Proceedings of International Conference on Microwave - 08

Epoxy Resin modified Urea Formaldehyde and Silicon UreaFormaldehyde as Microwave Absorbers

M.Murugan1, V.K.Kokate2

, A.A.Athawale3, M.H.M. AIhousami4

IDepartment of Electronics and Telecommunication Engineering, Vishwakarma Institute ofInformation Technology, PUNE-48, M.S, India, 2Department of Electronics and

Telecommunication Engineering, College of Engineering, PUNE-5, M.S, India., 3,4 Departmentof Chemistry, University ofPune, Pune-7, M.S, India.

Email: muruganviit@rediffmail.com

Abstract - In recent days, various microwave absorbersare used for electromagnetic interference andcompatibility measurements in anechoic and semi-anechoicchambers. The authors have synthesized three differentpolymer composites of epoxy resin modified by ureaformaldehyde and silicon urea formaldehyde of differentwt%. The samples were made as small films of specificdimension in order to test them in the X-band frequencyrange by inserting them in the flange. The performancecharacteristics of samples were carried out by thetransmission/reflection method using a vector networkanalyzer R&S: ZVT8. The results are analyzed at theend for the suitability of the material in the X-band and isobserved that the urea formaldehyde provides betterreflection co-efficient over a larger bandwidth.

Index Termss - Anechoic chamber, electromagneticcompatibility, electromagnetic interference, microwaveabsorbers, reflection coefficient, silicon urea formaldehyde,urea formaldehyde.

I. INTRODUCTION

Now-a-days, electromagnetic interference andcompatibility (EMI&C) [1] has become one ofthe majorproblems due to the advances is radio frequencyequipments at all walks of our life. Overexposure ofmicrowave energy has been reported as potentiallyharmful to human and biological systems [2], and hencethe microwave energy should be completely absorbed inmany applications. Various microwave absorbers suchas carbon loaded pyramidal shaped polyurethane foamsand ferrite tiles are used in anechoic/ semi-anechoicchambers for different EMI&C measurements [3]-[6].Due to the limiting factors such cost of the materials,availability etc., polymers are studied intensively withrespect to their properties, temperature transitions,dielectric properties, modes of chemical synthesis, andtailoring of properties with different morphologies. Inthe work presented here, the efforts were made forfabricating and testing of few polymer compositematerials such as urea formaldehyde (UF) and siliconwith urea formaldehyde (SUF), modified with the epoxyresin for different wt%.

II. EXPERIMENTAL

A.. MaterialsAll the chemicals used were of AR grade. Epoxy

resin was procured from Shimo Resin Pvt. Ltd. under

978-1-4244-2690-4444/08/$25.00©2008 IEEE

480

the trade name SHIMOREZ- 400, the density at 25°Cbeing 1.11 g/ml, viscosity at 25°C being 12000 ± 300mPaS. Silicon metal powder sympol Si Mesh at wt28.09 was from AMRUT industrial products, P.B No 46Thana (India).B. Samples

Three monomers of each of epoxy resin modified[7]-[10] by urea formaldehyde and silicon ureaformaldehyde were prepared as samples with followingcombinations.1) Epoxy resin modified by urea formaldehyde

UF-1. Composite of epoxy and ureaformaldehyde with a ratio of 1.0: 0.1 wt.%respectively.

UF-2. Composite of epoxy and ureaformaldehyde with a ratio of 1.0: 0.2 wt.%respectively.

UF-3. Composite of epoxy and ureaformaldehyde with a ratio of 1.0: 0.5 wt.%respectively.

2) Epoxy resin modified by silicon urea formaldehydeSUF-1. Composite of epoxy, silicon and urea

formaldehyde with a ratio of 1.0: 0.3: 0.3wt.%.

SUF-2. Composite of epoxy, silicon and ureaformaldehyde with a ratio of 1.0: 0.4: 0.4wt.%.

SUF-3. Composite of epoxy, silicon and ureaformaldehyde with a ratio of 1.0: 0.5: 0.5wt.%.

