Design of piezoelectric energy harvester with additional springs for varying stiffness of module

Abstract

Piezoelectric energy harvesting systems are mainly used in low-power circuits and small sensors because of the low output power. To enhance the output power, we developed a new method that overcomes the weaknesses of piezoelectric ceramic products. In a single degree-of-freedom system, a piezoelectric cantilever composed of a piezoelectric ceramic and a substrate beam was analyzed by modeling the equivalent mechanical system. Based on this equivalent system model, a new method was designed to determine the total stiffness of module, which consists of the stiffnesses of the substrate beam and additional springs. Additional springs were connected to the free end of the substrate beam. The total stiffness of module was varied by connecting additional springs having different stiffness constants to the substrate beam. The results showed that a high total stiffness achieved using an additional spring led to a higher natural frequency of the beam. Therefore, the matching impedance was decreased, and the output power was increased. The advantage of the method is that the stiffness of the entire system can be varied using a detachable spring, without changing the piezoelectric ceramic material. Using this proposed system, the stiffness for a specific external energy can be optimized, and the efficiency of piezoelectric energy harvesting can be increased.