| Summary: | This project was to investigate the EM waves for transmission in seawater with a varied frequency from about 1 MHz up to 40 MHz. Trials were carried out in the laboratory tank, the Albert Dock and the Loch Linnhe. Standalone transmitter and receiver units were constructed for performing the experimental trials. A receiver is used to pick up the signal from the transmitter and the signal was analysed using ,a spectrum analyser. Frequency can be varied outside the transmitter from a lap top by using an optical fiber. Different types of antennae were built and tried in the experiments. In the Albert Dock, the results have shown that EM waves in the range of 1 to 5 MHz is possible to propagate about 100m using a 30W power amplifier. A new antenna design was developed and investigated in the laboratory tank. Results have shown that there is about 30dB gained by implementing the new antenna design. The signal strength can be further improved by 10 dB when the antenna and the signal generator were matched at 10MHz. In the near field, EM waves suffer from high attenuation in seawater but have a low attenuation in the far field. This is due to the generation of EM waves by dipole oscillations of the water molecules within the antenna field which can be used to explain results obtained from trials.
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