C. Method ofPreparationThe epoxy resins were first modified by adding

different materials. The reaction mixtures were preparedby mixing appropriate quantities of epoxy resinmonomer and hardener in a beaker. The mixture wasstirred to obtain a paste [ 11 ]-[13]. This was poured in atest tube and kept in a water bath maintained at a fixedtemperature and then dried.D. Preparation ofFilms

The monomers prepared with appropriate quantitiesof materials and epoxy resins in wt.% were taken in aglass beaker and heated on a hot plate at 80° C withcontinuous stirring for half an hour. After cooling, themixture [11]-[12] was made into a thin film having thedimensions 34 mm (Length) x 22 mm (Height) x 1 mm

Proceedings of International Conference on Microwave - 08

Port 2

Measurement setup.

Ua1erial(or SaJllllle) UMer Test

Fig. 2.

Port 1

IV. MEASUREMENT RESULTS AND DISCUSSIONS

On the basis of measurements and the subsequentobservations obtained, the results various samples arediscussed below.A) Epoxy resin modified by urea formaldehyde

Fig. 3. shows the performance characteristicsrecorded for the all three samples of ureaformaldehyde/epoxy resin with the varying epoxy andurea formaldehyde ratios in wt%. For all three ureaformaldehyde samples, in the entire range of 8.000 -12.500 GHz the reflection loss is well below -10 dB,with the bandwidth of 4500 MHz. For UF-l, theminimum reflection loss of - 16.647 dB takes place atthe frequency of 10.292 GHz.

For UF-2, between 10.100 - 10.359 GHz and11.736 - 12.050 GHz the measured reflection loss is lessthan -20 dB. The minimum reflection loss of -27.038dB takes place at 11.927 GHz. Similarly, for UF-3,between 8.082 - 8.641GHz and 11.874 - 12.112 GHz,the reflection loss is -20 dB or less, with the bandwidthof 797 MHz. The minimum reflection loss of -34.090dB takes place at the frequency of 11.938 GHz.

deduced on the basis of the reflection from the materialand the transmission through the material. Reflectionmeasurements are, in fact, far more popular thantransmission in guided wave geometries.

Vector Network AnalyzerR&SZVTS

Fig. 1. SEM for (a) epoxy resin blank and (b) Epoxy resinwith 0.5g Silicon

The magnifications were selected depending on theclarity of the morphology that could be observed. Incase of pure epoxy sample the crystallite size appears tobe rather fine with equal fraction of void spaces inbetween different crystallites indicating poor impactproperties or brittleness of sample [14] - [15]. On theother hand, the epoxy modified with silicon exhibitshomogeneity in morphology to render better impactstrength to the material. Further, modification withsilicon depicts agglomerates containing silicon, and themorphology appears to be similar as for pure epoxy.

III. MEASUREMENTS

(Thickness). Finally, they have been tested for theirmicrowave absorption properties.E. Morphological features

The SEM analysis of blank epoxy resin and epoxyresin with 0.5g silicon were performed on AnalyticalScanning Electron Microscope (SEM) JEOL-JSM-6360A. The samples were coated with Platinum beforeanalysis. The impact fracture surfaces were examined bySEM. The analysis was carried out at differentmagnifications for finding out the defects present in thematerial. Fig.l shows the SEM micrographs of pureepoxy together with modified epoxy containing 0.5g ofsilicon.

Once the samples were made as films, itsperformance characteristics [16] were studied using avector network analyzer, R&S ZVT8, in the X-bandfrequency range. The results are analyzed at the end.Prior to the measurement, the vector network analyzerwas calibrated. The practical measurement setupconfiguration used is given in Fig.2. In the transmission/reflection method [1 7] used here, the material under testis inserted in a piece of transmission line, an X-bandwaveguide flange and the properties of the material are

-- W1- ..2- ..~

10 11 12Frequency' (60Hz)

Fig. 3. Performance of urea formaldehyde/epoxy resin.B) Epoxy resin modified by silicon with urea

formaldehydeFig. 4. shows the performance characteristics

recorded for the all three samples of silicon ureaformaldehyde /epoxy resin with the varying epoxy,

