+publisher:"Virginia Tech" +contributor:("Safaai-Jazi, Ahmad")

Virginia Tech

1. Razavi Borghei, Seyyed Moein. The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis.

Degree: MS, Electrical Engineering, 2020, Virginia Tech

URL: http://hdl.handle.net/10919/98001

► To decarbonize and reduce energy consumption for commercial aviation, the development of lightweight and ultra-efficient all-electric powertrain including electric motors, drives, and associated thermal management… (more)

Subjects/Keywords: Finite element analysis; Partial discharge modeling; High frequency; Fast-rise square wave voltages; Insulation systems

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APA (6^th Edition):

Razavi Borghei, S. M. (2020). The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/98001

Chicago Manual of Style (16^th Edition):

Razavi Borghei, Seyyed Moein. “The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis.” 2020. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/98001.

MLA Handbook (7^th Edition):

Razavi Borghei, Seyyed Moein. “The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis.” 2020. Web. 07 Mar 2021.

Vancouver:

Razavi Borghei SM. The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis. [Internet] [Masters thesis]. Virginia Tech; 2020. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/98001.

Council of Science Editors:

Razavi Borghei SM. The Modeling of Partial Discharge under Fast, Repetitive Voltage Pulses Using Finite-Element Analysis. [Masters Thesis]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/98001

2. Gartland, Peter Lanier. Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme.

Degree: MS, Electrical Engineering, 2016, Virginia Tech

URL: http://hdl.handle.net/10919/73370

► For the past 40 years, acoustic sensing has been a major avenue for the growth of interfero- metric fiber-optic sensors. Fiber-optic acoustic sensors have found… (more)

Subjects/Keywords: Fiber Optics; Michelson Interferometer; 3 x 3 Coupler; Acoustic Sensing

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APA (6^th Edition):

Gartland, P. L. (2016). Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73370

Chicago Manual of Style (16^th Edition):

Gartland, Peter Lanier. “Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme.” 2016. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/73370.

MLA Handbook (7^th Edition):

Gartland, Peter Lanier. “Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme.” 2016. Web. 07 Mar 2021.

Vancouver:

Gartland PL. Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/73370.

Council of Science Editors:

Gartland PL. Fiber-Optic Michelson Interferometer with Faraday Mirrors for Acoustic Sensing using a 3 x 3 Coupler and Symmetric Demodulation Scheme. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73370

3. Khan, Iqtidar Ahmad. Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays.

Degree: MS, Electrical Engineering, 2018, Virginia Tech

URL: http://hdl.handle.net/10919/93222

► Numerical techniques for designing planar arrays with low side lobe level often require memory intensive optimization algorithms and also initialization in the form of some… (more)

▼ Numerical techniques for designing planar arrays with low side lobe level often require memory intensive optimization algorithms and also initialization in the form of some known values of radiation pattern parameters beforehand - information that may not be available when designing arrays. A few analytical methods exist in the literature that can be used to design rectangular lattices of isotropic elements for desired half-power beamwidth and side lobe level, but the number of elements of the array often should be known before the design process. Some array designs based on analytical techniques may suffer from severe performance limitations, an example is the uniformly excited array which cannot produce side lobe levels below ̶13.3 dB. The goal of this study is to present an analytical technique for synthesis of planar arrays that, for specified radiation pattern requirements, not only provides quick solutions for the required number of elements and its distribution along the length and width of the array rectangular lattice, but also produces low side lobes without any limitation. A new class of non-uniformly excited equally spaced planar arrays is introduced and investigated in this study. The new array uses the patterns of uniformly excited linear arrays as its building blocks and has a separable element current distribution, hence making it mathematically convenient to analyze its radiation properties in terms of those of its constituent linear arrays. The proposed planar array does not suffer from the side lobe level limitation of uniformly excited planar arrays, and its synthesis, due to the analytical nature of description of its radiation properties, does not require iterative procedures that are inherent to numerical techniques. Radiation characteristics of the proposed planar array, including directivity, side lobe level, half-power beamwidths, far-field three dimensional radiation patterns, and element excitation currents, are examined and simulation results for several example cases are presented. The analysis culminates with successfully mapping a continuous radiation pattern to discrete element currents in a rectangular lattice geometry. The synthesis procedure is validated by successfully designing various planar arrays with desired requirements in terms of side lobe level and half-power beamwidths in the principal planes. Several design examples are presented. Radiation characteristics of the synthesized arrays are compared with the desired design requirements which were used as input information in the synthesis process. For the cases studied, the achieved performance characteristics are close to the desired ones. Advisors/Committee Members: Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committeechair), Baker, Joseph B. H. (committee member), Reed, Jeffrey H. (committee member).

Subjects/Keywords: planar arrays; array synthesis; rectangular arrays; low side lobe planar arrays.

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APA (6^th Edition):

Khan, I. A. (2018). Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/93222

Chicago Manual of Style (16^th Edition):

Khan, Iqtidar Ahmad. “Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays.” 2018. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/93222.

MLA Handbook (7^th Edition):

Khan, Iqtidar Ahmad. “Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays.” 2018. Web. 07 Mar 2021.

Vancouver:

Khan IA. Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays. [Internet] [Masters thesis]. Virginia Tech; 2018. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/93222.

Council of Science Editors:

Khan IA. Analysis and Synthesis of a New Class of Low Side Lobe Planar Arrays. [Masters Thesis]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/93222

Virginia Tech

4. Zilevu, Kojo Sitsofe. A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas.

Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech

URL: http://hdl.handle.net/10919/76984

► Electrically small, low profile antennas have become the new frontier in wireless communication research. With the pressure to miniaturize wireless communication devices, engineers are turning… (more)

Subjects/Keywords: Nonlinear; Antennas; Narrowband; Bandwidth

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APA (6^th Edition):

Zilevu, K. S. (2012). A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/76984

Chicago Manual of Style (16^th Edition):

Zilevu, Kojo Sitsofe. “A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas.” 2012. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/76984.

MLA Handbook (7^th Edition):

Zilevu, Kojo Sitsofe. “A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas.” 2012. Web. 07 Mar 2021.

Vancouver:

Zilevu KS. A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/76984.

Council of Science Editors:

Zilevu KS. A Nonlinear Technique for Bandwidth Improvement in Narrowband Antennas. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/76984

Virginia Tech

5. Blischak, Andrew Travis. Analysis of an Embedded Singularity Chipless RFID Tag.

Degree: MS, Electrical and Computer Engineering, 2011, Virginia Tech

URL: http://hdl.handle.net/10919/43715

► The objective of this research is to explore the feasibility of a chipless RFID tag that stores a data signature in the form of complex… (more)

Subjects/Keywords: SEM; Matrix Pencil; RFID; Chipless

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APA (6^th Edition):

Blischak, A. T. (2011). Analysis of an Embedded Singularity Chipless RFID Tag. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/43715

Chicago Manual of Style (16^th Edition):

Blischak, Andrew Travis. “Analysis of an Embedded Singularity Chipless RFID Tag.” 2011. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/43715.

MLA Handbook (7^th Edition):

Blischak, Andrew Travis. “Analysis of an Embedded Singularity Chipless RFID Tag.” 2011. Web. 07 Mar 2021.

Vancouver:

Blischak AT. Analysis of an Embedded Singularity Chipless RFID Tag. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/43715.

Council of Science Editors:

Blischak AT. Analysis of an Embedded Singularity Chipless RFID Tag. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/43715

Virginia Tech

6. White, Natalie B. A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties.

Degree: MS, Electrical Engineering, 2018, Virginia Tech

URL: http://hdl.handle.net/10919/83535

► Pancreatic cancer results in 40,000 deaths every year in the U.S, making it one of the most challenging diseases to treat. The current treatments for… (more)

Subjects/Keywords: Irreversible electroporation; cancer treatment; tissue properties

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APA (6^th Edition):

White, N. B. (2018). A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/83535

Chicago Manual of Style (16^th Edition):

White, Natalie B. “A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties.” 2018. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/83535.

MLA Handbook (7^th Edition):

White, Natalie B. “A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties.” 2018. Web. 07 Mar 2021.

Vancouver:

White NB. A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties. [Internet] [Masters thesis]. Virginia Tech; 2018. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/83535.

