The performance of a magnetic loop transmitter-receiver system submerged in the sea

The theoretical predictions for an electromagnetic wave in both free-space and an infinite conducting medium are considered and an experimental technique is described which was used to measure the variation of signal strength with distance for a magnetic-loop transmitter-receiver system submerged in sea-water, at a mid-water depth (100 m) where boundary effects could be ignored safely. Underwater communication of audio-frequency signals in real time is normally carried out using acoustic techniques, but occasionally there are reports in the press of `magnetic carrier¿ or `conduction field¿ systems having ranges in the sea which apparently exceed those expected for a conventional electromagnetic wave.