<p>In this thesis work, a free space microwave sensing technique to be used for power process control was investigated. Evaluation of the possibility to apply this sensing technique for determination of permittivity properties is the primary objective. Further these properties could be related to the material physical properties such as moisture content and density. Due to the fact that the permittivity properties of the material under measurement determine its measured S-parameters, such were performed throughout the whole work for the calculation of materials properties. Free space type of measurements were the primary focus of this work. Some uncertainties of free space measurement resulting from limitations in the measurement setups, instrumentation, algorithm were explored and methods to secure our measurement results to be within a specified confidence level are also discussed.</p><p>Based on the configuration of the measurement setup, two types of free space measurement were carried out. One was the reflection method where a perfect conducting metal plate is inserted between two antennas for calibration purposes and the material is placed above the plate. Only one reflection coefficient was then measured. The other was the transmission method where the measured material as placed between two antennas and all S-parameters measured. In both cases the amplitude and the phase of the S-parameters were recorded.</p><p>Three models, Debye, Cole-Cole, and Cole-Davidson have been also tested in this work to model permittivity properties of materials. Used test materials were air, plastic plate, water and icrocrystalline cellulose(MCC). Different methods using measured S-parameters for permittivity reconstruction that have been explored in previous work also were utilized in this work for same purpose. The validity of this sensing technique is determined by checking out the deviation of the recovered dielectric constant. The investigation demonstrated that the transmission method works well for reconstruction of permittivity properties as long as the material under test is low-loss. The results of the reflection method were not as satisfactory as we expected. The method was insitive to the sample thickness and shape. Also very precise measurements of the S-parameters were necessary for the correct inversion to dielectric properties, which is generally difficult due to complex measurements environment(multipath). Some of the above could be compensated with good calibration method, but it is not enough, at least with the currently existing approaches. Precise sample preparation and some improvement on the antenna should be further carried out for the reflection method to be performed better.</p>

In this thesis work, a free space microwave sensing technique to be used for power process control was investigated. Evaluation of the possibility to apply this sensing technique for determination of permittivity properties is the primary objective. Further these properties could be related to the material physical properties such as moisture content and density. Due to the fact that the permittivity properties of the material under measurement determine its measured S-parameters, such were performed throughout the whole work for the calculation of materials properties. Free space type of measurements were the primary focus of this work. Some uncertainties of free space measurement resulting from limitations in the measurement setups, instrumentation, algorithm were explored and methods to secure our measurement results to be within a specified confidence level are also discussed. Based on the configuration of the measurement setup, two types of free space measurement were carried out. One was the reflection method where a perfect conducting metal plate is inserted between two antennas for calibration purposes and the material is placed above the plate. Only one reflection coefficient was then measured. The other was the transmission method where the measured material as placed between two antennas and all S-parameters measured. In both cases the amplitude and the phase of the S-parameters were recorded. Three models, Debye, Cole-Cole, and Cole-Davidson have been also tested in this work to model permittivity properties of materials. Used test materials were air, plastic plate, water and icrocrystalline cellulose(MCC). Different methods using measured S-parameters for permittivity reconstruction that have been explored in previous work also were utilized in this work for same purpose. The validity of this sensing technique is determined by checking out the deviation of the recovered dielectric constant. The investigation demonstrated that the transmission method works well for reconstruction of permittivity properties as long as the material under test is low-loss. The results of the reflection method were not as satisfactory as we expected. The method was insitive to the sample thickness and shape. Also very precise measurements of the S-parameters were necessary for the correct inversion to dielectric properties, which is generally difficult due to complex measurements environment(multipath). Some of the above could be compensated with good calibration method, but it is not enough, at least with the currently existing approaches. Precise sample preparation and some improvement on the antenna should be further carried out for the reflection method to be performed better.

