Very low-frequency (VLF) and ultralow-frequency (ULF) electromagnetic waves have the advantage of high penetration and low propagation loss in wireless communication systems and are mainly used for underwater and underground communications, as well as for earthquake and lightning forecasting. At present, VLF and ULF antennas are mostly bulky and require hundreds of antennas and more to be set up, which is costly and inefficient. In this paper, we propose to generate VLF and ULF signals by rotating a multilayer multipair electret thin-film electret driven by an excitation device, which improves the problem of low radiation efficiency of VLF and ULF signals and the large size of conventional low-frequency transmitting antennas. Based on a multilayer, multipair electret film mechanical antenna, a magnetic field propagation model is developed, and the relationship between the magnetic flux density mode and the number of layers of electret films, as well as the relationship between the antenna emission frequency and the motor rotation frequency and the number of pairs of electret films, is analyzed. The selection of a suitable model for practical situations based on conditions such as antenna size and propagation distance is illustrated. The research work is of great importance for guiding the design of mechanical antennas and optimizing antenna structures.
Solar flares are the most violent outbursts that occur in localized regions of the solar atmosphere. They emit large amounts of X-rays and energetic particles. X-rays reaching the earth at the speed of light will disrupt the calm ionospheric environment, causing sudden ionospheric disturbance (SID), which will make the very low frequency (VLF) signal to sudden phase anomaly (SPA), lead to the positioning error of satellite navigation system and interfere with satellite communication. Energetic particles will arrive near the satellite orbit in 1-3 days, causing direct damage to the satellite. They may also cause geomagnetic storms after reaching the Earth. In this paper, we mainly study to monitor solar activity and calculate solar flare class through the phase variation of VLF signal by combining the theory of VLF waveguide mode in order to forecast the environment of satellite navigation and communication. In addition, it can also predict energetic particles and geomagnetic storms 1-3 days in advance according to the time and class of flare outbreak, so that the protective measures for satellite to operate safely could be taken in advance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.