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Proceedings Paper

Biologically inspired highly efficient buoyancy engine
Author(s): Barbar Akle; Wassim Habchi; Rita Abdelnour; John Blottman III; Donald Leo
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Paper Abstract

Undersea distributed networked sensor systems require a miniaturization of platforms and a means of both spatial and temporal persistence. One aspect of this system is the necessity to modulate sensor depth for optimal positioning and station-keeping. Current approaches involve pneumatic bladders or electrolysis; both require mechanical subsystems and consume significant power. These are not suitable for the miniaturization of sensor platforms. Presented in this study is a novel biologically inspired method that relies on ionic motion and osmotic pressures to displace a volume of water from the ocean into and out of the proposed buoyancy engine. At a constant device volume, the displaced water will alter buoyancy leading to either sinking or floating. The engine is composed of an enclosure sided on the ocean's end by a Nafion ionomer and by a flexible membrane separating the water from a gas enclosure. Two electrodes are placed one inside the enclosure and the other attached to the engine on the outside. The semi-permeable membrane Nafion allows water motion in and out of the enclosure while blocking anions from being transferred. The two electrodes generate local concentration changes of ions upon the application of an electrical field; these changes lead to osmotic pressures and hence the transfer of water through the semi-permeable membrane. Some aquatic organisms such as pelagic crustacean perform this buoyancy control using an exchange of ions through their tissue to modulate its density relative to the ambient sea water. In this paper, the authors provide an experimental proof of concept of this buoyancy engine. The efficiency of changing the engine's buoyancy is calculated and optimized as a function of electrode surface area. For example electrodes made of a 3mm diameter Ag/AgCl proved to transfer approximately 4mm3 of water consuming 4 Joules of electrical energy. The speed of displacement is optimized as a function of the surface area of the Nafion membrane and its thickness. The 4mm3 displaced volume obtained with the Ag/AgCl electrodes required approximately 380 seconds. The thickness of the Nafion membrane is 180μm and it has an area of 133mm3.

Paper Details

Date Published: 4 April 2012
PDF: 7 pages
Proc. SPIE 8339, Bioinspiration, Biomimetics, and Bioreplication 2012, 83390O (4 April 2012); doi: 10.1117/12.916075
Show Author Affiliations
Barbar Akle, Lebanese American Univ. (Lebanon)
Wassim Habchi, Lebanese American Univ. (Lebanon)
Rita Abdelnour, Lebanese American Univ. (Lebanon)
John Blottman III, Naval Undersea Warfare Ctr. (United States)
Donald Leo, Virginia Polytechnic Institute and State Univ. (United States)

Published in SPIE Proceedings Vol. 8339:
Bioinspiration, Biomimetics, and Bioreplication 2012
Akhlesh Lakhtakia, Editor(s)

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