Fig. 1. Schematic diagram of piezoelectric energy harvesting vibrator.

Fig. 2. Schematic diagram of SECE circuit.

Fig. 3. Schematic diagram of thyristor switch.

Fig. 4. Schematic diagram of ISECE circuit.

Fig. 5. Schematic diagram of spring–damping–mass vibration model.

Fig. 6. Surface topography of sputtered ZnO film under magnification factor of 8000.

Fig. 7. XRD spectrum of sputtered ZnO film.

Fig. 8. Schematic diagram of experimental setup.

Fig. 9. Experimental apparatus of whole energy harvester testing system.

Fig. 10. Plots of theoretical voltage output Uversus frequency f for four different thickness values of ZnO film.

Fig. 11. Plots of theoretical voltage output Uversus frequency f of ZnO film under four different external forces.

Fig. 12. Plots of theoretical output power Pversus resistance in SECE and ISECE circuits.

Fig. 13. Plots of experimental voltage output Uversus frequency f under three different forces.

Fig. 14. Experimental output power Pversus resistance R in SECE and ISECE circuits.