Council of Science Editors:

White NB. A Patient-specific Irreversible Electroporation Treatment Planning Model Based on Human Tissue Properties. [Masters Thesis]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/83535

Virginia Tech

7. Thews, Brennan Nicholas. Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure.

Degree: MS, Electrical Engineering, 2015, Virginia Tech

URL: http://hdl.handle.net/10919/54583

► In the field of optical fiber sensors, one of the most versatile structures is the Fabry-Perot interferometer. This thesis will present a novel sensor based… (more)

Subjects/Keywords: Etched PCF; IFPI Cavity; Microfiber; Cantilever Beam

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APA (6^th Edition):

Thews, B. N. (2015). Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/54583

Chicago Manual of Style (16^th Edition):

Thews, Brennan Nicholas. “Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure.” 2015. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/54583.

MLA Handbook (7^th Edition):

Thews, Brennan Nicholas. “Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure.” 2015. Web. 07 Mar 2021.

Vancouver:

Thews BN. Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure. [Internet] [Masters thesis]. Virginia Tech; 2015. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/54583.

Council of Science Editors:

Thews BN. Measurement of Temperature, Refractive Index, or Axial Acceleration with Etched PCF Microfiber Structure. [Masters Thesis]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/54583

8. Bhonsle, Suyashree P. Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields.

Degree: PhD, Electrical Engineering, 2018, Virginia Tech

URL: http://hdl.handle.net/10919/91904

► Since its conception in 2005, irreversible electroporation (IRE), a non-thermal tumor ablation modality, was investigated for safety and efficacy in clinical applications concerning different organs.… (more)

▼ Since its conception in 2005, irreversible electroporation (IRE), a non-thermal tumor ablation modality, was investigated for safety and efficacy in clinical applications concerning different organs. IRE utilizes high voltage (~3kV), short duration (~100us) pulses to create transient nanoscale defects in the plasma membrane to cause cell death due to irreversible defects, osmotic imbalances and ATP loss. More recently, high-frequency irreversible electroporation (H-FIRE), which employs narrow bipolar pulses (~0.5-10us) delivered in bursts (on time ~100us), was invented to provide benefits such as the mitigation of intense muscle contractions associated with IRE-based treatments. Furthermore, H-FIRE exhibits the potential to improve lesion predictability in homogeneous and heterogeneous tissue masses. Therapeutic IRE and H-FIRE utilize source and sink electrodes inserted into or around the tumor to deliver the treatment. Prediction of the ablation size, for a set of parameters, can be achieved by the use of pre-treatment planning algorithms that calculate the induced electric field distribution in the target tissue. An electric field above a certain threshold induces cell death and parameters are tuned to ensure complete tumor coverage while sparing the nearby healthy tissue. IRE studies have shown that the underlying field is influenced by the increase in tissue conductivity due to enhanced membrane permeability, and treatment outcome can be improved when this nonlinearity is accounted for in numerical models. Since IRE pulses far exceed the time constant of the cell (~1us), the tissue response can be treated as essentially DC a static approximation can be used to predict the field distribution. Alternately, as H-FIRE pulses are on the order of the time constant of the membrane, the tissue response can no longer be treated as DC. The complexity of the H-FIRE-induced field distribution is further enhanced due to the dispersion and non-linearity in biological tissue impedance during treatment. In this dissertation, we have studied the electromagnetic fields induced in tissue during H-FIRE using several experimental and modeling techniques. In addition, we have characterized the nonlinearity and dispersion in tissue impedance during H-FIRE treatments and proposed simpler methods to predict the field distribution to enable easier translation to the clinic. Advisors/Committee Members: Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committeechair), Davalos, Rafael V. (committeechair), Zhu, Yizheng (committee member), Verbridge, Scott (committee member), Zhu, Yunhui (committee member).

Subjects/Keywords: Focal Ablation; Irreversible Electroporation; Bipolar Pulses; Dynamic Conductivity

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APA (6^th Edition):

Bhonsle, S. P. (2018). Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/91904

Chicago Manual of Style (16^th Edition):

Bhonsle, Suyashree P. “Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/91904.

MLA Handbook (7^th Edition):

Bhonsle, Suyashree P. “Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields.” 2018. Web. 07 Mar 2021.

Vancouver:

Bhonsle SP. Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/91904.

Council of Science Editors:

Bhonsle SP. Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/91904

Virginia Tech

9. Li, Chengshuai. Quantitative Anisotropy Imaging based on Spectral Interferometry.

Degree: PhD, Electrical Engineering, 2019, Virginia Tech

URL: http://hdl.handle.net/10919/99424

► Spectral interferometry, also known as spectral-domain white light or low coherence interferometry, has seen numerous applications in sensing and metrology of physical parameters. It can… (more)

▼ Spectral interferometry, also known as spectral-domain white light or low coherence interferometry, has seen numerous applications in sensing and metrology of physical parameters. It can provide phase or optical path information of interest in single shot measurements with exquisite sensitivity and large dynamic range. As fast spectrometer became more available in 21st century, spectral interferometric techniques start to dominate over time-domain interferometry, thanks to its speed and sensitivity advantage. In this work, a dual-modality phase/birefringence imaging system is proposed to offer a quantitative approach to characterize phase, polarization and spectroscopy properties on a variety of samples. An interferometric spectral multiplexing method is firstly introduced by generating polarization mixing with specially aligned polarizer and birefringence crystal. The retardation and orientation of sample birefringence can then be measured simultaneously from a single interference spectrum. Furthermore, with the addition of a Nomarski prism, the same setup can be used for quantitative differential interference contrast (DIC) imaging. The highly integrated system demonstrates its capability for noninvasive, label-free, highly sensitive birefringence, DIC and phase imaging on anisotropic materials and biological specimens, where multiple intrinsic contrasts are desired. Besides using different intrinsic contrast regime to quantitatively measure different biological samples, spectral multiplexing interferometry technique also finds an exquisite match in imaging single anisotropic nanoparticles, even its size is well below diffraction limit. Quantitative birefringence spectroscopy measurement over gold nanorod particles on glass substrate demonstrates that the proposed system can simultaneously determine the polarizability-induced birefringence orientation, as well as the scattering intensity and the phase differences between major/minor axes of single nanoparticles. With the anisotropic nanoparticles� spectroscopic polarizability defined prior to the measurement with calculation or simulation, the system can be further used to reveal size, aspect ratio and orientation information of the detected anisotropic nanoparticle. Alongside developing optical anisotropy imaging systems, the other part of this research describes our effort of investigating the sensitivity limit for general spectral interferometry based systems. A complete, realistic multi-parameter interference model is thus proposed, while corrupted by a combination of shot noise, dark noise and readout noise. With these multiple noise sources in the detected spectrum following different statistical behaviors, Cramer-Rao Bounds is derived for multiple unknown parameters, including optical pathlength, system-specific initial phase, spectrum intensity as well as fringe visibility. The significance of the work is to establish criteria to evaluate whether an interferometry-based optical measurement system has been optimized to its hardware best potential. An… Advisors/Committee Members: Zhu, Yizheng (committeechair), Wang, Anbo (committee member), Poon, Ting Chung (committee member), Robinson, Hans D. (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member).

Subjects/Keywords: spectral interferometry; quantitative phase imaging; quantitative polarization microscopy; frequency estimation; sensitivity analysis.

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APA (6^th Edition):

Li, C. (2019). Quantitative Anisotropy Imaging based on Spectral Interferometry. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/99424

Chicago Manual of Style (16^th Edition):

Li, Chengshuai. “Quantitative Anisotropy Imaging based on Spectral Interferometry.” 2019. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/99424.

MLA Handbook (7^th Edition):

Li, Chengshuai. “Quantitative Anisotropy Imaging based on Spectral Interferometry.” 2019. Web. 07 Mar 2021.

Vancouver:

Li C. Quantitative Anisotropy Imaging based on Spectral Interferometry. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/99424.

