Efield® time-domain solver

Efield® is the first commercial software vendor offering a combined FDTD-FEM solver allowing unstructured grids for modeling complex geometries and small details, together with a structured grid for the rest of the domain.

The Efield® time-domain solver combines an FDTD solver on Cartesian grids with an FEM solver on unstructured tetrahedral grids. In this way the Efield® time-domain solver solver allows local spatial refinement of the unstructured grids to resolve geometrical details or to model field singularities near sharp corners, edges or points. Stability is guaranteed through a careful design of the coupling of the FDTD and FEM solvers.

Time-domain modeling has the advantage of providing broadband results, for example S-parameters and far-field, in a single simulation using pulse excitation. Furthermore, 3D visualization of the time evolution of fields and currents can often give deeper understanding of electromagnetic effects in complicated environments.

Hybrid meshing

The generation of the Efield® hybrid grid is an automatic process that gives the user the option to choose which type of grid that should be used for different parts of the geometry. An important feature is that there may be several disconnected unstructured grids in the same problem.

Materials and boundary conditions

The Efield® time-domain solvers can handle a wide variety of materials. This includes inhomogeneous dielectric and diamagnetic materials as well linear dispersive material of Debye and Lorentz type. For dispersive materials there is also the option to define poles and residues of the electric susceptibility function to model a general linear dispersive material.

  • PEC/PMC
  • Dielectric & magnetic
  • Dispersive (Debye, Lorentz, General)
  • Lumped circuit elements (RLC)
  • Impedance boundary conditions

Outer boundary conditions

Several different boundary conditions can be applied in the Efield® FDTD-FEM hybrid solver including metallic boundary conditions such as PEC and PMC. Absorbing boundary conditions (ABC’s) such as Mur, PML and UPML are available and can be selected by the user.

  • Absorbing boundary conditions (PML, UPML, Mur)
  • PEC/PMC
  • Periodic boundary condition

Excitations

There are different ways to generate a source in the Efield® FDTD-FEM hybrid solver. Huygens’ sources are used to generate plane waves of arbitrary propagation direction and point sources are used to model dipoles. The plane waves can be defined using Cartesian as well as spherical polar coordinates. Other source options include ports, current sources, voltage sources on thin wires and point sources.

  • Plane waves
  • Voltage and current sources on wires
  • Lumped circuit source
  • Waveguide mode excitation using 2D numerical or analytical eigenmode solver (homogeneous or inhomogeneous)
  • Point sources

Subcell models

The ability to model features that are small relative to the cell size is often important. Thus accurate models that characterize the physics of such features without the need for highly resolved grids are often essential. The EfieldTD solver includes state-of-theart subcell models for thin wires, thin slots and thin sheets.

  • Thin wires
  • Thin sheets
  • Thin slots

Post-processing

Output from the EfieldTD solver includes:

  • S-parameters
  • Input impedance
  • Reflection loss
  • Far fields (2D, 3D, directivity, gain, field pattern, polarisation, power...)
  • Radar Cross section (RCS) calculation, bistatic and monostatic
  • Surface and wire currents
  • Power through user defined surfaces

Multi-block solver

The Efield® FDTD-FEM hybrid solver is parallelized using MPI multi-block technique. If the users supplies hardware information regarding expected number of flops, expected communication bandwidth and memory per processor an optimal load balance is used to solve the problem.

Detail of the hybrid mesh around the nose of a Saab 2000 aircraft



Surface currents on the interior walls of a shielded enclosure. The simulation was done using FDTD and subcell models.



Saab 2000 lightning simulation using the FDTD-FEM solver.



Interior currents in the Saab 2000 aircraft after a simulated lightning strike (FDTD).



Near field from an FDTD simulation of a tapered slot array.



Surface currents on a patch U-slot antenna from an FDTD-FEM simulation