Nonlinear Ultrasonic Phased Array Imaging

This Letter reports a technique for the imaging of acoustic nonlinearity. By contrasting the energy of the diffuse field produced through the focusing of an ultrasonic array by delayed parallel element transmission with that produced by postprocessing of sequential transmission data, acoustic nonlinearity local to the focal point is measured. Spatially isolated wave distortion is inferred without requiring interrogation of the wave at the inspection point, thereby allowing nonlinear imaging through depth.

Figure 1

Schematic of nonlinear array inspection configuration for (a) isolated fatigue crack and (b) fatigue crack and linear scatterers (dimensions in mm).

Figure 2

Fatigue crack images. (a) Sequential transmission energy $E_S$ (arb. units), (b) parallel transmission energy $E_P$ (arb. units), (c) nonlinear metric $(\gamma )$, and (d) linear TFM image (dB).

Figure 3

Fatigue crack with linear scatterer images. (a) Nonlinear metric $(\gamma )$ and (b) linear TFM (dB).