Difference Between Dielectric Constant and Permittivity

The study of dielectrics and their behavior in electric fields continue to fascinate physicists and electrical engineers alike. Despite the fact that dielectrics are poor conductors of electricity, they play a fundamental role in electronic circuits, which need a dielectric medium to build the circuit. A basic understanding of dielectrics and their properties is thus required.

A dielectric material is nothing but an insulator with a poor conductor of electricity meaning they do not allow current to flow. They are the exact opposite of conductors. Like any other material, a dielectric is an assembly of ions with positive and negative charges. The most important property of dielectrics is their permittivity along with dielectric constant.

The insulating medium separating charged surfaces is called a dielectric. Before we jump into the concept of permittivity, it is important to understand a closely related property, capacitance. Capacitance is the ability of a system to collect and store electrical charge. That being said, the dielectric constant is a measure of the ability of a material to store electrical energy and is defined as the ratio of the capacitance (or permittivity) of the dielectric material to the capacitance of a vacuum. Therefore, all the capacitance values are related to the permittivity of vacuum. Each different dielectric material has its own value of permittivity.

What is Dielectric Constant?

Dielectric constant is a measure of a material's ability to store electrical energy in an electric field. It is a dimensionless quantity that describes the ratio of the electric flux density produced in a material to the electric field strength applied to it. The dielectric constant of a material depends on its molecular structure, chemical composition, and temperature.

The dielectric constant is an important parameter in many applications, including capacitors, electronic circuits, and insulation materials. High dielectric constant materials are useful for storing more electrical energy in a given space and can therefore increase the capacitance of a capacitor. Low dielectric constant materials, on the other hand, are useful for minimizing the loss of electrical energy in electronic circuits, as they reduce the parasitic capacitance between different components.

Dielectric permittivity is associated with a number of other physical properties such as electrical capacitance and speed of light. For example, in a capacitor, the use of a material with a higher Dielectric permittivity allows a given electrical charge to accumulate at less voltage, resulting in a higher capacity of the capacitor at equal other parameters.

The dielectric constant coincides with the relative Dielectric permittivity in a homogeneous medium and is defined as the ratio of the Dielectric permittivity of the medium (ε) to the Dielectric permittivity in a vacuum (ε0).

$$\varepsilon _{r}=\varepsilon /\varepsilon _{0}$$

The Dielectric permittivity in a vacuum is one of the fundamental constants in physics. It equals to the ratio of the electric induction (D) to the intensity of the electric field (E) in a vacuum.

$$\varepsilon _{0}=D/E=\approx 8,8541878176 x 10 -12 F/m$$

It can also be defined as the ratio of the capacitance of a capacitor with a certain dielectric between the plates and the capacitance of the same capacitor with a vacuum between the plates.

It can be measured directly with specialized devices.

What is Permittivity?

Permittivity is the ability of a material to store an electric field in the polarization of the medium. Usually, the permittivity is expressed as the relative permittivity, which is defined as the ratio of the material permittivity to the permittivity of a vacuum. Air approximates to a perfect vacuum and so the dielectric constant for air is approximately zero.

The behavior of molecules in an electric field is characterized by permittivity, which is a very important value that characterizes the influence of any electric field on the behavior of molecules. In engineering applications, permittivity is often expressed in relative. If ε0 represents permittivity of free space and ε represents permittivity, then permittivity εr is expresseds as, $ε_{r} = ε/ ε0$.

Differences: Dielectric Constant and Permittivity

To understand the difference between dielectric constant and permittivity, it is first necessary to understand what these terms mean. Permittivity is a physical property of a material that describes how easily it can be polarized in the presence of an electric field. This polarization occurs when the electric field causes the electrons in the material to shift, resulting in an induced dipole moment. The permittivity of a material is a measure of how much charge can be stored per unit volume of the material, and is typically denoted by the symbol ε.

Dielectric constant, on the other hand, is a dimensionless quantity that is defined as the ratio of the permittivity of a material to the permittivity of free space. This ratio is often denoted by the symbol κ. In other words, the dielectric constant is a measure of how much more charge can be stored in a given volume of a material compared to free space.

The relationship between dielectric constant and permittivity can be expressed mathematically as follows −

$$ε = κε0$$

where ε0 is the permittivity of free space (approximately 8.85 × 10−12 F/m).

One important implication of this relationship is that the dielectric constant is always greater than or equal to 1. This is because the permittivity of a material can never be less than the permittivity of free space, and therefore the ratio of the two must always be greater than or equal to 1.

Another important difference between dielectric constant and permittivity is the units in which they are expressed. Permittivity is typically expressed in units of farads per meter (F/m), while dielectric constant is a dimensionless quantity. This means that the dielectric constant can be used to compare the relative ability of different materials to store charge, without being affected by the units in which the permittivity is expressed.

In practical applications, both dielectric constant and permittivity are important properties of materials that are used in electrical and electronic devices. For example, capacitors are devices that store electrical charge, and their performance is strongly influenced by the dielectric constant and permittivity of the materials used in their construction. Materials with high permittivity and dielectric constant are often used in capacitors to increase their capacitance and improve their performance.

The following table highlights the major differences between Dielectric Constant and Permittivity −

Characteristics	Dielectric Constant	Permittivity
Definition	The dielectric constant is the ratio of permittivity of the dielectric in use to the permittivity of a vacuum. It refers to the relative permittivity of a dielectric material which holds the ability to collect and store energy in the form of electrical charge.	Permittivity, on the other hand, is the ability of a material to store an electric field in the polarization of the medium. Usually, the permittivity is expressed as the relative permittivity, which is defined as the ratio of the material permittivity to the permittivity of a vacuum.
Unit	Since the dielectric constant is a relative measure of ratio of two similar quantities, it has no unit or dimension; it is simply represented by numbers. All materials have a dielectric constant greater than 1. Air approximates to a perfect vacuum and so the dielectric constant for air is approximately zero.	The most important property of a dielectric material is its permittivity. The permittivity of a dielectric material is symbolized as ε which is related to the permittivity of vacuum. The permittivity of a dielectric material is measured in Farad per meter (F/m). The permittivity of vacuum, sometimes called the electric constant is 8.85 × 10−12 F/m

Conclusion

In summary, while dielectric constant and permittivity are related concepts that both describe the ability of a material to store electrical charge, they are not interchangeable.

Permittivity is a physical property of a material that describes how easily it can be polarized by an electric field, while dielectric constant is a dimensionless quantity that describes the relative ability of a material to store charge compared to free space. Understanding the difference between these two concepts is important in the design and optimization of electrical and electronic devices.