Trout-like multifunctional piezoelectric robotic fish and energy harvester

Abstract

This work presents our experimental studies on a trout-inspired multifunctional robotic fish as an underwater swimmer and energy harvester. Fiber-based flexible piezoelectric composites with interdigitated electrodes, specifically macro-fiber composite (MFC) structures, strike a balance between the deformation and actuation force capabilities to generate hydrodynamic propulsion without requiring additional mechanisms for motion amplification. A pair of MFC laminates bracketing a passive fin functions like artificial muscle when driven out of phase to expand and contract on each side to create bending. The trout-like robotic fish design explored in this work was tested for both unconstrained swimming in a quiescent water tank and under imposed flow in a water tunnel to estimate the maximum swimming speed, which exceeded 0.25 m s −1 , i.e., 0.8 body lengths per second. Hydrodynamic thrust characterization was also performed in a quiescent water setting, revealing that the fin can easily produce tens of mN of thrust, similar to its biological counterpart for comparable swimming speeds. Overall, the prototype presented here generates thrust levels higher than other smart material-based concepts (such as soft polymeric material-based actuators which provide large deformation but low force), while offering simple design, geometric scalability, and silent operation unlike motor-based robotic fish (which often use bulky actuators and complex mechanisms). Additionally, energy harvesting experiments were performed to convert flow-induced vibrations in the wake of a cylindrical bluff body (for different diameters) in a water tunnel. The shed vortex frequency range for a set of bluff body diameters covered the first vibration mode of the tail, yielding an average electrical power of 120 μW at resonance for a flow speed around 0.3 m s −1 and a bluff body diameter of 28.6 mm. Such low-power electricity can find applications to power small sensors of the robotic fish in scenarios such as ecological monitoring, among others.

Robot Fish Caudal Propulsive Mechanisms: A Mini-Review

“…Figure 2(c) shows a subcarangiform swimming robot fish as the one reported in [27]. This work presented studies on a trout-inspired multi-functional soft-robotic fish.…”

A comprehensive review on fish-inspired robots

“…Macro fiber composite (MFC), another type of piezoelectric material, comprises rectangular cross-sectional piezoelectric fibers and interdigitated electrodes. 95 In addition to good flexibility and large driving force, MFC strikes a balance between the deformation and actuation force, which means that the additional magnifying mechanism is not required. Govindarajan et al 96 tested the performance of the MFC flapping beam underwater.…”

“…The robot reaches a swimming speed of 7.5 cm/s (0.3 BL/s), which shows the feasibility of the MFC-actuated robotic fish. In addition, Tan et al 95 designed a modular MFC bimorph tail connected to the body. With the actuation of the MFC actuator, the prototype reaches the maximum speed of 0.25 m/s (0.8 BL/s).…”

Recent advancement of flow-induced piezoelectric vibration energy harvesting techniques: principles, structures, and nonlinear designs

“…In this section, few advanced FIV-based energy harvesting studies conducive to fluid engineering applications are briefly introduced. For instance, Tan et al [110] experimentally studied a trout-inspired multi-functional robotic fish as an underwater swimmer and energy harvester. For the purpose of energy harvesting, the designed bionic fish was modelled as a WIV-based energy harvester with different diameters of cylindrical bluff bodies in a water tunnel.…”