Novel acoustic arrays and array pattern synthesis methods
Date
2018-07-04
Authors
Wu, Lixue
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Directional acoustic beams are used in diverse sonar systems. For efficient
transmission of a sonar signal, the sound energy is projected in a narrow beam .
For reduced interference in reception, the sound signal is received from a narrow
spatial sector. Typically, such beams have associated sidelobes which adversely
affect sonar performance.
The goal of this thesis is to propose several novel acoustic arrays which are
capable of generating desired search-light-type and fan-type beams with greatly
reduced sidelobes. These novel acoustic arrays have fewer elements than conventional
arrays of similar performance. The design of such novel arrays is inherently
more difficult, however, since it involves nonlinear optimization. Such
an optimization is normally computationally intensive and may not be globally
convergent.
This difficulty has been overcome by newly developed concepts and associated
array pattern synthesis methods. A new concept called the equivalent linear array
is introduced; a design method based on this concept benefits from existing design
techniques developed for linear arrays. The equivalent linear array concept is further developed to lead to a new and effective method for array radiation pattern
synthesis. A second new concept called the scale-invariance radiation pattern is
introduced, and the subsequent relation between two novel arrays is discovered.
Using this concept an angle mapping approach is developed which transforms a
radiation pattern generated by a circular ring array to that of an elliptic ring array.
This approach takes advantage of methodologies developed for the design of
circular ring arrays. A third concept, constraint directions, is introduced; a subsequent
new iterative method for array pattern synthesis is developed to meet the
need in compact receiving/transmitting array design. With the help of these new
concepts, the proposed synthesis methods avoid the use of nonlinear optimization
techniques and merely require simple matrix operations. The methods can be applied
to the problems of synthesizing radiation patterns of arrays with arbitrary
sidelobe envelopes, with nonisotropic elements, and with nonuniform spacing between
elements. The usefulness of the developed methodologies is demonstrated
in various design examples. The methods developed provide powerfuI tools not
only to design novel acoustic arrays but also to design antenna arrays.
Description
Keywords
Acoustic surface waves, Sound-waves, Signal processing