Master of Science / Department of Biological and Agricultural Engineering / Naiqian Zhang / Permittivity, displayed when a dielectric material is exposed to an electric field, is a useful property for measuring impurities in a dielectric medium. These impurities often have a dipole moment different from the pure material, and the dipoles align through polarization and impede electric current. By measuring the resulting impedance in a known geometry, the permittivity can be determined. Four permittivity sensors were utilized to measure contaminants that are associated with biofuels, specifically glycerol, ethanol, and ammonia. These sensors were based around either stainless steel or aluminum plates to ensure durability and reliability. By connecting each of these sensors to a signal generating control box, the gain and phase can be measured at 609 frequencies, from 10 kHz up to 120 MHz. Data from each of the three contaminants were run through a method for detection. Measurements for ambient air and air with the contaminants were compared with a statistical analysis. Glycerol, ethanol, and ammonia each had significantly different measurements in the gain and phase data at a unique set of frequencies. Using a neural network analysis for detection resulted in a 95.8%, 93.9%, and 97.1% success rate for detecting glycerol, ethanol, and ammonia, respectively. For ethanol and ammonia, where multiple concentrations were measured, regression methods were used to relate the frequency response data to the contaminant concentration. Stepwise regression, wavelet transformation followed by stepwise regression, partial least squares regression, and neural network regression were the four methods used to establish these relationships. Several regressions over-fit the data, showing coefficient of determination (R[superscript]2) values of 1.000 for training data, yet very low R[superscript]2 values for validation data. However, the best R[superscript]2 values of all the regressions were 1.000 and 0.996 for the training and validation data, respectively, from measuring ammonia.

Dans la situation d’un radar monostatique la configuration diédrique présente l’avantage de renvoyer un signal fort grâce au mécanisme de double rebond. De plus, il s’agit d’une configuration omniprésente par exemple en zone urbaine, avec des structures rue-bâtiment, ou en forêt, avec des structures de type sol-arbre. Les signaux rétrodiffusés sont donc liés à ces structures, plus précisément aux matériaux les composant, via leurs permittivités diélectriques. Retrouver ces permittivités depuis la mesure des champs rétrodiffusés permettrait l’identification des matériaux de la structure diédrique. Ceci mène à des applications telles que la détection de défauts dans la structure, l’estimation de la teneur en eau des sols ou du béton, ou in fine à des thématiques de classification, pour des objets dans des images radar par exemple, ou de détection de changement. En modélisant le mécanisme de double rebond lié à la structure de dièdre par deux réflexions successives via les coefficients de Fresnel, trois méthodes d’inversion des permittivités ont été mises en place au cours de la thèse. La première, analytique, utilise à un angle d’incidence donné la mesure des champs copolarisés. Les deux autres méthodes, alliant une partie analytique et une partie numérique, nécessitent la mesure, du ratio polarimétrique pour l’une, du champ horizontal pour l’autre, effectuée à deux angles d’incidence différents. Ces méthodes ont été validées numériquement à l’aide de la méthode d’Optique Géométrique fournie par le logiciel FEKO. Des mesures en chambre anéchoique ont été effectuées afin de valider ces méthodes. De même une mesure in-situ a été effectuée sur un dièdre en béton formé par un angle entre deux murs. / For a monostatic radar, the dihedral arrangementexhibits a strong response compare tobare surface. This phenomenon can be seen in radarimages of urban areas or forestry as building andstreets and trunks and ground are forming such structures.This signature can be modelled with the doublebounce equation as a cascade of Fresnel reflectioncoefficients. These coefficients depend on the permittivitiesof the structures. Finding these permittivitiesfrom the backscattered fields may allowed to identifythe materials involved in the dihedral. Thereforethiscan be applied for default detection, moisture retrievaland classification topics for instance.By modelling the double bounce scattering with Fresnelcoefficients, three methods have been developedto retrieve these permittivities. The first one uses asingle incidence angle and the measurements of copolarisedfields. The last two methods need the measurementof the copolarised fields ratio or of the horizontalelectric field alone at two different incidenceangles. All these methods have been validated, firstnumerically using FEKO RL-GO method, then experimentally,with measurements in anechoic chamber. Atlast, in-situ measurements have been performed on awall corner made of concrete to assess the methodon a real case.

