Got to be a reason. Fish finder vs metal detector

[Dancer]

Got a inexpensive fish finder. No trouble detecting fish down to 30 feet, maybe more. Metal detectors fighting to get past a foot.
(Mostly) I know most fish are bigger than a quarter, but anyone got a detector that can air test a aluminum can at 5-10 feet?
Now I'm talking coin shooting not the industrial machines. Ya got to admit the fish finders can get you a ton of information for around 4-5 hundred bucks. Where as its a big deal for a back light to be included on most detectors. Just saying.

Dancer

 

[Dave J.]

Fish finders and metal detectors both work on a transmit-receive principle, but that's all they have in common. Metal detectors work by AC magnetic field dipoles and the signal power vs. "depth" is negative twelfth power. Fish finders are sonar and the signal power vs. "depth" is negative 4th power.

The reason we don't do metal detection by sonar is because soil does a terrible job of transmitting sound. Water on the other hand does a superb job of transmitting sound.

Funny historical note: the VLF induction balance discriminator was patented in the late 1800's as a benchtop unit for distinguishing counterfeit coins from genuine. This was before the invention of the vacuum tube, the thing was entirely electromechanical. But underwater echolocation and imaging is even older than that, cetaceans have been doing that for millions of years.

 

[Dancer]

Fish finders and metal detectors both work on a transmit-receive principle, but that's all they have in common. Metal detectors work by AC magnetic field dipoles and the signal power vs. "depth" is negative twelfth power. Fish finders are sonar and the signal power vs. "depth" is negative 4th power.

The reason we don't do metal detection by sonar is because soil does a terrible job of transmitting sound. Water on the other hand does a superb job of transmitting sound.

Funny historical note: the VLF induction balance discriminator was patented in the late 1800's as a benchtop unit for distinguishing counterfeit coins from genuine. This was before the invention of the vacuum tube, the thing was entirely electromechanical. But underwater echolocation and imaging is even older than that, cetaceans have been doing that for millions of years.[/quote

Dave, glad for your expert input. My question was way above my pay grade.
Along the lines though, does it seem to you the fish/sonar units have progressed much faster than our detectors?
I was reading up on one that claims to be able to see your lure, while stationary of course. Than all the graphics and reduction in prices. Pretty amazing.

 

[Dave_E]

There are fish finders that can see a teardrop size lure, while moving, while ice fishing.

 

[Tom_in_CA]

Dancer, to the degree that sonar fish finders (and cell phones and computers, etc....) have seen more advancements than metal detectors, is d/t the laws of physics Dave was telling you about. No amount of "smaller and faster" electronics, and nothing that sonar-fish finders do, will change the fact that soil (terra firma) is extremely difficult to see through. Versus water, which is easy to see through. You can't change the laws of physics.

 

[still looking 52]

Not sure I would want a metal detector that could detect down five feet, that's like digging a grave. There could be some commercial reasons for a machine like that but not for the average metal detector.
Talking about sonar, the Navy is still trying to get sonar as good as a dophin but hasn't got there yet.

 

[Flintstone]

If a detector could go 5' and could tell what you were looking at, I would dig 5' for a 20.00 gold coin or two.

 

[vlad]

was used to find the bodies of some Scots killed--I think during the time of Robert The Bruce. I believe a transponder was used along with water to make the transmission work.
Some type of image on a screen showed skeletons, accoutrements and weapons--so there is something to it.
Whether ultrasound or what, I just don't recall.
The bigger problem with metal detectors is the amount of unwanted targets to be found--or a straight P.I. of high power would be the end all of finding things.
(Go to Nasa Tom's Forum and read his articles on "The Painful Truth" (about masking) in his hunts on some forts from the Seminole Wars....you will see what I mean)

 

[vlad]

which will go so deep (in bad ground) you need a backhoe.
The problem though is it is for large targets and has no resolution on a coin {s}.
The same holds true on constant wave (TR) units.

 

[ROBOCOP]

Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.

 

[bootyhoundpa]

Ground penetrating rader might give you a little extra depth,lol.

 

[Dancer]

Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.

Wow, now ain't that something! Some pretty smart cookies on this site.

 

[stephenscool]

Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.

A lot of potential in something like this. It,could be used a discriminator in a pi. The idea needs some tweeking and trial and error though... lots of potential

 

[vlad]

n/t

 

[Tom_in_CA]

Magnetometers technology is also very interesting. ....

Magnetometers are only for finding iron. But the metal detector hobbyists , as you know, TRY THEIR DURNDEST NOT to find iron. We all go out of our way to reject iron. Unless, of course, you're looking for 5 ft. deep iron cannon-balls I suppose. Or scanning the ocean floor for shipwreck sites.

But for the casual metal detector, they are of no use. Unless you're objective is to dig the most nails you can find ? If so, then you really don't even need a "magnetometer". You merely turn on your detector, put it into all-metal mode, head out to the nearest ghost town or cellar hole. Then I GUARANTEE you that you will no shortage or iron to choose from

 

[Tom_in_CA]

Ground penetrating rader might give you a little extra depth,lol.

For GPR, the trouble is, and always will be: Pixel size. The smallest the pixel resolution is, is about 1" across squares. Thus anything that md'rs look for (rings, tabs, coins, nails, foil wads, etc...) are all ........ doh .... one pixel. And as far as their depth, I believe you can accomplish the same depth on larger sized targets with most 2 box machines.

