Inductance of different metals

Discussion in 'General Electronics Chat' started by Shagas, Dec 15, 2013.

  1. Shagas

    Thread Starter Active Member

    May 13, 2013
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    Hello

    So while having dinner I decided to refresh my knowledge on LC tuned circuits
    by watching a video from this Guy : and one thing led to another which ended up with me coming across this inductance calculator.
    I noticed that an increase of wire length increases the inductance more than linearly but more interestingly that picking different metals had almost no effect on the value of inductance except ...Nickel. When I pick nickel the inductance value shoots up dramatically .
    Are those numbers legit? Is nickel really that inductive?
    Does nickel have any specific use in electronics or PCBs?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Nickel is ferromagnetic so has a much higher permeability than, say, copper. The inductance of a coil depends on the permeability of material used in its construction, as well as on the coil dimensions and wire length.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    Iron, Cobalt , an Nickel are the only magnetic metals and will each exhibit this jump in the numbers, per Alec_t's reasoning...
     
  4. Shagas

    Thread Starter Active Member

    May 13, 2013
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    Hmm yes makes sense .
    What I didn't expect though is that the inductance increases more than linearly with increasing length.
    At 1Mhz , 1cm of 1mm copper wire has inductance of about 6nH and at 10cm about 105nH which is more than 10 times the amount.
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    For a high Q, you want DC resistance to be as low as possible. Copper is generally preferred for high Q inductors. Ferrites, iron powder, silicon-steel (ferrosilicon), permalloy are generally the core materials used to increase inductance.
     
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  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That depends how the wire is configured. If it's wound uni-directionally into a cylindrical coil the coil inductance varies as the square of the number of turns; which tallies with the figures you quoted.
     
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  7. Shagas

    Thread Starter Active Member

    May 13, 2013
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    Interesting to know , but this calculator shows values for a straight wire.
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    Back in the dark ages, I had a phenolic rod about 1/4" diameter, 6" long, with a ferrite slug on one end and a brass slug on the other. It was used to determine whether the tuning slug of a tank circuit needed to be screwed further into or further out of the coil. If the ferrite slug was placed close to the tank, and the signal response improved, the slug needed to be screwed into the coil. Likewise, if the brass slug placed near the tank improved response, the slug needed to be moved outward from the tank.
     
  9. Tesla23

    Active Member

    May 10, 2009
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    These formulas are based on the work of Rosa
    "The Self and Mutual Inductances of Linear Conductors", E B Rosa, Bulletin of the Bureau of Standards, Vol:4, No:2, 1908

    where he considers the self-linkage of flux for a fixed length of wire. There is a certain arbitrariness in the calculation in that he ignores flux past the perpendicular planes at each end of the wire, but the results have proved useful. The reason that it increases faster than linear in 'l' is similar to the coil analogy. Consider connecting two half sections to double the length. Each section has a self inductance, but some flux from each half also links the other, resulting in the self inductance increasing by more than a factor of 2.

    The original calculations are understandable, see here:

    http://www.g3ynh.info/zdocs/refs/NBS/Rosa1908.pdf

    I'm surprised that using the calculator you linked that the inductance for copper and nickel don't converge more at high frequencies (e.g. 10GHz) as then there would be minimal fields in the conductor, but I haven't investigated.
     
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