Force Characterization of Insect-Scale Aquatic Propulsion Based on Fluid-Structure Interaction

The authors present two insect-scale aquatic propulsor designs (single-tailed and double-tailed) intended for microrobotic swimmers. The propulsors are inspired by anguilliform swimming and use soft tails actuated by high-work-density shape-memory alloy (SMA) wires. They note that although these propulsors are suitable for microrobotic aquatic locomotion and can be controlled for 2D trajectory tracking, the force characteristics—especially magnitudes and instantaneous thrust—had not been studied systematically. To address this, the study uses a theoretical framework based on reactive forces and performs experiments with a custom micro-N-resolution force sensor. Reported multi-test mean forces include maximum and cycle-averaged values for the single-tail propulsor (0.45 mN and 2.97 micro-N) and for the dual-tail propulsor (0.61 mN and 22.6 micro-N). The authors describe these as first measurements of instantaneous thrust for this class of insect-scale propulsors and as providing insights into FSI for efficient microrobotic propulsion.