Application of carbon fibre reinforced polymer (CFRP) for manufacturing microwave components

Carbon Fibre Reinforced Polymers (CFRP) have drawn a significant attention in different industries due to their superior mechanical characteristics. RF and microwave industry are not an exception. However, the low conductivity in the direction of fibre in CFRP materials restricts their applications for manufacturing RF and microwave components such as antennas and waveguides. The aim of this research includes introducing a simple method for CFPR characterization, presenting high frequency characteristics (shielding effectiveness and conductivity) of some CFRP samples used in the defence and automotive industry, introducing a technique to improve the conductivity of the CFRP samples and manufacturing a waveguide from CFRP with represents an acceptable insertion loss. Determining the high-frequency conductivity of a CFRP materials is one of the critical steps in designing microwave components. In this research, we introduce a new technique for determining the equivalent conductivity which is based on shielding effectiveness measurement in a rectangular waveguide. The proposed method has been validated using the simulation and measurement. The proposed method has shown a very good accuracy for determining the conductivity and has significant advantages over traditional techniques, such as simple setup/postprocessing, no need for vector measurement, high repeatability, and being capable of measuring high conductivities precisely. Besides these advantages, the proposed method has some limitation which restricts the application to good and/or thick conductors (not suitable for poor and/or extremely thin conductors). It is not a method that can be used for the full material characterization and is not capable of determining all material properties (real/imaginary part of the permittivity/permeability). Different approaches for modelling and characterizing CFRP is presented in this thesis. Multiple samples of CFRP (uncured carbon fibre cloth with different fibre densities and Cytec IM7/977-3 prepreg laminates) with different ply configurations have been fabricated and their shielding effectiveness and conductivity characterized. The conductivity of the samples was determined using a method based on shielding effectiveness measurement. The characterisation in this research is limited to the two major field polarizations (parallel and orthogonal to the direction of fibres). CFRP characterization has also been performed using the Finite Element Method (FEM). Characterization has been performed at ply level using a full-size model followed by a reduced size model with Periodic Boundary Condition (PBC) to examine the suitability of the PBC approach for material characterization. Finally, the thin layer approach was introduced as the most practical method for modelling components made from CFRP (modelling at component level). The attenuation of CFRP waveguides has been improved in this research by investigating and comparing three different manufacturing techniques. WR-90 waveguides have been manufactured from Cytec IM7/977-3 prepreg and their transmission performance have been evaluated. Three different techniques were implemented to reduce waveguide losses including: copper foil lining, conductive paint, and a new integrated metalized carbon fibre veil (CFV) material. The new lightweight high conductivity CFV was integrated into the walls of a CFRP waveguide which reduced the per unit length attenuation to below 1 dB/m. This was an improvement of up to 5.5 dB over raw carbon fibre and similar to the performance of a copper foil-lined waveguide. Two loss mechanism in a rectangular waveguide made from anisotropic materials (conductive loss and loss due to the mode conversion) have been investigated in this research. Studying the loss due to the mode conversion has shown that this element of loss can be reduced when the waveguide carries higher order modes. It has been shown through simulation and experiment that waveguides made from anisotropic materials present lower amount of loss when used for the transmission of higher order modes.