Electrical & Computer Engineering Masters Theses

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An Active Power Supply Filter with Ultra Wide Bandwidth
(North Dakota State University, 2016) Booth, Brian
An active transformerless common mode ﬁlter is designed for use with switching mode power supplies with a switching frequency greater than 1MHz. The ﬁlter utilizes an ampliﬁer in a voltage sensing current adjusting architecture to cancel out common mode noise generated by the switching power supply. The ﬁlter is analyzed using a transfer function, simulation, and measurements. Several possible feedback conﬁgurations are examined and beneﬁts of diﬀerent conﬁgurations are explained. The active ﬁlter is shown to have superior performance to only passive components at frequencies up to 20MHz. Spectral domain, time domain, and S21 measurements are given to show the ﬁlter’s eﬀectiveness.
An Analysis and Improvement of Brushless DC Motor Control System
(North Dakota State University, 2013) Sumon, Md Yiasin
Trapezoidal Back-EMF (Brushless DC) motors are gaining increasing importance in automotive industries, HVAC applications, home appliances etc. Traditionally, Brushless DC motors are commutated electronically using position sensors. In these systems, mechanical or electromagnetic sensors are used. In sensorless control, rotor back EMF detection is the most popular technique for speed and position control. Detection of back EMF by novel speed independent commutation function is a very well researched topic that has overcome most of the problems of traditional back EMF detection scheme. In this thesis, a thorough study and speed control scheme for Brushless DC motors using position sensor is presented along with simulation and experimental results. An improved sensorless scheme based on speed independent commutation and state observer based back EMF sensing is analyzed. Both methods use hysteresis control for the current loop and a PI controller for the speed loop to reduce steady state speed error.
The Analysis of Noise Voltage Coupling Between Right-Handed and Meta-Materials Transmission Lines on Printed Circuit Boards
(North Dakota State University, 2013) Nariyal, Sanjay
An important consideration of RF circuitry in terms of Electromagnetic Compatibility is the correct modeling of the coupling between printed transmission lines. This is very important because the coupled noise voltages that are generated between two lines may cause adverse eects on sensitive components placed in the close vicinity. To study this problem of coupling in terms of noise voltages, rst the analytical expressions for computing the near-end and far-end voltages between the conventional Right-Handed (RH) and Composite Right-/Left-Handed Transmission Lines (CRLH-TLs) and then RH and Complementary Split Ring Resonators (CSRR-TLs) were derived. The obtained expressions were then successfully validated with the simulation and measurements results. These expressions will give us an insight on how to reduce the induced noise voltages on the CRLH- and CSRR-TLs by varying the capacitance and inductance values that support left-handed propagation. In particular, it will be shown that the noise voltages coupled to the CRLH-TL are approximately 10 dB lower than the voltages coupled to the CSRR-TL. This could prove to be a useful alternative to conventional sheilding.
Automating the design of deep learning models using neural architecture search for medical image classification
(North Dakota State University, 2024) Balamurugan, Ridhanya
Designing Deep Learning (DL) models for medical image classification tasks poses significant challenges, demanding substantial expertise owing to the intricate nature and critical importance of the undertaking. Creating a DL model tailored for such purposes entails iterative processes of designing, implementing, and fine-tuning algorithms to achieve optimal performance. To mitigate these difficulties, Neural Architecture Search (NAS) has risen as a key field to generate the most effective DL models automatically. However, much of the previous studies involving NAS focus on automating the design of DL models for well-established datasets such as CIFAR-10 and ImageNet. This technique should also be extended to medical image datasets where detecting crucial features accurately in medical images is essential to detect specific illnesses correctly. Therefore, in this study, we investigate NAS to autonomously design best performing DL models for skin lesion detection, thereby demonstrating its usefulness for additional medical image classification endeavours.
