Modulation of complex permittivity of carbon nanotubes/epoxy foam composites reinforced by three-dimensional woven spacer fabric

3D woven spacer composites (3DWSC) with integrated structure have immense potential as design platforms for high-performance microwave absorbent materials. In this work, the complex dielectric constant of 3DWSC was modulated by the content of carbon nanotubes (CNTs) in the epoxy foam sandwich. The theoretical model was proposed for predicting the dielectric constant of 3DWSC-CNT/epoxy foam. The error between model prediction, measured results and finite element results was less than 5%. The excellent mechanical properties of 3DWSC-CNT/epoxy foam were demonstrated by compression and impact experiments. The absorption performance and radar cross section (RCS) reduction in the frequency range of 4–18 GHz were calculated by finite element method. The maximum effective absorption bandwidth was 5.5 GHz. The RCS of 3DWSC- CNT/epoxy foam of the same size at 10 GHz was only 1% of that of carbon fiber composites. 3DWSC endowed with microwave absorption function have great potential in the practical application of anti-radar detection.