Integrated RF oscillators and LO signal generation circuits

This thesis deals with fully integrated LC oscillators and local oscillator (LO) signal generation circuits. In communication systems a good-quality LO signal for up- and down-conversion in transmitters is needed. The LO signal needs to span the required frequency range and have good frequency stability and low phase noise. Furthermore, most modern systems require accurate quadrature (IQ) LO signals. This thesis tackles these challenges by presenting a detailed study of LC oscillators, monolithic elements for good-quality LC resonators, and circuits for IQ-signal generation and for frequency conversion, as well as many experimental circuits. Monolithic coils and variable capacitors are essential, and this thesis deals with good structures of these devices and their proper modeling. As experimental test devices, over forty monolithic inductors and thirty varactors have been implemented, measured and modeled. Actively synthesized reactive elements were studied as replacements for these passive devices. At first glance these circuits show promising characteristics, but closer noise and nonlinearity analysis reveals that these circuits suffer from high noise levels and a small dynamic range. Nine circuit implementations with various actively synthesized variable capacitors were done. Quadrature signal generation can be performed with three different methods, and these are analyzed in the thesis. Frequency conversion circuits are used for alleviating coupling problems or to expand the number of frequency bands covered. The thesis includes an analysis of single-sideband mixing, frequency dividers, and frequency multipliers, which are used to perform the four basic arithmetical operations for the frequency tone. Two design cases are presented. The first one is a single-sideband mixing method for the generation of WiMedia UWB LO-signals, and the second one is a frequency conversion unit for a digital period synthesizer. The last part of the thesis presents five research projects. In the first one a temperature-compensated GaAs MESFET VCO was developed. The second one deals with circuit and device development for an experimental-level BiCMOS process. A cable-modem RF tuner IC using a SiGe process was developed in the third project, and a CMOS flip-chip VCO module in the fourth one. Finally, two frequency synthesizers for UWB radios are presented

Space Communications: Theory and Applications. Volume 3: Information Processing and Advanced Techniques. A Bibliography, 1958 - 1963

Annotated bibliography on information processing and advanced communication techniques - theory and applications of space communication

Longitudinal oxygen imaging in 3D (bio)printed models

Electron paramagnetic resonance (EPR), and its molecular imaging modality, is a powerful tool to noninvasively map various biological and chemical markers within objects of interest. Reliable data acquisition is a major impeding factor for longitudinal hands-off measurements. Measurements are especially challenging in biomedical applications, as live objects are not static. Frequent changes occur that require constant fine recalibration of the EPR detection system, called the resonator. To enable longitudinal imaging, a technology permitting automatic digital control of resonator coupling, tuning, and EPR data acquisition was developed. Automation was achieved through the utilization of a microcontroller and digital peripheral components such as digitally controlled capacitors, a digital frequency source, and a printed circuit board resonator. Several applications of this technology have been suggested and tested, including in vivo EPR imaging. The first was to develop a tool for the optimization of light-based 3D printing, for which oxygen plays a major role. Towards this goal, an EPR oxygen-sensitive probe was incorporated into 3D printing resin. Oxygen depletion was measured during the 3D printing process as the polymerization front progressed. After printing, oxygen depletion was again measured during the post-curing process, proposed as a method to optimize post-curing light intensity, temperature, and duration in order to produce quality 3D printed constructs. The second application of longitudinal EPR imaging was directed toward resolving an important problem of oxygen delivery to thick (\u3e1 cm) bioprinted models. Oxygen-sensitive EPR probes (water-soluble trityls or crystalline lithium octa-n-butoxynaphthalocyanine) were introduced into bioinks (liquid hydrogels containing cells, nutrients, and other biological factors) before printing. Bioinks become solid structures after printing due to crosslinking. EPR imaging was demonstrated to measure oxygen consumption by the cells embedded in the bioprints. As expected, an increase of oxygen depletion was observed by introducing a nutrient (pyruvate) to bioink. A numerical MATLAB simulation program was developed to predict rates of oxygen consumption by the cells in the bioprint. The input parameters for the mathematical model include the size and number of cells, the diffusion coefficient of the media, and rates of oxygen transfer through the cell membrane. The software is being further refined and optimized for computational speed. Future efforts will be aimed at improving the speed and scope of EPR automatic digital control, imaging the oxygen depletion process in commercial 3D printers, and applying EPR mapping of oxygen consumption rate to quantify the delivery of oxygen to cells deep inside bioprinted tissue models. Optimizing the delivery of oxygen to cells would overcome the challenge of the limit of diffusion, facilitating the development of larger and more complex bioprinted tissues and organs. These complex tissue and organ models are envisioned for use in drug testing, biomedical research, and, in the distant future, implants in humans

