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Self-Resonant Frequency and Resonant Frequency

Discussion in 'Electronic Basics' started by [email protected], Aug 22, 2006.

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  1. Guest

  2. w2aew

    w2aew Guest

    Resonance (in electrical parlance) refers to the frequency where the
    capacitive reactance is equal to the inductive reactance. At this
    point, the phases cancel and you get a sharp change in the overall
    impedance. For example, a parallel LC circuit (capacitor in parallel
    with an inductor) will be in resonance at a frequency where 2*pi*f*L =
    1/(2*pi*f*C). At this frequency, the impedance of this parallel LC
    circuit will be extremely high due to the phase combination.

    Normally, the term "self-resonant" frequency refers to the resonant
    frequency of a component due to the parasitic characteristics of the
    component. For example, the physical construction of a capacitor will
    determine the parasitic inductance of the leads/connections to the cap.
    The frequency where the capacitive reactance of the cap and the
    inductive reactance of the lead's parasitic inductance, is the
    self-resonant frequency. It is a property of the physical
    characteristics of the device - and to some extent, defines where the
    cap no longer behaves like a cap, but begins to behave like an
    inductor.

    When designing resonant circuits, you pick the capacitance and
    inductance. Ideally, you will operate at frequencies that are far away
    from the self-resonant frequency of the individual components. Of
    course, there are special circumstances where you might do a design
    that involves utilizing components near their self-resonant frequency,
    but it isn't that common.
     
  3. Jim Land

    Jim Land Guest

    wrote in @m73g2000cwd.googlegroups.com:
    It would help if you tell us what kind of transducer you're talking about.
     
  4. default

    default Guest

    An inductor has a "self resonant" frequency bacause the turns of wire
    have small "parasitic" capacitors to each other and its surroundings.
    Two wires laying next to each other form a capacitor . . . the self
    resonance in a tesla coil produces higher voltages than the simple
    turns ratio of the transformer might account for. Electrical
    resonance.

    Self resonance in a transducer may be electrical and mechanical. For
    instance, a piezo transducer when struck will produce voltage, but it
    will also vibrate for a period (like striking a steel bar) after it is
    struck. The mechanical vibration also produces voltage till it dies
    out.

    If you drive a transducer at its resonant frequency it is much more
    efficient at producing output. The analogy is to push a swing just as
    it is about to start its return motion.
     
  5. Guest

    I would like to clarify the components I talked about.

    For Inductor:
    http://www.mouser.com/catalog/627/782.pdf

    For Transducer:
    http://web.pui.com/AudioCommerce/images/catalog/audiopdfs/AI-4228-P-SP250.pdf

    They use "Self-Resonant Frequency" for Inductor and "Resonant
    Frequency" for Transducer. I wonder if that is the same term. Is the
    word "Self" implied something?

    Thanks...
     

  6. No, they are not the same. Self resonant frequency happens because
    no inductor is pure inductance. It also has resistance and capacitance.
    As the frequency goes up, you reach a point where the inductor no longer
    has the characteristics you need. When you choose an inductor, you want
    to make sure that the SRF is above the frequency you need. I prefer at
    least a 50% margin.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  7. Guest

    No, they are not the same. Self resonant frequency happens because
    Thanks. I understand Self-Resonant Frequency now. However, I may miss
    this but let me make sure I got everything correctly. So Resonant
    Frequency of a Transducer is to get to the max output (the closer, the
    better), while Self-Resonant Frequency of an Inductor is to "stay away"
    (the higher, the better). Am I wrong?
     


  8. No, that's it in it's simplest form.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
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