Half Dime at 9" and iron bolt at 5" - Same Hole

I am pretty pleasantly shocked at this and let it be known in the following thread (note pic): [www.findmall.com]

I just asked how far apart the two targets were on the X-axis/plane as I am VERY CURIOUS regarding this. I believe Tom was saying this is the one BIG TEST for a VLF detector to do. Ok, it wasn't in a controlled environment. But if the coin was at 9", the iron bolt at 5", then that means there was 4" between the two, or there abouts. Depending on how wide the whole was (meaning how close on the X plane could the targets have been), it seems amazing to me. Even if the bolt was 4" away on the X-axis (waiting on that answer), I am still impressed to see that with an 11" coil.

What do you all think of this?

This was on the Minelab CTX btw and it picked up both targets with target trace. I guess we'll have to wait and see if more reports like this start coming in.

Albert

Video of it or it didn't happen
Seriously though, if that is real, it has to be a first for a metal detector.

Was the bolt laying vertical or horizontal?

Can't say he dug a false and got lucky, because the trace revealed the two targets.

These types of recoveries are exciting to hear about. It helps to swallow the price tag a little bit. I look forward to some good detecting reports from a few out there. Right now we are experiencing mass spending justification. Put it up against an E Trac or at wait for some veteran hunter reports. Probably this weekend many will hve their first hunt.

Sorry, but not buying it. Especially not with 11" coil...

Call me a skeptic, but that iron bolt, 4" above a TINY half dime? Not buying it...

Steve

I want to see this scenario replicated. Shouldn't be hard to do. After folks get their CTX's, this scenario needs to be put on video, so there will be no doubts as to it's validity.



Edited 1 time(s). Last edit at 05/31/2012 08:00PM by TerraDigger.

Yeah, the scenario needs to be repeated. The guy that dug the two targets really didn't know how far apart they were, but still pretty nice that the bolt was so far above the coin. Unless the whole was 12" wide, which I doubt, it seems like very good unmasking.

I am seeing a larger number of finds with iron in the whole and often people are mentioning the target trace feature. Yeah, we can't go by the "I pounded this spot with the E-Trac" or such as our only proof, but things are still interesting.

What I would like to see is how it stacks up against fast recovery machines like the Deus.

Albert

Very hard to believe this happened this way.
I'd imagine he detected the bolt as a high tone, then after recovering the bolt, he re-scanned the hole to find another target. But a half dime at 9" would be a very small target to hit with the air space already in the hole.



Edited 1 time(s). Last edit at 05/31/2012 02:19PM by markg.

Mark - It is truly hard to believe. But here are his words and it's clear what you said wasn't the case:

A target hit at 12-37 with a high tone and a low tone and I thought I had a penny with surrounding trash. I had
target trace and pinpoint on and noticed some trash. The good target showed 9 inches. I started digging and at 5 inches
I found an old rusty bolt. Damn I thought. I ran the 3030 over the hole again and the good target was still there. I kept digging
and out pops this 1872 Seated half dime. - End Quote

Now, a friend of Mine (recently banned from Finds) just emailed me and told me he is getting quite a few silver from a pounded park (yeah we have heard that before) and the park is hit a lot by an old Guru detectorist.

I'm not saying the CTX is all that, but some of the reports coming out, IF TRUE, mean that something better is happening with unmasking.

Albert

Impossible. The bolt had to be off to the side. All I know about detection fields says they can't travel past the first metal object they see in the field. Even the "Beneath The Mask" article on this website shows how a tiny paper staple blocks magnetic fields. They warp, bend, and wrap around the first metal item they see. It's not like a flash light beam that can hit an object and still have the rest of the beam go past it and hit something further away. I saw a test video with a nail above a coin about a half inch or so. Impressive....And impossible...Is what I thought at first, and then I heard others raise concerns that the coin was off to the side. Nothing a good machine with a good sharp DD detection line can't do, so I'm waiting to see more.

