Ground Balance Theory

[Prospector_Al]

Allan

You don't reckon that some of the falsing,coil overloading,and just plain false
signals can be attributed to highly conductive metallic mineral salts as a binder for magnetite
do you? I dug 4 large holes in an area that gave a perfect target signal. No target
was present in any hole. The dirt from the holes would not give a peep on the detector
either. Once the soil was disturbed to a certain depth the signals went away.

There was no hot rocks or charcoal either. A few feet away a detector will over load until
you stir up the soil.

Conductivity of salty soil usually generates a signal with a very short time constant. In a PI detector, increasing the sample delay will therefore eliminate the signal.

In contrast to that scenario, magnetic material that has been sitting undisturbed for a very long time has acquired a certain degree of remanent magnetism which may be viscous. In fact, that's how it was discovered that the earth's poles switch polarity every now and then. In one stratum the remanent magnetism is aligned with the north pole, and in a deeper stratum with the south pole. When you date the strata you'll find the length of the time intervals between the "flips". We are due for one now.

Of course, when you disturb the soil, the remanent magnetism cancels out. The folks who study paleomagnetism remove the sample very carefully. They note its orientation with the geographic pole, and then they spin the sample in a lathe to determine the difference between the magnetic and geographic noth poles.

Last I heard, the magnetic north pole is now on the move into Canada. Mid-flip, the field strength will be near zero.
The magnetosphere that normally deflects the ionized solar wind from impinging on us will allow the ionized particles to hit us straight on. Get out your tin hat!

You can see that the study of the ground signals has profound implications beyond metal detectors...

Allan

[Prospector_Al]

Interesting. So.. perhaps a center-tap coil one half of which you drive in the usual fashion, the other can have DC current periodically switched in (perhaps automatically, perhaps under operator control) to test whether a signal is affected and hence likely to be viscocity related. Sounds highly patentable, hopefully this discussion prevents that from happening.

Midas

Hi Midas,

Unfortunately, the amount of current required to elicit this effect is prohibitive. I would have patented the implementation of this idea if it had been practical. I even considered putting a strong rare-earth magnet in the search coil to "freeze" the domains to at least identify the hot rocks. Only the very superficial soil and rocks can be affected this way.

Discussing this on the forum is unlikely to stop anybody from patenting anything. Patent examiners don't read posts on a forum. If they did, they would find out that many patents that are allowed are actually old ideas that were not patented, either because the inventions were considered trivial or they didn't work well enough to make it worth while to spend the time and money.

I'm convinced that many patented contraptions don't work at all. In the good old days you had to "reduce the idea to practice". If it couldn't be reduced to practice, i.e., it didn't work--no patent. Now, just filing an application is considered "constructive reduction to practice". As a consequence, you may get a patent allowed whether the device works or not. Only perpetual motion devices are prima facie no good.

Interesting times we live in...

Allan

[moodz]

Hi moodz,

There's no attempt here to make Oz look bad. It's an attempt to establish some important facts about ground signals. There's a lot of misinformation floating around--part ignorance and part deliberate deception. A detector's ability to distinguish between ground signals and a desirable target is still the limiting factor for a metal detector.

The information that can be gleaned from Eric's last post will probably not interest everybody, but it's of vital importance to me. He replicated a phenomenon which I also have observed and it has immence implications for the detector technology: It's now clear that the vicous signal from hot soil and hot rocks has a relaxation time that can vary from microseconds to thousands of years. That means that ground signals can mimic a gold nugget of any size and shape.

Those looking for an explanation for the "electronic holes" in a detector's response need not look any further. Algebraic combinations of multiple signal samples can not entirely eliminate the holes--perhaps make them disappear for nuggets of certain sizes and shapes, but considering the great variation of these factors, it's apparent that the current technology has gone up an evolutionary blind alley. All those patents filed in vain! (Of course, I include myself in this futile effort.)

Several prospectors in Oz have kindly sent me samples, for which I'm grateful. The big nuggets just beyond the reach of the current crop of PI detectors are now getting nervous...
By pooling knowledge on forums such as this one, the art will evolve and everybody will be happy...

Hot rocks are just rocks that have not eroded into hot soil, yet, and soil is everywhere.

All the best,

Allan
Just my personal opinion.

