Copper-plated 3D porous polymer structure for radar absorption at 8-12 GHz

Abstract

Porous 3d networks or structures from conductive polymer composites are the promising candidate for electromagnetic wave attenuation at different frequencies, especially at X- band frequency range i.e., 8-12 GHz. Such materials attenuate the electromagnetic waves by multi-reflection mechanism resulting in both low front and back reflectance and transmission. These materials are also considered to show better mechanical performance in lightweight, corrosion resistance, and cost-effectiveness. One potential solution to prepare porous conductive 3D polymer composites is to involve 3D printing technology as it is easy to create 3D structures of different layer thicknesses.

The main objective of this thesis is to evaluate the attenuation properties of three-dimensional metal-polymer composite at radar frequency range (X-band range). This included fabricating polymer with a thin metal layer and then studying its electrical conductivity and reflection attenuation measurements.

To meet these objectives, 3D printing technology is used to create three-dimensional porous polymer structure. This structure is then coated with thin layer of copper. Copper is chosen as it has high electrical conductivity. Its conductivity can be tailored by controlling the thickness of Cu using electroless Cu plating. 3D samples of thickness 2.1 mm, with different structural configuration such as 3D-mesh and square-pyramids were printed using fused deposition modelling.

The reflection attenuation measurement results indicated that the Cu plated truncated square pyramidal structural configuration with Cu thickness of 18 μm (3 mins deposition time) shows better attenuating properties of -7 dB at 8-12 GHz than mesh structure of -3 dB attenuation despite having same number of layers of equal thickness. Resistivity of 18 μm Cu film was measured to be 2.85 mΩ cm which is similar to previously reported values for electroless deposited copper. Also, pyramid structure was found to show reflection attenuation of -7 dB at 8-12 GHz with a very low transmission of -20 dB which is higher in comparison to previously reported Cu-polymer 3D networks. Therefore, structural configuration makes an impact for radar absorbing capabilities.