Magnetic Pendulum Arrays for Efficient ULF Transmission

TLDR

Ultra‑low‑frequency (ULF) signals (300 Hz–3 kHz, 100–1000 km wavelengths) are reliable, penetrating, and jam‑resistant, making them attractive for underwater and underground communication, but electrically small ULF antennas (≤1 m diameter) are inherently inefficient due to their extremely short electrical length. We propose a portable electromechanical system, the Magnetic Pendulum Array (MPA), to efficiently generate ULF radiation. The MPA employs a mechanical antenna concept—magnetic pendulums—to convert mechanical motion into electromagnetic radiation, thereby overcoming the radiation limits of conventional coils. A proof‑of‑concept demonstration at 1.03 kHz shows that the MPA achieves a significantly higher quality factor and an order‑of‑magnitude greater transmission efficiency than conventional coils, and the concept can be scaled to the full ULF frequency range.

Abstract

Abstract The frequencies lying between 300 Hz to 3 kHz have been designated as Ultra Low Frequency (ULF) with corresponding wavelengths from 1000 Km to 100 Km. Although ULF has very low bandwidth it is very reliable, penetrating and difficult to jam which makes it a great choice for communication in underwater and underground environments. Small and portable ULF antennas within a diameter of 1 meter would operate under an electrical length on the order of 10 −4 to 10 −6 wavelengths in free space, making them very inefficient because of fundamental limits on radiation from electrically small antennas. To overcome this problem, Mechanical Antennas or ‘Mechtennas’ for Ultra Low Frequency Communications have been proposed recently. For efficient generation of ULF radiation, we propose a portable electromechanical system called a Magnetic Pendulum Array (MPA). A proof of concept demonstration of the system at 1.03 kHz is presented. The theory and experimental results demonstrate that such a system can achieve a significantly higher quality factor than conventional coils and thus order of magnitude higher transmission efficiency. The concept can be easily scaled to the ULF range of frequencies.