Faculty of Engineeringhttps://dspace.library.uvic.ca//handle/1828/742018-07-20T18:20:40Z2018-07-20T18:20:40ZBroadband acoustical superresolution imaging of breaking ocean wavesAndrew, Rex Kelleyhttps://dspace.library.uvic.ca//handle/1828/97512018-07-19T22:54:35Z2018-07-19T00:00:00ZBroadband acoustical superresolution imaging of breaking ocean waves
Andrew, Rex Kelley
An acoustic array was deployed in the nearsurface layer in Saanich Inlet, B.C. to
image breaking waves using only the naturally occurring acoustical radiation from the
breaking region over the band [160 Hz, 2000 Hz]. The 1.5-element array was configured
as a horizontal cross with an 8 m aperture, bottom-moored, and positioned nominally
3 m beneath the surface.
Due to sensor sparseness, the array PSF at any particular frequency was badly contaminated by grating lobes. A novel broadband scheme was devised to combine information at multiple
independent frequencies to yield unambiguous images with resolution of about 0.2 m at the sea surface.
The broadband scheme assumed space-time separability in the source mutual spectral density. This is only considered valid for breaking waves above about 400 Hz.
Nonstationarity and time-bandwidth constraints yielded at most six independent frequency
bands within the system passband.
A parametric image analysis showed that the images align closely with the wind
and can be observed moving downwind with a speed about two-thirds the phase speed
of the dominant component of the wind waves.
Absolute power levels were found to be consistent with previously published results.
The absolute power levels were parameterized by where [special characters omitted] and
λ (f) is well-described by a simple first order relation [special characters omitted], where [special characters omitted] varied
depending on the size of the wave but b1 appeared to be a more universal constant
estimated at -4.55 ± 0.47.
The source mechanism for frequencies below about, 400 Hz was modeled two ways:
(1) as a point source (which would follow if an acoustically compact “collective oscillation"
region had formed), and (2) as due to off-peak spectral contributions from
bubbles resonant at 400 Hz. Neither model achieved a satisfactory fit to the observed
data. This seems to imply that the mechanism below about 400 Hz was acoustically
extended and radiating as energetically as any resonant bubbles.
2018-07-19T00:00:00ZAnalysis of self-resonant bent antennasAli, Mohammodhttps://dspace.library.uvic.ca//handle/1828/97502018-07-19T22:21:06Z2018-07-19T00:00:00ZAnalysis of self-resonant bent antennas
Ali, Mohammod
The primary focus of this dissertation is on the analyses of self-resonant bent
antennas. The need for the accurate characterization of such antennas due to their
growing importance in present day wireless communications is the motivation for this
work. To this end, several self-resonant bent antennas are analyzed which includes
an inverted-L antenna (ILA), a meander-line dipole (MLD) antenna, a meander-line
bow-tie (MLBT) antenna, a dual meander antenna, and a printed meander antenna.
A simple analytical model, based on the induced EMF method, is presented to
compute the input impedance of the ILA. First, a sinusoidal distribution of current
on the antenna, with zero current at the end is assumed, and then an expression for
the input impedance is derived using the near-fields of the antenna. The accuracy
of the formulation is verified by comparing the results computed using it with that
from NEC [1] computation. Unlike the analytical solutions available in the literature,
our proposed solution is not restricted to antennas that are electrically small. In
addition the new formulation can be extended to treat other antennas, such as the
T-antenna, the folded unipole antenna, and the loop-loaded monopole antenna.
The input impedance, radiation pattern, and gain of the MLD and MLBT antennas
are computed and correlated with their parameters. Input impedances of both
antennas are computed using NEC. Simple analytical models are presented to compute
the radiation patterns of the MLD and the MLBT antennas. For each antenna,
a sinusoidal distribution of current is assumed and closed-form expressions for the
radiation fields are derived. The results computed using the analytical models are
verified by comparing them with the results from the NEC computation. Since in
each model the radiation pattern of an antenna is expressed in terms of ready to
evaluate algebraic expressions, the computation of such pattern is fast and easy.
The input impedance and radiation characteristics of a dual meander antenna
are computed using NEC. Similarly as before the input impedance, radiation pattern,
and gain of this antenna are also correlated with its parameters. The input
impedance and radiation pattern of a planar printed meander antenna are investigated
using the Finite-Difference Time-Domain (FDTD) technique. The antenna is modeled on a dielectric substrate both in the presence and absence of a metallic
ground plane. Characteristics of the antenna are examined as function of dielectric
constant, and substrate thickness. New results of input impedance, radiation
pattern, and gain are presented which are vital for the design of such antennas.
