Photonics

Photonics

Ansys Insight: How to measure power radiated by a dipole in a dispersive, lossy medium

    • Shin-Sung Kim
      Ansys Employee
      Measuring the power radiated by a dipole source requires special considerations, especially when the dipole is placed in a dispersive material with a non-zero imaginary part of the refractive index.nThe issue of using dipoles in a dispersive material is a theoretical issue, rather than a numerical issue. In dispersive materials, the imaginary part of the Green's function begins to diverge, leading to infinite amounts of power. Here are two possible ways to deal with this issue in FDTD:nCreate a small volume of dielectric material right near the dipole location (maybe 5 mesh cells in size). This avoids the entire problem since the dipole is not located in a dispersive material. You can then use the dipole power function or monitor box to measure the radiated power. When using the dielectric material, set the real part of the refractive index to be matched with the surrounding lossy material. Obviously, this works better with single frequency or narrow band simulations due to the dispersive nature of the surrounding material. Also, make sure to set the correct mesh order for the dielectric.nPlace the dipole within the dispersive material as you want and use the transmission box to measure the power (don?t use the dipolepower). The box should have some finite size (minimum ~5 mesh cells). You will be able to measure the amount of power radiated out of that box, but you will not have information about power absorbed within this box, which might make this approach less suitable for highly lossy materials.n
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