Nexus Coil Design

[Max]

Hi,
read here tons of BS... about that not-iron targets haven't any so called "HALO"... BS.

Some right things...

BUT

"Only iron can cause halo effect, non ferrous metals can not."

Oh man

In which world you live ?
Have you ever used one real metal detector on the field ?

Many people here prospecting e.g. for coins know what I mean.

There is a kind of phenomenon that makes you find the coin out of the detection range of MD for that coin dimension when coin is copper, bronze etc (not iron) and buried for a long time.
If the target is in the detection range "you'll see" it wider.

And the coin doesn't always to drop into the hole... to explain why it was at higher depth... like some jocker here say.

This is a fact.
Buy a metal detector and see with your eyes.

Then come back and register first of writing some more BS.

You can call it HALO, or JOHN or MARY... or whatever you want... and maybe don't fully understand how it works... the chemistry involved... but it exists like me and you.

Best regards,
Max

[Max]

"If you use a particular coin for an air test and then bury the same coin in the ground,
all detectors will detect this coin further away in the air test. I don't think there is
any dispute that this is a fact."
Huh...Yes Quiaozhi! I agree! Now when i think again; i missunderstood the point! If you
put back "fresh" coin to soil and cover with it, of course detection would be weak, much
worse than in the air! I absolute agree!
I was thinking on undisturbed soil and long time buried coin.....

"..I wonder how much of this is caused by compacted soil rather than disturbed soil.
Has anyone ever tested whether there is a difference?"
I tested it many times...Oposite stories from compacted and disturbed soils...

"In fact we are in total agreement"
Heh,heh,heh!
Yes, after reading again, i can see what you ment! I agree now! It was missunderstood.

"If you also made this OO coil fully resonant, there would be an even greater improvement."
Now,there i made mistake! I tried to avoid fully resonant OO coils!? This gives me idea
to make another for TGS and see changes. I'll do that for sure, in next few days...
If i gain even better results....than i own you!

"For me the best detector is the detector that has everyone of us...
Geo is right and I add: The best is the detector used properly. I see persons with excellent MD, and I gain them with my homemade. EVER!!! Experience, come here!!! "

Absolute truth! Minelab Musketeer is not best detector i saw, but best finds i had with it,
cose i was pretty used on it. Other hand, Sovereign is much better but i had a lot of trouble
to make it work, at the time...not used at all on its "phylosophy"...!
My friend has DFX which is also very good, but he still dont know how to use it properly so
i always collect more items with my hand made than he with DFX!
"Well Max, you must a master coil constructor.
Exactly 51 minutes after I posted that information you managed to read my post, dash to the workbench, construct a 4" OO coil, go out in the field to do some testing, then return to post your own reply about the superiority of your new coil. Bloody amazing..."

Hah,hah,hah,hah!!! Oh guys! This forum is nice place to be!
Max,Quiaozhi...i appreciate both of you much!
Best regards!

Hi Ivconic,
"Now,there i made mistake! I tried to avoid fully resonant OO coils!? This gives me idea
to make another for TGS and see changes. I'll do that for sure, in next few days...
If i gain even better results....than i own you!"

You didn't make any mistake.
Georgi's oscillator/circuit is a resonant one and need a resonant coil to work as expected.
It pumps out hundred of volts and so also nulling must be made with extreme care I think... to avoid saturating everything.

Best regards,
Max

[Qiaozhi]

Correct. Halo effect can occur around any non ferrous object.
There is one way only to measure the exact distance to "out of range" signals. It is by brushing out the soil above the signal inch by inch until is recovered in its original position.
There is another explanation.
Many detectors are picking up signals from air gaps in the soil or small areas with different chemical content, result of contamination on the original soil background. If a non ferrous target happen to be in that kind of spot it will be the ground disturbance which combined with the non ferrous target would produce strong enough signal that would create illusion of halo effect.
Ones disturbed that soil will no longer have those properties. That is why after recovery no one can confirm the halo effect.
If the soil is been galvanised by the non ferrous target, when it is placed back in the hole with the target most of the signal should still be detectable, at least 85%, but it never happens that way.
The so called halo effect appears as a result of random ground mineral phenomenons in proximity to non ferrous targets, but not because coins were in the soil for so long before they were detected.

Yes - I like this explanation. It makes perfect sense.

[Qiaozhi]

Hi Ivconic,
"Now,there i made mistake! I tried to avoid fully resonant OO coils!? This gives me idea
to make another for TGS and see changes. I'll do that for sure, in next few days...
If i gain even better results....than i own you!"

