Guided waves based structural health monitoring, mainly Lamb waves, have a great potential for localization of wavelength-order damage within plate-like composite structures. Baseline algorithms are often criticized for not taking into account environmental conditions such as temperature and damage prior to the creation of baseline signals. The current trend is to develop new algorithms using only measurements in the current state. This thesis work aims to implement and apply new baseline-free algorithms coupled with the optimization of the placement and the number of sensors, in order to achieve a good diagnosis of complex composite structures.