TGSL Experiments

[6666]

Thanks for sharing your results all
is it just an illusion or is the mylar damaged

[der_fisherman]

This mylar stuff is a bit of a witch to work with...

Tried wrapping a strip. I estimate it may overlap such as to give 3 layer thickness, not sure.

-SB

Your strip is too wide I feel, try making it thinner and keeping the overlap down to one overlap of no more than max 5mm wherever possible. On corners you may have to go slightly more overlap, but still only one max....that's how I did it with kitchen foil.
My next one will be with real silver leaf.....
Best of luck.
Andy

[simonbaker]

Thanks for sharing your results all
is it just an illusion or is the mylar damaged

It doesn't show in the photo -- you're probably seeing reflections.

However, if you hold the mylar up to the light, you can see the coating is rubbed off in places along creases.

This stuff is witchy. Even after wrapping the coil with a ground wire, there are disconnected sections.

I need higher quality coated mylar I guess. But maybe this stuff will give some data.

-SB

[simonbaker]

Your strip is too wide I feel, try making it thinner and keeping the overlap down to one overlap of no more than max 5mm wherever possible. On corners you may have to go slightly more overlap, but still only one max....that's how I did it with kitchen foil.
My next one will be with real silver leaf.....
Best of luck.
Andy

Ok, that's an idea for next time. I'm not sure my strips are long enough to use thinner ones.

I'll see what the data looks like with these, then try again with better mylar if I can find some. I'll do kitchen foil next.

-SB

[der_fisherman]

Layering of shield on coil

Ok, that's an idea for next time. I'm not sure my strips are long enough to use thinner ones.
I'll see what the data looks like with these, then try again with better mylar if I can find some. I'll do kitchen foil next.SB

Sorry, I was not clear enough in what I wrote, my apologies. I am only recommending "narrow strips", not Aluminium foil.

I am of the opinion now, rightly or wrongly - who knows?, through reading Geotech, that maybe Aluminium is not as good as other stuff around. The opinion of several people here (knowledgeable ones like yourself) is that thinner is better.....it could well be true.

Originally Mylar blankets was my next port of call till I read the other posts....and I still think that is probably the best shield around for the price, provided that all the strips used are the same way round and make good contact with the ground wire.

I also think that putting the conductive side outwards with Mylar (careful set up and testing of the strips before starting is called for to stop accidentally putting one on the wrong way round) is the best way, securing the ends of each strip with either contact adhesive or super glue to the coil and the previous strip.

Then winding the ground wire on top of the shield, checking with an Ohmmeter that each portion is electrically making good contact with that wire......and that the loop of the shield has a space in it (eg. its not a full circle).

There is some thought around as to EXACTLY how wide the space should be, maybe this also has an effect on the working of the MD, I certainly do not know..I used about 1.5 CM gap on my last coil and alufoil!!! But the MD is NOT working as I wish, still playing....a new coil is almost on the horizon....

Then I use insulating tape to hold the ground wire firmly on the foil, wound as tight as I can make it.

Sometime this year I want to make a new coil with Mylar shield and also another one with silver leaf (its not as expensive as many believe as I estimate it will only add about $10 to the total cost, maybe even less). Don't hold me to a date though!!

Silver leaf is only a few millionths of a meter thick.......according to some here (and they could well be right!), that should be good for the best operation of the MD!!! We will see!!

Regards

Andy

PS. Silver & Gold leaf is about 4 microns thick, that is (if my maths don't let me down!):

Silver and Gold leaf = 0.000004 mm
Then its Alumium Foil = 0.0125 = over 3000 x thicker.....!!!!(from my kitchen!)aprox..
What a difference......Sadly I don't have Mylar handy to measure, I guess it will fall somewhere in between......
IMPORTANT!!!
To anyone measuring thickness of very thin material, fold the material (and accurately note how many times) AT LEAST 4 times, that means the result needs to be divided by 16.

This makes the accuracy of the measurement much better. I use an electronic vernier gauge with a best accuracy value of Plus/minus 0.0005mm, so folding the sample improves the accuracy somewhat with such units.

