A fast ultrasonic synthetic aperture imaging method: Application to NDT

The present study describes an efficient ultrasonic synthetic aperture imaging method with an application to NDT. The method employs monostatic data acquisition and a Fourier-domain algorithm for numerical focusing. One-dimensional holography and wavefront curvature compensation in the spatial frequency domain make the method fast and allow the development of a realtime, hand-held and low-cost scanner. In experiment, a mechanically scanned transducer consisting of 16 weighed elements of a 3.2 MHz phased array was used both in transmission and in reception. The -6 dB angular beam aperture was about 17 degrees in water. The point-spread function (PSF), which was measured from a circle divide 0.4 mm steel wire in a water bath showed that the -6 dB lateral resolution was about 1 mn with a side lobe level at about -40 dB. The lateral resolution of about 1.5 mm was achieved in a steel and in an aluminum test object.