PVC Smart Sensing Foil for Advanced Strain Measurements

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 45$^{\circ}$ 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$\,^{\circ}\hbox{C}$ temperature change.