Inductors are one of the three fundamental passive components (along with resistors and capacitors). They store energy in a magnetic field when current flows through them and release it when the current changes. In the MicroBasement, inductors are everywhere: from vintage tube radio coils to modern power supplies and RF circuits. This write-up covers the theory and history of inductance, what constitutes an inductor, manufacturing evolution (wirewound, ferrite core, air core, SMD), identification (color codes, markings), sizes (large to SMD), inductors on semiconductor chips, and their enduring importance.
The concept of inductance was discovered by **Michael Faraday** in 1831 when he observed electromagnetic induction: a changing magnetic field induces voltage in a conductor. Joseph Henry independently discovered it in the US around the same time. The unit of inductance is the **henry** (H), named after Henry. Faraday's law (V = -L di/dt) defines inductance L as the ratio of induced voltage to rate of change of current. Complex formulas evolved in the 19th century with Maxwell's equations (1860s), describing magnetic fields and energy storage (1/2 LI˛). Inductors became essential in early radio (tuning coils), power supplies (chokes), and transformers.
An inductor is a coil of wire (usually copper) that creates a magnetic field when current flows. Energy is stored in the magnetic field and opposes changes in current (back EMF). Inductance is measured in henries (H); practical values range from microhenries (µH) to henries (H). Core materials (air, ferrite, iron powder) increase inductance. Inductors are non-polarized and have low DC resistance but high impedance at high frequencies (XL = 2pfL).
Inductors have evolved from large coils to tiny SMD components:
Inductors are identified by:
Inductor sizes have shrunk dramatically:
SMD inductors use numerical codes (e.g., 102 = 1 µH).
On ICs, inductors are fabricated using spiral metal coils (aluminum or copper) on-chip or in package. Sizes: Nanohenries to microhenries. Used in RF circuits, voltage regulators, filters, and oscillators. On-chip inductors have lower Q (quality factor) due to substrate losses but enable integration in RFICs (e.g., Wi-Fi, Bluetooth chips). Off-chip or package inductors are used for higher Q or power applications.
Inductors evolved from large coils to tiny SMD chips, enabling filtering, energy storage, and RF tuning in every electronic device. In the MicroBasement, they remind us that the simplest components are the most essential — storing magnetic energy, blocking high frequencies, and shaping signals since Faraday's 1831 discovery.