A Flexible, Magnet-Based Miniaturized Low-Frequency Mechanical Antenna Enabling Cross-medium Communication and Collaboration among Unmanned Systems

Extremely low frequency (ELF, 3–30 Hz) signals possess strong cross-medium communication capabilities, making them particularly well-suited for underground and underwater environments. However, traditional low-frequency (LF) transmission systems are large and inefficient, posing significant limitations in practical applications. In recent studies, mechanical antennas have been explored to generate LF signals, but current approaches rely on bulky equipment with limited range, making them unsuitable for personal use or integration into small unmanned devices. To address this challenge, this study introduces a flexible, magnet-based miniaturized LF mechanical antenna, fabricated using 3D printing. The antenna consists of a macro-fiber composite layer and a flexible permanent magnet film, and features an extremely compact volume (<6.8 cm³) and low weight (<50 g). It is also highly flexible, allowing for easy integration into diverse applications. Its transmitted signal can reach 60 m before the magnetic field strength attenuates to 1 pT. Mounted on a unmanned aerial vehicle (UAV), the antenna facilitates reliable communication between quadruped robots operating outside caves and aerial robots located deep within cave interiors, where high-frequency (HF) signals cannot penetrate. To the best of our knowledge, this study is the first to demonstrate robust LF cross-medium communication between UAV and ground robots in cave environments, paving the way for unmanned collaboration in scenarios inaccessible to HF wireless signals.