Council of Science Editors:

Li C. Quantitative Anisotropy Imaging based on Spectral Interferometry. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/99424

Virginia Tech

10. Mesgarpour Tousi, Maryam. Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules.

Degree: PhD, Electrical Engineering, 2020, Virginia Tech

URL: http://hdl.handle.net/10919/100621

► In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude… (more)

▼ In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude or frequency of AC or DC voltage or current, or some combination of these. The main components of a power electronic conversion system are power semiconductor devices acted as switches. A power module provides the physical containment and package for several power semiconductor devices. There is a trend towards the manufacturing of electrification apparatuses with higher power density, which means handling higher power per unit volume, leading to less weight and size of apparatuses for a given power. This is the case for power modules as well. Conventional "silicon (Si)-based semiconductor technology" cannot handle the power levels and switching frequencies required by "next-generation" utility applications. In this regard, "wide bandgap (WBG) semiconductor materials", such as "silicon carbide (SiC)"," gallium nitride (GaN)", and, soon, "gallium oxide" and "diamond" are capable of higher switching frequencies and higher voltages, while providing for lower switching losses, better thermal conductivities, and the ability to withstand higher operating temperatures. Regarding the high power density concept mentioned above, the challenge here, now and in the future, is to design compact WBG-based modules. To this end, the extremely nonuniform high electric field stress within the power module caused by the aforementioned trend and emerging WBG semiconductor switches should be graded and mitigated to prevent partial discharges that can eventually lead to breakdown of the module. In this Ph.D. work, new electric field grading methods including various geometrical techniques combined with applying nonlinear field-dependent conductivity (FDC) materials to high field regions are introduced and developed through simulation results obtained from the models developed in this thesis. Advisors/Committee Members: Ghassemi, Mona (committeechair), Xie, Weijun (committee member), Kekatos, Vasileios (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Centeno, Virgilio A. (committee member).

Subjects/Keywords: Nonlinear Field-Dependent Conductivity Composites; Geometrical Techniques; Electric Field Grading; Electrical Insulation Design; High Voltage; High Power Density; Wide Bandgap (WBG) Power Modules

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APA (6^th Edition):

Mesgarpour Tousi, M. (2020). Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/100621

Chicago Manual of Style (16^th Edition):

Mesgarpour Tousi, Maryam. “Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules.” 2020. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/100621.

MLA Handbook (7^th Edition):

Mesgarpour Tousi, Maryam. “Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules.” 2020. Web. 07 Mar 2021.

Vancouver:

Mesgarpour Tousi M. Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/100621.

Council of Science Editors:

Mesgarpour Tousi M. Electric Field Grading and Electrical Insulation Design for High Voltage, High Power Density Wide Bandgap Power Modules. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/100621

Virginia Tech

11. Yi, Jihaeng. Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection.

Degree: PhD, Electrical and Computer Engineering, 2012, Virginia Tech

URL: http://hdl.handle.net/10919/77229

► In this thesis, we report the development of two types of optical sensors, one for high temperature pressure measurements and the other for real-time particle… (more)

▼ In this thesis, we report the development of two types of optical sensors, one for high temperature pressure measurements and the other for real-time particle detection. With a high melting temperature (over 2000°C), low optical loss, and excellent corrosion resistance, sapphire (α-Al₂O₃) is ideal for high temperature sensing applications. Fabry-Perot (FP) cavity with optical interrogation of pressure response. The prototype is based on an extrinsic FP interferometer design and is constructed by combining reactive ion etching (RIE) with direct wafer bonding. Long-term testing proves that the adhesive-free wafer bond is sufficient to create a sealed Fabry-Perot cavity as a pressure transducer. Pressure measurement over a range of 6 to 200 psi has been demonstrated at room temperature using white-light interferometry. For the other sensor, the goal is to detect the presence of micro- and nanoparticles in real time. The sensor is based on a silica fiber taper, and we aim to detect particle presence by measuring optical scattering and absorption induced by particles attached to the taper surface. To establish the relationship between particle density and optical transmission loss, we first consider a model where Au nanospheres are self-assembled on taper surface through electrostatic interaction. An analytical model is established to describe the adsorption of gold nanospheres onto cylindrical and spherical silica surfaces from quiescent aqueous particle suspensions. The curved surfaces of the fiber taper and microspheres are coated with nm-thick layer of a polycation, enabling irreversible adsorption of the negatively charged spheres. Our results fit well with theory, which predicts that the rates of particle adsorption will depend strongly on the surface geometry. In particular, adsorption is significantly faster on curved than on planar surfaces at times long enough that the particle diffusion length is large compared to the surface curvature. This is of particular importance for plasmonic sensors and other devices where particles are deposited from a suspension onto surfaces which may have non-trivial geometries. We have established a theoretical model that can describe optical loss generated by particles on taper surface. This theory is validated by measuring, in real time, optical loss during the self-assembly of gold nanoparticles. We find that the measured optical loss can be quantitatively explained by the presence of multiple guided modes within the fiber taper region. Based on this work, we incorporate a fiber taper into a cascade impactor and show that welding aerosols attached to the fiber taper surface can induce measurable transmission loss during the welding process. Advisors/Committee Members: Xu, Yong (committeechair), Heflin, James R. (committee member), Meehan, Kathleen (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Wang, Anbo (committee member).

Subjects/Keywords: Fiber Taper Loss; Sapphire Fabry-Perot Cavity; Plasmon Resonance; Direct Bonding; Sapphire Etching; Irreversible adsorption; Welding Aerosol

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APA (6^th Edition):

Yi, J. (2012). Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/77229

Chicago Manual of Style (16^th Edition):

Yi, Jihaeng. “Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/77229.

MLA Handbook (7^th Edition):

Yi, Jihaeng. “Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection.” 2012. Web. 07 Mar 2021.

Vancouver:

Yi J. Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/77229.

Council of Science Editors:

Yi J. Optical Sensors for High-Temperature Pressure Measurement and Real-Time Particle Detection. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/77229

Virginia Tech

12. Zhang, Yingchen. New Methods for Synchrophasor Measurement.

Degree: PhD, Electrical and Computer Engineering, 2011, Virginia Tech

URL: http://hdl.handle.net/10919/77297

► Recent developments in smart grid technology have spawned interest in the use of phasor measurement units to help create a reliable power system transmission and… (more)

▼ Recent developments in smart grid technology have spawned interest in the use of phasor measurement units to help create a reliable power system transmission and distribution infrastructure. Wide-area monitoring systems (WAMSs) utilizing synchrophasor measurements can help with understanding, forecasting, or even controlling the status of power grid stability in real-time. A power system Frequency Monitoring Network (FNET) was first proposed in 2001 and was established in 2004. As a pioneering WAMS, it serves the entire North American power grid through advanced situational awareness techniques, such as real-time event alerts, accurate event location estimation, animated event visualization, and post event analysis. Traditionally, Phasor Measurement Units (PMUs) have utilized signals obtained from current transformers (CTs) to compute current phasors. Unfortunately, this requires that CTs must be directly connected with buses, transformers or power lines. Chapters 2, 3 will introduce an innovative phasor measurement instrument, the Non-contact Frequency Disturbance Recorder (NFDR), which uses the magnetic and electric fields generated by power transmission lines to obtain current phasor measurements. The NFDR is developed on the same hardware platform as the Frequency Disturbance Recorder (FDR), which is actually a single phase PMU. Prototype testing of the NFDR in both the laboratory and the field environments were performed. Testing results show that measurement accuracy of the NFDR satisfies the requirements for power system dynamics observation. Researchers have been developing various techniques in power system phasor measurement and frequency estimation, due to their importance in reflecting system health. Each method has its own pros and cons regarding accuracy and speed. The DFT (Discrete Fourier Transform) based algorithm that is adopted by the FDR device is particularly suitable for tracking system dynamic changes and is immune to harmonic distortions, but it has not proven to be very robust when the input signal is polluted by random noise. Chapter 4 will discuss the Least Mean Squares-based methods for power system frequency tracking, compared with a DFT-based algorithm. Wide-area monitoring systems based on real time PMU measurements can provide great visibility to the angle instability conditions. Chapter 5 focuses on developing an early warning algorithm on the FNET platform. Advisors/Committee Members: Conners, Richard W. (committee member), Lin, Tao (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Centeno, Virgilio A. (committeecochair), Liu, Yilu (committeecochair).

Subjects/Keywords: Electric and magnetic fields; Nonlinear least squares; Angle instability; Discrete Fourier transform; Synchrophasor measurement

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APA (6^th Edition):

Zhang, Y. (2011). New Methods for Synchrophasor Measurement. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/77297

Chicago Manual of Style (16^th Edition):

Zhang, Yingchen. “New Methods for Synchrophasor Measurement.” 2011. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/77297.

MLA Handbook (7^th Edition):

Zhang, Yingchen. “New Methods for Synchrophasor Measurement.” 2011. Web. 07 Mar 2021.

Vancouver:

Zhang Y. New Methods for Synchrophasor Measurement. [Internet] [Doctoral dissertation]. Virginia Tech; 2011. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/77297.

