L.D. Smullin. / Errata inserted. "October 24, 1949." / Bibliography: p. 9.

[by] L.A. Harris ... [et al.]. / 3665947 Archives / "January 21, 1949." / Bibliography: p. 11. / Army Signal Corps Contract No. W36-039-sc-32037 Project No. 102B Dept. of the Army Project No. 3-99-10-022

Abstract In this thesis, we propose a new geometrical structure of waveguide for the application of traveling-wave electroabsorption modulator (TWEAM). As approaching to high-speed performance in TWEAM, low parasitic capacitance in the waveguide is necessary to get good microwave propagation properties. In this work, a novel processing called two-step undercut-etching the active region (UEAR) is developed to reduce the parasitic capacitance. First of all, Beam Propagation Method (BPM) is used to calculate this 2-D structure optical modes ensuring the guiding capability in such kind of waveguides. Based on an equivalent circuit model, the microwave propagation on different structures of waveguide is then investigated to decide the UEAR waveguide structure. By the selectively etching solution on InP/InGaAsP, the processing by two-step UEAR is developed to reduce the parasitic capacitance in the waveguide core. H3PO4:HCl is used to selectively etch P-InP layer on the top of InGaAsP M.Q.W. (multiple quantum wells, active region). H3PO4:H2O2:H2O is subsequently and selectively remove InGaAsP M.Q.W.s to define the waveguide core. This processing has been successfully developed. The electrical transmission measurement on this kind of TWEAM shows low reflection S11 of < -17.5dB and a low insertion loss S21 of < ¡V2.7dB from D.C. to 40GHz, indicating high microwave performance on such two-step UEAR waveguide can be achieved due to the low parasitic capacitance.

Electro¡VAbsorption Modulator has become a very important element in optical fiber communication due to its capability of integrating with other semiconductor devices. In order to get high-speed performance, the small size of waveguides is necessary. But it also brings to high coupling loss, resulting in low optical fiber link. In general, the waveguide mode is elliptical shape with sizes of 1¡Ñ2£gm to 1¡Ñ3£gm, which will definitely lead to high mode mismatch as adapted to conventional single¡Vmode optical fibers of 8£gm circular mode and cause 7~10 dB insertion loss[21]. Typically, micro lens, tapered fibers or taper optical waveguides are used to confine optical fiber mode to waveguide in order to reduce the insertion loss. In the thesis, we have developed a novel structure of tapered optical spot-size mode converter monolithically integrated with traveling-wave electro-absorption modulator (TWEAM) by using whole wet-etching processing. The optical waveguides are fabricated by wet-etching and subsequent selective undercut etching. By adjusting the wet-etching time, the waveguide core for TWEAM and the tapered spot-size mode converter can thus be engineered. The selective undercut wet etching not only can reduce the optical scattering loss, but also decrease the parasitic capacitance, leading to high optical and microwave transmission of TWEAM. Based on the model described in literature [4-8] and also Beam Propagation Method (BPM), the optical index of epi-layers is used to calculate the three¡Vdimension modal of optical mode and coupling efficiency. The microwave equivalent circuit is used to calculate and design device structure. In this thesis, the Spot¡VSize Converter monolithically with Traveling¡VWave Electro¡VAbsorption Modulator device is successfully fabricated and demonstrated. TWEAM integrated spot-size optical mode converter is measured and compared with single TWEAM (without converter) with optical wavelength of from 1550nm to 1570nm. The average optical insertion loss of about 4dB is found. The maximum extinction-ratio is about 21dB with modulation efficiency of 21dB/V, E-O response about 12GHz of ¡V3dB bandwidth at 50£[ termination is demonstrated.

Traveling-wave semiconductor optical amplifiers¡]TWSOAs¡^of symmetric and asymmetric multiple quantum wells¡]MQWs¡^have been implemented by using angled-facet structures. The asymmetric MQWs structures are designed to increase the wavelength range of the gain spectrum. The angled-facet structures, which can suppress gain ripple from FP resonance, are of 3mm-wide and 700mm-long ridge waveguides, and of different angles¡]q¡^at 3o, 5o, 7o, and 9o. From Marcuse¡¦s model, the calculation shows that the angled-facet structures have reflectivities lower than 10-4. We have also developed a single-trench process to fabricate the angled-facet TWSOAs. The l=1.55mm asymmetric structure, which shows a low epitaxial quality of large leakage current, is not suitable for SOA application. For the l=1.3mm asymmetric structure, the threshold current¡]Ith¡^at q=0o was 22.5mA, while at q=7o the Ith increased to 45mA. We have also measured the spectrum below threshold current. The differences between FP resonance peak and valley become smaller at larger q. We estimated that the reflectivity is about 0.2 at 5o. The results show that the reflectivity was decreased by angled-facet structure.

