abstract: This thesis presents a novel, thorough approach to the application of low frequency electromagnetic (EM) wave wireless communication in marine environment. This investigation is both theoretical and experimental, and is oriented towards marine sensor network applications. Different solutions within the underwater low frequency EM communication area are compared on the basis of their feasibility and practicality, especially in relation to scientific environmental monitoring applications. As a result, this thesis gathers a coordinated series of application oriented analyses of devices, such as antennas, transmitters, receivers, and of propagation issues, like signal attenuation and antenna positioning. The concluding step in this analysis is constituted by experimental field tests. As a final outcome, this works provides facts, guidelines and prototype designs related to the application of EM communication in shallow water environment, and demonstrates this communication technique is convenient for shallow water sensor networks implementation. The process followed in this analysis starts from practical considerations regarding the characteristics required by scientific equipment used in environmental monitoring. A case study is presented where a hybrid (partially wired) marine sensor network is deployed in Moreton Bay, Queensland. Strengths and weaknesses of this system are analysed, and, based on this experience, new requirements and constraints are set for a prospective improved fully wireless sensor network. In particular, the shallow water marine environment is recognized as the most likely target for scientific investigation because of its biological, economical and social importance. Firstly, various underwater communication techniques are analysed and compared. This is done on the basis of two factors: the first one is the final use of the sensor network, and the second one is the peculiar nature of the shallow water marine environment. From this analysis, it emerges that EM communication may be, in the shallow water environment, a viable and good alternative to acoustic- and optical-based techniques. From this point on, this work is aimed to prove this possibility. The next step undertaken is the theoretical analysis of EM propagation in the shallow water environment, which is modelled as a stratified lossy dielectric. The outcome of theoretical calculations is that, within a certain distance, and for a given transmitter power, low frequency EM waves are a communication channel exploitable by underwater wireless sensor networks. This is particularly true when the required data rate is low, as it is in the case of monitoring variables such as temperatures or concentrations of dissolved substances in the sea. Following this, the electric dipole and the loop antenna are studied and compared when immersed in a lossy medium such as seawater. In particular, the comparison is drawn in terms of antenna size, with absorbed power and radiated field level held equal. This, together with other practical considerations, allows the choice of the electric dipole – with some variations with respect to free space applications – as the preferred transmitting and receiving antenna. Theoretical results are verified and completed by simulations, and final prototype design guidelines are presented, together with best deployment practice suggestions. Finally, measurements are conducted in order to verify the previous calculations and considerations. In addition to them, a sensor network prototype that uses EM underwater communication is presented and tested. The field tests verify, in a real situation and at several frequencies, the maximum distance coverable with a 100 mW power source. Moreover, the same test is also conducted in fresh water, and results are compared. The instruments used for the measurements are thoroughly described, as it is the wireless sensor prototype presented. The main feature of this design is its simplicity, demonstrating that shallow water EM communication is easily achievable and that it meets the standards required by a local area marine sensor network. It can be concluded that this work offers a thorough theoretical analysis of EM propagation in shallow water environment: in parallel with this, a synthesis of practical issues that are encountered in the design of EM communication devices for underwater sensor networks is also presented. In particular, EM underwater propagation, antennas, transmitters and receiver circuits and deployment issues are thoroughly covered. Aspects such as the application of advanced signal modulations and communication protocols, however, are intentionally left open to further investigation. In fact, the range of research topics opened by this work is very wide, and they could not be all covered within this work: they span from energy harvesting to communication protocols, from antenna design to power management. All these areas are well covered by literature for terrestrial sensor networks, but they are not covered for underwater sensor networks that use EM communication: these latter are, in fact, a novelty by themselves. The problems related to this particular application have been, therefore, thoroughly exposed and opened to future research.
| Identifer | oai:union.ndltd.org:ADTP/290701 |
| Creators | Umberto Cella |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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