You didn't make any mistake.
Georgi's oscillator/circuit is a resonant one and need a resonant coil to work as expected.
It pumps out hundred of volts and so also nulling must be made with extreme care I think... to avoid saturating everything.

Best regards,
Max

Hi Max,

You are just speculating...

[Qiaozhi]

Hi,
read here tons of BS... about that not-iron targets haven't any so called "HALO"... BS.

Some right things...

BUT

"Only iron can cause halo effect, non ferrous metals can not."

Oh man

In which world you live ?
Have you ever used one real metal detector on the field ?

Many people here prospecting e.g. for coins know what I mean.

There is a kind of phenomenon that makes you find the coin out of the detection range of MD for that coin dimension when coin is copper, bronze etc (not iron) and buried for a long time.
If the target is in the detection range "you'll see" it wider.

And the coin doesn't always to drop into the hole... to explain why it was at higher depth... like some jocker here say.

This is a fact.
Buy a metal detector and see with your eyes.

Then come back and register first of writing some more BS.

You can call it HALO, or JOHN or MARY... or whatever you want... and maybe don't fully understand how it works... the chemistry involved... but it exists like me and you.

Best regards,
Max

Hi Max,

Neither Ivconic or myself disagree that on occassions coins appear to be detected at a greater than expected depth. This has been attributed to the so-called "halo" effect. It is well known that ferrous targets can produce this effect, but it has always been dubious that the same thing applies to non-ferrous targets. So far we've not been able to explain this phenomenon. However, "unregistered" has put forward a very rational explanation that makes perfect sense. I would propose that this is the real underlying cause of this effect.

[Qiaozhi]

Hi Qiaozhi,

Has any testing been done with the Nexus in difficult hot soil like found in the Australian gold fields? I am curious to know about the discriminating abilities in the iron rocks that make it nearly impossible for most PI detectors to find the deep gold nuggets there. Currently, Minelabs makes the only PI detector that gives much success in these fields. But I was wondering if the Nexus can perform there as well as these PI detectors in the iron soil found in Australia.

Best wishes,
J_P

Georgi tells me there have been no specific tests done using Australian soil, but a new Nexus detector is currently undergoing tests in an area with black sand.
Nexus Detectors are not yet able to disclose the results of these tests.
More later...

[Max]

Hi,
I'm not speculating at all. He is right on some things, but wrong when he said that only iron gives halo.
It's absolutely false.
His explaination of the absence of halo in not-iron targets due to patina oxides is absolutely wrong. He stated that cause patina oxides are low conductive there couldn't be an halo effect cause no eddy currents could be involved.

Too simple attempt of explaining what he doesn't understand.

For me halo, when present, work that way:

- the non-iron metal buried develop chemical interactions with the sorrounding matrix during years
- part of the external metal (few) is dissolved by chemical reactions at surface of e.g. coin
- the reactions take place even passing through microscopic fractures and porosity in the oxide patina and at the patina itself
- some of the metal dispersed in the matrix by chemical is then reduced by other kind of chemical reactions (ionic reduction, the atoms get missings electrons... so-called REDOX reactions)
- a dispersion of atomic metal particles in soil tend to concentrate/migrate in nodules due to microscopic interactions around a suitable center/core

Result is, after long time, that part of the metal migrate in micro-nodules all sorrounding the target, and then inside that nodules . Inner parts of nodules are (often) made of pure metal, so they develop in cores eddy currents, like the target itself.

It's not my science or my science fiction. It's geology.

This is from wikipedia... about manganese nodules but not only.

"
Growth and composition
Nodule growth is one of the slowest of all geological phenomena – in the order of a centimeter over several million years. Several processes are involved in the formation of nodules, including the precipitation of metals from seawater (hydrogenous), the remobilization of manganese in the water column (diagenetic), the derivation of metals from hot springs associated with volcanic activity (hydrothermal), the decomposition of basaltic debris by seawater (halmyrolitic) and the precipitation of metal hydroxides through the activity of microorganisms (biogenic). Several of these processes may operate concurrently or they may follow one another during the formation of a nodule.
The chemical composition of nodules varies according to the kind of manganese minerals and the size and characteristics of the core. Those of greatest economic interest contain manganese (27-30 %), nickel (1.25-1.5 %), copper (1-1.4 %) and cobalt (0.2-0.25 %). Other constituents include iron (6 %), silicon (5%) and aluminum (3%), with lesser amounts of calcium, sodium, magnesium, potassium, titanium and barium, along with hydrogen and oxygen."

As you can see copper follow the rule, like iron and manganese.

The fact that you can detect such small dispersion of eddy currents can be seen by what we call here "HALO" detected by metal detectors.

