Application of Phase-Reversal Fresnel Zone Plates for Improving The Elevation Resolution in Ultrasonic Testing with Phased Arrays

Currently, phased arrays have found wide application in ultrasonic nondestructive testing. Volumetric results provided by the inspections with linear phased arrays have low lateral resolution in the elevation direction of such probes. This fact complicates the defects characterization task. In this paper, we suggest the application of the Phase-Reversal Fresnel Zone Plate to increase the resolution of volumetric imaging with linear phased arrays. Application of such plates is aimed at ultrasonic focusing in the elevation plane whereas focusing on the active aperture plane is provided by the application of the Sampling Phased Array. Furthermore, the use of the Phase-Reversal Fresnel Zone Plate is advantageous due to the capability of its 3D printing and introduction to the existing automated testing systems avoiding making changes to the current software and hardware. The effectiveness of the plates was verified experimentally on the existing automated testing system. The obtained experimental results demonstrate that the application of the Phase-Reversal Fresnel Zone Plate allowed achieving the results of the higher resolution as well as improving the signal to noise ratio.