This thesis is concerned with the problem of estimating broadband acoustic impedance from normal incidence reflection seismograms. This topic is covered by following the linear inverse formalisms described by Parker (1977) and Oldenburg (1980). The measured seismogram is modelled as a convolution of subsurface reflectivity with a source wavelet. Then an appraisal of the seismogram is performed to obtain unique bandlimited reflectivity information. This bandlimited reflecitivity information is then utilized in two different construction algorithms which provide a broadband estimate of reflectivity; from which a broadband impedance function may be computed. The first construction method is a maximum entropy method which uses an autoregressive representation of a small portion of the reflectivity spectrum to predict spectral values outside that small portion. The second and most versatile construction method is the linear programming approach of Levy and Fullagar (1981) which utilizes the unique bandlimited spectral information obtained from an appraisal and provides a broadband reflectivity function which has a minimum 1( norm. Both methods have been tested on synthetic and real seismic data and have shown good success at recovering interpretable broadband impedance models. Errors in the data and the uniqueness of constructed reflectivity models play important roles in estimating the impedance function and in assessing its uniqueness. The Karhunen-Loeve transformation is discussed and applied on real data to stabilize the construction results in the presence of noise. The generally accepted idea that low frequency impedance information must be supplied from well log or velocity analyses because of the bandlimited nature of seismic data has been challenged. When accurate, bandlimited reflectivity information can be recovered from the seismic trace, then an interpretable, broadband impedance model may be recovered using the two construction algorithms presented in this thesis. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

There is a rising need for inline sensors for continuous and non-destructive monitoring of crops status. As growth in agricultural productivity stagnates, farmers are increasingly adopting soil-implanted sensors that allow them to optimize their yields. In existing literature, plant bio-impedance has been shown to change accordingly with various biotic and abiotic stress factors, and thereby may constitute a marker of interest. Yet, to date, there is no widespread adoption of bio-impedance for plant health monitoring due to the low sensitivity of planar electrodes. This thesis is dedicated to the development of a plant impedimetric biosensor that utilizes micro-needles electrodes for enhanced sensitivity. The micro-needles have been designed to pierce the upper waxy layer (cuticle) of plants to measure impedance from the underlying layers. Moreover, a micromolding process has been utilized to fabricate the micro-needles at scale without sacrificing fidelity. The molds were fabricated using dip-in laser lithography to benefit from the high resolution and flexibility of the technique. Standard metal sputtering processes were then used to confer conductivity onto the micro-needles. Several micro-needle aspect ratios and geometries were explored and adapted for use on Barley (Hordeum vulgare L,) and Date Palm (Phoenix dactylifera). In order to assess the performance of the sensors, the impedance of several plant specimens was monitored using the developed sensors alongside planar electrodes. The impedance measured by the sensors was lower than that reported by planar electrodes at low frequencies, indicating successful bypassing of the cuticle, as desired. No adverse effects were observed on the plant tissue post micro-needle attachment for seven days. Furthermore, a cyclical diurnal pattern of impedance was observed in both plants that was entrained by light. Finally, the micromolding technique developed in this thesis can help produce high- fidelity 3D electrodes for bio-impedance monitoring. Once the mold is fabricated, the electrodes can be produced at scale without the need of clean-room equipment. Furthermore, the fabricated sensors can monitor bio-impedance of plant specimens for extended durations of time and may offer a platform that can be functionalized to selectively quantify specific phytohormones of interest.

