Self-Focusing of Rayleigh Waves and Lamb Waves with a Linear Phased Array

Abstract

A simple idea for self-focusing of a linear array has been extended to Rayleigh and Lamb waves. The self-focusing procedure first measures the backscattered signals for a first transmission by a single element of the array. A cross-correlation technique is used to determine the time-of-flight differences of the backscattered signals received by the elements of the array. These time delays are used to adjust the times of excitation of the elements for transmission focusing on the defect. Using the differences in arrival time once more, the backscattered signals after transmission focusing are aligned for reception focusing. Experimental results demonstrate the ability to self-focus on single defects. For multiple defects, the technique has been extended to focus on the defect that produces the largest backscattered signal.

Calculation and Measurement of Scattering Coefficients for Surface-Breaking Cracks Sonified by a Focused Array

“…Next, the self-focusing procedure [4] was applied to obtain the excitation times of the array and to sonify the crack with a focused Rayleigh wave. The excitation times can be used to ensure that the crack is located on the center axis of the array.…”

“…The specimen surface defines the ~1 x 2 plane. Focused surface wave motion at the flaw location is generated by the transducer array, which is coupled to the specimen surface with an acrylic wedge [4]. The focal distance is XF.…”

“…Comparisons of theoretical and experimental results, where the latter were obtained by the use of a laser interferometer [3], showed excellent agreement for the normal displacement both along a radial line and across the width of the beam. The transducer array with a center frequency of 5 MHz was used for surface-defect detection, whereby the focal region was automatically adjusted to the defect location [4].…”

Embedded Non-destructive Evaluation for Structural Health Monitoring, Damage Detection, and Failure Prevention

“…⁄ = the time reversal method. Deutsch et al (1997) also used to concept of reversing the reflected waves in order to focus a linear array of conventional ultrasonic transducers transmitting Rayleigh and Lamb waves. The time reversal method has proven especially useful in ultrasonic imaging of difficult media (Berryman et al, 2002).…”

Ultrasonic phased array with surface acoustic wave for imaging cracks

“…On the other hand, the combination a Email: ohara@material.tohoku.ac.jp 2158-3226/2017/7(6)/065214/7 7, 065214-1of an array transducer and a Rayleigh wave has been proposed. 20,21 The array transducer was positioned on the top of a wedge whose angle is equal to the third critical angle that allows the Rayleigh wave to be generated on the surface of the specimen. A surface defect was detected with high sensitivity based on a time-reversal process.…”