Dielectric Materials

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High performance electrical properties can be obtained by chemical and physical property control.

A dielectric material is an electrical insulator which can be polarized in an electric field (Fig.1).

Elektrik alan altında dielektrik malzemenin polarizasyonu, polarization of dielectric material under applied electric field

Figure 1. Polarization of dielectric material under applied electric field.

Some of the related important terms  about dielectric materials are:

  • Permitivity: The ability of a material to polarize and store charge within it.
  • Dielectric Strength: The maximum electric field that can be maintained between two conductor plates without causing a breakdown.
  • Dielectric Loss: Loss of energy that goes into heating a dielectric material in a varyig electric field.

Table 1. Dielectric constants of different materials.

Dielectric constants of some materials are shown in Table 1.

MATERIALDIELECTRIC CONSTANT
Air1
Silica4
Alumina10
Tantalum Pentoxide27
Niobium Pentoxide42
Strontium Titanate300
Barium Titanate2000-10000

Dielectric materials can be used in various applications. Cables, electronic equipments (capacitors, semiconductors, transducers, sensors etc.) are fabricated from insulating (dielectric materials). Liquid dielectrics are also electrical insulators (silicone oil, organic esters etc).

Capacitors

Capacitors are electrical elements which have two conductor plates seperated by dielectric material. Capacitors can be used for filtering frequencies or storing energy. Supercapacitors are improved for the usage in cars.

There are three types of capacitors and the most basic is the electrostatic capacitor with a dry separator. This classic capacitor has very low capacitance and is mainly used to tune radio frequencies and filtering. The size ranges from a few pico-farads (pf) to low microfarad (μF).

The electrolytic capacitor provides higher capacitance than the electrostatic capacitor and is rated in microfarads (μF), which is a million times larger than a pico-farad. These capacitors deploy a moist separator and are used for filtering, buffering and signal coupling. Similar to a battery, the electrostatic capacity has a positive and negative that must be observed.

The third type is the supercapacitor, rated in farads, which is thousands of times higher than the electrolytic capacitor. The supercapacitor is used for energy storage undergoing frequent charge and discharge cycles at high current and short duration.

BaTiO3 nano particles can be used to develop ceramic/polymer nano composite super capacitor materials with high permitivity, low leakage and high dielectric breakdown strength. Surface modification is an important topic to disperse ceramic nano particles in polymer recipies. Various types of functional ligands are used to control wetting, contact angle, friction, encapsulation, passivation properties. Super capacitors are good substitutes for lithium ion and lead acid battery technologies. Super capacitors have much potantial to store energy per kilogram as a lithium – ion battery and charge up in less than four minutes.

For electronic design engineers, other important supercapacitor characteristics include high power densities and very long lifetimes regardless of the number of charge cycles. This is a distinct advantage over batteries.

These characteristics complement many new applications characterized by widely varying energy requirements such as with smartphones. In these applications, they can be used to extend battery life. Supercapacitors are also displacing both conventional capacitors and batteries in many mature applications (http://www.mouser.com.tr/applications/new-supercapacitor-applications/). Trains, planes, and automobiles (as well as trucks) account for about 40 percent of today’s $400 million worldwide supercapacitor market, according to market researcher Paumanok Publications Inc. Transportation applications include maglev trains, power and braking recuperation systems, truck lifts, and track switching.

Of more interest to the typical design engineer are consumer electronics, computer, and communications applications. Supercapacitors are frequently designed into these products for memory protection. Internal back-up power is another common application. The supercapacitor can be used either as a battery replacement or as a short-term redundant back-up supply.

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Ceramic Capacitor Code

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Supercapacitor technology for electric cars

Polymer-Inorganic Dielectric Composites 

Using micro and nano Technologies offers new approaches for insulating systems to use at relatively high temperatures and electrical stress. Barium titanate, barium strontium titanate, aluminium nitride, doped zinc oxide etc. can be used as fillers to increase the dielectric coefficient of polymers. For example nuclear plants require advanced materials for electrical equipment which are resistant to low and high energy radiations.

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Wang Lab/Penn State