A quasi-modal approach to overcome FBG limitations in vibration control of smart structures

Embedding FBG sensors in carbon ???ber structures is a very attractive procedure, due to the small ???ber cross section and to the possibility of manufacturing arrays of many gratings into a single optical ???ber. This embedding is particularly useful for the manufacturing of smart structures, enabling improvement of their characteristics thanks to the embedded sensors and actuators. However, the low precision of FBG measurements makes the effectiveness of such signals in control applications limited. This paper deals with the possibility of reducing vibrations in structures by using distributed sensors embedded in carbon ???ber structures through the so-called sensor-averaging technique. This method provides a properly weighted average of the outputs of a distributed array of sensors generating spatial ???lters on a broad range of undesired resonance modes without adversely affecting phase and amplitude. This approach combines the positive aspects of decentralized control techniques, because the control forces applied to the system are independent, with, as for centralized controls, the possibility of exploiting the information from all the sensors. Theoretical aspects are supported by experimental applications on a large ???exible system composed by a thin cantilever beam with 30 longitudinal FBG sensors and six piezoelectric actuators (PZT).