What is inductor and its history? An inductor is a device which stores the energy in the form of a magnetic field and this property to store energy is called electro magnetism. It is passive electrical component, usually consists of wire which is wrapped around a ferromagnetic material in the form of coil, when current is passed through this coil then magnetic field is produced and the strength of this magnetic field is depending upon number of turns of coil. Means if number of turns are low then the strength of magnetic field would be low similarly if number of tuns are high then the strength of magnetic field would be high. Because it stores energy in the form of a magnetic field therefore it does not change the current suddenly. First time, inductor was discovered by Michael Faraday in 1830 by a simple but a strange way. He just wraps a wire around a cylindrical paper then he attached both ends of this wire with a galvanometer which is current measuring device, then he moved the magnet inside and outside of this cylindrical paper then current produced in a galvanometer that was saw by Michael Faraday by the movement of needle of galvanometer. After that, Nicholas Calland was discovered the inductor coil. Which has been currently used in the form of an inductor. Figure 1 shows the inductor symbols with core, length of wire and number of turns of coil,
Figure 1 Symbols, Length of wire and Number of turns of Coil.
Types of Inductor
Different types of coils has been currently in used and here we have divided them based on their core.
- Toroidal Core Inductor: This type has ring or donut shaped surface and wire is wounded around this surface. This is made up with different types of materials such as tape wound, powered iron or ferrite etc. This gives the high coupling results but it early saturate at high frequency therefore it is only used for low frequency applications. It is mainly used in medical devices, telecommunication devices switching regulators, air conditioners, refrigerators, digital and analogue power supplies. A simple toroidal is shown in figure 2
Figure 2 Toroidal types
- Air Core Inductor: This type is mainly made up with a ceramic material therefore ceramic inductors are commonly known as air core inductor. It has very low thermal co-efficient expansion, but it has no any magnetic property therefore when it will use as core then it does not increase the magnetic permeability. Its main purpose to use in an inductor is to just give the proper shape of coil. The main advantage of this core is it gives high quality factor and low core loss. It is mostly used in high frequency application where low inductance is required. A simple air core coils is shown in figure 3
Figure 3 Air core
- Iron Core Inductor: This is the type whose core is made up with iron material and this type is best for that places where low space inductors are in need. These are used for high power, high inductance but low frequency applications such as in audio equipment’s. Its applications are limited as compared to other types of inductors. A simple iron core coil is shown in figure 4
Figure 4 Iron Core
- Ferrite Core Inductor: This is the type whose core is made up with ferromagnetic material which is referred as a ferrite core. Ferromagnetic material is compound of metal oxide with iron and other elements are mixed with this to form a crystalline structure There are two types of ferrite cores are currently in used first one is soft ferrite core and second one is hard ferrite core. Soft ferrite core has ability to change the polarity of its magnetism with out using any amount of energy. Similarly, hard ferrite core is just like a permanent magnet some where it is also called a permanent and its polarity becomes always same even when it will move from one direction to another direction. This type of ferrite core also helps the inductor to increase its performance by increasing the permeability of the coil, which leads the inductor to increase its inductance. The increasing permeability range is in between 20 to 15000 but also depend ferrite material. If its inductance is compared with air, then it is so much high. A simple ferrite core type is shown in figure 5
Figure 5 Ferrite Core
- Powdered Iron Core Inductor: This type of inductor core is made up with 100% pure iron material but its outer surface in coated with insulating powder material therefore it is called powdered iron inductor. Because this core is made up with 100% iron therefore it gives the solid structure but for making this powdered iron, it is compressed at high pressure then a binder such as epoxy or phenolic is mixed with this to form a powdered iron. When both materials are mixed then a distributed air gap is produced, and this air gap stores high magnetic flux. This air gap also prevents core to become saturate as well as high dc current could be passed without core saturation. It has high temperature co-efficient therefore it is mainly used in switching power supplies. A simple powdered iron is shown in figure 6
Figure 6 Powdered Iron Core
- Laminated Core Inductor: This type of inductor core is made up with laminated sheets and these sheets are made up with steel material. These sheets are arranged with each other from top to bottom to make a proper laminated core. Because these sheets have different length and thickness therefore these are joint with each other through insulating material which make the core flexible. In this inductor core because each is sheet is separated from other sheets through insulating material therefore this structure saves the core from eddy current losses. These types of cores are used for high power applications, therefor it has low frequency and mostly used in filtering devices where excitation frequencies are high normally in KHz. A simple laminated core inductor is shown in figure 7.
Figure 7 Laminated Core
- Variable Inductor: It is the type of inductor in which magnetic core is moved around inductor winding and by adjusting magnetic core the user can easily adjust the inductor value. These types of inductors are mainly used for high frequency applications where tuning is required such as in radio etc. These are easily available in market in range from 10uH to 100uH and 10nH to 10mH. A simple variable inductor is shown in figure 8,
Figure 8 Variable type
Coupled Inductor: It is the type in which two inductors are connected together by electro magnetic induction. As we know the mutual induction phenomena in which when voltage is flows in one then voltage is generated in other which is coupled with this through mutual induction. Similarly, the coupled inductor works on this phenomenon. These inductors are used for isolation purposes where two circuits are electrically isolated from each other. A simple coupled type is shown in figure 9