A Mechanical Transmitter for Undersea Magnetic Induction Communication

The radio waves commonly used in terrestrial wireless communication are severely absorbed by the conductive seawater. However, the low-frequency magnetic fields can penetrate a much farther distance in seawater to realize wireless communication by magnetic induction (MI). An electromagnetic coil is generally used as a magnetic field generator, but it will consume excessive power when generating a strong magnetic field to achieve long-range communication. Instead, this study investigated the use of a motor-driven rotating permanent magnet as a mechanical transmitter for undersea MI communication. The frequency-dependent power consumption and the power-efficient operating frequency range of the mechanical transmitter were analyzed. To establish the undersea MI communication channel model, we derived exact analytic expressions for the fields generated by a rotating permanent magnet in seawater and explored the path loss of the undersea MI channel. A prototype mechanical transmitter using a cylindrical rare-earth magnet (Nd–Fe–B) with a diameter of 4 cm and a length of 15 cm driven by a servo motor was created, which consumes only about 2.74% of the power of the equivalent coil at 30 Hz. The surface-to-undersea MI communication using this prototype mechanical transmitter was demonstrated at a distance of 10 m.