SPACEFBG · FOBG - Design and validation of FOBG for SHM application

Fiber Bragg grating sensors (FBG) for structural health monitoring has gained increasing importance in aerospace applications, since it enables large-scale measurement of most relevant structural parameters while mitigating well-know technical constrains of conventional sensors.The main drawback of a fiber Bragg grating strain sensor is its thermal cross-sensitivity. Currently such a single parameter measurement is difficult to implement, since cross-sensitivity to temperature compels the use of an additional temperature reference.In this project a passive athermal FBG strain gage that renders optional the measurement of temperature is proposed. Such a design will benefit large scale system design and performance. The innovative design will ensure athermal operation of the strain gage by canceling the intrinsic fiber optic thermal sensitivity. Moreover the passive athermal design may be adjusted to further compensate for structural thermal expansion, thus enabling stress and load-induced strain-components to be measured.Special care will be taken on the design of the sensor enclosure to enable multiplexing of several sensors over a single optical fiber and ease installation procedures in aerospace applications. Qualified space fiber optic cables for sensing network deployment will be employed.Commercially available industrial interrogation unit equipment will be taken as a base to evaluate the optoelectronic hardware adaptation that would be required in order to fulfill aerospace specifications. The design requirements will be assessed in terms of mechanical (mass, volume, vibration and shock), thermal (heat dissipation and operation temperature range) and electrical parameters (power consumption and communication interface).Embedded software will allow for data conversion from wavelength measurements to engineering parameters (strain, temperature, load) that will afterwards be processed considering SHM requirements to provide automatic alarm generation.