I just posted a bunch of messages about unmasking ability and the factors that govern them in this thread. There are certain phsyical laws that govern detection fields that can't be changed, no matter how much electronics you cram in the box. It's like trying to get a flash light beam to go around corners. Just can't happen. And, at least a flash light beam can hit a closer object and have part of it's beam still go deeper and hit something further away. With detection fields the first metal object they hit and it's game over. It's like bursting a soap bubble. More details here...

[www.detectingequipment.com]

And you can read my concerns about this machine that I want addressed before I'll buy one here...

[www.detectingequipment.com]

It's a lengthy read on the pros and cons going through my head as well as what I've heard others voice concerns about, but it also dives into some skeptical questions about any new unmasking abilities here. All that I've seen *thus far* (this could change) is telling me this is simply a prior target history and so no real benefit to most people, as we all know trying to watch the screen while hunting is a major PITA. Most guys listen for high tones among the lows and then only look at the screen when they wiggle over two targets next to each other to see what each is. Also, if it's such a big advancement in separation or unmasking ability then why did Minelab word the description so vague so that it can be read several different ways? And, if indeed it's a big breakthrough in separation/unmasking then why the need for a 6" coil they are making for it?

I'm still sitting on the fence before I fork out a dime. The only two things I care about are depth and separation on a machine. Everything else is eye candy and bells and whistles to me, so if it doesn't show me something another Minelab with a good aftermarket coil can't match in those two respects then my wallet stays in my pants. I'm waiting for field tests of another Minelab using a good after market coil such as the 12x10 going head to head with it on undug targets.Then we'll see just what it can do, so long as it's put on video for all to see.



Edited 2 time(s). Last edit at 06/02/2012 05:55PM by critterhunter.

I understand what you are saying, but our own Tom stated that detecting targets like this are not possible, unless there could be a huge jump in technology.
?CTX?
If all is 100% truthful, (not saying it's a lie) then staging the same type of targets and their responses would not be hard. Find a clean area, no trash and bury the said size bolt and coin at the depths mentioned. It should be easier because the bolt would have rusted in the original find with a lot of halo affect from the rust.
.

I don't see what the big deal is.
I find bolts, nails, other whatzit's next to coins all the time with various machines.

?????

More than likely the head of the bolt was reading as the coin signal...the shaft was the iron signal...

Every detector I have ever used except a sovereign..reads the heads of bolts alot different than the shaft...I did it yesterday on the DEUS...I thought I had a good target beside a nail..it was just a pan head bolt..Sounded like 2 seperate target's...One good one bad...All I got was one bad,,LOL!!

Anything is possible though...Within reason..

Keith

Again, I'm not saying this is the holy grail, I know it's not. But it does appear to be unmasking better than the E-Trac. If I didn't hear it from the horses mouth in a friend, I would take it less serious. Time will tell. I just wanted to post this as it seemed extreme.

Critterhunter - With my Jupiter (from only one angle) I can see a coin cleanly 1" under a nail. [www.youtube.com]
I have to try it deeper. Regarding bells and whistles - You know, there is a saying "You have to be able to see the truth in the false." In this case, well, to me the bells and whistles might not be important, but see past them - the false, something true might be there or it might not, but it might...

Now, even if the bolt was off to the side, which I'm betting it was, unless that hole was REALLY WIDE, the machine still had to see below it to a point as bolt at 5" is blocking a lot of what is below it. Just think of the staple on the ground above a coin example..
He sounded like it was a good hit, but didn't go into details, so all we have is something to ponder, that is all. Makes me want to look deeper into things and do some testing when I get one.

Coilfishing - The thing here is that the coin was substantially below the nail. That shouldn't really be possible, at least not quite so cleanly. 1" yeah, as I did above in my Jupiter test.

Keith - His CTX said the good target was at 9" and that is what happened. The bolt was around 5". So, the 9" depth of the good target on the meter complicates things. The Deus is just using sound, so perhaps something in the 2D screen and FBS2 technology is opening things up a bit more than we are used to? Also that chip in the coil that we don't exactly what it is doing.

