Dynamic focusing through arbitrary geometry interfaces

This paper introduces the fast focal law calculator (FFLC), a Newton-Raphson based algorithm that performs such task accurately at high speed. It is especially well suited for dynamic focusing through arbitrary geometry interfaces, where other algorithms are order of magnitude slower. In spite of the high speed of the FFLC, errors are kept very small, typically within a few tens of picoseconds. Besides a short background theory, the paper compares the results of the FFLC with regard to exact solutions (for planar interfaces) and those based on search algorithms. Field simulations are performed to assess the correctness of the method. Also, experiments are carried out with a curved interface showing the advantages of the FFLC for dynamic focusing to improve the image quality and the flaw detection and evaluation capabilities.

I. Introduction

During the last years, phased array technology has widespread in the Non Destructive Evaluation field (NDE). It provides beam steering and focusing by electronic means, producing images that speeds up the inspection process. The focal law is the set of delays applied in emission and/or reception to get the desired steer angle and focus position.