This paper investigates the potential of a non linear wave modulation SHM methodology with piezoelectric wafers as actuators and sensors to reveal impact damage in cross-ply Glass/ Epoxy composite plates. In the experimental procedure an electromechanical shaker and piezoceramic wafers are simultaneously used to provide the low and high frequency wave excitation, respectively, while for the acquisition of the modulated carrier wave a piezoceramic sensor was used. Two sets of piezoceramic actuators-sensor pairs are used to propagate the ultrasonic carrier wave into two directions, one parallel and transversely to the fibers of the outer unidirectional ply. Nonlinearities induced by the damage are detected as sidebands in the spectral components of the carrier signal. Experimental results quantify the potential of the method in detecting damage created by very low energy impacts (4 Joules). Additionally, the modulation factor of the sensor signal is proposed as damage index, and is shown to be a consistent and sensitive damage indicator in the impacted plates, for a broad range of carrier wave frequencies.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.