OPTIMAL GAIN DISTRIBUTION FOR TWO-DIMENSIONAL MODAL TRANSDUCER AND ITS IMPLEMENTATION USING MULTI-LAYERED PVDF FILMS

Using finite element techniques to optimize the spatial gain distribution of PVDF film, we developed a modal transducer for specific modes to perform real-time vibration control of integrated smart structures. This method makes it possible to design the modal transducer for two-dimensional structure with arbitrary geometry and boundary conditions. As a practical means for implementation, the gain distribution was approximated by optimizing electrode patterns, lamination angles, and relative poling directions of the multi-layered PVDF transducer. This corresponds to the approximation of a continuous function using discrete values. A genetic algorithm was used in the optimization of the electrode pattern and lamination angle of each PVDF layer. For this purpose, the continuous value of the lamination angle was encoded into discrete values using binary 5-bit strings. Validity of the proposed concept was demonstrated experimentally. A modal sensor for the first and second modes of cantilevered composite plate was designed using two layers of PVDF films. The experimental results show that spillover signals by residual modes were successfully reduced using the optimized multi-layered PVDF sensor. The actuator was designed also using two layers of PVDF films to minimize the system energy in the control modes. Real-time vibration control system was successfully realized using the optimized sensor, actuator, and a discrete LQG controller. Closed-loop test showed that modal peaks of the first and second modes were reduced by amounts of 13 and 4 dB respectively.