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  • spiral PCB coil

    A while back I presented the question "what if the coil loops were put in parallel instead of series?". One of the subquestions that's been chewing at me is just how one would go about accomplishing that. I drew up a possible way to accomplish this on a PCB layout (see attached jpeg).
    The trace widths and start/stop points for each loop were strictly arbitrary for the sake of example. Working trace widths would have to be determined, I drew each loop at 360 deg but 180 or 90 could just as easily be generated, and I used an inner dia 1/2 the OD because I'm still stuck on the idea of concentric coils. The area could be divided with xmt coil on outer third, rcv on middle third and hole for inner third.

    The idea behind this layout is to mechanically shorten the actual distance the xmt signal has to travel, to hopefully shorten the xmt pulse decay.
    In this case it travels at most two turns, instead of twenty.

    I don't know if this would be effective or not, but it's been bugging me, so I thought I'd present the idea to the forum and see what you guys think...

    gm
    Attached Files

  • #2
    I'm thinking it would have a Boat load of capacitance!

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    • #3
      Interesting idea, please report how you deal with (small) resistance and inductance of coil.


      Originally posted by grungymike View Post
      The area could be divided with xmt coil on outer third, rcv on middle third and hole for inner third.
      What is on your picture, only TX coil?

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      • #4
        My guess

        While we are all just taking guesses, I'd say that 1 turn is going to have a very small inductance. If you parallel 20 turns together, the inductance of the coil is going to continue to get much smaller, approaching zero (not zero but very small). This will appear as a short to your detector and your FET might not be happy with it. Let us know what you find out.
        Boattow

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        • #5
          This is interesting... yes, L & R will be very low but for a PI I doubt it will matter... the FET already sees an almost-short. C should be about the same but with a much lower L it will have a much smaller effect. In the end, the coil should be blazing fast, question is does it give equivalent ampere-turns? I can't see why not, yet.

          - Carl

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          • #6
            pcb coil

            Hi All,
            Did some quick calcs and there would be 30.4 meters of wire which would be comparable to a normal coil of 600mm dia. , Im guessing that the ind. and res. wouldn't be far off either , so like carl says should be one fast bleedin coil, also pcb coils are better with smaller nuggy's....maybe it's a goer!!!

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            • #7
              a little followup...

              Yeah, what I drew was strictly the xmt coil, for a PI, figured a rcv coil could go inside (concentric layout). Hadn't thought much about wether rcv coil should be traces on board or separate windings. Just wanted to present the raw concept to you guys.

              I literally live in my truck right now, and have my hands full designing the control box for a detector. I have no idea when I'm gonna have time to play with this idea, and am not really set up to be etching boards. If somebody else wants to explore this idea, by all means, please go for it!
              Thanx...
              gm

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              • #8
                pcb coil

                Hi grungymike,
                Instead of etching the coil i was leaning more to laying down insulated wires for a trial run,not racing in to try at the moment as i have a couple of other projects but its on the list

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                • #9
                  wrapped up in the wresearch...

                  Right on! The one glitch ya might run into is connecting the individual wires. I suspect solder might cause problems, maybe a conductive adhesive?

                  I attached the wireframe I built the pattern on, I developed it in a CAD program. It (or similar) might help in laying out the pattern on whatever substrate you use.

                  I'm looking forward to reading what the results are...

                  gm
                  Attached Files

                  Comment


                  • #10
                    PCB PI COIL

                    How would this work if we used heavy copper (say 2,3 or 4oz.) tracks then used a multilayer PCB?

                    Also, could a flooded area in top and bottom of the board be used as a screen?

                    Any ideas on this one anyone?

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                    • #11
                      Originally posted by Sean_Goddard View Post
                      How would this work if we used heavy copper (say 2,3 or 4oz.) tracks then used a multilayer PCB?

                      Also, could a flooded area in top and bottom of the board be used as a screen?

                      Any ideas on this one anyone?
                      A large chunk of copper ground plane next to the coil will look like a target to the detector.

                      I've just performed a simple test with a non-etched board in front of the coil, and with it connected to the shield. As I suspected - no chance.

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                      • #12
                        Hi Sean,

                        PCB coil? Not the money really worth. Too expensive and it isn't necessarily work better than copper wire.
                        Aziz

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                        • #13
                          OK SO....What about a thin crosshatch matrix instead of a flood? With tracks down to 0.02mm with reasonable spacing, it might work.

                          Reason for PCB coils = CONSISTENCY (hopefully). Could use Rogers or PTFE but the price would be astronomical. I'm not interested in the cost, I just don't have time to wind coils and spend a day tweaking them (it's a two coil PI I'm working on) besides a PCB can be calculated and expected to work first time (mostly) .

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                          • #14
                            Here's a thread where TEC had a pcb coil made. I machined one with so so results. Need multi-layer

                            http://www.geotech1.com/forums/showthread.php?t=17789

                            Comment


                            • #15
                              Originally posted by Altra View Post
                              Here's a thread where TEC had a pcb coil made. I machined one with so so results. Need multi-layer

                              http://www.geotech1.com/forums/showthread.php?t=17789
                              What make and model of CNC milling machine do you have?

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