Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
46 results
Search Results
Item MONTE CARLO SIMULATIONS OF BRILLOUIN SCATTERING IN TURBID MEDIA(2023) Lashley, Stephanie; Chembo, Yanne K; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Brillouin microscopy is a non-invasive, label-free optical elastography method for measuring mechanical properties of cells. It provides information on the longitudinal modulus and viscosity of a medium, which can be indicators of traumatic brain injury, cancerous tumors, or fibrosis. All optical techniques face difficulties imaging turbid media, and Monte Carlo simulations are considered the gold-standard to model these scenarios. Brillouin microscopy adds a unique challenge to this problem due to the angular dependence of the scattering event. This thesis extends a traditional Monte Carlo simulation software by adding the capability to simulate Brillouin scattering in turbid media, which provides a method to test strategies to mitigate the effects of multiple elastic scattering without the time and cost associated with physical experiments. Experimental results have shown potential methods to alleviate the problems caused by multiple elastic scattering, and this thesis will verify the simulation results against the experimental findings.Item Wave Chaos Studies and The Realization of Photonic Topological Insulators(2022) Xiao, Bo; Anlage, Steven; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wave propagation in various complex media is an interesting and practical field that has a huge impact in our daily life. Two common types of wave propagation are examined in this thesis: electromagnetic wave propagation in complex wave chaotic enclosures, where I studied its statistical properties and explored time-domain pulse focusing, and unidirectional edge modes propagating in a reciprocal photonic topological insulator waveguide. Several theories, e.g. the Random Matrix Theory and the Random Coupling Model, have been developed and validated in experiments to understand the statistical properties of the electromagnetic waves inside wave chaotic enclosures. This thesis extends the subject from a single cavity to a network of coupled cavities by creating an innovative experimental setup that scales down complex structures, which would otherwise be too large and cumbersome to study, to a miniature version that retains its original electromagnetic properties. The process involves shrinking down the metal cavity in size by a factor of 20, increasing the electromagnetic wave frequency by the same factor and cooling down the cavity by a dilution refrigerator to reduce its ohmic loss. This experimental setup is validated by comparison with results from a full-scale setup with a single cavity and it is then extended for multiple coupled cavities. In the time domain, I utilized the time-reversal mirror technique to focus electromagnetic waves at an arbitrary location inside a wave chaotic enclosure by injecting a numerically calculated wave excitation signal. I used a semi-classical ray algorithm to calculate the signal that would be received at a transceiver port resulting from the injection of a short pulse at the desired target location. The time-reversed version of this signal is then injected into the transceiver port and an approximate reconstruction of the short pulse is observed at the target port. Photonic topological insulators are an interesting class of materials whose photonic band structure can have a bandgap in the bulk while supporting topologically protected unidirectional edge modes. This thesis presents a rotating magnetic dipole antenna, composed of two perpendicularly oriented coils fed with variable phase difference, that can efficiently excite the unidirectional topologically protected surface waves in the bianisotropic metawaveguide (BMW) structure recently realized by Ma, et al., despite the fact that the BMW medium does not break time-reversal invariance. In addition to achieving high directivity, the antenna can be tuned continuously to excite reflectionless edge modes to the two opposite directions with various amplitude ratios. Overall, this thesis establishes the foundation for further studies of the universal statistical properties of wave chaotic enclosures, and tested the limits of its deterministic properties defined by the cavity geometry. It also demonstrated in experiment the excitation of a unidirectional edge mode in a Bianisotropic Meta-waveguide, allowing for novel applications in the field of communications, for example phased array antennas.Item WAVE SCATTERING PROPERTIES IN COMPLEX SCATTERING SYSTEMS: ZEROS AND POLES OF THE SCATTERING MATRIX(2022) Chen, Lei; Anlage, Steven M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wave scattering properties in complex scattering systems have been of great interest to both the physics and engineering communities because of their useful characterizations of such systems and significant value for applications. The most common tool for studying such properties – the scattering (S)-matrix, can be fully represented by its zeros and poles in the complex energy/frequency plane. There has been substantial effort to understand the scattering properties and wave phenomena inside complex systems in the past, both theoretical and experimental, which in turn has led to significant advancement in many applications: wavefront shaping (WFS), coherent perfect absorption (CPA), wireless power