Flexible piezoelectric strain energy harvester responsive to multi-directional input forces and its application to self-powered motion sensor

A design of flexible piezoelectric strain energy harvester responsive to multi-directional forces from arbitrary human motions was developed by using polydimethylsiloxane (PDMS) and polyvinylidene fluoride (PVDF). Unlike the most of conventional strain energy harvesters designed to be functional only for single directional motion, our suggested design demonstrated the energy harvesting capability for all the input forces applied in multiple different directions. The measured output voltage was 1.75, 1.29, and 0.98 V for the input force of 4 N at 2 Hz applied in the direction of 0°, 45°, and 90°, respectively. The variation of output peak voltage was within 54% of the maximum value for the identical magnitude of forces when the applied direction varies from pure normal direction to pure shear direction. The harvester could keep output voltage in the similar order of magnitude upon diverse directional forces applied. Through the harvester mounted on a curved human body, the motion between body and arm was successfully converted to electricity.