Preparation and motion study of a micro soft robot mimicking the cownose ray driven by external magnetic field.

In narrow, unstructured underwater environments such as target monitoring and minimally invasive medical procedures, micro soft robots exhibit unique advantages due to their flexible movement capabilities and small size. At the same time, bionic design of a micro soft robot, can significantly improve their swimming performance. However, limited by their small size, these robots are difficult to power internally and usually adopt a wireless power supply design. This study designs and fabricates a magnetically responsive, bionic micro soft robot based on the swimming principle of the cownose ray. The robot is made of a mixture of neodymium iron boron (NdFeB) and polydimethylsiloxane in a certain proportion. Then, a three-dimensional Helmholtz coil is used to generate an oscillating harmonic magnetic field, allowing for swimming experiments on the robot to explore the influence of magnetic field parameters on its swimming performance. The experimental results show that the swimming speed is fastest atB= 5 mT andf= 11 Hz, reaching 5.25 mm s-1, about 0.5 body lengths per second. Additionally, by adjusting the current direction and frequency of the coil, the robot can execute various swimming modes, including straight swimming, turning swimming, and directional swimming. By employing a stepwise adjustment method, the impact of response errors on the robot's trajectory can be effectively reduced. This study demonstrates the feasibility of a magnetically driven micro soft robot, laying the foundation for the application of wirelessly driven robots in underwater narrow spaces.