Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors

In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications. A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement

Paper-based Screen-printed Passive Electronic Components

This thesis investigates paper-based electronics in terms of various substrates, fabrication methods and example devices, including touch sensors and microwave resonators. The term ‘paper’ is very broad and covers a wide range of substrates. A decision matrix has been created to determine the optimum paper for an application, based on a range of properties. Thermal evaporation and screen printing are compared for their use as fabrication methods for paper-based electronics and a second decision matrix has been compiled. Based on these decision matrices, screen printing onto a thicker matt paper was determined to be optimal. The printing process was further optimised to achieve the best results from the in-house process. Using this well-developed screen-printing method, passive components (including inductors and interdigitated capacitive touch sensors) were fabricated and found to be comparable with state-of-the- art results reported in the literature. Measurements from the touch pads were compared to modelling, with little variation between the two, and were confirmed to work under a wide range of conditions, showing that they are compatible with any user. The microwave characteristics, up to 3GHz, of both the chosen substrate and silver-flake ink were investigated through production of screen-printed transmission lines. These characteristics were then used to create microwave resonators. The frequency range is important for applications as the industrial, scientific and medical radio band (ISM band) lies between 2.45 and 2.55 GHz which includes Wi-Fi and Bluetooth. Initially, stub resonators were considered to determine the cause of differences between theoretical and measured results. Then spiral defected ground structures were made, with multiple resonances, and sensitivity to touch and humidity demonstrated. As paper is hygroscopic, the effect of humidity on paper-based electronics is of key importance. This has been considered for all the devices fabricated in this work and it has been determined that the change in permittivity of the substrate, as a result of absorbed water within paper, is the most dominant factor

Polymer waveguide based optical interconnects for high-speed on-board communications

This dissertation presents a study of multimode polymer waveguide technology for use in board-level communication links for future data centres and supercomputers. The motivation for this work comes from the severe interconnection bandwidth challenges faced by the conventional electrical interconnections technology and the potential performance advantages of optical interconnections. This thesis presents the work to address the bandwidth bottleneck by developing high-bandwidth multimode polymer waveguides. The use of multimode waveguides provides relaxed alignment tolerances enabling low-cost assembly tools. Siloxane polymer materials developed by Dow Corning Corporation are chosen to form the waveguides in this work due to their favourable optical properties (optical losses as low as 0.03 dB/cm and the ability to withstand temperatures in excess of 350 °C) that allow the waveguides to be directly integrated on printed circuits boards (PCBs) using conventional manufacturing processes. Useful design rules for the use of the multimode polymer waveguides are theoretically derived while the bandwidth-length products are investigated under various launch conditions. Frequency-domain measurements and ultra-short pulse measurements are then carried out to investigate the bandwidth performance of the polymer waveguides under different launch conditions and with lateral misalignments. The instrument-limited frequency-domain measurements show that these waveguides exhibit bandwidth-length products (BLPs) of at least 35 GHz×m, while the pulse broadening measurements reveal the actual BLPs to be in excess of 70 GHz×m under a 50 μm multimode-fibre (MMF) launch and 100 GHz×m for a restricted launch across a wide range of input offsets (>±10 μm). This shows the potential for data transmission rates of 100 Gb/s and beyond over a single waveguide channel. A theoretical model is developed using the measured refractive index profile and good agreement with the above experimental results is found. The effects of graded refractive index profiles on the performance of waveguide components (bends, crossings) are also investigated, demonstrating that appropriate refractive index engineering can provide enhanced waveguide loss performance while exhibiting adequate bandwidth. Waveguide bends with excess loss below 1 dB for a radius >6 mm, crossings with loss less than 0.02 dB/crossing while exhibiting adequate link bandwidth (>47 GHz×m) can be achieved for a MMF launch. On this basis, advanced modulation formats are investigated across the board-level waveguide links for further increasing the on-board data rates. Record NRZ-based 40 Gb/s and 56 Gb/s PAM-4 based data transmission over a 1 m long multimode polymer spiral waveguide are theoretically and experimentally demonstrated