transfer, electromagnetic interference (EMI), etc. In this dissertation, I will summarize the recent progress and interest regarding an intriguing wave phenomenon – coherent perfect absorption (CPA) in complex scattering systems. We have successfully implemented CPA protocols in generic complex scattering systems without any geometric or hidden symmetries, which greatly extends CPA beyond its initial concept as the time-reversal of a laser cavity. Under such efforts, we have also established a convenient approach for control of the local losses inside the network system, which helped us to uncover the mystery of matching the imaginary part of the S-matrix zero to the uniform loss of the system. We thus developed the theoretical representation of the S-matrix by its zeros and poles, and generalized the traditional Wigner time delay to a complex quantity in sub-unitary scattering systems. We have revealed the inherent connection between the complex Wigner time delay and coherent perfect absorption, and can utilize the new complex Wigner time delay idea for extracting S-matrix zeros and poles in a practical system. We have also studied the statistical properties of the complex generalization of Wigner time delay for subunitary wave-chaotic scattering systems, and demonstrated excellent agreement between theory and experiments. Finally, we have extended this scheme to a comprehensive time delay analysis framework, including Wigner, transmission, and reflection time delays. This approach offers us the capability to systematically analyze the poles and zeros of the scattering matrix of any complex scattering system. We then apply the new transmission time delay method on a two-channel microwave graph realization of the Aharonov--Bohm ring from mesoscopic physics, and demonstrate the dependence of non-reciprocal transport behavior on the de-phasing rate. The ultimate goal is to completely control the scattering properties of complex systems by manipulating the zeros and poles of the S-matrix, for example by adding losses in the system or changing the coupling of the scattering channels, etc. Such a capability will be extremely useful for understanding the wave properties of complex scattering systems, and for controlling the wave behavior in optics, electromagnetics, acoustics, quantum transport in condensed matter systems, etc.Item Electromagnetic Characterization of Misaligned Serpentine Waveguide Structures in Traveling-Wave Tubes at Microwave Frequencies(2022) Kuhn, Kyle; Antonsen, Jr., Thomas M; Beaudoin, Brian L; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Modern-day millimeter and microwave source technology has advanced considerably over the past century, but to meet the defense industry’s demand for high power and large bandwidth, vacuum electronic devices (VEDs) are still the ideal candidate to fulfill such requirements as opposed to their solid-state semiconductor counterparts. Of the numerous VEDs available, the traveling-wave tube (TWT) amplifier provides novel solutions in areas where size, weight, and power (SWaP), and bandwidth are of great importance such as on satellites and in electronic warfare applications. The advancement in computer-aided design (CAD) and simulation has allowed for increasingly complicated device configurations to be designed with ease. Instead, challenges arise in fabrication as extremely tight manufacturing tolerances on the order of micron to submicron levels are necessary due to the very short wavelengths in the mm-wave and sub-mm-wave regimes. Without this level of manufacturing precision, VEDs will not operate at optimal levels in power, bandwidth, and efficiency. We present a serpentine waveguide (SWG) design to be used as the slow-wave structure (SWS) in a TWT amplifier. Manufacturing techniques for the design are discussed, and a detailed study into how one-dimensional and two dimensional misalignments in the circuit’s half-plane affect the radio frequency (RF) signal that propagates through the device. Figures of merit include the device’s reflected power, or S11, the transmitted power through the SWG, or S21, the device’s cutoff frequency, and the SWG’s dispersion curves. Computer simulations using Ansys’s High Frequency Structure Simulator, or HFSS, and cold test laboratory measurements for aligned and misaligned Ka-band (26.5 GHz – 40 GHz) SWG circuits are presented. Upon completing a thorough RF characterization of the Ka-band device, efforts will shift focus to designing a SWG circuit for a W-band (75 GHz – 110 GHz) TWT amplifier prototype.Item MATERIALS CHARACTERIZATION FOR SUB-MICRON SUPERCONDUCTING INTERCONNECTS IN RECIPROCAL QUANTUM LOGIC CIRCUITS(2022) Garcia, Cougar Alessandro Tomas; Anlage, Steven M; Talanov, Vladimir V; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Today's server based computing consumes a considerable amount of energy.Reciprocal Quantum Logic (RQL) is a classical logic family within superconducting electronics, and is a candidate for energy efficient computing technologies. Similar to the current complimentary metal-oxide semiconductor technologies, RQL interconnects are responsible for dissipating the majority of the energy. The energy dissipated in RQL interconnects comes from finite resistive losses in the superconducting wires and embedded dielectrics at radio frequencies. Therefore, material properties, processing, and performance are critical to understanding the mechanisms of loss and mitigation of