An Autonomous Reconfigurable Antenna
(North Dakota State University, 2019) Hinsz, Lee
Today’s wireless communications involve more antenna capabilities while occupying the same amount of space. Antennas are able to operate at multiple frequencies [1]-[2], change polarizations [6], have selectable radiation patterns [1] and are becoming smaller. Likewise, antennas are serving multiple applications. However, many reconfigurable antennas use a separate power source to operate or use software defined radios. In certain instances this can be a limiting factor. To address this limit a novel autonomously reconfigurable antenna is presented in this thesis which allows for simple use at multiple frequencies [21]. This design uses power harvesting circuitry in combination with a reconfigurable antenna to demonstrate the ability to transmit at different frequencies, without the use of a separate power source. Furthermore this thesis presents a prototype for an autonomous reconfigurable antenna that operates at 1.25 GHz and 1.6 GHz.
Calculating Cardiovascular Lumped-Parameter Model Values by Injecting Small Volume Perturbations in an Isovolumic Heart
(North Dakota State University, 2011) Wandler, Jeff
Diagnosing cardiac patient problems contains many uncertainties, and to fully diagnose the patient's condition usually requires a lengthy drug regimen to see what works and what does not. Compounding this problem is that even after the correct drug regimen has been discovered, the underlying cause for the problem may remain a mystery. Thus, the uncertainty and the length of time required to provide an accurate and adequate solution makes it very difficult to provide quality care to the patient. Templeton and others have shown that lumped cardiac muscle parameters can be extracted from an isolated heart by injecting small volumes at high frequencies relative to the heart rate and measuring the pressure response to this volume change. Using the Hill muscle model of two springs and a dash pot to portray the different elements of the cardiac muscle, the pressure and volume relationship makes it possible to calculate these muscle parameters using frequency response analysis techniques. The hypothesis to be tested is "Is it possible to develop a method to test cardiac muscle for stiffness, resistance, and contractile force from measuring ventricular pressure and injected flow?" To test this hypothesis, an isovolumic heart model is developed and allowed to develop pressure, along with a small volume injected to create a pressure response. Analysis of the pressure and flow waveforms produces a measured value of the cardiac model parameter values to compare to the model values. Results from injecting small volume changes into a mathematical heart model show that it is possible to extract the muscle model parameters of non-linear resistance, inertia of the fluid and muscle, and stiffness of the muscle while filling and contracting. The injected frequency and volume were varied to find usable conditions, both with regard to the calculations and the practical limits. Analyzing the error between the measured and model values for a large number of different combinations of model parameters shows an average error of less than 1%.
The Capacity Region of the Gaussian Z-Interference Channel with Gaussian Input and Weak Interference
(North Dakota State University, 2016) Sarkar, Avik
We consider a wireless communication scenario with two transmit-receive pairs where each of the transmitters has a message for its corresponding receiver and only one of the receivers face interference from the undesired transmitter. In our research, we focused on devising optimal ways to manage this undesired interference and characterize the best communication rates for both transmit-receive pairs. Currently, this problem of interference is dealt with by restricting the two communications in di erent frequency or time bands. We explore the possibility of achieving better rates by allowing them to operate in the same band. Such channels were identi ed about 4 decades ago, but the maximum rate of communication when the transmitters have a power constraint is still unknown. In this work, we characterize the best rates for this channel under a reasonable practical constraint of using Gaussian signals at both the transmitters.
Capacity Region of Two Interfering Mimo Multiple Access Channels With Strong Interference
(North Dakota State University, 2015) Modi, Noopur
We consider a communication network, where two mutually interfering 2-user MIMO Multiple Access Channels (MAC) operate simultaneously via the same time-frequency space, and characterize the capacity region of this network when the channel matrices satisfy a strong interference condition. This interfering MAC (IMAC) with aforementioned channel matrices is called strongly ordered IMAC in this work. We characterize the capacity region first using the genie aided approach to find out several constraints that must be satisfied by any achievable rate tuple. Then we show that independent Gaussian coding at each transmitter and joint decoding of the messages at the receivers can achieve all the rate pairs that satisfy all the aforementioned constraints. In an IMAC, there are two types of tradeoffs between rates of communication; it is between the rates of users from different MACs and among rates of users belonging to the same MAC. Result shows two tradeoffs are homogeneous.
