Magneto-Mechanical Antenna Array for Extremely Low-Frequency Communication

This letter presents a compact magneto-mechanical antenna array for extremely low-frequency (ELF, 3 Hz to 30 Hz) transmission. The array consists of four independently controlled units, each featuring a rotating permanent magnet pair (RPMP) with a magnetic moment of 406.6 A·m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and dimensions of 550 mm × 150 mm × 96 mm. This array can produce a 200 fT magnetic field signal at a distance of 1176 m in the air when all four units operate in perfect synchrony. Moreover, the independently controlled structure enables parallel signal transmission to improve the communication rate. Utilizing this array as a transmitter, we conducted non-line-of-sight (NLOS) communications through concrete walls at distances of ∼95 m. The experimental results showed that four RPMPs transmitted distinct frequency-shift keying (FSK) signals with varying carrier frequencies at a modulation rate of 1 bps, demonstrating the feasibility of frequency division multiplexing (FDM).