Experimental Investigations of Electromagnetic Wave Propagation in Seawater

Abstract

It is often preferable to avoid using divers to undertake sub-sea activities, the alternatives being autonomous or remotely operated robotic vehicles and manipulators. This will only be achievable if robust communications can be established through seawater. Presently for such sub-sea activities it is necessary to use acoustic modems, which are only capable of operating with data rates of up to 50kbs -1 . Optical sensors can also be used but these rely on clear water and in many sea conditions propagation beyond 10m is not possible. This paper will present new experimental results for electromagnetic wave propagation through seawater at MHz frequencies. These frequencies would enable the use of high speed data rates, suitable for a wide range of sub-sea activities.

Electromagnetic (EM) wave propagation for the development of an underwater Wireless Sensor Network (WSN)

“…According to table 1, attenuation in seawater at 2.4GHz is very high but propagation is feasible in its lowest frequency band (ISM subject to local acceptance) at 6.7 MHz. This theoretical value is in accord with fellow researchers' experiments results [6]. Although propagation of EM waves in seawater is more affected by attenuation in the near field, it depends on the launching technique.…”

“…In seawater, conductivity is approximately 4S/m whereas for freshwater it is in the mS/m range. Underwater communication research conducted at Liverpool John Moores University has shown that transmission at 5MHz frequency is feasible in seawater up to 90m giving a data rate of 500kbps that allows duplex video and data streams [6]. In [7], propagation at frequencies of 6 and 10.7MHz in a tank was also possible.…”

Electromagnetic field radiated in air from a horizontal/vertical magnetic dipole in sea

“…[5] Since then, many researchers have determined the fields near the earth surface (or the seawater). Al-Shamma'a et al [6,7] and Siegel and King [8] investigated EM wave propagation in the seawater. MHz frequencies and loop antennas have been considered to present wave propagation characteristics in seawater.…”

Sistema de Visión Subacuático Inalámbrico Usando un Algoritmo de Compresión Progresivo con Región de Interés

“…No obstante, el principal problema del uso de RF es la alta atenuación que sufre en el ambiente acuático, especialmente en agua salada. Sin embargo, diferentes estudios (Zhang and Meng, 2012;Siegel and King, 1973;Shaw et al, 2006) y empresas como WFS (Wireless For Subsea) indican que, con las antenas necesarias, a frecuencias más bajas, y utilizando los mejores métodos de codificación y modulación, es posible establecer un enlace de comunicación hasta varias decenas de metros a través del agua (incluso en agua salada).…”