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Optimum coil shielding method/material

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  • #31
    What might be "cool" would be a hot glue reservoir with a little resistive heater that you switch on. Then it would never require cleaning out, just heat it up and restock as needed. This assumes the glue would stay liquid long enough to reach the coil. Maybe depends on the type of glue.

    -SB

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    • #32
      I use thin lead with sticky back, it comes in 25m reels about 10mm wide, I used to use it on shop windows for security, I am almost out of it now and none of my suppliers stock it anymore, but im still looking, its perfect for the job.

      Regards

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      • #33
        Is this what you are talking about: http://cgi.ebay.com/3M-Lead-Foil-Tap...item1c1a7996b6

        Lots of Lead tape on EBAY

        Dave Frank

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        • #34
          Thats the stuff Vortxrex, I never thought of Ebay, later I will see if I can get it in the Ebay UK.
          Your a star
          Regards

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          • #35
            Originally posted by satdaveuk View Post
            Thats the stuff Vortxrex, I never thought of Ebay, later I will see if I can get it in the Ebay UK.
            Your a star
            Regards
            Yes - you can buy it on the UK ebay. Golfers use it to adjust the weight of their clubs.

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            • #36
              Is it suitable graphite scotch with resistance about 3 kiloohms/centimeter for shielding 27cm DDcoil,operating at frequencies from 6 to 16 khz?

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              • #37
                I forgot about this forum, ive saved it because theres alot of good information on here from them that knows.
                After reading about rubbing graphite onto mylar on here I will do some experments down them lines, far as the bonding bars contacting the graphite im going to use thin copper tape at the start and end points of each coil which at one point will be a soldered earth connection.

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                • #38
                  Try to keep the shielding to 1K or lower.

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                  • #39
                    My guess theory on why metallised mylar film gives better sensitivity is...


                    You want all of the target magnetic flux component to intercept the coil windings - to generate a signal voltage.

                    You do not want metal objects local to where this microscopic feild is, as they would soak up available flux and waste it in eddy current in that metal object.


                    My guess is,

                    1) when you use Al foil the metal content and its thickness are absorbing available flux from the target return - generating eddys in the foil wrap loosing flux that should be getting thru the coil windings and generating signal volts for you.

                    2) With the metallised film - the metal layer is so thin - (you can see light through it) - it cant support eddys, very little incident flux on the shield gets absorbed and lost in the sheild. The bulk of the available flux field can then pass though the coil windings - which generates more target signal volts.

                    Steve

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                    • #40
                      Originally posted by dfbowers View Post
                      I have also tried metallized mylar from a survival blanket. For a few dollars you can get a life time supply. It's only conductive on one side. you cannot solder to it, but you can run a bare wire around the outside of the coil. Then cut the material into long strips and wrap around the coil, conductive side inward.

                      Don
                      I just got one of these:
                      http://www.dealextreme.com/p/outdoor...ival-mat-59697

                      and it doesn't appear to be conductive - just a heads up to others.

                      Maybe video tape would be a better alternative?

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                      • #41
                        A company called Tech-Etch make the following EMI Sheildings. I am currently making my first mono coil so I dont know how good they work.


                        Monel
                        Monel Wire: Per QQ-N-281 - Class A - 0.0045 in. dia.

                        TCS
                        Tin plated copper clad steel has similar characteristics to Monel, with improved shielding at lower frequencies but slightly lower corrosion resistance.
                        TCS Wire: ASTM-B-520 - 0.0045 in. dia.

                        Aluminum

                        Aluminum wire is normally used only when galvanic compatibility with aluminum housing is required.
                        Aluminum Wire: AMS 4182 - Alloy 5056, 0.005 in. dia.

                        Silver/Monel

                        Silver/Monel is silver plated nylon filament with a fine strand of Monel wire knitted over a soft elastomer core to provide a very low compression force while achieving excellent attenuation values.

                        Stainless Steel

                        Stainless steel is used typically when heat and corrosion resistance is required and high attenuation is not needed.
                        S/S Wire: AMS 5697, Type 304, .0045 in. dia.

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                        • #42
                          Farside, there will be metal.

                          It is just between two layers of thin plastic///



                          S

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                          • #43
                            Today i striped down some 50 ohm sat coax to get at copper braid, as part of shielding was a mylar like material
                            low resistance but even when stretched to half it's width twisted and bent with force it did not go o/c like mylar film, measured it's thickness as 0.001" about 1/2" wide
                            will this be suitable for shielding
                            Last edited by woodbob123; 03-08-2012, 06:54 PM. Reason: was RG6 75 Ohm cable

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                            • #44
                              hello

                              i had a fully new idea for coil shielding
                              its a coil shield which you can paint on
                              (i know we had thes thinks already - conductive paint etc. like emv 35)

                              BUT i will test next days a composition of latex with graphite powder (conductive rubber)
                              i have not the best values now, but i think i can be done by starting the mixture by 50/50
                              for testing i put a multimeter into the liquid and stop adding graphit when resistance falls
                              in a range und 10K for test distance of 2cm or so - looks like no pro but i think i can do so

                              regards bernd

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                              • #45
                                Hi Woodbob, Id take a punt its aluminium coated polyester - should be fine. Make sure its weather proof or the sputtered ally will corrode off in hours - being 1000 atoms thick!

                                Never really know until U make it all though, thats the pain of it.


                                If poss go for a 50" overlap to get a good continuous sheild..

                                Dont forget to leave a gap as per other guys instructions

                                S

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