Dissertations / Theses on the topic 'Impedance'
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Sánchez, Terrones Benjamín. "Broadband electrical impedance spectroscopy for dynamic electrical bio-impedance characterization." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/132281.
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The electrical impedance of biological samples is known in the literature as Electrical Bioimpedance (EBI). The Electrical Bioimpedance enables to characterize physiological conditions and events that are interesting for physiological research and medical diagnosis. Although the Electrical Bioimpedance weakness is that it depends on many physiological parameters, on the other hand, it is suitable for many medical applications where minimally invasive and real-time measurements with simple and practical implementations are needed.
The Electrical Impedance Spectroscopy (EIS) techniques based on broadband excitations are expected to help to understand various unsolved problems in biomedical applications. Broadband EIS opens up the possibility to reduce drastically the measuring time for acquiring EBI time-variations but, at the same time, measuring in a short time compromises the EBI accuracy. The way to overcome this intrinsic loss of accuracy relies on the design of the appropriate time/frequency input excitation properties and the use of the suitable spectral analysis processing techniques.
The presented thesis covers the topics related to study of broadband excitations for Impedance Spectroscopy in biomedical applications and, more specific, the influence of the multisine excitation time/frequency properties on the impedance spectrum accuracy and its optimization. Furthermore, an advanced fast signal processing method has been implemented to process in real-time EBI data corrupted by transients, a common situation when measuring in a short measuring time. Despite being the goal to apply all this knowledge for myocardial tissue regeneration monitoring, at the moment of drafting the thesis, any of the research projects that have supported this thesis have issued functional beating tissue. For that reason, the theory presented has been validated by a set of experimental measurements over animals and patients where the impedance spectrum time-varying properties were pretended to be characterized.
The thesis presents novel findings of relevance of a successful application of broadband EIS in two different measurement campaigns where it has been put in practice: (1) within the collaboration of the pneumology and cardiology service from Hospital Santa Creu i Sant Pau for in-vivo human lung tissue characterization, and (2), within the measurement of animal healthy myocardium tissue electrical impedance including its dynamic behavior during the cardiac cycle.
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Leung, Hing Tong Lucullus. "Development of an electrical impedance tomograph for complex impedance imaging." Thesis, University of South Wales, 1991. https://pure.southwales.ac.uk/en/studentthesis/development-of-an-electrical-impedance-tomograph-for-complex-impedance-imaging(b3f26e76-490d-4364-a270-28cff1dccd70).html.
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This project concerns the development of electrical impedance tomography towards the production of complex impedance images. The prime intention was to investigate the feasibility of developing suitable instrumentation; but not clinical applications. It was aimed to develop techniques for the performance evaluation of data collection systems. To achieve this it was necessary to design and develop a multi· current source type impedance tomography system, to act as a platform for the current study and for future work. The system developed is capable of producing conductivity and permittivity images. It employs microprocessor based data collection electronics, providing portability between a range of possible host computers. The development of the system included a study of constant amplitude current source circuits leading to the design and employment of a novel circuit. In order to aid system testing, a surface mount technology resistor-mesh test object was produced. This has been adopted by the EEC Concerted Action on Impedance Tomography (CAIT) programme as the first standard test object. A computer model of the phantom was produced using the industry standard ASTEC3 circuit simulation package. This development allows the theoretical performance of any system topology, at any level of detail, to be established. The imaging system has been used to produce images from test objects, as well as forearm and lung images on humans. Whilst the conductivity images produced were good, the permittivity in-vivo images were noisy, despite good permittivity images from test objects. A study of the relative merits of multiple and single stimulus type systems was carried out as a result of the discrepancies in the in-vivo and test object images. This study involved a comparison of the author's system with that of Griffiths at the University Hospital of Wales. The results showed that the multi current source type system, whilst able to reduce stray capacitance, creates other more significant errors due to circuit matching; future development in semiconductor device technology may help to overcome this difficulty. It was identified that contact impedances together with the effective capacitance between the measurement electrode pairs in four-electrode systems reduces the measurability of changes in phase. A number of benchmarking indices were developed and implemented, both for system characterisation and for practical/theoretical design comparisons.
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Doyon, Michel. "Decentralized impedance control." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26384.
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Many applications of manipulators to date have been based on position control, but when a robot manipulator makes contact with the environment, the control of force and position is required. One approach, impedance control, is to control the manipulator such that the relationship between position and force is well defined. For example, such that the robot behaves like a mass-spring-damper system whose parameters can be specified arbitrarily. In the recent years, many of the impedance control implementations were using force feedback from an end-effector force sensor and the impedance control was performed by forming the error in Cartesian coordinates. The implementation proposed here requires instead co-located torque sensors and the feedback control signals are based solely on joint variables, torque and displacement. Co-located torque sensors lead to a larger control bandwidth since the structural dynamics of the arm is seen as a perturbation, but is not part of the plant to be controlled. Simple SISO controllers, designed to modulate individual joint impedances, can achieve diagonal (decoupled) impedance matrices in Cartesian coordinates, provided that a set of SISO compensators, called her "decouplers", are set up to cancel the non-linear coupling among the joints. This strategy results in a simple computational architecture which does not require complex coordinates transformations to be performed at servo rate. The method can be used with non-redundant and redundant manipulators and experimental results are discussed using a seven DOF manipulator available at the Institut de recherche d'Hydro-Quebec.
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Love, Lonnie J. "Adaptive impedance control." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/15911.
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Bernabini, Catia. "Micro-impedance cytometry." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/178259/.