The Capillary-Centric Model of Coupling-As-Thermodynamics
(North Dakota State University, 2015) Taylor, Andrew James David
Models of ventricular-arterial coupling (VAC) have historically described the heart as a function of its energetic interaction with the arterial system. However, these models either represent the dynamic, adaptive cardiovascular system (CVS) in isolation or sacrifice cardiac mechanics to use simplified, time-averaged values across the cardiac cycle. In this thesis a facsimile CVS is constructed that characterizes ventricular-arterial interactions with intact cardiac mechanics as a function of whole-body thermo-fluid homeostatic regulation. Simulation results indicate proportional-integral (PI) control of heart rate and arterial resistance is conditionally sufficient to maintain body temperature during square-wave exercise, but further elements may be required to mimic genuine physiological responses. These simulations of the primitive model lay the framework of capillary-centric VAC through the perspective of coupling-as-thermodynamics.
CMOS Phase Shifter for Conformal Phased Array Beamformer Applications
(North Dakota State University, 2015) Sanyal, Alarka
A vector modulator based phase shifter is developed using 0.18um CMOS process at S-band frequency to be integrated into a conformal phased array antenna to recover the desired radiation pattern in the entire 360° range. The phase shifter has a variable gain amplifier integrated into the circuit in order to vary gain along with phase for precise control to correct the degraded radiation pattern due to the conformal shaping. The results show state-of-the-art performances including more than 7dB conversion gain with variable feature, a continuous phase rotation of 360° with steps as low as 11.25° and very low power consumption of 17mW, for the first time to the best of the authors’ knowledge. The chip size including all pads is 1.5mm X 0.75mm.
Content Dissemination Schemes for Mobile Clouds: Modeling, Analysis, and Verification
(North Dakota State University, 2014) Ghosh, Ankan
In this work, we capitalize on our previous work on the Hybrid Scheme for Message Replication (HSM) for opportunistic networks, to develop two content dissemination schemes for mobile clouds, namely, the Forecast and Relay (FAR) and Utility-Based Scheme (UBS). Simulation results with synthetic mobility models validate that the proposed schemes outperform existing routing strategies, such as the PRoPHET, Epidemic, Random, and Wave. We have exploited High-Level Petri Nets to model and analyze the communication processes encompassing HSM, FAR, and UBS. The UBS has been conceived to overcome a crucial design limitation of HSM and FAR, made evident through formal analysis. We have used the New Symbolic Model Verifier (NuSMV) to verify the three schemes against the identified limitation, by using optimization techniques. The verification results affirm the correctness and scalability of the models. The work corroborates that formal verification can be leveraged to design newer and efficient content dissemination schemes.
A Corrective Strategy for Voltage Regulation in Distribution Grids with Plug-in Hybrid Electric Vehicles
(North Dakota State University, 2013) Sharma, Anushree
The increasing integration of Plug-in Hybrid Electric Vehicles (PHEV) poses unique challenges for voltage and frequency regulation in electric distribution grids. The mobility and variability due to PHEV loads exacerbates the problem of voltage regulation in distribution grids that are characterized by high R/X ratios. Numerous studies have explored the impact of PHEV integration on distribution grids, corrective strategies have been mainly limited to designing constrained charging profiles. This thesis examines the effect of different charging profiles and then presents a corrective strategy for voltage regulation in distribution grids without specifically constraining a user's charging profile. The proposed scheme is based on reactive power management, utilizing voltage sensitivity analysis. The compensatory scheme calculates reactive (or active when available) power injection for a bus to ensure voltage regulation at the charging bus. Simulations on the IEEE-13 bus for the scheme provides significant improvements (up to 9 %) in voltage profiles.
