Signal transmission through seawater for MHz frequencies and medium distances (O-30 m) using ionic current waves

摘要

Electromagnetic (EM) signals can only be transmitted through seawater for short distances (1 MHz). Therefore a new technique, the ionic current wave (ICW), has been developed for signal propagation at MHz frequency. This technique uses the conduction currentproduced in seawater as a result of thermal ionisation releasing H+ and OH– ions. A small voltage ( A detailed theoreticalanalysis of the ICW process has shown that ionic currents can be transmitted at MHz frequency over distances of 10 m with low signal loss per decade. For longer propagation distances of 100 m the theory predicts a signal loss of –20 dB per decade. Propagation experiments havebeen carried out in Liverpool dock seawater for distances of 2 m–28 m between parallel 0.5 m × 0.3 m electrodes placed vertically in the seawater at a depth of 2 m. Signal frequencies within the range of 1 MHz–8 MHz have been investigated. In each experiment the receivedpropa gated signal power was approximately –67 dBm (well above the dock electrical noise of –140 dBm) and only showed a small power loss over the full range of propagation. The ICW system will be able to measure longer propagation distances in deep seawater conditionssuitable for ship and submarine communications. Its performance is comparable to that of sonar systems.