Propagation Characteristics Of Electromagnetic Signals In Shallow Underground Beacons

The sounding logger may fall into the sand,lake,or buried by the soil after landing.The beacon's search signal is severely attenuated by the soil,making it difficult for radio search.In this paper,based on the analysis of the characteristics of the low frequency propagation window of the soil and the optimal working frequency of the shallow soil communication system,the paper proposes a new method of using the magnetic field Dipole in the shallow soil induced by the current,ground current secondary radiation magnetic field to slow down the signal attenuation,so as to increase the signal transmission distance method,and carried out experimental verification.The main work of this paper mainly includes:1.The characteristics of the magnetic field in the space are analyzed in detail,and the propagation characteristics of the electromagnetic wave and the low frequency magnetic field in the depleted medium are discussed.The influence of the characteristics of the soil medium and other parameters on the signal transmission characteristics is analyzed in detail,The soil conductivity and signal frequency are the main factors that affect the signal attenuation: the higher the signal frequency,the greater the soil conductivity,the greater the attenuation of the signal,the signal propagation in the soil closer.2.The main factors affecting the soil conductivity were soil moisture content,and the higher the soil moisture content was obtained through the experimental study,the higher the conductivity was.Through the experiment of the magnetic field attenuation of shallow soil,the optimal frequency window suitable for shallow soil is found at about 70 k Hz.3.The low frequency magnetic signal transmitter with small volume,low power consumption and strong excitation capability is designed,and the attenuation characteristic of low frequency magnetic signal is experimented.It is verified that the low frequency magnetic signal has a small attenuation characteristic in the soil.4.Through the electromagnetic simulation and experiment,the propagation characteristics of the near-field magnetic field of the magnetic dipole antenna through the shallow soil are studied,and the near field field intensity of the magnetic dipole is obtained with the distance Decay law,which is fundamentally different from the theoretical inverse of the third-order inverse law,which extends the propagation distance of the near-field magnetic signal in the soil.In this paper,we obtain the semi-planar planar transmission medium of shallow soil,and the attenuation of the near-field magnetic signal excited by the magnetic dipole is slower than that of the fully open space.This slow propagation mode The propagation distance of the near field magnetic signal can improve the efficiency of beacon search positioning.This long-distance signal transmission,but also can be used in shallow ground beacon search,mine underground tunnel communication,shallow water communication,wall sensor detection and other fields.