Albert

Let's boil this down to brass tacks here...I'm dealing with strictly what I've read on the technical aspects that govern how detection fields interact with metals. I'm by no means an expert, nor college educated in this field of science, but I've got enough smarts (I hope) to grasp certain laws of nature that just can't be changed. According to what I've read by those a lot smarter than me and with backgrounds in this stuff, detection fields stop and interact with the first metal object they see. There is no further ability to reach deeper and see something else, UNLESS the shallower object is NO LONGER in the detection field. The eddy currents warp around, bend, and interact with the first thing they hit that is metal. There is some small ability in rare circumstances for the field to curl around the bottom of the object, but only a little bit and not really with any ability to really "see" a second object that is also now in the field.

In some rare situations, such as two targets at the same depth and so close that they are overlapping, the detection field can wash over both items at once, but when that happens they become "one" and thus the conductive properties of the two are averaged on the scale and the detector reports the "one" target of combined conductivity. There is just not enough "words" in the vocabularly of a detection field to relate that there are even two targets in the field, let alone ID them separately. It's not a problem with the limits of technology, it's a brick wall in terms of what can be gleamed from detection fields. Think of it like trying to ask a 2 year old about the nature of the universe. He just doesn't have enough words to relate those kinds of details. No amount of technology in the box is going to change what the detection field can do (according to the laws of physics that govern it's existance and interaction with objects), and there is very little that can be gleamed from a detection field. Ferrous and non-ferrous traits, conductivity, strength....That's about it. Again, it's not the limits of technology, is what the field is able to do, how it interacts, and just how much it can tell the detector about an object.

*IF* Minelab has somehow broke or at least bent these seemingly static laws of physics in relation to detection fields, and *IF* it can say see two targets at differing depths and even spaced out a distance from each other under the coil (impossible I still say on both these counts, but I'm basing that on what I've read and been told about detection fields so who's to say...what I've read might be wrong?)...Then where is the bold statement announcing that? What I've read can be taken two very different ways. Why be vague about such a strong selling point? And what's the deal with the 6" coil they are already coming out with? Why the need for a small coil if a larger one can really see two targets at once under it?

But let's for the sake of argument (who really knows?) say that it can indeed see two targets in the field at the same time. How is that any better than any other machine using a sharp detection field? Sure, you don't get to see the *prior target* (as they word it...Make a note of that in reading the above debate...That alone might make up your mind on things) on the screen, but do I really care about that? I've said this a few times but I'll say it again, detecting requires coil movement. Virtually none of us watch the screen as we hunt. It gets old real quick and also makes for poor coil control. Instead, we listen for any hint of a high tone mixed in with the lows. Then we stop, wiggle over the targets to isolate and separate them, and then note the ID on the screen as we do that to each. Even a slow machine such as the Sovereign, but using a good sharp DD detection field like that generated by the 12x10, can easily isolate and split apart two targets that are so close that they can even be somewhat overlapping. That's easy, and I don't need a second target ID to help me with that because my 2 second memory is just fine. Long term memory? Ok, that's another story...:')



Edited 1 time(s). Last edit at 05/31/2012 06:02PM by critterhunter.

Here's one more point of for now on the ability to "see" two targets under the coil at the same time. Let's say there are two targets...One being a coin and one being a pulltab, and they are both under the coil but separated by several inches or so. Far as I know even though both are at the same depth, the first one the field hits is what gets "seen". The detection field pops like a bubble and won't reach out and see the other item a bit off to the side. It's only a "one or the other at a time" kind of deal from all that I've read. That's what makes me also think this is just a prior target history.

The only real ability for a detection field to "see" two targets at a time is at the same depth and so close that they would probably be overlapping a bit. Only then are both being washed in the field at the same time. Far as I know there is no ability with technology to bust those two targets apart and ID them separately. To the field, and thus the detector it relates details to, the two targets are now "one", and thus will be ID'd as such and at an averaged conductivity number half way between them on the scale. However, there is some appearant ability of some machines (such as a Sovereign, for example with it's Iron Mask) to bust a non-ferrous signal out of one with ferrous qualities. IE: A coin and a nail at the same depth and overlapping that are both being in the field at the same time. But, again we are talking about the ferrous/non-ferrous properties of the signal that can be played with somewhat to do that, but there isn't any further information the field can tell you about the targets, like the very fact that there are indeed two targets present, or what the conductivity properties of each other. There just isn't enough information you can gleam from a detection field to do that.

