Project on under water ultrasonic communication

Abstract:

Underwater conummication differs considerably from other types of signal propagation — both in terms of the physics and technology involved, and the applications that use it. This thesis explores one possible method of conununicating underwater: using high-frequency acoustic waves. The properties of the channel (water) mean that conventional ultrasonic techniques are only partially applicable. Piezoceramic transducers are used both to transmit and receive the acoustic signal underwater. The transmitting transducer must be excited by a high-voltage signal, at close to its resonating frequency. Micro-controllers both generate the outgoing signal, and interpret the received signal (which is first amplified and filtered by hardware). Different transmission protocols were considered, and 'Frequency Shift Keying' was settled on as the simplest and most robust (this uses a high-frequency carrier wave, which is modulated by different amounts, to send binary data). A large part of this Thesis is devoted to reviewing the nature of underwater acoustics, specifically factors that affect reliable communication (and possible countermeasures).

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