Abstract
Antennas in the ultra low frequency (ULF, 300 Hz to 3 kHz) and very low frequency (VLF, 3∼30 kHz) bands are usually very large. In this study, we developed a very small antenna, which can radiate electromagnetic waves in these frequency bands. The antenna consisted of two rotating charged plates (RCPs), which were charged by the voltage source. Numerical results of the radiated far field and its frequency spectrum are presented for three cases: (a) the antenna is charged with DC voltage, (b) the antenna is charged with AC voltage, and (c) the antenna rotates with variable speed and is fed with DC voltage. The predominant frequency component was equal to the rotating frequency of the RCPs fed with DC voltage. If the RCPs were fed with AC voltage two dominant frequencies were generated, which were determined by the difference in frequency between the RCP rotation frequency and the AC source frequency. When the RCPs rotated with variable speed and were fed with DC voltage, many frequency components were generated, which were determined by the initial rotational speed of the RCPs and their acceleration.
Highlights
The frequency spectrum of the low frequency electromagnetic wave is used in a large number of military applications
The frequency spectrum was analyzed for three cases: (a) the antenna is charged with DC voltage, (b) the antenna is charged with AC voltage, (c) the antenna rotates with variable speed and is fed with DC voltage
This antenna consisted of two rotating parallel conductor plates, which were connected to a voltage source
Summary
The frequency spectrum of the low frequency electromagnetic wave is used in a large number of military applications. The most important benefit of the ultra low frequency (ULF, frequency range 300 Hz to 3 kHz) signal is that it can penetrate conductive media such as sea water[1] and is suitable for underwater military communications. The very low frequency (VLF, frequency range of 3∼30 kHz) is suitable for military communication. New types of ULF and VLF antennas, which use the physical motion of an electret(or magnet) to generate electromagnetic waves have been developed. These antennas are called mechanical (or spinning) antennas.[2,3,4]. Size, for example 1×1×1m, while the radiation efficiency of a 1m scale conventional VLF antenna (for example a dipole at 10kHz) is less than 1×10-12 and is impractical for transmitting to the far field.[2]
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