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Electrical impedance spectroscopy is a non-invasive and label free technique that allows for rapid counting and characterisation of particles in suspension based on their response to applied AC potentials. In recent years, lab-on-a-chip technologies have been developed to enable single-cell impedance detection and a wide range of impedance-based microfluidic devices have been reported. Despite the number of contributions and the achievements of this field, micro-impedance cytometry still suffers from a lack of sensitivity and specificity compared to traditional flow cytometry, which limits the potential commercialization of microfluidic impedance devices. While impedance measurements of beads and cells are well established, discrimination between particles that are very similar in size or detection of small particles (around 1 μm in diameter) such as bacteria, still represents a difficult task. A number of issues limit the sensitivity and specificity of these microfluidic systems. Primarily, the sensitivity is governed by the dimension of the sample analysis volume. A small volume gives a high sensitivity, but this can lead to practical problems, including fabrication and clogging of the device. In addition, the spatial location of each particle needs to be controlled accurately within the field. Therefore, an efficient and accurate method for focussing the particles in the centre of the electric field is important. In this thesis, a micro-impedance cytometer for the detection of small particles and bacteria and for the discrimination of particles that are very similar in size is presented. The device consists of a microfluidic channel where two pairs of microfabricated electrodes are provided to perform differential measurements of single particles in suspension at high speed. Different electrode configurations and different techniques for focussing the sample within the detection region of the device are investigated in order to improve the sensitivity of the system without reducing the dimensions of the microfluidic channel. Detection at a volume ratio of particle to an estimated sensing volume of 0.007% and discrimination of 1 μm and 2 μm diameter polystyrene beads and E. coli are demonstrated. The micro-impedance cytometer is also proven to be a reliable and effective system to investigate and determine the unknown dielectric properties of particles in suspension, such as polyelectrolyte microcapsules
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Liu, Hongze. "A High-Resolution Microscopic Electrical Impedance Imaging Modality: Scanning Impedance Imaging." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1729.pdf.
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Zhang, Guidong [Verfasser]. "Impedance networks matching mechanism and design of impedance networks converters / Guidong Zhang." Hagen : Fernuniversität Hagen, 2015. http://d-nb.info/1079393064/34.
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Talabani, Habib. "Investigation into the impedance imaging technique scanning photo-induced impedance microscropy (SPIM)." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412789.
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Sun, Tao. "Single cell impedance spectroscopy." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/265320/.
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Foley, John J. "Microfluidic Electrical Impedance Spectroscopy." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1950.
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The goal of this study is to design and manufacture a microfluidic device capable of measuring changes in impedance valuesof microfluidic cell cultures. Tocharacterize this, an interdigitated array of electrodes was patterned over glass, where it was then bonded to a series of fluidic networks created in PDMS via soft lithography. The device measured ethanol impedance initially to show that values remain consistent over time. Impedance values of water and 1% wt. saltwater were compared to show that the device is able to detect changes in impedance, with up to a 60% reduction in electrical impedance in saltwater. Cells were introduced into the device, where changes in impedance were seen across multiple frequencies, indicating that the device is capable of detecting the presence of biologic elements within a system. Cell measurements were performed using NIH-3T3 fibroblasts.
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Abrahamsson, Johan. "Loop impedance measurement tool." Thesis, Linköpings universitet, Fysik och elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-169109.
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This master´s thesis presents a prototype of a hand-held measurement tool used to measure the loop impedance of ground loops using two current probes. This tool allows the user to find bad shield connections in a system without disconnecting the shielded cables. The thesis explains the theory behind the measurement method, hardware requirements and design, how the software works and a demonstration of the implemented graphical user interface. The tool is powered by a two-cell lithium-ion battery and has an integrated battery charger with cell balancing.
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Lu, Xiaolin. "Seismic ray impedance inversion." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6085.
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This thesis investigates a prestack seismic inversion scheme implemented in the ray parameter domain. Conventionally, most prestack seismic inversion methods are performed in the incidence angle domain. However, inversion using the concept of ray impedance, as it honours ray path variation following the elastic parameter variation according to Snell’s law, shows the capacity to discriminate different lithologies if compared to conventional elastic impedance inversion. The procedure starts with data transformation into the ray-parameter domain and then implements the ray impedance inversion along constant ray-parameter profiles. With different constant-ray-parameter profiles, mixed-phase wavelets are initially estimated based on the high-order statistics of the data and further refined after a proper well-to-seismic tie. With the estimated wavelets ready, a Cauchy inversion method is used to invert for seismic reflectivity sequences, aiming at recovering seismic reflectivity sequences for blocky impedance inversion. The impedance inversion from reflectivity sequences adopts a standard generalised linear inversion scheme, whose results are utilised to identify rock properties and facilitate quantitative interpretation. It has also been demonstrated that we can further invert elastic parameters from ray impedance values, without eliminating an extra density term or introducing a Gardner’s relation to absorb this term. Ray impedance inversion is extended to P-S converted waves by introducing the definition of converted-wave ray impedance. This quantity shows some advantages in connecting prestack converted wave data with well logs, if compared with the shearwave elastic impedance derived from the Aki and Richards approximation to the Zoeppritz equations. An analysis of P-P and P-S wave data under the framework of ray impedance is conducted through a real multicomponent dataset, which can reduce the uncertainty in lithology identification.Inversion is the key method in generating those examples throughout the entire thesis as we believe it can render robust solutions to geophysical problems. Apart from the reflectivity sequence, ray impedance and elastic parameter inversion mentioned above, inversion methods are also adopted in transforming the prestack data from the offset domain to the ray-parameter domain, mixed-phase wavelet estimation, as well as the registration of P-P and P-S waves for the joint analysis. The ray impedance inversion methods are successfully applied to different types of datasets. In each individual step to achieving the ray impedance inversion, advantages, disadvantages as well as limitations of the algorithms adopted are detailed. As a conclusion, the ray impedance related analyses demonstrated in this thesis are highly competent compared with the classical elastic impedance methods and the author would like to recommend it for a wider application.
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Bohlen, Oliver. "Impedance-based battery monitoring /." Aachen : Shaker, 2008. http://d-nb.info/991224523/04.
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Chang, Shuai, Andy Gee, Benjamin Ramos, Kyle Province, Dan Harcourt, and Matthew Hendrick. "Smart Grid Impedance Meter." Thesis, The University of Arizona, 2013. http://hdl.handle.net/10150/297527.
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Texas Instruments has been developing Power Line Communication (PLC) technology to provide a form of communication for worldwide applications. By utilizing power grids within an infrastructure, it is possible to transmit a signal through the existing power lines such as a network would. Transmission of data within the electrical grid proves to be inherently noisy, thus compromising any information that is sent over the network. In order to provide a reliable platform of communication, frequency and impedance variation needs to be analyzed in order to provide proper development into PLC solutions. Within the scope of this project an analytical tool was developed to provide engineers with a method to determine impedance and frequency variations. Analysis and testing has been conducted to ensure the device satisfies the design requirements.
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Wiesner, Jiří. "Návrh vf měřiče impedance." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221235.
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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.
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Cheung, Sung-man, and 張宋文. "Electric control of acoustic impedance." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45985376.
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Schneider, Ingo D. "Investigations in electrical impedance tomography." Thesis, Cardiff University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427798.
