Theoretical and experimental study of the Lamb wave eigenmodes of vibration in terms of the transducer thickness-to-width ratio

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Abstract
In order to improve ultrasonic systems, like imagers, it is more probably necessary to get a better understanding of the transducer behavior, rather than refine the associated electronic parts. For the completion of this study of transducer behavior, the mathematical finite element model may be used, and then the transducer vibration may be analyzed at a particular frequency. Here, the simpler method of modal analysis has been chosen, since it gives a clearer physical insight. It is shown that a Lamb waves model describes well the propagating modes along the three principal directions of the transducer. Among these modes, those which resonate along the width W have been observed experimentally. The particular interest in these modes arise from the fact that they induce severe distortions in the acoustic radiation pattern and must therefore be suppressed. Moreover, the modes which resonate along the thickness t must be retained, since their contribution to the radiation pattern is essential. Then an optimal geometry may be found for a transducer operating at a given nominal frequency.