If using a micrometer, do use the slipping clutch on the end of the handle.....and fold a lot!!

[simonbaker]

Sorry, I was not clear enough in what I wrote, my apologies. I am only recommending "narrow strips", not Aluminium foil.

Yes I understood, but I had too much momentum so I finished a test using wide strips. Narrow does sound better, so if I can locate some better quality aluminized mylar, I hope to try again.

Overall, I'm trying to compare the effects of various shield types on the null signal voltage vs phase relationship. Probably won't be that important, but an easy experiment for me. Eventually, we want to see how the different shields affect MD operation, particulary depth.

I am of the opinion now, rightly or wrongly - who knows?, through reading Geotech, that maybe Aluminium is not as good as other stuff around. The opinion of several people here (knowledgeable ones like yourself) is that thinner is better.....it could well be true.

You may be correct; let's try to find out. The importance of kitchen foil is that it is so convenient, cheap, and easy to work with. One of my goals is to find the easiest, cheapest, simplest MD for hobbiests to build that still works quite well. If it loses a couple of centimeters of depth, that is probably OK for the purpose.

The other goal of course is to keep improving our techniques and make deeper and better MDs. However, I tend to look for clever ways to do it rather than exotic or expensive construction techniques.

Originally Mylar blankets was my next port of call till I read the other posts....and I still think that is probably the best shield around for the price, provided that all the strips used are the same way round and make good contact with the ground wire.

I also think that putting the conductive side outwards with Mylar (careful set up and testing of the strips before starting is called for to stop accidentally putting one on the wrong way round) is the best way, securing the ends of each strip with either contact adhesive or super glue to the coil and the previous strip.

Then winding the ground wire on top of the shield, checking with an Ohmmeter that each portion is electrically making good contact with that wire......and that the loop of the shield has a space in it (eg. its not a full circle).

There is some thought around as to EXACTLY how wide the space should be, maybe this also has an effect on the working of the MD, I certainly do not know..I used about 1.5 CM gap on my last coil and alufoil!!! But the MD is NOT working as I wish, still playing....a new coil is almost on the horizon....

Then I use insulating tape to hold the ground wire firmly on the foil, wound as tight as I can make it.

Sounds like good advice. I toyed with the idea of the reverse order, using the mylar strip for double purpose -- to tightly wrap over the ground wire, and leave the insulating side upward so you don't need to worry about insulating the two shields from each other and skip the final tape wrap. But the stuff is too devilish, I'd go with your technique for stability.

Sometime this year I want to make a new coil with Mylar shield and also another one with silver leaf (its not as expensive as many believe as I estimate it will only add about $10 to the total cost, maybe even less). Don't hold me to a date though!!

Silver leaf is only a few millionths of a meter thick.......according to some here (and they could well be right!), that should be good for the best operation of the MD!!! We will see!!

Regards

Andy

PS. Silver & Gold leaf is about 4 microns thick, that is (if my maths don't let me down!):

Silver and Gold leaf = 0.000004 mm
Then its Alumium Foil = 0.0125 = over 3000 x thicker.....!!!!(from my kitchen!)aprox..
What a difference......Sadly I don't have Mylar handy to measure, I guess it will fall somewhere in between......
IMPORTANT!!!
To anyone measuring thickness of very thin material, fold the material (and accurately note how many times) AT LEAST 4 times, that means the result needs to be divided by 16.

This makes the accuracy of the measurement much better. I use an electronic vernier gauge with a best accuracy value of Plus/minus 0.0005mm, so folding the sample improves the accuracy somewhat with such units.

If using a micrometer, do use the slipping clutch on the end of the handle.....and fold a lot!!

Interesting ideas that seem promising. Thin shields seem more appealing than thick ones; we just need some good tests to show it.

I'm still not sure exactly what the shields are doing for us. I believe some manufacturers are "painting" on shields that are low-conductivity, such as graphite mixtures -- so are high-conductivity shields really necessary? Depends on what they are supposed to do I guess. If it's to discharge static buildup, higher resistance should be fine. If it is EMI blocking (I am very skeptical), then high conductivity seems necessary. Also, PI and VLF detectors may have different shielding requirements. I read all kinds of statements and theories, but I'd like to see some experiments verifying the claims.

Cheers,

-SB

[simonbaker]

nulling comparison - mylar shields and cables

Here is another graph of the "Rx null signal", comparing cable/coil shield combinations:

1. USB cable, no coil shields.
2. Belden cable, no coil shields.
3. USB cable, mylar-aluminum coil shields.
4. Belden cable, mylar-aluminum coil shields.

As usual, the graph plots the Rx voltage vs phase while shifting the coil overlap from one side of null to other.

Conclusions:

A) The Belden cable plus mylar shielded coil combo looks the most "ideal", with the deepest, squarest curve.

B) The choice of cable is more influential than the mylar shield/unshielded choice on the nulling graph.

C) Mylar-aluminum shields seem to actually reduce what I call the "capacitive" (or non-magnetic) coupling effect between the RX and TX signals. I conclude this because the mylar shielded cases have a more "square" graph which is more like a pure transformer.

Note: my mylar-aluminum shields are not perfect. I'm fairly sure some small sections were not grounded.

Note also that this does not imply any combination is "better" for detecting targets -- that requires a field test.

It will be interesting to see how aluminum foil shields compare.

-SB

[der_fisherman]

Thickness comparison of shielding foils and leaves.

Interesting ideas that seem promising. Thin shields seem more appealing than thick ones; we just need some good tests to show it.
I'm still not sure exactly what the shields are doing for us. I believe some manufacturers are "painting" on shields that are low-conductivity, such as graphite mixtures -- so are high-conductivity shields really necessary? Depends on what they are supposed to do I guess. If it's to discharge static buildup, higher resistance should be fine. If it is EMI blocking (I am very skeptical), then high conductivity seems necessary. Also, PI and VLF detectors may have different shielding requirements. I read all kinds of statements and theories, but I'd like to see some experiments verifying the claims.
Cheers,
-SB

Simon, I some how feel that we are on a very similar wavelength, though a lot needs to be proved for us all here. I hope people like Don B. and others are keeping a close eye on us and will "nudge" us back to the straight and narrow if we stray too far away.

I think it was Don that posted something some time ago that tended to support thinner shielding material, as well as telling us what the shield actually does (from memory, it helps "against" such things as wet grass, provided the shield is properly connected using good cable and no ground loops. Don, can you put that into a better wording for me and everyone else please?). Static being a possibility that it shields the coil from, but I vaguely remember something else, the "magnetic" effects of some sort maybe......

It was that and what someone else wrote (sorry, I forget who it was) about that real silver has/should have really good shielding properties, that I think real Gold leaf may exhibit even better as its an even better conductor! But I won't bet my life on it yet, it must be tested fully first!!

Today I looked at Mylar from a crisp packet and it is quite thick, I was very surprised, but it was NOT from a blanket. The Crisp packet was 0.04mm thick.........thicker than
From before.

So to summarise:-:-
Silver and Gold leaf = 0.000004 mm
Then its Aluminium Foil = 0.0125 = over 3000 x thicker.....!!!!(from my kitchen!)aprox..
Mylar from Crisps packet = 0.04mm or 10,000 times thicker than Gold/Silver leaf....
Can someone measure a Mylar blanket for me? (us!), if it's the same tickness as I measured we must not forget that the "carrier" plastic is relatively thick, but the metal deposited is far far thinner, I would think similar to Gold and Silver leaf at a guess. The question is then simply,"Is it Aluminium or not?". Does anyone know of an easy test for metal type? Possibly or similar to:-

http://heavymetalstest.com/aluminiumtest.php

Regards

Andy

[simonbaker]

Simon, I some how feel that we are on a very similar wavelength, though a lot needs to be proved for us all here. I hope people like Don B. and others are keeping a close eye on us and will "nudge" us back to the straight and narrow if we stray too far away.