A combination of magnetic sensors with magnetic nanoparticles offers a promising approach for highly sensitive, simple, and rapid detection of cancer cells and biomolecules. The challenge facing the field of magnetic biosensing is the development of low-cost devices capable of superconducting quantum interference device (SQUID)-like field sensitivity at room temperature. In another area of interest, improving the sensitivity of existing electromagnetic field sensors for microwave energy sensing applications is an important and challenging task. In this dissertation, we have explored the excellent magnetoimpedance and microwave absorption responses of soft ferromagnetic amorphous ribbons and microwires for the development of high-performance magnetic biodetectors and microwave energy sensors. We have developed the effective approaches to improve the magnetoimpedance response of Co65Fe4Ni2Si15B14 amorphous ribbons by tuning their dimension and/or coating them with thin layers of CoFe2O4. Coating amorphous and crystalline CoFe2O4 films on the ribbon surface have opposite impacts on the magnetoimpedance response. Pulsed laser deposition (PLD) is shown to be a novel in-situ annealing and coating method for improving the magnetoimpedance response of the soft ferromagnetic amorphous ribbons for advanced sensor applications. The magnetoimpedance responses are also enhanced in multi-microwire systems relative to their single microwires. We have introduced a new method of combining the magnetoresistance (MR), magnetoreactance (MX), and magnetoimpedance (MI) effects of a soft ferromagnetic amorphous ribbon to develop an integrated biosensor with enhanced sensitivity and tunable frequency. While existing MI biosensors have limited sensitivities, we show that by exploiting the MR and MX effects it is possible to improve the sensitivity of the biosensor by up to 50% and 100%, respectively. The MX-based approach shows the most sensitive detection of superparamagnetic (Fe3O4) nanoparticles at low concentrations, demonstrating a sensitivity level comparable to that of a SQUID-based biosensor. Unlike a SQUID, however, the proposed MX technique is cryogen-free and operates at room temperature, providing a promising avenue to the development of low-cost highly sensitive biosensors. We have further improved the detection sensitivity of the MI and MX biosensors by patterning the sensing (ribbon) surface with nano/micro-sized holes, using the etching or focused ion beam (FIB) technique. These biosensors have been successfully employed to detect and quantify various bioanalytes, such as Curcumin-type anticancer drugs, bovine serum albumen (BSA) proteins, and Lewis lung carcinoma (LLC) cancer cells that have taken up the surface-functionalized Fe3O4 nanoparticles. Since Fe3O4 nanoparticles are widely used as magnetic resonance imaging (MRI) contrast agents, our biosensing technique can also be used as a new, low-cost, fast and easy pre-detection method before MRI. Finally, we have developed a new method of using a soft ferromagnetic glass-coated amorphous microwire as a microwave absorber for fabrication of a fiber Bragg grating-based microwave energy sensor with improved sensitivity and less perturbation of the microwave field. As compared to a similar approach that uses gold to absorb electromagnetic radiation, the microwire yields a device with greater sensitivity (~10 times at f = 3.25 GHz) relative to the perturbation of the microwave field. A correlation between the magnetic softness and microwave absorption in the microwires has been established, paving the way to improve the performance of the microwave energy sensor by tailoring their soft magnetic properties.

There is a need in the dairy industry for instrumentation capable of providing on-line information about the moisture content of cheese during manufacture. Present measurement techniques are usually performed off-line and can be susceptible to human error. It is demonstrated that microwave-based moisture sensing techniques offer a number of potential advantages over conventional methods due to the strong interaction of microwaves with water. The permittivity of cream cheese curd and low-fat cheddar cheese curd has been measured over a range of frequencies and moisture contents in order to establish the relationship between these variables. A vector reflection coefficient measurement engine based on a six-port reflectometer has been built and tested. A suitable sensing head has been fabricated from a short length of microstrip transmission line. Two sensor characterisation models have been developed and compared with measured data. A novel algorithm has been developed to resolve the ambiguity inherent in many permittivity measurement techniques. It has been discovered that surface waves can propagate on a grounded dielectric slab covered by a material with a higher dielectric constant, provided the loss factor of the covering medium is greater than zero. It has also been found that the dominant mode of microstrip can radiate when the line is covered by a high-permittivity material, although this can be suppressed if the covering material is sufficiently lossy. There are three principal conclusions to draw from the investigation in this thesis. Firstly, changes in the moisture content of cheese curd during manufacture produce measurable variations in permittivity. Secondly, these changes can be measured accurately and cheaply using off-the-shelf microwave hardware. Finally, considerable attention must be paid to the characterisation of the sensing head if the instrument is to achieve its full potential. Promising results have been obtained in this area, however certain issues pertaining to the propagation of multiple dominant modes and higher order modes have not been fully resolved and would repay further theoretical analysis.