Prospects for energy harvesting using ferroelectric/ferroelastic switching

Piezoelectric transducers have been widely employed for energy harvesting from vibration or kinetic energy sources. These systems, however, suffer from low energy density and consequently low power density at frequencies corresponding to common ambient vibrations. An alternative approach, using ferroelectric and ferroelastic switching offers potentially much greater energy density, at the cost of loss of linearity. Using a simple model of switching, a working cycle that could generate electrical energy from a harmonically varying source of stress is explored. The cycle uses depolarization by stress, followed by repolarization with combined electromechanical loading. A harvesting electric field and bias electric field are imposed to ensure a stable repeatable working cycle during the depolarization process and repolarization process, respectively. The bias electric field affects ferroelectric/ferroelastic switching, leading to a preferred direction of repolarization. By contrast, without bias electric field, stress alone would not trigger repolarization because of mechanically equivalent states with opposite polarization. The results illustrate that the bias electric field can be much lower than the harvesting electric field, requiring only a small electrical energy input during the cycle. Finally, the conversion efficiency of this cycle is estimated and improvements to the cycle are explored by adjusting the electrical and mechanical field amplitudes.