Fiber optic sensors system for high temperature monitoring of aerospace structures

The study and development of Structural Health Monitoring (SHM) systems for aerospace applications is one of the best challenges for the research in the field of fiber optic (FO) sensors. The harsh environments in which these aerospace structures have to work are the major limit for the employment of standard fiber optic sensors for the thermo-mechanical monitoring processes. Thermal loads which act on these structures do not allow using standard fiber optic sensors used for classic avionics application. In fact, many aerospace structures can be exposed to temperatures up to 1000 degrees C, higher than the operation temperature of the standard fiber optic sensors. In this paper a new fiber optic system for structural analysis of ultra high temperature ceramic (UHTC) materials is proposed. A tunable laser source is used to easily measure the spectral response of different fiber optic sensors. Moreover the employment of an in-fiber optical circulator and TLC 1x4 optical switch, allows to perform a multi-sensor interrogation, to analyse many physical parameters, such as: temperature, strain, pressure, etc.. In particular the monitoring system has been used to test high temperature resistant Fiber Bragg Grating sensors. The first tests at high temperature, up to 600 degrees C, have shown a good response in terms of: sensitivity, resolution, repeatability and dynamic range of the measurement. At last, the flexibility of the electro-optical system developed for the interrogation of the fiber optic sensors, allows the extension of the instruments to mechanical stress analysis, using custom fiber optic strain sensors currently under development.