Abstract: Quiet underwater propulsion is an ideal goal of underwater vehicles (UVs). However, almost all mature UVs are propelled by screws. The problems of the screws, such as noise and propulsion efficiency, restrict the application of UVs. It is found that the basic motion of most fish and squid/cuttlefish with fin undulation propulsion is flexible bending, and a shape memory alloy wire actuated flexible biomimetic fin, which can realize flexible bending, is developed. The biomimetic fin gets an idea from the fins musculature of squid/cuttlefish and it is based on the principle of muscular hydrostat. Theorem analysis is conducted to get the bending angle of the biomimetic fin and experiments are carried out in water. A micro robot fish employing the biomimetic fin is developed and it verifies the concept. The electric current driven biomimetic fins can be equipped as modules to realize the body and/or caudal fin propulsion, and pectoral fin undulation propulsion. With the characteristics of quiet actuation, large bending angle, no relative moving mechanical parts, adequate output force, simple structure and good concealing, the flexible biomimetic fin can be applied for quiet propulsion, and it is fit for micro UVs especially.

Key words: Flexible biomimetic fin, Micro robot fish, Quiet underwater propulsion, Shape memory alloy wire, Squid/cuttlefish fin