No abstract

Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.

No abstract

Electric surface excitation of ultrasound in the Coulomb field of scanned electrically conductive spherical local probes and similar detection has been employed for imaging of the transport properties of acoustic waves in piezoelectric materials including singlecrystalline wafers. The employed Coulomb scheme leads to a fully predictable and almost ideal point excitation and detection. In combination with two-channel quadrature transient detection it allows high precision spatially and temporally resolved holographic imaging. Via modeling of the excitation and propagation properties, the effective elastic tensor and the piezoelectric properties of the observed materials can be determined with high resolution from a single measurement. The generation and detection scheme as well as the theoretical background are demonstrated and applications are exemplified.

No abstract