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This thesis presents an investigation of various designs and implementation aspects of multi-frequency Electrical Impedance Tomography (EIT) systems for medical applications. EIT presents a relatively new imaging modality that involves the measurement of the complex impedance of a body through voltage measurements around the body's surface, when it is subjected to electrical excitation. The primary region of interest for measurement involves excitation in the frequency range from several kHz to about a few MHz. EIT system design objectives were defined which are the starting point of a detailed error analysis of an EIT system. The analysis undertaken introduced new aspects in terms of the multiplexers' on-resistance, the CMV error analysis and the investigation of the feedthrough errors incorporating the frequency dependence of the skin-electrode interface. A specification of a novel multi-frequency EIT system has been derived through careful consideration of the design objectives based on the results of the error analysis. The merits and drawbacks of different types of stimulus signal for bio-impedance measurements are reviewed and a novel multi-frequency signal for the in vivo measurement of biological impedances has been introduced. An active electrode was built for differential voltage measurement which combines a superior CMRR performance, compared to previously reported implementations, with high input impedance. The implemented circuit has been designed to allow further miniaturisation by means of hybrid semiconductor technologies. Prototypes of several digital subsystem components of the specified EIT system were designed and validated the concept of the novel multi-frequency EIT system. For testing and calibrating the developed front-end electronics, a novel EIT phantom systems is presented, which employs active impedance elements. Utilising active impedance elements enables computer control of the actual impedance values which simplifies and automates the measurement of phantom impedances over a wide range.
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Zhu, Q. S. "Precision electrical impedance tomography instrumentation." Thesis, Oxford Brookes University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332494.
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Folayan, Olanike. "Compact high impedance plane antennas." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440945.
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Purvis, W. R. "Impedance imaging using induced current." Thesis, University of Sheffield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306447.
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Ye, Haitao. "Impedance spectroscopy of diamond films." Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405607.
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Richardson, Robert Raymond. "Impedance-based battery temperature monitoring." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:be4393bf-d516-4cb4-8362-82ebe7e1b78d.
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Accurate on-board temperature monitoring of lithium-ion batteries is important for safety and control purposes. Impedance temperature detection (ITD) is a promising approach for temperature estimation, whereby the internal cell temperature is directly inferred from online electrochemical impedance spectroscopy (EIS) measurements at a single frequency. Previously, ITD was used to infer the volume-average cell temperature; the present work focuses on extending ITD to enable estimation of the spatially-resolved temperature distribution of cells with internal temperature gradients. Two novel hybrid methods for temperature monitoring are introduced, based on combining impedance measurements with (i) an additional surface temperature measurement, and (ii) a thermal model. These methods predict the temperature distribution of the cell in either 1-D or 2-D, and can therefore identify localised hot spots, and hence the global maximum cell temperature. In each case, the methods are experimentally validated using cylindrical LiFePO4 cells (26650 for the 1-D experiments, 32113 for the 2-D experiments) monitored with periodic 215 Hz impedance measurements, and fitted with an internal thermocouple and one or more surface thermocouples for validation. Method (i) is shown to be more accurate than a standard ITD method based on impedance measurement only: e = 0.6?C vs. 2.6?C respectively, over a 3500 s drive cycle. In method (ii), the impedance measurement forms part of a state/parameter estimation algorithm; in this case, the performance of an extended Kalman filter using impedance measurement is shown to be comparable - although slightly inferior - to an equivalent Kalman Filter using a conventional surface temperature measurement. This work also presents a novel low-order 2-D thermal model based on the spectral-Galerkin (SG) method. The model can be used in conjunction with the proposed hybrid methods or in a conventional temperature monitoring scheme. Time- and frequency domain simulations show that the SG model using as few as 4 states is capable of accurately modelling the thermal dynamics of a large format cylindrical cell with a highly transient heat generation input. The model can account for different external temperatures and/or convection coefficients at each surface - a generality which makes it suitable for simulating various battery cooling configurations.
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Krishna, Karthik. "Estimation of Impedance About the." Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-theses/278.
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In performing manual tasks, muscles are voluntarily contracted in order to produce force and orient the limb in the desired direction. Many occupational tasks are associated with frequent musculoskeletal disorders. In tasks involving skilful manipulation, very frequently the forces are focused on the upper limb and neck. Upper extremity cumulative trauma disorders are among the more common worker related injuries. These muscle disorders may be related to repetitive exertions, excessive muscle loads and extreme postures. One of the major challenges is to quantify the muscle load and researchers have tried various measures to quantify muscle load. Joint mechanical impedance can be a robust method to quantify muscle load. Joint mechanical impedance characterizes the dynamic torque-angle relationship of the joint. Joint impedance has been measured by earlier researchers, for limited tasks, by imparting force (or angle) perturbations on the joint and relating resultant angular (or force) changes. The joint impedance gives a quantitative measure related to muscle co-contraction level. Measurement of the mechanical impedance at the workplace may provide useful information relevant to the understanding of upper limb disorders. Electromyogram (EMG) is the electrical activity of the muscle. Usually, an estimate of the EMG amplitude is obtained from the raw waveform recorded from the surface of the skin. EMG amplitude estimates can be used to non-invasively estimate torque about joints. Presently, there exists no means by which mechanical impedance can be estimated non-invasively (i.e., without external perturbations). Therefore, we proposed the use of EMG to noninvasively estimate the joint mechanical impedance. Our objective in this project was to determine the extent to which surface EMG can be used to estimate mechanical impedance. Simulation studies were first performed to understand the extent to which this tool could be useful and to determine methods to be used for the experiment. The simulations were followed by evaluating and estimating mechanical impedance using data collected from one experimental subject. Simulations helped to devise processing techniques for the measured signals and also to determine the length of data to be collected. Low pass filters for derivatives (used in the development of impedance estimates) were designed. Subtracting out a polynomial was the best approach to attenuate a low frequency drift (artifact) that occurs in torque measurements. Thirty seconds of data provided impedance estimates with a relative error of 5% when EMG amplitude estimates with SNR of 15 were used. Experimental data from constant-posture, slowly force-varying background torque level showed that the elbow joint system behaved like a second order linear system between 2 Hz and 10 Hz. Co-contraction by subjects during experiments caused impedance estimates to be unexpectedly high even at low background torque. Further experiments would need to be conducted with the subjects being instructed to avoid co-contraction.
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Wang, Albert Duan. "Directional impedance of geared transmissions." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78190.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39).
