3D Particle Tracking Velocimetry Method: Advances and Error Analysis

A full three-dimensional particle tracking system was developed and tested. By using three separate CCDs placed at the vertices of an equilateral triangle, the threedimensional location of particles can be determined. Particle locations measured at two different times can then be used to create a three-component, three-dimensional velocity field. Key developments are: the ability to accurately process overlapping particle images, offset CCDs to significantly improve effective resolution, allowance for dim particle images, and a hybrid particle tracking technique ideal for three-dimensional flows when only two sets of images exist. An in-depth theoretical error analysis was performed which gives the important sources of error and their effect on the overall system. This error analysis was verified through a series of experiments, which utilized a test target with 100 small dots per square inch. For displacements of 2.54mm the mean errors were less than 2% and the 90% confidence limits were less than 5.2 μm in the plane perpendicular to the camera axis, and 66 μm in the direction of the camera axis. The system was used for flow measurements around a delta wing at an angle of attack. These measurements show the successful implementation of the system for three-dimensional flow velocimetry

DETERMINING HEAD POSITION TO ASSIST ELECTRIC-POWERED WHEELCHAIR OPERATION FOR PERSONS WITH TRAUMATIC BRAIN INJURY

Monitoring head position in persons with a traumatic brain injury may provide a means for independent powered mobility. Given the often limited residual functions of attending, visual processing, and motor control, the operation of an electric-powered wheelchair must be constantly monitored to ensure the safety of these users. Human-directed support is not always available and does not encourage independent mobility. The solution proposed for this problem is placement of a magnet on the rear of the person's head. Strategically placed linear analog Hall effect sensors that are fixed in a stationary headrest can then track the magnet; thus, accurately determining head positioning. With this proposed head tracking, a specialized interface to the electric-powered wheelchair controller can be used to ensure the person's head is attending the direction of travel asserted by a conventional, direction-sensing joystick

Wideband data-independent beamforming for subarrays

The desire to operate large antenna arrays for e.g. RADAR applications over a wider frequency range is currently limited by the hardware, which due to weight, cost and size only permits complex multipliers behind each element. In contrast, wideband processing would have to rely on tap delay lines enabling digital filters for every element.As an intermediate step, in this thesis we consider a design where elements are grouped into subarrays, within which elements are still individually controlled by narrowband complex weights, but where each subarray output is given a tap delay line or finite impulse response digital filter for further wideband processing. Firstly, this thesis explores how a tap delay line attached to every subarray can be designed as a delay-and-sum beamformer. This filter is set to realised a fractional delay design based on a windowed sinc function. At the element level, we show that designing a narrowband beam w.r.t. a centre frequency of wideband operation is suboptimal,and suggest an optimisation technique that can yield sufficiently accurate gain over a frequency band of interest for an arbitrary look direction, which however comes at the cost of reduced aperture efficiency, as well as significantly increased sidelobes. We also suggest an adaptive method to enhance the frequency characteristic of a partial wideband array design, by utilising subarrays pointing in different directions in different frequency bands - resolved by means of a filter bank - to adaptively suppress undesired components in the beam patterns of the subarrays. Finally, the thesis proposes a novel array design approach obtained by rotational tiling of subarrays such that the overall array aperture is densely constructed from the same geometric subarray by rotation and translation only. Since the grating lobes of differently oriented subarrays do not necessarily align, an effective grating lobe attenuation w.r.t. the main beam is achieved. Based on a review of findings from geometry,a number of designs are highlight and transformed into numerical examples, and the theoretically expected grating lobe suppression is compared to uniformly spaced arrays.Supported by a number of models and simulations, the thesis thus suggests various numerical and hardware design techniques, mainly the addition of tap-delay-line per subarray and some added processing overhead, that can help to construct a large partial wideband array close in wideband performance to currently existing hardware.The desire to operate large antenna arrays for e.g. RADAR applications over a wider frequency range is currently limited by the hardware, which due to weight, cost and size only permits complex multipliers behind each element. In contrast, wideband processing would have to rely on tap delay lines enabling digital filters for every element.As an intermediate step, in this thesis we consider a design where elements are grouped into subarrays, within which elements are still individually controlled by narrowband complex weights, but where each subarray output is given a tap delay line or finite impulse response digital filter for further wideband processing. Firstly, this thesis explores how a tap delay line attached to every subarray can be designed as a delay-and-sum beamformer. This filter is set to realised a fractional delay design based on a windowed sinc function. At the element level, we show that designing a narrowband beam w.r.t. a centre frequency of wideband operation is suboptimal,and suggest an optimisation technique that can yield sufficiently accurate gain over a frequency band of interest for an arbitrary look direction, which however comes at the cost of reduced aperture efficiency, as well as significantly increased sidelobes. We also suggest an adaptive method to enhance the frequency characteristic of a partial wideband array design, by utilising subarrays pointing in different directions in different frequency bands - resolved by means of a filter bank - to adaptively suppress undesired components in the beam patterns of the subarrays. Finally, the thesis proposes a novel array design approach obtained by rotational tiling of subarrays such that the overall array aperture is densely constructed from the same geometric subarray by rotation and translation only. Since the grating lobes of differently oriented subarrays do not necessarily align, an effective grating lobe attenuation w.r.t. the main beam is achieved. Based on a review of findings from geometry,a number of designs are highlight and transformed into numerical examples, and the theoretically expected grating lobe suppression is compared to uniformly spaced arrays.Supported by a number of models and simulations, the thesis thus suggests various numerical and hardware design techniques, mainly the addition of tap-delay-line per subarray and some added processing overhead, that can help to construct a large partial wideband array close in wideband performance to currently existing hardware