Council of Science Editors:

Zhang Y. New Methods for Synchrophasor Measurement. [Doctoral Dissertation]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/77297

Virginia Tech

13. Harun, Mahmud. Modification of Large Reflector Antennas for Low Frequency Operation.

Degree: PhD, Electrical and Computer Engineering, 2011, Virginia Tech

URL: http://hdl.handle.net/10919/29455

► Modifications of large reflector antennas, such that their observing capabilities are enhanced in the range of about 10-500~MHz without affecting operation of the pre-existing higher-frequency… (more)

▼ Modifications of large reflector antennas, such that their observing capabilities are enhanced in the range of about 10-500~MHz without affecting operation of the pre-existing higher-frequency systems, are addressed in this dissertation. The major contributions of this dissertation can be divided into two parts: 1) designing new low frequency feeds, and 2) developing new analysis methodologies which, as opposed to traditional techniques, are suitable for analyzing low frequency systems. First, we consider the performance of existing schemes that provide low frequency capability. Then, a new class of dipole-based low frequency feeds - namely, the ``distributed feed array'' - is designed to cover the frequency range of interest without affecting operation at higher frequencies. As an example, distributed feed arrays are designed for the Expanded Very Large Array (EVLA) to cover the range of 50-250~MHz. A method of moments (MoM) model of an EVLA antenna is developed for this purpose. The new design shows performance comparable to the existing 4 m system on the EVLA in the range of 50-88~MHz, and introduces observing capabilities in the range of 110-250~MHz (currently not covered by the EVLA). Moreover, the blockage presented to the existing EVLA L-band system is reduced significantly when the existing 4 m system is replaced by the proposed system. At low frequencies, external noise can be a significant or dominant contribution to the total noise of the system. This, combined with mutual coupling between the array elements of the distributed feed array, makes it difficult to predict the sensitivity of these systems. This dissertation describes a system model and procedure for estimating the system equivalent flux density (SEFD) - a useful and meaningful metric of the sensitivity of a radio telescope - that accounts for these issues. We consider the efficiency of methods other than MoM - in particular, Physical Optics (PO), Uniform Geometrical Theory of Diffraction (UTD), and hybrid methods - for accelerated computation at low frequencies. A method for estimating the blockage presented by low frequency systems to the pre-existing higher-frequency systems is also described. Advisors/Committee Members: Ellingson, Steven W. (committeechair), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Manteghi, Majid (committee member), Patterson, Cameron D. (committee member), Simonetti, John H. (committee member).

Subjects/Keywords: Low Frequency Radio Astronomy; Reflector Antennas; Feeds; Sensitivity

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APA (6^th Edition):

Harun, M. (2011). Modification of Large Reflector Antennas for Low Frequency Operation. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29455

Chicago Manual of Style (16^th Edition):

Harun, Mahmud. “Modification of Large Reflector Antennas for Low Frequency Operation.” 2011. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/29455.

MLA Handbook (7^th Edition):

Harun, Mahmud. “Modification of Large Reflector Antennas for Low Frequency Operation.” 2011. Web. 07 Mar 2021.

Vancouver:

Harun M. Modification of Large Reflector Antennas for Low Frequency Operation. [Internet] [Doctoral dissertation]. Virginia Tech; 2011. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/29455.

Council of Science Editors:

Harun M. Modification of Large Reflector Antennas for Low Frequency Operation. [Doctoral Dissertation]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/29455

Virginia Tech

14. Diomedi II, Kevin Paul. A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method.

Degree: PhD, Electrical Engineering, 2019, Virginia Tech

URL: http://hdl.handle.net/10919/88512

► A new technique is presented to study the interaction of electromagnetic waves with rough surfaces. Building on the technique called the Magnetic Field Integral Equation… (more)

Subjects/Keywords: electromagnetics; rough surface scattering; single-scatter; integral equations

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APA (6^th Edition):

Diomedi II, K. P. (2019). A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88512

Chicago Manual of Style (16^th Edition):

Diomedi II, Kevin Paul. “A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method.” 2019. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/88512.

MLA Handbook (7^th Edition):

Diomedi II, Kevin Paul. “A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method.” 2019. Web. 07 Mar 2021.

Vancouver:

Diomedi II KP. A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/88512.

Council of Science Editors:

Diomedi II KP. A Curvature-Corrected Rough Surface Scattering Theory Through The Single-Scatter Subtraction Method. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/88512

Virginia Tech

15. Hu, Di. Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings.

Degree: PhD, Electrical Engineering, 2017, Virginia Tech

URL: http://hdl.handle.net/10919/85112

► A fully distributed multi-parameter acoustic sensing technology is proposed. Current fully distributed sensing techniques are exclusively based on intrinsic scatterings in optical fibers. They demonstrate… (more)

▼ A fully distributed multi-parameter acoustic sensing technology is proposed. Current fully distributed sensing techniques are exclusively based on intrinsic scatterings in optical fibers. They demonstrate long sensing span, but their limited applicable parameters (temperature and strain) and costly interrogation systems have prevented their widespread applications. A novel concept of acoustic fiber Bragg grating (AFBG) is conceived with inspiration from optical fiber Bragg grating (FBG). This AFBG structure exploits periodic spatial perturbations on an elongated waveguide to sense variations in the spectrum of an acoustic wave. It achieves ten times higher sensitivity than the traditional time-of-flight measurement system using acoustic pulses. A fast interrogation method is developed to avoid frequency scan, reducing both the system response time (from 3min to <1ms) and total cost. Since acoustic wave propagates with low attenuation along varieties of solid materials (metal, silica, sapphire, etc.), AFBG can be fabricated on a number of waveguides and to sense multiple parameters. Sub-millimeter metal wire and optical fiber based AFBGs have been demonstrated experimentally for effective temperature (25~700 degC) and corrosion sensing. A hollow borosilicate tube is demonstrated for simultaneous temperature (25~200 degC) and pressure (15~75 psi) sensing using two types of acoustic modes. Furthermore, a continuous 0.6 m AFBG is employed for distributed temperature sensing up to 500 degC and to accurately locate the 0.18 m long heated section. Sensing parameters, sensitivity and range of an AFBG can be tuned to fit a specific application by selecting acoustic waveguides with different materials and/or geometries. Therefore, AFBG is a fully distributed sensing technology with tremendous potentiality. Advisors/Committee Members: Wang, Anbo (committeechair), Pickrell, Gary R. (committee member), Zhu, Yizheng (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Li, Qiang (committee member).

Subjects/Keywords: Sensors; acoustic; fiber Bragg grating; distributed sensing

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APA (6^th Edition):

Hu, D. (2017). Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/85112

Chicago Manual of Style (16^th Edition):

Hu, Di. “Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/85112.

MLA Handbook (7^th Edition):

Hu, Di. “Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings.” 2017. Web. 07 Mar 2021.

Vancouver:

Hu D. Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/85112.

Council of Science Editors:

Hu D. Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/85112

Virginia Tech

16. Amin, Farooq Ul. Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation.

Degree: PhD, Electrical Engineering, 2018, Virginia Tech

URL: http://hdl.handle.net/10919/91481

► Modern and future communication and radar systems require highly reconfigurable RF front-ends to realize the vision of Software-Defined Radio (SDR), where a single digitally-enabled radio… (more)

▼ Modern and future communication and radar systems require highly reconfigurable RF front-ends to realize the vision of Software-Defined Radio (SDR), where a single digitally-enabled radio is able to cover multiple bands and multiple operating standards. However, in the increasingly hostile RF environment, filtering becomes a bottleneck for SDRs as the traditional off-chip filters are fixed frequency and bulky. Therefore, tunable filtering is a critical building block for the reconfigurable RF front-ends and on-chip implementations are needed to meet size and weight constraints. On-chip passive components are lossy, especially inductors, and to fulfill the tunability requirements a number of active circuit techniques, e.g. N-path, Q-enhanced, discrete-time filters etc., have been developed. Most of these active filtering techniques, however, are limited to RF frequency range of few GHz and below. Additionally, these techniques lack or have very limited bandwidth tunability. On the other hand, Q-enhanced tunable LC filtering has the potential to be implemented at Microwave frequencies from 4~20 GHz and beyond. In this dissertation, a number of Q-enhanced parallel synthesis techniques have been proposed and implemented to achieve high-order, frequency tunable, and wide bandwidth tunable filters. First, a tunable 4th-order BPF was proposed and implemented in Silicon Germanium (SiGe) BiCMOS technology. Along with center frequency tuning, the filter achieves first ever reported 3-dB bandwidth tuning from 2% to 25%, representing 120 MHz to 1.5 GHz of bandwidth at 6 GHz. A new set of design equations were developed for the 4th-order parallel synthesis of BPF. A practical switched varactor control scheme is proposed for large tuning ratio varactors to reduce the nonlinear contribution from the varactor substantially which improves the tunable LC BPF filter linearity. Second, parallel addition and subtraction techniques were proposed to realize tunable dual-band filters. The subtraction technique is implemented in SiGe BiCMOS technology at X and Ku bands with more than 50 dB of out-of-band attenuation. Finally, a true wideband band-reject filter technique was proposed for microwave frequencies using parallel synthesis of two band-pass filters and an all-pass path. The proposed band-reject scheme is tunable and wide 20 dB attenuation bandwidths on the order of 10s of MHz to 100s of MHz can be achieved using this scheme. The implementation of the proposed parallel synthesis techniques in silicon technology along with measured results demonstrate that Q-enhanced filtering is favorable at higher microwave frequencies. Therefore, such implementations are suitable for future wireless communication and radar systems particularly wide bandwidth systems on the order of 100s of MHz to GHz. Future research includes, high-order reconfigurable band-pass and band-reject filters, automatic tuning control, and exploring the parallel synthesis techniques in Gallium Nitride (GaN) technology for high RF power applications. Advisors/Committee Members: Koh, Kwang-Jin (committeechair), Raman, Sanjay (committeechair), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Orlowski, Mariusz Kriysztof (committee member), Nguyen, Vinh (committee member).

