Abstract
The signal fading in wireless underground sensor networks (WUSNs), which is caused by lossy media such as soil and sand, can be reduced by applying technology of magnetoinductive (MI) propagation. This technology can effectively establish a communication at very low frequency (VLF). In contrast to the previous studies in the literature, which mostly focus on the propagation of plane waves, we propose a new approach based on the plane wave expansion (PWE) to model the near field MI waves. The proposed approach is based on excitation of a point source, which is a common case in a practical WUSN. The frequent usage of square lattice MI structure is investigated. To verify the mathematical derivation, the simulation of time domain based on the fourth-order Runge-Kutta (RK) method is carried out. Simulation results show that the new model can provide a precise prediction to the MI wave’s propagation, with the computation load being one-tenth of that of the time domain simulation. The characteristics of the propagation of the MI waves are presented and discussed. Finally, the reflection on the edge of the MI structure is reduced by analysing the terminal matching conditions and calculating a method for matching impedances.
Highlights
Wireless underground sensor networks (WUSNs) become an active research in monitoring underground environments such as mineral contents, oil leakage, and formation stress [1,2,3,4]
In contrast to the previous studies in the literature, which mostly focus on the propagation of plane waves, we propose a new approach based on the plane wave expansion (PWE) to model the near field MI waves
Since the waves with low frequency EM suffer from lower fading in loss media, this can be helpful to set the WUSN working at the very low frequency (VLF) band similar to most of the telecommunication systems [8,9,10]
Summary
Wireless underground sensor networks (WUSNs) become an active research in monitoring underground environments such as mineral contents, oil leakage, and formation stress [1,2,3,4]. Large size antennae and high drive voltage are required to transmit EM waves in VLF band. This approach is usually impracticable in underground environments. In a real WUSN, signals are always transmitted by a single loop, and the wave excited by the point source cannot be considered as a plane wave. Since the frequency of MI networks only depends on the resonance frequency of the split ring resonators, this can be exploited to adjust the load capacitor and the number of windings to set the MI structure working at the VLF band, keeping the transmit antenna at a low size level.
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