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PhD Defense
Waveguide based Millimeter wave liquid sensors


Mr Yuchen Zhang - ETRO, Vrije Universiteit Brussel [Email]


In the frequency range from 30 to 300 GHz, the response of liquid materials is determined by the collective
behavior of constituting molecules in the liquids. The addition of bio/chemical compounds causes the change in
the frequency response which will also appear in the sensor response of electronic systems. The phenomena can be
exploited to develop millimeter wave sensor configurations for accurate liquid sensing applications. However,
water absorption together with wavelength to particle ratio severely affects the sensitivity of such system. In
order to overcome these limitations, various factors such as microfluidic design, liquid volume, sensor
material, fabrication method, the availability of theoretical model etc. need to be taken into consideration.
This PhD thesis deals with the passive parts of a label-free immobilization free millimeter wave sensor
configuration operating in V-band. Two types of waveguide based sensor configurations are proposed: a)
reflection type: based on impedance tuning method. The reflection (S11) parameter is very sensitive to changes of
liquid (80dB water-alcohol signal contrast) with a very narrow operation bandwidth. b) transmission type: based
on differential method. The transmission(S21) parameter sensitivity to liquid change is on par with reflection
sensor with a wider operating frequency band. Different design aspects such as theoretical modelling, numerical
validation and optimization with CST microwave studio, fabrication by 3D printing technology and evaluation of
sensor with vector-network-analyzer are discussed within this thesis. Reflection sensor is also applied to
different applications. For example, it is demonstrated that the millimeter wave sensor is able to detect both
ultra-violet(UV) and non-UV absorbing compounds without the work of labeling for liquid chromatography systems.
It has also shown the capability to detect protein binding activities and DNA multiplications. Finally, we
discuss the future development and applications of the proposed technique.

Short CV

Master of Science in Electrical Engineering, KU Leuven, 2012


Date: 19.10.2017

Time: 16:00

Location: Room D.2.01 Building D

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