But, again, let's assume this machine can see two targets at the same depth, and so close to each other that they are touching probably if not overlapping, and that indeed it can break apart and isolate both targets through some wonder in processing and ID them separately. How exactly is that any big advantage over another machine using a good sharp coil? You can still wiggle over one or the other with proper coil control and easily isolate and ID each separetly. Even a slow machine such as the Sovereign but using a sharp detection field can do that. It's a no-brainer for anybody with any kind of experience.

One other thought to pounder for now. Let's say you lay a nail over a coin and with the nail in vertical orientation to you, and thus the DD detection line, which goes from tip to tail of the coil, runs from the tip to the tail of the nail. Now wiggle over the nail and coin. Any good machine with a sharp detection line can easily see them both separetly? How? By wiggling the DD line is at one time parallel to the nail and so is seeing the side of the coin and not the nail, and then when moved over the nail it's seeing the nail being that it is higher than the coin (remember that thing about detection fields stopping with the first thing they hit?). So you go nail/coin/nail/coin, or high/low/high/low/high/low as you wiggle. You aren't seeing two items at once here, you are seeing one and then the other. Any machine can do that, and the only difference I see *at this time* (that could change) is that this new machine is putting the prior target it saw on the screen too. Sure, it can do that, but it still isn't telling me anything about whether it can see two targets at once. There is a BIG distinction between those two things, and so it's either a breakthrough in technology or just a prior target history on the screen. If that's all it is it isn't worth the money to me. Nice feature? Sure, for some, but then some people think tire pressure sensors on their cars are nice features. I don't want to pay extra for that, because I can easily walk around the car before I get in to see if a tire is low. That's the same way I look at detecting technology. All that matters to me is depth and separation. Throw in tone alerts and a high resolution VDI and I'm happy. The rest is up to me.

Critterhunter - I don't deny or outright disagree with what you are saying. But science is an interesting thing. You see, the very means that we all agree to use is also the very thing which often stops us from going forward. It tells us what is possible and what is impossible. It allows discovery if things go according to the scientific method. But there are plenty of loopholes in it I think. In a way, in it's very limited understanding (at this time) it sets an "event horizon" so to speak of what is possible and impossible. I mean, to bring that to this discussion, FBS technology is a branch of VLF and in that maybe some things can be twisted? Maybe.

Not to base my argument on that, but I do believe some major breakthroughs can happen and they will be under our noses perhaps, maybe in their simplicity. Mike Hillis in your thread (I think) on Finds showed how a coils field reacts under a search coil by progressively burying a coin an inch deeper and progressively testing its detection field - sort of a mapping process. The field went in at the middle I think and out. So, I feel that perhaps a bolt could be setting in a so called "dead area" and the coin still in the active area. Maybe, maybe not.

All I'm saying is I won't let rules that are relatively speaking, quite limited in the grand scope of things, allow me to say what is possible or impossible. I've had a pretty miraculous life outside of detecting, enough to write a book on. I was just open for it, so I feel the micro is like the macro (and so does quantum physics and string theory I believe), so you know what we can really, positively say?

We don't know.

There is wisdom and room for expansion in that. I'll just stay at that and once I get a CTX I will test it. I don't expect a miracle, but I'm open for it.

Albert



Edited 1 time(s). Last edit at 05/31/2012 07:30PM by earthmansurfer.

Keith brought up a very good point about the head/shaft of nails/bolts. That has been my experience also. The head reads as a coin.

Physics precludes. ((( Unless paradigm-shift paradox exists )))

------------------------------------------------------------------------------------------

((( Starting to see where scientific testing is required??? )))

TerraDigger Wrote:
-------------------------------------------------------
> Keith brought up a very good point about the
> head/shaft of nails/bolts. That has been my
> experience also. The head reads as a coin.

