Know all About Inductors (Inductance Calculation)

Before knowing the definition and working of what is inductor we should know what is inductance. Whenever a changing flux is connected with a conductor’s coil there would be an emf. If a changing flux is linked with a coil of a conductor there would be an electromagnetic force (emf) induced in it. The inductance of the coil can be defined as the property of the coil of inducing electromagnetic force due to the varying flux connected with it. Due to this reason all electrical coils can be stated as an inductor. An alternative way, an inductor can be defined as it is a one type of device which is used to store energy in the form of magnetic field.This article a brief information about what is inductor, working, conductance calculation and applications.

Inductor and Inductance Calculation
Inductor and Inductance Calculation

What is Inductor?

An inductor is also named as a reactor, coil and choke. It is a two terminal electrical component used in various electrical and electronic circuits. An inductor is used to store energy in the form of a magnetic field. It comprises of a wire, usually twisted into a coil. When a current passes through it, energy stored temporarily in the coil. A supreme inductor is equal to a short circuit for DC, and grants an opposite force to AC that depends on the frequency of the current. The opposition to current flow of an inductor is related to the frequency of the current flowing through it. Sometimes inductors are denoted to as “coils” because the physical construction of maximum inductors is designed with coiled sections of wire.


Construction of Inductor

An inductor generally comprises of a coil with a conducting material, usually protected copper wire covered around a plastic material or a ferromagnetic material. The high permeability of the ferromagnetic core rises the magnetic field and limits it thoroughly to the inductor, thus increasing the inductance. Low frequency inductors are built like transformers, with centers of electrical steel laminated to stop eddy currents.

Soft ferrites are extensively used for cores above audio frequencies. Meanwhile, they do not root the large energy losses at high frequencies. Inductors come in different shapes. Most of the inductors are designed with a magnetic wire covered around a ferrite bobbin with wire visible on the outside, while some enfold the wire totally in ferrite and are stated to as “shielded”. Some kinds of inductors have a changeable core, which allows changing of the inductance.

Construction of Inductor
Construction of Inductor

Small inductors can be fixed directly onto a PCB (printed circuit board) by placing out the trace in a curved design. Small value inductors can also be constructed on ICs (Integrated Circuits) using the similar procedures that are used to make transistors. However, the small sizes limit the inductance, and it is common in various circuits like gyrator that includes a capacitor & active components to perform similarly to an inductor.

Equivalent Circuit of Inductor

Inductors are made with physical components and when these devices are present in an AC circuit, it exhibits a pure inductance. A common circuit of an inductor is shown below. It comprises of an ideal inductor with a parallel resistive component, that replies to AC. The direct current resistive component is in series with the inductor, and a capacitor is placed across the whole assembly and signifies the capacitance existing due to the proximity of the coil windings.

Equivalent Circuit of Inductor
Equivalent Circuit of Inductor

Formulas for Inductance Calculation

The following dimensional variables and physical constants are used to apply to formulas. Units for formulas are also given at the end of equations. For example [in, uH] means the length is in inch and inductance is in Henries.

  • Capacitance is denoted by C
  • Inductance is denoted by L
  • No.of turns are denoted by N
  • Energy is denoted with W
  • Relative permitivity is denoted by εr
  • The value of ε0 is 8.85 x 10-12 F/mRelative permeability is denoted by µr
  • The value of µ0 is 4π x 10-7 H/m
  • One meter is equal to 3.2808 feet and one foot is equal to 0.3048 meters
  • One mm is equal to 0.03937 inches and one inch is equal to 25.4 mm
  • Also, dots are used to specify multiplication in order to avoid ambiguity.

Formulas for Inductance Calculation for connecting inductors in series & parallel are shown below. And also an extra equation is given for various configurations of inductors.

Inductance for Series Connected Inductors

In series connected inductors, the total inductance is equal to the amount of the separate inductances

Inductors in Series
Inductors in Series

LTotal =L1+L2+L3+………….+LN[H]

Inductance for Parallel Connected Inductors

The total inductance of parallel connected inductors is equivalent to the common of the sum of the reciprocals of the separate inductances.

Parallel Connected Inductors
Parallel Connected Inductors

1/Ltotal = 1/L1+1/L2+…………+1/LN [H]

Inductance for Rectangular Cross-Section Inductors

The inductance formula for rectangular cross section inductor is given below

Rectangular Cross-Section Inductors
Rectangular Cross-Section Inductors

L=0.00508.μr . N2.h.ln (b/a) [in, μH]

Inductance of Coaxial Cable

The inductance formula for Coaxial Cable Inductance is given below

Inductance  of Coaxial Cable
Inductance of Coaxial Cable

L= μ0. μr.l/2.π . ln (b/a) [in, μH]
L= 0.140.l.μr.l/2.π . log10 (b/a) [ft, μH]
L= 0.0427. l .μr. log10 (b/a) [m, μH]

Inductance of Straight Wire

The following equations are used for when the length of the wire is longer than the diameter of the wire. The following formula is used for low frequencies – up through about VHF

Inductance of Straight Wire
Inductance of Straight Wire

L=0.00508. l. μr .[ln(2.l/a) -0.75] [in, μH]

The following equation is used for Above VHF, skin effect affects the 3/4the in the above equation to get unity.

L=0.00508. l. μr .[ln(2.l/a) -1] [in, μH]

Applications of Inductors

In general, the applications of different types of inductors mainly include for

  • High power applications
  • Transformers
  • Suppressing noise signals
  • Sensors
  • Filters
  • Radio frequency
  • Energy Storage
  • Isolation
  • Motors

Thus, this is all about what is inductor, construction, inductor working. The usage of these devices somehow is controlled due to its capacity of radiation of electromagnetic interference. In addition, it is a side effect which makes the device depart a little bit from it is actual behavior.Furthermore, any queries regarding this concept or inductor calculator, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of inductor?

Photo Credits:

  • Inductor Basics
  • Inductor
  • Construction of Inductor
  • Series Connected Inductors
  • Parallel Connected Inductors
  • Inductance of Coaxial Cable


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