Dielectric Constant

Introduction:

Take a small tour to your kitchen, did you ever notice the ceramic cookwares or utensils have some commonality with glass, plastic, mica or even the air? Did you ever think about building an electronic component out of them? Probably not! Because the property of these materials is often overlooked.

What is Dielectric?

A dielectric is a material which has poor electrical conductivity but inherits an ability to store an electrical charge(due to Dielectric polarization). Thus exhibiting only displacement current making it ideal to build a capacitor; to store and return electrical energy.

What is Dielectric Constant?

The dielectric constant of a substance can be defined as:

The ratio of the permittivity of the substance to the permittivity of the free space

It expresses the extent to which a material can hold electric flux in it.

Dielectric Constant Formula

It is mathematically expressed as:

\(\kappa =\frac{\varepsilon }{\varepsilon _{0}}\)
Where,

  • κ is the dielectric constant
  • 𝜺 is the permittivity of the substance
  • 𝜺0 is the permittivity of the free space

Dielectric Constant Units

As it is the ratio of two like entities, it is a unitless, dimensionless quantity.

Dielectric Constant Symbol

The relative permittivity of a dielectric substance is also called a Dielectric Constant, expressed using the Greek letter kappa ‘κ’.

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The Theory Behind Dielectric Constant

This is a prime parameter to characterize a capacitor. A capacitor is an electronic component designed to store electric charge. This is widely built by sandwiching a dielectric insulating plate in between the metal conducting plates. The dielectric property plays a major role in the functioning of a capacitor.

The layer made up of dielectric material decides, how effectively the capacitor can store the charge. Picking the right dielectric material is crucial. Thus, we can also define it as ‘the ratio of the electric field without a dielectric(E0) to the net field with a dielectric(E).’

\(\kappa =\frac{E_{o} }{E}\)
Here, the value of E0 always greater than or equal to E. Thus, The value of a dielectric constant is always greater than 1.

The greater the value of κ more charge can be stored in a capacitor.

In the capacitor, the capacitance is given by C = κC0

Thus, filling the gap between the plates completely by dielectric material will increase its capacitance by the factor of dielectric constant value.

In the parallel plate capacitor, the capacitance is given by:

\(C=\frac{\kappa \varepsilon _{0}A}{d}\)
Where,

  • C is the capacitance of the parallel plate capacitor.
  • κ is the dielectric constant.
  • 𝜺0 is the permittivity of the free space.
  • A is the area of parallel conducting plates
  • D is the separation between parallel conducting plates

The capacitance value can be maximized by increasing the value of the dielectric constant and by decreasing the separation between the parallel conducting plates.

Dielectric Constant Value

Thus, the value of the dielectric constant is crucial in building various electronic components. The following table gives some typical values of dielectric constants:

Dielectric Materials Dielectric Constant Value
The dielectric constant of vacuum 1.00
The dielectric constant of air 1.00059
The dielectric constant of water 80
The dielectric constant of paper 3.6

Factors Affecting Dielectric Constant

The dielectric constant depends on various factors such as:

  • Frequency: The frequency of the applied voltage is one of the factors affecting dielectric constant. As the frequency of the applied voltage increases, the value of the dielectric constant becomes non-linear.
  • Applied voltage: When a direct current voltage is applied, the value of the dielectric constant reduces while applying alternating current voltage would increase the value of the dielectric constant.
  • Temperature: When the temperature is low, the alignment of the molecules in the dielectric material is difficult. By increasing the temperature, the dipoles in the dielectric material become dominant resulting in an increase in the dielectric constant. This temperature is known as the transition temperature. If the temperature rises above the transition temperature, then there will be a gradual decrease in the dielectric constant.
  • Humidity and moisture: The strength of the dielectric material decreased when either the humidity or the moisture is increased.
  • Heating effect: When the dielectric material is heated, the dielectric loss takes place. Dielectric loss is defined as the dissipation of energy in the form of heat when there is a movement of the molecules in the material, as it is exposed to the alternating current voltage. This takes place as the material absorbs electrical energy.
  • The structure and morphology of the material also influence the dielectric constant.
  • Deterioration and weathering of the material also affect the dielectric constant.

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Frequently Asked Questions – FAQs

Define polarization of a dielectric material.

The polarization of dielectric material is defined as the process of production of electrical dipoles inside the dielectric by the application of an external electrical field.

What are the four polarization mechanisms?

The following are the four polarization mechanisms:

  • Electronic polarization
  • Orientational polarization
  • Ionic polarization
  • Space-charge polarization

What is the difference between active and passive dielectrics?

The difference between active and passive dielectrics is that the dielectrics which adapt easily for the storage of electrical energy are known as active dielectrics whereas the dielectrics that restrict the storage of electrical energy are known as passive dielectrics.
Piezoelectric is an example of an active dielectric while the glass is an example of a passive dielectric.

List the various breakdown mechanisms in dielectrics.

The following are the various breakdown mechanisms in dielectrics:

  • Intrinsic and avalanche breakdown
  • Chemical and electrochemical breakdown
  • Thermal breakdown
  • Defect breakdown
  • Discharge breakdown

What is pyro-electricity?

Pyro-electricity is defined as the creation of electronic polarization by thermal stress.

1 Comment

  1. Nice explanation

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