Kind regards,
Max

[Max]

Hi Max,

You are just speculating...

Hi Qiaozhi,
about my "speculations" on Nexus...
as a reminder...

after your nice PSPICE simulation, of some months ago, of osc section that gave you something 99.8Volts , (that personally I think it's also incorrect... cause voltage is actually higher but anyway... maybe you forget your past writings in this thread)

on page 2 of this thread "Nexus" (Georgi) wrote:

"Very scientific analisys. Good work.
Now about the power of the transistors needed. I use 250mW BC type transistors and they are more than enough. This type oscilators do not require high power transistors since the the power disipation of the oscilator system falls on the coil it self due to the resonance.
This type of transmitters are called paralel resonance circuits.The voltage and the current gets amplified in electromagnetic process by the coil, not by the transistors."

So I'm speculating what ?

That is a resonant oscillator ? He said that !

If you say that I'm speculating here you actually say that Georgi was speculating about Nexus circuit.

About the hundreds volts ?

Your spice simulator told you that... not me.

About what I'm speculating ? I don't understand.

Best regards,
Max

[Qiaozhi]

Hi,
I'm not speculating at all. He is right on some things, but wrong when he said that only iron gives halo.
It's absolutely false.
His explaination of the absence of halo in not-iron targets due to patina oxides is absolutely wrong. He stated that cause patina oxides are low conductive there couldn't be an halo effect cause no eddy currents could be involved.

Too simple attempt of explaining what he doesn't understand.

For me halo, when present, work that way:

- the non-iron metal buried develop chemical interactions with the sorrounding matrix during years
- part of the external metal (few) is dissolved by chemical reactions at surface of e.g. coin
- the reactions take place even passing through microscopic fractures and porosity in the oxide patina and at the patina itself
- some of the metal dispersed in the matrix by chemical is then reduced by other kind of chemical reactions (ionic reduction, the atoms get missings electrons... so-called REDOX reactions)
- a dispersion of atomic metal particles in soil tend to concentrate/migrate in nodules due to microscopic interactions around a suitable center/core

Result is, after long time, that part of the metal migrate in micro-nodules all sorrounding the target, and then inside that nodules . Inner parts of nodules are (often) made of pure metal, so they develop in cores eddy currents, like the target itself.

It's not my science or my science fiction. It's geology.

This is from wikipedia... about manganese nodules but not only.

"
Growth and composition
Nodule growth is one of the slowest of all geological phenomena – in the order of a centimeter over several million years. Several processes are involved in the formation of nodules, including the precipitation of metals from seawater (hydrogenous), the remobilization of manganese in the water column (diagenetic), the derivation of metals from hot springs associated with volcanic activity (hydrothermal), the decomposition of basaltic debris by seawater (halmyrolitic) and the precipitation of metal hydroxides through the activity of microorganisms (biogenic). Several of these processes may operate concurrently or they may follow one another during the formation of a nodule.
The chemical composition of nodules varies according to the kind of manganese minerals and the size and characteristics of the core. Those of greatest economic interest contain manganese (27-30 %), nickel (1.25-1.5 %), copper (1-1.4 %) and cobalt (0.2-0.25 %). Other constituents include iron (6 %), silicon (5%) and aluminum (3%), with lesser amounts of calcium, sodium, magnesium, potassium, titanium and barium, along with hydrogen and oxygen."

As you can see copper follow the rule, like iron and manganese.

The fact that you can detect such small dispersion of eddy currents can be seen by what we call here "HALO" detected by metal detectors.

Kind regards,
Max

OK - let's think about this.

According to your statement above, it takes several million years for nodules of 1cm to be created.
Let's say that several million years means 10 million years (for arguments sake).
In that case:
10 million years = 1cm = 100mm = 100,000um
1 million years = 10,000um
1 year = 0.01um
20 years = 0.2um (for a longtime buried item)

Not much of a halo, don't you think?

[Qiaozhi]

Hi Qiaozhi,
about my "speculations" on Nexus...
as a reminder...

after your nice PSPICE simulation, of some months ago, of osc section that gave you something 99.8Volts , (that personally I think it's also incorrect... cause voltage is actually higher but anyway... maybe you forget your past writings in this thread)

on page 2 of this thread "Nexus" (Georgi) wrote:

"Very scientific analisys. Good work.
Now about the power of the transistors needed. I use 250mW BC type transistors and they are more than enough. This type oscilators do not require high power transistors since the the power disipation of the oscilator system falls on the coil it self due to the resonance.
This type of transmitters are called paralel resonance circuits.The voltage and the current gets amplified in electromagnetic process by the coil, not by the transistors."

