Ultrasonic Array Imaging for Non-Destructive Testing (PDF)
Bruce Drinkwater, Professor of Ultrasonic Engineering at the University of Bristol
A FESI Publishing Monograph (2021)
ISBN 978-09935485-4-3 | 112 PAGES | £50 (FESI MEMBERS 10% OFF)
“Ultrasonics is one of the most widely used non-destructive testing (NDT) methods due to its ability to receive signals from defects hidden deep within structures. Traditional ultrasonic inspection is performed by scanning a single transducer over the structure, but often the resolution achieved is limited and the interpretation challenging. Recent years have seen shift from this traditional approach to the use of ultrasonic arrays, capable of forming images of the interior of the structure. Array images allow any defects found to be mapped onto engineering drawings, leading to an intuitive interpretation of the results. The high resolution of array images also means that smaller defects can be found and their shape extracted.
This book aims to describe the current ultrasonic array imaging methods and the on-going research efforts to maximise the potential of arrays. A key theme is that an array measures the defect scattering behaviour and this encodes all the available information about the size and shape of the defect. In this way the scattering is the fingerprint of the defect. This defect focused approach leads naturally to an understanding of how to optimally design an array and the associated inspection strategy.”
Preface by the author
1. Introduction
1.1 Introduction—1.2 Overview of key ideas—1.2.1 Array design as a process of compromise—1.2.2 The difference between the detection and characterisation problems—1.2.3 The importance of both the signal and the noise—1.3 The link between NDT and structural integrity—1.4 Array geometries and inspection configurations—1.5 Array imaging algorithms—1.6 A short history of ultrasonic arrays—1.7 Conclusions
2. Imaging
2.1 Introduction—2.2 The B-scan—2.3 B-scan through an interface—2.4 Full matrix capture and the total focusing method—2.4.1 Random noise considerations—2.5 TFM through an interface—2.6 Hybrid imaging techniques—2.6.1 Dynamic depth focusing—2.6.2 Plane wave imaging—2.7 Comparison of the algorithms—2.8 Calibration—2.9 Conclusions
3. Simulation of array data
3.1 Introduction—3.2 Some brief thoughts on the frequency domain—3.3 Creating the array element signals—3.4 Creating the transfer function—3.4.1 Transmitter and receiver directivity functions—3.4.2 Attenuation and beam divergence transfer functions—3.4.3 Propagation time transfer function—3.4.4 Scattering and reflection transfer functions—3.5 Creating an example output signal—3.5.1 Modelling noise—3.5.2 Simulating propagation through an interface—3.5.3 Scattering from defects—3.6 Conclusions
4. Array design
4.1 Introduction—4.2 Detection theory—4.3 Beam modelling—4.3.1 Grating lobes—4.3.2 Varying array parameters—4.4 Overview of inspection strategies—4.4.1 Embedded volumetric defects—4.4.2 Defects close to geometric reflectors such as a planar back wall—4.4.3 Embedded planar defects—4.4.4 Surface-breaking cracks—4.4.5 Rough and partially closed defects—4.4.6 Imaging through noisy media—4.5 Conclusions
5. Characterisation of defects
5.1 Introduction—5.2 Characterisation from the image—5.3 Characterisation from the scattering behaviour—5.3.1 Extracting the scattering matrix from array data—5.3.2 Crack characterisation using the scattering matrix—5.3.3 Amplitude based sizing—5.3.4 Probabilistic scattering matrix-based characterisation—5.4 Conclusions
6. Advanced imaging and characterisation
6.1 Introduction—6.2 Speed—6.3 Resolution—6.4 Information—6.4.1 Additional scattering information—6.4.2 Nonlinear imaging—6.5 Uncertainty in imaging parameters—6.6 Conclusions
Bibliography