I think it was Don that posted something some time ago that tended to support thinner shielding material, as well as telling us what the shield actually does (from memory, it helps "against" such things as wet grass, provided the shield is properly connected using good cable and no ground loops. Don, can you put that into a better wording for me and everyone else please?). Static being a possibility that it shields the coil from, but I vaguely remember something else, the "magnetic" effects of some sort maybe......

It was that and what someone else wrote (sorry, I forget who it was) about that real silver has/should have really good shielding properties, that I think real Gold leaf may exhibit even better as its an even better conductor! But I won't bet my life on it yet, it must be tested fully first!!

Today I looked at Mylar from a crisp packet and it is quite thick, I was very surprised, but it was NOT from a blanket. The Crisp packet was 0.04mm thick.........thicker than
From before.

So to summarise:-:-
Silver and Gold leaf = 0.000004 mm
Then its Aluminium Foil = 0.0125 = over 3000 x thicker.....!!!!(from my kitchen!)aprox..
Mylar from Crisps packet = 0.04mm or 10,000 times thicker than Gold/Silver leaf....
Can someone measure a Mylar blanket for me? (us!), if it's the same tickness as I measured we must not forget that the "carrier" plastic is relatively thick, but the metal deposited is far far thinner, I would think similar to Gold and Silver leaf at a guess. The question is then simply,"Is it Aluminium or not?". Does anyone know of an easy test for metal type? Possibly or similar to:-

http://heavymetalstest.com/aluminiumtest.php

Regards

Andy

I agree, I'll bet the conductive coating on the mylar blanket is extremely thin; have no idea how to measure. If you ever cut some long strips of mylar, try putting an ohmmeter probe at one end and then test along the length of the strip to see if you have conductivity everywhere.

I hope you or someone can eventually do depth tests with different shields and some field tests too to get some performance data. I'd like to quantify it; if mylar is better than foil, how much better? etc.

-SB

[Jerry]

I agree, I'll bet the conductive coating on the mylar blanket is extremely thin; have no idea how to measure. If you ever cut some long strips of mylar, try putting an ohmmeter probe at one end and then test along the length of the strip to see if you have conductivity everywhere.

I hope you or someone can eventually do depth tests with different shields and some field tests too to get some performance data. I'd like to quantify it; if mylar is better than foil, how much better? etc.

-SB

I would like to be able to quantify it also but at this point I am not convinced that it is going to have a great influence on depth. The TGSL coil I made a couple years ago used aluminum tape meant for furnace duct pipes and is pretty heavy stuff but I was able to get well over 32 cm air tests with 20 cm (8 inch) coil. I bought a mylar blanket last fall with the intent on making another test coil but life got in the way and have been busy providing health care for the wife ever since.

I did some experiments many years ago that I think may be shed some light on what we are talking about. I used to be into AM broadcast band and Long Wave DXing.
I still have a couple of antenna's that are a quarter mile long left over from those days and they still work.

For a couple years I was really into small loop antennas since they provided a very sharp null for direction finding. I made many unshielded loops which worked well but picked up a lot of noise. I then started shielding them and one of the very best loop antenna's I made was shielded with half inch (12.5mm) diameter copper tubing. I would post a picture of it but I dont have it anymore. That was at least 20 years ago.

My point is the construction was pretty much the same as one our our metal detecting coils except it was much larger and was only one loop. It also had a half inch air gap.

The difference in performance was amazing. If you put your hand close to an unshielded loop it would de-tune and were a pain to adjust because of this. No so with my copper tubing loop, I could grap the loop and move it anywhere I wanted and it would not detune at all.

The overall receiving performance of the shielded loop was far better than unshielded because it was much quieter which permitted the reception of weaker signals, and it was not touchy to make adjustments with.

I know we are talking apples and oranges but at the same time I think there are enough similarities to make it valid food for thought. I am certainly not going to advocate making a metal detector coil shielded with copper tubing but you have to admit it would be an "interesting" experiment.

