Design, Array, and Test of Super-Low-Frequency Mechanical Antenna Based on Permanent Magnet

Abstract

As a new type of super-low-frequency (SLF, 30–300 Hz) 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 3-D array prototype operating in the frequency band of 75–125 Hz is developed for testing. The test results show that when the phase difference is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{26}^{\circ} $ </tex-math></inline-formula> , the effect on the radiation intensity of the array is negligible. When the array element spacing is 0.15 m, the motor cannot drive the mechanical structure, and when the array element spacing increases to 0.3 m, it can operate normally. Communication experiments were conducted, and the transmission rate could reach 2 bps.