Finite element simulation and frequency optimization for wireless signal transmission through RC structures

The enclosed civil structures pose a challenging environment for wireless communication between sensor nodes. Wireless electromagnetic (EM) signal attenuates significantly when transmitting through reinforced concrete structures. This paper simulates the signal attenuation for plain concrete, pure steel rebar lattice and reinforced concrete using finite element method (FEM) in Ansoft High Frequency Structure Simulator (HFSS). Jonscher model is found to be a better concrete dielectric model than Debye model from the attenuation test results. FEM simulation for signal attenuation of reinforced concrete (RC) slab is validated by finite difference time domain (FDTD) simulation and test results from literature. Optimal frequency to minimize the signal attenuation through RC structure is in the range of 0.35 GHz ~ 0.5 GHz. Resonance occurs at <i>t</i> / (<i>&#955;</i>_c/4) = 2<i>n</i> and <i>t</i> / (<i>&#955;</i>_c/4) = 2<i>n</i> + 1, <i>n</i> = 1, 2, 3, 4, ... for low concrete volumetric water content (VWC). Signal attenuation is highly linear with slab thickness t for high concrete VWC. 433 MHz is suggested for real application of wireless sensor network considering the antenna size and optimization results. FEM simulation is validated by the experiment using intact wireless sensor nodes.