A comparative study is presented between Bragg grating (FBG) and polarimetric sensors (PS), two of the most promising fiber optic sensing techniques for the structural health monitoring of smart materials based on carbon fiber composites. The paper describes the realization of a test plate equipped with both types of sensors and reports the characterization under static and dynamic conditions, highlighting pros and cons of both technologies. The FBG setup achieves 1.15 ± 0.0016？pm/kg static load response and reproduces dynamic excitation with 0.1% frequency uncertainty; the PS system exhibits a sensitivity of 1.74 ± 0.001？mV/kg and reproduces dynamic excitation with 0.5% frequency uncertainty. It is shown that the PS technology is a good and cheap alternative to FBG for vibration-monitoring of small structures at high frequency. 1. Introduction Carbon-fiber composites (CFCs), also known as carbon-fiber-reinforced polymers (CFRP), carbon-fiber-reinforced plastics (CRP), or carbon-fiber reinforced thermoplastics (CFRTP), represent an important class of composite materials that are finding an increasing application in several technological contexts, ranging from industry to aerospace, bioengineering, construction, and automotive industry, just to mention a few [1]. CFCs are widely employed in the transportation industry thanks to the their extremely advantageous strength-to-weight and stiffness-to-weight ratios. Since sensors and actuators can be embedded directly into the materials, they are promising candidates for the realization of smart structures; for example, they are able to implement advanced stiffness control techniques leading to the virtual stiffness concept [2, 3]. Fiber optic sensors (FOS) represent one of the most valuable sensing technologies for smart structures based on CFCs, because they have minimum invasive impact, can be easily embedded, are immune from electromagnetic disturbances, and can measure submicrometric deformations [4]. The study of embedded optical sensors in CFCs dates back to the nineties [5]; with the exception of former experimental investigations on sensing techniques such as Brillouin time domain reflectometry [6], the most researched sensing principle has involved fiber Bragg gratings (FBG) [7]. The primary reason for the interest in FBGs is that they offer the unique feature of encoding the strain response in a spectral signature and are therefore immune from power fluctuations and environmental factors other than mechanical and thermal stresses. In the case of FBGs the bibliography is broad and only a subset of
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