Iron in blood

[Mark-VA]

Is it normal for a detector to detect your hand as you pass it in front of your coil. If it's not then I must have a very HOT machine.
But I guess I should ground balance to my hand first. hee hee.

[Carl-NC]

It's detecting body salt.

[mikebg]

Is it normal for a detector to detect your hand as you pass it in front of your coil. If it's not then I must have a very HOT machine.
But I guess I should ground balance to my hand first. hee hee.

Why hee hee? Sometimes we need very hot machines, for example to search for jewelry meteorites.

Metal detectors can not detect such a small increase in permeability may have the blood due to iron content. May be it is negligible, because the iron participates in bloods hemoglobin as an ion, which can't cause paramagnetizam. To obtain ferromagnetism, the iron should participate in an appropriate crystal lattice. For example, some types of stainless steels contain iron but are not attracted by a magnet, but there are stainless steels, which are attracted.

Carl is right that the conductivity of the fluids in the body cause signal. To illustrate this, peed on the soil that does not cause GND signal and see that a sensitive metal detector will detect the place that is wet with urine.

You're joking, that you have to make ground balance to the hand, but does not take into account that your legs are much closer to the search head rather than your hands. I became convinced of this when I tested one sensitive metal detector designed to detect jewelry meteorites. They do not generate a signal when in the air, but the machine locates them buried in the bad soil because they cause locally amend the GND signal. It turned out, however, that the mschine responds when when I make great strides and my foot appears closer to search head. As the the method is opposite to ground balance, needed the operator to reduce sensitivity and to use longer stick.

CONCLUSION: If your machine detects your hand, try to search for jewelry meteorites.

[Qiaozhi]

Is it normal for a detector to detect your hand as you pass it in front of your coil. If it's not then I must have a very HOT machine.
But I guess I should ground balance to my hand first. hee hee.

What detector were you using for the test?
I assume the coil is unshielded.

[Mark-VA]

Fisher F75/LTD

[Skippy]

I also have an F75, and I also get hand pickup (iron tone) when running it 'hot'. When I had a spare moment, I was going to devise a test to see if it was 'salty-fluid' pickup or a capacitive effect, but my feeling is the 'salty-fluid' is the answer.

[Mark-VA]

So it will sound off if you peck on the side of the coil and sweep your hand in front of the coil too?

[Prospector_Al]

I also have an F75, and I also get hand pickup (iron tone) when running it 'hot'. When I had a spare moment, I was going to devise a test to see if it was 'salty-fluid' pickup or a capacitive effect, but my feeling is the 'salty-fluid' is the answer.

Hi Skippy,

A sine wave detector running at 50 kHz will pick up the conductivity in your tissues. ( 0.9% salt...) If the coil is not properly shielded, it could be hand-capacitance as well. Depending on the nature of the shield, it can become bad, or the connection to it can break.

There's a simple means to diagnose the problem: Fill a flask with saturated salt solution. (Add salt until some remains solid...) Hold the flask over the coil, holding it with a glove to eliminate any conductive path. If the flask gives you a response, the detecor frequency can't handle salt soils too well.

If the detector responds only to your hand, the coil needs a better shield.

The time constant of the salt signal is usually very short--A PI detector won't see the signal, unless you are under water.


All the Best,

Prospector_Al

[F117]

I have been working on infrared vein locator devices in the past.
Could this hand-detect problem be turned into a feature ? In other words would it be possible to design a metal detector with a very "narrow" coil that detects the veins/blood in your arm accurately ?

Best regards,
- Bernard

[Prospector_Al]

Hi Bernard,

A metal detector is not specific enough to pin-point a vein. Arterial blood, venous blood, the interstitial fluid and the tissues all have the same salinity and respond to a metal detector running at a high frequency.

In contrast. hemoglobin and oxihemoglobin reflect light at two distinct wave-lenghts. By using a monochromatic filter you can isolate the pertinent wave length and find the area where the reflection from a vein peaks.

When you look up oximeters, you'll find the specific LEDs and filters to use.

All the best,

Prospector_Al

[F117]

Thanks for this detailed explanation, Prospector_Al

[Prospector_Al]

I also have an F75, and I also get hand pickup (iron tone) when running it 'hot'. When I had a spare moment, I was going to devise a test to see if it was 'salty-fluid' pickup or a capacitive effect, but my feeling is the 'salty-fluid' is the answer.

Hi Skippy,

It's peculiar that you get an "iron tone". I don't know the detector you are using, but generally, a phase relationship is used to determine the nature of a target. A signal from saline should be identified as a gum wrapper or any paper with thin aluminum backing. The detector istself may be faulty...

Prospector_Al

[Skippy]

I don't know what to imply from the 'iron tone', either. If you use the assumption that ferrite ground gives a -90 degree shift (phase lead) and typical ground is -85 degrees, wouldn't my salty hand slightly mimic a wet salt beach and give a phase more towards Zero degrees, say -75 degrees, and hence would register as a small nail? I will try and do some static (ie. non-moving, not 'static electricity') tests in the next few days to see if that sheds any light on the effect.

[scs]

this signal is stronger for resonant circuits with high "Q"factor.