An inductor is a passive
electronic component that stores energy in the form of a magnetic field. In its
simplest form, an inductor consists of a wire loop or coil. The inductance is
directly proportional to the number of turns in the coil. Inductance also
depends on the radius of the coil and on the type of material around which the
coil is wound. For a given coil radius and number of turns, air cores result in the least
inductance. Materials such as wood, glass, and plastic - known as dielectric materials
- are essentially the same as air for the purposes of inductor winding.
Ferromagnetic substances such as iron, laminated iron, and powdered iron
increase the inductance obtainable with a coil having a given number of turns.
In some cases, this increase is on the order of thousands of times. The shape
of the core is also significant. Toroidal (donut-shaped) cores provide more
inductance, for a given core material and number of turns, than solenoidal
(rod-shaped) cores.
The standard unit of inductance
is the henry, abbreviated H. This is a large unit. More common units are
the micro henry, abbreviated µH (1 µH =10-6H) and
the millihenry, abbreviated mH (1 mH =10-3 H).
Occasionally, the nanohenry (nH) is used (1 nH = 10-9 H).
It is difficult to fabricate
inductors onto integratedcircuit (IC) chips. Fortunately, resistors can be
substituted for inductors in most microcircuit applications. In some cases,
inductance can be simulated by simple electronic circuits using transistors,
resistors, and capacitors fabricated onto ICchips.
Inductors are used with
capacitors in various wirelesscommunications applications. An inductor
connected in series or parallel with a capacitor can provide discrimination
against unwanted signals. Large inductors are used in the power supplies of
electronic equipment of all types, including computers and their peripherals.
In these systems, the inductors help to smooth out the rectified utility AC,
providing pure, battery-like DC.
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