Introduction Dielectric Materials Classification of Dielectrics Applications of Dielectrics Microwaves Applications of Microwaves Risk of risk Research Microwave Dielectrics Summary and Conclusion
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.
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”. Lenon I.Missel, R.Glang (Ed.) Hand Book of Thin film Technology McGraw-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 2 1 4 n 1 4 e N (CGS ) Nk 2 3 2 k n 2 3 k Clausius- Mossotti equation At high frequency =n2 n= refractive index α= electronic polarisability
Microwaves and MetalsBy 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
Fig. Classification of crystals showing the classes withpiezoelectric, Pyroelectric and Ferro electric
Ability of certain crystals to generate a voltage in response to applied mechanical stress. Quartz Silica ( SiO2) –repeated Strecture (but not ferroelectric) Piezoelectric effect The potential created in certain materials when they are heatedPyroelectric effect Lithium tantalate LiTaO3 The phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. Lithium niobateLiNbO3Ferroelectric effect
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 on1. Frequency of applied electric field2. Chemical structure3. Imperfections4. Temperature and pressure of material Do IT PoMS University of Cambridge
Dielectric constants and Strengths for SomeDielectric Materials William D. Callister, Jr. Materials Science and Engineering An Introduction
SensorsArthur Von Hippel (Ed.)Dielectric Materials and ApplicationsArtech House ,London (1995)
Mailadil ,T. SebastianDielectric Materials for Wireless Communication
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
Interaction of the Electromagnetic field Frequency dependence of the polarizationwith materials mechanism for dielectrics Microwaves and Metals By Manoj Gupta, Eugene Wong Wai Leong
Microwave heating Communications Industrials Power transmissions Medical Scientific Rader detection Weather control Microwaves and Metals By Manoj Gupta, Eugene Wong Wai Leong
APPLICATIONS OF MICROWAVES Blackout Bomb: Air Forces High- Powered Microwave Weapons Fry Enemy Equipment Active Denial System (ADS)
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.
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
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