Dielectrics and Microwaves

By E SIVANAGI REDDY12ACPA02

ACRHEM

Introduction

Dielectric Materials

Classification of Dielectrics

Applications of Dielectrics

Microwaves

Applications of Microwaves

Risk of risk Research

Microwave Dielectrics

Summary and Conclusion

Outline of talk

Dielectric is a material that permits the passage of electric field or flux

Eg : Rubber, glass, waxed paper Dielectrics are insulating materials that exhibit the

property of electrical polarization No ideal dielectric in the planet.

Introduction

Bulk Single crystals Polycrystals Ceramics Thin films Polymers Nano dielectrics rubber

Dielectric Materials

Good Mechanical and Chemical Stability Minimum number of defects and impurities Large forbidden band gap Amorphous Structure Small reaction to physical change i.e, low aging and temperature behavior Lack of sensitivity to moisture No pin holes or weak points that have to be “burnt

out”.

Thin film Dielectrics

Lenon I.Missel, R.Glang (Ed.)Hand Book of Thin film TechnologyMcGraw-Hill Book Company

A dielectric is an electrical insulator that can be polarized by an applied electric field.

The polarization of a region is defined as the dipole moment per unit volume

The relation between electronic polarization to dielectric constant is

Dielectrics

N3

4

2

1(CGS )

Clausius- Mossotti equation

n

nN k k

e

k

2

2

1

2

4

3

At high frequency =n2

n= refractive index

α= electronic polarisability

Microwaves and Metals By Manoj Gupta, Eugene Wong Wai Leong

A dielectric material is made up of atoms or molecules that possess electric polarization

basing on it they are classified as Linear dielectric materialsI. Non Polar dielectrics (E)II. polar dielectrics(E+I)III. Dipolar dielectrics (E+I+O)

Non linear dielectrics(spontaneous polarization )• absence of a center of symmetry

Classification of Dielectric materials

Fig. Classification of crystals showing the classes with piezoelectric, Pyroelectric and Ferro electric

Piezoelectric effect

Pyroelectric effect

Ferroelectric effect

The potential created in certain materials when they are heated

Ability of certain crystals to generate a voltage in response to applied mechanical stress.

The phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment.

Lithium tantalate LiTaO3

Lithium niobateLiNbO3

Quartz Silica ( SiO2) –repeated Strecture (but not ferroelectric)

N.IZYUMSKAYA et. al Critical Reviews in Solid State and Materials Sciences,34:89–179,2009

D.C is a measure of the extent to which the electrical charge distribution in the material can be distorted or polarized by the application of electric field.

Dielectric constant depend on 1. Frequency of applied electric field 2. Chemical structure 3. Imperfections4. Temperature and pressure of material

Dielectric constant

University of CambridgeDo IT PoMS

William D. Callister, Jr.Materials Science and Engineering An Introduction

Dielectric constants and Strengths for Some Dielectric Materials

Applications of dielectrics

Sensors

Arthur Von Hippel (Ed.)Dielectric Materials and ApplicationsArtech House ,London (1995)

Microwaves

Mailadil ,T. Sebastian Dielectric Materials for Wireless Communication

Frequencies Range

Electromagnetic Spectrum MW have wavelengths 1mm - 1m , frequencies of 0.3 - 300 GHz.

To avoid interference with telecommunication, cellular phones and radar, by International convention most domestic and commercial MW heating operate wavelength of 12.2 cm, 2.45 GHz.

MW can be divided in an electric field and a magnetic field component and the former is responsible for heating.

MW is generated by vacuum tubes, magnetron, multimode or mono-mode Commercial ovens

General Principles

Microwaves interaction with materials

Microwaves and Metals By Manoj Gupta, Eugene Wong Wai Leong

Frequency dependence of the polarization mechanism for dielectrics

Interaction of the Electromagnetic field with materials

Microwave heating Communications Industrials Power transmissions Medical Scientific Rader detection Weather control

Applications of Microwaves

Microwaves and Metals By Manoj Gupta, Eugene Wong Wai Leong

APPLICATIONS OF MICROWAVES

Blackout Bomb: Air Force's High-Powered Microwave Weapons Fry Enemy Equipment

Active Denial System (ADS)

Remote Sensing Applications in India

ISRO

Risk of Risk Research

Microwave Dielectric materials

Dielectric resonators

Dielectrics are the materials having perment electric dipole moment .

Different type of dielectrics(Piezo, Ferro, Pyro electrics) have Potential applications in various fields.

Microwaves form part of the EM spectrum, with frequency ranging from 300MHz to 300GHz.

Microwave usage is extremely diverse, with applications in heating, radar, communication, industry, Science, medicine and power transmission.

Summery

1.Gupta,Wong : Microwaves and Metals John Wiley & Sons (Asia)Pt Ltd, 2007 2. Kenji Uchino :Ferroelectric Devices 2/e CRC Press ,2010 3. Kwan Chi Kao :Dielectric Phenomena in Solids Elsevier Academic Press,2004 4. Charles Kittel: Introduction to Solid State Physics 7/e WILEY-INDIA,2007 5. Arthur Von Hipple(Ed.): Dielectric Materials and waves Artech House, London ,1995

References