Why no mag on metal detectors?

[Midden-marauder]

So modern metal detectors of course feature VDI as we all know, identifying iron is generally not an issue but.....
I know with the detector I have, which is definitely entry level, iron is readily detectable up to a certain depth or can be detected once the "halo" is disrupted if the iron is deep, in some cases if it's very deep I get falsing issues leaving me assuming that it's probably iron but it's not 100%. Iron signals can in some cases actually be something like gold which adds to confusion on id.
Now, I've been running experiments with my lowly cellphone hall sensor using detailed physics apps and it identifies iron targets with VERY reliable ability, at considerable depth to boot. Deeper indeed than my metal detector can even sense anything. It ONLY responds to ferrous targets and minerals/objects with a strong magnetic character and it does so with a level of reliability that is absolutely second to none. It can likewise help to determine object geometry in ways the metal detector cannot due to dipolar qualities in magnetic targets. I know the orientation of a target far better using the mag. It makes a pretty decent magnetic locator in my opinion.
If they can put a reliable hall sensor in an Android smart phone cheaply why then can't they include this device into a metal detector? If my metal detector had a hall sensor mag it would take iron discrimination to a whole other level and might make the detector a bit better at finding things like meteorites or dense magnetic mineral deposits at depth. Personally I'd love to see such a feature included in metal detectors.
Is there a reason this isn't a thing in basically all modern metal detectors? Some complications I'm not aware of? Using a graphical display definitely makes using the hall sensor a more viable option for finding ferrous targets be the field negative or positive. I'd think this would be a killer feature in a metal detector. Why is this just not a thing?

 

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[TORRERO]

I've been running experiments with my lowly cellphone hall sensor using detailed physics apps and it identifies iron targets with VERY reliable ability, at considerable depth to boot.

I'm completely lost as to what your talking about, some kind of app on your phone that can detect iron deeper than a metal detector with complete accuracy ??
Are you saying that when you get a signal in the ground with your metal detector, you can place your phone on the ground and determine if the target is Ferrous or nonferrous ? 😳

 

[Midden-marauder]

I'm completely lost as to what your talking about, some kind of app on your phone that can detect iron deeper than a metal detector with complete accuracy ??
Are you saying that when you get a signal in the ground with your metal detector, you can place your phone on the ground and determine if the target is Ferrous or nonferrous ? 😳

Yes. The vast bulk of modern smart phones have a hall sensor in them, it was originally incorporated to make a digital compass possible but as it turns out it can be exploited as a ferrous detecting metal detector, a hall sensor, in case you don't know, is a magnetometer. Many analytical apps have been created for phone mags and other sensors as well. Phyphox, physics toolbox and a few others present very detailed graphical outputs that can accurately describe the background magnetic field and the distortions thereof. I've been able to very accurately map out the utilities on our property and determine the orientation based on magnetic domains/dipolar characteristics. It finds ONLY those materials which have a magnetic character and it does so with a high degree of accuracy, I can even estimate depth with it. Some of the magnetogram apps allow for pretty fine tuning. The noise floor is high enough that attempting to spot very faint anomalies might be challenging but overall it's pretty effective at what it does. There's a few published experiments that have been done demonstrating the cellphone mags capacity to accurately characterize the subsurface, the experiments I've been running confirm this. I walk it in a grid on the end of a selfie stick just like a metal detector and it seems to work quite well. There are designated metal detecting apps available but they absolutely stink, they only look for positive anomalies completely overlooking that negative anomalies are just as meaningful so I only use the apps providing detailed magnetograms in real time. Some even allow recording of said magnetograms.
Yes, it locates objects with a magnetic character with far greater sensitivity and at a rather greater depth per object size than a metal detector ever could. It's a real thing and they're so cheap to install on phones that they don't meaningfully increase the price which is cool. There's a ton I could say more about it and the nuances of how they work but suffice it to say they work well for this one thing: finding ferrous objects, that's basically what they find and they do it bloody well.
I think they should be an included feature in metal detectors

 

[pepperj]

