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We proposed a method for visualizing wave propagation in ultrasonic fields. This method generates thermal-excitation ultrasonic waves on a specimen through pulsed laser scanning and detects the propagating signals via a reception transducer mounted on a fixed point. Dynamic images of ultrasonic waves propagated from a fixed point are created using the reciprocity principle of wave propagation. This method has the excellent feature that enables a visible and quick flaw inspection for actual objects. However, since this method visualizes all waves propagating on an object, it is disadvantageous in that defect echoes are often hidden in the forward traveling wave. In this research, we developed a data processing method for image enhancement of defect echoes. In the ultrasonic tests with aluminum plates or pipes with rear defects, we could visualize the defect echoes as they scatter in a radial manner, like water rings, on the surface of the specimen, which proved the validity of this data processing method. These results demonstrated the usefulness of the laser-based ultrasonic visualization technique in flaw inspection. [ABSTRACT FROM AUTHOR]

The non-destructive characterization of multiple embedded void inclusions forms an important part of the assessment of the integrity and quality of materials. In this report, we present an ultrasonic sensing method for detecting void inclusions. The idea is based upon the arrival probability of ultrasonic rays. When incident rays impinge on voids, they are diffracted around the voids to increase propagation time. We analyzed this phenomenon from a probabilistic view point, and found that the probability with which ultrasonic rays will impinge on pores plays an important role in determining both sound velocity and waveform of arrival rays. On the basis of this theory, we derived the relational equations between void distributions (volume fraction and mean size) and ultrasonic characteristics (velocity and pulse width). Although this theory is very simple, it gives a reasonable explanation of the changes in both velocity and waveform. In order to examine the theory for its validity, we carried out ultrasonic tests using aluminum specimens with multiple drilled holes and ceramic specimens with artificial voids. The experimental results demonstrated the validity of this theory. We propose this method as a smart sensing technique for evaluating the integrity of materials containing multiple defects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]