Numerical Investigation of Excitation of Various Lamb Waves Modes in Thin Plastic Films

Abstract

Ultrasonic-guided waves are widely used for the non-destructive testing and material characterization of plates and thin films. In the case of thin plastic polyvinyl chloride (PVC), films up to 3.2 MHz with only two Lamb wave modes, antisymmetrical A0 and symmetrical S0, may propagate. At frequencies lower that 240 kHz, the velocity of the A0 mode becomes slower than the ultrasonic velocity in air which makes excitation and reception of such mode complicated. For excitation of both modes, we propose instead a single air-coupled ultrasonic transducer to use linear air-coupled arrays, which can be electronically readjusted to optimally excite and receive the A0 and S0 guided wave modes. The objective of this article was the numerical investigation of feasibility to excite different types of ultrasonic-guided waves, such as S0 and A0 modes in thin plastic films with the same electronically readjusted linear phased array. Three-dimensional and two-dimensional simulations of A0 and S0 Lamb wave modes using a single ultrasonic transducer and a linear phased array were performed. The obtained results clearly demonstrate feasibility to excite efficiently different guided wave modes in thin plastic films with readjusted phased array.

Time Reversal Method for Lamb−Wave−Based Diagnostics of Multiple−Sleeve Grouting Connections

“…The best excitation signal of a single sleeve, as verified by Hu Y. [18], is found to be cycle number 4 at a center frequency of 15 kHz, so 15 kHz, and a total of five other frequencies of 5 kHz, 10 kHz, 20 kHz, 25 kHz, and 30 kHz were studied under cycle number 4. The time−domain signals extracted by the secondary receiver are shown in Figure 6.…”

“…Research presented in the article of Hu Y. [18] showed that the optimal excitation signal for a single embedded grouting sleeve was determined as the Lamb wave signal of cycle 4 and the frequency of 15 kHz. In this paper, multiple embedded grouting sleeves are studied, and the arrangement forms are distinguished.…”

“…et al used a phenomenon (the response signal propagation speed of Lamb waves from different types of injury areas is different) to propose an improved, fully focused imaging algorithm for different types of injury. This method can not only give the accurate injury location but also determine the injury types [17,18]. For the detection of a sleeve grouting connection, Hu Y.…”