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Proceedings of International Conference on Microwave - 08

silicon and urea formaldehyde ratios in wt%. In SUF-1,it is seen that, between 8.000 - 10.925 & 11.150- 12.303GHz the reflection loss is -10 dB or less, with thebandwidth of 4078 MHz. The minimum reflection lossof - 17.351dB takes place at the frequency of 11.919GHz. For SUF-2, between 8.000 - 12.463 and 12.610 -13.825 GHz the reflection loss is -10 dB or less, withthe bandwidth of5678 MHz, whereas, between 14.213-14.364 GHz, the reflection loss is -20 dB or less, withthe bandwidth of 151 MHz. The minimum reflectionloss of - 24.158dB takes place at the frequency of14.224 GHz.

In a similar way, for SUF-3, It is seen that, between8.000 - 12.850 & 13.600 - 14.650 GHz the reflection lossis -10 dB or less, with the bandwidth of 5900 MHz andbetween 14.174 - 14.374 GHz, the reflection loss is -20dB or less, with the bandwidth of 200 MHz. Theminimum reflection loss of - 27.006 dB takes place atthe frequency ~f 14.230 GHz.

-- Ut- ..2

-"I

10 11 12 13 14Frequencv(GHz)

Fig. 4.Perfonnance of silicon urea fonnaldehyde/epoxyresin.

v. CONCLUSION

On the basis of performance characteristicsrecorded for various samples of urea formaldehyde/epoxy resin and silicon urea formaldehyde /epoxy resin,the results are summarized in the Table I and Table IIrespectively.

TABLE. ISUMMARY OF RESULTS FOR UREA FORMALDEHYDE /

Epoxy REsINUF-l UF-2 UF-3

Frequency rangein GHz with 8.000 8.000 8.000reflection loss is to to to-10 dB or less 12.500 12.500 12.500Bandwidth 4.5 GHz 4.5 GHz 4.5 GHz

Frequency range 10.100 to 8.082 -in GHz with - 10.359 8.641reflection loss is & &-20 dB or less 11.736 to 11.874 -

12.050 12.112Bandwidth - 573 MHz 797 MHz

Minimum -16.647 - 27.038 -34.090reflection (dB)Frequency ofmin. reflection in 10.292 11.927 11.938GHz

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TABLE IISUMMARY OF RESULTS FOR SILICON UREA

FORMALDEHYDE / EpOXY RESINSUF-l SUF-2 SUF-3

Frequency range 8.000- 8.000- 8.000-in GHz with 10.925 12.463 12.850reflection loss is & & &-10 dB or less 11.150 - 12.610 - 13.600 -

12.303 13.825 14.650Bandwidth(MHz 4078 5678 5900)Frequency range - 14.213 - 14.174 -in GHz with 14.364 14.374reflection loss is-20 dB or lessBandwidth in - 151 200MHzMinimum - 17.351 - 24.158 - 27.006reflection (dB)Frequency ofmin. reflection 11.919 14.224 14.230inGHz

It may be observed that the reflection loss of -10dB or less, is obtained for almost all samples of epoxymodified urea formaldehyde and silicon with ureaformaldehyde. In terms of minimum reflectioncoefficient, the UF-3 and SUF-3 shows betterperformance as compared to their counterparts.However, the UF-3 may be a better choice forapplications in wide band operation. This also providesminimum reflection or maximum absorption ofmicrowave energy. Hence, these microwave materialsmay be used as a substitute to the existing conventionalmaterials, in terms of cost effectiveness and ease ofsynthesis. Also, by means of increasing the wt.% ofureaformaldehyde, it is possible to optimize the bandwidthover which the reflection characteristics are better as perthe requirement. Hence, the materials presented may bedeemed as better choice for electromagnetic interferenceand compatibility measurements in the anechoicchamber / semi anechoic chamber in the X-band.

ACKNOWLEDGEMENTS

Authors would like to acknowledge ChemistryDept., University of Pune. Author Muruganacknowledges BCUD, University of Pune for financialsupport and thank Dr. Rajkumar of DIAT, Pune for hisvaluable guidance. Author Mohamed would like tothank the Ministry of Higher Education, Republic ofYemen for their financial supports.

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