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published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Manos M. Tentzeris; Committee Co-Chair: John Papapolymerou; Committee Member: Andrew F. Peterson; Committee Member: Chang-Ho Lee; Committee Member: John D. Cressler; Committee Member: Joy Laskar.

The objective of this research is to realize compact and reconfigurable antennas for next generation Ultra Wide Band (UWB) and Wireless Local Area Network (WLAN) applications. The contributions of this research are, a methodology for designing compact UWB antennas, a compact WLAN prototype antenna with reconfigurable characteristics in both radiation pattern and frequency of operation, and compact UWB antennas with reconfigurable WLAN band rejection characteristics. For the completion of this dissertation, five research projects have been studied. First, a double exponentially tapered slot antenna with conformal shape, high gain, and consistent radiation patterns is implemented. The radiation pattern consistency results in minimum distortion for any transmitted pulse. The second and third projects involve an elliptical slot with a tuning uneven U-shaped stub and two cactus-shaped monopoles. The elliptical slot demonstrates omni-directional radiation patterns and compact size. As an improved iteration of the elliptical slot antenna, two cactus-shaped monopoles are implemented. The two prototypes occupy only 60% and 40%, respectively, of the area that the original elliptical slot occupies resulting in a significant size reduction, while maintaining omni-directional radiation patterns. Through the cactus-shaped monopoles some general design methodologies for UWB antennas are introduced and successfully applied. The fourth research topic introduced, concerns the study of compact elliptical UWB monopoles. Several prototypes of different geometrical characteristics were designed and tested. Broadband matching techniques and the integration of reconfigurable features on the elliptical radiator are investigated. For the reconfigurable UWB antenna, resonating elements are used to create a rejection band in the frequency range that is occupied by WLAN applications. The performance of several of the introduced slot and monopole antennas are tested when the antennas under detection are mounted and operate on non-planar surfaces. Finally, a reconfigurable annular slot antenna operating at the wireless local area network (WLAN) band is implemented. The proposed antenna demonstrates reconfigurable characteristics in both radiation pattern and return loss. All of the UWB antennas are fabricated on liquid crystal polymer (LCP) and can be easily integrated with active components on the same module using system on package (SoP) technology.

An essential task for a pacemaker or implantable defibrillator is the accurate identification of rhythm categories so that the correct electrotherapy can be administered. Because some rhythms cause a rapid dangerous drop in cardiac output, it is necessary to categorize depolarization waveforms on a beat-to-beat basis to accomplish rhythm classification as rapidly as possible. In this thesis, a depolarization waveform classifier based on the Lifting Line Wavelet Transform is described. It overcomes problems in existing rate-based event classifiers; namely, (1) they are insensitive to the conduction path of the heart rhythm and (2) they are not robust to pseudo-events. The performance of the Lifting Line Wavelet Transform based classifier is illustrated with representative examples. Although rate based methods of event categorization have served well in implanted devices, these methods suffer in sensitivity and specificity when atrial, and ventricular rates are similar. Human experts differentiate rhythms by morphological features of strip chart electrocardiograms. The wavelet transform is a simple approximation of this human expert analysis function because it correlates distinct morphological features at multiple scales. The accuracy of implanted rhythm determination can then be improved by using human-appreciable time domain features enhanced by time scale decomposition of depolarization waveforms. The purpose of the present work was to determine the feasibility of implementing such a system on a limited-resolution platform. 78 patient recordings were split into equal segments of reference, confirmation, and evaluation sets. Each recording had a sampling rate of 512Hz, and a significant change in rhythm in the recording. The wavelet feature generator implemented in Matlab performs anti-alias pre-filtering, quantization, and threshold-based event detection, to produce indications of events to submit to wavelet transformation. The receiver operating characteristic curve was used to rank the discriminating power of the feature accomplishing dimension reduction. Accuracy was used to confirm the feature choice. Evaluation accuracy was greater than or equal to 95% over the IEGM recordings.

Optical current sensors (OCSs) are initially developed to measure relatively large current over a wide range of frequency band. They are also used as protective devices in the event a fault occurs due to a short circuit, in the power generation and distribution industries. The basic principal used in OCS is the Faraday effect. When a light guiding faraday medium is placed in a magnetic field which is produced by the current flowing in the conductor around the magnetic core, the plane of polarization of the linearly polarized light is rotated. The angle of rotation is proportional to the magnetic field strength, proportionality constant and the interaction length. The proportionality constant is the Verdet constant V (λ, T), which is dependent on both temperature and wavelength of the light. Opto electrical methods are used to measure the angle of rotation of the polarization plane. By measuring the angle the current flowing in the current carrying conductor can be calculated. But the accuracy of the OCS is lost of the angle of rotation of the polarization plane is dependent on the Verdet constant, apart from the magnetic field strength. As temperature increases the Verdet constant decreases, so the angle of rotation decreases. To compensate the effect of temperature on the OCS, a new method has been proposed. The current and temperature are measured with the help of a duel frequency method. To detect the line current in the conductor or coil, a small signal from the line current is fed to the reference of the lock in. To detect the temperature, the coil is excited with an electrical signal of a frequency different from the line frequency, and a small sample of this frequency signal is applied to the reference of the lock in. The temperature and current readings obtained are look up at the database value to give the actual output. Controlled environment is maintained to record the values in the database that maps the current and temperature magnitude values at the DSP lock in amplifier, to the actual temperature and current. By this method we can achieve better compensation to the temperature changes, with a large dynamic range and better sensitivity and accuracy.