pts&sclient=psy-ab&q=metal+detector&oq=metal+detector&gs_l=hp.3..0l4.0.0.1.16.0.0.0.0.0.0.0.0..0.0...0.0...1c.cAaK96Incl4&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=956604e6f44a6451&biw=1920&bih=932

Another simple search "google detector do it yourself"  reveals these pages with a lot of info

* http://www.easytreasure.co.uk/bfo.htm
* http://www.instructables.com/id/Home-Made-BFO-metal-detector/
* http://nevada-outback-gems.com/design_plans/DIY_metal_detect/metal_detector.htm
 

[ElectMan]

Thanks. That info helped. Eddy currents do affect signals on frequency.