Microwave excitation of ultrasound in graphite-fiber reinforced composite plates.
In this paper is demonstrated the effect of microwave beam polarization on the thermal generation of acoustic waves in continuous fiber-reinforced composite laminates. It is found that beam polarization strongly influences the dielectric interaction that leads to thermal losses, bulk expansion, and acoustic wave generation. The oriented graphite fibers in the composite laminate effectively short the microwave fields and reduce the generation efficiency nearly to zero. Ultrasonic waves at several hundred kHz generated in the composite are detected by air-coupled acoustic transducers located on the opposite side of the plate specimen from the 9.41 GHz incident microwave beam. With some averaging signal-to-noise ratios of better than 26 dB are obtained. Applying a conventional model of electromagnetic wave scattering in anisotropic media to this experiment yields good agreement between calculations and measured data. Implications for microwave-acoustic testing of graphite-reinforced composites are also discussed.
Guilliorit
Emmanuel
E
Laboratoire de Mécanique Physique, Université Bordeaux 1, UMR 5469 CNRS 351, cours de la Libération, 33405 Talence Cedex, France.
Hosten
Bernard
B
Bacon
Christophe
C
Chimenti
D E
DE