Two parallel conductors form an inductor?

Discussion in 'General Electronics Chat' started by alphacat, Jun 29, 2009.

  1. alphacat

    Thread Starter Active Member

    Jun 6, 2009
    In a course I take, the lecturer has modelled two transmission lines as two parallel plates, with width W, distance d from each other, and lenght l, and has said that the two parallel plates form an inductor which its inductance equals to μ*d*l/W (l is considered to be very short).

    Could you please explain to me, how come two parallel plates form an inductor?
    It is also weird to me that the farther the plates are, the larger the inductance they form.
    Since in that way, placing conductors far from each other forms a very large inductor.

    Here is an illustration.

    Thank you very much.


    Senior Member

    May 26, 2009
    The distance of the places will account for the impedance. Each plate will have inductance.
  3. DC_Kid

    Distinguished Member

    Feb 25, 2008
    parallel, but are they connected to each other at their ends? if not you'll get more capacitance than inductance.

    every conductor has both and varies with frequency. once you start changing their shape and proximity to each other the cap and ind can vary quite a bit, etc.
  4. alphacat

    Thread Starter Active Member

    Jun 6, 2009
    Thanks guys.

    You're right, large inductance means great characteristic impedance and therefore the characterictic impedance will have much less influence on the circuit.
    The other note you remarkeed is something I dont understand, why each plate has an inductance?

    DC KID,
    Yes they are connected at there ends by a load, but the transmission line is considered to be very long, and these plates are only a small part of it, so it takes time until these plates sense the load (by sensing the returned wave that returns from the load).
    As I said, I dont understand why every conductor has inductance, and why two parallel conductors (modelled as plates) have an inductance that depends on the distance between each other.
    I mean, I learned that two plates form a capacitor, not an inductor.
  5. bertus


    Apr 5, 2008
  6. alphacat

    Thread Starter Active Member

    Jun 6, 2009
    Hey Betrus,
    Thanks for the link, there's great info there.
    As my lecturer, they take it for granted that every conductor forms an inductor, which I try to understand why is that.

    BTW, awesome cat :)
  7. Wendy


    Mar 24, 2008
    Because it is inherent in any current conductor. Anytime a magnetic field is formed, that is inductance. Any current forms a magnetic field. The longer the wire, the more magnetic field is formed, the greater its inductance. With really high frequencies you have to calculate it into the design.

    One of the reasons surface mount technology (SMT) is taking over is because the smaller sizes reduce the so called trivial things like capacitance and inductance on leads. The shorter the lead the smaller the inductance it has. I once built two identical RF filters, one with through hole components and one with SMT. The rolloffs were identical, but the SMT had 10db greater rejection.

    Senior Member

    May 26, 2009
    Yes, that's what I was trying to explain. Any conductor will form a magnetic field around it when current flows through.

    SMT parts are difficult! I cannot connect to A BGA package! Yikes!