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Non-destructive evaluation of engineering ceramics by high-frequency acoustic techniques

: Arnold, W.; Herzer, R.; Pangraz, S.; Simon, H.

Acoustical Imaging. Vol.18
1990 (Acoustical imaging 18)
International Symposium on Acoustical Imaging <18, 1989, Santa Barbara>
Fraunhofer IZFP ()
Breitbandanregung; broadband excitation; ceramic; defect detection; Fehlernachweis; Keramik; narrowband excitation; PVDF-Schallwandler; PVDF-transducer; schmalbandige Anregung; Ultraschall; ultrasound

In order to detect defects by ultrasound efficiently, it is necessary to make the wavelength comparable to the defect size. Due to fracture mechanics considerations, it is necessary to detect defects smaller than 100 um in engineering ceramics by NDT-techniques. This requires high-frequency ultrasonics due to the large sound velocity in ceramics and, in order to obtain sufficient spatial resolution, pulses shorter than 100 ns are needed. A large bandwidth for both the electronics and the transducer are then needed. The transducer employed may be excited by either an exponentially decayimg step-pulse (broadband excitation) or by a rf carrier-pulse. Both excitation techniques were employed in the well-known imaging techniques like A- and C-Scans, and as well in the synthetic aperture technique.