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
Anaesthetic aspects of bronchial fistula.
SINCE the term bronchial fistula can, from the practical point of view, be applied to any abnormal connection between the inside of the intrathoracic respiratory system and the outside, it includes a very wide assortment of cases. Fistulae vary in their acuteness and duration from a few minutes up to thirty years or more (Huizinga and Smelt, 1950), and in their consequences from the rapidly fatal to the almost insignificant. Although the anaesthetic management of these cases falls mainly within the province of those working in specialized units, any anaesthetist may be caught unawares from time to time. Quite apart from this consideration the subject is well worth discussing because of its intrinsic interest and because it has probably called for as much anaesthetic ingenuity and resourcefulness as any other subject within the specialty.