Detection of coatings within liquid-filled tubes and containers by mode conversion of leaky Lamb waves

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.

Build-up detection and level monitoring by using capacitive glocal technique

“…Manufactures used different contact and contactless approaches to overcome build-up effects. An acoustic principle based material coating detection sensor was also reported in [7] which operates on the principle of lamb wave's mode conversion. Due to the presence of material's coating in the container wall, the propagation time of waves are changed, resulting in the alteration of the waves properties and is detected by implementing two receivers on the outer side of the container wall.…”

Design and FEM analysis of multi segment capacitive level sensor based on local and global E-fields)

“…Several solutions are contributed to overcome the material coating problem in level detection approaches e.g. using electronic circuit in RF impedance based sensor, shielding effect in point detection sensor and high spray pressure washing in floating and ultrasonic sensor [12][13][14].…”

Monitoring of Soft Deposition Layers in Liquid-Filled Tubes with Guided Acoustic Waves Excited by Clamp-on Transducers

“…In this work a non-invasive ultrasonic approach has been realized by exciting Lamb-type guided acoustic waves on the outer surface of the wall of the tube by piezoelectric transducers and utilizing changes of their transmission behaviour along the tube wall, which reflect the formation of deposition layers on the inner surface of the pipe wall [ 10 , 11 , 12 , 13 , 14 ]. However, one has to be aware that in liquid-filled tubes with metallic walls Lamb wave modes and similar wave modes with sagittal displacements at the surface experience mode conversion into compressional waves in the liquid [ 15 , 16 ], which limits the range of inspection of the inner wall surface.…”

“…This study demonstrated that proper mode and frequency selection is a crucial issue with respect to optimal sensitivity to film buildup in view of the complex wave structure of guided waves in solids [ 17 ]. In another approach, employing leaky A 0 Lamb-type waves excited and detected with wavelength-selective piezoelectric single-phase transducers and travelling on the tube wall in axial directions, a sensitivity to adhesive tape layers on the inner surface of a water-filled plastic tube has been demonstrated [ 12 , 13 ].…”