So modern metal detectors of course feature VDI as we all know, identifying iron is generally not an issue but.....
I know with the detector I have, which is definitely entry level, iron is readily detectable up to a certain depth or can be detected once the "halo" is disrupted if the iron is deep, in some cases if it's very deep I get falsing issues leaving me assuming that it's probably iron but it's not 100%. Iron signals can in some cases actually be something like gold which adds to confusion on id.
Now, I've been running experiments with my lowly cellphone hall sensor using detailed physics apps and it identifies iron targets with VERY reliable ability, at considerable depth to boot. Deeper indeed than my metal detector can even sense anything. It ONLY responds to ferrous targets and minerals/objects with a strong magnetic character and it does so with a level of reliability that is absolutely second to none. It can likewise help to determine object geometry in ways the metal detector cannot due to dipolar qualities in magnetic targets. I know the orientation of a target far better using the mag. It makes a pretty decent magnetic locator in my opinion.
If they can put a reliable hall sensor in an Android smart phone cheaply why then can't they include this device into a metal detector? If my metal detector had a hall sensor mag it would take iron discrimination to a whole other level and might make the detector a bit better at finding things like meteorites or dense magnetic mineral deposits at depth. Personally I'd love to see such a feature included in metal detectors.
Is there a reason this isn't a thing in basically all modern metal detectors? Some complications I'm not aware of? Using a graphical display definitely makes using the hall sensor a more viable option for finding ferrous targets be the field negative or positive. I'd think this would be a killer feature in a metal detector. Why is this just not a thing?

Questions:
1: How long does it take you to determine if there is something ferrous?

2: At what depth is your falsing occurring?

3: If this hall sensor is only good for objects of strong magnetic character what good is for finding Non-ferrous?
(Would it be for just clarifying the ferrous targets?)
4: What depth are you taking about using you phone over your metal detector?

 

[Midden-marauder]

Questions:
1: How long does it take you to determine if there is something ferrous?

2: At what depth is your falsing occurring?

3: If this hall sensor is only good for objects of strong magnetic character what good is for finding Non-ferrous?
(Would it be for just clarifying the ferrous targets?)
4: What depth are you taking about using you phone over your metal detector?

With the regular detector I can reliably detect ferrous at maybe 4" though I haven't run the official test on depth there. An iron pipe a foot down will register as metal but it's only semi repeatable in some cases and that's about the point the falsing starts. Probably a limitation of my detector but that's where that stands. In terms of the cellphone mag I know, beyond an absolute shadow of a doubt that the pipe a foot down is ferrous and the signal response is VERY strong. We could probably put the pipe down another foot, maybe even two or three and still get a readable response that can ONLY be ferrous, nothing else unless it's basalt or magnetite or similar which have magnetic character.
It's 110% only ferrous, no non magnetic metals will give a response at all, that's both the limitation and advantage of a mag.
In terms of depth it's difficult to say without extensive testing to get a precise figure, the mag can detect a car at no less than 6 feet, further honestly based on my experiments, I can detect them driving down the street from inside the house, 20-25 yards perhaps, granted it's a faint signal, only just perceptible above background noise but it can do it. How much further than a metal detector can a mag find steel and iron? It depends on part on the exact composition of the metal be it steel but pretty far. That's why mags get towed to find shipwrecks many, many feet below the surface. Likewise that's why a surveyors magnetic locator can spot a buried pipe 15 to 20 feet away. Mags, even the basic hall sensor, are very sensitive to changes in the magnetic field. Iron distorts the field pretty substantially so it can be picked up a good way off.
They are NOT substitutes for classic metal detectors but historically they've been used in a rather different way, they can augment a metal detector though for sure. Definitely miles better at ferrous ID than any detector I'm aware of barring the most high end models which, I think, in some cases actually do incorporate mags especially the 3d mapping variety. the hall sensor works well enough that I see real application for it in the field when relic hunting and mineral prospecting. I just wish the engineers could incorporate them into standard detectors, it would definitely up the game in interesting ways

 

[Midden-marauder]

