Negative Group Velocities of Lamb-Type Waves in a Glass/Water/Glass Structure Controlled by the Thickness of Water Layer

Abstract

In this paper, we described the characteristics of negative group velocities of Lamb-type waves in a glass/water/glass structure controlled by the thickness of the water layer. Lamb waves in an elastic plate have negative group velocities. It is known that the range of existence of negative group velocities depends on the Poisson's ratio of the elastic plate. However, in the case of Lamb waves, their negative group velocities depend on the physical parameters of each material; therefore, we fabricated a structure such that the negative group velocities of Lamb waves are controllable without the limitation of the parameters of each material. The waves in such a structure are referred to as the Lamb-type waves. Using numerical calculations, we determined that the negative group velocities of the Lamb-type waves can be varied by changing the geometric parameters, and the negative group velocities are changed although the frequencies are fixed. Additionally, we found that the Lamb-type waves have various characteristics corresponding to the propagation modes.

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…55) As mentioned above, ultrasound interacts with light, and various measurement methods, devices, and applications based on this principle have been researched, forming a research field called acousto-optics. 30,31,34,39,40,[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75] Brillouin scattering is caused when light is incident to a medium in which an ultrasonic wave propagates and the light and the ultrasonic wave interact with each other. This phenomenon itself is interesting and is also utilized to measure material properties such as elasticity and so forth.…”

Characteristics of group velocities of backward waves in a hollow cylinder

“…Generally, a large group velocity and a wide range of frequencies over which the backward mode exists (i.e., the backward-propagation effect is strong) is often required for the purpose of designing new acoustic devices utilizing backward waves. [10][11] For Lamb waves in elastic homogeneous plates, group velocities of backward wave branches are determined by only one factor -Poisson's ratio or the bulk velocity ratio 12 , the bulk velocity ratio ps VV   is related to the Poisson's ratio by 22 ( 2 One application of interest is the design of an acoustic isolator of the Logging-While-Drilling (LWD) monopole acoustic tool utilizing the backward-propagation effect. The LWD monopole acoustic technology is aimed at the real-time measurement of compressional wave velocities of earth formations during drilling.…”

“…The value of f up can be obtained from the cutoff frequency given by Equations (6-7) and (9)(10)(11)(12). The f down corresponds to the zero-group-velocity (ZGV) point at which the phase velocity is finite, the wavenumber is nonzero, and the group velocity is zero, i.e., , 0, 0.…”

Optical visualization of coupling modes of leaky Lamb waves with negative group velocity in the solid/fluid/solid trilayer

“…Theoretical negative group velocities for the A2-GSMs propagating through a solid/fluid/solid trilayer [8,9] as the function of the frequency-thickness product fd are shown in Fig. 1 for several different fluid thicknesses.…”