Monitoring systems can already be found in common applications, from automotive to aeronautics or biomedical. However, the application of these monitoring systems has not yet been a very easy task, especially, at the sensor application step. A smart structure with sensing capabilities would allow to overcome the existing issues in the installation of sensor networks. As the size of this type of systems and the market requirements are significant, an industrial manufacturing process needed to be considered. An integrated solution based in Fiber Bragg Grating sensors embedded in PVC laminates was manufactured by industrial spread-coating process. The resultant structure is a temperature and strain sensitive foil that was characterized in terms of surface structure, optical response and overall performance. The integrated solution behavior had a slope of 0.8 pm by microstrain with a measurement range of 1.2 mm when the fiber was straight in the foil. Different fiber layouts were also tested and defined the minimum curve radius in 10 mm. The foil also presented a dimensional stability above 99%, ensuring the capability to sustain molding process. A mechanical analysis to evaluate the elongation capabilities and optical response was conducted. Three samples with different sensor positioning were subjected to the test. In the end, a sample, with the sensor in a 45à ° angle regarding the displacement axis, achieved the best compromise between maximum elongation range (25%) and optical response linearity. For the temperature response, a wavelength deviation of 1.7 nm was obtained for a 100 ºC temperature change.

A multipoint fiber-optic temperature sensor network integrated inside a power transformer for continuous monitoring of hot-spots on windings, cellulose insulations, and oil, is demon- strated and tested. The temperature sensors are based on propri- etary encapsulated fiber Bragg grating (FBG) sensors and the op- tical interrogation unit uses a special designed narrowband high power broadband fiber source. The fiber-optic sensing network is integrated into a 20MVA, 345/ kV kV power transformer (CORE type) having 12 temperature sensing points, distributed over several physical locations inside the transformer (windings, cellulose insulators, magnetic circuit, and cooling oil entrance and exit).