Jerry

[simonbaker]

I would like to be able to quantify it also but at this point I am not convinced that it is going to have a great influence on depth. The TGSL coil I made a couple years ago used aluminum tape meant for furnace duct pipes and is pretty heavy stuff but I was able to get well over 32 cm air tests with 20 cm (8 inch) coil. I bought a mylar blanket last fall with the intent on making another test coil but life got in the way and have been busy providing health care for the wife ever since.

I did some experiments many years ago that I think may be shed some light on what we are talking about. I used to be into AM broadcast band and Long Wave DXing.
I still have a couple of antenna's that are a quarter mile long left over from those days and they still work.

For a couple years I was really into small loop antennas since they provided a very sharp null for direction finding. I made many unshielded loops which worked well but picked up a lot of noise. I then started shielding them and one of the very best loop antenna's I made was shielded with half inch (12.5mm) diameter copper tubing. I would post a picture of it but I dont have it anymore. That was at least 20 years ago.

My point is the construction was pretty much the same as one our our metal detecting coils except it was much larger and was only one loop. It also had a half inch air gap.

The difference in performance was amazing. If you put your hand close to an unshielded loop it would de-tune and were a pain to adjust because of this. No so with my copper tubing loop, I could grap the loop and move it anywhere I wanted and it would not detune at all.

The overall receiving performance of the shielded loop was far better than unshielded because it was much quieter which permitted the reception of weaker signals, and it was not touchy to make adjustments with.

I know we are talking apples and oranges but at the same time I think there are enough similarities to make it valid food for thought. I am certainly not going to advocate making a metal detector coil shielded with copper tubing but you have to admit it would be an "interesting" experiment.

Jerry

Well, that is interesting information and gets me thinking. I could see that a grounded shield could help isolate the antenna from coupling to nearby conductors/grounds such as your hand. The real problem with your hand is that the coupling is changing, which basically modulates something and makes trouble. The shield may be similar to your hand, but at least it is very constant.

I would like to see a picture of the shielding arrangement you used. Did it have the gap we leave in our coil shields?

I don't yet understand what kind of fields a "toroidal" shield blocks. Mainly static, or also changing (like radiation or our near-field TX signals)?

My thinking is that in some ways the shield resembles strongly the loop of wire contained inside it, and that any longitudinal current in the shield would couple strongly to the interior loop -- in a sense, it is just like another transformer winding. Also, how does it block "noise" without blocking signal?

I'd like to know the theory, but usually these things are described at the practical level, and often authors assume things they haven't really proved.

I hope we can keep thinking about it and maybe dig up more info.

Regards,

-SB

[der_fisherman]

I would like to be able to quantify it also but at this point I am not convinced that it is going to have a great influence on depth. The TGSL coil I made a couple years ago used aluminum tape meant for furnace duct pipes and is pretty heavy stuff but I was able to get well over 32 cm air tests with 20 cm (8 inch) coil. I bought a mylar blanket last fall with the intent on making another test coil but life got in the way and have been busy providing health care for the wife ever since.

I did some experiments many years ago that I think may be shed some light on what we are talking about. I used to be into AM broadcast band and Long Wave DXing.
I still have a couple of antenna's that are a quarter mile long left over from those days and they still work.

For a couple years I was really into small loop antennas since they provided a very sharp null for direction finding. I made many unshielded loops which worked well but picked up a lot of noise. I then started shielding them and one of the very best loop antenna's I made was shielded with half inch (12.5mm) diameter copper tubing. I would post a picture of it but I dont have it anymore. That was at least 20 years ago.

My point is the construction was pretty much the same as one our our metal detecting coils except it was much larger and was only one loop. It also had a half inch air gap.

The difference in performance was amazing. If you put your hand close to an unshielded loop it would de-tune and were a pain to adjust because of this. No so with my copper tubing loop, I could grap the loop and move it anywhere I wanted and it would not detune at all.

The overall receiving performance of the shielded loop was far better than unshielded because it was much quieter which permitted the reception of weaker signals, and it was not touchy to make adjustments with.

