STUDY OF LAMB WAVES BASED UPON THE FREQUENCY AND ANGULAR DERIVATIVES OF THE PHASE OF THE REFLECTION COEFFICIENT

This article deals with the introduction of a new method which allows the complete characterization of an elastic plate, on the one hand, in terms of resonances and, on the other hand, in terms of Lamb wave pro pagation. It is based upon the study of the derivatives of the reflect ion coefficient phase, considered either as a function of a frequency variable or as a function of an angular variable. When the Breit-Wigne r approximation is valid, i.e., when the poles of the reflection coeff icient are close to the real axis, the comparison with the resonant sc attering theory (RST) leads to the characterization of frequency or an gular resonances in terms of positions and widths, by means of the loc ation and of the magnitude of the phase derivative peaks. Moreover, th is method allows one to establish the important link between this reso nant theory derived from the RST and the normal mode theory of propaga tion. So, the width of a resonance is explicitly related to the imagin ary part of the wave vector of the associated Lamb wave.