**2. Bio-inspired robotic manta ray powered by IPMC artificial pectoral fin**

In this section, we present a bio-inspired, free-swimming robotic manta ray propelled by artificial pectoral fins. In our previous work, we developed an assembly-based fabrication process to bond four IPMC actuators with Polydimethylsiloxane (PDMS) elastomer to create an actuating membrane capable of 3D kinematic motions (Chen et al, 2011). However, the control strategy for four IPMCs is too complicated to be implemented on-board. In this study, a pectoral fin, with the planform shape of a manta ray pectoral fin and consisting of one IPMC artificial muscle in the leading edge and a passive PDMS membrane in the trailing edge, has been designed. When the IPMC is actuated, the passive PDMS membrane follows the bending of IPMC with a phase delay, which causes an undulatory motion of the fin. The pectoral fin has been characterized by key factors as they relate to the function of the robot: tip deflection; twist angle; and power consumption. Since only one IPMC is needed for actuation in the pectoral fin, the control strategy is greatly simplified. To test the performance with a free-swimming robot, a light, compact on-board control unit with a lithium ion polymer battery has been developed. Experimental results have shown that the robot is capable of free swimming.