ATS-6 engineering performance report. Volume 3: Telecommunications and power

Functional design requirements and in-orbit operations, performance, and anomalies are discussed for (1) the communications subsystem, (2) the electrical power system, and (3) the telemetry and command subsystem. The latter includes a review of ground support. Tracking and data relay experiments and the Apollo-Soyuz test program are reviewed

A selective list of acronyms and abbreviations

A glossary of acronyms, abbreviations, initials, code words, and phrases used at the John F. Kennedy Space Center is presented. The revision contains more than 12,100 entries

Development of tunable terahertz quantum cascade wire lasers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 179-188).For a long time, terahertz (THz) radiation has been of great interest to scientific community because of its spectroscopic and imaging applications based on its unique properties, such as the capabilities to penetrate many materials which are opaque in other frequency range (e.g. packaging, plastics, paints and semiconductors), and spectroscopic signatures of many important materials. In this thesis, a continuously tunable THz wire QC laser, which comprises a QC laser with deep sub-wavelength transverse dimensions, and a movable side object, termed as "plunger", is demonstrated. This deep sub-wavelength cross-section results in a large fraction of mode propagating outside of the laser core (GaAs/A1₀.₁₅Ga₀.₈₅As material system). The frequency tuning is achieved by changing the transverse wave vector, using a plunger made by metal (metal plunger) or silicon (dielectric plunger). When nudged close to the wire laser core, the metal plunger can push modes to the opposite side of the waveguide. Confined by a metal-metal waveguide, the mode is squeezed and the transverse wave vector is increased, resulting in a blue-shifted frequency. In contrast, a silicon plunger can suck the mode out due to its similar refractive index to GaAs/Al₀.₁₅Ga₀.₈₅As material system of laser core. Thus a decreased transverse wave vector results in a redshifted frequency. Although a tuning record of 138GHz (3.6%) was achieved, a discontinuous tuning resulted from a jittering movement of the plungers due to its friction with the guiding system. To solve this problem, an improved plunger based on micro-mechanical system (MEMS) was implemented. This MEMS plunger uses a two-stage folded-beam flexure to isolate the misaligned external actuation. The plunger is attached with the flexure which suspends above a silicon substrate to eliminate friction. Eventually, this MEMS flexure was actuated by a mechanical system which comprised a lever to de-amplify the displacement of a linear mechanical feedthrough. This MEMS plunger enabled a restorable and frictionless movement which led to a continuous tuning range of 330GHz (8.6%) centered at ~3.85 THz. The challenges posted by the weak mode discrimination led to the development of comb-shape connectors which electrically connect the top metal of wire lasers and the side bonding pad. This design can significantly increase the mode discrimination by selectively guiding undesired mode into the lossy bonding pad. This robust design of single mode operation enables the initial lasing at a frequency far below the gain peak, which can potentially increase the tuning range significantly.by Qi Qin.Ph.D

The quantification of Achilles tendon neovascularity

In the investigation of the correlation between VON and clinical severity, the mean VON was definitely greater than that in healthy Achilles tendon. Neovascularization was noted in 97.5% (n = 39) symptomatic Achilles tendons in 30 patients. The VAS showed a positive correlation with VON with a Spearman correlation coefficient of 0.326 (p = 0.04, power = 0.89), while no significant correlation was found between VISA-A score and VON.EThOS - Electronic Theses Online ServiceGBUnited Kingdo