This method involves acoustically coupling a transducer to a porous film, producing a plate wave
in the porous film and generating a signal characteristic of the film.
The symmetrical or extensional plate wave velocities are independent of frequency, i.
The plate wave velocities within the composite plates were found by measuring the time taken for the waves to propagate along a 10 cm distance through the plate, Two surface mounted sensors were situated 10 cm apart and a lead break was made on the surface of the plates 10 cm away from the first sensor.
It can be clearly seen from this Figure the two plate wave modes of propagation.
0 cm respectively for a plate wave traveling along the direction of the fibers in a unidirectional composite plate.
The bimorphs have essentially differentiated between the two types of plate wave propagation, although the differentiation has been determined by the wavelength of the acoustic wave compared to the sensor dimensions.
The extensional modes will be sensed prior to the flexural modes at a time that will depend on the distance, from the source, that the plate waves have propagated.
Because of this mismatch in mode velocities the signal produced, when a sensor detects an elastic plate wave originating from an acoustic emission, will comprise of two distinct components.
The signal produced by the PTCa/P(VDF-TrFE) transducer shows that this transducer has been able to detect and distinguish both the extensional and flexural modes of a plate wave traveling in the 0 [degree] direction.
6 pC/N, showed the lower response to the extensional mode of the plate wave.
In this case the waves are called plate waves and are derived from classical plate theory.
Embedding of composite transducers in glass reinforced epoxy laminate plates has been achieved and the ability of these sensors to detect plate waves generated by a simulated acoustic emission source has been studied.