Optimum coil shielding method/material

[Monk]

What is the optimum (material) way to shield Induction Balance and PI coils?

My list of materials includes:

Copper foil tape
Aluminum foil tape
Scotch 24 Screen
Super Shield Nickel Conductive Coating
Graphite Spray

Thanks.

Monk

[mikebg]

NO SHIELDING!

Monk, I think your term "PI coil" means "Monocoil". I have a wideband (PI) metal detector, which operates much better than the conventional PI with Monocoil sensor, because my search head contains IB (induction balanced) TX and RX windings.
Coil shielding involves a serious problem for induction balance in wideband metal detectors (PI). The eddy currents in coil shielding and in cable shielding make impossible to adjust whole induction balance for all frequencies in the operating spectrum.
The best design solution for an IB search head is NO SHIELDING.
To avoid shielding in electronics is used circuit symmetry. For example we can make the RX winding with center tap and connect it to ground, but more easy is to use full differential front end or a single preamp with input symmetry. Look how simple is the circuit of front end in a TWIN LOOP metal detector when we use amplifier with input symmetry, for example LM386.

[maikl]

What is the optimum (material) way to shield Induction Balance and PI coils?

My list of materials includes:

Copper foil tape
Aluminum foil tape
Scotch 24 Screen
Super Shield Nickel Conductive Coating
Graphite Spray

Thanks.

Monk

The best is this: "Graphite Spray"- Graphite-based Conductive Lacquer (http://www.itwcp.de/contentcenter/co...odukte_en.html)."Copper Spray"- Effective Shielding from Electromagnetic Waves (http://www.itwcp.de/contentcenter/co...odukte_en.html). A good finish would be a simple job aluminum foil (thin kitchen).

[mikebg]

Symmetry in TX power amp

And here is a symmetrical circuit diagram of transmitter that uses the same type of IC as in preamp - LM386.

[porkluvr]

What is the optimum (material) way to shield Induction Balance and PI coils?

My list of materials includes:

Copper foil tape
Aluminum foil tape
Scotch 24 Screen
Super Shield Nickel Conductive Coating
Graphite Spray

Thanks.

Monk

Don't use the nickel spray in your search head. Nickel acts like an iron target.
You shouldn't just throw IB and PI coils into one basket and expect that what works well for shielding (gluing, etc.) for one type coil should be also good for the other.

[Monk]

Don't use the nickel spray in your search head. Nickel acts like an iron target.
You shouldn't just throw IB and PI coils into one basket and expect that what works well for shielding (gluing, etc.) for one type coil should be also good for the other.

Sorry that I did not ask the question more clearly. I do understand the difference between Induction Balance (transmit-receive) and Pulse Induction (typically mono coil). I was asking for shielding experienced/opinions for each.

I found this forum back in December 2009 and as I stated back then I've always had a yearning to build a metal detector after my first experience back in 1968-1969 with my father's metal detector. And finding this forum has rekindled my interest in doing so.

From these forums I have learned that coil construction is probably the biggest variable with respect to obtaining good/repeatable performance. And therefore I spent a lot of time trying to create the capability to produce good coils. My first attempts were very crude simply winding wire around a jig made from particle board and pieces of 1/4 inch wood dowels.

I became very interested in the work of dfbowers and simonbaker and their attempts to wind tight and repeatable coils. After much trial and error I've come up with a way to produce tight and repeatable coils in approximately 7 or eight different configurations. Having tight and repeatable quote is very important to determine optimum parameters such as shielding (hence my original question).

I'm posting a few pictures of what I've achieved thus far. I will have more as time permits. The coils shown were wound with 30gauge enameled, 25.4 cm. One coil is 100 turns, 6.0 mhH and 19.3 ohms. The other coil is 110 turns, 6.2 mH and 19.6 ohms.

Each individual coil takes approximately 30 minutes to produce not counting cure time.

[detectormods]

Best shielding is metallic mesh as it reduces rf interference, big flat sections of graphite material induce huge shield to ground capacitance and can upset ground balance.

[Rov]

Best shielding is metallic mesh as it reduces rf interference, big flat sections of graphite material induce huge shield to ground capacitance and can upset ground balance.

But the commercial manufacturers,still persist in using it to effect ok.as you know im sure.looks pretty rough an sloppy construct in some of them,an just taped fine shield wires to a graphite painted paper sheet.an a smear of paint here or there gets them by.

