A question for Carl_NC or anyone that might know.

[Diga]

Given a field populated by otherwise identical spheres of gold and aluminum, a metal detector could distinguish between the two with 100% accuracy. This is because TID would represent a bijective mapping in this scenario. e.g. All gold balls give TID of 20 and all aluminum balls give TID of 30)

Given a field populated with aluminum and gold objects with randomized properties (shape, size, orientation, etc), a metal detector could not distinguish between the two with any accuracy beyond randomly guessing.

...and since the real world is your 2nd paragraph...we're screwed!

 

[AccurateCalls]

...and since the real world is your 2nd paragraph...we're screwed!

At least as far as hobby metal detecting goes yeah. But perhaps not in Sewage / other particular scenarios...

...which means we need to get our butts down in those sewers and score us some poop gold!

 

[Carl-NC]

So that means the guys who claim they can tell aluminum from gold have managed to break the laws of physics! WOW!

Unless you also have access to mass. A vending machine, for example, could have the ability to reject aluminum slugs that exactly mimic the tau of a coin.

 

[Tom_in_CA]

Nothing in your reply has anything to do with .....

Well, as I read your two posts, I can't help but conclude that TID has *at least* some part of your speculation. WHICH IS FINE ! And all the other musings are sounding like variations on size (by audio), roundness, smooth vs abrupt, and so forth. Which is all within the same category of "ring enhancement" YES YOU DIDN'T USE THAT TERMINOLOGY, but ... it's criss-crossing with what you're saying.

Which is fine. Don't run from it. Many people have tried it . I've even had people (even a dealer, uugghhh) tell me that with practice, you can learn to tell aluminum apart from gold. And their theories and speculations sound sort of like what you're saying.

But the devil is always in the details. No one can ever produce beyond random eventual chance, and selective memory bias.

 

[Cherry Picker]

For the first half of my career, my job was making the impossible happen in the computer world. That is why I have such a tough time accepting someone just claiming it can't be done. I have developed the habit of taking "it can't be done" as a challenge. I mean no offense to those who I refuse to accept that because they, or anyone else, can't do it, it can't be done.

I did a whole lot of it can't be dones for the hospital.

 

[CountyWorker]

For the first half of my career, my job was making the impossible happen in the computer world. That is why I have such a tough time accepting someone just claiming it can't be done. I have developed the habit of taking "it can't be done" as a challenge. I mean no offense to those who I refuse to accept that because they, or anyone else, can't do it, it can't be done.

I did a whole lot of it can't be dones for the hospital.

We just need to get the Japanese into the game.

 

[Rattlehead]

I just have a few questions...

What the hell are all you nerds talking about? Who TF is Eddy and how does he know the difference between aluminum and gold?

 

[Tom_in_CA]

For the first half of my career, my job was making the impossible happen in the computer world. That is why I have such a tough time accepting someone just claiming it can't be done. I have developed the habit of taking "it can't be done" as a challenge. I mean no offense to those who I refuse to accept that because they, or anyone else, can't do it, it can't be done.

I did a whole lot of it can't be dones for the hospital.

Cherry picker, you can not compare the wonderful lightening fast world of computers (and cell phones and digital cameras, etc....) with the topic we're on now. Here's why : All the "impossible things that happened" in computerization were all a function of : Faster and smaller.

But with what we're talking about NOW is : The laws of physics. There is only so much information you can pump into the ground, and only so much information you can extract back OUT of the ground. And : No added amount of "faster and smaller" changes this.

We are looking through SOLID GROUND. Thus there's a 3rd party influence that has nothing to do with "faster and smaller".

Example : In the 1950s, you could scarcely find a detector which could find coin sized objects, right ? (they were mostly all for bigger items, like hubcaps, jars, land mines, etc...)

In the 1960s, lightening fast "impossible" improvements were seen, where ..... now you could find coin sized objects to 4" deep. Woohoo.

Then in the early 1970s, we added TR disc, and then VLF all metal Woohoo

Then in the later 1970s, we came out with VLF disc. Now you could effortlessly cherry pick coins to 8" deep with ease !!

Then in the early 1980s we added TID. Woohoo

Then dept was added during the 1990s, and you could now reliably disc. down to 10 to 11" with ease, blah blah.


Notice that from the 1950s to the 1990s, that : Every 5 or 7 years was an amazing improvement. Such that if you didn't keep up YOU HAD A DINOSAUR . Leaps and bounds at first, but then notice that: the progress slowed down to a crawl. No more amazing leaps. Like today, for example, you could have some 20 to 25 yr. old machine, and still be every bit as competitive as today's machines (albeit maybe having to swap back and forth for different machines depending on venue/objective). But notice the amazing better cell phones, computers, smart phones, cameras, etc.... IN THAT SAME 20 to 25 yrs.

Ask yourself : Why didn't detectors keep improving along that same trajectory path line ? It's because we've hit the point of diminishing returns. You can't break the laws of physics. And no amount of "faster and smaller" (that drove the 'puter revolution) has anything at all to do with this .

