Introduction to the dielectric and dielectric material
The word ‘Dielectric’ originates from Greek prefix ‘di’ or ‘dia’ meaning ‘across’. That means a material that is positioned across the plates of a capacitor. Dielectric materials are principally plain and simple electrical insulators. Dielectric, materials are a very poor conductor of electric current. When dielectrics are located in an electric field, basically no current flows within them because they do not have loosely bounded electrons (free electrons) that may drift through the material. Instead, electric polarization occurs in dielectrics. The +ve charges inside the dielectric material are displaced minutely in the direction of the electric field, and the negative charges are moved minutely in the opposite direction to the electric field. This slight separation of charge, called polarization, this reduces the electric field within the dielectric.
Fig. Molecular model of a dielectric Material
So polarisation is defined as the alignment of the dipole moments or induced a dipole in the direction of the peripheral electric field. Here it is explained.
Dielectric materials have no free electron because; all the electrons are bounded with the nearest atom. The polar molecules will be in random alignment when there is no peripheral electric field as shown in figure 1. Now, when an electric field is applied to this material, it will get polarised through aligning dipole moments of polar molecules. When a dielectric material is placed in an electric field, it transfers electrical energy through the shifting of current and not through the process of conduction. This is shown in Figure 2.
The dielectric materials are basically used in capacitor performs the following functions:
• Increases the capacitance of the capacitor plate structure.
• Keep conducting away from each other.
• Reduce the possibility of shorting out by sparking during high
As discussed above the presence of dielectric material decrease the voltages. Hence electric field prompted by the charge density.
The effective electric field which is induced by the charge density is given by
σ – Charge density units in A/m2
κ – Dielectric constant.
The effective field is diminished by the polarisation of dielectric material by a factor of κ. This is called the dielectric constant of the material. For a vacuum, its value is
The dielectric constant is defined as the property of an electrically insulating material that is equal to the ratio of the capacitance of a capacitor, (filled with the given dielectric material) to the capacitance of an identical capacitor in a vacuum (without the dielectric material). The addition of a dielectric between the plates of a parallel-plate capacitor raises its ability to store, more charges on each plate, as compared when the plates are separated by a vacuum. A dielectric constant is a number without dimensions. It represents a large-scale property of dielectric materials without knowing its electrical behavior.
At room temperature (25° C, or 77° F) the value of the dielectric constant is 1.00059 for air, 78.2 for water,2.25 for paraffin, and about 2,000 for barium titanate (BaTiO3).
The dielectric constant is sometimes also called relative permittivity or specific inductive capacity. In the centimeter–gram–a second system the dielectric constant is identical to the permittivity.
ε0 – Permittivity of free space units in F/m = 8.854 × 10-12 F/m.
Types of Dielectric Materials
Solids, Liquid, vacuum, and Gases can work as a dielectric. Some examples of solid dielectric materials are paper, mica ceramics, glass, etc. Liquid dielectric materials are also possible are distilled water, transformer oil, etc. Gas dielectrics are nitrogen, dry air, helium, oxides of various metals, etc. A perfect vacuum is also a dielectric.
Application of Dielectric Materials
Dielectric materials can be used in capacitors for the purpose of energy storage. It is used in photosensitive materials to store charge in laser printers and copying machines. It is used for mechanical actuation, sound generation, piezoelectricity, cap sense, etc.
Definition of dielectric strength
The maximum voltage which will be applied to a given material without causing it to interrupt down. it’s usually expressed in volts or kilovolts per unit of thickness.