Halo Effect - WTF !!!!

[simonbaker]

Simonbaker,

take a look a the MIT WEB PAGE http://web.mit.edu/8.02t/www/802TEAL...tics/index.htm


Tinkerer

Nice visualizations. They talk about the superposition principle which is basically what I was referring to. And then you add in the signal processing stuff inside the metal detector which is another whole ball of twine. But any knowledge of these ideas can help us use our detectors a little better I think. When it comes to building them I'm more of a tinkerer than a theorist! I hope to learn a lot from this forum.

[Tinkerer]

Do magnetic fields interact?

Simonbaker,

take a look a the MIT WEB PAGE http://web.mit.edu/8.02t/www/802TEAL...tics/index.htm


Tinkerer

[simonbaker]

Simonbaker,

Do magnetic fields interact? OK, maybe I have been using the wrong word. What I mean by interaction, is that a magnetic field can deflect or distort another magnetic field. If you take 2 magnets and force them together with the same poles, the fields of both magnets are pushed aside, forced into a different shape.

If you look at my Avatar picture, you see 2 distorted magnetic fields. The picture is a computer simulation of 2 coils with the current running in opposite directions.
You can see that the resulting field is totally asymmetrical. this is what I mean by the fields interacting. There is probably a better word for it.

Tinkerer

(by the way I'm not arguing in any way, it's more like thinking out loud as we speculate about possible ways auras could happen)

Right, for sure, the two fields will combine, but the key point I was making is that they are not "aware" of each other. In other words, they don't bounce off each other or modulate each other in any way. It may look like they distort each other, but they really just superimpose. Now it is possible your detector is sensitive to a magnetic field other than the one it is transmitting, but it would probably be sensitive whether you are transmitting a field or not, in other words, if your receiver picks it up when you are transmitting, it would also pick it up if you are not transmitting*.

* Now I need to disclaim that. Most metal detectors use a piece of the transmit signal as part of detecting a receive signal, but that could be done theoretically without transmitting the magnetic field.

* Also, even though magnetic fields don't interact in space, they could interact in a material if it responds "nonlinearly". Usually to make physical things act nonlinearly takes a lot of "power", but I don't know enough about that, so I'd believe you could get some significant interaction of magnetic fields in some materials maybe. It would probably take some pretty unusual circumstances to be significant.

If we take your avatar for an example - if one of the coils were DC current and the other were 10Khz from your TX coil, I don't think the mag field from the DC current would bother the detector at all. What would bother the detector would be the second coil itself, because it would be like any other conductive object responding to the TX frequency in a big way.

That's how I see it but I'm going on basic school learning and I'm open to all kinds of secondary or hard to imagine effects coming in. I like to theorize about it all so I hope I don't sound argumentative, just throwing in my 2 cents (which is about what I found my first time out).

[Tinkerer]

Do magnetic fields interact?

Magnetic fields don't interact with other magnetic fields per se, so zapping a field with another field should do nothing. Charging a battery with a field... ok, could have a physical basis. I would think the actual effect is that you would be inducing some current in a conductive circuit that flows in and out of a battery (batteries are usually like short circuits to AC), so it is the presence of the conductive path that really is being detected.

If the battery effect manages to set up conductive paths in the ground that weren't there before, then I see a real "aura" being created. But I believe it is the conductive path that your metal detector is detecting (by inducing some current at the TX frequency), not any DC current flowing from a battery effect.

To test if your metal detector can detect stationary magnetic fields, raise it well above the ground and swing it through the earth's magnetic field. If it doesn't detect it, then I think there is almost no chance it could detect any feeble mag field from tiny galvanic currents -- I can't work out the numbers, but that is my guess.

But physics/chemistry can be subtle and fool us, so I'm open to surprises and won't close my mind to any possibilities.

Simonbaker,

Do magnetic fields interact? OK, maybe I have been using the wrong word. What I mean by interaction, is that a magnetic field can deflect or distort another magnetic field. If you take 2 magnets and force them together with the same poles, the fields of both magnets are pushed aside, forced into a different shape.

If you look at my Avatar picture, you see 2 distorted magnetic fields. The picture is a computer simulation of 2 coils with the current running in opposite directions.
You can see that the resulting field is totally asymmetrical. this is what I mean by the fields interacting. There is probably a better word for it.

Tinkerer

[simonbaker]

I agree with you that the magnetic fields created by the galvanic currents are static..... until the target and its field are zapped by the dynamic field of the metal detector. I am not sure what happens then.

Does something similar happen to a battery when you apply external power to recharge it?

Is it possible that this "recharge" takes a few micro seconds to decay and can thus be sensed?

Tinkerer

Magnetic fields don't interact with other magnetic fields per se, so zapping a field with another field should do nothing. Charging a battery with a field... ok, could have a physical basis. I would think the actual effect is that you would be inducing some current in a conductive circuit that flows in and out of a battery (batteries are usually like short circuits to AC), so it is the presence of the conductive path that really is being detected.

