The Dielectric Material Used in Capacitors

Key Takeaways

• The dielectric material used in capacitors influences the property of capacitance.

• Capacitors can be classified based on polarization; there are polarized capacitors and non-polarized capacitors.

• The permittivity is dependent on the frequency of the voltage applied across the capacitor.

The dielectric material used in capacitors influences the property of capacitance

You might already be familiar with the basic capacitance equation, which relates the capacitance and dielectric material. This equation states that as the relative permittivity of the dielectric material used in the capacitor increases, the capacitance also increases.

ε₀ is the permittivity of vacuum

ε_r is the relative permittivity of the material

A is the area of the plates

d is the distance between the plates

C is the capacitance in Farad

From this equation, we can see that the capacitance value is directly proportional to the relative permittivity of the material that is filled between the conducting plates of the capacitor. This article will explore the different dielectrics and how they influence capacitor performance and dimensions.

The dielectric material used in capacitors influences the property of capacitance. When voltage is applied across the capacitor plates, the dielectric material blocks the flow of current through the material. There are changes in the dielectric material at the atomic level; this phenomenon is called polarization.

Polarization in Capacitors

When voltage is applied across capacitor plates, the electrons in the dielectric material atoms shift towards the positive plate or positive voltage terminal. Electrons only shift at the microscopic level and there is no flow of electrons to create current. This effect is called polarization of the dielectric material, and it has a heavy impact on capacitors; capacitors can be classified by polarization.

Polarized capacitors - The direction of polarized capacitors needs to be taken into account when connecting them to a circuit, as they only work in only one direction (e.g., electrolytic capacitors).

Non-polarized capacitors - Non-polarized capacitors work in both directions and can be used in circuits without paying attention to the polarity. Whenever applied voltage polarity changes rapidly, non-polarized capacitors should be used.

Dielectric Constant of a Material

The electrical energy stored in the electric field is dependent on the amount of polarization. The dielectric constant is the property that indicates the material's ability to store charge. The dielectric constant, also called permittivity, is the material's capability to store electric energy when placed in an electric field.

The absolute permittivity of a material is given by the product of the permittivity of vacuum and a number called relative permittivity. The relative permittivity indicates the ability of the material to store charge in comparison to vacuum. Generally, the relative permittivity of the dielectric materials used in capacitors is greater than 1.

Dielectric Materials Used in Capacitors

Most capacitors use dielectric materials other than vacuum. The dielectric material used in a capacitor is chosen based on its relative permittivity. Some common dielectric materials used in capacitors are given in the table below.
 

How Do Physical Parameters Affect Dielectric Materials?

The physical factors affecting relative permittivity are temperature, pressure, and the frequency of the applied voltage. In certain capacitor applications, the value of the capacitor varies with the ambient or circuit conditions as the dielectric material behaves differently. To achieve a stable capacitance property, materials with stable dielectric constants are often preferred.

The discontinuities in the permittivity of the material caused by temperature variations adversely affect the capacitance value of the capacitor. The increasing temperature drops the permittivity or dielectric constant of the material. The capacitance value diminishes with a rise in temperature.

Frequency of the Voltage Applied

The permittivity is dependent on the frequency of the voltage applied across the capacitor. In the case of DC voltage, there is no frequency and the permittivity of the material remains constant as it is subjected to a static electric field. Such permittivity is called static permittivity. When AC voltage is applied across the dielectric material used in a capacitor, the permittivity of the material changes. The permittivity decreases with an increase in the frequency of the applied voltage.

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