power dissipation in RQL interconnects. This dissertation presents work on three aspects of materials characterization of RQL interconnects: implementing a method to deconvolve superconducting and dielectric losses, evaluating losses in three generations of RQL fabrication, and understanding the microscopic physics that determines the performance of RQL interconnects in a temperature and frequency range from 1.5-6 K and 3-12 GHz, respectively. A novel method to accurately deconvolve superconducting and dielectric losses by exploiting their frequency dependence is described. Furthermore, a finite element modeler is used to accurately extract the losses. This method is termed Dispersive Loss Deconvolution. The designed microstrip transmission line resonators are fabricated in a 0.25 $\mu m$ RQL fabrication process composed of Nb wires embedded in Tetraethyl orthosilicate (TEOS) dielectric. The Nb and TEOS losses as a function of microstrip width down to 0.25 $\mu m$ are modeled and measured. The electrical and physical material properties for 3 RQL processes over 5 wafers are evaluated.The electrical properties were evaluated by characterizing resonators in cryogenic dip probes and a dry system with $\pm 10 \: mK$ temperature control. The physical properties were evaluated using Transmission Electron Microscopy and Energy-Dispersive Spectroscopy. Two of the processes use chemical mechanical polishing (CMP) to planarize the Nb wires, and the other using reactive ion etching (RIE) to define Nb wires. At 4.2 K, the Nb loss in the 0.25 $\mu m$ resonators between the 3 processes were surprisingly distinct. The two CMP processes yield Nb losses up to 2 times higher relative to the RIE process, and have a discernible increase in loss by as much as 20\% going from 4 to 0.25 $\mu m$ microstrip widths. For the RIE process, there is no detectable upturn in Nb losses for microstrip widths down to 0.25 $\mu m$. Most notably, the RIE process produced 0.25 $\mu m$ Nb wires with loss reaching the theoretical lower limit of intrinsic surface resistance $R_s = 17 \: \mu \Omega$ at 4.2 K and 10 GHz. The superior RIE process may be linked to the incorporation of thin metal passivation layers protecting the Nb, which prevented Nb oxide from participating in additional loss mechanisms. %The CMP processes had detectable Ar concentrations in the Nb up to 1 $at\%$ most likely due to the trench filling process. For all 3 processes and microstrip widths from 0.25-4 $\mu m$, the TEOS losses had negligible width dependence and varied by as much as $\pm 20\%$. From the electrical characterization at 4.2 K, it was found that the Nb wires are the limiting loss mechanisms in RQL interconnects. As temperature is decreased below 4.2 K, it is well known that Nb loss will exponentially decrease and amorphous dielectrics like TEOS can have loss with a non-monotonic temperature dependence depending on the input power. This offered the opportunity to explore a possible optimum operating temperature to minimize power dissipation by the RQL interconnects. At relatively low input powers, TEOS became the limiting loss mechanism for temperatures below 3 K, and I conclude this can be attributed to losses coming from two-level system tunneling relaxation and resonant absorption processes. %Estimates of peak currents and voltages are used to %A loss spectroscopy method is presented as a tool to The work in this dissertation describes the development of methods to aid in characterization, design, and fabrication of RQL interconnects, and can be extended to potentially other Single Flux Quantum and Quantum Computing technologies.Item Wavefront Shaping in a Complex Reverberant Environment with a Binary Tunable Metasurface(2021) Frazier, Benjamin West; Antonsen, Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electromagnetic environments are becoming increasingly complex and congested, creating a growing challenge for systems that rely on electromagnetic waves for communication, sensing, or imaging. The use of intelligent, reconfigurable metasurfaces provides a potential means for achieving a radio environment that is capable of directing propagating waves to optimize wireless channels on-demand, ensuring reliable operation and protecting sensitive electronic components. The capability to isolate or reject unwanted signals in order to mitigate vulnerabilities is critical for any practical application. In the first part of this dissertation, I describe the use of a binary programmable metasurface to (i) control the spatial degrees of freedom for waves propagating inside an electromagnetic cavity and demonstrate the ability to create nulls in the transmission coefficient between selected ports; and (ii) create the conditions for coherent perfect absorption. Both objectives are performed at arbitrary frequencies. In the first case a novel and effective stochastic optimization algorithm is presented that selectively generates coldspots over a single frequency band or simultaneously over multiple frequency bands. I show that this algorithm is successful with multiple input port configurations and varying optimization bandwidths. In the second case I establish how this technique can be used to establish a multi-port coherent perfect absorption state for the cavity. In the second part of this dissertation, I introduce a technique that combines a deep learning network with a binary programmable metasurface to shape waves in complex electromagnetic