<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.

The objective of the proposed research is to devise a methodology for sensing and tracking environmental variables using a passive wireless sensor based on reflected electro-material signatures. Viability of item level tracking demands the sensor to be extraordinary low cost, thus eliminating the use of any active sensor or memory circuitry. Recent developments of materials whose electrical properties can change significantly with the environmental conditions suggest the possibility of developing a passive sensor that can be interrogated remotely to extract data about the time tracked environmental changes at the sensor. A simple passive sensor, based on the concept of reflected electro-material signatures (REMS), consists of an antenna attached to a microstrip transmission line, which in turn is routed over one or more sections of variable permittivity material before being terminated in a load. The basic idea revolves around sensing the electrical properties of thermotropic liquid crystal (LCs) trapped in a polymer substrate to record the temperature data. As the temperature changes with time, the polymerization process through the material line records the historical temperature profile in the spatial distribution of the electrical properties, thus enabling the system to extract the historical profile of temperature without using any active memory circuitry. This concept can possibly be used to track a variety of variables of interest; however, the proposed research is focused on sensing and extracting the time profile of temperature. The problem of identifying medium properties from waves reflected from a device of this type is a form of the classical one dimensional inverse scattering problem. For profile inversion in a lossy inhomogeneous media, analytical techniques are difficult to implement in most practical situations. In the proposed research, neural networks with a back-propagation algorithm are used to reconstruct the historical temperature profile of the material by extracting the spatially distributed material properties of the electro-material line. After the initial proof of concept for a lossless medium, the methodology is extended to extract spatially distributed properties for a dissipative medium. Finally, for the implementation of REMS sensor concept, a neural network based methodology is developed to reconstruct the spatially distributed permittivity profile of a lossy electro-material line.

This work is aimed at developing a high sensitivity salinity (conductivity) sensor for marine applications. The principle of sensing involves the use of parallel plate capacitors, which minimizes the proximity effects associated with inductive measurement techniques. The barrier properties of two different materials, AZ5214 and Honeywell's ACCUFLO T3027, were investigated for use as the insulation layer for the sensor. Impedance analysis performed on the two coatings using Agilent's 4924A Precision Impedance Analyzer served to prove that ACCUFLO was a better dielectric material for this application when compared to AZ5214.Two separate detection circuits have been proposed for the salinity sensor. In the Twin-T filter method, a variation in capacitance tends to shift the resonant frequency of a Twin-T oscillator, comprising the sensor. Simulations of the oscillator circuit were performed using Pspice. Experiments were performed on calibrated ocean water samples of 34.996 psu and a shift of 410 Hz/psu was obtained. To avoid the problems associated with the frequency drift in the oscillator, an alternate detection scheme is proposed which employs frequency-to-voltage converters. The sensitivity of this detection scheme was observed to be 10 mV/psu.

Piezoelectric composite materials, consisting of a ferroelectric ceramic in an electrically-inactive polymer matrix, have been shown to greatly outperform single phase materials for certain applications. A new assembly technique, which electrically controls the spatial distribution of the ceramic within the polymer, promises to enhance the sensitivity of 0-3 type piezoelectric composites. The materials so-produced have a quasi 1-3 structure and it is intended that they will exhibit some of the advantages of 1- 3 piezoelectric composites, whilst retaining the simplicity of 0-3 manufacturing. The electric field structuring technique exploits the electrokinetic phenomenon of dielectrophoresis, which is responsible for the electrorheological effect. When a suspension of ceramic particles in an insulating fluid is exposed to a moderate AC electric field, the particles polarize and as a result they exhibit a mutually attractive force. Under suitable conditions the particles assemble into 'pearl-chains', 'fibrils' or columns, oriented parallel to the applied field. If the fluid is a resin pre-polymer, this can then be cured and the newly formed structures frozen into place to form a composite material with anisotropic properties. The key process parameters are explored and the implications of employing this method to produce technologically useful materials are discussed. It is demonstrated, for the first time, that dielectrophoresis can be used to induce anisotropic dielectric and piezoelectric properties in 55%vol. fraction ceramic/polymer composites. A model composite system of pure lead titanate in an epoxy resin is considered in basic detail. A method of producing a lead zirconate titanate (PZT) powder with a narrow particle size distribution, by flux growth, has been shown to be effective. New concepts in multiphase composites are introduced, whereby chains are formed within the confines of a second immiscible fluid or where particles of two different materials are mixed in a suspension, each material having its own 'polarization signature'.

