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NDT.net Issue - 2016-07 - Articles
NDT.net Issue: 2016-07
Publication: 19th World Conference on Non-Destructive Testing (WCNDT 2016), 13-17 June 2016 in Munich, Germany (WCNDT 2016)
Session: Non-Contact Ultrasonics
ARTICLE

Focusing Air-Coupled Ultrasonic Transducers Based on Ferroelectrets

Florian Schadow7, Mate Gaal43, Jürgen Bartusch23, Elmar Dohse20, Enrico Köppe4
Akustische und elektromagnetische Verfahren; BAM Federal Institute for Materials Research and Testing1326, Berlin, Germany

Abstract: Rising importance of composite lightweight structures in aircraft and automobile industries increases the demand on reliable non-destructive testing methods for these structures. Air-coupled ultrasonic testing emerged to suit these requirements as it does not require any liquid coupling medium. In conventional air-coupled ultrasonic transducers, matching layers are used in order to decrease the impedance mismatch between transducer and air. Matching layers can be omitted by using ferroelectrets, which are charged cellular polymers having ferroelectric and piezoelectric properties. Especially a low Young’s modulus, low density and low sound velocity of cellular polypropylene (cPP) are properties being required for well-matched air-coupled ultrasonic transducers. In our contribution we show recent enhancements of cPP transducers resulting in focused sound fields and thus improved lateral sensitivity. The influence of different transmitter apertures was evaluated using measurements of the emitted sound field. Further we show a transmission of a test specimen of carbon-fiber-reinforced plastic (CFRP) containing artificial damages. Results of focused transducers were compared to planar ferroelectret transducers, as well as to conventional air-coupled transducers.

Keywords: transducer (342), focusing (17), ferroelectret (10), Non-Contact Ultrasonics (3),
*Keywords are freely formed keywords from the authors and thus you may Search also for similar terms.

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