Radiation Study of Low-Power Ultracompact Rotating Permanent Magnetized Mechanical Antenna Array

Antennas operating at the extremely low frequency (ELF, 30–300 Hz) are desirable for undersea and underground wireless communications as well as engineering detection thanks to their strong penetration and interference resistance. However, the efficiency and portability of wireless communication are greatly limited by the size of the conventional antenna and the large current required. This has stimulated the need for a new approach to low-frequency antenna design. Here, we propose a rotating permanent magnet mechanical antenna (RPMMA) based on a large volume permanent magnet. Based on the mechanical antenna (MA) radiation model, the magnetization direction and radiation efficiency of the single permanent magnets are analyzed. The heteroaxial array magnetic torque model was derived. Radiation patterns and initial phase angles of the two array geometries were analyzed; a transmitter with 16 cylindrical permanent magnets axially magnetized in a coaxial arrangement was determined. Test results show that axial magnetization increases the strength of permanent magnets by 13 dB over radial magnetization for the same volume. The transmitter can generate the time-varying magnetic field strength of 117 pT at 100 m. The experiments also tested the system to verify the feasibility of transmission in air-seawater media. Finally, communication experiments were conducted to realize digital coded modulation communication.