environments, in particular ones where there is no direct line-of-sight. I applied this technique for wavefront reconstruction and accurately determined metasurface configurations based on measured system scattering responses in a chaotic microwave cavity. The state of the metasurface that realizes desired electromagnetic wave field distribution properties was successfully determined even in cases previously unseen by the deep learning algorithm. My technique is enabled by the reverberant nature of the cavity, and is effective with a metasurface that covers only ~1.5% of the total cavity surface area.Item GaN-based High-Frequency Isolated Single-Stage AC-DC Converters for More Electric Aircrafts(2021) Singh, Akshay; Khaligh, Alireza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There has been an increased focus on the electrification of aircrafts, with the objective of improving overall system efficiency, weight and reliability. Power electronics is a key enabling technology for this transition, and there is a greater emphasis on the design of lightweight and efficient power electronic interfaces. Traditionally, the generation of the low-voltage 28 V DC bus from the high voltage variable frequency output of the turbine generators has been performed using passive diode-bridge rectifier systems, known as transformer rectifier units (TRU). Compared to active power electronic interfaces, TRUs have higher weight, lower efficiency, and inferior voltage regulation. This work proposes an active power electronic converter architecture to replace the TRU, referred to as the Regulated Transformer Rectifier Unit (RTRU). The proposed RTRU converter topology and control are specifically formulated to harness the advantages of wide-bandgap Gallium Nitride (GaN) power transistors. The system comprises three modular single-stage high step-down isolated AC-DC converters based on the Dual Active Bridge (DAB) circuit. The modular design allows for improved failure-tolerant operation, resulting in increased overall reliability which is critical for aircraft applications. The proposed DAB AC-DC converter achieves the functions of power factor correction and isolated voltage step-down with soft switching in a single power stage, thus eliminating the bulky intermediate DC-link capacitor typically associated with two-stage converter topologies. Furthermore, the three-phase converter architecture allows for automatic pulsating power cancellation at the output DC port. In the first part of this work, the suitability of the single-stage converter topology for a modular RTRU architecture is established through a comprehensive analytical comparison framework that considers the volume and efficiency tradeoffs for all passive components, including heat sinks. On the modeling aspect, the steady-state operation of the DAB AC-DC converter can show a high dependence on the circuit non-idealities and on the transient nature of the consistently changing phase shifts necessary to achieve AC-DC operation. These aspects are not fully captured using traditional modeling approaches derived for the DC-DC DAB converter. To address these issues, an improved unified modeling approach is presented – comprising of hybrid frequency and time-domain analyses that encompass the transient nature of the AC-DC converter while providing the advantages of highly generalized steady-state frequency-domain analysis. The proposed modeling approach demonstrates a significant reduction in modeling inaccuracies, which in turn lead to more accurate tracking of optimal operating points (i.e. higher efficiency) and improved power quality. In the second part of this work, the low passive component requirement of the single-stage topology is harnessed to develop a power-dense converter design featuring a compact, high-efficiency planar integrated magnetic structure with adjustable leakage inductance. The detailed modeling, design, and optimization of the planar magnetics are presented, with a special focus on unique PCB winding layouts to achieve low AC resistance in high step-down high-current applications. Moreover, the use of paralleled GaN transistors in high current applications presents several challenges with regards to current sharing and conduction loss optimization, which are addressed by a new design approach presented in this work, that leads to optimized layouts with low parasitics. Lastly, a holistic design process is formulated to analytically estimate the differential-mode (DM) conducted emissions in a DAB AC-DC converter, which is then coupled with a multi-objective EMI filter optimization algorithm to minimize the DM EMI filter weight and converter losses. Through these improvements, the developed hardware prototype achieves a 40% higher power density than the existing state-of-the-art. In the third part of this work, the proposed modeling approach is combined with a numerical optimization routine is proposed to find the optimal-conduction-loss modulation trajectories. A hybrid closed-loop control method with offline-generated feedforward lookup tables is subsequently realized for optimal loss tracking over the entire operation range, while satisfying the stringent transient operating requirements for airborne equipment. The implementation of the closed-loop control for the multi-phase modular RTRU with variable input frequency and variable switching frequency is carried out on a single microcontroller with parallelized execution. Finally, to