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We investigate the time-frequency localization of the continuous wavelet transform as a tool for extracting useful informations about targets from their ultrasonic echoes. A disbond problem is presented as an example. We also present and discuss the use of experimental ultrasonic echoes as analyzing wavelets. This technique is used to study the effect of targets geometry on the received echoes.

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This paper présents an extension of a model présentée! by the same authors in the previous CFA [1]. The model allows fast computations of the acoustical impulse-response of the problem of the radiation of ultrasonic puises by realistic transducers, their scattering by immersed targets and their réception. In the previous version, the model was restricted to the case of small targets centered on the transducer axis. Hère, it is shown that a more gênerai formula can be derived allowing the computation of the echo-responses from targets not necessarely centered on axis which can be of arbitrary size. It is shown that the présent model may be considered as an extension to the transient case of the well-known Freedman's model which derived from a CW theory. Basically, the idea is to restrict the computation to the contributions arising from the onJy parts of the target where interférences are constructive.

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