Electromagnetic wave absorption properties of rice husks carbonized at 2500 °C

Abstract

The rice husk (RH) samples were prepared by pre-carbonization at 800 °C, and then further carbonization at 2500 °C (RH2500), under the presence of Argon gas. The RHs were characterized using Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, and X-ray Photoelectron Spectroscopy. The RH2500 were then incorporated into paraffin wax with different weight percentage (20, 30, 40 wt.%), and designed into toroidal shape with thickness of 1.0 mm to evaluate their complex permittivity and complex permeability using vector network analyzer. The reflection loss (R.L.) of the samples was calculated according to their measured complex permittivity and permeability. The RH 30 wt.%, with thickness of 1.0 mm showed highest electromagnetic wave absorption performance in contrast to the samples with similar thickness but different weight percentage, with minimum R.L. of ∼-14.04 dB (over 96% absorption) at 10.0 GHz. Furthermore, based on the calculation using transmission line theory, RH 30 wt.% with thickness of 1.6 mm exhibited minimum R.L. of ∼-18.76 dB (over 98 % absorption) at 9.6 GHz, the best absorber when compared with the other samples of different thicknesses. The capability to modulate the absorption band of these samples to suit various applications in different frequency bands simply by manipulating their weight percentage and thickness indicates that the RH2500 could be a promising electromagnetic wave absorber.