verify the modeling, design, optimizations, and control methods, a 5 kW 230 V – 28 V fully-GaN based RTRU is developed as a hardware proof-of-concept, which achieves a peak efficiency of 96.8% and a power density of 1.2 kW/L, and satisfies the power quality and transient requirements for airborne equipment.Item WAVE CHAOS STUDIES FOR TWO-DIMENSIONAL CAVITIES USING THE RANDOM COUPLING MODEL (RCM) AND OTHER HIGH FREQUENCY METHODS(2021) Adnan, Farasatul; Antonsen, Thomas; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wave coupling within systems with irregular boundaries is a common phenomenon in many branches of science such as acoustics, vibrations, electromagnetics, and others. If the wavelength of the incident wave is small compared with the structure size, and the dynamics of the ray trajectories within the scattering region are chaotic, the scattering properties of the cavity will be extremely sensitive to small perturbations. These structures are then termed wave chaotic. Exact solutions of such systems are not feasible and various alternative methods are sought. In the first part of this dissertation, such alternative methods are used to calculate the power delivered to a port in a two-dimensional wave chaotic enclosure. These methods are the ray tracing (RT), the Dynamical Energy Analysis (DEA) and the Power Balance methods (PWB). Particularly, the RT and DEA are used to calculate power received at an aperture and are compared with the established PWB. These results indicate that the RT and DEA are equivalent methods. Additionally, RT is compared with direct numerical simulations of the wave fields and found to be accurate if the wavelength is sufficiently small. The Random Coupling Model (RCM) gives a statistical description of coupling of radiation in and out of large enclosures through localized and/or distributed ports. The RCM, in contrast to DEA, PWB, and standard RT, includes both amplitude and phase information. It combines both deterministic and statistical information and makes use of wave chaos theory to extend the classical modal description of the cavity fields in the presence of boundaries that lead to chaotic ray trajectories. In the second part of this dissertation, a correction to the RCM termed the Short Orbit Formulation (SOF) is used to calculate successfully the impedance of a two-port wave chaotic enclosure in two dimensions using RT. Also, a directed beam approach was used to launch energy in a wave chaotic enclosure to break the so called 'random plane wave hypothesis', a fundamental basis of the RCM formulations. Results show that launching of such directed beams lead to enhanced short orbit effects which make the RCM inapplicable.Item Highly Efficient, Megawatt Class RF Power Sources for Mobile Ionospheric Heaters(2020) Appanam Karakkad, Jayakrishnan Appanam; Antonsen Jr., Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we consider the development of a highly efficient, grid-less tetrode as a megawatt-level RF source in the 3 to 10 MHz range for application in a mobile ionospheric heater. Such a heater has potential advantages over the stationary facilities, such as HAARP (High-Frequency Active Auroral Research Program), found at high latitude. The considered device operates in class D mode with an annular electron beam allowing realization of high efficiency. The beam current is controlled using an annular modulating electrode (mod-anode) placed around the annular emitter on the cathode. This feature removes the traditional semi-transparent grid and the problems associated with interception of current beam at the grid. Three different device configurations based on differing magnetic field confinement were considered. Model A, which has a constant focusing magnetic field and no beam compression, offers the highest interaction efficiency. However, to generate a uniform and constant magnetic field over the whole device length would require the use of a large and bulky solenoid. This makes the setup in the case of Model A much larger (and much heavier). Model B has a magnetic field that is up-tapered from the cathode towards the anode and collector where the bulk part of the solenoid is located. This configuration retains the compression of the electron beam to maintain a high efficiency while keeping the size of the device manageable. It has a lower efficiency than Model A, but it provides a larger cathode area in than in Model A which mitigates cathode loading. In the case of Model C, there no guiding magnetic field and is the most compact, but its interaction efficiency is the lowest among the three device types. Model C also uses two modulating anodes maintained at varying voltages to provide electrostatic focusing of the electron beam. It is still operated in the class D regime by switching the two mod-anodes of Model C on and off together. However, the voltage swing will be much larger compared to Model A. A theoretical analysis to find the optimal operating point for model A is presented. In particular, the trade-off between the peak current and the duration of the current pulse is analyzed. The beam distributions in axial and transverse momenta and in total electron energies, before and after the decelerating gap, calculated using the Michelle code are presented for Model A. Using static-case Michelle simulation results, the instantaneous and average device efficiencies of the three models were maximized while reducing the device size by studying