[detectormods]

It would cost 25% using better material and incorporate adjustable coil damping. Everything is built using the cheapest materials, so we get sub par coils.

[dfbowers]

Sorry that I did not ask the question more clearly. I do understand the difference between Induction Balance (transmit-receive) and Pulse Induction (typically mono coil). I was asking for shielding experienced/opinions for each.

I found this forum back in December 2009 and as I stated back then I've always had a yearning to build a metal detector after my first experience back in 1968-1969 with my father's metal detector. And finding this forum has rekindled my interest in doing so.

From these forums I have learned that coil construction is probably the biggest variable with respect to obtaining good/repeatable performance. And therefore I spent a lot of time trying to create the capability to produce good coils. My first attempts were very crude simply winding wire around a jig made from particle board and pieces of 1/4 inch wood dowels.

I became very interested in the work of dfbowers and simonbaker and their attempts to wind tight and repeatable coils. After much trial and error I've come up with a way to produce tight and repeatable coils in approximately 7 or eight different configurations. Having tight and repeatable quote is very important to determine optimum parameters such as shielding (hence my original question).

I'm posting a few pictures of what I've achieved thus far. I will have more as time permits. The coils shown were wound with 30gauge enameled, 25.4 cm. One coil is 100 turns, 6.0 mhH and 19.3 ohms. The other coil is 110 turns, 6.2 mH and 19.6 ohms.

Each individual coil takes approximately 30 minutes to produce not counting cure time.

Hey, that looks good! Do you have a pic of your forms? Do you put the wire on "sticky" or apply glue after you wind?

[Monk]

Hey, that looks good! Do you have a pic of your forms? Do you put the wire on "sticky" or apply glue after you wind?

As I said previous you and simonbaker were the inspiration for for trying to find a way to produce a quantity of repeatable and compact coils.

I put the wire on "sticky". I tried using varnish but had the same problem simonbaker ( http://www.geotech1.com/forums/showthread.php?t=16828 ).

After some experimenting I found a way to use 30 minute or 2 hour epoxy (length of cure time depending on how long I need to wind coil). With 30 minute epoxy I have 5 minutes to wind and then coil is ready in 30 minutes.

Will try to get pictures as time permits.

[Monk]

Pictures of my coil winder.








This is my "epoxy coater".






The amount of epoxy deposited is determined by the size of the exit orifice. For the .012 diameter magnet wire that I've been using I've settled on a .018 inch orifice which gives me the amount of epoxy I need to produce a good coil. It's quite easy to use either five minutes or 30 minute epoxy in this form of a two-part syringe. Depending upon wire size I can get 3-4 coils from one syringe. A syringe cost approximately 3 dollars USA. If I'm winding a single coil I will use five minute epoxy. If I'm winding to coils I'll use 30 minute epoxy.

Setup is fairly easy takes about 10 minutes. And once you are done winding there's nothing else to do other than let the epoxy cure. You end up with very consistent, very solid and very repeatable coils.

The forms are made from three-quarter inch plywood. They are faced with .100 Plexiglas. I have tried different release agents and find that Teflon spray works fine. The real secret is the Plexiglas facing that has been glued to the plywood forms.

Using this setup I can make at least six different coil configurations. 2 DD, 2 concentric and 2 Mono.

As stated previously and from my "too many years" working with low-level instrumentation and data acquisition, the transducer (search coil ) and its "care and feeding" (construction and interconnect) is probably the weakest link that the home constructor faces in producing a quality detector,

From a testing/performance standpoint you must be able to reproduce consistent and repeatable coils. My plan is to build several different configurations of the same coil form to test shielding and construction variations.

From a grounding/shielding perspective there is a wealth of information in these forums, especially early on. I've attached some of the input/comments that I think are most pertinent at the end of this post. For the DD, IB coil I'm going with a build up to different configurations .

Configuration number one: starting with the coil then adding spiral wrap then adding Millipore tape than spraying with graphite, adding a spiral drain wire, and covering with .002 mill mylar tape.

Configuration number two: starting with the coil then adding spiral wrap then adding 3M AL-25BT Aluminum Foil with Conductive Acrylic Adhesive, adding a spiral drain wire and covering with .002 mill mylar tape.

Not sure what I'll do for concentric PI mono coils. For PI mono coils I will experiment with graphite, nickel spray, copper spray and 3M aluminum foil.

