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# Điện môi là gì? Tính chất của điện môi? Phân loại … – Cơ Khí Việt Hàn

## Introduction: Understanding Dielectrics

Have you ever wondered what exactly dielectrics are? What are their properties? And how do they differ from one another? In this article, we will explore these questions and more.

## What are Dielectrics?

Dielectrics refer to a group of materials with insulating properties. In the molecules of dielectric substances, the number of free charges is very low, resulting in their poor electrical conductivity. However, when the electric field exceeds a certain limit, the dielectric will be “pierced” (lose its insulating properties). Each dielectric material has a unique breakdown field, and the dielectric constant ε depends on the properties of the dielectric. The dielectric constant of a vacuum is equal to 1.

### Properties of Dielectric Substances

These are the characteristic properties of dielectric substances:

• Dielectric loss factor (Pa)
• Relative permittivity (dielectric constant – ε)
• Temperature tolerance
• Dielectric strength (Eđ.t)
• Dielectric resistivity
• Electric current in dielectric materials (l)

### Classification of Dielectrics

Dielectric materials are classified into two types: passive dielectrics and active dielectrics. Let’s find out how they differ:

#### Passive Dielectrics

Passive dielectric materials are insulating materials and capacitor materials. They are used as both insulating materials and dielectrics in capacitors, such as mica, ceramics, glass, linear polymers, rubber, paint, paper, synthetic powder, adhesive, etc.

#### Active Dielectrics

Active dielectrics are materials with a variable dielectric constant that can be controlled by:

• Electric fields, such as ceramics, glass, etc.
• Mechanics: Dielectric materials like quartz.
• Light: Fluorescent materials.

## Dielectric Constant

The dielectric constant of a medium characterizes its electrical properties. It is a dimensionless quantity, representing the relative permittivity of the medium compared to vacuum or air. The dielectric constant is denoted by ε and indicates the polarizability of the dielectric material. The formula for calculating the dielectric constant is as follows:

``Dielectric constant = Cd / C0``

Where:

• Cd: Capacitance of the capacitor using the dielectric material
• C0: Capacitance of the capacitor using a vacuum or air as the dielectric material

Dielectric materials used in capacitors require a high dielectric constant (ε), while dielectric materials used as conductive materials have a low dielectric constant (ε).

## Electrical Conductivity of Dielectrics

The electrical conductivity of liquid dielectric substances depends on factors such as molecular structure, temperature, impurities, and the presence of electric charges from electrons and ions. For liquid dielectric substances, surface and impurities play a significant role. In the case of gaseous dielectric substances, the relative electrical conductivity is low. This can occur due to the presence of free charges, external and internal factors, electrons, and ions. X-ray radiation or various types of radiation, molecular collision, and thermal factors can affect the conductivity.

The conductivity of polar substances is created by using a liquid containing dissociated ions. Polar and non-polar liquids have different conductivities. Therefore, if you clean the liquid from impurities, it will reduce ongoing processes. Along with the increase in the conductivity of a liquid and its temperature, decreasing viscosity will occur. This leads to increased mobility of ions.

For solid dielectrics, electrical conductivity is caused by the movement of electric charges of the dielectric material and impurities. In strong current cases, the conductive properties are discovered.

## Electric Current in Dielectrics (I)

The displacement current Ic.m (induced current) is generated by the polarization process of bound charges in the dielectric material until equilibrium is reached.

Leakage current Irò: Generated by free charges and electrons moving under the influence of electric fields. If the leakage current is large, it will cause the dielectric to lose its insulating properties.

The total current passing through the dielectric material is calculated by the formula: I = ICM + Irò. After the polarization process ends, only leakage current remains.

## Applications of Dielectric Constants

Currently, the dielectric constant is applied in various fields, such as:

• Microvalve development.
• Selection and creation of the best dielectric materials for installation in microelectromechanical systems (MEMS). The electronics field is constantly striving to create faster circuits in smaller packages.
• Space exploration with highly sensitive transmission devices for astronomy.
• Defense systems based on steel technology with large quantities.
• Automation with faster reaction times for airbag deployment.

Dielectric constants are also applied in many high-tech devices.