# FDTD Boundary Conditions

### From openEMS

## Contents |

# Usage

function FDTD = SetBoundaryCond(FDTD, BC, varargin)

BC = [xmin xmax ymin ymax zmin zmax];

# Types of Boundary Conditions (BC)

**PEC**: Perfect electric conductor (default BC)**PMC**: Perfect magnetic conductor**MUR**: A simple absorbing boundary condition (ABC)**PML_x**: Perfectly Matched Layer absorbing boundary condition, using x number of cells

### openEMS example

BC = {'PEC' 'PMC' 'MUR' 'PML_8' 'PML_8' 'PML_10'}; FDTD = SetBoundaryCond( FDTD, BC );

## Perfect electric conductor (PEC)

- All tangential electric fields on this boundary will be set to zero. This results in the behavior as a perfect electric conductor. This BC is the default in a FDTD simulation.

For example, this BC can be used to model waveguide walls or a infinite ground-plane for PCB board.

## Perfect magnetic conductor (PMC)

- All tangential magnetic fields on this boundary will be set to zero.
- This results in the behavior as a perfect magnetic conductor. Since there is no real material with such a behavior, it is usually used as
**symmetry boundary condition**. - Since in FDTD all magnetic fields are shifted by half a cell, this wall is effectively located in the middle of the last two lines of the respective direction.

## MUR ABC

- Simple absorbing boundary condition (ABC)
- Only works perfect for a completely orthogonal impinging waves with a known phase-velocity (e.g. speed of light)

## PML_x ABC

- Artificial x-cells thick layer that effectively absorbs incoming EM waves. (default x=8)
- PML thickness can be 6 to 20 cells. PML_8 is a good default.
**Warning:**In openEMS the last x lines in the respective direction are defined as this artificial absorbing material: Keep your structures far enough away!**Info:**This ABC is not optimally implemented regarding the simulation speed. Use the Mur-ABC for faster simulations.