Using Appropriate Models and Synthetic Data to Study the Properties of TFM Ultrasonic Imaging

Mora, P.; Fraunhofer Institute for Nondestructive Testing IZFP; Germany

Oetiker, M.; GE Inspection Robotics Ltd; Switzerland
Baur, W.; GE Inspection Robotics Ltd; Switzerland
Zesch, W.; GE Inspection Robotics Ltd; Switzerland
Mora, P.; Fraunhofer Institute for Nondestructive Testing IZFP; Germany
Spies, M.; Fraunhofer Institute for Nondestructive Testing IZFP; Germany

ID: ECNDT-0375-2018
Download: PDF
Session: Data Processing - UT
Room: G2
Date: 2018-06-15
Time: 11:50 - 12:10

Ultrasonic inspection techniques on the basis of phased arrays classically exploit the capabilities to focus and steer the ultrasonic beam fields. An alternative to these beam forming methods is the ‚Full-Matrix-Capture‘ (FMC) approach which steps through all pairs of transmitter-receiver element combinations for data acquisition, thus recording the full data matrix. Imaging is then performed using the Total Focusing Method (TFM) by applying the respective delay laws to focus via algorithmic data processing. In view of defect sizing and characterization with respect to defect type, geometry and orientation such imaging techniques gain increasing relevance. The efficiency of the applied reconstruction techniques with respect to a specific inspection situation depends on the material and component parameters on the one hand as well as on the defect configuration and geometry on the other.

In this contribution, we investigate the imaging capabilities of the Total Focusing Method by first addressing side-drilled holes (SDH) as model defects. For simulating the FMC data acquisition by an array transducer we have used a 2D Fraunhofer-approximation. For the scattering of the ultrasonic waves at the SDH we have used two model approaches – a Kirchhoff type far-field approximation and the Separation of Variables method as an exact technique [1]. On this basis we have simulated time-domain ultrasonic data for various scenarios where the defect parameters SDH diameter and distance between two SDHs have been varied. Addressing a commercial contact phased array probe (16 elements, 5 MHz frequency) we have generated synthetic data to perform TFM imaging, also addressing the influence of noise on the image quality. We will also report on further results obtained e.g. in simulating data acquisition using immersion technique. Investigations on the basis of synthetic data help in evaluating the performance of such imaging techniques for specific inspection situations under concern.

[1] Schmerr, L. W., & Song, J. S. (2007). Ultrasonic nondestructive evaluation systems: models and measurements. Springer Science & Business Media