Microwave enabled microfluidic devices
Creators: name: Abdelwahab, Haneen
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400601
subject: Antennas and propagation

description: This research investigates the application of microfluidic technology in the design of mi­crowave devices and components with enhanced functionalities. The first part of the thesis covers the design of a very high-sensitivity microwave microfluidic dielectric sensor. Sensi­tivity enhancement is achieved and described theoretically and experimentally by eliminating any extra parasitic capacitance not contributing to the sensing mechanism. The sensor con­sists of a microstrip transmission line loaded with a series connected shunt LC resonator. A microfluidic channel is implemented within the capacitive gap of the sensor, where there is a high concentration of the fringing electric field. The electric field distribution and therefore, the resonance characteristics of the sensor are modified by injecting microfluidic dielectric samples. The sensor performance and working principle are described through a circuit model analysis. Sensor prototype is fabricated and validated with water/methanol samples. A comparison with the state-of-the-art planar sensor shows the superiority of the sensor performance in terms of sensitivity, profile, and amount of LUT. 

The second part of the thesis is on the design of a planar switchable bandpass filter using liq­uid metals (LMs). A second-order bandpass filter is designed using a microstrip transmission line loaded with stepped impedance resonators (SIRs). Filter switching is achieved by filling and draining liquid metal from two capsules integrated into each filtering cell resulting in four switching states. External adjacent patches are used to increase the capacitance of the stepped impedance resonator when the liquid metal capsules are filled. The designed filter offers a tuning range of 1.2 to 2.2 GHz is achieved, together with a fractional bandwidth from 3.5% to 7.6% among the four switching states. The measured insertion loss (IL) varies from 2 to 3.9 dB during the four states. In addition, The filter shows a compact profile together with a wide out-of-band rejection. 

The third part of this research presents the design of a microfluidic-based switchable reflective-­type phase shifter. The design incorporates a quadrature hybrid terminated with a microfluidic ­switchable series LC reflective loads. A circuit-based mathematical analysis method is developed to optimize the L and C values aimed at achieving the required phase tuning at the operational frequency. Microfluidic channels are implemented within the capacitive gaps of the tunable reflective loads, where different channel loading results in phase shifts according to the dielectric properties of the liquids. Prototype measurements show a maximum phase shift of 156◦ together with maximum 2.5 dB insertion loss at the operating frequency of 1.7 GHz.

Overall, the research outcomes in this dissertation verify the potential efficiency of microfluidic technology in the design of frequency agile circuit components and sensing devices with enhanced features at microwave frequency ranges.