**4. Chapter conclusion**

In this Chapter, we presented two studies on IPMC artificial muscles in bio-inspired engineering research. In the first study, we developed a bio-inspired robotic manta ray powered by IPMC pectoral fin. We developed a novel synthesis process to fabricate IPMC pectoral fin that is capable of 3D kinematic motion and characterized the pectoral fin in terms of tip deflection (up to 100%), bode plot (0.4 Hz cut-off frequency), twist angle (up to 40o), and power consumption (below 1.5 W). A small size free-swimming robotic manta ray has been developed and experimental results have demonstrated its free-swimming capability with speed at 0.067 body length per second and 2.5 W power consumption. In the second study, we developed a novel buoyancy control device as an artificial swimming bladder. IPMC acted as an efficient, environmentally friendly water electrolysis generator to gain volume of the device while a solenoid valve was used as gas releasing controller. A compact and low power device has been assembled with an on-board open loop controller. Experimental results have shown that the device was able to control its 0.9 m depth within 3 minutes.

In both studies, advantages and challenges of IPMC in bio-inspired engineering research have been addressed. In this first study, the advantages of using IPMC as artificial muscle are: 1) low actuation voltage; 2) working well in wet condition; 3) low noise; 4) simple mechanical structure; 5) able to be shaped into bio-inspired engineering design. The disadvantages are: 1) low generated force; 2) slow response time. The challenge in this study comes from optimal design of the pectoral fin. In future research, we will focus on modeling an IPMC powered pectoral fin and modeling of the fluid dynamics introduced by the 3D kinematic motions of the fin. In the second study, the advantages of using IPMC as electrolysis generator are: 1) low noise; 2) compact design; 3) low Ionic Polymer-Metal Composite Artificial Muscles in Bio-Inspired Engineering Research: Underwater Propulsion 245

activation voltage and low power consumption. The disadvantage arises from 1) slow gas generation rate that limits its capability of feedback depth control; 2) unstable nonlinear dynamics. The challenge in this study is feedback depth control that requires high gas generation rates and complex nonlinear control algorithms. In future work, we will focus on nonlinear feedback control and improved device design that can gain gas volume rapidly.