Background: Non-obstructive Dysphagia (NOD) is one of the most common symptoms evaluated using esophageal manometry. Although manometry is considered the gold standard, many NOD patients have normal evaluations. Esophageal function testing with combined multichannel intraluminal impedance and esophageal manometry (MII-EM) is performed using ten 5-mL swallows of a liquid and a viscous material and provides supplemental information about bolus transit. The aim of this study was to evaluate esophageal function using combined MII-EM in patients with NOD who had normal evaluations with liquid manometry. Methods: Multichannel intraluminal impedance and esophageal manometry was performed in consecutive patients presenting for evaluation of NOD. Patients were excluded if any abnormality was detected during liquid manometry. Viscous manometry and liquid and viscous impedance data were analyzed to detect manometric or bolus transit abnormalities. Patients referred for GERD evaluation without any swallowing complaints were used as patient controls and were subject to the same exclusion criteria as the NOD group. All swallow evaluations were performed with 10 liquid and 10 viscous swallows. Key Results: Data from 240 patients were evaluated, 129 with NOD and 111 patient controls. In the NOD group, 9% (12/129) had abnormal liquid impedance and 29% (37/129) had abnormal viscous impedance. In the control group, 4% (4/111) had abnormal liquid impedance and 16% (18/111) had abnormal viscous impedance. Chi-square analysis showed a significant difference between the two study groups for viscous impedance (P = 0.02) but not for liquid impedance (P = 0.12). Conclusions and Inferences: Our data support our belief that a normal liquid manometry with an abnormal viscous impedance analysis in a patient with NOD indicates abnormal esophageal motility. Therefore, viscous impedance should be performed on all patients during the evaluation of NOD.

Background: Non-obstructive Dysphagia (NOD) is one of the most common symptoms evaluated using esophageal manometry. Although manometry is considered the gold standard, many NOD patients have normal evaluations. Esophageal function testing with combined multichannel intraluminal impedance and esophageal manometry (MII-EM) is performed using ten 5-mL swallows of a liquid and a viscous material and provides supplemental information about bolus transit. The aim of this study was to evaluate esophageal function using combined MII-EM in patients with NOD who had normal evaluations with liquid manometry. Methods: Multichannel intraluminal impedance and esophageal manometry was performed in consecutive patients presenting for evaluation of NOD. Patients were excluded if any abnormality was detected during liquid manometry. Viscous manometry and liquid and viscous impedance data were analyzed to detect manometric or bolus transit abnormalities. Patients referred for GERD evaluation without any swallowing complaints were used as patient controls and were subject to the same exclusion criteria as the NOD group. All swallow evaluations were performed with 10 liquid and 10 viscous swallows. Key Results: Data from 240 patients were evaluated, 129 with NOD and 111 patient controls. In the NOD group, 9% (12/129) had abnormal liquid impedance and 29% (37/129) had abnormal viscous impedance. In the control group, 4% (4/111) had abnormal liquid impedance and 16% (18/111) had abnormal viscous impedance. Chi-square analysis showed a significant difference between the two study groups for viscous impedance (P = 0.02) but not for liquid impedance (P = 0.12). Conclusions and Inferences: Our data support our belief that a normal liquid manometry with an abnormal viscous impedance analysis in a patient with NOD indicates abnormal esophageal motility. Therefore, viscous impedance should be performed on all patients during the evaluation of NOD.

Series impedances, including source and transfer impedances, are commonly used to model a variety of noise sources and noise treatment elements in duct systems. Particle velocity is assumed to be constant on the plane where the series impedances are defined. The research reported herein details investigations into measuring source and transfer impedance. Especially, the measurement and prediction of the transfer impedance of micro-perforated panel (MPP) absorbers is considered. A wave decomposition method for measuring source impedance and source strength was developed that was purely based on acoustic concepts instead of the equivalent circuit analysis. The method developed is a two-load method. However, it is not necessary to know the impedances of either load a priori. The selection of proper loads was investigated via an error analysis, and the results suggested that it was best to choose one resistive and one reactive load. In addition, a novel type of perforated element was investigated. MPP absorbers are metal or plastic panels with sub-millimeter size holes or slits. In the past, Maa's equation has been used to characterize their performance. However, Maa's equation is only valid for circular perforations. In this research, an inverse method using a nonlinear least square data fitting algorithm was developed to estimate effective parameters that could be used in Maa's theory. This inverse approach was also used to aid in understanding the effect of dust and fluid contamination on the performance of MPP absorbers. In addition, an approach to enhance the attenuation of MPP absorbers by partitioning the backing cavity was investigated experimentally and numerically. Results indicated that partitioning improved the attenuating of grazing sound waves. The effect of modifying both the source and transfer impedances on the system response was also studied using the Moebius transformation. It was demonstrated that the Moebius transformation is a mathematical tool that can be employed to aid in determining and understanding the impact of acoustic impedance modifications on a vibro-acoustic system.