 

[jmaclen]

As Carl has alluded to, specific gravity used in the gravity separation part of the ways sewage wastewater companies separate metals would certainly work well for separating aluminum from gold whether it has been shredded or powdered.

 

[Cherry Picker]

Cherry picker, you can not compare the wonderful lightening fast world of computers (and cell phones and digital cameras, etc....) with the topic we're on now. Here's why : All the "impossible things that happened" in computerization were all a function of : Faster and smaller.

But with what we're talking about NOW is : The laws of physics. There is only so much information you can pump into the ground, and only so much information you can extract back OUT of the ground. And : No added amount of "faster and smaller" changes this.

We are looking through SOLID GROUND. Thus there's a 3rd party influence that has nothing to do with "faster and smaller".

Example : In the 1950s, you could scarcely find a detector which could find coin sized objects, right ? (they were mostly all for bigger items, like hubcaps, jars, land mines, etc...)

In the 1960s, lightening fast "impossible" improvements were seen, where ..... now you could find coin sized objects to 4" deep. Woohoo.

Then in the early 1970s, we added TR disc, and then VLF all metal Woohoo

Then in the later 1970s, we came out with VLF disc. Now you could effortlessly cherry pick coins to 8" deep with ease !!

Then in the early 1980s we added TID. Woohoo

Then dept was added during the 1990s, and you could now reliably disc. down to 10 to 11" with ease, blah blah.


Notice that from the 1950s to the 1990s, that : Every 5 or 7 years was an amazing improvement. Such that if you didn't keep up YOU HAD A DINOSAUR . Leaps and bounds at first, but then notice that: the progress slowed down to a crawl. No more amazing leaps. Like today, for example, you could have some 20 to 25 yr. old machine, and still be every bit as competitive as today's machines (albeit maybe having to swap back and forth for different machines depending on venue/objective). But notice the amazing better cell phones, computers, smart phones, cameras, etc.... IN THAT SAME 20 to 25 yrs.

Ask yourself : Why didn't detectors keep improving along that same trajectory path line ? It's because we've hit the point of diminishing returns. You can't break the laws of physics. And no amount of "faster and smaller" (that drove the 'puter revolution) has anything at all to do with this .

Well, I'm not referring to hardware for computers, but the limitations put on what they, the computer as a whole, are capable of. But my point is that I know the Eddy current already contains the information needed to tell gold from aluminum. What we lack is the process to use that information. That is where my computer skills came in. My hands were never tied by the it can't be done often used just because they can't do it yet, so I made it happen because I felt it could happen.

I always felt mass could be a good possible base. All aluminum, including tabs, are a flat thin piece, whereas the vast majority of gold items have much more mass for the same size target. comparing mass to size?

It may never happen, although, I believe in time it will, but I'd love to be around when it does. Before the good lord calls me home, let me witness the ability for a detector to tell gold from aluminum LOL.

 

[Rudy]

So that means the guys who claim they can tell aluminum from gold have managed to break the laws of physics! WOW!

Like Carl and I have both said, Eddy currents alone can not differentiate between aluminum and gold. Anyone that claims otherwise is ...just plain wrong.

 

[tnsharpshooter]

I’ll make it simple for you all.
If and when a vlf detector gets created that can tell gold from aluminum.
How will you know it can do? Hmm
How about the price.
When you see model going for $5K -10k plus in today’s dollars. It might be the one.
You reckon.

 

[Rudy]

<SNIP>

But my point is that I know the Eddy current already contains the information needed to tell gold from aluminum. What we lack is the process to use that information. That is where my computer skills came in. My hands were never tied by the it can't be done often used just because they can't do it yet, so I made it happen because I felt it could happen.
<SNIP>

Eddy current only contains information about the targets conductance and reactance. It does not, in any way, contain the information needed to uniquely tell gold from aluminum.

 

[Tom_in_CA]

Eddy current only contains information about the targets conductance and reactance. It does not, in any way, contain the information needed to uniquely tell gold from aluminum.

Oh golly, but shucks, won't added computer power ("faster and smaller") change that ??

I say it's all just a giant conspiracy, to "keep the technology away from us". Or how about this one: Those lazy metal detector engineer designers are just "asleep at the wheel". Because, shucks, look how far 'puters have come in the last 25 yrs, while detector tech (depth, aluminum from gold, etc...) seems to have hit a standstill.

I smell a rat, don't you ?

 

[Rudy]

I’ll make it simple for you all.
If and when a vlf detector gets created that can tell gold from aluminum.
How will you know it can do? Hmm
How about the price.
When you see model going for $5K -10k plus in today’s dollars. It might be the one.
You reckon.

If high prices are an indication of how well they can make you rich then, you should buy a Long Range Locator (LRL). Someone will get rich and I bet it won't be you.

 

[Diga]

Like Carl and I have both said, Eddy currents alone can not differentiate between aluminum and gold. Anyone that claims otherwise is ...just plain wrong.

Yes, I know Rudy. I thought my emojis showed that I was dripping with sarcasm

 

[tnsharpshooter]

If high prices are an indication of how well they can make you rich then, you should buy a Long Range Locator (LRL). Someone will get rich and I bet it won't be you.

