Due to the problems of dispersion and multi-modes overlap for ultrasonic Lamb wave propagation, it is difficult to use it in many fields, such as long-range inspection. After ultrasonic Lamb waves are generated by a broadband ultrasonic pulse, these problems make the wave packets to spread out and various modes overlap in both time and space domain as they propagate through a plate or pipe. It ...

The equivalence of the energy velocity and the group velocity is often taught in university physics. An early proof of the equivalence of the two velocities for one-dimensional water waves was given by Rayleigh [1]. In the 1950s and 1960s many studies [2}4] were done to show the equivalence of the two velocities for more general systems. Later, in the 1990s, Awati and Howes raised a question as...

Previously we have reported the possibility of observing the fundamental antisymmetric (A0) Lamb wave propagating in the human tibia and radius. However, A0 velocity (1300-2000 m/s) overlaps that of soft tissue (1500 m/s), and it is therefore possible that signals propagating through soft tissue may be mistaken for an A0 wave in bone. In order to clarify this issue, measurements were performed ...

In this article, ultrasonic guided wave propagation and interaction with the rivet hole cracks has been formulated using closed-form analytical solution while the local damage interaction, scattering, and mode conversion have been obtained from finite element analysis. The rivet hole cracks (damage) in the plate structure gives rise to the non-axisymmetric scattering of Lamb wave, as well as sh...

Wave scattering analysis implemented by boundary element methods (BEM) and the normal mode expansion technique is used to study the sizing potential of two-dimensional shaped defects in a wave guide. Surface breaking halfelliptical shaped defects of three opening lengths (0.3, 6.35 and 12.7 mm) and through-wall depths of 10–90% on a 10 mm thick steel plate were considered. The reflection and tr...

A Lamb wave-based damage identification method called damage imaging method for composite shells is presented. A damage index (DI) is generated from the delay matrix of the Lamb wave response signals, and it is used to indicate the location and approximate area of the damage. A piezoelectric actuator is employed to generate the Lamb waves that are subsequently captured by a fiber Bragg grating ...

The objective is to develop a hybrid one-dimensional finite element (FE)/analytical method to analyze the Lamb Wave propagation characteristics in a composite panel for the purpose of detecting the specific structural defects in the composite panel. Here, it is proposed to use a composite panel using a finite element approximation in the thickness direction while wave solutions are assumed in t...

This work reports on theoretical and experimental study of zero-order as well as high-order symmetric and asymmetric modes of Lamb-wave resonators and delay line structures realized in single-crystalline GaN thin films. We investigate the phase velocity, dispersion characteristics, electromechanical coupling (kt), motional impedance (Rm) and Quality factor (Q) of different Lamb-wave modes (e.g....

It is well known that harmonic bounded Gaussian beams undergo a transformation into two bounded beams upon reflection on a solid immersed in a liquid. The effect is known as the Schoch effect and can be found at the Rayleigh angle for thick plates and at the different Lamb angles for thin plates. Here, a study is made on the effect of pulsed Gaussian beams reflected on solids. It is found exper...

Laminate composites which are widely used in the aeronautical industry, are usually subjected to frequency variation of environmental temperature and excessive humidity in the in-service environment. The thermal fatigue and moisture absorption in composites may induce material degradation. There is a demand to investigate the coupling damages mechanism and characterize the degradation evolution...