Theories about coil-shielding

[green]

Another plot that I think shows pattern length might not make a difference.

[green]

Another plot. Cut four pieces, 3/16 x 2, 3/8 x 2, 3/4 x 2, 3/2 x 2 inches. The 3/16 x 2 measured the same TC as the 2 x 2 inch piece cut in a 3/16 pattern. I'll try a longer cut piece the next time I cut one

[Waikiki_Sweep]

Measure some length of foil than weight it on jewelers scale. If you know density of aluminum you can calculate thickness.

[baum7154]

Regular Reynolds foil is about .001" thick

[green]

It was regular Reynolds aluminum foil. All I have is a vernier calipers. I folded a piece a few times and measured it to be about .001. Not sure how to measure a piece that long but a will try some different length pieces. Maybe some with more cuts/inch. Was looking at my copy of ITMD and saw a section on cutting targets. Might be where I got the idea to cut the foil.

[baum7154]

Not suggesting aluminum foil is the way to go. A plot showing why I think it didn't change the 9 inch coil sensitivity. First image is a 2x2 inch piece of aluminum foil not cut and cut in a pattern shown in second image The cut foil has a TC of .4usec vs 3usec for the not cut.

Fascinating result from just cutting! It is always important to specify the thickness of the foil as this has the largest effect on T/C. Do you know how thick it is?
It would be interesting to see how a piece of foil at a specified thickness, cut as you describe, and long enough to do your 9" coil comes out on the T/C test. We know that long rectangular strips do have an effect of increasing T/C in addition to the thickness per our discussion in the Target Time Constants thread. It would be interesting to compare one with the cuts versus one without the cuts.

Good Stuff!

Dan

[6666]

Ok thanks Green

[green]

[Green would you mind sharing the design you have been playing with please ?]

I want to try another design first. Will share when I have one I'm happy with, soon I hope. I'm still learning, haven't built a PI detector yet, not sure how the amplifier will operate off the bench.

[6666]

Been playing with difference amplifier lately for IB coils,

Green would you mind sharing the design you have been playing with please ? thanks

[maikl]

And this

[maikl]

Here's how he did ...

[Waikiki_Sweep]

Not suggesting aluminum foil is the way to go. A plot showing why I think it didn't change the 9 inch coil sensitivity. First image is a 2x2 inch piece of aluminum foil not cut and cut in a pattern shown in second image The cut foil has a TC of .4usec vs 3usec for the not cut.

Cutting is a great idea!!!! Thank you!!! Should be used widely in such construction with different shield meterials.

I am not suggesting aluminum too also because of corrosion of aluminum and bad contact to cooper wires.

[green]

Not suggesting aluminum foil is the way to go. A plot showing why I think it didn't change the 9 inch coil sensitivity. First image is a 2x2 inch piece of aluminum foil not cut and cut in a pattern shown in second image The cut foil has a TC of .4usec vs 3usec for the not cut.

[baum7154]

You are right about performance of insulated wires.

I am using AWG 24 in all my PI coils which is near 0.5 mm diameter and it conducts current much better than AWG 26 OR 28.

I told about AWG 28 stranded WIRE only because Green already using AWG 28 soild wire. Anyway stranded wire is better than solid.

But also I have one more observation - smaller diameter wire creates less inter-wire capacitance. May be some day we will go that direction by increasing power supply voltage with voltage converter to keep current the same.

Also you are right about PTFE. It has low dielectric constant. Teflon is one of the best dielectrics to create low capacitance coil.
Once I saw on sale 24 AWG PTFE wire with thicker insulation that has 1000V rate.
That 1000V is better for sure because coil will have even less inter-wire capacitance.

Yes, the reason I did order 26AWG and 28AWG is precisely because it gives much lower inter wire capacitance and I want to see how far I can push down the wire size without sacrificing detector performance. Also the silver plating on the smaller wire size will have less eddy current effect, though I have not seen a problem with the 24 AWG silver plated wire. Maybe it is an issue with larger wire sizes (18 to 22) but I have no need for those with my present builds.

Dan

[mykaitch]

I am not sure that you need to put so much metal into metal detector coil because that cooper tape and aluminum foil acting like targets shifting phases in VLF and prolonging decays in PI detectors.

Yeah, should do. To be honest it was a FUBAR. The Alu yape ket snapping so I got mad and covered the lot in copper - still works great but if I do another one I now have some mylar backed Alu. Waiting for a Garret spider cover to arrive for my next concentric