Underwater thrust and power generation using flexible piezoelectric composites: anexperimental investigation toward self-powered swimmer-sensor platforms

Abstract

Fiber-based flexible piezoelectric composites offer several advantages to use in energyharvesting and biomimetic locomotion. These advantages include ease of application,high power density, effective bending actuation, silent operation over a rangeof frequencies, and light weight. Piezoelectric materials exhibit the well-knowndirect and converse piezoelectric effects. The direct piezoelectric effect has receivedgrowing attention for low-power generation to use in wireless electronic applicationswhile the converse piezoelectric effect constitutes an alternative to replace theconventional actuators used in biomimetic locomotion. In this paper, underwaterthrust and electricity generation are investigated experimentally by focusing onbiomimetic structures with macro-fiber composite piezoelectrics. Fish-like bimorphconfigurations with and without a passive caudal fin (tail) are fabricated andcompared. The favorable effect of having a passive caudal fin on the frequencybandwidth is reported. The presence of a passive caudal fin is observed to bringthe second bending mode close to the first one, yielding a wideband behavior inthrust generation. The same smart fish configuration is tested for underwaterpiezoelectric power generation in response to harmonic excitation from its head.Resonant piezohydroelastic actuation is reported to generate milli-newton levelhydrodynamic thrust using milli-watt level actuation power input. The average actuationpower requirement for generating a mean thrust of 19 mN at 6 Hz using a 10 gpiezoelastic fish with a caudal fin is measured as 120 mW. This work also discussesthe feasibility of thrust generation using the harvested energy toward enablingself-powered swimmer-sensor platforms with comparisons based on the capacity levels ofstructural thin-film battery layers as well as harvested solar and vibrational energy.