The purpose of this research is to develop a design tool for geared actuation systems that experience bidirectional exchange of energy with the environment. Despite the asymmetry of efficiency depending on the direction of power transfer in geared systems, typical dynamic models consider a fixed transmission efficiency for all conditions which can result in significant error depending on specific gear selection and the number of stages. This error can cause issues especially in dynamic legged robots and haptic devices when accurate force control is desired. In this paper we present directional impedance, a characteristic of geared transmissions in which the amount of power loss through the transmission differs according to the direction of power flow. Typical robots use electric motors with high gear reduction which introduces larger impedance when power flows from the output back to the motor than when the power flows from motor to output. To investigate the dependence on power flow direction, friction loss from gear teeth sliding in the gear mesh is modeled by a single gear tooth contact model and dynamic models are presented for each power transfer direction. Combinations of 0.5 mod gears were tested in experiment over a range of sizes between 16 and 120 teeth to characterize the directional effects over multiple gear selections. The experiments confirmed that for a set of differently sized gears, power loss is greater when the larger gear drives the smaller one than in the reverse case, and the asymmetry was up to 17% in the 16 and 120 tooth gear set. With a multiple stage gearbox, the difference in loss is further amplified. These findings show that directional loss in gears is a non-negligible effect and must be considered in both dynamic modeling and gear selection of robotic actuators. The gear loss model enables the modeling of motor and gearbox as a single package which can then be optimized for desired performance parameters such as peak torque, torque per mass, and mechanical impedance.
by Albert Duan Wang.
S.M.
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Wlassich, John J. (John James). "Nonlinear force feedback impedance control." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15032.
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Raju, Vinod. "Implementing Impedance - Based Health Monitoring." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35657.
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This work is an experimental study of applying an impedance-based health monitoring technique to complex structures. The work is presented in three parts.
In the first part we consider effects of the following three factors on damage detection abilities: actuator excitation level, test wire length and ambient conditions (temperature, structural loading and vibration). It was concluded that increasing the applied voltage improves the signal to noise ratio and damage detection abilities. Test wire lengths under 30m do not affect damage detection abilities. The technique is able to distinguish and detect damage even with variations in temperature, structural loading and vibration.
In the second part we apply our health monitoring technique to a complex truss structure and a massive steel steam header. We discovered that with multiplexing (acquiring a single signal from distributed actuators) the actuators on the truss structure we could detect damage but with less location information. Damage detection on the steel pipe ended in inconclusive results. The use of this technique on massive structures needs further investigation.
Finally, we conducted a detailed experimental study of monitoring the integrity of composite-reinforced masonry structures. We developed a software package which enables even a casual user to determine if significant damage has occurred in these structures. The technique was successfully applied to detect damage (particularly due to delamination) in these composite-concrete structures. Most significantly, the technique was also able to detect damage well in advance of actual failure.
This work relies mainly on frequency response plots and damage metric charts to present the data and to arrive at any conclusions. While frequency response plots give a qualitative approach to the analysis, damage metric charts attempt to quantify the data.Master of Science
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Naohiro, Hirose. "Impedance characterisation of conducting materials." Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU603182.
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Impedance spectroscopy is a powerful technique for characterising electrical microstructure of materials and has been increasingly useful in material science. The characteristic equivalent circuit elements give useful information on the nature of materials under study. This thesis describes impedance characterisation of conducting materials using non-Debye circuits including constant phase elements (CPE) as a superior data processing method to the conventional Debye approach which is customarily used for impedance characterisation. First, impedance spectroscopy is interpreted by inclusion of CPE components into the Debye circuits. The response was simulated in several impedance formalisms considering many possible changes in parameters. Most responses are totally different from the Debye response and cannot be interpreted in the same manner. Some key features are explained using characteristic parameters in Almond-West theory. Impedance data for yttria-stabilised zirconia with variable Y2O3 content were fitted well with circuits including CPE elements. The non-Debye character of the bulk and grain boundary components was successfully interpreted in terms of the circuits simulated previously. However, some samples showed small, but significant deviations from these approximate circuits. The discrepancy was ascribed to the existence of an additional capacitance, resulting from dipole reorientation. The data were fully fitted using the modified bulk circuit. It is also found that multi-impedance formalism analysis is the best method to obtain the most reliable equivalent circuits and fitted parameters. The conductivity data are analysed with Almond-West theory. The equality of activation energy for conduction and hopping suggests that V"O can contribute to dc conduction using direct hops among Y' defects. This energy can be represented as the sum of the dissociation energy needed to break the Coulomb interaction and the activation energy of local V'o migration. Impedance data of lithium disilicate glass were also examined using the non- Debye approach. The data for the bulk component fit well with the circuit including CPE. Annealed samples showed larger activation energy than that for an as-quenched sample. Using Almond-West theory, the difference is directly attributed to increase in the activation energy for hopping, which is explained by narrowing of the conduction pathway for the conducting cation in the annealed sample; this may be caused by reorganisation of the anion framework with decreasing volume while annealing. Barium titanate ceramics were chosen as the third example. The Debye approach is discussed first with the impedance data above the Curie temperature, Tc. The analysis showed that, in conventional fixed frequency measurements, grain boundary impedances influence the Curie-Weiss plots in two ways: at high temperatures, they increasingly dominate the permittivities; at lower temperatures, closer to Tc, the permittivity contains a contribution from grain boundary effects. Methods for extraction of bulk and grain boundary permittivities using impedance spectroscopy are discussed and the importance of selecting the appropriate equivalent circuit to model the impedance response is stressed. A constriction impedance model for the grain boundary in BaTiO3 ceramics is proposed from the temperature variation of grain boundary capacitance. The grain boundary is ferroelectric, similar to the grains, but its impedance is modified by high impedance electrical inhomogeneity in the region of the necks between grains; the activation energy of the constriction grain boundary impedance differs from that of the bulk, suggesting differences in defect states or impurity levels. The analysis for the same BaTiO3 impedance data is extended to a non-Debye approach. The non-Debye character of the bulk response is successfully analysed using CPE elements with manual fitting while the computer fitting was of limited success for both the bulk and grain boundary responses. The reason is ascribed to data limitation and additional, unknown bulk response appeared at high frequencies; the further development and analysis of BaTiO3 impedance data is a future problem.
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Bécot, François-Xavier Guyader Jean-Louis Kropp Wolfgang. "Tyre noise over impedance surfaces." Villeurbanne : Doc'INSA, 2004. http://docinsa.insa-lyon.fr/these/2003/becot/index.html.
