Abstract
Traditional MHz and GHz electromagnetic antennas face challenges of high attenuation rate in cross-medium communication; while mechanical antennas are hindered by their large size, high energy consumption and weak radiation capacity. Here, we report a centimeter-scale, wearable ultrasonically-actuated magnetic-dipole rotating resonator (UA-MDRR) for efficient extremely low frequency (ELF) electromagnetic wave transmission in extreme environments. The UA-MDRR employs a small multilayer piezoelectric ceramic (0.11 cm³) to rotate a disc-type NdFeB magnet, generating ELF radiation through an electro-mechanical-magnetic (EMM) coupling effect. This device achieves a high emission capacity of 24,000 nT/cm³@1 m, outperforming the state-of-the-art resonators/antennas by one to two orders of magnitude. It can emit a magnetic field strength of 2.64 pT in air and 2.12 pT underwater at 100 m, respectively, while consuming only 0.61 W of power. This innovation represents a groundbreaking advancement in cross-medium communication, offering a mobile wearable device for emergency communication in seawater for life saving.