Split coil drive (PI mono coil)

[Carl-NC]

Your drawing ignited my memory. Back at White's I was looking at various experimental coils for PI: scramble, spiral, solenoidal, and some others. I think they were all 24 turns and 10"/25cm mean diameter. The one that your drawing reminds me of is something I called a "vortex" coil. I managed to find a Visio drawing I did for it but I cannot find any photos or measurements.



There is an inner ring of heavy copper wire and also an outer ring. Then there are 24 wires that make a 1-turn spiral from the inner ring to the outer ring (the first one is highlighted as a heavy line). A cable is connected to the inner & outer rings where you see a 90° spur. Since there are 24 parallel turns (instead of 24 series turns) the currents need to be both balanced and limited, so I placed an 0805 chip resistor just where each spiral connects to the inner ring. I don't remember what value I used, maybe 10Ω.

Performance sucked. It had little sensitivity compare to a normal coil. On the RX side it is obvious: the parallel induced voltages on each 1-turn coil does not sum up to anything stronger, so on the RX side it is always equivalent to a 1-turn coil. On the TX side there are 24 1-turn coils and even if each one has the same current as a normal 24-turn coil it is not clear that you get the same TX field strength. There are 2 ways to test for this: use a magnetic field probe to measure the TX field directly, or add a normal 24T RX coil to get back the RX-side sensitivity. I did not try this so I don't know the answer. The coil was exceptionally hard to build so I doubt I will try it again.

Moral of the story: don't get too wrapped up in simulations. Build it and see what it does.

[Teleno]

Your drawing ignited my memory. Back at White's I was looking at various experimental coils for PI: scramble, spiral, solenoidal, and some others. I think they were all 24 turns and 10"/25cm mean diameter. The one that your drawing reminds me of is something I called a "vortex" coil. I managed to find a Visio drawing I did for it but I cannot find any photos or measurements.



There is an inner ring of heavy copper wire and also an outer ring. Then there are 24 wires that make a 1-turn spiral from the inner ring to the outer ring (the first one is highlighted as a heavy line). A cable is connected to the inner & outer rings where you see a 90° spur. Since there are 24 parallel turns (instead of 24 series turns) the currents need to be both balanced and limited, so I placed an 0805 chip resistor just where each spiral connects to the inner ring. I don't remember what value I used, maybe 10Ω.

Performance sucked. It had little sensitivity compare to a normal coil. On the RX side it is obvious: the parallel induced voltages on each 1-turn coil does not sum up to anything stronger, so on the RX side it is always equivalent to a 1-turn coil. On the TX side there are 24 1-turn coils and even if each one has the same current as a normal 24-turn coil it is not clear that you get the same TX field strength. There are 2 ways to test for this: use a magnetic field probe to measure the TX field directly, or add a normal 24T RX coil to get back the RX-side sensitivity. I did not try this so I don't know the answer. The coil was exceptionally hard to build so I doubt I will try it again.

Moral of the story: don't get too wrapped up in simulations. Build it and see what it does.

A very daring design!

The spiral coils I built for my PI has a good sensitivity for small gold (spiral with basket weave). I'm decided to try a split version and see if I can get a faster decay. I only have to add an additional preamp to the existing design so it shouldn't be lots of work.

https://www.geotech1.com/forums/foru...791#post312791



This one works even better:

[lucifer]

My next coil experiment might be a spider coil but printed on a two layer PCB. I've already developed the tool to draw it automatically having control over the number of turns, number of sides of the polygon shape, trace width, spacing between turns, etc. But currently I'm focused on other coil improvements and new shielding methods which are a bit complicated to do at home but will see how it goes.

[Teleno]

My next coil experiment might be a spider coil but printed on a two layer PCB. I've already developed the tool to draw it automatically having control over the number of turns, number of sides of the polygon shape, trace width, spacing between turns, etc. But currently I'm focused on other coil improvements and new shielding methods which are a bit complicated to do at home but will see how it goes.

I've done a small batch of spiral PCB coils, double sided, but they were useless for PI because of the high resistance. I've been looking at more ounces of copper but I'm afraid the more expensive version isn't as good as a wired one.