So given that I may have turned right ( where everyone else turned left ) up the evolutionary alley ..... for the same magnetic volume of dirt ( eg 1 cubic meter ) are you saying that the dirt with the nugget will not be distinguishable from the dirt without the nugget ? ... ( leaving electronic holes aside ).

[sawmill]

Allan

Metal sulfides are salts,and some are highly conductive, and in a high enough
concentration will cause a detector to overload or even give a real target signal.
Remember those funky brown rocks on the upper claim ,that made a detector,
go nuts? Remember that dark red soil where a detector darn near blanked out ,
and wouldn't even balance? Guess what is up the hill about 50 feet and no it is
not magnetite.

[Midas]

Hi Midas,

Unfortunately, the amount of current required to elicit this effect is prohibitive. I would have patented the implementation of this idea if it had been practical. I even considered putting a strong rare-earth magnet in the search coil to "freeze" the domains to at least identify the hot rocks. Only the very superficial soil and rocks can be affected this way.

Discussing this on the forum is unlikely to stop anybody from patenting anything. Patent examiners don't read posts on a forum. If they did, they would find out that many patents that are allowed are actually old ideas that were not patented, either because the inventions were considered trivial or they didn't work well enough to make it worth while to spend the time and money.

I'm convinced that many patented contraptions don't work at all. In the good old days you had to "reduce the idea to practice". If it couldn't be reduced to practice, i.e., it didn't work--no patent. Now, just filing an application is considered "constructive reduction to practice". As a consequence, you may get a patent allowed whether the device works or not. Only perpetual motion devices are prima facie no good.

Interesting times we live in...

Allan

Did you actually test to see if it still works when the static magnetic field is moving relative to the target and ground? ie. mounted on the coil
I'm thinking now it probably won't... Which makes making use of the effect even more completely impractical.

I'd say your probably right about the patent examiners not reading forums routinely, but perhaps if it was brought to their attention at the right time they would. Also you could possibly use a forum post in court as part of your invalidation suit. I'm not sure how reliable it would be considered, probably not very. Any forum admin can change dates to whatever. So you would need some (more the better) reliable independent cache(s) of the site stored elsewhere, and a few 100 grand to play with. Its pretty weak protection, but maybe slightly better than nothing.

Midas

[Aziz]

*LOL*
Patent examiners are dumb! Incredible dumb and aren't skilled in the art.
You can mind **** and dribble them easily by putting some (complex) formulas into the description.

The only good advice is to save/print the forum posting and keep it save in case of patent trolling procedure. Collect as many publications as you can do.
(Like I do it.)

Aziz

[Ferric Toes]

... you guys are painting a funny picture about OZ detecting .... anyone would think that the joint over here is made out of hot rock ... well guess what ... it isnt and you generally have to go out of your way to find hot rocks. If you have an AGB system it is not an issue anyway.

Hi Moodz,

You live on the doorstep of the Golden Triangle. Have you not been to Wedderburn, Beggary Hill, Tarnagulla etc? I have visited Victoria five times since 1982 and each time went out with prospectors where the big topic of discussion was the bad ground and how to find gold in it. In many areas the ground is a mish mash of ironstone of all sizes mixed with clay and quartz where it has been dug over by early miners around the turn of the century, or natural river washes. You do not have to go out of your way to find hot rocks, they are just there in all shapes and sizes. By hot rock, In this context I mean a rock fragment that gives a strong viscosity signal. I have not found any on the goldfields that exhibit conductivity. On each visit I have brought material back for measurement both for susceptibility and viscosity. In 1982 I brought back a few pounds of mixed gravel just scraped from the surface, and which I still have. Some of the ironstone also has remanent magnetisation, so sweeping a coil over it gives a bumpy ride magnetically as well as the viscous signal. The latest ML offering struggles on some ground, as I witnessed last September. So, with all the soil and rock samples that I have acquired from different countries, and the measurements I have seen recorded in the demining literature, those from Oz still top the league tables. If the ground is not an issue with the AGB system, then that is what we are all waiting for, to rid the world of mines, and find gold.

Just a final thought, hot rock is a term that originated in US and the context in which it is used implies an isolated natural rock or stone that gives a response on a metal detector. Sometimes it appears that these are conductive objects rather than magnetic. I prefer to refer to Australian goldfield matrix as Oz Ironstone as the material I have experienced is not in the form of isolated pieces.

