Microfluidic capillary in a waveguide resonator for chemical and biochemical sensing

Abstract

This thesis presents a novel microwave sensor for the characterisation of fluids with the integration of a microfluidic capillary. Various designs and fabrication methods were investigated for the integrated microfluidic capillary. SU-8 and PDMS were investigated as possible materials, however proved difficult to produce large volumes of capillaries. PMMA a cheap readily available material was also investigated. Using an Epilog CO2 laser ablation machine rapid prototyping of microfluidic capillaries was achieved using PMMA. Two microwave resonator designs are proposed as non-contact sensing devices. The first design utilizes an E-plane filter in a split-block rectangular waveguide housing. This offers advantages in enhanced near fields and simple manufacturing techniques. Simulation and experimental results are presented, demonstrating sensitivity of such microwave sensors. Various materials under test were used: Methylated spirit/water concentrations, lubricant and motor oils and animal red blood cell concentrations. Resonant frequency shifts in the region of 10s of MHz were observed. However most notably in the methylated spirit concentrations there was no resonant frequency shift, only a shift in the return losses were observed. The integration of the E-plane filter and the microfluidic capillary resulted in poor repeatability due to alignment issues of the filter and capillary. The second design incorporates the use of Distributed Bragg Reflectors for a compact and fully integrated, no moving parts, device. The simulation results produced a Q-factor 1,942 at a resonant frequency of 23.3 GHz. The Bragg sensor produced promising simulation results as well as initial experimental results. There was up to 20 MHz resonant frequency shift between the samples. Samples included Eppendorf tubes filled with water and oil.