But the screen said the good target was at 9".

Tom - I don't deny physics. In a way, I'm just saying until I do some testing it's a bit fun reading these reports. I'm not putting too much stakes in them, but it is a bit exciting to think unmasking might have gotten better.
I just wonder how much and how far FBS can go regarding unmasking. The E-Trac was pretty slow recovery wise in my opinion. But it did better in iron (not super heavy) than my V3i and Omega. Now, maybe that had to do with my somewhat iron mineralized ground, but I have a different perspective now. I avoided Minelabs for years as I didn't want to go over the other side so to speak, but it was my own undoing as they do great in my soil, as I now think CZ's would.

My Jupiter is awfully fast and unmasks incredibly well, so I don't discount raw speed. It is faster than my Omega was and appears close to the Deus. I mean for 300 bucks (used, 600 new) and the way that it is built, it is just a great complimentary site machine. Being that I really am a coin hunter it makes more sense.
I am going with CTX (soon I hope) and Jupiter over Deus and E-Trac, for roughly the same price. Think it will be better on my back as well ;-)

Earthmansurfer, I don't deny that there can be advances in technology that can do wonders, but those wonders still have to follow certain natural laws that govern things. All I'm saying is that with great claims comes the requirement of great proof. And that proof has to be carefully proven and shown by some actual controlled conditions of those tests performed to demonstrate such ability. Thus far what I've seen in videos and tests on this new machine...I'm not seeing anything that any other good machine with a good sharp detection field can't do, or the video is so distant and the conditions so loosely described that there isn't enough "meat" there for me to say "Aha! It really can't do something new." I'm not seeing that, yet. And if I am to believe and fork out that much cash, then I need good, solid, hard, see it with my own eyes evidence that nails it down for me.

Every test thus far I've seen that I can roughly gage the performance factors involved in, I honestly feel any good machine with a good sharp detection field can do just as well. The nail a half inch above a coin test was impressive to me at first, and went against everything I *think* I know about detection fields. As I was pondering that delima in my mind and reading on, I saw the probable answer that others noticed and I didn't. That being that the coin was off to the side of the nail somewhat. Once again, I feel the right machine with the right coil can thus see that coin. I need more evidence than that to buy myself.

Let me try to demonstrate what I'm trying to say here...Let's say you turn on a light bulb in a room. You have no real way to control what the light does, short of putting a lamp shade on it to focus it's beam into the right direction. Same deal with coil detection fields. The only real way to control them is by using a sharper field such as that generated by an SEF coil to focus it a bit more on what you want to see and not what you don't. The beam of light still can't be made to go around corners by controlling it at the source. Sure, you can stick a mirror on a wall, aim the light at it, and so have the beam reflect off of it and around a corner, but there simply isn't any method that I'm aware of to control the detection field from a coil in such a way.

Boiling it down to the last bit of water in the pot, we are talking about the ability of this new machine to supposedly see two targets in the detection field at the same time. I don't see any way the detection field can hit a shallower metal object (even one a good bit off to the side but still in the detection field), and yet still be able to reach deeper and see a coin it's masking. Far as I know it's game over when the field hits something metal. I've used the soap bubble analogy but that's not exactly the right way to put it. The field doesn't "pop", but rather it interacts and warps around the first metal item it hits *as far as what I've read over the years*, so I guess I could be wrong about that and was reading faulty information in that respect. Even two objects at the same depth but a good distance away from each other seems impossible to both be detected (washed in the field) at the same time. It's luck of the draw. Whichever one the field is the first to interact with, that's the object it "sees" and stops with. It's like pulling the plug on a bathtub and watching the water drain out. It's drawn to and wraps around the thing it's attracted to. In water's case gravity is the "attraction" that draws the water to it. In detection fields it's the first metal object that draws the field to it.