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Thèse doctorat : Acoustique : INSA LYON : 2003. Thèse doctorat : Acoustique : Chalmers University of Technology, Göteborg : 2003.Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Le titre en français ne figure pas sur la page de titre. Bibliogr. p. 140-152.
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Li, Jiahao. "Heterogeneously integrated impedance based biosensors." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277259.
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The salient issues of integrated biosensors on a complementary metal-oxide semiconductor (CMOS) platform are the limited transducer design and the need for post-processing. To overcome these issues, a heterogeneously integrated system, which employs both CMOS and large-area processing, was proposed and developed. The system presented, could become a rapid, low-cost and disposable sensing platform for point-of-care applications. The heterogeneously integrated system, comprising a CMOS front-end circuit and disposable electrodes, was applied to measure the impedance of suspended DNA at different concentrations. The measurement showed a double sensitivity compared to the one carried out on the CMOS platform only. The noise analysis of CMOS transimpedance amplifiers was performed, and the impact of technology scaling on low-noise transimpedance amplifiers was studied using the Enz-Krummenacher-Vittoz (EKV) model. It was found that the noise performance improves slowly with device scaling down to 90 nm. Further device scaling may increase the gate leakage current noise due to the very thin gate oxide. Disposable electrodes fabricated using large-area processing are low cost and flexible in terms of design. In particular, inkjet-printed silver electrodes on glossy paper and gold electrodes on the glass substrate were characterised. Both electrodes with the same dimension agreed well in determining solution resistance. In addition, the paper-based electrodes presented an improved sensitivity of impedance measurement at low frequencies. The amorphous oxide thin-film transistor (TFT) is promising for implementing active circuits on disposable substrates. In particular, the low-frequency noise of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs was characterised, and a TFT-based regulated cascade transimpedance amplifier was designed and simulated with the extracted device parameters. The a-IGZO TFT showed a comparable noise performance to the PMOS device in deep submicron processes. The simulated circuit featured a transimpedance gain up to 120 dB, a bandwidth of 29.4 kHz, input-referred noise PSD of 2.91 pA/√Hz, and a power consumption of 18.55 μW, indicating that TFT-based front-end circuits are promising for implementing low-cost, low-noise and low-power biosensors.
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Matušek, Adam. "Modelling of cardiac impedance signals." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219669.
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Tato diplomová práce se zabývá vytvořením modelu signálu impedančního měření srdce (ICG signál). Impedanční kardiografie podává informaci o změně srdečního objemu během srdečního cyklu. Modelování signálu předchází statistická analýza vzájemné pozice ICG signálu vzhledem k dalším mechanickým srdečním signálům. Konstrukce modelu vychází z reálných nasnímaných signálů. Konečný ICG model je začleněn do již existujícího modelu mechanických interakcí mezi srdcem a plícemi. Výsledkem je funkční model kardio-respiračních interakcí, který bude sloužit v dalších částech výzkumu laboratoře PRETA.
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Liang, Zhibang. "High impedance fault detection in power distribution systems with impedance-based methods in frequency domain." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59530.
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High Impedance Faults (HIFs) in electrical distribution systems generally present serious public safety hazards, utility liability problems and equipment damage due to a risk of arcing ignition of fires. However, it is extremely difficult to detect HIFs in electrical distribution systems by conventional overcurrent relays or fuses because they do not generate enough fault current to be detectable. This thesis presents a new detection scheme for HIFs in electrical distribution systems based on observing the harmonic content in the one-sided amplitude spectrum of the impedance. The proposed new HIF detection algorithm can distinguish HIF events from other non-fault events with current waveforms that similar to HIF current waveforms. Four simulation cases have been tested in this thesis to verify the new HIF detection algorithm. The simulation results indicate a potential ability to establish a high impedance fault detection function block in BC Hydro’s distribution system protective devices.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Liu, Jinghao. "ADVANCED STUDIES ON SERIES IMPEDANCE IN WAVEGUIDES WITH AN EMPHASIS ON SOURCE AND TRANSFER IMPEDANCE." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/821.
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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.
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[UNESP], Tiago Azevedo Benites. "Estudo das propriedades dielétricas e de bloqueio das monocamadas automontadas." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/88011.
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000721769.pdf: 1532537 bytes, checksum: 1f1f903eabe42a2227cf65971f622a31 (MD5)O estudo das propriedades dielétricas das monocamadas automontadas de alcanotióis sobre o ouro (SAMs) é importante no campo da biotecnologia, já que essas camadas proporcionam uma estrutura fundamental na construção dos eletrodos quimicamente modificados, com sua principal aplicação na confecção dos biossensores. A análise das propriedades de bloqueio pelas SAMs é frequentemente feita por meio de técnicas eletroquímicas e de resposta em frequência, pois são extremamente eficazes no entendimento das características físico-químicas interfaciais de modificação desses filmes, além de apresentarem praticidade e velocidade de realização. Uma forma bastante apropriada de analisar a capacidade dielétrica das SAMs é quantificando a velocidade de transferência eletrônica frente a uma espécie eletroativa. Nesse trabalho foram caracterizadas monocamadas de diferentes espessuras em um meio com espécie eletroativa em concentrações variadas, a partir do cálculo da constante de transferência heterogênea de elétrons, feitas pelas metodologias propostas por diferentes autores e por uma metodologia inédita que será detalhada no corpo do trabalho
The study of the dielectric properties of self-assembled monolayers of alkanethiols on gold (SAMs) is of paramount importance to biotechnology, as these layers provide a fundamental structure in the construction of chemically modified electrodes, with its main application in fabrication of biosensors. The analysis of the blocking properties of SAMs is often done by electroanalytical techniques and frequency response, as they are extremely effective in understanding the physico-chemical interfacial modification of these films, and offer convenience and speed of execution. A very appropriate manner of evaluating the blocking ability of SAMs is quantifying dielectric constant and the heterogeneous electron transfer rate across from one electroactive species in solution. In this study monolayers of different thicknesses were characterized in a medium with electroactive species in different concentrations to calculate of the heterogeneous electron transfer constant by classical methods which were compared with a new methodology detailed in the present work
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Boissinot, Philippe. "Impedance acoustique de rayonnement dans les antennes planes : impedances mutuelles avec un milieu de propagation de type viscoelastique et application aux directivites d'antenne." Paris 6, 1988. http://www.theses.fr/1988PA066092.
