Abstract
The integration of radio frequency (RF) functionality into carbon fibre reinforced plastic (CFRP) composites is an important step towards the development of next generation lightweight conformal multifunctional communication and sensing devices. Many current applications are limited both by a lack of understanding regarding the electrical properties of CFRP, and the development of methodologies through which efficient devices can be introduced to the structural composite. The objectives of this dissertation are to explore the impact of CFRP conductivity on the design of RF circuits, and to develop efficient integrated components which have minimal impact on the composite mechanical properties. A methodology is proposed by which the electrical properties of different CFRP materials can be characterised by extracting the complex propagation constant from a set of a CFRP-backed co-planar waveguides from 0.5 - 10 GHz. The sensitivity of the measurement system to electrical anisotropy is demonstrated by rotating the orientation of the co-planar waveguides on the surface of the composite, creating a useful tool for the design of CFRP-based microwave circuits. The integration of efficient RF components is achieved using CFRP-based substrate integrated waveguides (SIW), where the conductive walls are created using a copper coated carbon veil. Transmission coefficients of -2.18 +- 0.19 dB and -4.04 +- 0.57 dB are presented for two SIW designs at 3 and 5.3 GHz respectively. Mechanisms are considered through which the efficiency of future integrated SIWs can be improved, for use in integrated sensors and antenna networks. The application of CFRP-based SIWs as a method of structural health monitoring (SHM) is also demonstrated by the detection of damage to composite structures using microwave transmission measurements. The combination of integrated composite RF circuits with applications such as structural health monitoring presents the possibility to design integrated RF devices that are adaptive and resilient to complex composite environments.