If the battery effect manages to set up conductive paths in the ground that weren't there before, then I see a real "aura" being created. But I believe it is the conductive path that your metal detector is detecting (by inducing some current at the TX frequency), not any DC current flowing from a battery effect.

To test if your metal detector can detect stationary magnetic fields, raise it well above the ground and swing it through the earth's magnetic field. If it doesn't detect it, then I think there is almost no chance it could detect any feeble mag field from tiny galvanic currents -- I can't work out the numbers, but that is my guess.

But physics/chemistry can be subtle and fool us, so I'm open to surprises and won't close my mind to any possibilities.

[Tinkerer]

Static magnetic fields

Am I ignorant if I say that I don't think most VLF TR metal detectors respond to static magnetic fields really. They respond to changing magnetic flux at the frequency they transmit. Yes they do respond to ionic solutions as we know from salt water at the beach, because any substance that can respond to the transmit signal either by conductance or a magnetic quality (parametic) can affect the receive signal. But they don't respond to a magnetic field itself unless it is oscillating so the receive circuit would pick it up.

So I think the "galvanic current" magnetic field, which is static, would not really affect the detector or be detected. However, any conductive paths or paramagnetic materials created by the "battery in the ground" could respond to the transmit signal.

Also, magnetic fields don't interact, they just superimpose, don't they, like electric fields?

However, it is perfectly possible to design a detector to be sensitive to static magnetic fields. Just use a receive coil without a transmitter, and amplify signals at your sweep frequency -- very noisy, but would work. You would want sweep at constant angle to earth magnetic field to cancel it out.

Those are my ideas from school physics. I may experiment with it.

I agree with you that the magnetic fields created by the galvanic currents are static..... until the target and its field are zapped by the dynamic field of the metal detector. I am not sure what happens then.

Does something similar happen to a battery when you apply external power to recharge it?

Is it possible that this "recharge" takes a few micro seconds to decay and can thus be sensed?

Tinkerer

[amtech2005]

Halo Effect-WTF !!!!

GO TO THE GOOGLE SEARCH ENGINE AND TYPE IN " HALO EFFECT METEORITES" AND ALL KINDS OF THINGS WILL POP UP FOR YOUR RESEARCH !!!!!!! IT DOES EXIST. BUT WHAT IT'S TRUE DEFINITION IS ? I DO NOT UNDERSTAND YET !!! BYE ................EUGENE

[ivconic]

"...As often happens, several actually different topics got mixed up again...."

"Wide" questions usually give "wide" answers. It is hard to focus only on one thing here, to much questions involved.

[simonbaker]

A better test would be to bury a sheet of copper and a sheet of galvanized steel parallel in a sand box.
Before you bury, attach a wire lead on each plate
Then poor an electrolyte into the space between the 2 metal sheets.
For an electrolyte you can dissolve one pound of baking soda in 5 gallon of water.

You can now measure a voltage between the 2 wires. If you connect the 2 wires, you can measure a current.
The amplitude of the current or voltage is dependent upon the size and the distance of the dissimilar metal sheets.

This IS a single cell battery. In the case you used baking soda, it is an alkaline battery.

Now, if you do nothing else, the current will flow from the copper sheet ( Cathode ) to the zinc sheet (Anode) until the zinc has all migrated, ion after ion, to the copper sheet.

The electro magnetic field the surrounding your ground battery is proportional to the amount of current flowing.

Now, what will happen if you connect a car battery to the leads that reverses the current?

Or what happens if you apply an external magnetic field?

You know the magnetic fields do not cancel each other, they deflect and distort.

Now figure out the complex interaction between the earth's magnetic field, your ground battery magnetic field and the magnetic field produced by your metal detector......

I am really enjoying this discussion. It reminds me of my times as an under water welder when I used the seawater as a conductor instead of the ground cable, to weld with 550 Amps on the rod. Bit of a magnetic field there. Used to zap the fish and octopus for my lunch.

Tinkerer

Am I ignorant if I say that I don't think most VLF TR metal detectors respond to static magnetic fields really. They respond to changing magnetic flux at the frequency they transmit. Yes they do respond to ionic solutions as we know from salt water at the beach, because any substance that can respond to the transmit signal either by conductance or a magnetic quality (parametic) can affect the receive signal. But they don't respond to a magnetic field itself unless it is oscillating so the receive circuit would pick it up.

So I think the "galvanic current" magnetic field, which is static, would not really affect the detector or be detected. However, any conductive paths or paramagnetic materials created by the "battery in the ground" could respond to the transmit signal.

Also, magnetic fields don't interact, they just superimpose, don't they, like electric fields?

However, it is perfectly possible to design a detector to be sensitive to static magnetic fields. Just use a receive coil without a transmitter, and amplify signals at your sweep frequency -- very noisy, but would work. You would want sweep at constant angle to earth magnetic field to cancel it out.

