Study of the vertical modes of a periodic plane medium immersed in water
Résumé
We are interested in a medium composed of N periods including two perfectly bonded plates which exhibit a high acoustic impedance contrast. N is varied from 2 to 10. Among the propagative modes in this structure, we can detect the so-called vertical modes at low frequency. Their labeling is due to the fact that their dispersion curves are vertical in the (frequency, angle) plane. In addition, their cutoff frequencies are inferior to the lowest cutoff frequency of the modes propagating in each plate. These vertical modes are linked with the coupling effect occurring between the plates which have the strongest acoustic impedance in the periodic medium. Comparisons between the dispersion curves obtained in vacuum and the zeroes of the reflection coefficient of the water loaded periodic medium are presented. Approximate analytical expressions of the cutoff frequencies of the vertical modes are obtained by developing at the fourth order the trigonometric functions appearing in the dispersion equations. It can be of use for the inverse problem, to find phase velocities or thicknesses.
Domaines
Acoustique [physics.class-ph]
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2011 - Khaled - Study of the vertical modes of a periodic plane medium immersed in water.pdf (368.42 Ko)
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