Microphone windscreens are typically used to reduce the noise associated with wind flowing over a microphone diaphragm by reducing the velocity of the airflow. While most windscreens are effective at reducing this noise, they do not protect the microphone from many natural elements, such as moisture, sand, and other small particles. The focus of this research was to design a windscreen that protects an array of five microphones located around a 4.5-inch diameter cylinder from these natural elements. The design goals were to have a wind noise attenuation of at least 8 dB, an insertion loss of less than 1 dB from 5-1000 Hz, and a phase shift error of less than 3% over the same range. Computer simulations and experimental testing were used to select two basic designs. Four experimental tests consisting of wind noise attenuation, sand entrapment, insertion loss, and phase change measurements were used to optimize the geometry of these designs. The wind noise attenuation was tested by spinning the microphone array on a long boom and by setting the array in front of a fan. Sand was blown at the windscreen in order to test how well the windscreen protects the microphone array from small particles in the velocity stream. The insertion loss of the windscreen was tested by comparing an incoming signal traveling through the windscreen to the same signal without the windscreen. Finally, the phase shift between microphones was measured using a single frequency and comparing the microphone measurements with and without the windscreen. These four tests were performed on two designs. The first design consists of two foam filled concentric cones set around the microphone array. The second design consists of tubes that project outward from each microphone diaphragm, and then curve downwards. Both final windscreen designs meet the desired requirements. They both reduce wind noise attenuation by approximately 9 dB in a 13 mph wind and over 16 dB in a 20 mph wind. They also have negligible insertion loss, have a phase shift error of less than 3%, and are very efficient at blocking particles from entering the windscreen.

<p> A Cellular Computing Memory Array consisting of twenty cells of three words plus logic per cell has been constructed and interfaced to a digital computer. Both arithmetic and logic operations can be performed between words of a cell and those of adjacent cells, the results of which may be stored in any of the three words of the cell. The cells are organized in a two dimensional array so that each cell can communicate with the four nearest neighbours. In addition to the ordinary communication between cells to perform operations on data in adjacent cells, data can be transferred in the memory plane on a mass basis.</p> / Thesis / Master of Engineering (MEngr)

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The thesis presents a compact, miniature, and low cost antenna array designed for millimeter-wave frequencies for future 5th generation (5G) mobile applications. The proposed antenna array is a geometrically modified structure of the Franklin array, which allowed to transform a conventional narrowband array into a wideband antenna array. It is composed of five millimetre-wave circular patch radiation elements with phasing stubs. The designed array, fabricated on the commercial Rogers RO3003 substrate with small form factor of 8x25x0.5 mm3, covers the upcoming 5G band of 23.6-30.3 GHz, with peak gain as 10.8 dB, and high radiation efficiency over the whole operating band. In addition, with frequency sweeping, the proposed antenna array radiation pattern is directive and offers beam steering at the desired angles, acting similarly as a leaky-wave antenna.

