How do I calculate the inductance of an air core inductor?
Air core inductor inductance is calculated using Wheeler's formula: L = (r²N²)/(9r + 10l), where r is the coil radius, N is the number of turns, and l is the coil length. This formula provides accurate results for single-layer solenoid coils. See also our Inductor Impedance Calculator.
What is the difference between air core and ferrite core inductors?
Air core inductors have no magnetic core material, resulting in lower inductance but better linearity and no core saturation. Ferrite core inductors have higher inductance in smaller packages but can saturate at high currents and have temperature-dependent properties.
How does coil geometry affect inductance?
Inductance increases with the square of the number of turns and coil diameter, but decreases with coil length. A shorter, wider coil with more turns will have higher inductance than a longer, narrower coil with the same number of turns.
What is the Q factor and why is it important?
Q factor is the ratio of reactance to resistance at a specific frequency, indicating the inductor's efficiency. Higher Q means lower losses and better performance in resonant circuits. Q factor decreases with frequency due to skin effect and proximity losses.
How do I choose the right wire diameter for my inductor?
Wire diameter affects both DC resistance and current handling capacity. Thicker wire has lower resistance but requires more space. For RF applications, consider skin depth - using wire much thicker than 2-3 skin depths provides diminishing returns.
What factors affect the accuracy of inductance calculations?
Calculation accuracy depends on coil geometry assumptions. The formula works best for single-layer solenoids where length is at least 0.8 times the diameter. Very short or very long coils, or multi-layer windings require different formulas.
How does frequency affect inductor performance?
At higher frequencies, skin effect increases wire resistance, proximity effect between turns adds losses, and parasitic capacitance becomes significant. These effects reduce Q factor and can cause self-resonance where the inductor behaves like a capacitor. You might also find our calculate Inductor Color Code useful.