Calculate inductance of single-layer air core solenoid coils using Wheeler's formula.
| AWG | Diameter (mm) | Max Turns/cm | Typical Use |
|---|---|---|---|
| 22 | 0.64 | ~15 | RF coils, low power |
| 18 | 1.02 | ~10 | Medium power, general |
| 14 | 1.63 | ~6 | High power, low freq |
| 12 | 2.05 | ~5 | Tesla coils, high current |
L = (r² × n²) / (9r + 10l)
Where L is inductance in µH, r is coil radius in inches, n is number of turns, and l is coil length in inches. This formula is accurate for single-layer solenoid coils where l > 0.4r.
Air core inductors are essential in radio frequency circuits where ferrite cores would introduce losses or saturate at high frequencies.
Used with capacitors to create resonant circuits for oscillators, filters, and tuned amplifiers at frequencies from kHz to GHz.
Air core inductors help match antenna impedance to transmission lines without the frequency limitations of ferrite cores.
Air core coils provide high Q-factor (quality factor) for sharp filtering in receiver front-ends and frequency-selective circuits.
Large air core inductors are the primary and secondary coils in Tesla coils, operating at high voltages where cores would saturate.
Transmitter and receiver coils for wireless charging use air core designs to allow magnetic field coupling through the gap.
Thicker wire (lower AWG) reduces resistance and increases Q-factor, but limits how tightly you can wind turns. Balance wire size with desired inductance.
Use non-conductive forms (plastic, ceramic, or air) to maintain the air core properties. Metal forms would act as shorted turns.
Every inductor has parasitic capacitance between turns, creating a self-resonant frequency. Stay well below this frequency for proper operation.
Air core inductors radiate magnetic fields and are susceptible to interference. Use shielding or orient coils perpendicular to minimize coupling.