### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 5aPA4. Relation between the damping coefficient and the excitation
coefficient of leaking Lamb waves.

**M. Ech Cherif El Kettani
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F. Luppe
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J. M. Conoir
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J. Ripoche
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**
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*L.A.U.E., U.R.A. C.N.R.S. 1373, Univ. du Havre, pl. R. Schuman, 76610 Le
Havre, France
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*
*
The relation between the leaking ability and the excitation coefficient of
a propagating Lamb wave on an immersed plate is studied. The more the Lamb wave
radiates during its propagation, the more strongly it is expected to be excited
from the incidence of an ultrasonic beam at the appropriate angle. The
excitation coefficient of a given Lamb wave at a given frequency--thickness
product is obtained from a residue calculation. It is numerically achieved from
the exact formulation of the reflection coefficient, and analytically performed
with the help of the resonance scattering theory approximations. Both methods
exhibit clearly the proportionality of the excitation coefficient with the
normalized damping coefficient. The direct measurement of the excitation
coefficient is not possible because of the interference phenomenon of the Lamb
wave radiation with the specularly reflected beam. Consequently, the
measurements are performed far away from the interference area. The linearity
of the pressure amplitude (in dB) with the propagation distance allows the
direct determination of the damping coefficient, as well as the extension of
the experimental data to the interference area. The excitation coefficient is
herefrom deduced. The results confirm the theoretical ones. [Work supported by
D. R. E. T., France.]