Nanocomposite absorbers based on dielectric/magnetic materials are prepared by in situ incorporation of MWCNTs and NiFe alloy nanopowder into epoxy matrix. SEM micrographs and EDAX studies of these nanocomposites clearly revealed the incorporation of MWCNTs/NiFe nanoparticles in the epoxy matrix. Dielectric measurement revealed that the real part of permittivity and permeability of NiFe-filled MWCNT composites increased with an increase in NiFe concentration. The consolidated loss tangent values revealed that the total losses were highest for 15% of NiFe alloy nanopowder, thus accounting for the highest absorption loss. The two-layer RAS composed of NiFe alloy nanopowder-filled MWCNTs/epoxy composite achieves a minimum reflection loss of À12 dB (95% of absorption) in the range of 8.2-9.8 GHz and a maximum peak of À19 dB at 8.2 GHz with a thickness of 4 mm for 15 wt% NiFe alloy nanopowder MWCNTs/epoxy composites. In addition, À10 dB absorption bandwidths of composite material are <2 GHz, i.e., 8.2-9.8 GHz. Microwave absorption was attributed to both the dielectric and magnetic nature of MWCNTs and NiFe alloy nanopowder. The frequency of microwave absorption complies with the quarter wavelength (k/4) matching model.

In this paper we presented the electromagnetic analysis of multilayered Radar Absorbing Structure (RAS) composed of Multi-Wall Carbon Nano Tubes (MWCNTs) with different weight percentages.The complex permittivity and permeability of MWCNT/epoxy composites with different wt% are analysed and the microwave absorbing characteristics are evaluated. The permittivity and permeability of MWCNT composites increased with increase in MWCNT concentration. Absorption properties like reflection loss of multilayered RAS are estimated analytically using electromagnetic wave theory for different layers and with different layer order based on impedance matching condition. The quartic layer MWCNT/epoxy composite achieves a better microwave absorption when compared to other multilayer RAS. The microwave absorption was attributed to dielectric loss of the material. The simulated quartic layer RAS is fabricated and validation of reflection loss is done experimentally using free space measurement technique. From free space measurement the minimum reflection loss in entire X-band is observed to be approximately-12 dB (95% of absorption),-15 dB (97% of absorption), with 3 GHz band width,-20 dB (99% of absorption) with 2 GHz bandwidth and maximum peak of-44 dB at 11.5 GHz. Hence the composite material has great potential of application as highly efficient microwave absorber.

The present work focused on electromagnetic (EM) absorption performance comparison of different polymer nanocomposite structures. Synthesis and fabrication of polymer nanocomposite composed of graphene, polyurethane (PU), epoxy was done using in situ polymerization and resin transfer moulding respectively. The effect of polymer on EM properties of composite was carried out using waveguide measurement technique in X-band. Reflection Loss (RL) and shielding effectiveness (SE) were measured for various nanocomposites using EM wave theory. From the results it is observed that 2.5 wt% of PU/epoxy graphene nanocomposite has shown RL value −35 dB at 12.1 GHz and SE value of −45 dB.

No abstract

No abstract