Abstract The recent trend in low temperature co-fired ceramic (LTCC) technology is to integrate more elements into multilayer modules. This thesis describes work specifically aimed at developing ferroelectric barium strontium titanate (BST) for integration into such modules. In particular, an objective was the development of a novel, electric field controlled, tunable component to be used at microwave frequencies (2–26 GHz). For the application envisaged, relative permittivity is required to be low (100–1000) and adjustable by a suitable applied electric field, the dissipation factor at room temperature must be low (~0.001) at 2–26 GHz, and most importantly, the sintering temperature must be suited to the LTCC technology (~900 °C) Initial work was focused on sol-gel derived Ba0.7Sr0.3TiO3 powders with boron oxide addition, which were sintered at 900 °C, the dissipation factor was 0.006. The dissipation factor was not low enough for the desired microwave application, and attention turned to powders prepared by the mixed-oxide route. The Ba0.7Sr0.3TiO3 powders, fluxed with the optimum amounts of boron oxide and lithium carbonate, could be sintered at 890 °C to the same density as is achieved with un-fluxed Ba0.7Sr0.3TiO3 sintered at 1360 °C. The dissipation factor for this fluxed powder was acceptably low, although permittivity was too high for the particular objective. Subsequently, research was on BST modified by magnesia, 0.4Ba0.55Sr0.45TiO3-0.6MgO (BSTM). With the optimum fluxing additives, the sintering temperature necessary to achieve a dense BSTM-based ceramic was reduced to 950 °C. The developed microstructure was good, and the relative permittivity and dissipation factor values (221, 0.0012 at 1 kHz) at room temperature indicated good microwave properties. Studies were also undertaken with organic-based tape-casting slurries, laminating procedures and burn-out and sintering schedules. Several kinds of tapes were fabricated and characterized. A test structure for the measurement of dielectric properties at 26 GHz of the optimized BSTM-based ceramic was constructed. The specimen was 50 μm thick layer of BST on an alumina substrate. The relative permittivity and tunability were 130 and >15 % at 4 V μm-1 at room temperature. A tunable phase-shifter was fabricated from the same BSTM-based tape using a novel gravure printing technique, and measurements at 26 GHz showed phase shift from 10 to 35° when the electric field was increased from 1 V μm-1 to 2.5 V μm-1. Some exploratory experiments are described to assess the compatibility of the developed BST-based LTCC with commercial LTCC and some electroceramics.

Electrical insulating liquids, organic esters, conductivity, dielectric, permittivity

Permittivity values of a co-solvent system decrease with increasing temperature and decrease as mole fraction of water decreases. Fit to a cubic polynomial, the coefficients can be used to determine relative permittivity of the co-solvent system knowing temperature and mole fraction. A Brookhaven Instruments BI 870 Dielectric Meter was used. Pure water from 15.0 to 55.0 °C was measured to validate the method. Solutions of acetone and tetrahydrofuran were measured from 15.0 to 55.0 °C. A cubic polynomial fit was used to determine the polynomial coefficients for determining permittivity as a function of temperature and mole fraction. These coefficients may also be used to interpolate the dielectric constant between temperatures. Literature values for acetonitrile, 1,4-dioxane, methanol, ethanol, isopropanol and N,N-dimethylformamide in water were used to determine the polynomial coefficients.