Effect of polymer layer on the performance of piezoelectric harvester in thickness-shear vibration

Because of its relatively high resonant frequency, a thickness-shear mode piezoelectric harvester composed of a cylindrical piezoelectric ceramic shell is not suitable for converting mechanical energy to electrical energy from ambient vibration sources, most of which are of low frequencies. Therefore, it´s important for us to reduce the resonant frequency so as to enlarge the application domain of the harvester, and the traditional method is to increasing the attached mass or the thickness of the piezoelectric shell. But if we want to decrease the system resonant frequency much more, some new ideals must be proposed. This article presents an efficient approach to decrease the resonant frequency by fixing a polymer layer at the inner surface of the piezoelectric shell. Based on the linear piezoelectricity theory, the effects of the geometrical parameters of the polymer layer on the performance of the piezoelectric harvester are analyzed. Numerical results indicate that the use of polymer layer can considerably reduce the system resonant frequency.