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
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