But, as said, let's just assume that I'm way off base with what I've read and *think* I know about detection fields and this machine can see two targets at once in the field. OK then, how exactly is that an improvement in terms of separation? At the very least it still has to see both targets distinctly (meaning, one can't be right on top of the other and thus block it's ability to be "seen" by the field). Under those circumstances to me there still isn't any better ability here. You still have to wiggle the coil as you hear hints of high tones, and investigate each distinctly...And so can easily see each target one at a time as you check them out. So, even if this machine has some vast breakthrough in ability to "see" two targets at once, that still doesn't mean it can beat another machine using a good sharp field. After all, as said a few times already, why the need for a 6" coil then? That alone tells me something here, beyond all my arm chair speculating and various theories on how detection fields may or may not work.

NASA-Tom Wrote:
-------------------------------------------------------
> Physics precludes. ((( Unless paradigm-shift
> paradox exists )))
>
> --------------------------------------------------
> ----------------------------------------
>
> ((( Starting to see where scientific testing is
> required??? )))

When are you going to do some tests on this machine against a few others. That's a story I'd love to read, as I'm sure many others would just love to too.

Critterhunter - Again, I'm not really disagreeing with you. I'm just saying there is more than one way to get something done. The danger is we may not be seeing the whole picture. Let me run quickly with this.

Mike Hillis' diagram showed the detecting field was not exactly cone shaped below a search coil. It kind of went in and then back out again. Well, what is using FBS or another technology you could just slightly vary that dead space and vary it quickly? What if, I'm not saying they are doing that but who know. Well, theoretically (according to Mikes diagram) you could see under things somewhat, maybe not exactly below, but enough to the point that no other machine with a static field would be able to do it regularly. Now, the CTX has a chip in a coil, who really knows what it is doing. And since FBS has a time domain component, I really just wonder. Not that it is doing something unbeleivable, but just that it's going a bit farther with current technology. And on the other hand maybe it's not doing anything special.

I'm rather trying to figure out a way where it might happen, and you are using science to tell me how it can't happen. Try to think outside the box and just join me on this. I'm not saying your wrong, but I know what your saying and proving it isn't possible is straight foward enough. You did your job. But trying to give a glimmer of how it might be possible, that is much harder imo. Especially if you stick with the rules ;-) And apparently you know more than me about this.

Must be a way to unmask better without raw speed...

Regarding my Jupiter video, the coin was exactly 1" below (not 1/2") the nail and exactly in the center, not off to the side (The camera might not have been dead center, but I made sure the nail was). I did that test so many times (outside of the video) at different positions and it just continually picked it up - in that configuration, not with the nail crossways of course. I have to try it at 2" as well, at least see how far I can get it.
Another recent video I have on my channel is of the Jupiter hitting a small washer like object (coin size) right next to a pretty big piece of T shaped iron and it does it cleanly. Not a super big deal to me, but it shows me how fast it is.

Thx,
Albert

"But it does appear to be unmasking better than the E-Trac"

That isn't a real hard thing to do in my opinion. I realize there are E Trac fans out there. I liked it. But unmasking was not what it did best. I need more than that to hop in the wagon.

For your viewing pleasure.

[www.youtube.com]

OK I am not sure the assumption that the first object in the path absorbed all the field. I used to work at a magnetic company that made inductors and coils. I am not an engineer but have a very strong engineering background. All I will say for now is that Magnetic fields are very complex in how they interact with each other and and inductors (read coils). It is very complex when only dealing with one Freq, but when you add multiple Freq along with complex algorithms that look at reflected signals much is possible. Yes physics prevails but trust me this is way more complex then you or I could deal with with out lots of complex analysis. We did a lot of amazing things with Coils and Transformers. So to put in simple words I am not saying it is true but I am also not convinced it is not true. If any alternate explication sounds plausible I am in the camp of the bolt head reading different then the shaft.

Goodmore - The E-Trac nulled a lot in iron. But it still pulled coins out of the null. It isn't as good in heavy iron as fast machines. But, it was better than my V3i and Omega (in my soil), and both of those machines are very good. My T2 was very fast, but just not great on coins - might have had more to do with the iron mineralization in my soil. We need more comparison videos to really know. I think because the E-Trac was slower recovery wise that people think it doesn't do good around iron. (I was never a big Minelab fan, but on coins it really did well in my soil).

