DEVELOPMENT of (Co-Mn-Ti) SUBSTITUTED

DEVELOPMENT OF (Co-Mn-Ti) SUBSTITUTED

M TYPE BARIUM HEXAGONAL FERRITE BASED MICROWAVE ABSORBER AT X- BAND

M.R.MESHRAM, BHAROTI SINHA, NAWAL K. AGRAWAL*

ROORKEE

P.S.MISRA**

*DEPARTMENT OF ELECTRONICS & COMPUTER ENGINEERING, ** DEPARTMENT OF METALLURGICAL ENGINEERING,

INDIAN INSTITUTE OF TECHNOLOGY ROORKEE

ABSTRACT

This paper present the design, development and characterization of the hexagonal ferrite powder [BaCo0.5Ti0.5Mn0.1Fe()O19] at =1.6 as microwave absorber. The hexagonal ferrite powder has been developed by dry attrition and sintering procedure. The developed ferrite powder 60% by weight has been mixed in epoxy resin to form a microwave absorbing paint. This paint was coated on conducting aluminum sheet to study absorption characteristics of linearly polarized TE wave at X band. The Experimental and computed results for different coating thicknesses have been reported. It has been found that It shows the broadband characteristics with minimum absorption of 6.5 dB from 8 to 12 GHz for a coating thickness of 2 mm. These paints are very useful in military application such as RCS reduction , camouflaging of the target and preventation of EMI etc.

Key Words:- Hexagonal Ferrite, Radar Cross Section, Microwave Absorbing Paint

INTRODUCTION:-

The reduction of electromagnetic backscatter with the use of radar absorbing material (RAM) has important implication in the field of radar and electromagnetic compatibility. A typical RAM usually consist of a thin lossy coating of dielectric or magnetic material over the surface of prefect electric conductor (PEC). These RAM have a particular depth of coating and as such are inherently narrow band. Currently in this field there is interest in the use of Hexagonal Ferrite based microwave absorber to act as a RAM and provide absorption over a wide bandwidth [ 1 ] [ 2 ].

Ferrite is an very important class of magnetic material, more especially it is a metal oxide, which contain magnetic ions arranged in such a manner, which produces spontaneous magnetization, while maintains good dielectric properties. The hexagonal type ferrite absorb microwave energy by lossy interaction of the magnetic field of the wave with their individual magnetization .The hexagonal ferrite materials are suitable RAM due to significant value of permeability (>1), high value of magnetization and planar anisotropic behavior in microwave frequencies.[3 ] [4 ]

There are several types of hexagonal ferrite denoted as M,W and Y phase having complex crystal and magnetic structure. The magnetic ions can be removed by substituting divalent ion and the magnetization was reported to be increased with increasing amount of non magnetic substituition.The presence of large barium ions and the slightly modified crystal structure causes the barium hexaferrite to have high magnetic properties unlike spinel and garnets.The magnetization and the anisotropy of Barium Hexagonal ferrite can be further improved by the external doping of divalent ions(Zn,Co, Ni etc.).[4]

The principle of microwave absorber is based on the reflection reduction by impedance matching, in which the normalized input impedance is calculated with respect to the impedance in free space. Therefore the microwave absorption characteristics that are determined from the reflection loss depend on the frequency (f), thickness (t), complex permeability (r) and complex permittivity r determined by following expression. [ 6 ]

……(1)

…(2)

Where Zm is the normalized input impedance

r =(1-j2) is the relative complex permeability andr = (1-j2)is the complex permittivitty of the ferrite material

In the present communication the microwave absorption characteristics of cobalt manganese and Titanium substituted barium hexagonal ferrite paint of single layer coating of various thickness have been presented.

Preparation of Ferrite and Its Characterization

The sample of hexagonal ferrite powder of composition [BaCo0.5Ti0.5Mn0.1Fe()O19] at =1.6 was prepared by dry attrition and sintering process. The starting material were BaCO3, MnO2,TiO2, CoCO3 and Fe2O3. The sintering was carried out at 1150 oC for 8 hours. The fine particle of size 5 micron was obtained by milling. Fisher Sub Sieve Seizer instruments carried out the particle size analysis.

The developed ferrite powder 60% by weight mixed in epoxy resin to form a microwave absorbing paint. The  and  of ferrite material has been measured by open and short circuit method.[5] The absorption properties for different coating of absorbing paint on aluminum sheet having different thickness have been computed by using equation (1) & (2).

