Inductors & coils

In one line

An inductor is a coil of wire that stores energy in a magnetic field. It is the mirror image of a capacitor: a capacitor resists changes in voltage, an inductor resists changes in current.

<figure style="text-align:center;margin:1.5rem 0"> <svg viewBox="0 0 280 90" role="img" aria-label="Inductor symbol: coil humps between two wires" style="width:100%;max-width:320px;height:auto;color:var(--c-iot)"> <line x1="14" y1="52" x2="70" y2="52" stroke="currentColor" stroke-width="2"/> <path d="M70 52 a12 12 0 0 1 24 0 a12 12 0 0 1 24 0 a12 12 0 0 1 24 0 a12 12 0 0 1 24 0 a12 12 0 0 1 24 0" fill="none" stroke="currentColor" stroke-width="2.5"/> <line x1="190" y1="52" x2="266" y2="52" stroke="currentColor" stroke-width="2"/> <text x="140" y="84" font-size="11" fill="var(--text-3)" text-anchor="middle">inductance L (henries) — opposes change in current</text> </svg> </figure>

How it works

Changing current changes the magnetic field, which pushes back (Lenz's law).

• Smoothing & filtering — with a capacitor, the heart of power supplies (DC-DC converters) and filters.
• Coupling without contact — two nearby coils transfer energy through the shared field. Inductive coupling.

Where it shows up in digital health

• Wireless charging of implants — a pacemaker or cochlear implant charged through the skin, no wire through the body.
• MRI gradient coils create the changing fields that encode where a signal comes from (the knocking of an MRI).
• Switching power supplies in every device.

Watch for

Break a coil's current fast and the collapsing field makes a large spike — so a coil-driven load needs a flyback diode.