The main purpose of this thesis is to propose a broadband miniaturized spectroscopy system to detect dielectric constant and loss tangent of lossy organic materials at RF/Microwave frequencies. Complex permittivities of lossy liquids are measured using voltage variations across a sensing element embedded in a capacitive divider circuit. The methodology for characterization of complex permittivity of materials is explained in detail. The proposed method provides a unique detection algorithm to extract the dielectric constant and loss tangent of an unknown material exposed to the sensor. The complex permittivity of binary organic mixtures have been extracted to an accuracy better than 5% using sample volumes of 200-300 μL within the frequency range of 1-2 GHz. The results obtained from the measurements are compared to the reported values, and their agreements are presented in this work. To the best of the authors’ knowledge, this is the first work presented for broadband miniaturized self-sustained complex permittivity spectroscopy at microwave frequencies.

No description available.

Dielectric permittivity measurements provide important input to engineering and scientific disciplines due to the effects of permittivity on the interactions between electromagnetic energy and materials. A novel ring resonator design is presented for the measurement of permittivity of low dielectric constant foams. A review of dielectric material properties and currently available measurement methods is included. Measurements of expanded polystyrene are reported and compared with results from the literature; good agreement between measurements and published results is shown.

No description available.

In the field of electromagnetism, there are materials known as metamaterials which exhibit unique properties that can be exploited. Permittivity, defined as capacitance per meter, of a metamaterial can vary over frequency , time, or even be negative. This can be useful for tuning antennas, changing their operating frequency or direction of propagation, or even designing cloaking systems. However, the theory behind metamaterials needs to be studied further. One of the biggest issues to address is in determining the constitutive parameters of metamaterials which may be varying. Previous research has shown the issue of branches, or mathematical discontinuities, occurring in the derivation of permittivity from the scattering parameters of a metamaterial. This thesis provides further understanding to the theory behind these branches and presents a new method to compensate for them. This new method, called the phase tracking method, may be considered a modern adaptation of the Nicolson-Ross-Weir method.

No description available.

This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.

This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.

This article describes some methods of measuring complex permitivity in milimeter – wave band, their characteristics, anvatages and disadvantages. Discused are here the reasons for their use in the construction of work place. On the basis these reasons is chosen the best method for practical measurement. That is cavity resonant method. Article contain description of designed measurement system. Whitch is verified by computer simulating of developed model in HFSS Ansoft. Text contain also result of simulations and execute computing of comlex permittivity and tangent loss. In Conclusion is desribed results of practical permittivity measure with realized measurement system.

Approved for public release / This research was part of an ongoing program studying the concept of multi-material dielectrics (MMD) with dielectric constants much higher than homogenous materials. MMD described in this study have dielectric constants six orders of magnitude greater than the best single materials. This is achieved by mixing conductive particles with an insulating surface layer into a composite matrix phase composed of high surface area ceramic powder and aqueous electrolyte. Specifically examined in this study was micron-scale nickel powder treated in hydrogen peroxide (H2O2) loaded into high surface area alumina powder and aqueous boric acid solution. This new class of dielectric, composite electrolyte dielectrics (CED), is employed in an electrostatic capacitor configuration and demonstrated dielectric constant of order 10 [raised to the 10th power] at approximately 1 Volt. Additionally, it is demonstrated that treated nickel can be loaded in high volume fractions in the CED configuration. Prior studies of composite capacitors indicated a general limitation due to shorting. This results from the onset of percolation due to excess loading of conductive phases. Insulated particles described herein are successfully loaded up to 40% by volume, far above typical percolation thresholds. Simple models are presented to explain results. / Lieutenant, United States Navy