Damping Interarea Oscillations in Power Systems with DFIG
(North Dakota State University, 2011) Thapa, Ravi Chandra
With rapid depletion of fossil fuels and increasing environmental concerns, the trend to capture renewable energy, especially through wind energy resources, is increasing. The doubly fed induction generator (DFIG) is the most widely used generator for wind energy conversion because of its various advantages over other types of generators. In a DFIG, the rotor is fed through back to back converters via slip rings. The converters enable the generation control. This control property can be used to support reliable operation of a grid network system. Interarea oscillation has been a major factor in limiting power transfers in interconnected power systems. Poorly damped modes can trigger oscillatory instability, potentially leading to cascading blackouts in such systems. We consider a two-area system where DFIG based wind generation is integrated with conventional synchronous generators. A simple controller is proposed for the DFIG to improve damping of interarca oscillations. To support the proposition, case studies are conducted in Matlab/Simulink. The effectiveness of the proposed controller is then analyzed by eigenvalue analysis and verified with time domain simulation results. The results show that a properly tuned controller can increase the damping of dominant oscillatory mode by nearly 5% while improving the area transfer by about 200 MW of wind power. The results further show that with the proposed control strategy, damping of dominant oscillatory mode increased by more than 10%.
Dc'sign of Piezoelectric Energy Harvesting and Supercnpacitor Charging Circuits Using Optimized Duty-Cycle of Buck Converter
(North Dakota State University, 2009) Zhao, Zhou
Energy harvesting has been proved to be an innovative solution to replace the batteries in remote power supply applications. Unfortunately, the limited capacity aucl low efficiency of power conversion restrict the practical applications of energy harvesting in daily-life. After a systematic review of research on energy harvesting iu power management perspective, a circuit design, which targets low-frequency mechanical vibrations, is presented. With the classical piezoelectric cantilever setup, the maximum charging current of a supercapacitor can be obtained by optimizing the duty-cycle of a buck converter through software implemented pulse width modulation. The results of experiments prove the capacitive electric model of the piezoelectric element, the existence of maximum charging current of the supercapacitor, and the adaptive control of the designed circuits. With the duty-cycle optimized to 2.17%, a maximum charging current of 17.36 mA is measured, which is approximately 4 times that obtained in related researches. An active radio frequency identification (RFID) application is proposed to utilize the harvested power of 67.2 µW. In addition, the digital design in field programmable gate array (FPGA) is integrated using AMIS 0.5 µrn CMOS process technology to reduce system power dissipation.
The Design and Analysis of a Conformal Spiral Antenna Structure for an Ultra-Wide-Band Radar System
(North Dakota State University, 2016) Schuette, David Benjamin
This thesis explores the design, simulation, and analysis of two conformal spiral antenna structures that are used for an ultra-wide-band (UWB) bistatic radar. The radar antenna system operates over a frequency range from 0.9 GHz to 6.5 GHz. The UWB spiral antenna was initially derived for a planar substrate, then conformed to the spherical embodiment. A microstrip tapered balun feed structure was designed to provide a balanced signal from the radar to the antennas. This work focuses on how well the newly designed antenna system compares to the radar kit's pro- vided planar bow-tie antennas. In particular, the comparisons between simulations and prototype measurements are presented. It is shown that a spiral antenna and structure can be conformed to a 127.0 mm diameter sphere and have little e ect on the radar's performance when compared to a larger planar bow-tie antenna design.
The Design and Analysis of a Microstrip Line Which Utilizes Capacitive Gaps and Magnetic Responsive Particles to Vary the Reactance of the Surface Impedance
(North Dakota State University, 2019) Cleveland, Jerika Dawn
This thesis presents the work of using magnetic responsive particles as a method to manipulate the surface impedance reactance of a microstrip line containing uniform capacitive gaps and cavities containing the particles. In order to determine the transmission line’s surface impedances created by each gap and particle containing cavities, a sub-unit cell that centers the gap and cavities was used. Shown in simulation, the magnetic responsive particles can then be manipulated to increase or decrease the reactance of the surface impedance based on the strength of the magnetic field present. The sub-unit cell with the greatest reactance change was then implemented into a unit cell, which is a cascade of sub-unit cells. This unit cell design was simulated, milled and tested to determine the response a unit cell should see based on extreme states of the particles represented by copper vias and open air cavities.
