STUDY AND DEVELOPMENT OF RAM FOR MICROWAVE ABSORPTION ENHANCEMENT AT X-BAND

Abstract

This dissertation discusses the development, characterization and microwave absorption properties of nanostructured Nickel Ferrite and Nickel-Zinc Ferrite and the influence of temperature on crystallite size, lattice constant, saturation magnetization and reflection loss. The effect of loading frequency selective surface (FSS) of double square and triple square loop on reflection loss was also investigated. Synthesis of the material was carried out by a sol-gel mediated auto-combustion technique and phase purity was determined by X-ray diffraction studies and as prepared Nickel Ferrite and Nickel-Zinc Ferrite showed a minimum reflection loss of-14 dB at 8.3 GHz with a layer thickness of 1.5 mm and -35 dB at 9.7 GHz with 2.5 mm thickness, respectively. Nickel Ferrite and Nickel-Zinc Ferrite were heat treated at 500°C and 700°C. The crystallite size of as synthesized samples of nickel ferrite and nickel-zinc ferrite is 10.8 nm and 16.34 nm, respectively, as calculated by Scherrer's formula. The complex permittivity, permeability and the reflection loss of the materials were measured in X-band (8.2 GHz to 12.4 GHz) and the properties were compared for as prepared and heat treated samples. The parameters such as thickness of layers and material sequences were optimized using Genetic Algorithm and Artificial Neural Network (ANN). A comparison has been done on the basis of optimised values for multilaycr absorber provided by two techniques. The optimized values were then simulated using Ansys l-ligh Frequency Structure Simulator' for multilayer, double-square and triple-square FSS elements. The broadening of bandwidth was observed for as prepared Nickel Ferrite and Nickel-Zinc Ferrite by almost 1 GHz and 1.5 GHz, respectively by the loading of double square FSS. The fabrication process was proceeded with the as prepared samples and the experimental verification was done through Attenuation Testing Device (ATD).