Dielectric Constant

Many materials possess a tremendous property to hold their electrical charge for long intervals and in large quantities as well. Such property of materials refers to dielectric property. Many students get confused with the term dielectric constant, property, and often ask what is relative permittivity. This guide is beneficial to understand the meaning and factors affecting the dielectric constant. 

What are Dielectric Materials?

Dielectric materials have weak electrical conductivity but possess the ability to store an electrical charge. There are several dielectric materials, including vacuum, air, and more. The values of dielectric constants of some dielectric materials include:

• For air- 1.00059

• For glass- 3.8-14.5

• For paper- 3.6

• For vacuum- 1.00

• For PVC- 4.0 

What Is Meant By Dielectric Constant?

The dielectric constant of any substance refers to the relative permittivity of the dielectric substance. It is the proportion of the permittivity of the material to the permittivity of the free space. Mathematically, the dielectric constant can be expressed as:

K = \[\frac{\epsilon }{\epsilon_{0} }\]

where K refers to Dielectric constant

             \[\epsilon\] refers to the permittivity of the substance

             \[\epsilon_{0}\] is defined as the permittivity of the free space

Dielectric Constant Theory

Many students ask what the meaning of dielectric constant is. In order to understand the meaning of dielectric constant, it’s crucial to first understand the theory behind it. Dielectric constant serves as the major factor required to describe a capacitor. A capacitor is an electronic device built by inserting a dielectric insulating plate in-between the metal conducting plates. It’s the layer made from a dielectric material that decides if a capacitor can store a high charge or not. That’s why it is essential to choose the best dielectric material depending on the dielectric property. 

From the dielectric constant formula:

K = \[\frac{\epsilon }{\epsilon_{0} }\], we get the value of relative permittivity of free space is always greater than or equal to relative permittivity of substance. Hence, the value of the dielectric constant (K) is always either equal to greater than 1. 

What does a High Dielectric Constant Mean?

The high value of the dielectric constant means the value of capacitance can be maximised. It can be seen from the capacitance formula in the parallel plate capacitor:

C = Kϵ0 A/d

where K refers to the dielectric constant

C refers to the capacitance of a parallel plate capacitor.

A refers to the area of parallel conducting plates

\[\epsilon_{0}\] is defined as permittivity of free space

d refers to the separation between parallel conducting plates

Hence, from this formula, it’s clear that there are two ways to increase the value of capacitance. The first is to decrease the separation between parallel conducting plates, and the second is to enhance the dielectric constant value. 

What Do You Mean by Dielectric Constant Equation?

According to the dielectric constant equation:

K = \[\frac{\epsilon }{\epsilon_{0} }\]

K is the ratio of two entities with the same dimension. Hence, the dielectric constant is a unitless and dimensionless quantity. 

What Factors Affect the Value of the Dielectric Constant?

After knowing what is dielectric constant, there come different factors that affect the dielectric constant value such as:

• Temperature: The arrangement of molecules in the dielectric material is tough at the low temperature. However, with the increase in temperature, the dipole moment increases, and hence there is a rise in the dielectric constant value. The temperature at which the dielectric constant starts increasing refers to the transition temperature. Moreover, if the temperature goes above the transition temperature, the dielectric constant will start decreasing. 

• Heating Effect: The students asking what is dielectric property can understand from the fact that on heating any dielectric material, there is a dielectric loss. It is due to the dielectric property of the material due to which whenever there is any movement of molecules inside the material, there is the dissipation of energy. When the dielectric material absorbs electrical energy, it dissipates energy in the form of heat.

• Applied Voltage: The value of the dielectric constant decreases in the presence of a direct current voltage. However, the dielectric constant value increases when an alternating current voltage is applied. 

• Frequency: The frequency of the applied voltage serves as one of the critical factors that affect the dielectric constant to a great extent. Whenever there is an increase in the frequency of the external voltage applied, the dielectric constant value becomes non-linear. 

• Humidity and Moisture: When there is an increase in humidity or moisture, there is a decrease in the strength of dielectric material. 

The Coulomb force present between the two-point charges in a material is affected by material property; this process is termed as relative permittivity of a material. The factor relative permittivity is used to decrease the charges present between the electric field relative to the vacuum.

While comparing the relative permittivity of two similar capacitors, the relative permittivity can be easily defined as the ratio between the capacitance of the capacitor of a material to the capacitance of that of a vacuum. 

Relative permittivity is widely known as dielectric constant also.

The historic name for the relative permittivity is the dielectric constant. Because of its ambiguity, some older records used it widely as absolute permittivity instead of the term dielectric constant. This term is deprecated by the standard organizations. The permittivity is considered as either a static property or a frequency-dependent variant.

Applications

Relative permittivity has a huge number of applications too. Some of the major applications which are common are described in detail below:

Energy:

Relative permittivity in the case of energy is used as an essential piece of information that is further used in designing Capacitors. The following material might be expected to introduce capacitance into a circuit. The materials which are having high relative permittivity when placed in an electric field reduces the magnitude of that particular field within the volume of the dielectric. The following process which is described above is used to increase the capacitance of a capacitor design. In printed circuit boards (PCBs) there exists a layer beneath the attached conductor's which act as a dielectric.

Communication:

These are majorly used in RF transmission lines. Polyethene is highly used in between the centre conductor and outside shield, in the case of a coaxial cable. When placed inside waveguides which are also used to form filters. The best example of dielectric waveguides is optical fibres. This waveguide consists of doped impurities which further helps in order to control the precise value of relative permittivity within the cross-sections. Being an appropriate factor to control the refractive index of the material, these are highly used in optical modes of transmission. However, technically the relative permittivity matters because they are not operated in the electrostatic limit while considering the above-mentioned case.

Environment:

Relative permittivity plays a vital role in changes in environmental factors. The air is highly affected by the changes in temperature, humidity and barometric pressure. Due to the changes in the relative permittivity, changes in the capacitance occur. These changes can be measured through sensors. As barometric pressure is always fairly stable, most of the changes occurring in the environment are due to the effect of temperature and humidity only. 

Taking into consideration capacitance and the measured temperature along with using the engineering formulas the relative humidity can be obtained.

Chemistry:

The measure of the chemical polarity is the relative static permittivity of a solvent. In order to understand the above statement let us consider an example. As we all know that water is highly polar in nature the relative static permittivity of water is 18.10 at 20⁰C. On the other hand, n-hexane is a nonpolar solvent with a relative permittivity of 1.89 at 20⁰C.  While dealing with analytical chemistry, this information is highly used in order to design separation, sample preparation and chromatography.

These are some of the major applications highly used on the basis of dielectric constant.