Connecting the coil to the electronics is the next hurdle. My instrumentation experience says that I want to shield both transmit and receive lines. The transmit line to keep noise in, and the received to keep noise out. Also want a separate conductor for the shield.

For the DD, and concentric IB coils I'm going to use this cable:




I haven't settled yet as to what I'm going to use for the PI mono coils.

Any comments/suggestions are appreciated. I especially appreciate the work of dedicated hobbyist/enthusiast such as dfbowers and simonbaker. From my readings of these forums (and specific to coil construction/shielding) there were some great early forum pioneers such as Eric Foster, Reg, Charles (Upstate NY USA), bbsailor to name a few. And from a general metal detector construction and tinkering perspective I miss very much previous contributors such as ivconic and max, posters who were not only more than willing to offer their help, support and opinions but also who put in tremendous amount of hours building and testing metal detectors.

Some posts that I found particularly informative regarding coil construction:

12-17-2003, 11:58 AM
Eric Foster
Guest

Posts: n/a
Default Reasons for Shielding
Hi Claude and all,

Shielding is essential for PI detectors if they are to have good sensitivity for small metal targets. Careful choice of the material for the shield, and also the positioning of the shield with respect to the coil, will result in no loss of sensitivity, in fact I can’t think of any negative effects that proper shielding has.

As has been said, if the shield is parallel to the lines of force generated during the transmit period, and the material is thin enough, then there will be no measurable eddy currents induced in the shield. The other important factor is the shield material’s conductivity. The lower this is, the faster any eddy currents will decay, and provided they decay before the sampling period of the detector, then they won’t be seen.

A flat sheet of shielding, either above or below the coil, is not the best, although it is often used for convenience. A field plot of the coil will show that only immediately under the winding is the field parallel to the shield. Most of the shield therefore has eddy currents generated in it and it has to be made of a relatively poorly conducting material. This is why graphite and nickel paints are often used here. Again, it depends on how thick a coat you put on as to the decay time of these currents.

If you wrap the coil with a metallic tape, then all points on the tape are parallel to the field. The field being coaxial with the coil cross section when close to it. You can then use a more conductive material, and as it is completely enclosing the coil, the shielding efficiency is much greater. You do, of course have to leave a small gap between the start of the wrapping and the end, otherwise the shield will form a complete ring of the same diameter as the coil. This would give a very strong signal as the flux is totally threading this ring.

Aluminium tape, or copper tape will certainly work, provided it is thin enough so that cross sectional eddy currents are not developed. I prefer lead tape as it has a lower conductivity for a given thickness. Copper and lead also have the advantage that the shield grounding wire is readily soldered to it.

Why is shielding needed? The primary reason is to prevent the capacitance between the ground surface and the coil giving false signals. For an unshielded coil, this effect is particularly severe on a wet salt water beach. Touching the wet surface, seaweed, and on land wet grass, can all cause problems without the shield, particularly with sample delays that are less the 25uS. With a shield that is connected to the electronics ground, the capacitance that the coil sees is only that of the shield, and is therefore constant. PI detectors such as the Pulstar and Superscan that are designed for finding large objects at depth, do not necessarily need a shielded coil. This is because the minimum pulse delay is greater than 25uS where the effect becomes much less noticeable.

The second purpose of the shield is to attenuate r.f. interference from various broadcast and other transmitters. It doesn’t get rid of it completely, as the shield is nowhere near as efficient as an aluminium enclosure, as it has to be thin enough to not cause attenuation of the wanted object signals. Also, low frequency r.f. signals from about 500kHz will not be attenuated to any degree. If they were, then you would start to lose sensitivity. Power line interference will also not be attenuated, and be just the same as for an unshielded coil.

A third purpose of the shield, which has a greater importance in these days of EMC, is to prevent any spurious emissions from the detector electronics causing interference with other electronic equipment. In the European Union, radiated emissions are measured from 30mHz upwards, to at least a 1GHz. With an unshielded coil a standard PI will likely fail this test, not because the transmitter itself is generating frequency components of this order, but other parts of the circuit, such as the clock generator, do have fast edges that leak into the coil circuit. I had the problem once where a 555 timer on the board was radiating sufficient energy via some over long pcb tracks on the output pin, to cause the detector to fail the test. A properly shielded coil and a well laid out pcb should have no trouble passing existing emissions tests, even when using a fairly high power pulse transmitter.

Eric.
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07-24-2004, 11:48 AM
Reg
Guest

Posts: n/a
Default Re: Coil shielding problems
Hi Stefano,

There are several different strange things one can try to shield their coils that should work. The key is the material has to be conductive.

