Annular Array Search Units and Their Potential Application in Conventional Ultrasonic Testing Systems
This paper is based on a program to investigate the potential of multi-element annular arrays for practical application in ultrasonic testing systems. The annular array is comprised of coaxially-located, ring-shaped piezoelectric elements. By providing excitation pulses in a spherical time relationship, the transmitted beam may be focused at a specific range. By electronic switching, the focal point can be placed at various distances in the material under examination, Of particular interest is the length over which the beam can be held in collimation. Fabrication methods, delayed excitation techniques, and beam patterns in water and steel are described,
Acoustic Imaging Techniques for Nondestructive Testing
The characterization of transducers for quantative NDE applications requires that the radiation pattern, conversion efficiency, and bandwidth be accurately determined. These quantities may, in principle, be determined if the transducer’s construction and constituent parts are independentiy known. However, most often the internal detai ls of the transducer are unknown and subject to statistical variations and aging. A measurement technique and system for characterizing transducers based upon external measurements is described, which does not rely upon knowledge of the transducer’s construction. Manuscript received April 19, 1976. This work was supported in p a t by the Center for Advanced NDE, operated by the Science Center, Rockwell International, for the Advanced Research Projects Agency and the Air Force Materials Laboratory under Contract F33615-74C-5180. The authors are with the Electronic Sciences Laboratory, University of Southern California, Los Angeles, CA 90007. T
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.