Continuous wavelet transform application in diagnostics of piezoelectric wafer active sensors

Piezoelectric wafer active sensors (PWAS) are employed in a variety of structural health monitoring (SHM) applications. Failure of these might lead to significant problems, so monitoring of actuators themselves is necessary. While totally debonded PWAS can be detected easily, small debondings could still occur. In that case PWAS is still capable of generating ultrasound waves, but might lead to false diagnostic results since the underlying baseline measurements are not valid anymore. Therefore an experimental setup with a specimen of 16 partially debonded actuators has been used. Phenomena accompanying wave excitation by debonded actuators are examined. Collected knowledge is analyzed in order to identify existence, location and shape of a debonded part of the actuator. For a sufficiently debonded PWAS some interesting abnormalities have been detected for high frequencies. Wavelet analysis has revealed that the velocities of the motion and carrier frequencies depend on the shape of the debonded part of the PWAS.