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Proceedings Paper

Noiseless propulsion for swimming robotic structures using polyelectrolyte ion-exchange membrane
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Paper Abstract

In this paper a NafionTM polyelectrolyte ion-exchange membrane (IEM) was used as a propulsion fin for robotic swimming structures such as a boat or fish-like object swimming in water or aqueous medium. The Nafion membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble a fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately plus or minus 2.0 V amplitude square wave at varying frequency up to 50 Hz. The circuit board was mounted on a buoyant styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement. It turned out that the forward speed of the object was directly proportional to the product of frequency and amplitude of the fin oscillation as in biological fishes. This relation was further simplified by keeping the voltage constant and therefore amplitude of the oscillation. The proportionality constant could be measured for a known geometry of the fin-boat assembly and reactivity of the Nafion membrane used. The system as a whole presented an autonomous robotic swimming structure with frequency modulated propulsion to investigate application of polyelectrolyte hydrogel membranes and their effect on hydrodynamic behavior of an undulating swimming object. As in fishes the thrust force of the robot was generated by evolution of vortices on the sides of the undulating fin. For a constant forward speed, this thrust is equal to the drag force due to geometry and skin friction of the swimming robot. It was observed that regardless of the laminar or turbulent flow pattern around the robot the relation between speed and frequency holds. This research was a proof of concept for investigating fish propulsion known best for undulatory swimming motion, using polyelectrolyte ion-exchange-metal composite membrane.

Paper Details

Date Published: 9 February 1996
PDF: 10 pages
Proc. SPIE 2716, Smart Structures and Materials 1996: Smart Materials Technologies and Biomimetics, (9 February 1996); doi: 10.1117/12.232139
Show Author Affiliations
Mehran Mojarrad, Univ. of New Mexico (United States)
Mohsen Shahinpoor, Univ. of New Mexico (United States)

Published in SPIE Proceedings Vol. 2716:
Smart Structures and Materials 1996: Smart Materials Technologies and Biomimetics
Andrew Crowson, Editor(s)

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