Browsing by Subject "polarization"
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Item Fluidic, Solid-State, and Hybrid Reconfiguration Techniques in a Frequency and Polarization Reconfigurable Antenna(2014-12-16) Barrera, Joel DanielThis work presents the development of a hybrid reconfiguration technique used to achieve both frequency and polarization diversity in a 2.4 ? 2.5 GHz microstrip antenna. This hybrid solution for the first time combines current state-of-the-art fluidic and solid-state reconfiguration mechanisms in a collaborative effort. Two orthogonally-crossed and co-located narrow microstrip patches with gap discontinuities separating a central probe-fed section from the radiating slots provides the base antenna structure. The fluidic mechanisms use high strength dielectric fluids or liquid metal loaded across the gap discontinuities and the solid-state mechanisms uses readily available RF PIN and varactor diodes integrated across the gaps to enable reconfiguration. Accurate and robust circuit modeling concepts are presented to provide insight on antenna performance and loss mechanisms from each reconfiguration technique. A polarization-only reconfigurable version of this antenna utilizing dielectric fluids, RF PIN didoes, and liquid metal in separate design iterations were examined to introduce design and circuit modeling concepts and provide a first comparison between the reconfiguration techniques. While all iterations achieved good linear polarization switching, dielectric fluids and the RF PIN didoes are found to have large negative impacts on radiation performance due to ohmic losses (radiation efficiencies between 8 ? 35%). In the liquid metal iteration, ohmic losses are significantly reduced to boost radiation efficiencies near that of a tradition patch antenna (near 80%). The hybrid reconfiguration solution utilizes liquid metal and solid-state varactors for polarization and frequency diversity, respectively. Non-hybrid design iterations using only dielectric fluids and solid-state RF PIN diodes with varactors provide a comparison between all reconfiguration techniques and demonstrate the advantages of the hybrid solution. It was found that broadly variable dielectric strength fluids used as a sole reconfiguration mechanism can achieve a wide frequency tuning range of 700 MHz, maintain linear polarization switching, and have radiation efficiencies near 60%. However, the fluids must have loss tangents less than 0.02 and are currently not readily available. The RF PIN and varactor diode combination provides a realizable solution, however, suffers from excessive DC control power requirements, a limited tuning range of 100 MHz, and low radiation efficiency around 16%. The hybrid solution combines the best aspects of all subsequent design iterations to achieve a realizable frequency and polarization reconfigurable antenna with a tuning range of 263 MHz and 41.7% radiation efficiency average across reconfiguration states.Item Global Distribution of Ice Cloud Particle Shape and Roughness from PARASOL Satellite Measurements(2013-07-29) Cole, BenjaminThe energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth?s energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 ?m. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at ? = 0.1 to severely rough at ? = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75.Item Mueller matrix imaging for skin cancer detection(Texas A&M University, 2004-09-30) Baldwin, Angela MichelleOver one million Americans are afflicted with skin cancer each year. Even though skin cancer has a 95% cure rate, approximately 10,000 people die in the United States each year of this disease. The current ABCDE(F) detection method is not sensitive enough to detect skin cancer in its early stages and requires a biopsy for any suspicious lesions. A lot of unnecessary biopsies, which are painful and costly to the patient, are taken. Therefore, a noninvasive technique is needed that can accurately detect the presence of skin cancer. In this thesis, an optical approach will be presented that has potential to be a noninvasive skin cancer detection technique. Several morphological and biochemical changes occur as tissue becomes cancerous, and therefore the optical properties of the tissue can be used to detect skin cancer. A Mueller matrix imaging system has been developed by our group that measures the 16 or 36-element Mueller matrix, which completely describes the optical properties of the tissue sample. The system is automated and can collect the Mueller matrix in less than one minute. This system will be used to image Sinclair swine, and data analysis techniques will be employed to determine if the system can distinguish between cancerous and noncancerous tissue. System software improvements will also be made, and a new calibration technique will be presented.Item On the Microphysical Properties of Ice Clouds as Inferred from the Polarization of Electromagnetic Waves(2012-10-19) Cole, BenjaminUncertainties associated with the microphysical and radiative properties of ice clouds remain an active research area because of the importance these clouds have in atmospheric radiative transfer problems and the energy balance of the Earth. In this study, an adding/doubling model is used to simulate the top of atmosphere (TOA) radiance and full Stokes vector from an ice cloud at the wavelength lambda = 865 nm with many different combinations of assumed ice habits (shapes) and different degrees of ice surface roughness, and the polarized radiance at a wide range of scattering angles is derived. Simulated results are compared with polarized radiance data from the POLDER (POLarization and Directionality of the Earth's Reflectances) instrument on board the PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) satellite. Bulk ice scattering properties are obtained by using five different size distributions collected during field campaigns ranging in effective diameter from 10 micrometers to 90 micrometers. Bulk scattering properties for the MODIS Collection 5 ice cloud product are used in this study, along with properties for two mid-latitude ice cloud models, a polar/mid-latitude ice model, and a model built for ice clouds over deep convection. Solid columns and hollow columns are used as well. The polarized radiance simulation results for the moderate surface roughness level best fit the satellite measurements for all ice models, though severely roughened ice crystals do fare well in a few cases. Hollow columns are the best fit to the satellite polarization measurements, but of the ensemble ice models, the polar/mid-latitude model at an effective diameter of 90 micrometers best fits the polarized radiance measurements for the one day of PARASOL data considered. This model should be the best to simulate ice cloud properties on a global scale.Item Programmable two-port polarization independent electro-optically tunable wavelength filter in lithium niobate(2009-05-15) Ping, YangProgrammable two-port polarization independent electro-optically wavelength tunable filters based on asymmetric Mach-Zehnder structure in LiNbO3 substrate have been developed for 1.55 ?m application. The operation principle is based on Mach-Zehnder interference and TE?TM polarization conversion. Fabrication parameters for channel waveguides, polarization converters and bandpass filters have been optimized. Straight channel waveguides 7 ?m in width were produced by diffusing 1116 ? thick Ti into LiNbO3 substrate at 1035?C for 10 hours. Single mode guiding has been realized for both TE and TM polarization. Insertion loss of 2.9 dB for TE polarization input and 3.3 dB for TM polarization input were achieved on a 46 mm long sample. Single sideband programmable polarization mode converters were produced with 16 electrode sets, each containing 64 grating periods. Programmability was achieved by applying spatially periodic weighted independent voltages to interdigital electrode sets, and controlled electronically via a personal computer through a digital-to-analog converter array chip. Maximum conversion efficiency of more than 99% was realized for both TM?TE and TE?TM, and was observed at 1530.48 nm. Two-port polarization independent electro-optically tunable wavelength filters were produced based on the results obtained above. The 3 dB bandwidth is 1.1 nm and the nearest side lobes to the main transmission are down by about 9 dB for uniform coupling. Side lobes are reduced to about 20 dB below peak transmission after apodization, and the 3 dB bandwidths increased to ~ 1.3 nm as a result. Seven channels (channel -4, -2, -1, 0, +1, +2 and +4) were selectable by programming the voltages on each electrode set. Channel spacing is 1.1~1.2 nm. The tuning ranges from 1524.04 to 1533.56 nm. Fiber-to-fiber insertion loss of the filter at center frequency is 4.3 dB for TE input and 4.2 dB for TM input. The polarization dependent loss is < 0.5 dB for all selectable channels. The temporal response to a 21 V step change in applied voltages was measured to be 586 ns for the 10%-90% rise time and 2.308 ?s for the 90%-10% fall time. This research work provides a convenient scheme for making programmable two-port tunable bandpass filters and ROADMs.Item Sensitivity of the Mueller matrix to the optical and microphysical properties of cirrus clouds(Texas A&M University, 2006-10-30) Lawless, Ryan LeeAn adding-doubling method is employed to calculate the reflected Stokes parameters for cirrus cloud layers composed of different habits and effective sizes. The elements of the Mueller matrix are determined from the reflected Stokes parameters by considering four different incident polarization states. The sensitivity of these elements is observed by comparing different ice crystal habits, effective sizes, and optical depth. The Mueller elements are strongly dependent on habit. The three habits, aggregate, bullet rosette, and plate, are observed and the M12/M11,M43/M11 and M44/M11 elements are discussed. The wavelength used is 0.532????m, which is the lidar wavelength used on the CALIPSO satellite. The linear depolarization ratio is also discussed. The method of subtracting the two depolarization ratios, is noted as another way to possibly better distinguish ice crystal habits. The sensitivity of the Mueller matrix to effective size is also observed. For three size distributions, the Mueller elements indicate no strong dependence. This may be due to the assumption of randomly oriented ice. Also, using an absorbing wavelength might provide dependence. Finally, the Mueller elements are dependent on optical depth. For a greater optical depth, the strength of reflection increases while the polarization decreases. As the optical depth increases, any peak-like features become non-existent.