the influence of electrode geometry (Anode-Cathode Gap, and Anode-Collector gap and shapes) on the device efficiency. After optimizing the device geometry for these three different models, time-domain simulations with secondary electrons were performed. For model A, it is found that during the portion of the RF cycle when the beam current is on, secondaries emitted from the collector are driven back into the collector by the incoming primary beam. When the beam is switched off, secondaries can stream back into the tetrode and have a small negative impact on efficiency. We present a design in which the secondary electrons are eventually absorbed at the collector, rather than at the cathode or anode. For model B, most of the secondary electrons are trapped in the collecting region due to an effect called magnetic mirroring from the up tapering of the magnetic field towards the collector region. In Model C, the secondary electrons are largely scattered throughout the tetrode due to the lack of magnetic field confinement making it much harder to prevent the loss of efficiency. In short, three different versions of the grid-less tetrode have been proposed and studied. The optimized version of these devices have efficiencies ranging from 81% to 91.5%. The choice of the optimal design for real systems may depend on a number of tradeoffs. In the situations where the weight and size of a system play a crucial role, Model C could be more preferable with the penalty of lower efficiency. In turn, Model A can offer the highest efficiency, but the solenoids required for maintaining a constant magnetic field along the entire device could be very heavy and bulky. In comparison, Model B offers a middle ground among the three models on compactness and efficiency.Item A HIGHLY EFFICIENT, MEGAWATT CLASS CONSTANT IMPEDANCE TUNABLE POWER EXTRACTION CIRCUIT FOR MOBILE IONOSPHERIC HEATERS(2020) Narayan, Amith Hulikal; Antonsen Jr, Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ionospheric modification (IM) refers to changes in the ambient properties of the ionosphere that are produced by humans. The ability to control and exploit ionospheric processes helps us understand naturally occurring phenomena like aurora, scintillations, and airglow. It also helps us improve trans-ionospheric communication and develop new applications that take advantage of the ionosphere as an active plasma medium. Ionospheric Heaters broadcast high power radio waves, typically in the radio frequency (RF) band, to modify the ionosphere in a controlled manner. These facilities are permanent terrestrial installations and do not presently support study at different latitudes. However, past IM experiments conducted at high latitudes across the world indicate a strong dependence of ionospheric processes on the geomagnetic latitude. Mobile Ionospheric Heaters will allow for the first time, quantitative exploration of the ionosphere at different geomagnetic latitudes. These mobile structures must be relatively smaller the the existing arrays (small enough to fit on the barge of a ship) and highly efficient at the same time. The size and efficiency of the terrestrial heating units prevent their reuse in mobile structures. These factors motivate the need for developing novel heater units. Our research focused on a new high power, high-efficiency RF source that consists of a gridless tetrode RF tube and a highly efficient power extraction circuit. My research addresses the characterization and optimization of the power extraction circuit. The power extraction circuit in the RF device under study converts the kinetic energy of a temporally modulated electron beam into electromagnetic energy. The beam is collected on an electrode surface and the resulting current is passed through the circuit. The circuit generates a potential in response to the current, and that potential is used to decelerate the beam. The circuit must be tunable to cover the desired broad frequency range (3 - 10 MHz), and the decelerating voltage should be independent of frequency to maintain high efficiency. In this relatively low frequency range lumped element circuits are considered instead of cavities given the size limitations imposed. To achieve high power a high voltage beam is required. Consequently, matching the relatively high electron beam impedance (5 kΩ) to the load antenna (50 Ω) creates situations where high Q resonant circuits are necessary to achieve the high efficiencies required. We design a pi-circuit to achieve the impedance matching and validate the design experimentally. Although experiments validate our design, measured efficiencies are too low because of parasitics in the circuit elements. The parasitics include the proximity effect and self-resonance in the elements. We model these effects that enhance the losses and limit the efficiency of the circuit. Our research finds that the impedance transformation from beam to load (two orders of magnitude) imposes severe restrictions on single-stage design. Additionally, measurements of high Q components aren’t very reliable at higher frequencies. We propose a two-stage power extraction circuit that resolves both of these problems. Simulation results show a circuit design that is expected to yield the desired efficiency. The findings from the research in this thesis would help in the eventual construction and testing of the MW RF heating system that would facilitate a mobile heater for IM research in the future.