[lucifer]

With thicker traces and 2oz copper one can get the resistance down to 2-3ohm. For a 27-28 cm coil the cost would be about $20 / piece. Alternatively, you can increase the current by applying a higher voltage on the coil.

[Teleno]

With thicker traces and 2oz copper one can get the resistance down to 2-3ohm. For a 27-28 cm coil the cost would be about $20 / piece. Alternatively, you can increase the current by applying a higher voltage on the coil.

There are special heavy copper traces used in military PCBs

.https://www.epectec.com/articles/hea...cb-design.html

For a $300 coil, not bad.

[lucifer]

There are special heavy copper traces used in military PCBs

.https://www.epectec.com/articles/hea...cb-design.html

For a $300 coil, not bad.

Interesting.. Didn't know about these but I doubt I'll ever need to use this technology.
Btw, I don't use solder mask on my PCB coils so the traces get tinned which also lowers the resistance but only slightly.

[Teleno]

Interesting.. Didn't know about these but I doubt I'll ever need to use this technology.
Btw, I don't use solder mask on my PCB coils so the traces get tinned which also lowers the resistance but only slightly.

With some patience a naked copper wire could be soldered on top of the traces. Juwelery work.

[Teleno]

Interesting.. Didn't know about these but I doubt I'll ever need to use this technology.
Btw, I don't use solder mask on my PCB coils so the traces get tinned which also lowers the resistance but only slightly.

Another possibility would be laser cutting a copper plate.

[gallico58]

Could they work?
spare parts for induction plateCould they work?
spare parts for induction plate
measured about 100uh very thick liz wire resistance not measured but I think very low.

[Carl-NC]

There are special heavy copper traces used in military PCBs

.https://www.epectec.com/articles/hea...cb-design.html

For a $300 coil, not bad.

Wow, 30-ounce copper. Even the vias are heavy-plated.

[Teleno]

Wow, 30-ounce copper. Even the vias are heavy-plated.

Imagine the eddies.
With such a coil who needs a target?

[Teleno]

Your drawing ignited my memory. Back at White's I was looking at various experimental coils for PI: scramble, spiral, solenoidal, and some others. I think they were all 24 turns and 10"/25cm mean diameter. The one that your drawing reminds me of is something I called a "vortex" coil. I managed to find a Visio drawing I did for it but I cannot find any photos or measurements.



There is an inner ring of heavy copper wire and also an outer ring. Then there are 24 wires that make a 1-turn spiral from the inner ring to the outer ring (the first one is highlighted as a heavy line). A cable is connected to the inner & outer rings where you see a 90° spur. Since there are 24 parallel turns (instead of 24 series turns) the currents need to be both balanced and limited, so I placed an 0805 chip resistor just where each spiral connects to the inner ring. I don't remember what value I used, maybe 10Ω.

Performance sucked. It had little sensitivity compare to a normal coil. On the RX side it is obvious: the parallel induced voltages on each 1-turn coil does not sum up to anything stronger, so on the RX side it is always equivalent to a 1-turn coil. On the TX side there are 24 1-turn coils and even if each one has the same current as a normal 24-turn coil it is not clear that you get the same TX field strength. There are 2 ways to test for this: use a magnetic field probe to measure the TX field directly, or add a normal 24T RX coil to get back the RX-side sensitivity. I did not try this so I don't know the answer. The coil was exceptionally hard to build so I doubt I will try it again.

Moral of the story: don't get too wrapped up in simulations. Build it and see what it does.

To achieve tge same ampere turns of an equicalent regular spiral coil you would need 24 times as much current. I don't know if your driver was adjusted to that crazy requirement.

[Carl-NC]

I'm sure that is also correct. You get hit both ways, on the TX side and on the RX side.

[darov922]

I've never that particular technique, but did something similar:


This uses the center-tapped coil in a bipolar pulsing scheme. Because each half-coil is 1/4 the total inductance you get a higher current and faster flyback while getting the entire L on the RX side.

I find this bipolar concept very interesting since it is easier to implement than in an H-bridge design with NMOS and PMOS transistors. I would like to see the way to implement it in my hammerhead II circuit... what things have to be modified in the preamplifier? What would the sequence scheme of the pulses and their duration be like? I don't know how to ask you more about this circuit... should I open a new thread?

Dario