Design of a Reconfigurable Pulsed Quad-Cell for Cellular-Automata-Based Conformal Computing
(North Dakota State University, 2011) Tan, Zhou
This paper presents the design of a reconfigurable asynchronous unit, called the pulsed quad-cell (PQ-cell), for conformal computing. The conformal computing vision is to create computational materials that can conform to the physical and computational needs of an application. PQ-cells, like cellular automata, are assembled into arrays with nearest neighbor communication and are capable of general computation. They operate asynchronously to minimize power consumption and to allow sealing without the limitations imposed by a global clock. Cell operations are stimulated by pulses which use two wires to encode a data bit. Cells are individually reconfirgurable to perform logic, move and store information, and coordinate parallel activity. The PQ-cell design targets a 0.25 μm CMOS technology. Simulation results show that a PQ-cell, when pulsed at 1.3 GHz, consumes 16.9 pJ per operation. Examples of self-timed multi-cell structures include a 98 MHz ring oscillator and a 385 MHz pipeline.
Design of High Power Density Switched Capacitor DC-DC Converter
(North Dakota State University, 2017) Curuvija, Boris
Design and implementation of high power density and high efficiency dc-dc converters has been a primary component for reducing energy cost. Traditionally dc-dc converters are composed with silicon based technology that has limited switching frequency hence, increased volume of passive components and lower efficiency. This research presents a novel type of multilevel modular switched capacitor dc-dc converters with comprehensive design and multiple variant prototypes. Previous versions of traditional multilevel modular switched-capacitor dc-dc converters have a low switching device voltage rating. Additionally, the proposed circuits share all the advantages from the multilevel modular switched capacitor type converters such as soft switching, low voltage device rating, bidirectional operation, high conversion ratio, extremely high or low environment temperature operation, basic control algorithm, and modular structure. The converters in this research are found to be superior due to the simple structure, soft switching, and low conduction loss and, 97% or higher efficiency.
Designing of a Small Wearable Conformal Phased Array Antenna for Wireless Communications
(North Dakota State University, 2012) Roy, Sayan
In this thesis, a unique design of a self-adapting conformal phased-array antenna system for wireless communications is presented. The antenna system is comprised of one microstrip antenna array and a sensor circuit. A 1x4 printed microstrip patch antenna array was designed on a flexible substrate with a resonant frequency of 2.47 GHz. However, the performance of the antenna starts to degrade as the curvature of the surface of the substrate changes. To recover the performance of the system, a flexible sensor circuitry was designed. This sensor circuitry uses analog phase shifters, a flexible resistor and operational-amplifier circuitry to compensate the phase of each array element of the antenna. The proposed analytical method for phase compensation has been first verified by designing an RF test platform consisting of a microstrip antenna array, commercially available analog phase shifters, analog voltage attenuators, 4-port power dividers and amplifiers. The platform can be operated through a LabVIEW GUI interface using a 12-bit digital-to-analog converter. This test board was used to design and calibrate the sensor circuitry by observing the behavior of the antenna array system on surfaces with different curvatures. In particular, this phased array antenna system was designed to be used on the surface of a spacesuit or any other flexible prototype. This work was supported in part by the Defense Miroelectronics Activity (DMEA), NASA ND EPSCoR and DARPA/MTO.
A Dual-Band Antenna Enabled Using a Complimentory Split Ring Resonator (CSRR) Placed in the Ground Plane
(North Dakota State University, 2019) Ge, Ruisi
The microstrip patch antenna is regarded as one of the key components for compact, low cost RF communications and wireless power techniques. In some instances, there are requirements that a system communicate on a different band than the wireless power harvesting band. To address these multi-frequency, a novel dual-band patch antenna enabled with complementary split ring resonators (CSRRs) is designed and fabricated. This antenna operates at 2.4Ghz and 915 MHz, and the antenna miniaturization is achieved by etching the complementary split ring resonators (CSRRs) in the ground plane. A prototype antenna is fabricated and tested, and measured results are in good agreement with simulations. Furthermore, the influence of the CSRR on the behavior of the antenna is also explored and discussed.

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Browsing Electrical & Computer Engineering Masters Theses by browse.metadata.department "Electrical and Computer Engineering"