Adjustment of dielectric permittivity and loss of graphene/thermoplastic polyurethane flexible foam: Towards high microwave absorbing performance

An excellent microwave absorbing material should have wide effective bandwidth (EB) and low minimum reflection loss (min-RL), which depends on dielectric permittivity and loss. In this work, graphene/TPU composites with good microwave absorbing performance were prepared by changing the foam ratio and graphene content. Moreover, ceiling microwave absorbing performance of a dielectric material at a low thickness was investigated. When the foam ratio, graphene content, and thickness are, respectively, 3.9, 0.82 vol%, and 1.6 mm, the best microwave absorbing performance with a min-RL of -32.0 dB and an EB of 4.7 GHz is obtained. As a result, the graphene/TPU foams, which have better microwave absorbing performance, lower filler content, and thinner thickness than other reported polymer/graphene composites, are obtained. Additionally, this material exhibits a good flexibility.