Measurement of Microwave Absorption

Fig1 shows the experimental set up for measurement of microwave absorption at X band.The microwave absorption has been measured by ATD method.[4][5] [7]

ATD(Absorber Testing Device ) is basically a pyramidal horn antenna with extended wave guide section is connected at the aperture of the horn antenna .

(1)Microwave Source

(2) Isolator

(3)3 dB directional Coupler

(4)Power Meter

(5)Pyramidal horn antenna

(6)Extended wave guide section with Tuner

Fig.1 Experimental Setup for measurement

of Microwave Absorption

A reflected power is noted down without coating on aluminium plate.Then reflected power with absorber coated plate is noted. The difference in two Reading gives the power absorbed by the absorber.

RESULTS & DISCUSSION

The variation of complex permeability and complex permittivitty with frequency are shown in fig. 2and fig3. The microwave absorption characteristics for different thickness coating have been shown in fig 4 to fig 6

From figure 2 it is found that the peak value of imaginary part of permeability ” is 2.18 at 8.4 GHz. The complex permeability plays an important role in deciding the absorption properties of ferrite material.

Fig.3. represent the variation of complex permittivitty of ferrite material with frequency it is found that the peak value of real part of permittivity is 6.32 and 6 at 8 and 11.4 GHz respectively.

Fig.4 shows the Experimental and computed result of absorption for single layer coating of thickness t=0.98mm .It gives minimum absorption of 2.5 dB with broadband characteristics.It is observed that the nature of the curve for experimental and computed result are same.

Fig. 5 shows the experimental and computed result of single layer coating of ferrite paint for coating thickness of t=1.25 mm. From fig. it is observed that the minimum level of absorption of 4 dB is available at X band .The nature of curve for both experimental and computed results are nearly same

Fig.6 shows the experimental and computed result of single layer coating of ferrite paint for coating thickness t=2 mm .From fig. it is observed that the minimum level of absorption of 6.5 dB is available from 8 to 11.8 GHz.The maximum absorption of the order of 12 dB is obtained at 10.6 GHz. The variation in absorption with frequency for computed result and experimental results are same.at X band .

CONCLUSION

In this paper authours have gives the comparative study between experimental and computed results for single layer microwave absorber. In the present investigation it is concluded that the minimum level of absorption depends on coating thickness. The broadband characteristics of absorption is obtained between the frequency range of 8.5 GHz to 11.8 GHz with a minimum absorption of 6.5 dB at t=2 mm. Hence because of broad band nature of absorber ,this can be used for camouflaging the target.

References

[1] A. Charles , M.S.Towers and A.McCowen “Sensitivity analysis of Jaumann Absorbers, IEE proceedings Microwave Antennas Propagation ,Vol.146,no.4 ,pp257- 261,August 1999.

[2] M.R.Meshram, Nawal K. Agrawal ,Bharoti Sinha and P.S. Misra, Development and Characterization of Hexagonal Ferrite Based Microwave Absorbing Paints at Ku- Band, IETE Journal of Research Vol. 47, Nos. 5,pp.259- 264,September October 2001

[3] S Sugimoto , S kondo, K okayama, D Book, T Kagotani & M Homma, M type ferrite Composite as a Microwave Absorber with wide Bandwidth n the GHz Range, IEEE Transaction on Magnetics, Vol.35,no.5, and pp 3154- 3156.Sep.1999

[4] M.B. Amin and J.R.James, Techniques for the Utilization of Hexagonal Ferrites in Radar Absorber Part-I Broad band Planar Coating, The Radio and Electronics Engineers,Vol.51,pp.209-218,1981

[5] M.R.Meshram , Bharoti Sinha ,Nawal K. Agrawal & P.S.Misra ,Empirical Relationship between and Ferromagnetic Resonance Frequency in Hexagonal Ferrite Based Microwave Absorbing Paint, Microwave and optical Technology letters Vol.36,No.5, pp 352-355, March 2003 .

[6]M. R.Meshram,B.Sinha,N.K.Agrawal and P.S.Misra,Development and characterization of (Ba-Mn-Ti) hexagonal ferrite based Microwave Absorbing Paint,IEEE Antennas Propagation Society International Symposium USNC/URSI National Radio Science Meeting ,San Antonio ,Texas ,2002,pp.790-793