Wide bandwidth focal plane array receiver for radio astronomy

Reflective antennas equipped with phase array feeds (PAFs) have been proposed as part of the Square Kilometre Array reference design, since they offer a wide Field of View (FoV) and large collecting area. To achieve a contiguous FoV, and to cancel spill-over radiation, the Focal Plane Array (FPA) must sample the focal field of the reflector at least every half-wavelength at the upper operating frequency. Low-noise operation over a wide bandwidth requires appropriate impedance matching to the low-noise amplifiers, and this is a challenging research problem since the input impedance of the FPA elements can vary strongly with frequency.Advanced broadband design techniques for antenna arrays have resulted in antenna shapes getting more complex. Modelling of these antennas can only be carried out using numerical computational electromagnetic methods (CEM), and accurate modelling of complex antennas demand the full-wave analysis with fields and currents that vary in three dimensional space. The Frequency Domain Integral Equation model is adopted in this study and used via the Method of Moments (MoM) technique for simulation and modelling of the FPA. The "MoM Antenna Development Toolbox" (MoMADT), 64 bit version of the modelling software, is specifically developed in this study for designing, building and modelling of complex antenna and electromagnetic structures. MoMADT utilizes surface and volume integral equations and provides functions for generating precise meshes and accurate method of moments solutions. MoMADT enables structures to be assembled in an array formation to consist of conductive or dielectric materials, or a combination of both.Study of the wide bandwidth FPA receiver was achieved through analysis of broadband planar antenna structures. This research investigates a unique design solution for a FPA utilizing the diamond planar strip antenna elements arranged to provide three vectors of polarization (triple-polarized FPA). The most promising FPA identified is the 77 Hexagonal Diamond Tripole (HDT) array. This array yields an operating frequency range of 550 to 2100 MHz, providing bandwidth ratio of 3.8:1. It is shown that adequate impedance match can be achieved across the indicated frequency range with desired directivity and gain. In addition, the 77 HDT array offers optimized efficiency and allows the polarization to be distinguished at any angle about the axis normal to the antenna plane to within a theoretical uncertainty of ± 2.2°. This is also true for any function of the FoV allowed by the surface area of the FPA

A new multilateration optimization technique for air traffic management and surveillance.

Abstract not available

Primordial non-Gaussianity and Bispectrum Measurements in the Cosmic Microwave Background and Large-Scale Structure

The most direct probe of non-Gaussian initial conditions has come from bispectrum measurements of temperature fluctuations in the Cosmic Microwave Background and of the matter and galaxy distribution at large scales. Such bispectrum estimators are expected to continue to provide the best constraints on the non-Gaussian parameters in future observations. We review and compare the theoretical and observational problems, current results and future prospects for the detection of a non-vanishing primordial component in the bispectrum of the Cosmic Microwave Background and large-scale structure, and the relation to specific predictions from different inflationary models.Comment: 82 pages, 23 figures; Invited Review for the special issue "Testing the Gaussianity and Statistical Isotropy of the Universe" for Advances in Astronom

Design, Testing and Analysis of an Affordable Direction of Arrival System Using Off-The-Shelf SDR Hardware and Software

The growing use of wireless communication increases the need for devices to determine the location of the signal source. Affordable, accessible and universal devices can have a great role in addressing this aside precision tools. Combining popular off-the-shelf radio receivers with direction of arrival algorithms could provide a convenient tool. The setup is proven to give sufficient results for several location applications using HackRF radio and signal processing in software. The accuracy of the system can be improved by characterising the system for each use case. After the setup is completed, such system can still be convenient to use for non-technical end user