Question
What parasitic characteristic creates an inductor’s self-resonance?
Answer Options
- A) Skin effect
- B) Dielectric loss
- C) Coupling
- D) Inter-turn capacitance
Correct Answer: D
Explanation
An ideal inductor only possesses inductance. However, a physical coil of wire acts as a transmission line where each adjacent turn of wire is separated by a small air or insulation gap. This separation creates a small amount of unwanted capacitance in parallel with the main inductance of the coil.
This unwanted capacitance, known as inter-turn capacitance (or distributed capacitance), combines with the coil’s inductance to form a parallel LC resonant circuit. The frequency at which these two values resonate is the inductor’s self-resonant frequency. Above this frequency, the component is no longer an inductor but acts as a capacitor due to the dominance of the parasitic capacitance.
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