Publication

Attenuation of Lamb Modes and SH Waves near cut-off Frequencies

Soumya Yandrapalli, Victor Plessky
2020
Article de conférence
Résumé

Near cut-off frequencies, the shear horizontal (SH) and Lamb modes in a platelet are created by a bulk acoustic wave bouncing up and down between the platelet sides in an almost vertical direction. The small inclination angle corresponds to slow drift of energy along the platelet (low group velocity), but the attenuation of the bulk wave accumulates fast. Therefore, the attenuation of these waves along the platelet near the cut-off frequency is high, being roughly inversely proportional to the group velocity.

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Concepts associés (18)
Vitesse d'une onde
Une onde est une perturbation qui se déplace dans un milieu. Il est possible de lui associer deux vitesses d'onde, soit la vitesse de phase et la vitesse de groupe qui, parfois, ne sont pas égales : Dans un milieu homogène, la propagation dans une direction donnée d'une onde monochromatique (ou sinusoïdale) se traduit par une translation de la sinusoïde à une vitesse appelée « vitesse de phase » ou « célérité ». Dans un milieu non dispersif, cette vitesse ne dépend pas de la fréquence.
Group velocity
The group velocity of a wave is the velocity with which the overall envelope shape of the wave's amplitudes—known as the modulation or envelope of the wave—propagates through space. For example, if a stone is thrown into the middle of a very still pond, a circular pattern of waves with a quiescent center appears in the water, also known as a capillary wave. The expanding ring of waves is the wave group or wave packet, within which one can discern individual waves that travel faster than the group as a whole.
Signal velocity
The signal velocity is the speed at which a wave carries information. It describes how quickly a message can be communicated (using any particular method) between two separated parties. No signal velocity can exceed the speed of a light pulse in a vacuum (by Special Relativity). Signal velocity is usually equal to group velocity (the speed of a short "pulse" or of a wave-packet's middle or "envelope"). However, in a few special cases (e.g.
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