DEVELOPMENT OF NANOCOMPOSITES WITH FRACTAL BASED FSS FOR RADAR WAVE ABSORPTION

Abstract

Development of a thin radar wave absorber with good absorption and wide bandwidth corresponding to reflection loss (RL) < -10.0 dB is still very challenging job for researchers.This dissertation discusses the design of fractal frequency selective surl'aces (FSS) loaded single layer absorber for enhancement of absorption at minimal coating thickness. Two main types of ferrites i.e spinel and hexa ferrites and their composites are synthesized and tested for their radar wave absorption characteristics. The selection of these two materials is done on the basis of their high (spinel ferrites) and low (hexaferrites) values of dielectric constant so as to have comparative study of their effect on radar wave absorption .The waveguide measurements are performed to measure the complex permittivity and permeability values in the frequency regime of 8.2 to 12.4 GHz for all the prepared absorbers. The absorbers are classified into four categories according to their dielectric values (dielectric value from I to 20). i.e Class-i of hexaferrites with Cr5.4 and class-2 of hexaferrite-spinel ferrite composite of Cr = 8.67 , class-3 of spinel ferrite-titanium dioxide of Cr = 12.9 and class-4 of spinel ferrite with Cr =17.2.Parametric study is carried out over different fractals loaded over the synthesized materials for optimizing various parameters like periodicity, dimension of FSS and thickness of absorber. The optimization of the absorber have been carried out with the help of Ansoft 111gb Frequency Structure Simulator (lIFSS). The fractal shapes of Sierpinski carpet, Sierpinski triangle, 1' fractal and Minkowski are loaded over the all the four classes of the absorbers for the parametric analysis. The best fractal identified for the class-I absorber is Minkowski loop level-I having RL of-27 dB with band width of 3.18 GIIz at thickness of 2.9 mm of single layer absorber, class-2 is Minkowski levcl-2 covering the entire X-band frequency regime at 2.2 mm thickness of absorber with an RL value of -16.5 dB.'l'he Sierpinski carpet fractal works best for class-3 absorber with RL of'- 15 dB and BW of 2.856 Gl-iz at 1.8 mm thickness, whereas for class-4 absorber the Sierpinski triangle provides RL of -14.2 dB with BW of 2.94 GHz at 1.5 mm coating thickness of absorber. The best fractal-absorber combination from each class is fabricated on an aluminum sheet and the simulated results are experimentally validated using Attenuation Testing Device (ATD).