Inductor - also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores
energy in a form of magnetic field established when electric current flows through it.
Basic Inductor construction
Inductor images
Basic Inductor symbol
Inductance, L - is the ratio of the voltage induced in an inductor to the rate of change of current through
it. It is likewise the measure of the ability of an inductor to store magnetic energy. The symbol is L and
the unit is in Henry (H).
L = V/(di/dt) in Henry
Where: L = inductance in Henry
V = voltage induced in Volt
di/dt = rate of change of current through the coil in Ampere/second
In terms of its construction, the Inductance L, is
L = μrμoN2A/l in Henry
L = μN2A/l in Henry
Where: μ = permeability of the core, in H/m
μr = relative permeability of the core, unitless
μo = absolute permeability of free space or vacuum
= 4π x 10-7 H/m
N = number of turns of coil
A = cross-sectional area of the core, square meter (m2)
l = length of the coil in meter (m)
Permeability, μ = is the ratio of the magnetic flux density, B, in a given material to magnetic field
strength, H, of the magnetizing field. It is the measure of how easily or hardly magnetic line of forces
passes through a given material. The unit is Henry per meter (H/m).
Relative Permeability = the ratio of the permeability of a given material to the permeability of free
space.
Mutual Inductance = When two coils are brought in proximity with each other the magnetic field in one
of the coils tend to link with the other. This further leads to the generation of voltage in the second coil.
This property of a coil which affects or changes the current and voltage in a secondary coil is called
mutual inductance. This principle is applied in transformer system.
Transformer
Transformer symbol
Types of Inductors
Inductors are mainly classified based on the material of the core. It comes in different size and
shapes.
1. Air-core Inductor – the most commonly seen inductor, consisting of a simple winding is of wire.
This has nothing but air as the core material. The non-magnetic materials like plastic and
ceramic are also used as core materials. These Inductors offer a minimum signal loss at the
applications having a very high magnetic field strength. Also, there exists no core losses as there
is no solid core material.
Air core inductor
2. Iron-Core Inductor - uses Ferromagnetic materials, such as ferrite or iron, as the core material.
The usage of such core materials helps in the increase of inductance, due to their high magnetic
permeability. This type of inductor suffers from core losses and energy losses at high
frequencies. These Inductors are used in the manufacture of few types of transformers.
3. Toroidal Inductors - uses magnetic material as the core substance to which the wire is wounded
in a circular shape. The main advantage of this type of inductors is that, due to the circular
shape, symmetry is achieved in the whole shape of the inductor, to which there are minimum
losses in the magnetic flux. These inductors are mostly used in AC circuit applications.
Toroidal inductor
4. Laminated Core Inductors - uses laminated thin steel sheets, such as stacks, as the core
materials. Usually for an inductor, if the loop area is increased for the current to travel, the
energy losses will be more. Whereas, in these laminated core Inductors, thin steel sheets of
stacks are helpful in blocking the eddy currents, which minimize the loop action. The main
advantage of these inductors is minimizing the energy loss with its construction. These
laminated core inductors are mostly used in the manufacture of transformers.
5. Powdered Iron Core Inductors – are inductors using magnetic cores with some air gaps in it. This
kind of construction provides an advantage having an ability to store high level of energy
compared with the other type. These inductors provide very low eddy current losses and
hysteresis losses and have very good inductance stability.
6. Ferrite Core Inductor - are manufactured with a ferrite core inside their coil. Using Ferrite cores
provide high permeability to the coil, hence higher inductance. Ferrite core inductors are used in
a range of electric circuit applications including power conversion, broadband, and interference
suppression.
