Long-Range EM Communication Underwater With Ultracompact ELF Magneto-Mechanical Antenna

In this article, a long-range underwater electromagnetic (EM) communication system is proposed based on an ultracompact extremely low-frequency (ELF) magnetomechanical transmission antenna (UEMTA). The transmitter mainly includes a waveform generator, a variable frequency drive (VFD), and a three-phase induction motor. The receiver consists of a 200-turn coil and signal analyzer. Based on the equivalent model of a rotating magnetic dipole, the principles of the EM transmission underwater and across the interface of water and air are analyzed. ELF wave propagating underwater in the adjacent area was stronger and decays slowly, which was certificated by the experiment and simulation. Thus, the long-range transmission underwater in the ELF band with digital coding modulation based on the UEMTA is realized, and the longest distance can reach 210 m underwater in the experiment. The transmission of ELF wave across water–air medium based on the system is also tested by the experiment too. The long-range transmission of digital coding modulation across the water–air interface is realized with the longest distance of about 210 m. The ELF transmission technology based on the UEMTA can greatly promote flexible long-distance underwater transmission, the development of satellite-to-submarine communication, and ocean exploration.