Subjects/Keywords: Tunable Filter; Active Filter; Q-enhanced Filter; 4th-order BPF; Wideband filter; RFIC

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APA (6^th Edition):

Amin, F. U. (2018). Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/91481

Chicago Manual of Style (16^th Edition):

Amin, Farooq Ul. “Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/91481.

MLA Handbook (7^th Edition):

Amin, Farooq Ul. “Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation.” 2018. Web. 07 Mar 2021.

Vancouver:

Amin FU. Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/91481.

Council of Science Editors:

Amin FU. Integrated Tunable LC Higher-Order Microwave Filters for Interference Mitigation. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/91481

Virginia Tech

17. Black, Jacob A. Neural Networks For Phase Demodulation In Optical Interferometry.

Degree: MS, Electrical Engineering, 2019, Virginia Tech

URL: http://hdl.handle.net/10919/93263

► Neural Networks (NNs) (or 'deep' neural networks (DNNs)) have found great success in many applications across all fields of engineering, and in particular have found… (more)

Subjects/Keywords: Phase imaging; Neural Networks; Machine Learning; Biological Imaging

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APA (6^th Edition):

Black, J. A. (2019). Neural Networks For Phase Demodulation In Optical Interferometry. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/93263

Chicago Manual of Style (16^th Edition):

Black, Jacob A. “Neural Networks For Phase Demodulation In Optical Interferometry.” 2019. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/93263.

MLA Handbook (7^th Edition):

Black, Jacob A. “Neural Networks For Phase Demodulation In Optical Interferometry.” 2019. Web. 07 Mar 2021.

Vancouver:

Black JA. Neural Networks For Phase Demodulation In Optical Interferometry. [Internet] [Masters thesis]. Virginia Tech; 2019. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/93263.

Council of Science Editors:

Black JA. Neural Networks For Phase Demodulation In Optical Interferometry. [Masters Thesis]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/93263

18. Al-Mamun, Mohammad Shah. Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array.

Degree: PhD, Electrical Engineering, 2019, Virginia Tech

URL: http://hdl.handle.net/10919/95489

► Emerging memory technologies are being intensively investigated for extending Moore's scaling law in the next decade. The resistive random-access memory (ReRAM) is one of the… (more)

▼ Emerging memory technologies are being intensively investigated for extending Moore's scaling law in the next decade. The resistive random-access memory (ReRAM) is one of the most propitious contenders to replace the current ubiquitous FLASH memory. ReRAM shows unique nanoionics based filamentary switching mechanism. Compared to the current nonvolatile memory based on floating gate MOSFET transistor, the advantages of ReRAM include superior scalability, low power consumption, high OFF-/ON-state resistance ratio, excellent endurance, and long retention of the logic bit states. Besides the nonvolatile memory applications, resistive switching devices implement the function of a memristor which is the fourth basic electrical component and can be used for neuromorphic computing. A ReRAM device is in essence a metal-insulator-metal structure. One of the metal electrodes is called the active electrode and provides the building material for the filamentary connection between the electrodes. An important requirement of the second electrode, called the inert electrode, is to be immiscible with the metal atoms of the active electrode and to exhibit a minimum of susceptibility to structural changes and chemical reactions. This research presents a thorough investigation of the role and properties of the inert electrode and offers guideline for the optimal selection of the inert electrode in a commercially viable product. It has been found out that one important property of the inert electrode is its heat conductivity and also the way the inert electrode is embedded on a substrate. Consequently, the concept of the inert electrode has been replaced by the concept of engineered inert electrode module which evolved from a single metal layer to a multilayer stack displaying glue layers, high thermal conductivity layers dissipating the heat quickly, and diffusion stop layers eliminating unwanted chemical reactions. The investigation of the electro-thermal effects led to the discovery of the cell-to-cell thermal cross talk within the memory array which can seriously affect the performance of cells impacted by the remote heat transfer. When a memory cell is switched repeatedly a considerable amount of heat is dissipated in the cell and the heat may spread to neighboring cells that share the same metal lines. This heat transfer causes degradation of electrical performance of the neighboring cells. A method has been developed to characterize quantitatively how the electrical performance is affected by the thermal cross-talk impacting the electric performance of neighboring cells. Several novel mitigation strategies of new memory array architectures have been proposed and investigated. Advisors/Committee Members: Orlowski, Mariusz Kriysztof (committeechair), Jia, Xiaoting (committee member), Pickrell, Gary R. (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Guido, Louis J. (committee member).

Subjects/Keywords: Non-volatile memory; resistive switching; ReRAM; conductive filament; memristor; bottom electrode; reliability; switching cycle

10 more images…

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APA (6^th Edition):

Al-Mamun, M. S. (2019). Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/95489

Chicago Manual of Style (16^th Edition):

Al-Mamun, Mohammad Shah. “Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array.” 2019. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/95489.

MLA Handbook (7^th Edition):

Al-Mamun, Mohammad Shah. “Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array.” 2019. Web. 07 Mar 2021.

Vancouver:

Al-Mamun MS. Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/95489.

Council of Science Editors:

Al-Mamun MS. Impact of Inert-electrode on the Performance and Electro-thermal Reliability of ReRAM Memory Array. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/95489

Virginia Tech

19. Wang, Yunmiao. A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings.

Degree: PhD, Electrical Engineering, 2012, Virginia Tech

URL: http://hdl.handle.net/10919/39324

► Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and… (more)

▼ Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and mechanical engineering infrastructure. Health monitoring of these structures usually requires the sensors to have such features as large area coverage, maintenance free or minimum maintenance, ultra-low cost per measurement point, and capability of operation in harsh environments. Fiber Bragg grating (FBG) has attracted considerable interest for this application because of its compactness, electromagnetic immunity, and excellent multiplexing capability. Several FBG multiplexing techniques have been developed to increase the multiplexing number and further reduce the unit cost. To the authorâ s best knowledge, the current demonstrated maximum multiplexing number are 800 FBG sensors in a single array using optical frequency domain reflectometry (OFDR), whose maximum fiber span is limited by the coherence length of light source. In this work, we proposed and demonstrated a wavelength-scanning time-division multiplexing (WSTDM) of 1000 ultra-weak FBGs for distributed temperature sensing. In comparison with the OFDR method, the WSTDM method distinguishes the sensors by different time delays, and its maximum operation distance, which is limited by the transmission loss of the fiber, can be as high as tens of kilometers. The strong multiplexing capability and low crosstalk of the ultra-weak FBG sensors was investigated through both theoretical analysis and experiment. An automated FBG fabrication system was developed for fast FBG fabrication. With this WSTDM method, we multiplexed 1000 ultra-weak FBGs for distributed temperature sensing. Besides the demonstrated temperature measurement, the reported method can also be applied to measure other parameters, such as strain, pressure. Advisors/Committee Members: Wang, Anbo (committeechair), Pickrell, Gary R. (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Poon, Ting-Chung (committee member), Xu, Yong (committee member).

Subjects/Keywords: Structure health monitoring; Quasi-distributed sensing; Optical fiber sensor; Multiplexing; Fiber Bragg gratings

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APA (6^th Edition):

Wang, Y. (2012). A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/39324

Chicago Manual of Style (16^th Edition):

Wang, Yunmiao. “A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/39324.

MLA Handbook (7^th Edition):

Wang, Yunmiao. “A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings.” 2012. Web. 07 Mar 2021.

