Self-Resonant Frequency and Resonant Frequency

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 =

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.

snipped-for-privacy@gmail.com wrote in news:1156206438.807500.298720 @m73g2000cwd.googlegroups.com:

It would help if you tell us what kind of transducer you're talking about.

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.

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I would like to clarify the components I talked about.

For Inductor:

For Transducer:

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...

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.

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?

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