University of Bristol  

Supervisors: Dr Alexander (Sasha) Velichko & Prof Anthony Croxford 

The field of ultrasonic array imaging has significantly advanced over recent years. Substantial improvements in mathematical modelling, imaging algorithms and phased array hardware have been achieved, with many new methods already employed in practical testing. However, most of the work is related to 1D arrays and 2D imaging. On the other hand, volumetric 3D imaging using 2D arrays has clear advantages, allowing ready differentiation of point like and 3D defects and producing more data for characterization (with an example of this shown in figure 1). However its use is currently limited by high computational resources and hardware complexity.  

This project will address this limitation through two main tasks: 

1. Optimisation of data acquisition and imaging strategies using 2D arrays.  

The maximum information, which can be measured by an array, corresponds to the Full Matrix Capture (FMC) data acquisition technique, and contains all possible combinations of transmitter–receiver signals. However, this strategy does not take into account the structure and physical nature of measured signals. As a result, there are significant redundancies in the FMC dataset. In this task the fundamental question about the minimum number of array measurements without loss of information will be investigated. The key idea is to consider array element layout, data acquisition method and image reconstruction algorithm within one optimisation framework.  

2. Quantitative defect characterisation using 2D arrays. 

It has been recently shown that it is possible to extract transmit-receive data, corresponding to each local material region, from the complete array data, corresponding to the whole measurement area. This local scattering information (also called scattering matrix, or S-matrix) represents the ultrasonic footprint of a defect and can be used for the quantitative defect characterisation. In this task these ideas will be extended for the case of 2D arrays and volumetric material features.  

Figure 1. Example volumetric imaging for a 2D array 

The project will be primarily supervised by Dr Velichko, within the Bristol Ultrasonics and NDT group. The group have extensive experience in Ultrasonic arrays and a well equipped lab for research in this area. This ensures an excellent working environment for the student, complimentary to the broader FIND training.