摘要 |
<p>Uses electromagnetic waves which in the frequency range greater than 100 kilo Hertz do not propagate in water but do propagate in water between a frequency range from 10 to 100 kilo Hertz. The control system is based on the fact that electromagnetic waves in the range between 10 to 100 kilo Hertz propagate better in water than in air. The control system has a receiver (7) designed to receive waves either greater than 100 kilo Hertz or between 10 to 100 kilo Hertz, and a transmitter (8) separated from the receiver by an obstacle to wave propagation. Both transmitter and receiver are contained in a non metallic enclosure made from a composite material.</p> |