Bio-inspired aquatic robotics by untethered piezohydroelastic actuation

TLDR

Bimorph propulsors made of macro‑fiber composite piezoelectric laminates provide noiseless, efficient actuation across frequencies, geometric scalability, and a balance between force and velocity for enhanced bio‑inspired swimming performance. This study investigates fish‑like aquatic robotics employing flexible MFC bimorphs for carangiform locomotion. The authors experimentally characterize an elastically constrained MFC bimorph propulsor for thrust generation, develop an untethered robotic fish prototype powered by a microcontroller and PCB amplifier, and use a distributed‑parameter electroelastic model coupled with elongated‑body theory to predict thrust, validated by in‑air and underwater experiments across linear and nonlinear actuation regimes. Measured mean thrust of ~10 mN in quiescent water matches biological fish, and the untethered prototype achieves a swimming speed of 0.3 body‑lengths per second (7.5 cm s⁻¹) at 5 Hz with a non‑optimized bimorph configuration.

Abstract

This paper investigates fish-like aquatic robotics using flexible bimorphs made of macro-fiber composite (MFC) piezoelectric laminates for carangiform locomotion. In addition to noiseless and efficient actuation over a range of frequencies, geometric scalability, and simple design, bimorph propulsors made of MFCs offer a balance between the actuation force and velocity response for performance enhancement in bio-inspired swimming. The experimental component of the presented work focuses on the characterization of an elastically constrained MFC bimorph propulsor for thrust generation in quiescent water as well as the development of a robotic fish prototype combining a microcontroller and a printed-circuit-board amplifier to generate high actuation voltage for untethered locomotion. From the theoretical standpoint, a distributed-parameter electroelastic model including the hydrodynamic effects and actuator dynamics is coupled with the elongated-body theory for predicting the mean thrust in quiescent water. In-air and underwater experiments are performed to verify the incorporation of hydrodynamic effects in the linear actuation regime. For electroelastically nonlinear actuation levels, experimentally obtained underwater vibration response is coupled with the elongated-body theory to predict the thrust output. The measured mean thrust levels in quiescent water (on the order of ∼10 mN) compare favorably with thrust levels of biological fish. An untethered robotic fish prototype that employs a single bimorph fin (caudal fin) for straight swimming and turning motions is developed and tested in free locomotion. A swimming speed of 0.3 body-length/second (7.5 cm s−1 swimming speed for 24.3 cm body length) is achieved at 5 Hz for a non-optimized main body-propulsor bimorph combination under a moderate actuation voltage level.