Analysis and Compensation of Relative Humidity and Ice Formation Effects for Radar-Based SHM Systems Embedded in Wind Turbine Blades

This work aims at a structural health monitoring (SHM) system using radar sensors at 60 GHz embedded in a wind turbine blade. For a reliable operation of the system, the influences of changes in the ambient climate on the embedded sensors has to be taken into account and shall thus be studied and analyzed. Three sensors are embedded for experiments and are exposed to a defined environmental state in a climate chamber. The signals for different target states are measured, processed and discussed. An evaluation of the dependencies shows how critical these influences are on radar signals and baseline-based SHM methods working with them. These results motivate the development and classification of compensation methods. The considered methods are a baseline selection method and a polynomial fitting approach. Both methods are exemplarily applied to the measured data. Finally the sensors are used to measure ice formation. Conclusions on the detectability of ice are made, as well as on its influence to other measurements.