====== Inductor ======

An **inductor** stores energy in a magnetic field associated with electric current. A coil of wire is a common implementation. Inductors are used in filters, impedance matching networks, oscillators and power converters.

===== Ideal relationships =====

Using the passive sign convention, the voltage across an ideal inductor is:

<code>
v = L di/dt
E = ½ L I²
X_L = 2 π f L
</code>

L is inductance in henries (H), di/dt is the rate of change of current in amperes per second, E is energy in joules, and X_L is inductive reactance in ohms. Common radio values use μH (10^-6 H) or nH (10^-9 H).

An ideal 10 μH inductor has approximately 62.8 Ω reactance at 1 MHz. At a steady 1 A, its stored energy is 5 μJ. A constant DC current produces no voltage across an ideal inductor; a real coil still has winding resistance.

===== Phase and switching =====

For sinusoidal signals, an ideal inductor has [[impedance|impedance]] jX_L, so current lags voltage by 90 degrees. Rapidly interrupting current can produce a substantial voltage. This is why relay coils and switching circuits need an appropriate path for their stored energy.

===== Real RF inductors =====

Winding resistance, core losses and parasitic capacitance limit performance. A magnetic core can saturate, changing inductance and increasing distortion or loss. A coil also has a self-resonant frequency; above it, an ideal inductance model is unreliable.

Two nearby coils may couple magnetically. Their orientation and spacing therefore matter in an RF layout. Combining an inductor with a [[capacitor|capacitor]] produces [[lc_resonance|resonance]], which can select or reject a frequency range.

===== References =====

  * [[https://openstax.org/books/university-physics-volume-2/pages/14-2-self-inductance-and-inductors|OpenStax: self-inductance and inductors]].
  * [[https://openstax.org/books/university-physics-volume-2/pages/14-3-energy-in-a-magnetic-field|OpenStax: magnetic energy]].
  * [[https://openstax.org/books/university-physics-volume-2/pages/15-2-simple-ac-circuits|OpenStax: sinusoidal component behaviour]].
  * [[https://www.coilcraft.com/en-us/resources/application-notes/getting-started-an-introduction-to-inductor-specif/|Coilcraft: inductor specifications and practical limitations]].