Application of contrast optimisation autofocus to flexible ultrasonic arrays for non‐destructive testing

Abstract

Flexible ultrasonic arrays are used for imaging within objects with complicated geometries for non‐destructive testing and evaluation (NDT/NDE), e.g., thick‐walled pipes, weld caps, etc. We consider the application of autofocus techniques (routinely used in synthetic aperture sonar (SAS)) to this engineering problem. A flexible ultrasonic array is functionally similar to a wide‐beam, stripmap SAS with a single transmitter and receiver. Unfortunately, there are few autofocus algorithms available for this configuration. Popular algorithms, such as echo/image correlation, PGA, DPCA, etc., are better suited for use with a narrow‐beam or multiple‐receiver SAS. However, contrast optimisation is a more general technique that is well suited to the single transmitter/receiver geometry. In this presentation, we describe our implementation of contrast optimisation autofocus and show experimental results using a flexible array prototype.