Measurement of Electromagnetic Fields Peoduced by Underwater

Electrical Equipment

A0076 Hans G. Zachar School of Electrical Engineering, University of Witwatersrand

A0077 George 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.