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Ocaña, Tejada Cristina. "Aptasensors based on electrochemical impedance spectroscopy." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/305103.
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En els últims anys, a causa de la necessitat de diàgnostics ràpids i de millores en sensat, s’han utilitzat nous elements de reconeixement en biosensors. Un tipus d’aquests nous elements de reconeixement són els aptàmers. Els aptàmers són cadenes sintètiques de ADN o ARN les quals són seleccionades in vitro i tenen la capacitat d’unir-se a proteïnes, ions, cèl.lules, fàrmacs i lligands de baix pes molecular, reconeixent les seves molècules diana amb alta afinitat i especificitat. Diversos biosensors basats en aptàmers, també anomenats aptasensors, han sigut desenvolupats recentment. D’entre totes les tècniques de transducció utilitzades en biosensors, l’Espectrocòpia Electroquímica d’Impedància ha sigut àmpliament emprada como a eina per caracteritzar la superficies de sensors i estudiar esdeveniments en el biosensat en la superficie d’elèctrodes. La característica més important que presenta aquesta tècnica és que no requereix cap espècie marcada per a la transducció, per tant, aquesta tècnica de detecció pot utilitzar-se per dissenyar protocols de detecció directa sense marcatge, evitant assajos més cars i laboriosos.
El principal objectiu d’aquesta tesi doctoral va ser el desenvolupament d’aptasensors utilitzant la tècnica electroquímica d’impedància esmentada anteriorment. Per a això, diferents tipus d’elèctrodes van ser utilitzats, tals com elèctrodes de compòsit grafit-epoxi, elèctrodes de biocompòsit grafit-epoxi modificats amb molècules d’avidina i elèctrodes comercials serigrafiats de nanotubs de carboni de paret múltiple.
El treball es va dividir principalmente en dues parts d'acord amb la detecció de dues proteïnes diferents.
La primera part es va focalitzar en la detecció de trombina. Primer de tot, es van comparar i avaluar diversos aptasensors de detecció directa sense marcatge basat en diferents tècniques d'immobilització dels aptàmers, tals com: adsorció física humida, afinitat avidina-biotina i enllaç covalent mitjançant activació electroquímica de la superfície de l'elèctrode i mitjançant inserció electroquímica. Posteriorment, els elèctrodes de biocompòsit van ser comparats com a plataformes en genosensat i aptasensat. Amb la finalitat d'amplificar el senyal impedimètric obtingut utilitzant elèctrodes de biocompòsit, un protocol sàndwich va ser emprat incloent nanopartícules d'or modificades amb estreptavidina i tractament amplificador de plata.
La segona part de l'estudi es va basar en la detecció de citocrom c. Primerament, es va realitzar un simple aptasensor de detecció directa sense marcatge per a la detecció d'aquesta proteïna utilitzant la tècnica d'immobilització d'adsorció física humida. Finalment, i amb l'objectiu d'amplificar el señal impedimètric, es va desenvolupar un assaig tipus sándwich híbrid d’aptàmer i anticòs utilitzant elèctrodes serigrafiats de nanotubs de carboni de paret múltiple.
D'aquesta manera, la tesi explora i compara una àmplia gamma de procediments d'immobilització, l'ús de detecció directa sense marcatge o nanomaterial modificat amb biomolècules en diferents protocols directes o d'amplificació, i l'ús de reconeixement directe i sándwich per amplificar la sensibilitat i/o la selectivitat de l'assaig.In the recent years, due to the need for rapid diagnosis and improvements in sensing, new recognition elements are employed in biosensors. One kind of these new recognition elements are aptamers. Aptamers are synthetic strands of DNA or RNA which are selected in vitro and have the ability to bind to proteins, ions, whole cells, drugs and low molecular weight ligands recognizing their target with high affinity and specificity. Several aptamer-based biosensors, also called aptasensors, have been recently developed. Among all the transduction techniques employed in biosensors, Electrochemical Impedance Spectroscopy has widely used as a tool for characterizing sensor platforms and for studying biosensing events at the surface of the electrodes. The important feature presented by this technique is that it does not require any labelled species for the transduction; thus, this detection technique can be used for designing label-free protocols thus avoiding more expensive and time-consuming assays. The main aim of this PhD work was the development of aptasensors using the electrochemical impedance technique previously mentioned for protein detection. For that, different types of electrodes were used, such as Graphite Epoxy Composite electrodes (GECs), Avidin Graphite Epoxy Composite electrodes (AvGECs) and commercial Multi-Walled carbon nanotubes screen printed electrodes (MWCNT-SPE). The work was divided in two main parts according to the detection of the two different proteins. The first part was focused on thrombin detection. First of all, different impedimetric label-free aptasensors based on several aptamer immobilization techniques such as wet physical adsorption, avidin-biotin affinity and covalent bond via electrochemical activation of the electrode surface and via electrochemical grafting were developed and evaluated. Then, AvGECs electrodes were compared as a platform for genosensing and aptasensing. With the aim to amplying the obtained impedimetric signal using AvGECs, an aptamer sandwich protocol for thrombin detection was used including streptavidin gold-nanoparticles (Strep-AuNPs) and silver enhancement treatment. The second part of the study was based on cytochrome c detection. Firstly, a simple label-free aptasensor for the detection of this protein using a wet physical adsorption immobilization technique was performed. Finally, with the goal to amplify the impedimetric signal, a hybrid aptamer-antibody sandwich assay using MWCNT-SPE for the detection of the target protein was carried out. In this way, the thesis explores and compares a wide scope of immobilization procedures, the use of label-free or nanocomponent modified biomolecules in different direct or amplified protocols, and the use of direct recognition and sandwich alternatives to enhance sensitivity and/or selectivity of the assay
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Gomez-Laberge, Camille. "Electrical Impedance Tomography for deformable media." Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27458.
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In Electrical Impedance Tomography (EIT), electrical energy is applied and measured at the boundary of a medium to produce an image of its internal conductivity distribution. When imaging pulmonary ventilation, rib cage expansion and body posture introduce severe image artefacts in the reconstructed images due to electrode position error.
This thesis proposes a method to reduce such artefacts by determining the net displacement of electrodes between measurement frames, and effectively, adjusting the geometry of the reconstruction model. A novel regularization method is proposed and validated using data acquired from simulation, phantom, and human in vivo measurements.
The proposed method reduces artefacts by more than 70% in simulated reconstructions and phantom experiments. The in vivo images reveal the various breathing manoeuvres and thoracic movements recorded.
