Spiral 2D array designs for volumetric imaging

The use of linear phased arrays in NDE inspections has recently grown, resulting in faster inspection of components. Phased arrays are also used in underwater sonar and biomedical imaging. All applications require 2 dimensional (2D) arrays, capable of volumetric imaging, to further increase scan speed, and to allow tighter focussing on targets. However, 2D arrays have not found widespread use, mainly due to the large number of elements required to implement standard periodic designs. Alternative array configurations that feature a much lower element count offer a more pragmatic solution. This thesis investigates the design of sparse 2D arrays (i.e. using fewer elements than a periodic grid sampled at the Nyquist rate) based on geometric spiral structures, with the aim to reduce the number of array elements, and therefore transmit-receive channels required to meet a given acoustic specification. The aperiodic structure of these array designs is shown to minimise the height of sidelobes, by spatially distributing sidelobe energy, therefore avoiding artefacts in the resulting acoustic image. Furthermore, their mathematically determined position simplifies the layout of the array, and therefore its manufacture. The approach taken was to develop a logarithmic spiral structure, which is shown to minimise peak sidelobe height for a given number of array elements. A series of design rules was created, to allow the array designer to rapidly create sparse array designs to meet an acoustic specification. The acoustic field created by these designs was modelled, and it was shown that they have lower peak sidelobe levels than equivalent random 2D array designs. A 1.5 MHz, 127 element prototype array was then designed and manufactured for NDE inspection on thick section welds, which combined a -31 dB sidelobe floor with the capability for volumetric steering.

Name dc:type.qualificationname

engd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2011

Author dc:creator

• Tweedie, Andrew

DOI

10.48730/vk4e-7g56

Identifier

T12840

OAI identifier oai:identifier

oai:strathclyde:t435gd043