Thesis Defence: Integration of Conducting Polymer Films with Planar Microwave Resonators for Concurrent Radio-Frequency and Direct-Current Environmental Sensing
October 23 at 11:30 am - 3:30 pm
Jack McClelland, supervised by Dr. Mohammad Zarifi, will defend their thesis titled “Integration of Conducting Polymer Films with Planar Microwave Resonators for Concurrent Radio-Frequency and Direct-Current Environmental Sensing” in partial fulfillment of the requirements for the degree of Master of Applied Science in Electrical Engineering.
An abstract for Jack McClelland’s thesis is included below.
Defences are open to all members of the campus community as well as the general public. Please email mohammad.zarifi@ubc.ca to receive the Zoom link for this defence.
Abstract
The interaction of microwaves and materials has been well documented, culminating in well used measurements of permittivity and permeability across specified frequency ranges. This thesis investigates methods to improve the measurement capability of microwave resonator structures by facilitating the simultaneous measurement of transmission coefficients and instantaneous DC conductivity. This novel concept presented a challenge to design a resonator in a way in which the AC and DC paths are independent of one another during experimentation.
To produce this desired result, a microwave split ring resonator (SRR) dual gap variant was enhanced using DC bias lines and radial stubs to provide a measurement path through any conductive material placed across the main gap, essentially shorting it to leave a single gap similar to that of a conventional SRR.
The work was initiated by thoroughly simulating and tweaking the unique DC bias enhanced design to optimize resonator performance and confirm AC/DC measurement independence. Once the SRR design was optimized, a dummy material under test was added to the sensitive gap and its permittivity and conductance was varied to characterize the material in simulation. Further simulations placed a parallel RC tank across the gap with variable parameters to sweep and match with material property simulations. Initial findings determined that decreasing the resistance across the gap shorts the left resonant peak as expected, while adjusting capacitance follows permittivity variation.
The simulated design was fabricated, assembled, and experimented upon to validate these simulation results. To replicate the mock material RC tank in the real circuit, a conductive polymer commonly used in microwave SRR research, PEDOT:PSS, was integrated across the gap. The conductive polymer sample consisted of a glass slide plated with gold electrodes connected to either side of the SRR gap with conductive epoxy. The exposed glass and electrode sample was coated with a thin film of PEDOT:PSS, creating a path across the gap for DC measurement as the electromagnetic waves pierce the glass and PEDOT:PSS. Humidity experiments were undertaken to produce change within the PEDOT:PSS bulk to successfully correlate resonant amplitude, resonant frequency, and resistance to humidity variation.
Finally, the investigation was expanded to include film thickness variation to correlate and compare the rate and magnitude of change in PEDOT:PSS material characteristics in the microwave and DC frequency domain for three separate thicknesses of PEDOT:PSS. The main takeaways of this investigation shows that the thinner film acts similar to an open circuit and has little variation in its sensing parameters to humidity variation compared to the thicker film of PEDOT:PSS. The thicker films presented a low resonant amplitude due to the near-short across the gap interfering with resonance. Despite this, the thick film showed greatest variation and potential for detection applications.
