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Title: Development of an annular array through-transmission system for non-contact inspection applications
Author: Gao, Jie
ISNI:       0000 0004 8509 5781
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2019
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Ultrasound has found application in many different sectors, including inspection in the aerospace industry to investigate component structural integrity. In many cases, a liquid coupling medium is used to efficiently transfer energy between the transducer and the sample under investigation. There are some materials which are not suitable for liquid coupling, either through material properties or the complexity of the surface geometry. The alternative of using an air-coupled approach is inherently challenging due to a large acoustic impedance mismatch between the transducer and air, resulting in low system signal-to-noise ratio (SNR). This Thesis will consider an air-coupled inspection system, using an annular array and efficient matching layer combination. The matching layer is an important key transducer component to bridge the acoustic impedance mismatch between the transducer and the load medium. For air-coupled piezoelectric devices this is a critical factor in the transducer design. This work has concentrated on improving the manufacture methodology for an existing hybrid matching layer design, comprising membrane filter and silicone rubber. The key issue is to ensure repeatability of the fabrication process and reliability in the operating behaviour. Moreover, the developed approach has reduced the manufacture time for these layers and offers an opportunity for volume manufacture. A segmented annular array system has been designed for non-contact inspection applications, which provides control of the depth focussing within the sample coupled with a degree of beam steering off the central axis. A pitch-catch transducer system has been implemented, with the operating frequency of the transmitter and receiver matched to improve system SNR. Full characterisation of both arrays has been performed, with good correlation between theory and experiment. Unfortunately, the fabricated array devices only provided beam steering capability on-axis, but when combined with the matching layer designs, were able to be evaluated on fibre-reinforce composite and honeycomb samples. Assessment of the inspection capability of the developed array system was undertaken through manual scans of sandwich composite structures. Reasonable quality images have been acquired which indicate surface damage and impact damage within several samples, with the results correlating well with corresponding Scanning Acoustic Microscope measurements.
Supervisor: Gachagan, Anthony Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral