Validation of Novel Ultrasonic Phased Array Borehole Probe by Using Simulation and Measurement

Abstract

Low-frequency ultrasonic testing is a well-established non-destructive testing (NDT) method in civil engineering for material characterization and the localization of cracks, reinforcing bars and delamination. A novel ultrasonic borehole probe is developed for in situ quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The aim is to examine the sealing structures made of salt concrete for any possible cracks and delamination and to localize built-in components. A prototype has been developed using 12 individual horizontal dry point contact (DPC) shear wave transducers separated by equidistant transmitter/receiver arrays. The probe is equipped with a commercially available portable ultrasonic flaw detector used in the NDT civil engineering industry. To increase the sound pressure generated, the number of transducers in the novel probe is increased to 32 transducers. In addition, the timed excitation of each transducer directs a focused beam of sound to a specific angle and distance based on the previously calculated delay time. This narrows the sensitivity of test volume and improves the signal-to-noise ratio of the received signals. In this paper, the newly designed phased array borehole probe is validated by beam computation in the CIVA software and experimental investigations on a half-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction methods, it is expected that an optimised radiation pattern of the probe will improve the signal quality and thus increase the reliability of the imaging results. This is an important consideration for the construction of safe sealing structures for the safe disposal of radioactive or toxic waste.

Enhancing the Performance of a Large Aperture Ultrasound System (LAUS): A Combined Approach of Simulation and Measurement for Transmitter–Receiver Optimization

“…Within the ultrasonic testing module, there is a section dedicated to beam analysis, dealing with ultrasonic wave propagation characteristics. In addition, the inspection simulation module is tailored to simulate ray-based ultrasonic reflections that correspond to various reference defects and thus mimic real-world measurement scenarios [ 13 , 29 , 30 ].…”

“…We designed our simulation model and properties based on a specimen with a horizontal reference borehole (parallel to the surface on which the instrument is placed) used to assess borehole measurements [ 13 ]. For the purposes of our research, we designed four distinct simulation scenarios, described as follows: Retaining a consistent spacing between units while varying the diameter of the borehole to assess the impact of hole size on the results.…”

“…In terms of array operations, each unit sends out ultrasonic waves that are detected by the other units equivalently to real measurements. We designed our simulation model and properties based on a specimen with a horizontal reference borehole (parallel to the surface on which the instrument is placed) used to assess borehole measurements [13]. For the purposes of our research, we designed four distinct simulation scenarios, described as follows: a.…”

“… (a ) Single DPC shear wave transducer 50 kHz center frequency [ 13 ], ( b ) single ultrasound unit consisting of 32 DPC transducers. …”

“…The requirement to use an acoustical coupler on non-uniform surfaces sometimes limits the widespread application of ultrasonic evaluations in civil engineering. Nevertheless, recent advances, such as the introduction of DPC transducer systems and the transition to low-frequency transducers (with frequencies of 20–100 kHz), are gaining momentum in the field of non-destructive structural evaluation [ 6 , 12 , 13 ].…”