Remember, the object of the shield is two fold, with the first objective to eliminate the capacitance effect and the second to absorb external noise for noise reduction.

If a very thin shield material is used, then there should be little or no increase in the delay since any signal from the shielding would have disappeared before the desired sampling time. If the material is barely conductive enough, the capacitance effect can be eliminated but it might not work that well for the noise elimination. That is why there are preferred materials.

Again, the key to any material is that the material be conductive. A simple check with an ohmmeter will confirm this to be true.

One very simple material I have found in the US is a simple form of metallized ribbon. This is the kind used for bows and ribbons, party favors, etc. Generally, it is about 1/2" wide and is generally a silver color. Now, there are different kinds of ribbons that may look like they would work but many are not conductive so a person has to just check them with a meter until they find one that at least one side of the ribbon is conductive. Here, I have found some in our Walmart storess. This seems to work and is quite cheap.

This material seemed to be conductive enough to take care of the capacitance problem. The difficulty lied in connecting a wire to the ribbon. What I did was to simply take a piece of about 30 awg stranded wire, strip a couple of inches of insulation off and then tape the stranded wire to the ribbon, making sure the tape is tight.

Another simple material that seems to work is something we find on some of our insulation used in our houses. We have different sized foam boards with a very thin metallized mylar film attached to one side. This conductive mylar film can be stripped from the foam board and used as a form of shielding. One can wrap the windings, or simply lay a piece of the material on the bottom and top of the coil form between the windings and the form to shield the two sides.

Another material I have used is a conductive rubber tape used for high voltage splices. This can simply be wound around the windings.

In all cases, make sure you have some material as a spacer between the windings and the shielding. Spirawrap works well but if it isn't available, then one can split a thin plastic tubing and use it for a spacer.

If the material is to be glued inside an enclosed form, then there still needs to be a spacer between the windings and the shielding material. Something like a 1/8" to 1/4" foam or other rigid material could be used for the spacer.

Other strange things that could be tried might be some thicker litz wire, providing the individual strands are small enough. Just flatten and wind the litz wire around the coil windings leaving a small space between wraps. One would have to experiment with this technique.

There are some conductive cloths available so you might check with shops carrying sewing materials. Also, there are various types of metallized mylar materials available that most likely would work.

Finally, some people have used a stainless steel (ss) mesh or very small ss wire. I have not tried this so I don't know how well it works.

I hope this gives you some ideas.

Reg


07-25-2004, 10:10 AM
Eric Foster
Guest

Posts: n/a
Default Re: Open loop is not fully faraday shield!
Hi Jackdetect and All,

It is perhaps incorrect to describe shielding as cancelling noise. It is better to refer to shielding as attenuating noise. We also need to consider what frequency noise we hope to deal with by this method. As Reg mentioned, the front end of a PI has to be broad band. Not necessarily down to d.c., but it could be from a few hundred Hz, up to 100kHz or more, depending on how fast a decay curve we want to look at. This means that any coil shielding must be transparent within that frequency band. The aluminium shielding referred to in the first post, obviously was attenuating frequencies at 50kHz as it was increasing the useable delay to 20uS or more. In this case it was impeding the higher frequency components of the TX pulse from getting out. If the shielding starts attenuating at 100kHz, then for higher frequencies, there will be ever greater levels of attenuation, depending on the skin depth characteristic of the particular material used, and how thick it is. Aluminium or copper tape could be used, but it would have to be very thin, more like the aluminium film deposited on Mylar, for decorative material.

Even when the shielding is giving high levels of attenuation, it depends how near the source of the interference is, as to whether there is any effect. i.e if the shielding reduces the interference amplitude by a factor of 100, but the source is brought nearer, so that there is 100 fold increase in signal, you are no better off. R.f. interference has two effects on a PI detector. One is a beat note effect, such as experienced in here in England with the high power 200kHz transmitter at Rugby. A PI detector running at a pulse frequency which is a close sub multiple of 200kHz will experience beat interference. e.g. 200Hz, 2kHz, 20kHz. A low frequency warble of the audio will be the result. That is why a TX frequency control is very useful, as a small adjustment can increase the frequency of the beat note to the point where the integrator smooths out any residual effect. Obviously any reduction in the interference amplitude as seen by the receiver input, helps enormously. You can certainly see the reduction in the 200kHz signal when a coil is shielded, as compared with an unshielded one.

