Enhancement of Selectivity in Nonlinear Ultrasonic Imaging of Closed Cracks Using Amplitude Difference Phased Array

Abstract

Subharmonic waves realize a high selectivity for closed cracks. However, when a short-burst wave is used to achieve a high temporal resolution, not only closed cracks but also linear scatterers appear in the subharmonic image owing to leakage in frequency filtering. They are ghosts that degrade the selectivity for closed crack in the subharmonic image. Here, we propose an amplitude difference phased array (ADPA), where the ghosts are eliminated by subtracting a subharmonic image at a small input multiplied by the input amplitude ratio from that at a large input. We verified the ADPA method by a two-dimensional simulation based on the finite difference time domain (FDTD) method with damped double nodes (DDNs) for subharmonic imaging of closed cracks. Furthermore, the ADPA method was experimentally verified in a closed-crack specimen.

Subharmonic Wave Generation at Interfaces of a Thin Layer between Metal Blocks

“…Since experiments were carried out in the range of input voltage below 500 V in this study, the maximum displacement is about 7.4 nm. This result indicates that subharmonic wave is generated at the interfaces of the blocks and the thin layer with relatively small incident wave displacement compared to the previous experiments [9][10][11][12][13][14][15] .…”

“…Higher harmonic generation at interfaces was successfully modeled with dash-pot, spring-mass and/or nonlinear spring, which agreed well with the experimental results. However, for the subharmonic generation [6][7][8][9][10][11][12][13][14][15] , theoretical studies and fundamental experiments are insufficient to explain the phenomena clearly. This paper, therefore, discusses the mechanism of subharmonic generation from experimental results obtained for aluminum blocks with a thin aluminum foil.…”

Exploiting Slow Dynamics Effects for Damage Detection in Concrete

“…Several techniques for damage detection and localization have thus been developed based on the dynamics of the propagating wave to extract a nonlinear signature of the sample. Applications are reported for metals (Ohara et al, 2012;Hong et al, 2018;Li et al, 2019), composites (Amura and Meo, 2012;Genoves et al, 2015), rocks (Riviere et al, 2015), biological samples (Ulrich, 2007), etc. Damage related nonlinear elastic properties of materials of interest in civil engineering have also been widely studied: thermal induced damage (Payan et al, 2007;Scalerandi et al, 2013), corrosion cracks (Antonaci et al, 2013;Boukari et al, 2015), effects of carbonation (Bouchaala et al, 2011), or of static loads either external or shrinkage induced (Antonaci et al, 2010a,b;Kim et al, 2017), etc.…”

Fundamental wave amplitude difference imaging for detection and characterization of embedded cracks

“…Until about 10 years ago, the studies of nonlinear ultrasonics had been mainly based on waveform analyses received by monolithic transducers [7] making difficult rapid 3-D scan of specimen. Recently, new nonlinear imaging techniques based on phased arrays have been proposed to image with high sensitivity buried partially-closed cracks that remain mostly invisible to conventional imaging [8][9][10][11][12][13].…”