IB coil shielding

[Geo]

Hi . What are you say if i will use the follow tape for coil shielding??
http://cgi.ebay.com/Conductive-Coppe...QQcmdZViewItem

Regards

[bbsailor]

Coil Shielding

Geo,

The best test is to sample the shield material under the coil to see if or if not it is detected. But, you can not do that with ebay.

My guess is that this copper shielding tape is NOT good for a PI coil shield as it is too conductive at low delays.

Look on the ebay for "Scotch 24" mesh shielding. This is not detected at low delays.

I hope this helps?

bbsailor

[Geo]

Hi bbsailor. I want to shield a Ib coil (DD) for a VLF detector. So i want your opinion about it.
What says Reg about it ???
Best Wishes

BTW i will look for "Scotch 24".

[bbsailor]

Shield

Geo,

The tape is only .250" wide so it will need to be spiral wound around the coil.

If you know the wire bundle diameter, then mutiply that diameter by 3.14159 to get the circumference. Look for a tape that is about as wide as the circumference calculated above. This will make shielding the coil easier as you only need to wrap it around the coil and bend it over. It helps if you cut little .25" slits in the tape every 1.5" so it bends over without bunching up too much.

The Scotch 24 mesh tape is tubular and when laid out flat is 1" wide. It looks like a window screen with very thin wire.

Test what ever material you plan to use to see that it will not make your coil insensitive. Leave a gap just like in a PI coil.

bbsailor

[Leto]

Looks like advertisment...

Hi Geo..
I suggest folowing items:
Plastik 70 - very low dialectric constant (2.3) acrilic glue - film in spray.
Graphit 33 - ideal for shielding.
Produced by Kontakt Chemie from Danmark, do not know about Greece but very easy to find in electronic shops in my country.

PS: I followed your advice about that coil housings (MDetectors.com) - you were right, fast delivery without any problems .

[Geo]

Hi Geo..
I suggest folowing items:
Plastik 70 - very low dialectric constant (2.3) acrilic glue - film in spray.
Graphit 33 - ideal for shielding.
Produced by Kontakt Chemie from Danmark, do not know about Greece but very easy to find in electronic shops in my country.

PS: I followed your advice about that coil housings (MDetectors.com) - you were right, fast delivery without any problems .

Hi Leto. I want to use it at open DD Coil Housing, the same with one at your photo. I am afraid that i will not have good results because it is open from the down side. So i think that is better to make a Faraday Shield with copper. If you try with Kodakt sprays and have good results please tell me.

Bbsailor. I think to make spiral wound around the coil. The only thing that i am afraid is the coil sensitivity (maybe to be low with a "heavy" shield)
Anyway Thanks All of you
Regards

[Reg]

Hi Geo,

I suspect the copper tape will cause problems. An IB type detector would most likely detect the copper tape and cause phase shift problems among other things.

I would try something less conductive.

Now, I don't remember to told me about a technique they used, but they wrapped the windings with a cloth type tape and then sprayed the tape with conductive graphite spray. finally, a conductive wire was taped on to the conductive paint. They may have added the conductive wire and then painted over that also instead of adding it later. I think it was Plumabob who used this technique. Maybe he will jump in with more details.

Also, you might look at the technique used by Charles of NY. He dipped his windings in a special melted material and once cooled, sprayed conductive paint on it.

Reg

[Reg]

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-Surgical-Tape-1-2-x10-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

[Geo]

Hi Reg.
I will give a try with this method. I wait Leto who bought the same coil housings with me, to try shield the coil with Kontakt sprays.
The other that i can tell you is a big Thanks
Regards

[Geo]

Hi Reg.

I readed carefully your post and i have 2 questions.
1. Do we spiral a thin wire around all the coil or only one or two turns ?
If we spiral around all the coil i suppose that i must leave a gap at the end. Is this wire the gnd of coil ??
2. I suppose that we use Micropore tape only for stay better the graphite on the coil (electrical tape is glossy). If so may i use a simple paper tape ??

I wait...

[Reg]

Hi Geo,

I haven't tried this technique yet so I am going on the advice of Plumabob. He recommended spiraling around the windings with about a one inch gap between spirals. I don't thing it would matter too much if the spirals were a little closer or farther apart. The bare wire will form a partial shield, but the spray will do the rest. The bare wire will also assure the paint is making a good connection around the entire coil.

As for the tape to use, the micropore is a form of open paper tape. About any tape that will hold paint should work. So, a paper tape should work fine. Glossy smoothe tapes such as plastic tapes would have a tendency to allow the graphite paint to flake off.

Now, on a different note, I have used a rather unique tape for shielding of PI coils, and that is a semi-conductive rubber tape made by 3M. IIt is Scotch 13. One interesting feature of this tape is you can change its resistance just by stretching it. Most likely this tape would work fine on a VLF (IB) coil also.

Here is a link to the spec sheets of the tape.

http://multimedia.mmm.com/mws/mediaw...666WsKCOrrrrQ-

Cheers,

Reg

[plumabob]

The micropore tape is very flexible. Therefore it won't rip when final balancing adjustments are being made. The EZ-slide is also flexible. I guess you could try something similar but I wouldn't trust regular paper tape, perhaps a thin cloth tape would be OK. Reg is right the spiral wrapped wire does not have to be exactly 1 inch apart, a little more or less will not matter. What does matter is that it has good contact with the graphite shield. I spiral wrap each set of windings separately, then joint them together at the grounding point.

[Geo]

Hi Reg and Plumabob. Thanks for your reply. Coils shielding are not my "strong point" . Maybe i am lazy and i am looking to finish quickly the coil.... I will order the EZ slide and i"ll try to shield a open housing DD coil. What are you say if i"ll try the EZ slide for shielding a close housing concentric 36x22cm coil?
My Regards

[plumabob]

It should work fine, although I have never tried it. Dave Emery has a very informative post on applying spray shielding for a closed coil housing. You should give it a look.

[Geo]

It should work fine, although I have never tried it. Dave Emery has a very informative post on applying spray shielding for a closed coil housing. You should give it a look.

OK thanks