Over the past several years, there has been increasing interest in harvesting energy from ambient vibrations in the environment by converting mechanical energy into electrical energy. A popular method is to use a piezoelectric cantilever beam. In order to harvest the most energy with the device, the beam's fundamental mode must be excited. However, this is not always possible due to manufacturing of the device or fluctuations in the vibration source. By being able to change the frequencies of the beam, the device can be more effective in harvesting energy. In this paper, a model for a three layered piezoelectric cantilever beam utilizing a shunt tuning circuit will be presented. The fundamental frequency of a cantilever beam is dependent on the stiffness and mass of the beam. Either adding a tip mass to the end of the beam or increasing the dimensions of the beam can alter the mass. The stiffness of the beam is a function of the geometry, mechanical properties, and the electromechanical coupling of the piezoelectric element. In this paper we prepare the use of a piezoelectric layer with an attached shunt circuit for tuning its stiffness, and thus the beam frequency. The piezoelectric coefficients of this layer and its shunt circuit determine the amount of electromechanical coupling. By varying the shunt circuit, the beam can be tuned to a certain frequency. This paper presents a study of the effects additional harvesting and tuning layers have on the amount of tuning and generated power in the beam. These additional layers will add more piezoelectric material as well as mass to the beam and therefore there will be a balance between the amount of harvested energy and the tunable frequency range. By quantifying the effects of these parameters, it will be easier to design a harvester to be used in a particular frequency range as well as to produce a certain level of power.
Electricity Generation System with Piezoelectric Element Using Acoustic Radiation Energy