So I'm speculating what ?

That is a resonant oscillator ? He said that !

If you say that I'm speculating here you actually say that Georgi was speculating about Nexus circuit.

About the hundreds volts ?

Your spice simulator told you that... not me.

About what I'm speculating ? I don't understand.

Best regards,
Max

No - no mistake there.
Georgi has often stated that the coils are fully resonant. Although the TX circuit that was simulated by the SPICE simulator (not PSPICE, by the way) is not identical to the Nexus.

It was this bit I meant you were speculating about:

It pumps out hundred of volts and so also nulling must be made with extreme care I think... to avoid saturating everything.

[Max]

OK - let's think about this.

According to your statement above, it takes several million years for nodules of 1cm to be created.
Let's say that several million years means 10 million years (for arguments sake).
In that case:
10 million years = 1cm = 100mm = 100,000um
1 million years = 10,000um
1 year = 0.01um
20 years = 0.2um (for a longtime buried item)

Not much of a halo, don't you think?

Hi,
yes 20years is a short time to notice that.
I think that a consistent time is >1000years to notice the difference by a metal detector for e.g. a copper coin. But time required is truly a speculation, cause not every places are the same, so maybe in some places (e.g. near an hydrothermal source) it takes much less time to get the same effect.

But you have also consider that there would be many of these micro-nodules not just one... a kind of "cloud" around the target in the few cms around it.

Seems an LRL argumentation ! But I think that this a better explaination of the phenomenon.

Kind regards,
Max

[Max]

No - no mistake there.
Georgi has often stated that the coils are fully resonant. Although the TX circuit that was simulated by the SPICE simulator (not PSPICE, by the way) is not identical to the Nexus.

It was this bit I meant you were speculating about:

Why ?

In all similar circuits the voltage is around 100Vpp or more. If you don't null very carefully the coil you'll get RX preamp saturated easy on the field, and even on test bench.

Still don't understand.

Kind regards,
Max

[Qiaozhi]

Hi,
yes 20years is a short time to notice that.
I think that a consistent time is >1000years to notice the difference by a metal detector for e.g. a copper coin. But time required is truly a speculation, cause not every places are the same, so maybe in some places (e.g. near an hydrothermal souce) it takes much less time to get the same effect.

But you have also consider that there would be many of these micro-nodules not just one... a kind of "cloud" around the target in the few cms around it.

Seems an LRL argumentation ! But I think that this a better explaination of the phenomenon.

Kind regards,
Max

Even 1000 years would still only produce nodules of 10um. This also doesn't explain why the halo disappears when the coin is removed.

This statement below still sounds like the most rational answer:

The so called halo effect appears as a result of random ground mineral phenomenons in proximity to non ferrous targets, but not because coins were in the soil for so long before they were detected.

Remember Occam's Razor.

[J_Player]

Georgi tells me there have been no specific tests done using Australian soil, but a new Nexus detector is currently undergoing tests in an area with black sand.
Nexus Detectors are not yet able to disclose the results of these tests.
More later...

Thank you for the answer Qiaozhi.

From what I read about the earlier Nexus models, they needed frequent tuning to keep the coils resonant. I suspect this might make it difficult to use this detector in ground that keeps changing such as black sand deposits where I live. But maybe the modern version of the Nexus has circuitry to make the ground influence less critical. From what I heard, the Australian gold fields have the worst hot ground in the world, full of iron rocks, lead scraps, rusted tin can trash, nails, etc. There is currently a mad rush to build a detector that will outperform the top Minelabs models. The funny thing is someone recently found a cheap Chinese VLF that could find some good sized shallow nuggets that the Minelabs could not. I guess it just goes to show no detector is best for all situations. Maybe there is a place for the Nexus there.

Best wishes,
J_P

[Max]

Even 1000 years would still only produce nodules of 10um. This also doesn't explain why the halo disappears when the coin is removed.

This statement below still sounds like the most rational answer:

Remember Occam's Razor.

Hi,
yes but if you have thousand of 10um nodules around the target maybe it works. Eddy currents effects-sum gives the gain of depth.


I think that the fact that the halo disappears when coin is removed is instead, the proof of that behaviour.
Because micro-nodules are a very small dispersion of the metal around the real target... when you remove e.g. the coin you subtract the most part of the signal... and at the same time you alter the dispersion of them in the soil mass you dug... so that way is almost impossible detecting them if not by some accurate analisys of the soil removed.

So, I think, that if e.g. rebury the coin in the same place at same depth you'll notice a signal strenght reduction cause of the disturbance occourred.

Kind regards,
Max