Abstract: A variety of structure integrated damage monitoring systems is based on non destructive testing (NDT) techniques which require sensing only. Damage information can only be given through external stimuli such as loads or vibrations being generated from the structure. Independence is achieved through an actuation system built into the structure, that allows to generate stress waves at any time. This principle is used with ultrasonic or lamb wave techniques and allows NDT to become an integral part a material when piezoelectric elements are adapted or integrated into it. Monitoring of the structure can thus happen on a `push-button' basis. In addition a lot of effort is devoted to sensor signal processing. Sensor signals may be understandable for components of simple geometric shape and isotropic material. With increasing complexity in geometry, anisotropy or damage configuration, signal processing becomes more ambitious, being a challenge for techniques such as neural networks, genetic algorithms, wavelet analysis or fuzzy logic. This paper explains some background logic of an actuator/sensor- based monitoring technique built into the structure. Different techniques for identifying an optimum number of sensors as well as handling complex signals is discussed. Verification of the technique is done for tests performed on a center-cracked panel.!28
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