Furthermore, the displacement of each electrode is calculated, indicating the deformed boundary shape. This thesis supports EIT for clinical diagnostics and monitoring of pulmonary ventilation.
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Dai, Hong. "Network approach to impedance computerized tomography." Ohio : Ohio University, 1985. http://www.ohiolink.edu/etd/view.cgi?ohiou1183994407.
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Zou, Xiaodong. "Impedance spectroscopy of nickel base superalloys." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/20307.
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Lim, Wee-Lin. "Electrochemical impedance measurements of biological polyelectrolytes." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321776.
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Breckon, W. R. "Image reconstruction in Electrical Impedance Tomography." Thesis, Oxford Brookes University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292254.
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Chester, Christopher John. "Electrical-Impedance Biofeedback Instrumentfor Swallowing Rehabilitation." Thesis, University of Canterbury. Electrical and Computer Engineering, 2014. http://hdl.handle.net/10092/8961.
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Biofeedback is an important tool in the rehabilitation of several dysphagic conditions. This thesis presents an investigation into using bio-impedance as a technique for providing biofeedback of the swallowing sequence, specifically sequencing in the pharynx. The motivation behind this project was to find an alternative rehabilitation tool for detecting pharyngeal sequencing, as the current tool of pharyngeal manometry is invasive and non-portable. This investigation included the design and creation of a bio-impedance measuring device named the Guided Utility for Latency in Pharyngeal Sequencing (GULPS). This system was continued from a previous unpublished investigation at the University of Canterbury, where an initial prototype was designed and created. It was found that this pre-existing system had numerous faults in both its hardware and software, limiting the use of the device.
Electrical impedance across the throat can be determined by applying a known constant amplitude current signal across the throat and recording the corresponding voltage. This impedance has been shown to change during a swallowing sequence due to a change in the structure of the throat. The principle used in this project was to investigate if two positions of impedance measurement could be used to determine the sequencing of the pharynx during a swallow. The design of the GULPS device was influenced by the pre-existing system and several prototypes were built to obtain a system capable of providing two channels of impedance measurement. Software was adapted from the pre-existing system to interface with this hardware to provide a system that could be attached to an external computer.
Various electrode positions for the final device were trialled aimed at measuring two similar, but temporally separated, impedance waveforms. It was found that positioning the electrodes close to the approximate position of the pharynx with a 40 mm gap between channels allowed for two temporally separated channels to be produced with three distinct features: two peaks and one trough in each of the GULPS waveforms. The GULPS device with these electrode positions was trialled on three `healthy' subjects and one dysphagic subject. The three features could be identified in both impedance waveforms in all four subjects.
To determine if the identified features related to the sequencing of the pharynx, the GULPS device was trialled alongside the current conventional method for detecting pharyngeal sequencing, pharyngeal manometry. The results from these trials revealed a potential relationship between the temporal separation of the second peaks found in the GULPS waveforms and the temporal separation of the pressure peaks from pharyngeal manometry. The GULPS device was trialled alongside pharyngeal manometry on one `healthy' and one dysphagic subject. A linear regression between peak-to-peak latencies between the two methods had an R squared value of 0.347 for the `healthy' subject and 0.241 for the dysphagic subject. However, these peaks were often difficult to detect, and could only be detected in 64% of swallows in the `healthy' subjects using the GULPS device in a standalone fashion and in 23% of swallows when used concurrently with manometry.
As the current GULPS device is unable to produce the desired results in a consistent manner, no definitive conclusions can be drawn on the ability of using bio-impedance to measure the pharyngeal sequence. Notwithstanding, substantial progress has been made towards a device for reliable measurement of pharyngeal sequencing and, together with the clinical benefits to be gained, more than justify further research and development into GULPS for dysphagia rehabilitation.
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Tang, Mengxing. "Image reconstruction in electrical impedance mammography." Thesis, De Montfort University, 2003. http://hdl.handle.net/2086/6260.
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Breast cancer continues to be a leading cause of death in Western countries. One of the most important approaches to reduce this mortality is to detect the cancer as early as possible. Although current diagnostic imaging modalities are able to give useful information for diagnosis, development of new imaging technique is highly desirable in order to detect breast cancer in an earlier stage. This is the motive of the present study of Electrical Impedance Mammography (ElM), which applies Electrical Impedance Tomography (EIT) to image human breasts. The overall aim of the whole project is to develop impedance imaging techniques and system for early detection of breast cancer. The aim of the studies reported in this thesis is twofold, to investigate methods of improving EIT image quality and the feasibility of EIT in breast cancer detection. Focusing on these aims the following work is reported: 1) The study of three different image reconstruction algorithms is described. In this work the image reconstruction results are compared and the most appropriate algorithm was chosen for the subsequent study of breast imaging. 2) An investigation of two important factors in EIT image reconstruction, the number of electrodes (NOE) and the number of conductivity basis functions (NOCBF) whose effects on EIT images have yet been studied in detail so far, are described. In this work the image reconstruction is analysed with different combinations of NOE and NOCBF using Singular Value Decomposition (SVD) and spectrum expansion theory. Finally suggestions are given on which configuration could offer better image quality in breast imaging3) A comprehensive investigation is reported regarding compatibility of different types of prior information and its effect on an iterative image reconstruction algorithm, based on which a novel method is proposed to improve EIT image quality. This method selects compatible prior information by observing the convergence behaviour of an image reconstruction algorithm. The principle, implementation, and results are detailed. Results indicate the effectiveness of this method. 4) A two-dimensional breast imaging simulation system is introduced. In this work several breast models with different physiological and pathological conditions are made, based on clinical in vitro measurements and Cole-Cole model. Images with different current frequencies are reconstructed and analysed. Results indicate the potential of detecting and identifying breast abnormality by EIT. 5) A preliminary study on 3D EIT and 3D electrode placement has been conducted. The mathematic principle and implementation of 3D EIT are described, followed by a study on the sensitivity of boundary measurements to the conductivity changes in a cylindrical object with 2 different types of electrode placement. Suggestions are given on optimal electrode placement in EIT breast imaging. Finally suggestions are gIven for future work. These include a) investigating appropriate electrode placement for different applications and corresponding current & voltage patterns; b) incorporating more prior information into ElM image reconstruction; c) designing a more precise 3D breast forward model; and d) investigating appropriate regularization for image reconstruction
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Nicholson, Guy Charles. "The active control of acoustic impedance." Thesis, University of Salford, 1994. http://usir.salford.ac.uk/14778/.