Vancouver:

Wang Y. A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/39324.

Council of Science Editors:

Wang Y. A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/39324

Virginia Tech

20. Salehi, Mohsen. Time-varying Small Antennas for Wideband Applications.

Degree: PhD, Electrical Engineering, 2013, Virginia Tech

URL: http://hdl.handle.net/10919/25435

► A desirable goal in wireless communication systems is to achieve a high-rate data transmission through electrically small antennas. However, the overall transmission bandwidth is limited… (more)

▼ A desirable goal in wireless communication systems is to achieve a high-rate data transmission through electrically small antennas. However, the overall transmission bandwidth is limited by the antenna size. As a well-known physical limitation, maximum achievable bandwidth of a small antenna is governed by the fundamental limit which defines a lower bound on the antenna quality factor. This limit is a function of electrical size of the antenna and therefore, as the antenna shrinks in size the bandwidth decreases as well. This dissertation presents a new technique to decouple the impedance bandwidth of a high-Q antenna from the information bandwidth in order to provide a wideband data-transmission. This technique controls the natural resonant frequencies of an electrically small antenna in a time-varying fashion such that ultra-fast frequency-shift keying modulation can be achieved regardless of the narrow bandwidth of the antenna. A major advantage of the proposed technique is that the high-Q property of a miniaturized antenna is a desirable design parameter rather than a limiting factor. Therefore, the antenna size can be reduced as much as required. It is shown that if the fundamental resonance of an antenna is shifted in time, the frequency of the near-zone fields which construct the reactive stored energy, changes momentarily and hence, the radiating fields track any instantaneous variation of the antenna fundamental resonance. This characteristic is utilized to employ a single-mode high-Q antenna in the transient state and modulate the fundamental resonant frequency according to the baseband data information. This approach leads to a new class of compact transmitters with a minimized architecture and high data-rate transmission capability. Advisors/Committee Members: Manteghi, Majid (committeechair), Davis, William A. (committee member), Kohler, Werner E. (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Brown, Gary S. (committee member).

Subjects/Keywords: Antenna; Direct Modulation; Quality Factor; Small Antenna; Switched Antenna; Switched Resonator; Time Domain; Transient; Wideband

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APA (6^th Edition):

Salehi, M. (2013). Time-varying Small Antennas for Wideband Applications. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/25435

Chicago Manual of Style (16^th Edition):

Salehi, Mohsen. “Time-varying Small Antennas for Wideband Applications.” 2013. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/25435.

MLA Handbook (7^th Edition):

Salehi, Mohsen. “Time-varying Small Antennas for Wideband Applications.” 2013. Web. 07 Mar 2021.

Vancouver:

Salehi M. Time-varying Small Antennas for Wideband Applications. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/25435.

Council of Science Editors:

Salehi M. Time-varying Small Antennas for Wideband Applications. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/25435

Virginia Tech

21. Hong, Sun. Resonance-Based Techniques for Microwave Breast Cancer Applications.

Degree: PhD, Electrical and Computer Engineering, 2012, Virginia Tech

URL: http://hdl.handle.net/10919/29096

► It is well known that a finite-size scatterer has a set of natural resonances, which are uniquely determined by the physical properties of the scatterer.… (more)

Subjects/Keywords: natural resonance; breast cancer; microwave hyperthermia; residue; singularity expansion method; pole; ground penetrating radar

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APA (6^th Edition):

Hong, S. (2012). Resonance-Based Techniques for Microwave Breast Cancer Applications. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29096

Chicago Manual of Style (16^th Edition):

Hong, Sun. “Resonance-Based Techniques for Microwave Breast Cancer Applications.” 2012. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/29096.

MLA Handbook (7^th Edition):

Hong, Sun. “Resonance-Based Techniques for Microwave Breast Cancer Applications.” 2012. Web. 07 Mar 2021.

Vancouver:

Hong S. Resonance-Based Techniques for Microwave Breast Cancer Applications. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/29096.

Council of Science Editors:

Hong S. Resonance-Based Techniques for Microwave Breast Cancer Applications. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/29096

Virginia Tech

22. Sweeney, Daniel C. Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells.

Degree: PhD, Biomedical Engineering, 2018, Virginia Tech

URL: http://hdl.handle.net/10919/94416

► Electroporation-based treatments are motivated by the response of biological membranes to high- intensity pulsed electric fields. These fields rearrange the membrane structure to enhance the… (more)

▼ Electroporation-based treatments are motivated by the response of biological membranes to high- intensity pulsed electric fields. These fields rearrange the membrane structure to enhance the membrane's diffusive permeability, or the degree to which a membrane allows molecules to diffuse through it, is impacted by the structure, composition, and environment in which the cell resides. Tracer molecules have been developed that are unable to pass through intact cell membranes yet enter permeabilized cells. This dissertation investigates the hypothesis that the flow of such molecules may be used to quantify the effects of the electrical stimulus and environmental conditions leading to membrane electroporation. Specifically, a series of electrical pulses that alternates between positive and negative pulses permeabilizes cells more symmetrically than a longer pulse with the same total on-time. However, the magnitude of this symmetric entry decreases for the shorter alternating pulses. Furthermore, a method for quantitatively measuring the permeability of the cell membrane was proposed and validated. From data near the electroporation threshold, the response of cells varies widely in the manner in which cells become permeabilized. This method is applied to study the transient cell membrane permeability induced by electroporation and is used to demonstrate that the cell membrane remains permeable beyond 30 min following treatment. To analyze these experimental findings in the context of physical mechanisms, computational models of molecular uptake were developed to simulate electroporation. The results of these simulations indicate that the cell's local environment during electroporation facilitates the degree of molecular uptake. We use these models to predict how manipulating both the environment of cells during electroporation affects the induced membrane permeability. These experimental and computational results provide evidence that supports the hypothesis of this dissertation and provide a foundation for future investigation and simulation of membrane electroporation. Advisors/Committee Members: Davalos, Rafael V. (committeechair), Cimini, Daniela (committeechair), Verbridge, Scott (committee member), Poelzing, Steven (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member).

Subjects/Keywords: bioelectrics; electroporation; biotransport; quantitative microscopy; membrane permeability; pulsed electric fields

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APA (6^th Edition):

Sweeney, D. C. (2018). Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/94416

Chicago Manual of Style (16^th Edition):

Sweeney, Daniel C. “Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells.” 2018. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/94416.

MLA Handbook (7^th Edition):

Sweeney, Daniel C. “Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells.” 2018. Web. 07 Mar 2021.

Vancouver:

Sweeney DC. Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/94416.

Council of Science Editors:

Sweeney DC. Quantitative In Vitro Characterization of Membrane Permeability for Electroporated Mammalian Cells. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/94416

Virginia Tech

23. He, Jiaji. Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment.

Degree: PhD, Electrical Engineering, 2021, Virginia Tech

URL: http://hdl.handle.net/10919/101870

► Sensing in harsh environments, like high temperature, high pressure, and corrosive environment, is always in great need. Efficient and safe operation of instruments like nuclear… (more)

Subjects/Keywords: Acoustic wave; acoustic sensor; periodic structure; temperature sensor; gamma radiation

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APA (6^th Edition):

He, J. (2021). Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/101870

Chicago Manual of Style (16^th Edition):

He, Jiaji. “Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment.” 2021. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/101870.

MLA Handbook (7^th Edition):

He, Jiaji. “Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment.” 2021. Web. 07 Mar 2021.

Vancouver:

He J. Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment. [Internet] [Doctoral dissertation]. Virginia Tech; 2021. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/101870.

Council of Science Editors:

He J. Acoustic Waveguides and Sensors for High Temperature and Gamma Radiation Environment. [Doctoral Dissertation]. Virginia Tech; 2021. Available from: http://hdl.handle.net/10919/101870

24. Dobson, Kelly Katherine. Reconstruction Enhancements with Optical Scanning Holography.

Degree: PhD, Electrical Engineering, 2016, Virginia Tech

URL: http://hdl.handle.net/10919/71462

► Optical scanning holography (OSH) [1] has the benefit of recording the entire three-dimensional (3-D) volume of a specimen in the form of a two-dimensional (2-D)… (more)

Subjects/Keywords: Optical scanning holography; spiral phase plate; optical sectioning

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APA (6^th Edition):

Dobson, K. K. (2016). Reconstruction Enhancements with Optical Scanning Holography. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/71462

Chicago Manual of Style (16^th Edition):

Dobson, Kelly Katherine. “Reconstruction Enhancements with Optical Scanning Holography.” 2016. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/71462.

