Microwave absorbing properties of alternating multilayer composites consisting of poly (vinyl chloride) and multi-walled carbon nanotube filled poly (vinyl chloride) layers

The application of dielectric lossy absorbent, multi-walled carbon nanotubes (MWCNTs) filled polymer as a microwave absorbing material (MAM) is limited because of the high loading level. Optimizing the distribution of MWCNTs in a polymeric matrix was a key factor in obtaining better microwave absorption while keeping the MWCNT content low. According to the theory of transmission lines, we designed an alternating multilayer structure with MWCNTs distributed in the continuous and parallel layered spaces of a poly (vinyl chloride) matrix to improve its microwave absorbing properties. The effect of the layer number on the microwave absorbing capacity was studied by theoretical calculations and experimental measurements. The results showed that the −10 dB absorbing bandwidth and the absolute value of the minimum reflection loss of alternating layered samples were higher than those of a conventionally blended sample with the same MWCNT content and increased with the increasing layer number. This improvement of the microwave absorbing capacity was mainly attributed to the multi-reflection of microwaves between the layered interfaces. Interestingly, the matching frequency of the alternating layered MAMs could be adjusted by changing the layer number. The measured microwave absorbing properties were well predicted by the theoretical model. In addition, the mechanical properties improved with an increasing number of layers.