About Microwave ceramics, microwaves, synthesis of ceramics, dielectrics, applications, etc..

1. Microwave Ceramics
Vamsi Krishna. R
12ETMM10
Int. M.Tech / Ph.D
Materials Engineering
SEST, UoH

2. Contents
Ceramics
Microwaves
Microwave Interactions With Matter
Microwave Low Loss Dielectric Ceramic Materials
Synthesis Methods
Dielectric Resonators
Dielectric Resonator Applications
Conclusion
References

3. Ceramics
Ceramic materials are inorganic, non-
metallic materials made from compounds of a metal and
a non metal. Ceramic materials may be crystalline or
partly crystalline. They are formed by the action of heat
and subsequent cooling
Ceramic materials tend to be strong, brittle, and non-
conductors of heat and electricity
Classification of advanced ceramics
Oxides: alumina, beryllia, zirconia
Nonoxides: carbide, boride, nitride, silicide

4. Microwaves are radio waves with wavelengths ranging from
as long as one meter to as short as one mm, or equivalently,
with frequencies between 300 MHz (0.3 GHz) and 300 GHz

5. Example
Al2O3, MgO, SiO2,
Glass
Metals
Fe2O3, Cr2O3, SiC,
Glass
Microwave interactions with Matter

6. Microwave low loss dielectric ceramic materials
Titanates and titanium compound ceramics have great
potentialities because of their applications as microwave
dielectric resonators.
The ceramic materials should possess high dielectric
constant, low loss and small temperature coefficient of
resonant frequency . Such properties depend on the
method of synthesisation of ceramic materials
Examples : Ba2Ti902 , (ZrSn) TiO, BaTi,O ,
tantalates like Ba(Zr, Zn, Ta)03 or Ba(SnMgTa)O,
MgTi0,CaTiO,

7. Various methods are available in the literature for ceramic
synthesis, such as solid state reaction, oxalate technique and
Sol-Gel methods.
The oxalate method follows the titanium tetrachloride and
barium chloride added to oxalic acid to form barium titanyl
oxalate. This was filtered and the calcination temperature
varied from 550 to 900°C.
Sol-Gel technique is developed for the synthesis of various
ceramic powders.
SYNTHESIS METHODS

8. Synthesis of (BaMg1/3Ta2/3)O3

9. DIELECTRIC RESONATORS
A dielectric resonator or dielectric resonator oscillator is
an electronic component that exhibits resonance for a
narrow range of frequencies, generally inthe microwave band
Dielectric resonators consists of a short length of dielectric
waveguide, typically in the form of a small cylinder or cuboid.
Microwave Dielectric resonators are present in almost all
telecommunication systems.
They generally act as filters and waveguides for microwave
radiation over a large range of frequencies.

10. DIELECTRIC RESONATORS

11. Materials requirements for dielectric resonators
High dielectric constant
High quality factor(low dielectric loss) Q
Small temperature coefficient of resonant frequency.
Q = (maximum energy stored per cycle)/ (average energy
dissipated per cycle)
For an ideal crystal quality factor is approx equal to the
dielectric loss tangent.
Q greater than 2000 is required for practical applications.

12. Dielectric Resonator Applications
1. Microwave oscillators
2. Narrowband microwave filters
3. Radar detectors
4. Speed guns
5. Automatic door openers
6. Cellular telephones
7. Global positioning satellite (GPS) devices.

13. Many kinds of dielectric resonator materials have been
developed since 1970, and in the present decade, the Q
values of these have been remarkably improved.
Dielectric resonators with dielectric constant from 20
to 90 are nowavailable, and they are being used for
appilications such as microwave filters and oscillators.
Along with material development, new techniques and
designs have been developed and applied to dielectric
filters.
Conclusion

14. REVIEW OF PEROVSKITE CERAMICS MICROWAVE
DIELECTRIC RESONATOR MATERIALS
T. SUBBA RAO,V. R. K. MURTHY and B. VISWANATHANS
Department of Physics and Department of Chemistry, Indian
Institute of Technology, MADRAS 600-036, India
Ceramic processing and sintering text book by M.N.Rehaman
Dielectric materials for wireless communication by Mailadil
T.Sebastian.
References

15. 15 Thank you