Phased array ultrasonic imaging using angle beam virtual source full matrix capture-total focusing method

Abstract

Full matrix capture coupled with total focusing method (FMC-TFM) is one of the most advanced and popular phased array ultrasonic techniques used to achieve simultaneous focusing at all depths in a specimen. In case of conventional FMC-TFM technique, a single element is used for transmission that limits the transmitted energy. This leads to reduced sensitivity at larger depths particularly in attenuating materials such as austenitic alloys. An Angle Beam Virtual Source FMC (ABVSFMC) method is proposed in the present paper to enhance the sensitivity by increasing the transmitted energy with specific directivity. The methodology utilizes apertures of a few elements to obtain a diverging beam by focusing very near to the top surface (virtual source). Further, as a group of elements is used in transmission, a divergent beam with specific directivity can be achieved without using a wedge. In reception, all the available channels are used and an algorithm similar to the Total Focusing Method (TFM) is used to reconstruct the image. The methodology is demonstrated by imaging the tip diffracted signals obtained from slot type planar defects at various depths in the range of 25–175 mm in a 200 mm thick nickel base alloy forging.