Miniature Underwater Robot – An Experimental Case Study

Abstract

One of the easiest to observe conditions where waves occur in nature is the undulatory motion of aquatic animals and micro-organisms. In these bio-mechanisms, there is oscillatory locomotion which results in propulsion as the motion is accompanied by energy transfer from one end of the specimen or structure to the other end. Recent years have also seen a rise in the replication of the propulsive capabilities of these animals into aquatic robots. The use of smart materials to actuate and mimic the fin and tail characteristics of a fish has been attempted in various ways. Miniature robots actuated by piezoelectric materials have been effectively used for propulsion due to their simplicity and innovative actuating mechanism. These miniature robots find their application in the regime of underwater propulsion because of their size, flexibility, and ability to mimic fish locomotion. In most of these studies, the undulatory motion of these aquatic robots is achieved by discretizing the fin of the robot into multiple segments and synchronizing the oscillatory motion of individual segments to replicate continuous traveling waves. As a part of such endeavors, the present work attempts to use smart materials to actuate and mimic the fin motion characteristics of a fish. The bio-inspired design of the miniature robots consists of two brass shims supported by four piezoelectric bimorphs. The undulatory motion displayed by aquatic animals is mimicked by generating anechoic traveling waves in these brass fins. Anechoic traveling waves propagate in a structure without undergoing reflections at the structural boundaries. Such waves are generated by taking advantage of the structural dynamics of the fin under multi-input excitation.