I know we are talking apples and oranges but at the same time I think there are enough similarities to make it valid food for thought. I am certainly not going to advocate making a metal detector coil shielded with copper tubing but you have to admit it would be an "interesting" experiment.

Jerry

Love the post AND the humour too, thanks.
Andy

[golfnut]

Im with you here Jerry.

A wrapped sheild is sort of dicontinuous, as the wraps dont form a tube more an inductive and resistive spiral.

Commericial loops have a solid brass/bronze tube

S

[dfbowers]

Simon, I some how feel that we are on a very similar wavelength, though a lot needs to be proved for us all here. I hope people like Don B. and others are keeping a close eye on us and will "nudge" us back to the straight and narrow if we stray too far away.

I think it was Don that posted something some time ago that tended to support thinner shielding material, as well as telling us what the shield actually does (from memory, it helps "against" such things as wet grass, provided the shield is properly connected using good cable and no ground loops. Don, can you put that into a better wording for me and everyone else please?). Static being a possibility that it shields the coil from, but I vaguely remember something else, the "magnetic" effects of some sort maybe......

It was that and what someone else wrote (sorry, I forget who it was) about that real silver has/should have really good shielding properties, that I think real Gold leaf may exhibit even better as its an even better conductor! But I won't bet my life on it yet, it must be tested fully first!!

Today I looked at Mylar from a crisp packet and it is quite thick, I was very surprised, but it was NOT from a blanket. The Crisp packet was 0.04mm thick.........thicker than
From before.

So to summarise:-:-
Silver and Gold leaf = 0.000004 mm
Then its Aluminium Foil = 0.0125 = over 3000 x thicker.....!!!!(from my kitchen!)aprox..
Mylar from Crisps packet = 0.04mm or 10,000 times thicker than Gold/Silver leaf....
Can someone measure a Mylar blanket for me? (us!), if it's the same tickness as I measured we must not forget that the "carrier" plastic is relatively thick, but the metal deposited is far far thinner, I would think similar to Gold and Silver leaf at a guess. The question is then simply,"Is it Aluminium or not?". Does anyone know of an easy test for metal type? Possibly or similar to:-

http://heavymetalstest.com/aluminiumtest.php

Regards

Andy

Andy,

My first experience with mylar was when I built my second HH1 coil. I used mylar instead of aluminum tape for duct work. I noticed that the sensitivity was better with the mylar shielded coil. I did not take a very scientific approach to measuring the difference so my comments were purely subjective.

I dismissed the idea for a while until I started building TGSL coils and I made a similar observation when I switched to mylar. Again, my comments were purely subjective. I can tell you with 100% certainty the coil sensitivity was no worse that when using heavy aluminum duct tape. So, I am happy that Simon is kicking around the idea of quantifying the differences. It would only make sense though that a coil would perform better if it could not detect the material that is shielding it. I think the only way to do a side by side comparison would be to test one method, and then tear the shield off and install new shield on the same pair of coils.

Since I feel that I can build coils adequate for my purposes, and I have no issues with wet grass anymore I'm beating a dead horse. That's not to say that I would not want to learn the scientific reason why!!!

I have seen in one of my older books where a copper tube bent into an incomplete circle could be used for shielding as well.. along with a simple Faraday cage built with a bare wire wrap and several other methods. These were mostly for the old BFO type coils.

As far as the wet grass problems I can only conclude that it might have something to do with using a USB-2 cable instead of of individually shielded pairs like a Belden-M (8723) cable. Since Tesoro builds all their coils with a common ground inside the coil it adds merit to building that way. I can only say that I have been unsuccessful with several coils built to the Tesoro spec and totally successful with keeping the shield ground separate from the coil grounds. I even went to the trouble to completely build two coils to verify. At any rate, the mylar shielding method does it's job well at "shielding".

Don

[der_fisherman]

Valuable input Don, even if as you say, slightly subjective, many thanks....I do feel that its more than just an impression....
regards
Andy