As a new type of super-low frequency (SLF, 30~300Hz) magnetic antenna, the permanent magnetic mechanical antenna (PMMA) has great potential for applications in underwater communication, underground communication, and earthquake prediction. PMMAs use large volume permanent magnets to enhance the signal, posing a significant challenge to power consumption of the mechanical drive structure. We optimize the permanent magnets in terms of magnetization structure, magnetic material, and form factor to determine the optimal permanent magnet structure. We establish an analytical model of the magnetic torque of the array elements and the radiated field of the array to determine the optimal array form. Based on the analytical model, we analyze the effects of the array element spacing, the phase difference of the array elements and the number of array elements on the radiated time-varying magnetic field. Finally, a 3D array prototype operating in frequency band of 75Hz~125Hz is developed for testing. The test results show that when the phase difference is less than 26°, the effect on the radiation intensity of the array is negligible. When the array element spacing is 0.15m, the motor cannot drive the mechanical structure, and when the array element spacing increases to 0.3m, it can operate normally. Communication experiments were conducted and the transmission rate could reach 2bps.

Antennas operating at the extremely-low frequency (ELF, 30-300Hz) 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 is 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 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 13dB over radial magnetization for the same volume. The transmitter can generate the time-varying magnetic field strength of 117pT at 100m. 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.

Mechanical antennas (MAs) directly use the mechanical motion of electric or magnetic charges to excite electromagnetic waves. The radiation distance of rotating magnetic dipole type mechanical antennas is related to the volume of the radiation source, so the volume of the radiation source is too large for long-distance communication. To solve the above problem, we first establish the magnetic field model and differential equations of motion of the antenna array. Then, we design the prototype of antenna array with operating frequency of 75–125Hz. Finally, we experimentally established the radiation intensity relationship between a single permanent magnet and an array of permanent magnets. The results indicate that our driving model reduces the tolerance of the signal by 47%. Through 2FSK communication experiments, this article verifies the feasibility of extending the communication distance in the form of an array, which provides an important reference for long-distance low-frequency communication.