Microwave Ceramics

Vamsi Krishna. R12ETMM10

Int. M.Tech / Ph.DMaterials Engineering

SEST, UoH

Contents

CeramicsMicrowavesMicrowave Interactions With MatterMicrowave Low Loss Dielectric Ceramic MaterialsSynthesis MethodsDielectric ResonatorsDielectric Resonator ApplicationsConclusionReferences

CeramicsCeramic 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

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

Example

Al2O3, MgO, SiO2,Glass

Metals

Fe2O3, Cr2O3, SiC,Glass

Microwave interactions with Matter

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,

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

Synthesis of (BaMg1/3Ta2/3)O3

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.

DIELECTRIC RESONATORS

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.

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.

Many kinds of dielectric resonator materials have beendeveloped since 1970, and in the present decade, the Qvalues 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

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 Thank you