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The application of an active control force on a thin-walled acoustic boundary can modify the motional dynamics, and so influence the impedance presented to incident waves. This impedance determines transmission of acoustic energy, reflection of acoustic waves from the boundary and absorption of incident energy. This thesis studies control systems that generate control forces for the active control of surface acoustic impedance. The proposed systems rely on measurement of the acoustic pressure and surface velocity of the boundary. The systems can use adaptive digital signal processing, which offers significant advantages over non-adaptive techniques. The active control of the specific acoustic impedance of a loudspeaker that terminates a waveguide for axially propagating plane waves provides a motivating problem. Theoretical analysis establishes the control of specific acoustic impedance of a simple compliantly-suspended piston by a control force. Operational constraints of a physical piston define theoretical operating limits for controlled specific acoustic impedances. The control systems use either feedback or feed-forward techniques for which theoretical treatment reveals restrictions on the range of controlled specific acoustic impedance. A novel result is that conventional implementations of the control systems can be unstable for certain desired impedances unless feedback cancellation is used. Digital feedback techniques are less effective for broader frequency bandwidth where feed-forward techniques may work. Theoretical analysis produces solutions that confirm the feasibility of these control techniques for the active control of specific acoustic impedance. Potential errors in the implementation of the systems have predictable effects on the controlled specific acoustic impedance. Experimental results support the theoretical work presented in this thesis, demonstrating active control of specific acoustic impedance for normally incident acoustic plane waves. An adaptive digital feed-forward control system creates desired specific acoustic impedances for band-limited noise and transient signals.
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Bohlen, Oliver [Verfasser]. "Impedance-based battery monitoring / Oliver Bohlen." Aachen : Shaker, 2008. http://d-nb.info/1161305939/34.
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Olphert, Russell. "Impedance studies of liquid-liquid interfaces." Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236842.
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Cockcroft, Paul William. "Acoustic impedance measurement for underground surfaces." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328412.
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Al-Mashouk, Motaz. "The hydrodynamic impedance of harbour entrances." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47746.
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Ritzmann, Deborah. "Synchrophasor-based overhead line impedance monitoring." Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/74320/.
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Thermal limits of overhead transmission lines create network constraints that can result in curtailment of renewable energy generation. Thermal limits are conventionally static and based on worst-case, non-cooling ambient weather conditions, leading to under-utilization of overhead lines. Utilization can be increased and network constraints reduced by rating overhead lines dynamically, based on actual conductor temperature. Installation and maintenance of temperature and weather sensors along an overhead line is expensive and laborious. A more cost-effective solution is to derive average conductor temperature from overhead line impedance parameters, which can be calculated from measurements of electrical signals at each line end. Synchronized phasor measurement technology is becoming increasingly available in substations to capture voltage and current signals with high accuracy and reporting rates. It is known that the substation instrumentation channel can introduce significant systematic errors to the phasor measurements, which in turn cause inaccurate line impedance parameter and temperature values. This thesis presents novel methods for accurate, real-time monitoring of overhead line impedance parameters using synchronized phasor measurements that have systematic errors. In contrast to previous research, the time-variance and temperature dependence of line resistance as well as compensation of systematic errors is taken into account in the system model to increase parameter estimation accuracy. In addition, an algorithm for the selection of the best parameter estimates from different measurement sets is given. The effectiveness of the novel methods is demonstrated in several case studies on measurement data from simulations and an actual overhead line. The results show that the identified correction factors compensate systematic measurement errors, leading to a reduction in impedance parameter estimation errors of at least one order of magnitude compared to existing methods. Furthermore, the accuracy of real-time estimation of average conductor temperature was increased by at least one order of magnitude relative to previously proposed methods.
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Yang, Chuan Li. "Electrical impedance tomography : algorithms and applications." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646139.
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Electrical impedance tomography (EIT) is an imaging technique for detecting the internal conductivity distribution of an object by voltage measurements taken by an exterior electrode. EIT has been researched in many different application areas in the world as a simpler, cheaper alternative to many other imaging methods. The topic of this PhD study is mainly focused on a number of key developments in both hardware and software implementation. The basic theories of EIT, including forward problem, inverse problem of EIT and the sensor design have been described. Major contributions of the thesis are in computational and experimental aspects of EIT in a wide variety of geometries. A sparse and memory efficient method has been presented to solve large scale 3D EIT problems. A parallel conjugate gradient (PCG) has been applied to demonstrate computational improvements using synthetic and experimental data. 3D EIT has been implemented for planar array geometry for limited access tomography. Furthermore, multiple frequencies with complex conductivity reconstruction are presented and applied to an EIT-based fabric pressure mapping sensor. A comparative study with traditional tank phantom is presented to provide a context for a fabric pressure mapping sensor. As the motivation for different frequency response with different conductivity inclusions, frequency difference EIT has been implemented to overcome problems of time difference EIT.
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iyer, vishwanath. "Broadband Impedance Matching of Antenna Radiators." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-dissertations/388.
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"In the design of any antenna radiator, single or multi-element, a significant amount of time and resources is spent on impedance matching. There are broadly two approaches to impedance matching; the first is the distributed impedance matching approach which leads to modifying the antenna geometry itself by identifying appropriate degrees of freedom within the structure. The second option is the lumped element approach to impedance matching. In this approach instead of modifying the antenna geometry a passive network attempts to equalize the impedance mismatch between the source and the antenna load. This thesis introduces a new technique of impedance matching using lumped circuits (passive, lossless) for electrically small (short) non-resonant dipole/monopole antennas. A closed form upper-bound on the achievable transducer gain (and therefore the reflection coefficient) is derived starting with the Bode-Fano criterion. A 5 element equalizer is proposed which can equalize all dipole/monopole like antennas. Simulation and experimental results confirm our hypothesis. The second contribution of this thesis is in the design of broadband, small size, modular arrays (2, 4, 8 or 16 elements) using the distributed approach to impedance matching. The design of arrays comprising a small number of elements cannot follow the infinite array design paradigm. Instead, the central idea is to find a single optimized radiator (unit cell) which if used to build the 2x1, 4x1, 2x2 arrays, etc. (up to a 4x4 array) will provide at least the 2:1 bandwidth with a VSWR of 2:1 and stable directive gain (not greater than 3 dB variation) in each configuration. Simulation and experimental results for a solution to the 2x1, 4x1 and 2x2 array configurations is presented. "