The interconversion of α- and β-Ni(OH)₂ was studied using cyclic voltammetry and dynamic electrochemical impedance (dEIS). Holding experiments were done at 0.5 V, 0.6 V, 0.8 V and 1.0 V while subsequent cathodic holds were applied in selected experiments at -0.1, -0.2, -0.25 V. The number of thickness of Ni(OH)₂ formed increased with increasing anodic potential. After α-Ni(OH)₂ was formed (< 0.5 V), it was easily reduced by sweeping down to -0.15 V. However, sweeping further (> 0.5 V) resulted in its "irreversible" conversion to β-Ni(OH)₂. Since β-Ni(OH)₂ was not reduced by sweeping to -0.15 V, the current, capacitance and the conductance at the α-Ni(OH)₂ peak (at 0.2 V) decreased as a result. However, β-Ni(OH)₂ was shown to be reducible during potential holds at -0.2 V or lower. In contrast, holding at -0.1 V only resulted in partial reduction. Eventually, a link was established between the reduction of β-Ni(OH)₂ and hydrogen evolution. The relatively slow reduction of the β-Ni(OH)₂ to metallic nickel appears to inhibit the capacitance increase at -0.15 V which occurs when the potential is kept under 0.5 V. The retention of a low capacitance while β-Ni(OH)₂ persists suggests a blocking mechanism. A concerted adsorption-desorption step which generates adsorbed hydrogen prior to hydrogen evolution was proposed. An exponential increase in current and capacitance occurred during the potential hold at -0.2 V. The capacitance increase suggests a reversal of the blocking (low capacitance at -0.15 V) caused by the persistence of β-Ni(OH)₂. Additionally, the exponential current decay during the hold at -0.2 V was significantly slower than the conversion of α- to β-Ni(OH)₂ at 0.8 V. This further demonstrates the possibility of a slow step involving surface blocking during the reduction of β-Ni(OH)₂. These observations provide new information on the mechanism and kinetics of the interconversion of α-Ni(OH)₂ into β-Ni(OH)₂ and the interaction of the latter in the hydrogen evolution reaction. / Graduate

No description available.

This thesis targets on design of portable device for impedance measurement. Theoretical knowledge related to the construction of a portable impedance analyzer is summarized in a separate chapter. This section also compares some commercially available impedance analyzers. In addition, this thesis contains a description of the principle of operation of the impedance analyzer, which is divided into individual function blocks and supplemented by control circuits. A large part of the work focuses on the design of the analog measurement circuit, where suitable measuring methods are also presented. The functionality of the analog blocks of the device was verified by circuit simulation in the PSpice program and by experimental tests. Selection of some components is mentioned in the relevant chapters, where the essential parameters from datasheets are listed. The output of the work deals with a designed prototype of the device, which was tested. Based on the findings some modifications of the device were proposed for practical usability. The attachment of the thesis contains final version of designed printed circuit board.

The first part deals with the basic methods for measuring an unknown impedance. After determining the parameters of the desired impedance analyzer method was chosen AC unbalanced Wheatstone bridge. As a source of harmonic signal has been selected direct digital synthesis circuit and measure provides the analog vector voltmeter. Subsequently, it is discussed the issue of determining the sign of the unknown phase impedance. The thesis describes the wiring of circuit AD8302 and circuit AD9958 direct digital synthesis for which it is also an example of the code. It discusses the design and simulation of a reconstruction filter. Finally there are the measured output voltage and spectrum synthesizer.

Yes / This paper presents an approach to implement an automatically tuning antenna for optimising power transfer suitable for software defined radio (SDR). Automatic tuning is accomplished using a closed loop impedance tuning network comprising of an impedance sensor and control unit. The sensor provides the control unit with data on the transmit or receive power, and the algorithm is used to impedance of a T-network of LC components to optimize the antenna impedance to maximise power transmission or reception. The effectiveness of the proposed tuning algorithm in relation to impedance matching and convergence on the optimum matching network goal is shown to be superior compared with the conventional tuning algorithm. / This work is partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1