QA on Delectric Materials

Q1. Describe the definition of dielectric materials

Dielectric materials are electrical insulators which can be easily polarized by external electric field.  The presence of electric field results in charges re-arrangement in which the positive charges are displaced toward the field whereas negative charges are in opposite direction so called dielectric polarization. They are categorized as electrical insulator since there is no field induced-charges flow as it happens on conductor. This is due to large energy band gap and no free electron exists at conduction band. Closely seeing to the atomic model, the external electric field will distort electron cloud surrounding nucleus and give rise to electric dipole.

Q2. Categorize dielectric materials and describe their features individually

Category	Illustration/Features
Piezoelectric Materials	In piezoelectric materials, applying mechanical forces/stresses will induce spontaneous polarization inside materials due to ionic displacement (direct piezoelectric effect), or oppositely applying electric field will cause structural deformation (inverse piezoelectric effect)
Pyroelectric Materials	In pyroelectric materials, temporary voltage due to spontaneous polarization will be generated when the materials are heated or cooled. The change in temperature slightly modifies the atomic position within crystal structure.
Ferroelectric Materials	In ferroelectric materials, spontaneous electric polarization can be reversed by the application of external electric field. The reversibility of spontaneous polarization is observed as hysteresis in P-E curve.

Q3. Describe the real application of dielectric materials to electric devices

Applications	Descriptions
Motion  sensor (Passive Infra Red) PIR sensor	PIRs are basically made of a pyroelectric sensor (the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. That is why PIR sensors allow us to sense motion,　and they are almost always used to detect whether a human has moved in or out of the sensors range.
Piezoelectric Sounder	Basically, the sound source of a piezoelectric sounder is a piezoelectric diaphragm. A piezoelectric diaphragm consists of a piezoelectric ceramic plate which has electrodes on both sides and a metal plate. Applying D.C. voltage between electrodes of a piezoelectric diaphragm causes mechanical distortion due to the piezoelectric effect. When AC voltage is applied across electrodes, the bending is repeated and producing sound waves in the air.
FRAM (Ferroelectric Random Access Memory) with RFID (Radio Frequency Identity) interface	F-RAM performs reads and writes like a RAM. It provides reliable data retention for 20 years while eliminating the complexities, overhead, and system level reliability problems caused by EEPROM and other nonvolatile memories, combined with RFID to enable traceability through monitoring. Large amounts of information can be stored with each individual product, for example historical records and other tracking information as well as ID.