Airplane structure health monitoring by the optical frequency modulation Brillouin distributed measuring method

摘要

The necessity for Airplane structural health monitoring technology has been increasing, because of improvement of reliability and maintenance cost reduction. Optical fiber sensing system is an attractive scheme for airplane structural health monitoring. There are great hopes for applying the system to airplane structural health monitoring because of the light weight, non-electromagnetic interference, durability and capability of sensors to be embedded to composite structures. Especially the distributed optical fiber sensor fits the health monitoring for large-sized structures. However, the distributed optical fiber measurement system using the pulse light represented by the Brillouin optical time domain reflectometer (BOTDR) has low spatial resolution and long measurement interval. These performances have been the obstacle of application to airplane structure health monitoring system. Then, the authors have proposed the Brillouin optical frequency modulation method for improvement of the spatial resolution. In this work, we conducted basic approaches in order to develop the Brillouin optical frequency domain Analysis (BOFDA) measurement system, such as estimation of influences of a pump power property and a frequency modulation property for Brillouin stimulated light. We confirmed ability to measure stimulated Brillouin scattering light in 50mm section. Moreover, we considered the optical fiber sensor installation issue on the airplane structure. This issue is induced by optical fiber sensor birefringence under asymmetric load of installation method. We conducted two confirmatory tests for the issues to verify a proposed installation method has adequate performance. From these results, it was confirmed that BOFDA system has potential to be applied to an airplane structure health monitoring system.