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Design of a low-cost underwater acoustic modem for short- range sensor networks


Small, dense, wireless sensor networks are beginning to revolutionize our understanding of the physical world by providing fine resolution sampling of the surrounding environment. The ability to have many small devices streaming real-time data physically distributed near the objects being sensed brings new opportunities to observe and act on the world which could provide significant benefits to mankind. While wireless sensor-net systems are beginning to be fielded in applications today on the ground, underwater sensor nets remain quite limited by comparison. Still, a large portion of ocean research is conducted by placing sensors (that measure current speeds, temperature, salinity, pressure, bioluminescence, chemicals, etc.) into the ocean and later physically retrieving them to download and analyze their collected data. Real-time underwater wireless sensor networks that do exist are often sparsely deployed over wide areas. The existence of small, dense wireless sensor networks on land was made possible by the advent of low-cost radio platforms. These radio platforms cost a few hundred U.S. dollars enabling researchers to purchase many nodes with a fixed budget allowing for dense, short-range deployment. The aquatic counterpart to the terrestrial radio is the underwater acoustic modem. Existing underwater acoustic modems' power consumption, ranges, and price points are all designed for sparse, long-range, expensive systems rather than for small, dense, and inexpensive sensor-nets. It is widely recognized that an aquatic counterpart to inexpensive terrestrial radio would be required to enable deployment of small dense underwater wireless sensor networks for advanced underwater ecological analyses. This thesis describes the full design of an underwater acoustic modem for small, dense wireless sensor networks starting with the most critical component from a cost perspective - the transducer. The design replaces a commercial underwater transducer with a homemade underwater transducer using inexpensive piezoceramic material and builds the rest of the modem's components around the properties of the homemade transducer to extract as much performance as possible. By building the modem from inexpensive components, the design provides a low-cost, low-power alternative to existing commercial modems for use in short-range networks

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