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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
under the illumination of electromagnetic waves is determined by the collective
behaviour of constituting molecules in the liquids. The addition of bio/chemical
compounds causes the change in the spectral 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 a system. In order to overcome
these limitations, various factors such as microfluidic design, liquid volume,
sensor material, fabrication method, the availability of a 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 the liquid (84dB water-alcohol
signal contrast) with a very narrow operation bandwidth. b) transmission type:
based on differential method. The transmission (S21) parameter sensitivity to
changes in the liquid is on par with the reflection sensors but 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 the various sensor prototypes
with a vector-network-analyzer are discussed within this thesis. The usage of
the reflection sensors has also been demonstrated in a variety of application
domains. For example, it is proven that the millimeter wave sensor is able to
detect both ultra-violet (UV) and non-UV absorbing compounds without the
work of labelling for liquid chromatography systems. Also the capability to
detect protein binding activities and DNA multiplications is shown. Finally,
the future development and applications of the proposed sensor methodology
are discussed.

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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