Schultzie - I am very unimpressed by that video. I saw it yesterday. Most detectors would see that huge coin above a piece of iron that is off to the side. This is much much more impressive: [www.youtube.com]

Bryannagirl - That is exactly what I am talking about. Instead of saying how things aren't possible. How are they possible? Thanks,
I'd really like to see Critterhunter, or anyone with more understanding of VLF detectors, apply some of their knowledge in this way, as I said above.

Albert

Albert, I'll take a stab at it. (Tom, please jump in here)
This will be a little lenghty and may be pretty basic info but here goes. Stay with me until the end and hopefully it will make sense.
As I have said before I design cryostats that house superconducting magnets. The magnets themselves are designed by a different team of engineers but I have picked up on quite a bit from them over the last few years. I will be talking about cylindrical magnets but I think the information will apply to the flat wound coils on our detectors. To put things in perspective our magnets are anywhere between 9 and 21 Tesla. (The earth's magnetic field (gravity) is 0.00005 Tesla or .5 Gauss.) The cryocoolers that I use to cool the magnets cannot operate in a magnetic field higher than 500 Gauss and need to be as close to the magnet as possible in order to minimize resistive cooling loss. With 10,000 Gauss in a Tesla and the magnet running at 21 Tesla (210,000 Gauss) I have to be able to decrease the field strength by 209,500 Gauss at a point about 3' from the magnetic center of the coil. One way to do this is to reverse wind a coil outside the primary coil that will actively shield the primary coil and contain the field. The peak field in the bore of the magnet remains unaffected. This method is very expensive and time consuming.
Another, much less expensive and complicated, way to accomplish this is to put an iron sleeve around the OD of the coil. The iron basically absorbs the field greatly reducing it and allowing me to place the cryocooler close enough to the magnet to do it's job.
Once this is in place it is, more often than not, necessary to shape the magnetic field so that it will generate a specific force at different points along it's long axis. This is done by attaching small pieces of ferrous (magnetic) steel to the bore tube of the magnet in predetermined locations. I can't show an illustration but you would be amazed at how little steel, as thin as 0.02" thick, it takes to drastically deform the field of even a 21T magnet.
These fields cause eddy currents to flow through all of the resistive metal parts of the system. These eddy currents can in turn generate a field strong enough to rip the system apart in the event of a quench (loss of cooling).
Now, scale all of this down to the LOW field transmitted by our detectors which is microscopic when compared to one of the aforementioned magnets. If I understand it correctly it is these same eddy currents, caused by the deformation of the transmitted detecting field of a metal detector, that are read by the receive channel of the detector. If a relatively small piece of iron can contain or warp the field of a 21T magnet, it is easy to see (if I am thinking about this correctly) how a nail could obscure a non-ferrous target beneath it. I am not saying that it would stop the detection field dead in it's tracks but it would definitely generate eddy currents deforming the detection field; possibly in such a manner that the detector can no longer read the target below it.

It's kind of like looking into a clear pool of water. While the water is still it is possible to see the bottom of the pool. However if you drop a pebble into the water the resulting ripples distort the light waves entering the water and you cannot see the bottom, at least not as clearly as when it was still. When the transmitted signal from your detector hits a nail, or other ferrous object, the resulting eddy currents distort the signal obscuring any target below it.

Does this help or just further muddy up the waters.
As always, I could be completely wrong about this so feel free to correct any or all of it.

Chris



Edited 1 time(s). Last edit at 06/01/2012 01:54PM by Neugene.

Albert = "Inspirationally positive"
Me = "Physics bounded"
critterhunter = "present-technology/reality-incarcerated"
Breannagirl = "experience-based realism"
Chris = "Scientific/physics experience, mindset database"

All of us = Subconsciously 'hopeful'
All of us = Variety of tangential thought-process(s)

All of these qualities (collectively), creates the very fabric of humankinds ability to 'invent & advance'.

(((I need more time ..... in order to 'on-target' comment on this thread))).