Metal detectors and non-magnetic materials????

The sensitivity is not that good. This is a high frequency pulse that is sent and expects some absorption and detects that. Some that is absorbed reflects back.

Plastic can be, but the electric field has to be stronger and you have to tune for specifics. We did in the physics lab, and could identify what chemical was in the test tube. But normal for sale ones don't sense non-metallic.

Now remember rust is magnetic - rusty wood or rusty sand...

Martin

Mart> How do metal detectors locate non-magnetic materials?

By capacitance probably, anything in the feild will cause a very small change in capacitance to earth and hence inductance of the coil, i guess a high quality one would not be so susceptable to this. It would be very much down to the design how stray capacitance affects the detector, for example if the oscillator is very unstable or weak it will be badly affected when moved near any object or by changes in density and composition.

Actually magnetic feedback.

There is a transmit coil and a pickup coil. The transmitter dumps a frequency pulse (often sweeps in new ones) and the metal absorbs that energy if present and able. Then, since it can't hold on to the magnetic field, it de-energizes and a flip of the 'dipole' this is sensed in a balanced bridge. The experienced hunter knows how to spot different metal types by the reflection intensity, sound and signal strength, and ignores some and tries others.

The bear can tab (coke...) gave fits for a while - strong return due to the open ring. The Al doesn't return much in low frequencies.

Capacitive coupling would be to sensitive and not be able to reach down into the ground.

Martin

Mart>

Read here:

OBTW - have a degree in Physics and was a Sr. Professor and Sr. Staff Scientist... So some meters and instruments are fundamental. - yea semi and other backgrounds.

I often created mini-versions of various ones for general debug of circuit sniffing and the like. Looking for RF links isn't all that different - a generator driving output at you is like that of sending back a signal sent. Also altering sense is very common. Good 'ole Whetstone in the AC versions.

Thanks,

Martin Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.

Grimly Fiendish wrote:

Red rust (Fe2O3) is not magnetic. Only Fe3O4 is magnetic.

Is blue rust magnetic ?

Mill scale? For sure! :)

Cool, I'd like to know more about this. :)

Around here (SE AZ) we have "iron rocks" that are attracted to a magnet.

There are shiney-black ones and dull-red ones.

The dull red ones are more strongly attacted to a magnet.

But the dull red is only on the surface, cut into them with a masonary-type cut-off-wheel and they look the same inside.

The dull red ones are harder to cut by about double.

Got any idea what the two minerals are called? :)

Alvin in AZ

To flip an electron it doesn't take a magnetic material. Any electron can be flipped. Did this in labs.

You mean by a bar/horseshoe type - I don't recall seeing any on any magnet.

Martin

Mart> Red rust (Fe2O3) is not magnetic. Only Fe3O4 is magnetic.

Likely it is called black hematite. Pyrite is golden FeS2 [ fools gold ] Iron Sulfite or Troilite Bronze yellow to brownish FeS

The list of Iron and Sulfur minerals is large - due to the reactive nature of Sulfur.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.

snipped-for-privacy@XX.com wrote:

Wheatstone

??