Extremely low frequency communication using signal modulation of sphere-string structured mechanical antenna

Mechanical antennae have been considered a promising solution for the miniaturization of underwater low-frequency communication. The research on mechanical antennae mainly focuses on the use of strong magnetic fields rather than strong electric fields at present. This paper proposed a method to generate extremely low-frequency (ELF) electromagnetic waves by utilizing the periodic motion of conductive spheres to disturb a strong electrostatic field. Both theoretical analysis and experimental verification demonstrated that this method can effectively generate ELF electromagnetic waves matching the frequency of the conductive spheres. A mechanical antenna system was designed and fabricated combining a sphere-string structure next to a van de Graaff generator, based on the above principle. Leveraging the multi-modal rapid frequency-switching characteristics of the sphere-string structure, an effective information-loading method was proposed and realized for ELF communication. This study provides more options for the radiator and information modulation of mechanical antennae.