Design of broadband microwave absorbers using carbonyl iron filled silicon rubber sheets in the frequency range of 1 to 8 point 2 GHz

Abstract

quotFor microwave absorber applications, carbonyl iron (CI) powder is a commonly used filler material in silicon rubber because of the high value of attenuation coefficients newline(50.56 dB/cm), high curie temperature, good temperature stabilization and the higher specific saturation magnetization intensity. Silicon rubber is preferred as the host material because of many desirable properties such as excellent weathering resistance, resistance to aging, chemical resistance, insulating properties and compatibility with many kinds of fillers. Microwave absorbers using carbonyl iron filled silicone rubber sheets (CISR) are widely used to attenuate electromagnetic interference, eliminating cavity resonances, isolating components via insertion loss, reducing harmonics and termination signals in waveguides. The fabrication accuracies in thicknesses and concentrations of CISR sheets are ± 0.5 mm and ± 2% of CI by volume, respectively. Multilayer microwave absorbers designed in this thesis have two layers because of inaccuracies in fabrication of CISR sheets. Broadband microwave absorbers are designed by using conventional type and pixelated type Frequency Selective Surface (FSS) layers embedded between two different concentrations of CISR sheets in the frequency range of 3.95 GHz to 8.2 GHz which are light in weight and small in thickness. newlineWR-187 (3.95 to 5.85 GHz) and WR-137 (5.85 to 8.2 GHz) rectangular dielectric waveguide (RDWG) systems are designed for non destructive testing of reflectivity, r and and#956;r of broadband microwave absorbers. RDWG systems consist of vector network analyzer (VNA), coaxial cables, coaxial to rectangular waveguide transitions, sections of metallic waveguides, standard gain horn antennas and sections of dielectric waveguides. For 1 to 8.2 GHz, NRL arch method is used for measuring reflectivity of microwave absorbers in the anechoic chamber at normal incidence and 20° in TE/TM polarizations. This method involves measurements with two double ridge horn antennas, two long coaxial cables, wooden...