We need a geophysics expert and or a metal detector engineer to help clarify why this feature isn't found in basically all metal detectors or if it's literally a situation where no one has thought to do it. Reading a dynamic magnetogram takes some practice and some additional research but surely there must be a way of taking that data and making it more intuitive to understand. I'm not a geophysicist but I've studied up on a lot of subjects in that realm due to my growing fascination with subsurface sensors, I cannot, for any reason, imagine why cheap hall sensors have not been put into even the lowest cost metal detectors. If I were to design a metal detector it would definitely incorporate a magnetometer, maybe to be run in a separate mode but I'd want one in there.
Calling all geophysicists!! Come set me straight on the why or why not here please

 

[Midden-marauder]

I just ran another experiment at a local park. I was successfully able to detect lava rock from about 4" away on a smaller piece, certain other stones appeared to give responses as well but further experimentation will have to happen. I was likewise able to detect changes in soil composition particularly around the bases of trees, my assumption is that there's a deposit of magnetite or something similar that has built up in those spots. While it is not possible to build up a magnetic map using a cellphone magnetometer I can always use survey flags to mark the points where anomalies are encountered. There is, in the foothills of the mountain here, an unexcavated pueblito from the 1300s which is fairly visible from sat maps. Once weather conditions permit my plan is to grid the site using the mag and survey flags to see if I can trace the outline of the ruin based on magnetic variation in the soil where the wall foundations would have been. I'm semi optimistic about it, the more experiments I conduct with this thing the more the application becomes apparent. If I encounter success at the site I'll post the details on the forums here for public review. Fire pits are another one I wanna try this on, the heat from fires can produce magnetic remanence in rocks so it's a distinct possibility that I could successfully identify subsurface evidence of old encampments but that's an experiment for another day. Interesting stuff I tell ya

 

[TORRERO]

a hall sensor, in case you don't know, is a magnetometer.

No, I didn't know, and I didn't know all smart phones have one..

 

[TORRERO]

Another question you would have to ask would be related to whether a ferrous target is NEXT to a NON ferrous target.
Many machines like the DEUS II do well picking up those targets close by, but if your ferrous detector said its only Iron and its falsing because of that, couldn't you miss good targets ?

 

[Midden-marauder]

No, I didn't know, and I didn't know all smart phones have one..

Yeah, smartphones actually have a suite of sensors one can exploit in interesting ways but the mag is arguably the most useful in terms of relic hunting

 

[Midden-marauder]

Another question you would have to ask would be related to whether a ferrous target is NEXT to a NON ferrous target.
Many machines like the DEUS II do well picking up those targets close by, but if your ferrous detector said its only Iron and its falsing because of that, couldn't you miss good targets ?

Maybe I'm misunderstanding something here. Are you referring to the magnetometer or the metal detector? The two devices do something rather different. If there's a ferrous target in the ground and I run the mag over it there can be no falsing beyond possible noise errors but just like a metal detector we're seeking repeatable signals. If there's other non ferrous targets around it it won't catch them unless it's a magnetic rock or soil deposit and then we open up another can of worms in terms of how the signal shows up, gets complicated but there's still a signal.
In terms of my metal detector I think falsing may occur on targets at the edge of sensing range but mostly deep iron. In terms of the scenario you describe I'm not sure there, not yet at any rate. The two devices are rather different, one detects metal, the other detects changes in the magnetic field, you get rather different results using them

 

[invent4hir]

When I suspect falsing with my Whites V3i typically I look at the polar plot. If the strongest vector is between 9 & 12 o'clock - then it is usually ferrous. Not sure if/how other detectors resolve. I think polar plots are only accurate to a certain depth. If a target is deeper than that, than it sounds like what you're describing is a way for the detectorist to determine if it is ferrous. Perhaps like a magnetometer used in geophysical surveys - that fits in your hand. If it takes a short time for the device to collect and for the detectorist to interpret the data - it could help them decide if they want to dig it or not.

 

[Midden-marauder]

When I suspect falsing with my Whites V3i typically I look at the polar plot. If the strongest vector is between 9 & 12 o'clock - then it is usually ferrous. Not sure if/how other detectors resolve. I think polar plots are only accurate to a certain depth. If a target is deeper than that, than it sounds like what you're describing is a way for the detectorist to determine if it is ferrous. Perhaps like a magnetometer used in geophysical surveys - that fits in your hand. If it takes a short time for the device to collect and for the detectorist to interpret the data - it could help them decide if they want to dig it or not.

