Planar Microwave Sensors for Mechanical Applications and Materials Detection
Measurement and instrumentation play a fundamental role in scientific and technical knowledge acquisition. The ongoing evolution of sensing and measurement techniques, driven by technological advancements and societal needs, has led various industries to rely on sensors. Radio frequency (RF) and microwave-based sensors are of high importance among various sensing technologies due to the advantages such as low-cost, non-contact, and label-free detection together with potential passive operation that alleviates the requirement for power sources such as batteries.
With the growing interest in microwave sensors for different applications, this dissertation focuses on the design of advanced microwave-based sensors for mechanical displacement/rotation detection using the semi-lumped planar structures. The research is categorised into three main parts, each focusing on a specific microwave sensor type based on the operation principles. The first part of the thesis presents frequency shift-based microwave sensors with an emphasis on a reflective-mode displacement sensor with a wide dynamic range and high linearity using transmission lines terminated with semi-lumped RLC resonators. Transmission lines terminated with series LC resonators are proposed for the design of displacement and rotation sensors based on the variations of the reflection phase in the second part of the thesis. The phase variation sensing principle is also extended to the design of sensors for detection of solid dielectric composites. The third part focuses on the design of mechanical displacement sensors based on the amplitude variation principle. A wide dynamic range amplitude variation displacement sensor is proposed using transmission lines loaded with a π-shaped semi-lumped capacitive network. The simulations and measurement results confirm a wideband amplitude variation-based displacement sensing ensuring a high immunity of the sensing response to the fluctuations of the measurement frequency.
In conclusion, the research outcomes presented in this dissertation confirm the efficiency of the planar semi-lumped elements in the design of high-sensitivity and compact microwave sensors for various applications ranging from mechanical displacement and rotation detection up to characterisation of the dielectric materials.