A Study of the Anechoic Performance of Rice Husk-Based, Geometrically Tapered, Hollow Absorbers

Although solid, geometrically tapered microwave absorbers are preferred due to their better performance, they are bulky and must have a thickness on the order of lambda or more. The goal of this study was to design lightweight absorbers that can reduce the electromagnetic reflections to less than -10dB. We used a very simple approach; two waste materials, that is, rice husks and tire dust in powder form, were used to fabricate two independent samples. We measured and used their dielectric properties to determine and compare the propagation constants and quarter-wave thickness. The quarter-wave thickness for the tire dust was 3mm less than that of the rice husk material, but we preferred the rice-husk material. This preference was based on the fact that our goal was to achieve minimum backward reflections, and the rice-husk material, with its low dielectric constant, high loss factor, large attenuation per unit length, and ease of fabrication, provided a better opportunity to achieve that goal. The performance of the absorbers was found to be better (lower) than -20 dB, and comparison of the results proved that the hollow design with 58% less weight was a good alternative to the use of solid absorbers.