MLA Handbook (7^th Edition):

Dobson, Kelly Katherine. “Reconstruction Enhancements with Optical Scanning Holography.” 2016. Web. 07 Mar 2021.

Vancouver:

Dobson KK. Reconstruction Enhancements with Optical Scanning Holography. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/71462.

Council of Science Editors:

Dobson KK. Reconstruction Enhancements with Optical Scanning Holography. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/71462

25. Salem, Jebreel Mohamed Muftah. A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications.

Degree: PhD, Electrical Engineering, 2017, Virginia Tech

URL: http://hdl.handle.net/10919/88830

► Electronics are normally designed to operate at temperatures less than 125 °C. For high temperature applications, the use of those normal electronics becomes challenging and… (more)

▼ Electronics are normally designed to operate at temperatures less than 125 °C. For high temperature applications, the use of those normal electronics becomes challenging and sometimes impractical. Conventionally, many industries tried to push the maximum operating temperature of electronics by either using passive/active cooling systems or tolerating degraded performance. Recently, there has been a demand for more robust electronics that can operate at higher temperature without sacrificing the performance or the use of any weighty, power hungry, complex cooling systems. One of the major industries that need electronics operating at high temperature is the oil and gas industry. Electronics have been used within the field in many areas, such as well logging downhole telemetry systems, power networks, sensors, and actuators. In the past, the industry has managed to use the existing electronics at temperatures up to 150 °C. However, declining reserves of easily accessible natural resources have motivated the oil and gas industry to drill deeper. The main challenge at deep wells for downhole electronics is the high temperatures as the pressures are handled mechanically. The temperature in deep basins can exceed 210 °C. In addition, existing well logging telemetry systems achieve low data transmission rates of less than 2.0 Mbps at depth of 7.0 Km which do not meet the growing demand for higher data rates due to higher resolution sensors, faster logging speeds, and additional tools available for a single wireline cable. The main issues limiting the speed of the systems are the bandwidth of multi-conductor copper cable and the low speed communication system connecting the tools with the telemetry modem. The next generation of the well logging telemetry system replaces the multi-conductor wireline between the surface and the downhole with an optical fiber cable and uses a coaxial cable to connect tools with the optical node in downhole to meet the growing needs for higher data rates. However, the downhole communication system between the tools and the optical modulator remains the bottleneck for the system. The downhole system is required to provide full duplex and simultaneous communications between multiple downhole tools and the surface with high data rates and able to operate reliably at temperatures up to 230 °C. In this dissertation, a downhole communication system based on radio frequency (RF) transmission is investigated. The major contributions of our research lie in five areas. First, we proposed and designed a downhole communication system that employs RF systems to provide high speed communications between the downhole tools and the surface. The system supports up to six tools and utilizes frequency division multiple access to provide full duplex and simultaneous communications between downhole tools and the surface data acquisition system. The system achieves 20 Mbps per tool for uplink and 6 Mbps per tool for downlink with bit error rate (BER) less than 10-6. Second, a RF front-end of transceiver operating… Advisors/Committee Members: Ha, Dong S. (committeechair), Lu, Guo Quan (committee member), Koh, Kwang-Jin (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Raman, Sanjay (committee member).

Subjects/Keywords: High Temperature Electronics; Harsh Environment Electronics; Downhole Communications; GaN-based Transceiver; GaN for High temperature Applications

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APA (6^th Edition):

Salem, J. M. M. (2017). A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88830

Chicago Manual of Style (16^th Edition):

Salem, Jebreel Mohamed Muftah. “A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications.” 2017. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/88830.

MLA Handbook (7^th Edition):

Salem, Jebreel Mohamed Muftah. “A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications.” 2017. Web. 07 Mar 2021.

Vancouver:

Salem JMM. A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/88830.

Council of Science Editors:

Salem JMM. A High Temperature RF Front-End of a Transceiver for High Speed Downhole Communications. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/88830

Virginia Tech

26. Alsawaha, Hamad Waled. Synthesis of Ultra-Wideband Array Antennas.

Degree: PhD, Electrical Engineering, 2014, Virginia Tech

URL: http://hdl.handle.net/10919/54553

► Acquisition of ultra-wideband signals by means of array antennas requires essentially frequency-independent radiation characteristics over the entire bandwidth of the signal in order to avoid… (more)

▼ Acquisition of ultra-wideband signals by means of array antennas requires essentially frequency-independent radiation characteristics over the entire bandwidth of the signal in order to avoid distortions. Factors contributing to bandwidth limitation of arrays include array factor, radiation characteristics of the array element, and inter-element mutual coupling. Strictly speaking, distortion-free transmission or reception of ultra-wideband signals can be maintained if the magnitude of the radiated field of the array remains constant while its phase varies linearly with frequency over the bandwidth of interest. The existing wideband-array synthesis methods do not account for all factors affecting the array bandwidth and are often limited to considering the array factor and not the total field of the array in the synthesis process. The goal of this study is to present an ultra-wideband array synthesis technique taking into account all frequency-dependent properties, including array total pattern, phase of the total radiated field, element field, element input impedance, and inter-element mutual coupling. The proposed array synthesis technique is based on the utilization of frequency-adaptive element excitations in conjunction with expressing the total radiated field of the array as a complex Fourier series. Using the proposed method, element excitation currents required for achieving a desired radiation pattern, while compensating for frequency variations of the element radiation characteristics and the inter-element mutual coupling, are calculated. An important consideration in the proposed ultra-wideband array design is that the "phase bandwidth", defined as the frequency range over which the phase of the total radiated field of the array varies linearly with frequency, is taken into account as a design requirement in the synthesis process. Design examples of linear arrays with desired radiation patterns that are expected to remain unchanged over the bandwidth of interest are presented and simulated. Two example arrays, one with a wire dipole as its element and another using an elliptically-shaped disc dipole as the element are studied. Simulation results for far-field patterns, magnitude and phase characteristics, and other performance criteria such as side-lobe level and scanning range are presented. Synthesis of two-dimensional planar arrays is carried out by employing the formulations developed for linear arrays but generalized to accommodate the geometry of planar rectangular arrays. As example designs, planar arrays with wire dipoles and elliptical-shaped disc dipoles are studied. The simulation results indicate that synthesis of ultra-wideband arrays can be accomplished successfully using the technique presented in this work. The proposed technique is robust and comprehensive, nonetheless it is understood that the achieved performance of a synthesized array and how closely the desired performance is met also depends on some of the choices the array designer makes and other constraints, such as number of… Advisors/Committee Members: Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committeechair), Brown, Gary S. (committee member), Pratt, Timothy J. (committee member), Davis, William A. (committee member), Stutzman, Warren L. (committee member), Kohler, Werner E. (committee member).

Subjects/Keywords: antenna arrays; array synthesis; ultra-wideband antenna arrays

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APA (6^th Edition):

Alsawaha, H. W. (2014). Synthesis of Ultra-Wideband Array Antennas. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/54553

Chicago Manual of Style (16^th Edition):

Alsawaha, Hamad Waled. “Synthesis of Ultra-Wideband Array Antennas.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/54553.

MLA Handbook (7^th Edition):

Alsawaha, Hamad Waled. “Synthesis of Ultra-Wideband Array Antennas.” 2014. Web. 07 Mar 2021.

Vancouver:

Alsawaha HW. Synthesis of Ultra-Wideband Array Antennas. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/54553.

