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Understanding the dielectric of a capacitor

The dielectric of capacitors is in the insulating material used in demarcating the plates from contacting each other. Today you’ll learn the various types of dielectric materials used in a capacitor and how they affect the capacitance. You’ll also learn the equation, formula, and calculation of the capacitor’s electric material.

Read more: Understanding capacitor

Apart from the overall size of the conductive plates and their distance or spacing apart from each other, the type of dielectric material used in a capacitor is another factor that can affect the overall capacitance. This is also known as Permittivity (ε) of the dielectric. The conductive plates of a capacitor are generally made of a metal foil or a metal film allowing for the flow of electrons and charge, but insulator material is always used as a dielectric. Different types of insulating materials can be used as the dielectric in a capacitor. They differ in their ability to block or pass an electrical charge.

diagram-multilayer-capacitor-dielectric-material

Just as mentioned in the introduction of this article, the dielectric material can be made from a number of insulating materials or combinations of these materials. The most common types used are air, paper, polyester, polypropylene, Mylar, ceramic, glass, oil, or a variety of other materials.

The process in which the dielectric material or insulator increases the capacitance of the capacitor compared to air is known as the Dielectric constant, K. A dielectric with a high dielectric constant is a way better insulator than a dielectric material with a lower dielectric constant. The dielectric constant is a dimensionless quantity since it is relative to free space.

Read more: Understanding the charge in a capacitor

The actual permittivity or “complex permittivity” of the dielectric material between the plates is then the product of the permittivity of free space (εo) and the relative permittivity (εr) of the material being used as the dielectric. It is given as:

Complex Permittivity

complex permittivity

In other words, if the permittivity of free space is taken, εo as our base level and make it equal to one, when the vacuum of free space is replaced by some other type of insulating material, their permittivity of its dielectric is referenced to the base dielectric of free space giving a multiplication factor called as “relative permittivity”, εr. thus, the value of the complex permittivity, ε will always be equal to the relative permittivity times one.

The typical unit of dielectric permittivity, ε or dielectric constant for common materials are: Pure Vacuum = 1.0000, Air = 1.0006, Paper = 2.5 to 3.5, Glass = 3 to 10, Mica = 5 to 7, Wood = 3 to 8, Metal Oxide Powders = 6 to 20 etc. the final equation for all these materials is denoted as:

equation of a dielectric material

Read more: Understanding Capacitor Voltage Divider

The common method used to increase the overall capacitance of a capacitor with the size small is to interleave more plates together within a single capacitor body. For instance, instead of one set of parallel plats, a capacitor can have many individual plates connected together which increases the surface area, A of the plates.

A standard parallel plate capacitor has two plates, labeled A and B. we can say that n = 2 as the number of capacitor plates is two, where “n” stands for a number of plates. Then the equation above for a single parallel plate capacitor is given as:

equation of a single parallel plate capacitor

Well, the capacitor may have two parallel plates but only one side of each plate is in contact with the dielectric in the middle as the other side of each plate forms the outside of the capacitor. If two halves of the plates are brought and join them together, there will be an effective one whole plate in contact with the dielectric. For a single plate capacitor, n – 1 = 2 – 1 which equals 1 as C = (εor x 1 x A)/d which can also be written as C = (εor*A)/d which is the standard equation above.

Now let say we have a capacitor made up of 9 interleaved plates, then n = 9 as shown. Then we are discussing the multi-plate capacitor.

Let say we have five plates connected to one lead (A) and four plates to the other lead (B). then both sides of the four plates connected to lead B are in contact with the dielectric, whereas only one side of each of the outer plates connected to A is in contact with the dielectric. With the above explanation, the useful surface area of each set of plates is only eight, and its capacitance is given as:

Read more: Understanding capacitance in AC circuits

Modern capacitors can be classified according to the characteristics and properties of their insulating dielectric:

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Low Loss, High Stability such as Mica, Low-K Ceramic, Polystyrene.

Medium Loss, Medium Stability such as Paper, Plastic Film, High-K Ceramic.

Polarized Capacitors such as Electrolytic’s, Tantalums.

That is all for this article, where the various types of dielectric materials used in a capacitor and the calculation, equation, and formula were discussed. I hope you got a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!

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