The PEC and PMC boundary conditions are the most straightforward to set up and use. Assigning the PEC boundary to one of the bounding walls of the solution domain simply forces the tangential component of the electric field to vanish at all points along that wall. Similarly, assigning the PMC boundary to one of the bounding walls of the solution domain forces the tangential component of the magnetic field to vanish at all points along that wall. For planar structures with a conductor-backed substrate, you can use the PEC boundary condition to designate the bottom of the substrate (the -Z Domain Wall) as a PEC ground. For shielded waveguide structures, you can designate all the lateral walls as PEC. Similarly to model shielded cavity resonators, you designate all the six walls as PEC.
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In many electromagnetic modeling problems you need a boundary condition that simply absorbs all the incoming radiation. For problems of this nature, an absorbing boundary condition (ABC) is often chosen that effectively minimizes wave reflections at the boundary. EM.Tempo uses Convolutional Perfectly Matched Layers (CPML) for absorbing boundary conditions. The boundary CPML cells in the project workspace are transparent to the user. But, in effect, multiple rows of CPML cells are placed on the exterior side of each face of the visible domain box.
[[Image:Info_icon.png|40px]] Click here to learn more about the theory of '''[[Basic_FDTD_Theory#Why_Does_FDTD_Need_Domain_Termination.3F | Perfectly Matched Layer Termination]]'''.
[[Image:Info_icon.png|40px]] Click here to learn more about '''[[Perfectly_Matched_Layer_Termination#Advanced_CMPL_Setup | Advanced CPML Setup]]'''.
=== Advanced CMPL Setup in EM.Tempo ===
[[Image:fdtd_manual-11.png|thumb|400px|The boundary ABC cells placed outside the visible domain box.]]
[[Image:FDTD15.png|thumb|400px|CPML Settings dialog.]]
[[In many electromagnetic modeling problems you need a boundary condition that simply absorbs all the incoming radiation. For problems of this nature, an absorbing boundary condition (ABC) is often chosen that effectively minimizes wave reflections at the boundary. EM.Tempo]] provides uses Convolutional Perfectly Matched Layers (PMLCPML) as for absorbing boundary conditions. Usually two or more ABC layers must be placed at the boundaries of the physical structure to maximize wave absorption. The boundary ABC CPML cells in [[EM.Tempo]]'s the project workspace are transparent to the user. But, in effect, multiple rows of ABC CPML cells are placed on the exterior side of each face of the visible domain box.
You can set the number of CPML layers as well as their order. This is done through the CPML Settings Dialog, which can be accessed by right clicking on the '''CPML''' item in the '''Computational Domain''' section of the navigation tree and selecting '''CPML Settings...''' from the contextual menu. By default, four CPML layers of the third order are placed outside the FDTD problem domain. It is recommended that you always try a four-layer CPML first to assess the computational efficiency. The number of CPML layers may be increased only if a very low reflection is required (<-40dB).