Those are my ideas from school physics. I may experiment with it.

[Tinkerer]

Interaction of several magnetic fields

Tinkerer i envy you on underwater experiences! Among most of all things in life i adore water and underwater activities. Reminds me on splendid time i spent on Creta island, back in '90-eese.
Well...your experiences are showing some facts.
Yet...speaking of detecting at long distances, i keep imaging single bronze coin (bronze alloy), burried for more than 1500 years in soil. Such small volumen as coin, with such inpurified alloys even if evolved some "field" arround it, it is hard to beleive that field is enough significant in surrounding soil conditions to be detected at long distances, let's say more than 30-40cm away...personally i have doubts.

Esteban...skin resistance at only one person do change minute per minute.
Interesting subject to be examined in another, new thread. Some claims (and i do beleive) skin resistance changes are directly connected to many factors. Among others, the "mood" factor is one of major which influencing resistances. If you are clam,rested and just awaked, you will measure one resitance, but later when you are tired,exhausted or even nervous, you gonna measure quite different resitance....let's say between previously choosen spots on a skin. Try, experiment, and you will see...

Alternative medicine claims that healthfull person do have high skin resistances, other hand sick persons do have low resistances!? Is it true? I dont know.
I think this is directly correlated with amount of electrolitisc in skin tissue. That amount also changes from time to time....
Need to be explored more...

Ivconic,

As often happens, several actually different topics got mixed up again.
We were talking about the halo effect, what could cause it and how a metal detector could sense it.

I agree with you that the distance would be only as far as a metal detector normally reaches. Maybe a fraction more at best.
However if we speculate that a newly buried coin could be sensed at a distance of say 40 cm, the same coin after a few hundred years under conditions that favor ion migration, could be sensed maybe 50% further.

All depends on "favorable conditions".

What interests me more is to figure out how to design a metal detector that takes advantage of the interaction of the various magnetic fields, that can under favorable conditions, produce a magnetic field.

I am therefore going to start a new thread about the interactions of magnetic fields as pertaining to metal detecting. I would much appreciate your input to that discussion.

About LRL's, I would prefer to keep the subjects apart from the subject of metal detectors.

I will start a new thread also for LRL related observations. Maybe one day we will be able to unify the two different subjects, something like Einstein's unified field theory.

Tinkerer

[ivconic]

Tinkerer i envy you on underwater experiences! Among most of all things in life i adore water and underwater activities. Reminds me on splendid time i spent on Creta island, back in '90-eese.
Well...your experiences are showing some facts.
Yet...speaking of detecting at long distances, i keep imaging single bronze coin (bronze alloy), burried for more than 1500 years in soil. Such small volumen as coin, with such inpurified alloys even if evolved some "field" arround it, it is hard to beleive that field is enough significant in surrounding soil conditions to be detected at long distances, let's say more than 30-40cm away...personally i have doubts.

Esteban...skin resistance at only one person do change minute per minute.
Interesting subject to be examined in another, new thread. Some claims (and i do beleive) skin resistance changes are directly connected to many factors. Among others, the "mood" factor is one of major which influencing resistances. If you are clam,rested and just awaked, you will measure one resitance, but later when you are tired,exhausted or even nervous, you gonna measure quite different resitance....let's say between previously choosen spots on a skin. Try, experiment, and you will see...

Alternative medicine claims that healthfull person do have high skin resistances, other hand sick persons do have low resistances!? Is it true? I dont know.
I think this is directly correlated with amount of electrolitisc in skin tissue. That amount also changes from time to time....
Need to be explored more...

[Fred]

It would be very interesting to test it from a car.Then you will know exactly what influence has your isolation.In ionic detectors we need extra high resistence ,hundreds of Mhoms,so this could give some hint.
regards,
Fred.

[Esteban]

Your resistence is characteristic of any person, I think, maybe there are changes. Soil resistence varies, but your resistence stay more constant.

[Esteban]

R2 should be a capacitor...if you use shoes and it´s not raining... :-)

Yes, OK, look a capacitor when you use gum shoes, but also capacitor has resistence component. Leather shoes with nails is resistive and not capacitive, for example. Resistive I drawn regarding different resistences of material, gum, leather, etc.

Regards

Esteban

[Esteban]

I was just about to say same thing!
Ok...mostly in South America is hot, pretty hot, not a big issue - walkig bare feet arround. Yet...it presents variabile resistance not constant!? So...?
Take unimeter probes and pull those over your skin Esteban. You will see resistance is jumping randomly - not constant. How accurate could be your instrument with such unpredictable "element"?

Yes, but sometimes when I pass instrument to other person with leather shoes, for example, you need to readjust the sensibility point. Your resistence is constant include walking, maybe there is imperceptible changes. Soil resistence varies, but your resistence stay more constant.