Generation of negative group velocity Lamb waves by a moving laser source

Alexey M Lomonosov; Chenyin Ni; Zhonghua Shen; Zheng Li

doi:10.1016/j.ultras.2019.105950

Generation of negative group velocity Lamb waves by a moving laser source

Ultrasonics. 2019 Nov:99:105950. doi: 10.1016/j.ultras.2019.105950. Epub 2019 Jun 24.

Authors

Alexey M Lomonosov¹, Chenyin Ni², Zhonghua Shen³, Zheng Li⁴

Affiliations

¹ School of Science, Nanjing University of Science and Technology, Nanjing 210094, China; Prokhorov General Physics Institute of the Russian Academy of Sciences, 119911 Moscow, Russia; Scientific-Technological Center of Unique Instrumentation, Russian Academy of Sciences, 117342 Moscow, Russia.
² School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
³ School of Science, Nanjing University of Science and Technology, Nanjing 210094, China. Electronic address: shenzh@njust.edu.cn.
⁴ School of Science, Nanjing University of Science and Technology, Nanjing 210094, China.

PMID: 31386939
DOI: 10.1016/j.ultras.2019.105950

Abstract

Analytical existence conditions for negative group velocity (NGV) of an arbitrary mode Lamb waves in elastic plate was obtained. Experimentally, NGV waves were excited by means of a thermoelastic laser source moving across the sample plate with a controllable velocity. Such source is coupled with modes which phase velocity component parallel to the surface coincides with the source speed. Additional mode selection was performed by choosing a quasiperiodic shape of the laser spot, which specifies the range of the wavenumber k. This technique was successfully applied for generation of backward (NGV) waves. By tuning the speed of the source the propagation direction was switched from forward to reversal.