Wideband, wide-scan antenna arrays are a promising candidate for the future wireless networks and as well as an essential part of experimental radio astrophysics. Understanding the underline physics of the element performance in the array environment is paramount to develop and improve the performance of array systems. The focus of this thesis is to develop novel wideband antenna array technologies and develop new theoretical insights of the fundamental limits of antenna arrays. The developed methodologies have also been extended to include a radio astrophysics application for the global 21cm experiment.   Investigating the fundamental antenna array limits and extracting general performance measures can provide a priori estimates for any application of arrays. In this thesis, a general measure for antenna arrays, the array figure of merit is proposed. This measure couples bandwidth, height from the ground plane and reflection coefficient in a bounded quantity. An extension of the array figure of merit that is able to provide matching, bandwidth and directivity/gain limits is also introduced. The soft Vivaldi array is introduced as a novel wideband, wide-scan angle array technology. Periodic structure loading has been utilized to improve the array's performance and mold the electromagnetic wave behavior to our benefit. The soft condition has been utilized in the same manner as the conventional soft-horn antenna at the Vivaldi element. An integrated matching layer in the form of periodic strip loading is introduced. A single polarized soft Vivaldi array prototype has been developed fabricated and measured. The developed finite array has been loaded with a soft condition in the periphery to mitigate edge effects. The results indicated improved cross-polarization and side-lobe levels. A new class of wideband antenna arrays, the Strongly Coupled Asymmetric Dipole Array (SCADA) was also proposed in this thesis. Exploiting asymmetry in the array element introduces an additional degree of freedom that improves bandwidth and scanning performance. A novel methodology for terminating finite arrays is also proposed. The theory and an experimental antenna array is presented with good agreement between measured and simulated results. An effort to integrate a vertical wide angle matching layer was also addressed and a prototype array with this concept is presented. In the last part of this thesis, a methodology for the detection of the global cosmological 21cm signal from the Epoch of Reionization (EoR) is developed. The main sources of errors in this experiment, the foregrounds and the antenna chromaticity are evaluated. A new algorithmic methodology for extracting the global EoR signal is proposed. The method is based on piecewise polynomial fitting and has successfully been applied and evaluated. An antenna array that is based on the methodologies described in this thesis has been developed and evaluated with the proposed algorithm. / Bredbandiga gruppantenner med stor utstyrningsvinkel är en av de lovande kandidaterna för nästa generations trådlösa kommunikationsnätverk samt en väsentlig del av experimentell radioastrofysik. Att förstå de bakomliggande fysikaliska principerna hos gruppantennens element är avgörande för att kunna utveckla och förbättra prestandan hos ett gruppantennsystem. Denna avhandling är fokuserad på att utveckla nya bredbandstekniker samt nya teoretiska insikter om de grundläggande gränserna för gruppantenner. De här utvecklade metoderna har förutom kommunikationstillämpningar också tillämpats på en radioastrofysik tillämpning i det globala 21cm experimentet. Att undersöka de fundamentala gränserna för gruppantenner och att utröna allmängiltiga mått på deras prestandaegenskaper kan möjliggöra a priori uppskattningar om gruppantenns tillämpbarhet för dess planerade användning. I den här avhandlingen föreslås ett allmänt kvalitetsmått på gruppantenner: gruppantennkvaliten. Detta mått kopplar samman främst bandbredd, reflektionskoefficienten med antennens tjocklek över ett jordplanet. En utvidgning av begreppet gruppantennkvaliten, presenters också i avhandlingen det kopplar samman bandbredd, matchning med antennens direktivitet/förstärkningsfaktor. En Vivaldi-gruppantenn med mjuka ytor introduceras här som en ny sorts bredbandig gruppantenn med stor utstyrningsvinkel. I antennen har en periodisk belastning inkluderats för att förbättra dess egenskaper, och för att forma antennens elektromagnetiska utstrålning till vår fördel. Den mjuka ytan på elementet har används på ett liknande sätt som det välkända korrigerade Vivaldihornets design, och har integrerats direkt i elementets design. Den här utvecklade ändliga gruppantennen har också en mjuk yta på dess yttre delar för att minska kanteffekternas påverkan av antennprestandan. Resultaten indikerade både förbättrad korspolarisations och lägre sidlobsnivåer hos antennen. En ny klass av bredbandiga gruppantenner har utvecklas i denna avhandling, den kallas en Starkt Kopplad Asymmetrisk Dipol-gruppAntennen - SCADA. Genom att utnyttja geometrisk asymmetri i antennelementet introduceras ytterligare en frihetsgrad som möjliggör förbättrad bandbredd och utstyrning. Vidare presenteras här en ny metod för impedansterminering av ändliga gruppantenner. Både SCADA-teorin samt dess verifiering i forma av en experimentell gruppantenn presenteras här. Teori, simulering och experiment visar god överenskommelse, vilket validerar idéerna. En prototyp av ett matchande skikt som stöder stor utstyrbarhet har integrerats med gruppantennprototypen och presenteras i avhandlingen. I den sista delen av avhandling utvecklas också en metod för detektering av den globala kosmologiska 21 cm-signalen från universums rejoniseringsepok - EoR. Huvudkällorna för mätfel i detta experiment utvärderas, de är antennens kromaticiteten och förgrundsstrålningen. En ny algoritmbaserad metod för att extrahera den globala EoR-signalen föreslås. Metoden är baserad på anpassning med multipla polynom och har med framgång tillämpats och utvärderats. En gruppantenn som baseras på de metoder som beskrivs i avhandling har också föreslagits och dess prestanda har utvärderats med den föreslagna metoden. / <p>QC 20171121</p>

