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

Abstract

An ultrasonic technique for imaging nonlinear scatterers, such as partially-closed cracks, buried in a medium has been recently proposed. The method called fundamental wave amplitude difference (FAD) consists of a sequence of acquisitions with different subsets of elements for each line of the image. An image revealing nonlinear scatterers in the medium is reconstructed line by line by subtracting the responses measured with the subsets of elements from the response obtained with all elements transmitting. In order to get a better insight of the capabilities of FAD, two metallic samples having a fatigue or thermal crack are inspected by translating the probe with ultrasonic beam perpendicular (i.e. parallel) to the crack direction which is the most (i.e. less) favorable case. Each time, the responses of the linear scatterers (i.e. conventional image) and nonlinear scatterers (i.e. FAD image) are compared in term of intensity and spatial repartition. FAD exhibits higher detection specificity of the crack with a better contrast than conventional ultrasound imaging. Moreover, we observe that both methods give complementary results as nonlinear and linear scatterers are mostly not co-localized. In addition, we show experimentally that FAD resolution in elevation and lateral follows the same rule as the theoretical resolution of conventional ultrasonic technique. Finally, we report that FAD gives the possibility to perform parametric studies which let the opportunity to address the physical mechanisms causing the distortion of the signal. FAD is a promising and reliable tool which can be directly implemented on a conventional open scanner ultrasound device for real-time imaging. This might contribute to its fast and wide spread in the industry.

Nonlinear Maximization of the Sum-Frequency Component from Two Ultrasonic Signals in a Bubbly Liquid

“…The nonlinear interaction between the acoustic field p(x, t) and the bubble oscillations, expressed in volume variation, v(x, t) = V(x, t) − v 0g , can be described by the system of differential equations formed by the wave Equation (1) and a Rayleigh-Plesset Equation 2 [14,16,17], where x is the one-dimensional space coordinate, t is the time, T t is the last instant of the study, V is the current volume of bubble, and v 0g = 4 3 πR 3 0g is the initial bubble volume, with initial radius R 0g :…”

“…Ultrasound-based techniques have been widely used in material science to characterize the medium or to localize cracks (nondestructive evaluation) [1][2][3][4] and in medical imaging to diagnose pathologies [5,6]. These techniques rely on the detection of transmitted or reflected ultrasonic waves.…”

High-resolution 3D phased-array imaging of fatigue cracks using piezoelectric and laser ultrasonic system (PLUS)

“…Since crack depth is a critical parameter for the maintenance management of aging infrastructures, the accurate measurement of crack depth has been intensively studied. [6][7][8][9][10][11][12][13][14][15][16][17] On the other hand, fracture mechanics 18) indicates that crack depth can change in the crack-length direction. 19,20) However, B-scan images obtained by a linear array transducer give a spatially-averaged crack geometry over the elevation aperture of the linear array transducer.…”

A nonlinear ultrasonic modulation approach for the detection and localisation of contact defects

“…In addition, it is relatively easier to satisfy the conditions necessary for defect excitation by using input waves of two different frequencies instead of a single frequency [38]. For example, Haupert et al introduced an amplitude modulation method relying on image acquisition from phased arrays, where the linear material response is subtracted from the modulated signal revealing the image of nonlinear scattering in steel specimens with thermal fatigue cracks [39,40]. Alston et al focused on the detection of a kissing bond between two aluminium blocks based on non-collinear mixing of shear waves from two sources producing nonlinear longitudinal waves at sum-frequency that were captured by a phased array of sensors [41].…”