TABLE OF CONTENTS Extensive experiment were carried out to verify the detection ability of 1-D linear EUSR algorithm using the setup described in a previous section, with the only difference that the PWAS transducers consisted of eight 7-mm round wafers (Fig. 11.11)
In order to minimize the Lamb modes appearing in the wave and strengthen the signal, a frequency tuning process is established. The excitation frequency was selected as 282 kHz at which the low-dispersion S 0 mode is maximally excited. The data was collected in the round-robin pattern, resulting in a total of M 2 data sets where M is the number of elements in the array. EUSR algorithm processed the raw data and mapped the scanning beams in a 2D/3D image for further structural diagnosis.
To evaluate the capability of the EUSR PWAS phased array to detect very small defects, we performed experiments in which a pin hole of increasing size was placed at 90 azimuth at 315 mm away from the array. The size of the pin hole was progressively increased from 0.5 mm to 1.0 mm, 1.57 mm, and 2.0 mm (the sizes were determined by available drill bits). Experiment results showed that EUSR was unable to detect the very small holes of size 0.5 mm and 1.0 mm. This was not surprising...