Eric.

[dougAEGPF]

Allan

Metal sulfides are salts,and some are highly conductive, and in a high enough
concentration will cause a detector to overload or even give a real target signal.
Remember those funky brown rocks on the upper claim ,that made a detector,
go nuts? Remember that dark red soil where a detector darn near blanked out ,
and wouldn't even balance? Guess what is up the hill about 50 feet and no it is
not magnetite.

Do some mineralogy and geochemistry studies to find out if you have a VMS type deposit! Then do some resistivity studies to see if the undisturbed soil matrix is conductive!

Don't speculate do the studies!
dougAEGPF

[Ferric Toes]

Hi Midas,

Unfortunately, the amount of current required to elicit this effect is prohibitive. I would have patented the implementation of this idea if it had been practical. I even considered putting a strong rare-earth magnet in the search coil to "freeze" the domains to at least identify the hot rocks. Only the very superficial soil and rocks can be affected this way.

Interesting times we live in...

Allan

The problem with the built in magnet idea is that your seach head would gain weight very quickly if you were prospecting in Oz; or working in Black Sand in CA. For a viable patent you would need to combine the magnet idea with a motorised wiper blade on the underside of the coil. One wipe per sweep.

Eric.

[moodz]

Hi Moodz,

You live on the doorstep of the Golden Triangle. Have you not been to Wedderburn, Beggary Hill, Tarnagulla etc? I have visited Victoria five times since 1982 and each time went out with prospectors where the big topic of discussion was the bad ground and how to find gold in it. In many areas the ground is a mish mash of ironstone of all sizes mixed with clay and quartz where it has been dug over by early miners around the turn of the century, or natural river washes. You do not have to go out of your way to find hot rocks, they are just there in all shapes and sizes. By hot rock, In this context I mean a rock fragment that gives a strong viscosity signal. I have not found any on the goldfields that exhibit conductivity. On each visit I have brought material back for measurement both for susceptibility and viscosity. In 1982 I brought back a few pounds of mixed gravel just scraped from the surface, and which I still have. Some of the ironstone also has remanent magnetisation, so sweeping a coil over it gives a bumpy ride magnetically as well as the viscous signal. The latest ML offering struggles on some ground, as I witnessed last September. So, with all the soil and rock samples that I have acquired from different countries, and the measurements I have seen recorded in the demining literature, those from Oz still top the league tables. If the ground is not an issue with the AGB system, then that is what we are all waiting for, to rid the world of mines, and find gold.

Just a final thought, hot rock is a term that originated in US and the context in which it is used implies an isolated natural rock or stone that gives a response on a metal detector. Sometimes it appears that these are conductive objects rather than magnetic. I prefer to refer to Australian goldfield matrix as Oz Ironstone as the material I have experienced is not in the form of isolated pieces.

Eric.

Hi Eric ... you are right of course ....I am just trying to point out that the whole place is not made out of hotrocks.

[Ferric Toes]

This graph gives a visual image of how the viscosity signal varies with sample delay for a range of 10gm specimens. Red Hill soil the worst in US that I have so far, except for Yucca Tuff (sometimes called Tiva Canyon Tuff) from Nevada. Not a place you would go detecting anyway as it is being evaluated as a nuclear waste repository. YT is of special scientific interest though as it is composed of non-interacting single domain titanomagnetite grains rarely encountered in nature. See Institute of Rock Magnetism Journal, IRM Quarterly Fall 2004 Vol.14, No.3 and Spring 2006, Vol.16, No.1. These are downloadable and free from IRM website. I was lucky enough to get some samples a few years ago to do some viscosity tests.

The graphs are not fudged in any way and are from results measured this morning on a microprocessor timed viscosity meter under test at the moment. They do show that the viscous decay law is constant over the range of samples tested and it is only the amplitude that changes quite dramatically. Delay range 10uS through to 100uS. Amplitude in Viscosity Units (mine).

Eric.

[Ferric Toes]

Well, guess what. I have an OZ hot rock with very high susceptibility and viscosity and its viscosity signal increases considerably when you bring a ferrite magnet up to it. The magnet itself gives no signal; I checked that. The same magnet causes the viscous signal to disappear on a sample of Virginia Red Hill soil. These tests were done on 10gm samples of each in my Viscosity Meter, so very well controlled. On the RH soil the VM reading returns to its original one immediately the magnet is removed. The Oz ironstone takes about 15 mins. I will do some further tests as those opposing results are interesting.