In June 2003, the Littoral Acoustic Demonstration Center conducted an acoustic characterization experiment for a standard seismic exploration array. Two moorings with Environmental Acoustic Recording Systems (EARS) were deployed in the northern part of the Gulf of Mexico to measure ambient noise and collect shot information. A 21-element seismic airgun array was towed along five parallel linear tracks with horizontal closest approach points to the EARS buoy position of 63, 500, 1000, 2000, and 5000 m. Calibrated acoustic pressure measurements collected during the experiment were analyzed to obtain zero-to-peak sound pressures, sound exposure levels, and pressure levels in 1/3-octave frequency bands. In addition, the experimental data were modeled by using a modified underwater acoustic propagation model to fill in missing data measurements. The resulting modeling procedure showed good agreement between measured and modeled data in absolute pressure amplitudes and frequency interference patterns for frequencies up to 1000 Hz. The analysis is important for investigating the potential impact on marine mammals and fish and predicting the exposure levels for newly planned seismic surveys in other geographic areas. Based on results of the experiment conducted and data analysis performed, a new experimental design was proposed to maximize the amount of collected data using the available equipment while minimizing the time needed for the source ship. The design used three patches, one with 3º angular spacing between the lines at a reference depth. Embedded is a smaller patch with 1º spacing and within that a still smaller patch with one half degree spacing. This arrangement gives a reasonably uniform distribution of shots versus solid angle with a large variety of emission and azimuthal angles for different ranges. Due to the uncertainty of positioning systems, the angular space is divided into solid angle bins. Simulations predicted more than 200 shots per bin for emission angles greater than 13 degrees. Statistical analysis of collected data will be performed on the proposed bin basis. An experiment based on the proposed design was conducted in Fall 2007. The data measurements collected during the experiment are currently being analyzed and will be reported in the near future.

The high amount of scientific and communications data produced by low earth orbiting satellites necessitates economical methods of communication with these satellites. A volumetric phased array for demonstrating horizon-to-horizon electronic tracking of the NASA satellite EO-1 was developed and demonstrated. As a part of this research, methods of optimizing the elemental antenna as well as the antenna on-board the satellite were investigated. Using these optimized antennas removes the variations in received signal strength that are due to the angularly dependent propagation loss exhibited by the communications link. An exhaustive study using genetic algorithms characterized two antenna architectures, and included optimizations for radiation pattern, bandwidth, impedance, and polarization. Eleven antennas were constructed and their measured characteristics were compared to those of the simulated antennas. Additional studies were conducted regarding the optimization of aperiodic arrays. A pattern-space representation of volumetric arrays was developed and used with a novel tracking algorithm for these arrays. This algorithm allows high-resolution direction finding using a small number of antennas while mitigating aliasing ambiguities. Finally, a method of efficiently applying multiple beam synthesis using the Fast Fourier Transform to aperiodic arrays was developed. This algorithm enables the operation of phased arrays combining the benefits of aperiodic element position with the efficiency of FFT multiple beam synthesis. Results of this research are presented along with the characteristics of the volumetric array used to track EO-1. Experimental data and the interpretations of that data are presented, and possible areas of future research are discussed.

Masters of Science / Upcoming and ongoing 21cm surveys, such as the Square Kilometre Array (SKA), Hydrogen Epoch of Reionization Array (HERA) and Low Frequency Array (LOFAR), will enable imaging of the neutral hydrogen distribution on cosmological scales in the early Universe. These experiments are expected to generate huge imaging datasets that will encode more information than the power spectrum. This provides an alternative unique way to constrain the astrophysical and cosmological parameters, which might break the degeneracies in the power spectral analysis. The global history of reionization remains fairly unconstrained. In this thesis, we explore the viability of directly using the 21cm images to reconstruct and constrain the reionization history. Using Convolutional Neural Networks (CNN), we create a fast estimator of the global ionization fraction from the 21cm images as produced by our Large Semi-numerical Simulation (SimFast21). Our estimator is able to efficiently recover the ionization fraction (xHII) at several redshifts, z = 7; 8; 9; 10 with an accuracy of 99% as quantified by the coefficient of determination R2 without being given any additional information about the 21cm maps. This approach, contrary to estimations based on the power spectrum, is model independent. When adding the thermal noise and instrumental effects from these 21cm arrays, the results are sensitive to the foreground removal level, affecting the recovery of high neutral fractions. We also observe similar trend when combining all redshifts but with an improved accuracy. Our analysis can be easily extended to place additional constraints on other astrophysical parameters such as the photon escape fraction. This work represents a step forward to extract the astrophysical and cosmological information from upcoming 21cm surveys.