Eccentric Virtual Array Source Aperture (EVASA)—Ultrasound Imaging Technique Using Phased Array Excitation

Abstract

The traditional phased array ultrasound technique (PAUT) uses active focusing of elements to achieve beam forming and improved imaging capabilities. The recent approach involving FMC/TFM improves this method using synthetic reconstruction approaches. In this research, we introduce a novel hybrid approach that combines active and synthetic focusing at specific angle configurations, utilizing an Eccentric Virtual Array of Source Aperture (EVASA) in the Phased Array Ultrasonic Testing (PAUT) method. Some of the key advantages of this EVASA approach include (a) transmission at a specific angle with focus at a certain depth (b) lower time for inspection, (c) improved imaging of defect shapes and sizes, and (d) improved imaging of defects in regions where it was hard to reach (e) inspect the defects in much thicker samples with ease compared to FMC/TFM. The EVASA method employs a custom algorithm where array elements transmit ultrasound waves with pre-calculated delay laws, achieving beamforming focused at eccentric virtual sources located beneath the transducer. These virtual sources will focus on particular depths and angles, which will send a high-amplitude wave into the material for inspection at much deeper defects. Once the desired set of eccentric virtual sources has been formed within the material, the synthetic algorithms of FMC/TFM can be used to image the regions of inspection into the material. The parameters for forming the virtual sources, including their number, aperture position in the probe, and coordinates within the material, are based on the propagation angle and focal depth, extending up to the near-field distance. Comparative evaluation of EVASA with FMC/TFM shows its significant advantages, using metrics like Signal-to-Noise Ratio (SNR) which show substantial improvements. Importantly, EVASA is implemented using standard PAUT probes and instruments, requiring only customization in focal laws and reconstruction algorithms.