In this paper a physics-based model is proposed for a biomimetic robotic fish propelled by an ionic polymermetal composite (IPMC) actuator. Inspired by biological fins, a passive plastic foil is attached to the IPMC beam. The model incorporates both IPMC actuation dynamics and the hydrodynamics, and captures the interactions between the IPMC actuator and the plastic foil. Experimental results have shown that the proposed model is able to predict the steady-state cruising speed of the robotic fish under a periodic actuation input. Since the majority of the model parameters are expressed in terms of fundamental physical properties and geometric dimensions, the model is expected to be instrumental in optimal design of the robotic fish.

GPS-free localization is essential for navigation and information tagging in small robotic fish-based aquatic mobile sensor networks. Constraints on size, weight, and onboard computing power, together with noisy underwater environment, have made underwater localization a particularly challenging problem. In this paper a comprehensive experimental study is presented on underwater acoustic ranging methods based on time difference of arrival (TDOA). Performances of four methods are characterized and analyzed, including threshold-crossing, tone-detection, correlation integral, and sliding-window fast Fourier transform (FFT) methods. The study facilitates the understanding of capabilities and limitations of different underwater ranging methods and provides important insight into choice of hardware and algorithms for localization of networks of small aquatic robots.