Vacuum microwave tubes, such as klystron, traveling-wave tube, gyrotron are high efficiency devices, where the RF interaction structure facilitates efficient energy transfer from the kinetic energy of the high energy electron beam to the electromagnetic wave. Traveling-wave Tube is the most versatile microwave power amplifier widely used for terrestrial communication, radar and aerospace applications. The waveguide based slow-wave structures like Millman, Karp, inter digital, grated waveguide, ring-plane, ring-bar, millitron and folded-waveguide structure gathered importance for application in millimeter-wave traveling-wave tubes. Among these millimeter-wave interaction structures, the folded-waveguide slow-wave structure became the most popular due to its robust structure, high power capability, low RF loss, simpler coupling, reasonably wide bandwidth and ease of fabrication for millimeter-wave to terahertz frequencies. Hence this thesis aims to analyse the folded-waveguide slow-wave structure for broad-banding and efficiency enhancement. The existing approaches for the analysis of cold circuit parameters (dispersion and interaction impedance characteristics) of folded-waveguide slow-wave structure are reinvestigated and found that these have limitation, as the effects of E-plane bend and beam-hole discontinuities are ignored in the parametric analysis. A cascaded matrix equivalent circuit model includes the effect of E-plane and beam-hole discontinuities for the analysis, but reported only for the serpentine folded-waveguide slow-wave structure. The cold test measurement technique was reported only for the dispersion characteristics. Hence the measurement technique has to be extended for the measurement of interaction impedance. The author proposes to orient the present doctoral work to (i) extend the proposed cascaded transmission matrix equivalent model for the analysis of rectangular folded-waveguide slow-wave structure, (ii) develop a non-resonant perturbation technique for the measurement of interaction impedance characteristics of the folded-waveguide slow-wave structure and also to (iii) establish new analysis models for the folded-waveguide slow-wave structure. The effect of E-plane bend and beam-hole discontinuities on the RF characteristics have been considered and simple, yet accurate closed form expressions for the computation of dispersion and interaction impedance characteristics have been established by three different approaches namely: transmission line equivalent circuit model, conformal mapping equivalent circuit model and quasi-TEM approach. The analysis results are benchmarked against 3-D electromagnetic modeling. The non-resonant perturbation theory is developed for the interaction impedance measurement. Typical Ka-band structures are fabricated by wire-EDM process and cold test measurements are carried out to benchmark the analysis approaches. The equivalent circuit models based on lumped circuit model are simpler than the cascaded matrix equivalent circuit model and can give closed form expressions for the prediction of dispersion and interaction impedance characteristics. The quasi-TEM approach can be extended for the complicated structure like ridge-loaded FWG-SWS. Broad-banding of the conventional folded-waveguide slow-wave structure is attempted by ridge-loading on the broad wall of the structure. The ridge-loaded folded-waveguide slow-wave structure is analyzed by parametric approach, cascaded transmission matrix equivalent circuit model and quasi-TEM approach and validated against numerical simulation. The analysis is extended for exploring the efficacy of the ridge-loading on broad-banding of the traveling-wave tube. Finally efficiency enhancement of the folded-waveguide slow-wave structure is attempted by introducing grating on the broad wall of the structure. The analysis is carried out by numerical simulation for exploring the efficacy of the grating on efficiency enhancement of the traveling-wave tube.

Traveling wave solutions of integro-differential equations for modeling one-dimensional neuronal networks, are studied. Under moderate continuity assumptions, necessary and sufficient conditions for the existence and uniqueness of monotone increasing (decreasing) traveling wave solutions are established. Some faults in previous studies are corrected.

abstract: Scarcity of potable water is one of the major problems faced in the world today. Majority of this problem can be solved if technology is developed to obtain potable water from brackish or saline water. The present desalination methods face challenges such as high costs in terms of energy consumption and infrastructure, physical size of the system, requirement of membrane and high pressure systems and hence have been facing various issues in implementation of the same. This research provides a new low pressure, low energy, portable method to desalinate water without the need for separation membranes, heat or chemical reactions. This method is energy efficient, cost effective, compact, environment friendly and suitable for portable desalination units. This technology, named as Polyphase Alternating current Bi-Ionic Propulsion System (PACBIPS) makes use of polyphase alternating current source to create a gradient in salt concentration. The gradient in salt concentration is achieved due to the creation of a traveling wave which attracts anions on its positive peak (crests) and cations on its negative peak (troughs) and travels along a central pipe thereby flushing the ions down. Another method of PACBIPS is based on Helmholtz capacitor which involves the formation of an electric double layer between the electrode and electrolyte consisting of equal and opposite ions which can be approximated as a capacitor. Charging and discharging this capacitor helps adsorb the ions onto a carbon electrode which has high surface area and electrical conductivity. This desalinates seawater and provides pure water. Mathematical modeling, analysis and implementation of the two methods have been presented in this work. The effects of zeta potential, electric field screening, electric mobility on desalination have been discussed. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

Traveling wave solutions of integro-differential equations for modeling one-dimensional neuronal networks, are studied. Under moderate continuity assumptions, necessary and sufficient conditions for the existence and uniqueness of monotone increasing (decreasing) traveling wave solutions are established. Some faults in previous studies are corrected.

Most models for the spread of an invasive species into a new environment are based on Fisher's reaction-diffusion equation. They assume that habitat quality is independent of the presence or absence of the invading population. Ecosystem engineers are species that modify their environment to make it (more) suitable for them. A potentially more appropriate modeling approach for such an invasive species is to adapt the well-known Stefan problem of melting ice. Ahead of the front, the habitat is unsuitable for the species (the ice); behind the front, the habitat is suitable (the open water). The engineering action of the population moves the boundary ahead (the melting). This approach leads to a free boundary problem. In this thesis, we mathematically analyze a novel free-boundary model for the spread of ecosystem engineers that was recently derived from an individual random walk model. The Stefan condition for the moving boundary is replaced by a biologically derived two-sided condition that models the movement behavior of individuals at the boundary as well as the process by which the population moves the boundary to expand their territory. We first consider the model with logistic growth and study its well-posedness. We assign a convex functional to this problem so that the evolution system governed by this convex potential is exactly the system of evolution equations describing the above model. We then apply variational and fixed-point methods to deal with this free boundary problem and prove the existence of local in-time solutions. We next study traveling wave solutions of the model with the strong Allee growth function. We use phase plane analysis to find traveling wave solutions of different types and their corresponding existence range of speed for the model with an imposed speed of the moving boundary. We then find the speeds in those ranges at which the corresponding traveling wave follows the speed of the free boundary.