Abstract
Abstract. In this paper, a new acoustic sensor principle for coating detection within liquid-filled tubes and containers based on mode conversion of leaky Lamb waves is introduced. Leaky Lamb waves are excited and detected by single-phase transducers, which are attached on the outer side of a tube or container. By transmission time and amplitude measurements, coating formation within the liquid-filled tube and container is detected non-invasively. This new sensor principle is subdivided into the separate considerations of Lamb wave excitation, mode conversion and inverse mode conversion. The Lamb wave excitation by a single-phase transducer is visualized by scanning laser Doppler vibrometer imaging. The mode conversion process of leaky Lamb waves is measured by membrane hydrophone measurements and Schlieren visualization; afterwards, the measured emission angles are compared with the theoretical one. The inverse mode conversion process of pressure waves back to leaky Lamb waves is visualized by Schlieren images. By merging the results of Lamb wave excitation, mode conversion and inverse mode conversion, the new sensor concept is explained. Theoretical considerations and measurement results of adhesive tape coating inside a liquid-filled plastic tube and a liquid-filled stainless steel container verify the new acoustic sensor principle. Finally the measuring sensitivity and the technical realization are discussed.
Highlights
The detection of coatings within liquid-filled tubes and containers is relevant for many technical facilities
By transmission time and amplitude measurements, coating formation within the liquid-filled tube and container is detected non-invasively. This new sensor principle is subdivided into the separate considerations of Lamb wave excitation, mode conversion and inverse mode conversion
The inverse mode conversion process of pressure waves back to leaky Lamb waves is visualized by Schlieren images
Summary
The detection of coatings within liquid-filled tubes and containers is relevant for many technical facilities. Leaky Lamb waves, which have a dominant emission into the adjacent liquid, are excited and detected by single-phase transducers, which are attached to the outer side of the tube or the container structure. Only non-leaky Lamb wave (Lohr and Rose, 2003) on non-piezoelectric substrates or shear horizontal waves on piezoelectric substrates (Balantine et al, 1997; Thomson and Stone, 1997) were investigated, because it was thought that bulk acoustic waves or surface acoustic waves with a dominant vertical displacement would be inapplicable for coating detection in a liquid environment (Lange et al, 2008; Calabrese et al, 1987) In this journal paper, the new acoustical sensor concept based on mode conversion of Lamb waves will be introduced. The measuring sensitivity and the technical realization of the new acoustical sensor concept will be discussed
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