Transient analysis of energy harvesting from piezoelectric ceramic transducers under impulse mechanical excitation

Self-powered flexible and wearable sensors that conform to the human body are the futuristic trend in providing point-of-care health services. Body movements and resulting mechanical vibrations serve as one of the most reliable sources to power such a sensor. To this end, piezoelectric transducers provide efficient energy harvesting from mechanical vibrations. As such, this study is designed to investigate the transient response of energy harvesting from piezoelectric ceramic transducers for impulse excitation. A metal ball of 151 g falling from a height of 50 cm exerted 0.472 Ns of impulse excitation onto circular diaphragm piezoelectric transducers of different diameters. The generated voltage across a shunt load was measured using a benchtop digital voltmeter. An average of 7 V of energy was generated from a 50 mm diameter piezo transducer. Transient analysis was carried out with both shunt capacitors and resistors. The generated output voltage was critically damped within ~ 1100 ms for the shunt capacitor and over-damped within ~150 ms for the shunt resistor. Moreover, connecting multiple piezo transducers in parallel resulted in a higher output voltage of 14 V than the series connection of piezo transducers. The variation is mainly attributed to random changes in the polarity of the generated voltages. The results suggest that full wave rectification with a shunt capacitor would enhance the electrical energy extraction from impulse mechanical excitation.