Bingo. Based on experiments I'm still running you might be able to use it to identify other subsurface features but I need to explore the limits of the hall sensor further. So far things look promising if very low resolution but there's potential there.
In any case, in terms of metal detection a mag has real potential to augment existing metal detectors, I think they should be included in the design as a final, last word assessment for identifying ferrous objects beyond a shadow of a doubt likewise they enable the machine to find certain deeper objects reliably.

 

[Midden-marauder]

Of course the detector would have to be designed to compensate for large ferrous distortions in the area, chain link fence, car, large drainage pipe 10 yards away and etc. it would either be that or we'd all have to learn to read dynamic magnetograms and realize when the background field is being distorted the way I've been doing it which is amusing being able to do but it might be a bit much for most folks. Not exactly just turn on and go, very nuanced. I'm sure software programmers could probably figure something out perhaps based simply on the intensity of changes in the local field taking possible absolute number changes into account, self zeroing as it were

 

[pepperj]

When I suspect falsing with my Whites V3i typically I look at the polar plot. If the strongest vector is between 9 & 12 o'clock - then it is usually ferrous. Not sure if/how other detectors resolve. I think polar plots are only accurate to a certain depth. If a target is deeper than that, than it sounds like what you're describing is a way for the detectorist to determine if it is ferrous. Perhaps like a magnetometer used in geophysical surveys - that fits in your hand. If it takes a short time for the device to collect and for the detectorist to interpret the data - it could help them decide if they want to dig it or not.

Not understanding polar plot.
I had a Whites in the late 80's early 90s. Get a Signal, keeping the coil pressed to the ground, turn 90° if cut out anytime in the 1/4 rotation it was iron, or trash.

 

[Midden-marauder]

Not understanding polar plot.
I had a Whites in the late 80's early 90s. Get a Signal, keeping the coil pressed to the ground, turn 90° if cut out anytime in the 1/4 rotation it was iron, or trash.

Polar plot? I missed that part. Maybe that whites has a magnetic sensor of some type in it? Please talk to us about the polar plot

 

[FinderTravis]

Interesting topic.. Detectors i use can fairly reliably differentiate iron from non-ferrous targets through tone and target id readings, but not at anything deeper than 25 or so centimetres.. Maybe a hall sensor based machine would be suitable for a completely new detector/scanner design that does not use a magnetic or radio based field to pick up/detect metallic signatures..? A standard true north hand held compass will also give different readings depending nearby ground mineralization or large metal objects, but also does not give a depth or metal type reading for the difference..Have seen some interesting devices that will work with a modern smart phone to scan concrete for rebar, pipes and cables accurately as well, though not certain how well they would perform for detecting/viewing small metal objects in varying soil/ground matrix's/compositions? Have also been intrigued by SAR technology (Synthetic Aperture Radar) imagery since learning of and it's ability to literally see through dry terrain and objects like vehicles and buildings. Wonder if Superman ever used his X-ray vision to look for relics and treasure caches..?

 

[Midden-marauder]

Interesting topic.. Detectors i use can fairly reliably differentiate iron from non-ferrous targets through tone and target id readings, but not at anything deeper than 25 or so centimetres.. Maybe a hall sensor based machine would be suitable for a completely new detector/scanner design that does not use a magnetic or radio based field to pick up/detect metallic signatures..? A standard true north hand held compass will also give different readings depending nearby ground mineralization or large metal objects, but also does not give a depth or metal type reading for the difference..Have seen some interesting devices that will work with a modern smart phone to scan concrete for rebar, pipes and cables accurately as well, though not certain how well they would perform for detecting/viewing small metal objects in varying soil/ground matrix's/compositions? Have also been intrigued by SAR technology (Synthetic Aperture Radar) imagery since learning of and it's ability to literally see through dry terrain and objects like vehicles and buildings. Wonder if Superman ever used his X-ray vision to look for relics and treasure caches..?