Council of Science Editors:

Alsawaha HW. Synthesis of Ultra-Wideband Array Antennas. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/54553

Virginia Tech

27. Ibraheem, Ali Ahmed Younis. Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network.

Degree: PhD, Electrical Engineering, 2014, Virginia Tech

URL: http://hdl.handle.net/10919/50936

► Implanted Devices are important components of the Wireless Body Area Network (WBAN) as a promising technology in biotelemetry, e-health care and hyperthermia applications. The design… (more)

▼ Implanted Devices are important components of the Wireless Body Area Network (WBAN) as a promising technology in biotelemetry, e-health care and hyperthermia applications. The design of WBAN faces many challenges, such as frequency band selection, channel modeling, antenna design, physical layer (PHY) protocol design, medium access control (MAC) protocol design and power source. This research focuses on the design of implanted antennas, channel modeling between implanted devices and Wireless Power Transfer (WPT) for implanted devices. An implanted antenna needs to be small while it maintains Specific Absorption Rate (SAR) and is able to cope with the detuning effect due to the electrical properties of human body tissues. Most of the proposed antennas for implanted applications are electric field antennas, which have a high near-zone electric field and, therefore, a high SAR and are sensitive to the detuning effect. This work is devoted to designing a miniaturized magnetic field antenna to overcome the above limitations. The proposed Electrically Coupled Loop Antenna (ECLA) has a low electric field in the near-zone and, therefore, has a small SAR and is less sensitive to the detuning effect. The performance of ECLA, channel model between implanted devices using Path Loss (PL) and WPT for implanted devices are studied inside different human body models using simulation software and validated using experimental work. The study is done at different frequency bands: Medical Implanted Communication Services (MICS) band, Industrial Scientific and Medical (ISM) band and 3.5 GHz band using ECLA. It was found that the proposed ECLA has a better performance compared to the previous designs of implanted antennas. Based on our study, the MICS band has the best propagation channel inside the human body model among the allowed frequency bands. The maximum PL inside the human body between an implanted antenna and a base station on the surface is about 90 dB. WPT for implanted devices has been investigated as well, and it has been shown that for a device located at 2 cm inside the human body with an antenna radius of 1 cm an efficiency of 63% can be achieved using the proposed ECLA. Advisors/Committee Members: Manteghi, Majid (committeechair), Riad, Sedki Mohamed (committee member), Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committee member), Reed, Jeffrey H. (committee member), Attiya Salem, Ahmed Mohamed (committee member), Kohler, Werner E. (committee member).

Subjects/Keywords: Electrically Small Antenna; Specific Absorption Rate; Electrically Coupled Loop Antenna; Path Loss; Wireless Power Transfer

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APA (6^th Edition):

Ibraheem, A. A. Y. (2014). Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/50936

Chicago Manual of Style (16^th Edition):

Ibraheem, Ali Ahmed Younis. “Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network.” 2014. Doctoral Dissertation, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/50936.

MLA Handbook (7^th Edition):

Ibraheem, Ali Ahmed Younis. “Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network.” 2014. Web. 07 Mar 2021.

Vancouver:

Ibraheem AAY. Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/50936.

Council of Science Editors:

Ibraheem AAY. Implanted Antennas and Intra-Body Propagation Channel for Wireless Body Area Network. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/50936

Virginia Tech

28. Flax, Amy. Micro-optical fiber devices used with modal domain sensing.

Degree: MS, Electrical Engineering, 1988, Virginia Tech

URL: http://hdl.handle.net/10919/43749

► In order to develop more compact optical fiber sensing systems, modal filtering can be performed in-line by using micro-optical devices. Two such devices are… (more)

Subjects/Keywords: Remote sensing; LD5655.V855 1988.F592

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APA (6^th Edition):

Flax, A. (1988). Micro-optical fiber devices used with modal domain sensing. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/43749

Chicago Manual of Style (16^th Edition):

Flax, Amy. “Micro-optical fiber devices used with modal domain sensing.” 1988. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/43749.

MLA Handbook (7^th Edition):

Flax, Amy. “Micro-optical fiber devices used with modal domain sensing.” 1988. Web. 07 Mar 2021.

Vancouver:

Flax A. Micro-optical fiber devices used with modal domain sensing. [Internet] [Masters thesis]. Virginia Tech; 1988. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/43749.

Council of Science Editors:

Flax A. Micro-optical fiber devices used with modal domain sensing. [Masters Thesis]. Virginia Tech; 1988. Available from: http://hdl.handle.net/10919/43749

Virginia Tech

29. Alsawaha, Hamad Waled. New Designs for Wideband Hemispherical Helical Antennas.

Degree: MS, Electrical and Computer Engineering, 2008, Virginia Tech

URL: http://hdl.handle.net/10919/34285

► A unique property of spherical and hemispherical helical antennas is that they provide very broad half-power beamwdiths and circular polarization over a narrow bandwidth. In… (more)

▼ A unique property of spherical and hemispherical helical antennas is that they provide very broad half-power beamwdiths and circular polarization over a narrow bandwidth. In this thesis, new designs for hemispherical helical antennas are introduced that provide significant improvement in bandwidth, while maintaining the directivity and half-power beamwidth of the basic design. In the basic design, a simple wire of circular cross section is wound on the surface of a hemisphere, whereas in the proposed new designs a metallic strip forms the radiating element. Furthermore, the metallic strip may be tapered and tilted relative to the hemispherical surface, allowing wider bandwidth to be achieved. The antenna is fed by a coaxial cable with the inner conductor connected, through a matching section, to the radiating strip and its outer conductor connected to a ground plane. Radiation properties of the proposed hemispherical helical antennas are studied both theoretically and experimentally. A commercial software, based on the method of moments, is used to perform the numerical analysis of these helices. Three-dimensional far-field patterns, axial ratio, directivity, and voltage standing-wave ratio (VSWR) are calculated for several designs. The impacts of tapering as well as tilting of the metallic strip on radiation characteristics are examined. Also, matching of the proposed hemispherical antennas to 50â ¦ transmission lines is addressed. A 4.5-turn hemispherical helix with tapered radiating element and zero degree tilt angle, (metallic strip is perpendicular to the hemisphere axis of symmetry) provides the largest overall bandwidth. A nonlinearly tapered matching section is incorporated into the design in order to reduce the VSWR. For this design, an overall measured bandwidth of about 24% at a center frequency of 3.35 GHz is achieved. Over this bandwidth, the axial ratio remains below 3 dB, the VSWR is less than 2, and the directivity is about 9 Â±1 dB. A half- power beamwidth of 70Â° is also obtained. A prototype of the best design was fabricated and tested using the VT indoor antenna range. Radiation patterns, the scattering parameter S₁₁, and the axial ratio were measured. The measured and simulated results agree reasonably well. In particular, agreements between measured and calculated far-field patterns and VSWR are quite remarkable. This compact, low profile antenna might find useful applications in avionics, global positioning systems (GPS), and high data rate wireless communication systems. Advisors/Committee Members: Jazi%2C%20Ahmad%22%29&pagesize-30">Safaai-Jazi, Ahmad (committeechair), Davis, William A. (committee member), Scales, Wayne A. (committee member).

Subjects/Keywords: Hemispherical Helix; Helical Antenna; Wideband Antennas

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APA (6^th Edition):

Alsawaha, H. W. (2008). New Designs for Wideband Hemispherical Helical Antennas. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/34285

Chicago Manual of Style (16^th Edition):

Alsawaha, Hamad Waled. “New Designs for Wideband Hemispherical Helical Antennas.” 2008. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/34285.

MLA Handbook (7^th Edition):

Alsawaha, Hamad Waled. “New Designs for Wideband Hemispherical Helical Antennas.” 2008. Web. 07 Mar 2021.

Vancouver:

Alsawaha HW. New Designs for Wideband Hemispherical Helical Antennas. [Internet] [Masters thesis]. Virginia Tech; 2008. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/34285.

Council of Science Editors:

Alsawaha HW. New Designs for Wideband Hemispherical Helical Antennas. [Masters Thesis]. Virginia Tech; 2008. Available from: http://hdl.handle.net/10919/34285

Virginia Tech

30. Terril, Nathaniel D. Field Simulation for the Microwave Heating of Thin Ceramic Fibers.

Degree: MS, Electrical Engineering, 1998, Virginia Tech

URL: http://hdl.handle.net/10919/36863

► Microwave processing of ceramics has seen a growth in research and development efforts throughout the past decade. One area of interest is the exploration of… (more)

Subjects/Keywords: mode-matching; thermal runaway; non-uniform heating; microwave processing

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APA (6^th Edition):

Terril, N. D. (1998). Field Simulation for the Microwave Heating of Thin Ceramic Fibers. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/36863

Chicago Manual of Style (16^th Edition):

Terril, Nathaniel D. “Field Simulation for the Microwave Heating of Thin Ceramic Fibers.” 1998. Masters Thesis, Virginia Tech. Accessed March 07, 2021. http://hdl.handle.net/10919/36863.

MLA Handbook (7^th Edition):

Terril, Nathaniel D. “Field Simulation for the Microwave Heating of Thin Ceramic Fibers.” 1998. Web. 07 Mar 2021.

Vancouver:

Terril ND. Field Simulation for the Microwave Heating of Thin Ceramic Fibers. [Internet] [Masters thesis]. Virginia Tech; 1998. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/10919/36863.

Council of Science Editors:

Terril ND. Field Simulation for the Microwave Heating of Thin Ceramic Fibers. [Masters Thesis]. Virginia Tech; 1998. Available from: http://hdl.handle.net/10919/36863

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