The other type of r.f. interference results from much higher frequencies, even to 100’s of MHz. This is usually from very close range devices such as mobile phones, VHF transceivers etc. This results from the small amount of signal that gets through the shield and which is modulated with audio. The input circuitry of the detector, with its protection diodes, acts as a demodulator and presents the receiver with audio frequencies which are within its bandwidth. Even just switching a transceiver on without modulation can cause a dc offset at the receiver with a resulting bleep in the detector audio before the differential integrator cancels it. Again, any reduction rf pickup by shielding the coil is valuable here. Additional rf filtering is often used on industrial PI detectors in the form of ferrite sleeves and LC filters.

The effects of coil shielding is best observed on a spectrum analyser, and believe me, it does make a difference, particularly if you want to comply with EU rf emissions and immunity standards.

Low frequency interference within the passband of the detector is not reduced by coil shielding. It is then that you have to resort to figure of 8 or differential receiver coils in some situations.

Eric.
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Eric Foster
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Default Re: Differential coils!
Hi Jackdetect,

It is unlikely that capacitive changes have an effect on large loop geophysical PI's. My early PI's had sample delays no shorter than 50uS and used unshielded coils. There was no noticeable capacitance effect on a wet beach, which is where it is worst. It wasn't until I made a unit that sampled at 20uS, that it became apparent that a shield was necessary. Most of the earlier PI's were overdamped and coil/cable capacitance was relatively high in comparison with the coil ground capacitance changes.

I have found that figure of 8 and differential gradiometer configurations are excellent at cancelling power line noise and are probably good up to a few hundred hertz. However, they are not much use at higher frequencies. I found that 200kHz noise was not reduced much by a differential arrangement.

Eric.
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03-02-2006, 10:19 AM
Charles (Upstate NY) Charles (Upstate NY) is offline
Senior Member

Join Date: Mar 2005
Posts: 127
Default
It is my understanding that modern day VLF coil shields reduce capacitive coupling. They absolutely dissipate static charges and 100% coverage is required for this reason. The VLF coils are quite sensitive, at least the Minelab Explorer coils are. You can brush just a few blades of grass on an unshielded coil and get a false signal. These painted on shields are not effective against EMI/RFI however.

For the Minelab Explorer anything more conductive than the carbon black based shielding paints are too conductive. Electro-Dag measures about 75ohms per inch. It will not pass a continuity test even with the probes nearly touching. But with a thin drain wire they shield the coils nicely.

Nickel based shielding paint is too conductive. It will pass a continuity test and if you wave a shielded sample over an Explorer coil the Explorer will pick it up. Therefore if your coil flexes even a little, bumping it along the ground as you swing it, the coil will detect the shielding and false. The reduction in depth is also noticable.

For the Explorer the optimum seems to be about 75-100ohms per inch. 1-10 ohms per inch is too conductive. Note with the carbon black type shielding paints you don't have to worry about leaving a gap in the shielding.

An Explorer coil wrapped in foil would not work very well. You would see the coil is severely loaded on the scope. There was a noticable reduction in depth with nickel based paints, foil would be worse.

There's probably a happy medium, floor paints and such are probably not going to be conductive enough. Keep in mind that you have to wrap drain wires around the coil. A gap of about 2 inches with no drain wire is enough to cause the coil to false in that area. The higher the resistence, the more drain wire you would need.

My advice, save a lot of time and effort and just go with a carbon black/graphite based sheilding paint. I use Electro-dag but its nasty stuff, I think the solvent is MEK. The plus side is it dries really fast. I hear there are some water based graphite paints out there now which I will probably try after I use up this electro-dag.

Picking the shielding paint isn't the hard part, how to apply the shielding is what is difficult. You need a minimum spacing between the shielding and the winding. I suggest you look at this thread regarding a cheap and quick way to do this.

http://thunting.com/geotech/forums/s...d.php4?t=11164

Charles


11-28-2005, 05:46 PM
bbsailor bbsailor is offline
Guru

Join Date: Feb 2005
Location: Barnegat, NJ
Posts: 295
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You could probably make a shield using wire wrap, however you would need a lot of wire to make a close wound shield around the circumference of the coil. Some PI coil builders have mentioned using bare wire from wire wrap to do a few spirals around an aluminum shield to make the ground connection using black tape to secure it tight. Others have used nickel conductive paint to coat the plastic spacer and used the bare wire wrap as a way to make the ground connection.