Ah, like an old fashioned "dipping compass".
Those apps you describe sound like they exploit the mag in cellphones, you can definitely find utilities and other ferrous/magnetic structural components. That's actually a major use for the fancy gradiometers and mags employed in geophysical surveys.
In terms of estimating depth I'm still nailing down all the nuances there but certain general rules apply in terms of reading magnetograms and how the readings relate to depth and target size. I've been experimenting with the cell mag for over a year now but only just recently really have been attempting to detect novel targets I.E. magnetic soil deposits or rocks. That kind of thing can potentially be used to catch subsurface archaeological features the metal detector is likely to miss. I've been having intriguing results, promising results honestly but to what degree it can be used to identify such features is still something I'm exploring. How intense does the anomaly have to be for a phone hall sensor to meaningfully characterize it? Generating a magnetic map of anomalies is not something any apps I've encountered can really do. The crowdmag app can create magnetic anomaly maps but because phone GPS is only semi accurate and the sample rate of the app positively stinks it's not a good way to handle it. You're better off using survey flags and gridding to try to trace or mark anomalies, triangulation with a compass gives better positioning than the crowdmag app does for sure.
Still learning what it can really do but one thing is certain: it has second to none capacity to identify ferrous objects and is therefore beyond doubt in that way. It can detect them at considerable range/depth too. For now if I really need to clear up ambiguous VDI on deep targets the mag does it brilliantly. Phone on a selfie stick in one hand, metal detector in the other. It's a pretty compact set up and it breaks down very nicely for easy transport. I don't think it's a question of if it can pick up non metallic, magnetic subsurface features, it's more of a question of how intense do the magnetic fields/distortions created by such features have to be for it to catch it. My interest here goes a bit beyond ferrous discrimination though that would be a primary function for any metal detecting activities. It picks up iron for damn sure and it does it well. One of my ambitions with it is to try to detect LIRMs (lightning induced remnant magnetism) in the hopes of finding fulgurites, such anomalies are often high intensity so I don't think it's beyond reason but, again, I'm mostly experimenting with it at this point. If I locate fulgurites with it I'll post it in these forums

 

[FinderTravis]

Ah, like an old fashioned "dipping compass".
Those apps you describe sound like they exploit the mag in cellphones, you can definitely find utilities and other ferrous/magnetic structural components. That's actually a major use for the fancy gradiometers and mags employed in geophysical surveys.
In terms of estimating depth I'm still nailing down all the nuances there but certain general rules apply in terms of reading magnetograms and how the readings relate to depth and target size. I've been experimenting with the cell mag for over a year now but only just recently really have been attempting to detect novel targets I.E. magnetic soil deposits or rocks. That kind of thing can potentially be used to catch subsurface archaeological features the metal detector is likely to miss. I've been having intriguing results, promising results honestly but to what degree it can be used to identify such features is still something I'm exploring. How intense does the anomaly have to be for a phone hall sensor to meaningfully characterize it? Generating a magnetic map of anomalies is not something any apps I've encountered can really do. The crowdmag app can create magnetic anomaly maps but because phone GPS is only semi accurate and the sample rate of the app positively stinks it's not a good way to handle it. You're better off using survey flags and gridding to try to trace or mark anomalies, triangulation with a compass gives better positioning than the crowdmag app does for sure.
Still learning what it can really do but one thing is certain: it has second to none capacity to identify ferrous objects and is therefore beyond doubt in that way. It can detect them at considerable range/depth too. For now if I really need to clear up ambiguous VDI on deep targets the mag does it brilliantly. Phone on a selfie stick in one hand, metal detector in the other. It's a pretty compact set up and it breaks down very nicely for easy transport. I don't think it's a question of if it can pick up non metallic, magnetic subsurface features, it's more of a question of how intense do the magnetic fields/distortions created by such features have to be for it to catch it. My interest here goes a bit beyond ferrous discrimination though that would be a primary function for any metal detecting activities. It picks up iron for damn sure and it does it well. One of my ambitions with it is to try to detect LIRMs (lightning induced remnant magnetism) in the hopes of finding fulgurites, such anomalies are often high intensity so I don't think it's beyond reason but, again, I'm mostly experimenting with it at this point. If I locate fulgurites with it I'll post it in these forums

Best of luck in your endeavour!👍

 

[Midden-marauder]

Best of luck in your endeavour!👍

Thanks, it's all in good fun, I'm prone to nerding out on science topics lol.