AIR-COUPLED ULTRASONIC CAPACITANCE TRANSDUCERS FOR NDT

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WCNDT '96 - New Delhi
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AIR-COUPLED ULTRASONIC CAPACITANCE TRANSDUCERS FOR NDT

D. A. Hutchins*, A. G. Bashford*, W. M. D. Wright*, D. W. Schindel**, and A. Kumar***
*Department of Engineering, University of Warwick, Coventry CV4 7AL, UK
**National Research Council, Institute for Aerospace Research, Structures and Materials Lab, Montreal Road, Building M-14, Ottawa, Ontario, Canada, K1A OR6

***National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi - 110 012, India

Keywords: Air-Coupled Ultrasonic, Capacitance Transducer, Micromachined silicon, Wide bandwidth, Through Transmission

ABSTRACT

Air-coupled ultrasonic transducers, with enough sensitivity for non-contact NDT, have been manufactured and tested. These are based on electrostatic principles, using a carefully machined conducting electrostatic principles, using a carefully machined conducting backplate, and a thin flexible polymer membrane. The devices have used a range of backplate materials. In one design, a micromachined silicon backplate has been manufactured using etching technology. This gives a good response into the MHz range, with excellent sensitivity. In other designs, laser machining has been used to produce a series of patterns on the surface of both silicon and steel backplates, in the form regularly-spaced cylindrical holes. These transducers have been used as both sources and receivers, to perform NDT measurements on a range of materials and structures. It will be shown that they can be used to produce wide bandwidth through-transmission images of artificial and real defects in carbon fibre reinforced polymer composites, without contact to the sample. They can also be used for thickness determination. Additional work has shown that Lamb waves can be generated and detected using these transducers in air, and results will be shown of images obtained from non-contact Lamb-wave tomography, using a pulsed laser as a source.

Ultrasonic Testing - Instrumentation

Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2061 - 2066
Publisher: Ashgate Publishing Company