Another thing of interest for those who strive for short delay times is that the viscous signal amplitude is 2.2x as great at 5uS as it is at 10uS

Eric.

Just to add a bit of information - As the ferrite magnet is lowered over the specimen (Oz rock) the viscosity reading increases about 10% but then starts to decline as the magnet is brought still nearer. Can't get anywhere near cancelling the viscosity completely though. It doesn't matter which way round the polarity of the magnet is, and the effect is the same if I bring the magnet in at right angles to the TX field.

Eric.

[Prospector_Al]

So given that I may have turned right ( where everyone else turned left ) up the evolutionary alley ..... for the same magnetic volume of dirt ( eg 1 cubic meter ) are you saying that the dirt with the nugget will not be distinguishable from the dirt without the nugget ? ... ( leaving electronic holes aside ).

If you could count on the magnetic properties being homogeneous in the area, yes, if you suddenly get a different response, this could indicate the presence of a target. Unfortunately, the soil is very seldom homogeneous. An anomaly could be a nugget, a beer can, an inert quartz bolder, or it could be just a natural variation. The whole problem with GB is that the common methods can not reliably separate the signal from a desirable target from a natural variation in the ground matrix.

If you've found a solution to this problem, patent it fast, before someone else does!

A discussion of the genesis of anomalous signals and the mechanisms involved will eventually lead to a quantum jump in the detector art. You can't stop progress!

Allan

Optimist.

[Ferric Toes]

If you could count on the magnetic properties being homogeneous in the area, yes, if you suddenly get a different response, this could indicate the presence of a target. Unfortunately, the soil is very seldom homogeneous. An anomaly could be a nugget, a beer can, an inert quartz bolder, or it could be just a natural variation. The whole problem with GB is that the common methods can not reliably separate the signal from a desirable target from a natural variation in the ground matrix.

If you've found a solution to this problem, patent it fast, before someone else does!

A discussion of the genesis of anomalous signals and the mechanisms involved will eventually lead to a quantum jump in the detector art. You can't stop progress!

Allan

Optimist.

Hi Allan,

I am not in agreement with the argument re anomalous responses. Most GB methods at the moment work on weighting a sample of the decay curve to equal a sample at an earlier or later point on the same curve. Since the decay curve from one viscous material to another does not change (i.e. it is ideally always a 1/t^-1.00) law) then it does not matter if the matrix is not homogeneous. An included quartz rock, or a void, will only alter the amplitude and give no change in indication. Exactly the same as when the coil is bounced up and down to check for ground balance, the large changes in amplitude have no effect. In the real world there seems to be a small variation in the exponent. For four different materials I measured 1.03, 1.05, 1.06 and 1.07 as negative exponents. Hope to refine this later to measure at three decimal places. I have found with the above types of GB that small corrections are needed in the field when passing from say a red clay to a brown ironstone. It may be the result of a small change in the slope, or more likely the result of non-ideal TX pulses in a metal detector. With the foregoing viscosity measurements I make sure that the TX current pulse is as close to rectangular as possible.

Eric.

[Prospector_Al]

Allan

Metal sulfides are salts,and some are highly conductive, and in a high enough
concentration will cause a detector to overload or even give a real target signal.
Remember those funky brown rocks on the upper claim ,that made a detector,
go nuts? Remember that dark red soil where a detector darn near blanked out ,
and wouldn't even balance? Guess what is up the hill about 50 feet and no it is
not magnetite.

Hi Greg,

You're right, sulfides ca be very conductive and they can ovedrive the input stage of a detector. Although the Tc of such soil may be short, if the amplitude of the signal is high enough, you can't wait long enough to sample the signal without reducing the sensitivity to desired targets.

That's a problem which is not related to the magnetic properties and it requires a different solution than the usual GB system.

I found a solution to this problem and designed a detector specifically to eliminate the problem. This is an industrial detector now being used in several mines. A patent application is on file and it will be published any day now.

I don't think that problem exist on your claim, though. You can check for soil conductivity simply by sticking two metallic rods into the ground, about a foot apart, and measuring the resistance between them with a multimeter. If the resistance is less than about 33 ohms, you've got a problem.

Allan