Analysis of bottom echo through rough test surface using equivalent circuit of ultrasonic transducer
S. Wadaka, T. Kimura, S. Kameyama, Mitsubishi Electric Corporation Kanagawa, Japan
ABSTRACT
It is important in ultrasonic non destructive testing to understand quantitatively the influence of surface roughness of a test object on an ultrasonic echo signal, and some experimental and theoretical results have been reported. However, theoretical analysis, taking into account the characteristics of an ultrasonic transducer, has not been reported. In this paper, bottom echoes, obtained in normal beam testing of a test object with a rough surface, are analysed, using an equivalent circuit of an ultrasonic transducer. The frequency response and/or the impulse of the ultrasonic transducer can be included in the analysis by using the equivalent circuit. The surface roughness of the test object is taken into account in the analysis by inserting a couplant layer between the ultrasonic transducer and the test object, and choosing the thickness of the couplant layer to be the half of the maximum height of the surface roughness. The couplant layer is modelled as an acoustical transmission line in the analysis. The first bottom echo and multiple echoes are calculated for a broad band ultrasonic transducer and a narrow band one, varying the maximum height of the surface roughness. The nominal frequency and the diameter of the ultrasonic transducers are 5MHz and 20 mm, respectively. It is shown that both the first bottom echo (B1 echo) height and the second bottom echo (B2 echo) height decrease as the surface roughness increases and these variations of the echo heights differ depending on the characteristics of the ultrasonic transducers. It is also shown that the ratio of the second bottom echo height to the first one increases and the variation of the ratio also differs depending on the characteristics of the ultrasonic transducers.
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission. Publisher:Woodhead Publishing Limited
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