Energy scavenging using ZnO nanorods grown on flexible substrates

Vertical ZnO nanorods (NRs) were grown on flexible plastic substrates using the hydrothermal synthesis method. An energy scavenging piezoelectric device was developed by integrating two flexible substrates with the NR sides facing each other. With an applied mechanical compressive force, a maximum open-circuit voltage of 2.5 V (p-p) was measured. The ZnO piezoelectric device was also utilized to monitor human heartbeats that generated an output voltage of 150 mV per pulsation. The frequency response of the fabricated ZnO NR piezoelectric device was measured over a frequency range extending from 50 Hz to 20 kHz. The device exhibited a voltage ratio of 0.113 over the frequency range from 50 Hz to 800 Hz followed by a gradual decrease to 0.08 at 20 kHz. This is approximately eight times more sensitive at higher frequencies compared to commercial microphones.