A conventional contact piezoelectric transducer, excited by a broadband burst (chirp) that covers its whole frequency bandwidth, is used as a transmitter to simultaneously generate several Lamb waves in a plate. Throughout the propagation, these modes leak energy into the ambient air, producing bulk waves in many directions. The association of a parabolic mirror and an air-coupled transducer (PMAT) allows these waves to be received in air with a large angular aperture. By displacing the PMAT in a direction parallel to the plate, but without changing its orientation like when standard air-coupled receivers are used, a series of temporal waveforms are captured. Signal processing then allows the phase velocity of the several Lamb waves to be measured in large wave number and frequency domains. These resulting data are used to identify the moduli of ela sticity for composite plates made of long glass fibers and polymer matrix.
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