Microwave absorbing properties of MWCNT/carbon black-PU nano-composites

In this paper, we have investigated the microwave absorption properties of lightweight and thin Nano-composite absorber samples prepared by using two types of conducting fillers thoroughly homogenized in Poly-urethane (PU) matrix. Mix of carbon black powder (CBP) and multi-walled carbon nano-tubes (MWCNT) have been used as conducting nano-fillers. Poly-urethane (PU) has been selected as host matrix to prepare Nano-composite samples. The vector network analyser (Model PNA E8364B, Software module 85071E) attached with coaxial measurement set up has been utilised to investigate the EM and microwave absorbing properties of the samples in the frequency range of 2-18 GHz. The complex permittivity of the composite has been found to be frequency dependent. The finding reveals that the absorption performances of the Nano-composite samples having 75 mg MWCNT and 250 mg carbon black in 1 g polyurethane showed minimum absorption peak of -16.14 dB (RL, min.) at a matching frequency (f
_m
) of 11.92 GHz and more than -10 dB loss (90% absorption of microwave energy) in the frequency range (Band width) of 11.03 GHz to 13.00 GHz for the sample thickness of 2.0 mm. Analysis shows that by tuning the thickness (t) of the Nano-composite sample, minimum reflection loss (RL) i.e. maximum absorption can be tune to desired microwave frequency range. Due to noble properties of MWCNTs, these Nano-composites can be prominent candidate for stealth of aero-structures and EMI shielding in S, C, X and Ku radar bands. The morphology and thermal behaviour of the Nano-composite samples have also been investigated through scanning electron microscope (SEM) and thermo gravimetric analysis (TGA) techniques.