Several novel applications of self-resonant bent antennas are described. First, a
wide-band dual meander-sleeve antenna is designed, manufactured, and measured
for application in dual frequency vehicular personal communication. The antenna
can operate simultaneously in the 824-894 MHz and 1850-1990 MHz bands of the
PCS system. Second, an MLBT dipole is introduced as a feed for plane sheet
reflectors. Numerical results computed using NEC show that the feed when used
in front of a plane sheet reflector, results in superior radiation characteristics than
a conventional dipole feed, namely, it reduces the reflector dimension by 46% for
the same front to back ratio, beam width and gain. Finally, a compact plane sheet
reflector antenna is described that uses an MLBT monopole feed. Since the antenna uses a monopole, a balun is not required. This antenna has a gain and half-power
beam width of 8.4 dBi and 94° respectively.
2018-07-19T00:00:00ZAn approach to generate geometric models from multiple range imagesYao, Helaihttps://dspace.library.uvic.ca//handle/1828/97482018-07-19T21:34:15Z2018-07-19T00:00:00ZAn approach to generate geometric models from multiple range images
Yao, Helai
The research described in this dissertation focuses on the development of a new
approach for the generation of geometric models from multiple-view range image data.
Through intensive comparison and evaluation of different representations, the
cross-section contour based representation is concluded to be ideal for modeling with
range image data. The representation is shown to be at an intermediate level -
compatible with both the low-level of range image data and with the need to provide
relatively high-level geometric and topological information in models.
A new concept of generating partial models within device frames, frames
associated with the working principle and geometry of a range sensor, is introduced.
The range data are well distributed in the device frame. This good data
distribution facilitates computations relevant to rendering the cross-sections required
by the representation and relevent to identifying occlusions present in the image.
Methodology for merging the partial models with a current global model is developed
to allow the incorporation of redundancy between the partial model and the current
global model and to allow growth of the global model. A simulation of the ERIM
imaging-radar based range sensor, a prototype triangulation-based range sensor
developed for this research and a commercial HYMARC range sensing system are
used for approach verification. The device frames associated with the sensors are
derived, and used to test the modeling approaches and the developed system.
The presented research: demonstrates the suitability of the cross-section based
representation for range-image based modeling systems; introduces a new concept and
associated methods for generating cross-section contour models in range sensor device
frames to take advantage of well distributed data; develops a series of algorithms
for partial modeling in the device frame and for global model integration; and
demonstrates the feasibility of the developed new approaches for applications by
testing the system for multiple sensor types.
2018-07-19T00:00:00ZOn optimum system design for wireless communicationsWu, Bohttps://dspace.library.uvic.ca//handle/1828/97472018-07-19T20:04:59Z2018-07-19T00:00:00ZOn optimum system design for wireless communications
Wu, Bo
This dissertation addresses the issue of optimum system design to achieve reliable
communication in the presence of various types of interference. Multiobjective
formulation is used with noncooperative and cooperative approaches owing to the
nature of the problems under consideration.
Since intentional Jamming is one of the most severe kinds of interference, anti-jam
techniques are crucial for communications in a hostile environment. The jam
and anti-jam problem is modeled as a two-person zero-sum game in which the communicator and the jammer have antagonistic objectives and are viewed as the two
players. The concept of Nash equilibrium is introduced and its characterizations
such as existence, uniqueness, stability, robustness, and sensitivity are investigated.
This model is then applied to a frequency-hop spread spectrum M-ary frequency-shift-keying system where ratio-threshold diversity is used to combat partial-band
noise and multitone jamming. Equilibrium performance in terms of cutoff rate and
bit error rate is shown to be superior to that predicted by worst-case analysis.
When mutual interference caused by simultaneous transmissions is the major
concern in a heterogeneous packet network, a multiobjective framework is proposed
in this dissertation with the objectives and constraints of the individual users taken
into consideration. Near-far effect and Rayleigh fading may occasion packet capture
and therefore create unfairness in favor of closer users. Thus, multiobjective
optimality is introduced, in which criterion of fairness is embedded. Optimum
strategies controlling transmission probability and/or power are examined to yield
the Pareto optimal solution in a slotted ALOHA network. Then, the same control
strategies are studied with the channel utilization being the maximization objective.
Optimization results are obtained in various situations, and effectiveness of
different strategies is compared.
A multimedia direct-sequence spread spectrum system may support multiple
services with different transmission rates and diverse quality-of-service requirements. To facilitate multimedia applications and maximize the system capacity,
average power control, error correction coding, and time diversity are incorporated
into the system. The capacity of such a system is evaluated in multipath Rayleigh
fading channels. Average bit error rate, outage probability, and corresponding information theoretic bounds are discussed. Concatenation of Reed-Solomon codes
and convolutional codes is considered for error correction to account for different
quality and delay constraints. It is shown through a numerical example that the
system capacity can be increased significantly by an appropriate system design.
2018-07-19T00:00:00Z