What you use as a coil shield depends on the minimal delay that you are seeking. Faster delays require a shield that has less eddy currents capable of being generated in it. Thinner shielding is better for fast coils. Many things have been used for coil shields (listed below).

Household alum. foil
Opened and unwound electrolytic cap plates
3M copper fabric tape (recommended by Reg) (good shield)
3M Lead Tape (Eric Foster) (good shield)
Alum. tape (2" wide) as recommended by Carl on the Hammerhead coil (see his article)
Mylar, conductive, decorative ribbon
Copper foil

What you are trying to achieve is a low shield to coil capacitance of about 40 to 50 pf per foot of coil circumference (some of my best). When you wave a target under the coil listen to the response and lower the delay using a gold ring or nickel. If the target suddenly stops responding, you have reached the lower limit of that coil. The fix is to reduce the total capacitance and readjust the damping resistor value. Total TX capacitance is caused by the following things main things.

1. The coil winding-to-winding capacitance (1 to 1.2 Mhz self-resonance with no shield.
2. Coil-to-shield capacitance.
3. MOSFET output capacitance (COS) rating. About 50 pf is a good low nember.
4. Coax wire capacitance. 16 to 25 pf per foot is common. Lower is better.
5. RX input circuit stray capacitance and input circuit component loading (relatively fixed by the circuit design).

The value of the damping resistor reflects the total capacitance seen by the coil in the TX circuit. Higher is better, meaning there is less capacitance to damp thus a higher value of resistor will achieve critical damping and make a more potentially sensitive coil.

DD coils can be made more sensitive because the TX and RX circuits are separated. The RX coil does not see the MOSFET output capacitance. My own crude tests indicate that for each 100 pF I can eliminate form the TX circuit, as seen by the coil, I can speed the delay up by about 1uS. I would like others to verify these crude findings?

You need to have an LC meter to make relative measurements to see the effects of the coil-to-shield capacitance changes you make in you coil design.

bbsailor

01-26-2007, 10:59 PM
Reg Reg is offline
Guru

Join Date: Apr 2005
Posts: 395
Default
Hi Geo,

I got an email from Plumabob and he was the one who provided the technique he used to shield his windings he uses in open coil housings. Here is what he wrote;

"It was me. First I wrap with electrical tape, then the Micropore tape, spiral a thin wire around( I space it about and inch or so apart ) and spray with the EZ-Slide. I don't think that I have to mention but make sure you leave an 1/8th inch gap somewhere. I just cut a thin piece of tape, place it on the Micropore before spraying and remove afterwards. When dry I give it a double wrap with more electrical tape.

I bought this micropore on ebay and it works great and the price is right...

http://cgi.ebay.com/3M-Micropore-Sur...yd-24-pr-bx-2-

"

Now, EZ-Slide comes as either a graphite spray or quart of graphite paint, whichever you purchase. It is normally used as a dry form of lubrication rather than a conductive surface.

EZ Slide is cheap and convenient to obtain by people in the US. I am sure there is something similar in other countries. Here is a link to a site where I order mine.

http://pandrsupply.com/SearchResult.aspx?CategoryID=24

As you can tell by the label on the spray can, it is referred to a graphite base coating.

Hope this helps.

Reg

[Andygold]

Foil tape part numbers

There is a lot of advice regarding using foil tapes for shielding. Are these all 3M products? which ones would you fellows recommend? Copper, lead or the scotch 24 stuff? The 3M code or part numbers would be very useful.
This is for very fast sampling gold nugget detecting PI mono coil. Thanks

[greybeard]

i've used some self adhesive copper tape. I got it from ebay. search for snails and copper tape yes, that's right snails. the copper tape is used by gardeners to protect plants. It comes in different widths. I ended up with some 30mm wide tape that I cut to length then cut lengthwise into two.
so far i've been playing with mono coils for my HH1&2. it's very easy to solder to as well.

[WM6]

i've used some self adhesive copper tape. I got it from ebay. search for snails and copper tape yes, that's right snails. the copper tape is used by gardeners to protect plants. It comes in different widths. I ended up with some 30mm wide tape that I cut to length then cut lengthwise into two.
so far i've been playing with mono coils for my HH1&2. it's very easy to solder to as well.

If you can solder at it, thet it is maybe too conductive for coil shielding.

But thank you for info where to buy.


To Monks: Good construction for coil winder, thanks for idea.