And d/t the inhospitable ground through which it must see through (solid terra firma) I don't think we're going to see the pixel size or depth improve. And even if the pixel sizes came down to a fraction of what they are now (1/10" inch, let's say), I bet it would still be useless for the average md'r. You are simply NOT going to see magical ring or coin shapes (as if you were viewing a TV, or fish on a sonar where you can tell the difference between species of fish even).

The reason is: Everything would still be nothing but a "mess of blotchy pixels". Here's an example of what I mean: Consider a horseshoe. That has a distinct and large (7" x 5") shape, right ? And there's no mistaking the tell-tale "shape" of a horseshoe, right ? But even at 1" pixels, guess what you see ? Nothing but a mess of blotchy pixels. Not a "horseshoe shape". So to apply this logic to ... let's say ... a pulltab with a beaver tail versus a round coin (or ring) with no "tail": Even at 1/10" pixel size, you STILL only see a "mess of blotchy pixels". Not a magical tab versus ring shape. And also: The moment you add the SLIGHTEST tilt, you can kiss shape-showing goodbye.

 

[Dancer]

Ground penetrating rader might give you a little extra depth,lol.

For GPR, the trouble is, and always will be: Pixel size. The smallest the pixel resolution is, is about 1" across squares. Thus anything that md'rs look for (rings, tabs, coins, nails, foil wads, etc...) are all ........ doh .... one pixel. And as far as their depth, I believe you can accomplish the same depth on larger sized targets with most 2 box machines.

And d/t the inhospitable ground through which it must see through (solid terra firma) I don't think we're going to see the pixel size or depth improve. And even if the pixel sizes came down to a fraction of what they are now (1/10" inch, let's say), I bet it would still be useless for the average md'r. You are simply NOT going to see magical ring or coin shapes (as if you were viewing a TV, or fish on a sonar where you can tell the difference between species of fish even).

The reason is: Everything would still be nothing but a "mess of blotchy pixels". Here's an example of what I mean: Consider a horseshoe. That has a distinct and large (7" x 5") shape, right ? And there's no mistaking the tell-tale "shape" of a horseshoe, right ? But even at 1" pixels, guess what you see ? Nothing but a mess of blotchy pixels. Not a "horseshoe shape". So to apply this logic to ... let's say ... a pulltab with a beaver tail versus a round coin (or ring) with no "tail": Even at 1/10" pixel size, you STILL only see a "mess of blotchy pixels". Not a magical tab versus ring shape. And also: The moment you add the SLIGHTEST tilt, you can kiss shape-showing goodbye.

Tom, I believe everything you said. But
Remember when the Earth was flat, can't put a man on the moon, team going from last to first, horseless carriages, all these were impossible too. The pixels will shrink, we just might be around to see it. Lol

 

[Tom_in_CA]

..... Tom, I believe everything you said. But
Remember when the Earth was flat, can't put a man on the moon, team going from last to first, horseless carriages, all these were impossible too. The pixels will shrink, we just might be around to see it. Lol

Couple of responses:

a) The fact that science once-thought the earth was flat, or that heavier-than-air-flight was impossible, does not .... ergo ... mean: "Anything is possible". No more so than saying it's impossible to fit the Empire State building into a plastic sandwich baggie. Someone could say "You can't say that's impossible because .... after all, they once thought the earth was flat". Does not logically follow.

b) As I said in my post: Even if/when pixel sizes shrink (even to 10x better, for example), you still do not get a magical X-ray television quality picture. You will just have a messy blotch of pixels. And that the moment you add the slightest tilt, you can kiss shape showing goodbye. You can't change the laws of physics. Heavier than air flight, for example, did not change the laws of physics.

c) Something entirely new and different would need to come along. Not just "faster and smaller" changes to existing knowledge/tech. There has reached a point of diminishing returns on the metal detection techniques we currently use (VLF, TR, PI, GPR, etc....). That's why you notice ground-breaking leaps and strides during the mid 1960s to the mid 1980s, when all of this was developed and invented. Right ? Back then if your detector was a mere 3 yrs. old, you had a dinosaur , haha. But now, we have machines 10 or 15 yrs. in production, that are every bit as good as current offerings. Because technology's "faster and smaller" has reached a point where the laws of physics are involved. If something altogether different, that doesn't rely on existing transmit/receive methods, then there might be something to talk about.

 

[vlad]

It could be clipped onto the loop or shaft, & could be left turned on, or as needed. It would work on large iron but not very well on small,
Objects like a nail, washer or bottlecaps were difficult; orientation of the object, vertical vs horizontal made a difference. (vertical worked better)
Jimmy Sierra tried it with his units and said it just did not work.
Consider it a first step showing promise with a lot of development needed. (Mr.Bill has some knowledge of the ferr. hound)

 

[Dancer]

Some of a lot of what I say is baseless or tongue in cheek. But there's new frontiers being made all over. Like cancer cures, time machines, the Military is tinkering with invisibility. Cloning ,time warps, we can't even guess what's coming next. Not long ago no one believed in life in outer space, global warming. Much of this hasn't been proven of course. But they just made driverless cars.
Does anyone really believe that metal detector science has hit the wall? I don't know how long it'll take, but when it happens it won't be by a quarter inch. Just saying.