For example, a subgrid block is defined here which refines the mesh to a cell size of 0.5 mm in the Z direction from z=0 to z=5. The block's dimensions in the X and Y directions are not relevant, and can be set to any value.
In the simple microstrip model shown, the microstrip (viewed end-on) is shown in green on top of a purple dielectric layer (er=4). A blue ground plane appears below the dielectric layer. The area above the microstrip is fill with air. The microstrip is excited by a voltage source (shown in red) placed between the microstrip and the ground plane.
The original simulation size was 50 x 20 x 20 cells, with a cell size of 1 mm.
The subgrid block was created within the zone highlighted with a red/white
border, redefining the Z-axis cell size to 0.5 mm.
The new simulation size is 50 x 20 x 25.
A comparison was run of the microstrip model with the original uniform grid of cell size 1 mm, and of the non-uniform grid with the subgridzone cell size of 0.5 mm.
The source pulse rise time of 100 picoseconds is well represented
by the 1 mm mesh, however, it results in a substantial reflection from the
mesh boundary.
With the 0.5 mm refined mesh, the reflection is noticably reduced.
One effect of mesh refinement is that the mesh size, and thus the memory requirement, is increased. Conversely, mesh coarsening saves memory.
Another consequence is that the FDTD simulation time step size is set to accommodate the smallest cell size, resulting in the smallest time step size. Thus, more time step iterations are required to complete a given simulation. In the example given above, the mesh was refined by a factor of 2, and thus the time step size was reduced by a factor of 2 as well. Therefore, 1000 time step iterations were required for the non-uniform simulation, while only 500 time step iterations were required for the uniform simulation.
Currently, the non-uniform mesh is only functional with the first order Mur absorbing boundary condition (the default ABC). Work is underway on a new implementation of the PML ABC which will make it compatible with non-uniform meshes.
The non-uniform mesh is compatible with most of the other features of LC,
including dielectric and permeable materials, all forms of sources and
loads, and far field calculations.
However, not all combinations of features have been tested, so consider
the non-uniform mesh feature to be experimental.
If you use non-uniform meshing, please post your experiences to
the lc-users mailing list.
These are the same quantities that are available through the Step Pulses
dialog, but in a graphical form.
By default, the clipping is performed to all six limits.
Each limit can be deselected, and then no clip will be performed for that limit.
If Clip To Active Block is selected, then the clipping region is
initialized to the limits of the block displayed in the main window
block editing area.
The clip limits may be manually entered or changed as well.
By default, all of the blocks of the model are clipped.
If Clip Selected Blocks Only is selected, then only the selected
blocks are clipped, and any unselected blocks are not modified.
This feature is useful for reducing a model's simulation size by
focusing on a portion of the model.
A high resolution simulation could be run on a subset of a model, and
a coarser simulation could then be run on the entire model.
Sqrt(l/c) impedance and propagation delay pulse calculations
Two new calculations have been added to the Plot Pulses dialog,
impedance calculated by the sqrt(l/c) method, and propagation delay
calculated by the sqrt(l*c).
Both of these new output types require all four of the probe values,
voltage, current, charge, and magnetic flux, to be available.
The advantage of the sqrt(l/c) impedance over the simple v/i impedance
is that it gives more accurate impedance in dynamic environments and
complex model geometries.
First derivative Gaussian pulse source waveform
A new source waveform is available, a first derivative of a Gaussian pulse.
The pulse shown here was defined with a 100 ps rise time.
This waveform is similar to the modulated Gaussian in that it has a
controlled bandwidth but has no DC component.
Edit Clip dialog
The Edit Clip dialog clips blocks to a region.
Blocks completely outside of the region are deleted, blocks which
intersect the region boundary are clipped, and blocks completely
contained by the region are unchanged.
Other Changes and Bug Fixes
Return to What's New
Copyright © Cray Inc.
Maintained by Kevin Thomas (kjt@cray.com).
Last modified
Mon Dec 21 13:29:47 CST 1998