WHAT IS THE DIELECTRIC CONSTANT? - PHYSICAL - 2025

The dielectric constant is a value associated with the material that is placed between the plates of a capacitor (or capacitor - Figure 1) and that allows optimizing and increasing its function. (Giancoli, 2006). Dielectric is synonymous with electrical insulator, that is, they are materials that do not allow the passage of electrical current.

This value is important from many aspects, since it is common for everyone to use electrical and electronic equipment in our homes, recreational spaces, educational or workstations, but surely we are unaware of the complicated processes that occur in this equipment to be able to function.

Figure 1: Different types of capacitors.

For example, our minicomponents, televisions and multimedia devices, use direct current for their functions, but the domestic and industrial currents that reach our homes and workplaces are alternating currents. How is this possible?.

Figure 2: Electrical circuit of a domestic equipment

The answer to this question is within the same electrical and electronic equipment: capacitors (or capacitors). These components allow, among other things, to make possible the rectification of alternating current to direct current and their functionality depends on the geometry or shape of the capacitor and the dielectric material present in its design.

Dielectric materials play an important role, since they allow the plates that make up the capacitor to be very close, without touching, and completely cover the space between said plates with dielectric material to increase the functionality of the capacitors.

Origin of the dielectric constant: capacitors and dielectric materials

The value of this constant is an experimental result, that is, it comes from the experiments carried out with different types of insulating materials and resulting in the same phenomenon: increased functionality or efficiency of a capacitor.

Capacitors are associated with a physical quantity called capacitance "C", which defines the amount of electrical charge "Q" that a capacitor can store by supplying a certain potential difference "∆V" (Equation 1).

(Equation 1)

Experiments have concluded that by completely covering the space between the plates of a capacitor with a dielectric material, the capacitors increase their capacitance by a factor κ, called the "dielectric constant." (Equation 2).

(Equation 2)

An illustration of a flat parallel plate capacitor capacitance C charged and consequently with a uniform electric field directed downward between its plates is presented in Figure 3.

At the top of the figure is the capacitor with a vacuum between its plates (vacuum - permittivity ∊0). Then, at the bottom, the same capacitor with capacitance C '> C is presented, with a dielectric between its plates (of permittivity ∊).

Figure 3: Plan-parallel plate capacitor without dielectric and with dielectric.

Figueroa (2005), lists three functions for dielectric materials in capacitors:

1. They allow a rigid and compact construction with a small gap between the conductive plates.
2. They allow a higher voltage to be applied without causing a discharge (the breakdown electric field is greater than that of air)
3. Increases the capacitance of the capacitor by a factor κ known as the dielectric constant of the material.

Thus, the author indicates that, κ "is called the dielectric constant of the material and measures the response of its molecular dipoles to an external magnetic field". That is, the dielectric constant is higher the higher the polarity of the material's molecules.

Atomic models of dielectrics

In general, materials have specific molecular arrangements that depend on the molecules themselves and the elements that make them up in each material. Among the molecular arrangements that intervene in dielectric processes is that of the so-called "polar molecules" or polarized.

In polar molecules, there is a separation between the middle position of the negative charges and the middle position of the positive charges, causing them to have electrical poles.

For example, the water molecule (Figure 4) is permanently polarized because the center of the positive charge distribution is midway between the hydrogen atoms. (Serway and Jewett, 2005).

Figure 4: Distribution of the water molecule.

While in the BeH2 molecule (beryllium hydride - Figure 5), a linear molecule, there is no polarization, since the center of distribution of positive charges (hydrogens) is in the center of distribution of negative charges (beryllium), canceling any polarization that may exist. This is a nonpolar molecule.

Figure 5: Distribution of a beryllium hydride molecule.

In the same vein, when a dielectric material is in the presence of an electric field E, the molecules will align as a function of the electric field, causing a surface charge density on the faces of the dielectric that face the capacitor plates.

Due to this phenomenon, the electric field inside the dielectric is less than the external electric field generated by the capacitor. The following illustration (Figure 6) shows an electrically polarized dielectric within a planar-parallel plate capacitor.

It is important to note that this phenomenon results more easily in polar materials than in nonpolar ones, due to the existence of polarized molecules that interact more efficiently in the presence of the electric field. Although, the mere presence of the electric field causes the polarization of nonpolar molecules, resulting in the same phenomenon as with polar materials.

Figure 6: Models of the polarized molecules of a dielectric due to the electric field originated in the charged capacitor.

Dielectric constant values ​​in some materials

Depending on the functionality, economy, and ultimate utility of the capacitors, different insulating materials are used to optimize their performance.

Materials such as paper are very inexpensive, although they can fail at high temperatures or in contact with water. While rubber, it is still malleable but more resistant. We also have porcelain, which resists high temperatures although it cannot adapt to different shapes as needed.

Below is a table where the dielectric constant of some materials is specified, where the dielectric constants have no units (they are dimensionless):

Table 1: Dielectric constants of some materials at room temperature.

Some applications of dielectric materials

Dielectric materials are important in global society with a wide range of applications, from terrestrial and satellite communications including radio software, GPS, environmental monitoring through satellites, among others. (Sebastian, 2010)

Furthermore, Fiedziuszko and others (2002) describe the importance of dielectric materials for the development of wireless technology, including for cellular telephony. In their publication they describe the relevance of this type of materials in the miniaturization of equipment.

In this order of ideas, modernity has generated a great demand for materials with high and low dielectric constants for the development of a technological life. These materials are essential components for Internet devices in terms of data storage functions, communications and the performance of data transmissions. (Nalwa, 1999).

References

1. Fiedziuszko, SJ, Hunter, IC, Itoh, T., Kobayashi, Y., Nishikawa, T., Stitzer, SN, & Wakino, K. (2002). Dielectric materials, devices, and circuits. IEEE Transactions on microwave theory and techniques, 50 (3), 706-720.
2. Figueroa, D. (2001). Electrical Interaction. Caracas, Venezuela: Miguel Angel García and Son, SRL.
3. Giancoli, D. (2006). PHYSICAL. Beginning with applications. Mexico: PEARSON EDUCACION.
4. Nalwa, HS (Ed.). (1999). Handbook of low and high dielectric constant materials and their applications, two-volume set. Elsevier.
5. Sebastian, MT (2010). Dielectric materials for wireless communication. Elsevier.
6. Serway, R. & Jewett, J. (2005). Physics for Science and Engineering. Mexico: International Thomson Editores.