I don’t buy that junk.

 

[Rudy]

Yes, I know Rudy. I thought my emojis showed that I was dripping with sarcasm

Sorry, I didn't see an emoji in your post.

 

[Cherry Picker]

Like Carl and I have both said, Eddy currents alone can not differentiate between aluminum and gold. Anyone that claims otherwise is ...just plain wrong.

This is a compilation of answers from all over the world to can an Eddy current tell the difference between gold and aluminum. You can see why I have a problem just saying you're right and all these others are wrong.

Eddy currents behave differently in gold and aluminum due to their distinct physical properties, especially their electrical conductivity and magnetic permeability. Here are the key factors influencing the behavior of Eddy currents in these two metals:

1. Electrical Conductivity:
   • Gold: Gold has a very high electrical conductivity, which means that it allows electric currents, including Eddy currents, to flow with minimal resistance.
   • Aluminum: Aluminum also has high electrical conductivity, but it is slightly lower than that of gold.
2. Magnetic Permeability:
   • Both gold and aluminum are non-magnetic materials with low magnetic permeability, meaning they do not concentrate magnetic fields.
3. Resistivity:
   • Gold: Gold has a lower resistivity compared to aluminum, resulting in less energy loss when Eddy currents are generated.
   • Aluminum: Aluminum has a higher resistivity compared to gold, which causes more energy loss for the same current.
4. Skin Depth:
   • The skin depth, or the depth at which the current density decreases significantly, is influenced by the material’s conductivity and magnetic permeability. Gold’s higher conductivity results in a smaller skin depth compared to aluminum, meaning Eddy currents are more confined to the surface in gold.

Given these factors, the primary differences in Eddy currents between gold and aluminum are:

• Strength of Eddy Currents: Due to higher conductivity, Eddy currents in gold will be stronger compared to aluminum for the same induced electric field.
• Energy Loss: Aluminum, having higher resistivity, will exhibit more energy loss through Joule heating when Eddy currents are induced.
• Skin Effect: Eddy currents in gold will be more localized near the surface due to its higher conductivity and smaller skin depth, whereas in aluminum, they will penetrate slightly deeper.

In summary, while both gold and aluminum can support Eddy currents, gold will generally exhibit stronger and more surface-confined Eddy currents with lower energy losses compared to aluminum.

 

[Rudy]

This is a compilation of answers from all over the world to can an Eddy current tell the difference between gold and aluminum. You can see why I have a problem just saying you're right and all these others are wrong.

Eddy currents behave differently in gold and aluminum due to their distinct physical properties, especially their electrical conductivity and magnetic permeability. Here are the key factors influencing the behavior of Eddy currents in these two metals:

1. Electrical Conductivity:
   • Gold: Gold has a very high electrical conductivity, which means that it allows electric currents, including Eddy currents, to flow with minimal resistance.
   • Aluminum: Aluminum also has high electrical conductivity, but it is slightly lower than that of gold.
2. Magnetic Permeability:
   • Both gold and aluminum are non-magnetic materials with low magnetic permeability, meaning they do not concentrate magnetic fields.
3. Resistivity:
   • Gold: Gold has a lower resistivity compared to aluminum, resulting in less energy loss when Eddy currents are generated.
   • Aluminum: Aluminum has a higher resistivity compared to gold, which causes more energy loss for the same current.
4. Skin Depth:
   • The skin depth, or the depth at which the current density decreases significantly, is influenced by the material’s conductivity and magnetic permeability. Gold’s higher conductivity results in a smaller skin depth compared to aluminum, meaning Eddy currents are more confined to the surface in gold.

Given these factors, the primary differences in Eddy currents between gold and aluminum are:

• Strength of Eddy Currents: Due to higher conductivity, Eddy currents in gold will be stronger compared to aluminum for the same induced electric field.
• Energy Loss: Aluminum, having higher resistivity, will exhibit more energy loss through Joule heating when Eddy currents are induced.
• Skin Effect: Eddy currents in gold will be more localized near the surface due to its higher conductivity and smaller skin depth, whereas in aluminum, they will penetrate slightly deeper.

In summary, while both gold and aluminum can support Eddy currents, gold will generally exhibit stronger and more surface-confined Eddy currents with lower energy losses compared to aluminum.

All of that is correct. The fly in the ointment is that Aluminum, gold and all other potential targets come in an almost infinite array of sizes (masses). shapes (ie. target's geometrical shape) and orientation (angle between the transmit field and target). All of these factors greatly affect the detector's TID reading.

A couple of simple experiments. Take two otherwise identical gold rings except one is cracked through. Their TID will be different yet their mass and shape is the same. Or take a gold medal, detect it and record the TID. Now measure out the same weight in a gold chain with the same Karat value and detect it. Is the TID the same?

Take an empty aluminum can and detect it. What's the TID? Now squash it flat and detect it again. What's the TID now.

Or take an old fashioned beaver tail pull tab with the tail flat and detect it. What's the TID? Next. fold the tail over the ring several times and detect it again. What's the TID now?