Electrical & Computer Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2765
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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 An Integrated Photonic Platform For Quantum Information Processing(2021) Dutta, Subhojit; Waks, Edo EW; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quantum photonics provides a powerful toolbox with vast applications ranging from quantum simulation, photonic information processing, all optical universal quantum computation, secure quantum internet as well as quantum enhanced sensing. Many of these applications require the integration of several complex optical elements and material systems which pose a challenge to scalability. It is essential to integrate linear and non-linear photonics on a chip to tackle this issue leading to more compact, high bandwidth devices. In this thesis we demonstrate a pathway to achieving several components in the quantum photonic toolbox on the same integrated photonic platform. We focus particularly on two of the more nontrivial components, a single photon source and an integrated quantum light-matter interface. We address the problem of a scalable, chip integrated, fast single photon source, by using atomically thin layers of 2D materials interfaced with plasmonic waveguides. We further embark on the challenge of creating a new material system by integrating rare earth ions with the emerging commercial platform of thin film lithium niobate on insulator. Rare earth ions have found widespread use in classical and quantum information processing. However, these are traditionally doped in bulk crystals which hinder their scalability. We demonstrate an integrated photonic interface for rare earth ions in thin film lithium niobate that preserves the optical and coherence properties of the ions. This combination of rare earth ions with the chip-scale active interface of thin film lithium niobate opens a plethora of opportunities for compact optoelectronic devices. As an immediate application we demonstrate an integrated optical quantum memory with a rare earth atomic ensemble in the thin film. The new light matter interface in thin film lithium niobate acts as a key enabler in an already rich optical platform representing a significant advancement in the field of integrated quantum photonics.Item Testing and Optimization of Optical Illumination to Extract Cancer Cells from Tissue Samples(2020) Han, Chang-Mu; Waks, Edo; Shapiro, Benjamin; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study aims for mathematical modeling, experimental validation, and systematic optimization of Expression Microdissection (xMD). xMD selectively heats targeted cancer cells via a photothermal effect to enable their procurement from tumor tissue samples to provide highly pure cell populations for molecular analysis so that misdiagnoses caused by non-neoplastic cell contamination can be reduced. Several theoretical models have been validated for the photothermal effect in tissues. However, these models are not generally applicable to the physics behind the process of xMD. In this study, we proposed a mathematical model that analyzes the spatial and temporal temperature distribution and heat melt track in an xMD sample that is composed of a thermoplastic film and a tumor tissue section sandwiched by two glass slides. To experimentally validate the model, we designed and built a continuous-wave laser raster system from scratch to implement xMD on the sample in which the tissue was replaced by a tissue-mimicking phantom fabricated by spin-coating. The phantom is used to imitate the physical properties of an immunohistchemically-stained tissue, such as thickness, light absorption, and scattering, etc. Moreover, we proposed an indirect method that uses absorbance spectral slope of the xMD-treated film as temperature indicator for the sample in order to overcome the challenge of temperature measurement on a multilayered micro-scaled medium and experimentally validate the model. The result shows that the experimentally measured temperature of the phantom and melt track width on the film were in good consistency with those predicted by the model. Furthermore, based on the validated model, we systematically optimized the xMD process under realistic tissue variations for commercially-available laser raster systems, featuring two laser types (pulse v.s. continuous-wave) and two system configurations (top-down v.s. bottom-up). Specifically, we analyzed the temperature distribution of the xMD sample under three cases of the variations: (1) size of the stained cancer cell, (2) tissue section thickness, and (3) tissue stain intensity to find the optimal xMD operation space (i.e., laser intensity, scan speed, and pulse-on time) for the systems. In the optimization results, the optimal laser intensity and pulse time of the pulse xMD system for the sample variations range from 6 x 10^7 W/m^2 to 13 x 10^7 W/m^2 and from 2 ms to 10 ms, respectively. However, over-melting problem may occur when dealing with thicker tissue samples. The result suggests the pulse time of less than 0.8 ms. Similarly, for the continuous-wave xMD system, the optimal range of the intensity and speed are from 7 x 10^7 W/m^2 to 1 x 10^8 W/m^2 and from 60 mm/s to 100 mm/s, respectively. These ranges are overlapped by the specifications of the continuous-wave systems, indicating they are capable of processing the samples in real clinical practice. Furthermore, no obvious difference of the optimal range can be seen between the laser systems of the two configurations when extracting cancer cells from the thin tissues (5 um). When processing the think tissues (15 um), our simulations however show that the bottom-up pulse xMD system has better heating efficiency in tissue than the other xMD systems do, indicating it has smaller optimal operation window. Additionally, the top-down xMD system induces higher temperature on the film/tissue interface. Such result points out that the top-down xMD system can provide better xMD performance than the bottom-up system does. Our model demonstrated its validity to describe the xMD mechanism. The optimization results revealed the optimal xMD range for the varying realistic tissue samples. We anticipate the xMD model and parametric simulations enable researchers to facilitate the cell retrieval process and maximum the xMD performance without contaminating subsequent molecular profiling of cancer and other diseases so that cancer patients can receive molecular medical treatments in a timely manner.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.