Development of a Novel Microwave Sensing System for Lab on a Chip Applications
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Date
2018-12-20
Authors
Mao, Shinong
Journal Title
Journal ISSN
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Publisher
University of Waterloo
Abstract
Microwave technology presents tremendous potential as a remote-sensing technology for a wide
range of applications spanning from life science research to food industries, pharmaceutical research,
and new material discoveries. Integration of microwave sensing with microfluidics for sample
processing makes it an ideal choice for point of care applications highly demanded in resourcelimited
areas. The vast majority of the existing microwave sensors are manufactured using
sophisticated soft lithography technology which has largely limited its development and applications.
There is a large demand for developing new fabrication approaches for the feasibility of mass
production at a reasonable cost.
In this thesis, a new, yet simple method is developed to fabricate split ring resonator (SRR) based
microwave sensors. A simple RLC model is used to characterize the resonant frequency of the SRR,
and the equations for calculating the RLC’s resonant frequency is modified to predict the SRR’s
resonant frequency base on its geometry. The design is also validated by comparing the simulation
results obtained using the commercial software HFSS, and measurements from a real SRR developed
sensor. The double ring structure was fabricated onto a printed circuit board by using the industrial
photolithograph method. Coating with PDMS and epoxy layer as the passivation layer was tested and
compared.
Two testing approaches using the SRR sensor developed in this thesis are implemented in this
thesis. Their performance for real-time sensing is characterized by applying it to differentiate
chemical diary samples and other chemical solutions. In the dipping mode, the sensor is dipped in the
material under test (MUT), and in the microfluidic channel mode, the sensor is integrated with a
microchannel. The MUT is characterized by analyzing the spectrum data of the reflection coefficient
as the function of frequencies. Experimental results indicate that this sensor is capable of
differentiating various liquid samples such as DI water, ethanol, isopropanol, oil and salt solutions.
Linear relationships between the resonant frequency and the concentrations of chemical composites
are also observed in ethanol solutions (0-90%), and salt solutions (NaCl). This sensor is also used to
differentiate various milk samples and milk dilutions and it is capable of distinguishing milks with
different fat percentages and protein contents.
A fully customized vector network analyzer (VNA) is also developed. The circuit structure is
designed by referring the existing customized VNAs that were implemented in previous work by
iv
other lab colleagues. Modifications are made including replacement of the microwave source, using
Arduino platform to perform controlling and data acquisition, addition of a harmonic filtering device,
and development of a calibration algorithm. The device is validated by comparing its measuring result
with a commercial VNA. The customized VNA is able to output a similar spectrum pattern as the
commercial VNA, but with slightly shift of the peak frequency.
Description
Keywords
Microwave Sensing, Lab on a Chip