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Impedance spectroscopy (IS) is a powerful and sophisticated tool to characterize intrinsic electrical properties of any materials and its interface, measuring the electric and transport properties of the materials, investigating the mechanism of electrochemical reaction etc. The fundamental principle of IS is the measurement of the impedance (equivalent to resistance in DC analysis) of the system under investigation over a wide frequency range. The IS study provides quantitative information about the conductance, the dielectric coefficient, the static properties of the interfaces like contact resistance, and its dynamic change due to adsorption or charge transfer phenomenon. Commercial Impedance analyzers that are available today are bulky and cannot be carried or deployed at remote locations for monitoring so easily, also such systems are expensive. Though IS concept is not new, standard Impedance analyzers are interfaced to the computer and require detailed analysis of the data by experts. Advancement in data conversion and signal processing is opening up opportunities for handheld smart devices. Hence it is felt that there is a need to develop a versatile low cost, portable (handheld) impedance analyzer instrument which can be used to characterize non linear materials like semiconductors, biological objects, and electrochemical samples. The instrument should be capable accepting test parameters using a touch screen based keypad and display test results on a Graphical LCD for quick analysis. Hence a standalone handheld instrument is designed to work independently without any PC control. The designed instrument consists of Digital Direct Synthesis (DDS) signal generator, a constant current source, Analog to digital convertor, Microcontroller to control frequency sweep parameters and acquire data, TFT Graphics LCD for displaying various plots, touch screen user interface to input sweep parameters and data storage section for offline analysis of obtained data. The instrument is designed to work on a battery or a regulated power supply. The instrument has options to display Nyquist plot, capacitance versus frequency plot, real and imaginary value of impedance versus frequency plot etc. Experimental investigations are conducted using this instrument on few passive components like resistor, inductor, capacitor and combinations. The instrument is also used to monitor the performance of polyimide based capacitive humidity sensor and its characteristics like sensitivity, linearity, repeatability and hysteresis. The measurement accuracy of the impedance varies from 0.7% to 4.67% depending on the impedance range. Bio impedance measurements are carried out on biological samples like Banana and the measured values are compared with the standard LCR meter. The bio impedance measurements are repeatable and comparable with the standard LCR meter readings and it is found to be within ±1% accuracy at the calibrated frequency. The instrument is also validated using industry standard Gauge R & R procedure to understand the repeatability and reproducibility of the instrument. The instrument exhibited good Repeatability and Reproducibility in current mode excitation than voltage mode excitation and Gauge R & R is 55% with P/T ratio is less than 2.5%.

The objective of this thesis is to examine the possibility to determine the mechanical heart rate using intracardiac impedance in the time domain. Deducing the mechanical heartrate from the impedance could help improve the performance of implanted devices that today depend on the measurement of the heart’s electrical activity. Cardiogenic – also known as intracardiac – impedance is based on the difference in conductivity between heart muscle tissue and blood, making the impedance vary as the heart is filled and emptied. The data used in this thesis was acquired from three previous studies performed by St Jude Medical, two clinical and one preclinical. Two impedance measurement configurations were chosen from these studies, one bipolar and one quadropolar. To deduce the heart rate from the intracardiac impedance six algorithms were evaluated. Three using continuous peak detection and three evaluating small frames of the impedance signal.The peak detection algorithms were peak detection on the impedance signal itself, on its derivative  and on its integral. The three others were an Auto Correlation Function (ACF), an Average Magnutide Difference Function (AMDF) and an Average Wave Comparison Function (AWCF). In order to assess the heart rates deduced from the intracardiac impedance by the algorithms, these rates were compared to both the IEGM or the ECG (depending on which study was at hand) and the blood pressure. Several issues affected the performance of the algorithms. Impedance morphology can vary between patients. Some display so called “double peaks”, making it hard to decide whether a patient has for example a pulse of 80 bpm or of 160 bpm. The impedance morphology was also affected by amplitude modulation with the respiration frequency which in some patients cause difficulties to analyze the impedance signal. The results show that the two impedance measurement configurations perform equally well and that the ACF method was the overall best performing algorithm. They also show that individual patient impedance morphology has a large influence on the results and for future studies it should therefore be interesting to calibrate the algorithms for each patient, as this should improve performance.

The ceramic composite system containing Al₂O₃ and SiCw has seen multiple uses depending on its processing method. Both the thermomechanical properties and the electrical properties have piqued the interest for potential commercial applications. These include cutting tool inserts and microwave heating elements. Composite samples made by extrusion were pressureless sintered and characterized as a function of frequency, bias, sample length, and whisker orientation. Dry pressed percolated specimens containing different amounts of sintering aids were hot pressed and spark plasma sintered. The microstructure and electrical properties were compared.

This System-on-Chip implementation is aimed at measuring small impedance with high accuracy. This system consists of an Analog sensor, Analog to Digital converter and a computational unit that is used to calculate the magnitude and phase of the impedance. The SoC can find its application in affinity based biosensors that use impedance spectroscopy to determine the properties of the analyte. Other applications include measuring impedances from probes buried in building structures to monitor the health of he buildings. / text

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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