Measurement of Electromagnetic Fields Peoduced by Underwater
A0076Hans G. Zachar School of Electrical Engineering, University of Witwatersrand
A0077George J. Gibbon School of Electrical Engineering, University of Witwatersrand
The Elasmobranchii (Sharks, Rays and Skates) possess sensory organs
called the Ampullae of Lorentzini that enables them to detect
electromagnetic (EM) fields at intensities as low as 1?V/m at
frequencies between 0.1 and 20Hz. The increased use of underwater
electrical equipment and hence increased EM radiation could have
serious ecological effects on the marine environment. Divers have
observed a variety of reactions ranging from a passing interest
(mouthing)to a violent reaction to such equipment.
This report describes a land based laboratory measurement system used
to measure the EM fields produced by commercial and recreational
underwater electrical equipment. This measurement system includes a
tank containing seawater housed inside a Faraday cage to reduce noise
to acceptable levels to be able to measure these extremely small
signals. To eliminate ionization effects, carbon probes are used and
no metal is exposed to the water throughout the measurement system.
The system can measure signals of 150?V/m. The system makes use of
low noise electronic techniques to achieve this.
Initial results show that the level of EM radiation from electrical
equipment is well within the sensitivity of the Elasmobranchii. Using
these measurements and software modeling, predictions can be made
concerning the distance at which the Elasmobranchii would be able to
sense the presence of such equipment or the intensity of the fields at
any given distance from the source.