Tham khảo tài liệu 'electromagnetic waves propagation in complex matter part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Electromagnetic Waves in Contaminated Soils 127 a b Fig. 2. Antennae a Monopole antenna derived from a coaxial cable by removing a part of outer conductor b a UHF-Half-Wave Dipole Wikipedia 2011 . Monopole antenna case A The pilot-scale simulation of the SoilBED facility Farid et al. 2006 is explained in this section. In the first case a 5 mm-thick monopole antenna is modeled within a fully saturated sandy soil background. The size of the medium under study was selected to satisfy limitations of the FDTD code as well as the experiment. Table 2 a summarizes details about the geometry and grid size of the soil medium. The simulation is driven by a cosine modulated Gaussian time pulse at a reasonably high frequency GHz . To accommodate the simulation of the dispersive soil and stability of the FDTD code at this frequency the time increment At 2 psec was used. The dispersive properties of the soil for this choice of center frequency and time-step are modeled with the Z-transform function coefficient set sAve a1 bo bl and b2 given in Table 2 b . To relate the results to the field site the model can be scaled up in size while scaling down the frequency. To evaluate the feasibility of the DNAPL detection method using monopole antennae wave propagation through the background soil and scattered EM wave propagation by a DNAPL pool were modeled and analyzed. The geometry details of the monopole transmitting antenna modeled in this case are tabulated in Table 2 c . The drive signal excites the top of the simulated coaxial cable feeding the monopole antenna in a conventional radial field pattern. The electric field components on all grid points of different cross-sectional and depth slices of the medium were computed and then visualized using MATLAB. 128 Electromagnetic Waves Propagation in Complex Matter First the background medium was analyzed. Then a rectangular acrylic plate as a representative of a DNAPL pool was modeled within the soil medium. Fig. 3 schematically
