Abstract
This paper proposes a rotating shutter antenna that can directly generate 2FSK signals in the ULF band and it is expected to be used as the transmitter for magnetic induction (MI) underground communication systems. The antenna was modeled using ANSYS Maxwell and the magnetic field distribution was simulated. The results show that the interaction between the high-permeability shutter and the mutual cancellation of magnets decreased the transmitting magnetic moment of the antenna. A prototype antenna was manufactured and the time and frequency properties of the measured Bz field were the same as the simulated results, while the magnitude of the measured signal was larger. The propagation characteristics of the antenna in air–soil–rock were simulated using FEKO and the results show that the signal strength was greater than 1 fT at a depth of 450 m from the antenna whose magnetic moment as 1 Am2. The relationship between different magnetic components and azimuth could be used to enhance the signal strength. The formula of the Bz field was derived using the measured magnitude versus distance and the path loss was also analyzed. Finally, the 2FSK modulation property of the antenna was verified by indoor communication experiments with a code rate of 12.5 bps in the ULF band.
Highlights
Accepted: 14 February 2022The electromagnetic waves at radio frequencies have short wavelengths and poor penetrating capabilities, which make them lose part of their energy in a complex electromagnetic environment [1]
The formula shows that the path loss of the rotating shutter antenna in free space was 303 dB at a distance of 570 m, while the signal strength was 1 fT
This paper used ANSYS Maxwell to analyze the magnetic field distribution of the rotating shutter antenna and the results show that the interaction between the high-permeability shutter and the mutual cancellation of magnets decreased the transmitting magnetic moment
Summary
The electromagnetic waves at radio frequencies have short wavelengths and poor penetrating capabilities, which make them lose part of their energy in a complex electromagnetic environment [1]. The permittivity and conductivity of soil have a great relationship with the water content, which causes significant attenuation of high-frequency electromagnetic waves. This leads to the fact that radio-frequency communication cannot be widely used in underground communication. To effectively avoid the limitation of the motor to the antenna’s operating frequency range, we used a rotating shutter antenna as our transmitting antenna, which could obtain a magnetic field signal that is four times the rotating frequency. FEKO was used to analyze the propagation characteristics of the RPMA in air–soil–rock media and the simulated results show that the Bz -field at a depth of 450 m away from the antenna on ground with a magnetic moment of 1 Am2 was 1 fT.
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