An Electromechanically Modulated Permanent Magnet Antenna for Wireless Communication in Harsh Electromagnetic Environments

摘要

High-frequency electromagnetic waves are greatly scattered and attenuated by soil, rocks, water, and the human body, which impede their propagation across these media. However, low-frequency magnetic waves propagate with low attenuations through these dispersive media as long as these media are nonmagnetic. Unlike static electric fields that can be produced by “free” positiveegative charges, static magnetic fields are divergence-free and thus can be produced only by particles with noninteger spins (i.e., electrons), or permanent magnets, or current loops. Fields produced by these dipoles decay steeply as a third-order function of distance. Hence, magnetic current loops require excessively large currents to produce detectable magnetic field at large distances. However, rare-earth magnets with surface magnetic flux densities of 0.3-0.6 T, provide sufficiently large fields at large distances, thus the fields produced by these magnets that can be modulated by mechanically modulating the magnets for portable wireless magnetic field communication. Here, we present the development of an electromechanically modulated permanent magnet antenna operating at a frequency of 22 Hz, producing a magnetic flux density of $0.6~mu text{T}$ amplitude at 1 m. This antenna requires a starting energy of 0.48 J and it is capable of data rate of 8 b/s. This magnet antenna can reliably transmit binary data over a distance of up to 70 cm through obstacles that would severely hamper electromagnetic wave propagation.