Inductor

INDUCTOR

Inductor is a passive two‒terminal component that temporarily stores energy in the form of a magnetic field. It is usually called as a coil. The main property of an inductor is that it opposes any change in current.

According to the Faraday's law of Electromagnetic induction, When the current flowing through an inductor changes, the time‒varying magnetic field induces a voltage in the conductor. According to lens law, the direction of induced EMF opposes the change in current that created it. Hence, induced EMF is opposite to the voltage applied across the coil. This is the property of an inductor.

An inductor blocks any AC component present in a DC signal. The inductor is sometimes wrapped upon a core, for example a ferrite core. It then looks as in the Fig. 1.10.

The following figure 1.11 shows an inductor with various parts labelled.

Symbols

The symbols of various types of inductors are as given below.

Storage of Energy

One of the Basic properties of electromagnetism is that the current when flows through an inductor, a magnetic field gets created perpendicular to the current flow. This keeps on building up. It gets stabilized at some point, which means that the inductance won't build up after that. When the current stops flowing, the magnetic field gets decreased.

This magnetic energy gets turned into electrical energy. Hence energy gets stored in this temporarily in the form of magnetic field.

Working of an Inductor

According to the theory of Electromagnetic Induction, any varying electric current, flowing in a conductor, produces a magnetic field around that, which is perpendicular to the current. Also, any varying magnetic field, produces current in the conductor present in that field, whereas the current is perpendicular to the magnetic field.

Now, if we consider an inductor which is made up of a conducting coil and when some current passes through the inductor, a magnetic field is created perpendicular to it. The following figure indicates an inductor with magnetic field around it.

Now, here we have a varying magnetic field, which creates some current through the conductor. But this current is produced such that it opposes the main current, which has produced the magnetic field.

If this current is named as Im which means the current produced due to the magnetic field and the magnetic field is indicated by β, the following figure indicates it.

This opposing current gains strength with the varying magnetic field, which gains energy by the input supply frequency. Hence as the input current becomes more and more AC with high frequency, the resulting opposing current also gains its strength in opposite direction to the very cause producing it. Now, this opposing current, tries to stop the high frequency AC to pass through the inductor, which means "blocking of AC".

Inductance

The property of an inductor to get the voltage induced by the change of current flow, is defined as Inductance. Inductance is the ratio of voltage to the rate of change of current.

The rate of change of current produces change in the magnetic field, which induces an EMF in opposite direction to the voltage source. This property of induction of EMF is called as the Inductance.

The formula for inductance is

Inductance = Nϕ / I

Units

The unit of Inductance is Henry. It is indicated by L.

The inductors are mostly available in (mH) milliHenry and (μH) microHenry.

A coil is said to have an inductance of one Henry when an EMF of one volt is self‒induced in the coil where the current flowing changed at a rate of one ampere per second.

Inductors are available in different shapes and has different uses. Their sizes vary depending upon the material used to manufacture them. The main classification is done as fixed and variable inductors. An inductor of few Henries may be in a dumbbell shape at the size of a simple resistor. A fixed inductor always has silver as its first color in color coding.

The Core of the Inductor is its heart. There are many types of Inductors according to the core material used. Let us have a look at a few of them.

1. Air‒core Inductor

The commonly seen inductor, with a simple winding is this air‒Core Inductor. This has nothing but air as the core material. The non‒magnetic materials like plastic and ceramic are also used as core materials and they also come under this air‒core Inductors. The following figure 1.12 shows various air‒core inductors.

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.

2. Iron‒Core Inductor

These Inductors have 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. Permeability measures the ability of supporting the formation of magnetic fields within the materials. The following figure 1.13 shows how an Iron‒core Inductor looks like

The inductors that have ferromagnetic core materials just like these, suffer from core losses and energy losses at high frequencies. These Inductors are used in the manufacture of few types of transformers.

3. Toroidal Inductors

These Inductors have a magnetic material as the core substance to which the wire is wound. These are in circular ring shape, just as shown in the following figure 1.14.

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, due to which there are minimum losses in the magnetic flux. These inductors are mostly used in AC circuit applications.

4. Laminated Core Inductors

These are the inductors that have 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 following figure 1.15 shows an image of a laminated core inductor.

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

As the name implies, the core of these inductors have magnetic materials with some air gaps in it. But this kind of construction provides an advantage to the core, to store high level of energy compared with the other types. The following figure 1.16 shows an image of a Powdered Iron core Inductor.

These inductors provide very low eddy current losses and hysteresis losses. These are available at lowest prices and have very good inductance stability.