Fiber optic sensor network for structural health monitoring

Closed meshed instrument or sensor networks with conventional sensors for temperature and strain measurements may result in excessive penalties in terms of weight constraints, sensitivity to environmental conditions and complex interfaces. The FOS is a multiplexed sensor system for up to 50 single strain and temperature measurement points comprising of a fibre network and an optoelectronic unit. The FOS sensor was designed and developed by Kayser-Threde, Munich, for demanding space environment, but can also be emphasized as a promising sensor technology with high potential for non-space applications. A Fibre Optic Sensor (FOS) measures strain and temperature by means of wavelength shifts due to tensile stress on a Bragg grating. Slightly shifts in the reflected wavelength are proportional to temperature or strain acting on the fibre at the corresponding grating location. Dependent on the fixation of the fibre to the structure, either floating or attached to the surface, local thermal or mechanical loads can be determined. The fibres can be mounted at the monitored structure or embedded (e.g. into composite materials). The FOS sensor is very suitable for structural health monitoring of large structures, i. a. to determine thermal and mechanical load profiles during operation, assessment of residual strength of structural elements or to detect irregular conditions. In comparison to conventional sensors like thermocouples and strain gauges, a FOS network significantly reduces the amount of required Front End Electronics (FEE) and harness.