Wireless Chipless Liquid Sensing using a Slotted Cylindrical Resonator

This thesis presents a comprehensive study on the application of a slotted cylindrical resonator for the wireless assessment of liquids. Using simple geometry and measurement techniques, a method for the sensing of liquids within non-metal pipes is established, allowing for the prospect of non-contact, real-time, wireless monitoring of industrial liquid processes with no requirement for samples. The main contribution of this work is the development of a thorough understanding of the geometry, as well as an extensive presentation of measured data using liquids of wide-ranging properties. A full parametric and sensitivity study obtained through theory, simulation and measurement provides analysis on every aspect of the proposed sensor, including a number of potential future research topics. The slotted cylinder is placed directly on-pipe, requiring no additional circuitry, power or support structure, and is excited wirelessly by an external antenna. Its resonant frequency is very sensitive to the permittivity within the sensor cavity, and is shown to operate well across a relatively large range of permittivity. The structure is highly adaptable, even for fixed pipe dimensions, and simple adjustments provide a method for the tuning of resonant frequency and sensitivity control. Additionally, the placement of multiple sensors in close proximity allows for the measurement of high-loss liquids, which may otherwise not be possible. A number of measurement techniques for level sensing are presented, covering both frequency and amplitude detection methods using single and multiple sensors, where the geometry is shown to be highly sensitive to very small changes in liquid level. Measurements detecting relatively small changes in liquid temperature provide a further potential application of the sensor. The simultaneous monitoring of multiple liquids is easily achieved using a single measurement system, vastly reducing the complexity inherent in large-scale industrial processes. The sensor is shown to be resilient to changes in polarisation and position relative to the measurement antenna, as well larger read distances compared with other passive sensors.