Abstract
Electromagnetic signals in the ultralow frequency (ULF) range below 3 kHz are well suited for underwater and underground wireless communication thanks to low signal attenuation and high penetration depth. However, it is challenging to design ULF transmitters that are simultaneously compact and energy efficient using traditional approaches, e.g., using coils or dipole antennas. Recent works have considered magneto-mechanical alternatives, in which ULF magnetic fields are generated using the motion of permanent magnets, since they enable extremely compact ULF transmitters that can operate with low energy consumption and are suitable for human-portable applications. Here we explore the design and operating principles of resonant magneto-mechanical transmitters (MMT) that operate over frequencies spanning a few 10 s of Hz up to 1 kHz. We experimentally demonstrate two types of MMT designs using both single-rotor and multirotor architectures. We study the nonlinear electro-mechanical dynamics of MMTs using point dipole approximation and magneto-static simulations. We further experimentally explore techniques to control the operation frequency and demonstrate amplitude modulation up to 10 bits-per-second. We additionally demonstrate how using oppositely polarized MMT modules can permit systems that have low dc-field but do not sacrifice the ac magnetic field produced.
Highlights
Oscillatory sources of electromagnetic waves play a vital role in communications, navigation, and sensing systems [1]– [6]
Since the ultra-low frequency (ULF) near-field extends hundreds of kilometers, a non-propagating or quasi-static approach can be used for data transfer over 10’s to 1000’s of meters, e.g., using the magnetic field generated by an oscillating magnetic dipole as the carrier signal
We describe a magneto-mechanical transmitter (MMT) design that utilizes resonant angular oscillatory motion of a single or multiple permanent magnet rotors to produce the ULF carrier signal
Summary
Oscillatory sources of electromagnetic waves play a vital role in communications, navigation, and sensing systems [1]– [6]. While radio-frequency signals in the MHz-GHz range provide this functionality for above-ground communications, they experience significant attenuation when traveling through conductive media like seawater, rocks, and soil [7]. One solution is to instead use ultra-low frequency (ULF) signals below 3 kHz as they provide orders-of-magnitude greater signal penetration depth and lower signal attenuation than radio frequencies. Since the ULF near-field extends hundreds of kilometers, a non-propagating or quasi-static approach can be used for data transfer over 10’s to 1000’s of meters, e.g., using the magnetic field generated by an oscillating magnetic dipole as the carrier signal.
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