coil shiellding

[scrungy_doolittle]

I see all sorts of solutions to sheilding, and it seems to be a big deal. Graphite paint, graphite impregnated paper. Aluminum or copper foil. The obvious is overlooked.

1. cheap, conductive, common, non metalic. Anyone want to guess?

Black conductive foam that IC's are shipped in. This is available in sheets,and is quite flexible. Good electrical contact can be made to it.

This puts this idea out into the public domain, so it cannot be patented....

Cheers
Scrungy

[Qiaozhi]

Electronic boards are normally shipped in conductive bags, and I've seen the same material used in Garrett Crossfire coils. Contact to cable shield is made using a spring.

[Davor]

I've seen an amateur seismometer sensor made using this foam and a weight. Apparently the conductive foam changes resistivity when pressure is applied. I guess this will not affect shielding properties.
I must admit I've not seen this foam sold in bulk in electronic shops, and I never seek them online :/

[CAS]

I have also looked at the foam but I think it may add too much bulk when using the thicker litz wire. Not sure the coil would then fit in the housing.

I am going to try a spray conductive paint but need some advice - I have a choice of sprays that contain either copper, nickle, silver or graphite.

What is everyone's opinion on which would be the best to use and reasons?

[baum7154]

I have also looked at the foam but I think it may add too much bulk when using the thicker litz wire. Not sure the coil would then fit in the housing.

I am going to try a spray conductive paint but need some advice - I have a choice of sprays that contain either copper, nickle, silver or graphite.

What is everyone's opinion on which would be the best to use and reasons?

--------------------------------------------

If you are looking for the fastest targets such as small gold only the graphite spray should be used in my opinion. The metallic based sprays, especially copper and silver will look like targets of those metals to your detector impeding its ability to operate at short sample times (approximately 10 us). There are volumes written on this forum on the use of graphite as a shield.

Early on in my coil building efforts I tried using .001" copper foil and it was a coil killer for speed.

Regards,

Dan

[CAS]

--------------------------------------------

If you are looking for the fastest targets such as small gold only the graphite spray should be used in my opinion. The metallic based sprays, especially copper and silver will look like targets of those metals to your detector impeding its ability to operate at short sample times (approximately 10 us). There are volumes written on this forum on the use of graphite as a shield.

Early on in my coil building efforts I tried using .001" copper foil and it was a coil killer for speed.

Regards,

Dan

Thanks Dan. Thats what I thought but my supplier has no stock of the graphite spray until after xmas and being impatient I wanted to have something now. I think i am just going to have to wait. Otherwise I will be disappointed in the long run.

[multieagle]

Most autoparts stores, ie Canadian Tire in Canada, carry graphite spray.

[Altair]

What about old carbon copy sheets?
Is there someone who has tried them?

[Koala]

What about old carbon copy sheets?
Is there someone who has tried them?

Normally not carbon but use wax

[CAS]

Well seeing as I am impatient, I thought I would experiment with what I had on hand and I think I may have a good combination.

I used a mix of graphite powder and a mortar bonding agent (you can get it from hardware stores) and thinned it down with a bit of water. I brushed it on to some sports strapping tape and now have a flexible, conductive piece of tape.


Conductivity between the 2 wires - 60mm apart - is approx 1k (thats only 1 coat - more coats may reduce that resistance if needed)

I will wrap the coil and then brush the graphite coating on. As the mortar bond and tape remain flexible hopefully the shielding shouldnt suffer cracking. it seems to be pretty abrasion resistant too. The small shiny marks are where I tried to scratch it with sharp probe points.

[6666]

Cas would you mind telling us the name of the mortar bonding agent?

and was the tape Elastoplast Sport Elastic Adhesive Bandage 50mmX3m Roll

Thanks

[CAS]

Cas would you mind telling us the name of the mortar bonding agent?

and was the tape Elastoplast Sport Elastic Adhesive Bandage 50mmX3m Roll

Thanks

I use the sports tape because it has a stronger adhesion than others I have found while being porous enough to hold the graphite mixture (plus its what I had at the workshop).

[6666]

Thanks Cas, will check out these products.

[scrungy_doolittle]

The mortar bonding agent is just PVA i.e. Elmers white glue.

[6666]

I have tried PVA and graphite but never had any luck.