III. INPUT FILES

A. SIF FILES

This Section describes how input files for the EMAP4 code are written. The inputs are written in the form of a text file in the Standard Input File (SIF) format [10]. This type of an input file is meant to make the code easy to use and also to make the code portable. These input files can be composed using a simple text editor. EMAP4 takes care of all the mesh generation (see Section 4). The SIF format consists of a few keywords and their attributes.

B. KEYWORDS

The keywords that can be used with EMAP4 are summarized in Table I. A detailed description of these keywords is given below.

1. # : EMAP4 will skip any line that starts with a "#". Users can use "#" to add comments to their .sif files. These "comments" statements also appear in the output files which is convenient for documenting results.
2. box : The keyword "box" specifies a hollow rectangular conducting box. The EMAP4 code sets the value of the tangential electric field to zero along the surface of this box.
3. celldim : By default, the mesh size for the FEM volume is one cm along each axis. However, users can specify a mesh step in an interval along the x, y or z axes by using the keyword "celldim". For example, the following line defines the mesh step to be two cm along the x-axis from x=0 to x=5;
4. 
   celldim 0 5 2 cm
5. dielectric : The keyword "dielectric" defines a rectangular dielectric slab. (x_i, y_i, z_i), i=1, 2 specifies two nodes on opposing corners of the slab. e and s refer to the relative permittivity and the conductivity of the dielectric slab. All the quantities are in standard SI units.
6. PML : The keyword "PML" defines a perfectly matched layer (See Section 7). (x_i, y_i, z_i), i=1, 2 specifies two nodes on opposing corners of the slab. a and b refer to the properties of this PML region. The default is 1.0.
7. 
   Dir can be any one of the following.
   x,y or z : When the PML is on the corresponding face. e.g. "x" will attenuate the waves propagating in the x-direction.
   xy, yz or xz : When the PML is on an edge between two faces.
   xyz : When the PML is at a corner.
8. conductor : The conductor can be a one-dimensional wire, a two-dimensional plate or a three-dimensional block. The EMAP4 code sets the electric field on all surfaces of the conductor boundary to zero. Fields on the interior of three-dimensional conductors are also set to zero.
9. aperture : This keyword creates a rectangular aperture in a conducting wall, when the position coordinates specify two points on the surface of that wall.
10. esource : The keyword "esource" specifies the electric field along mesh edges. The "esource" statements can be 1-D, 2-D or 3-D statements. All the edges within the volume, surface or line between the two nodes (x₁, y₁, z₁) and (x₂, y₂, z₂) are initialized with the source attributes specified.
11. isource : The keyword "isource" defines an impressed current source. The two nodes specified by (x₁, y₁, z₁) and (x₂, y₂, z₂) in the parameter list specify a line which is the source location.

12.  

    Table I: Keywords for EMAP4

    Keyword	Position coordinates	Attributes
    #
    box	x1 y1 z1 x2 y2 z2
    celldim	p1 p2	dir value units
    PML	x1 y1 z1 x2 y2 z2	dir a b
    dielectric	x1 y1 z1 x2 y2 z2	e s
    aperture	x1 y1 z1 x2 y2 z2
    conductor	x1 y1 z1 x2 y2 z2
    esource	x1 y1 z1 x2 y2 z2	frequency  polarization (x, y, or z) magnitude
    jsource	x1 y1 z1 x2 y2 z2	frequency  polarization (x, y, or z) magnitude
    efield_output	x1 y1 z1 x2 y2 z2	filename
    default_out		filename

     

     

13. efield_output : The keyword "efield_output" defines the region in which fields of interest will be printed out by EMAP4. (x₁, y₁, z₁) and (x₂, y₂, z₂) specify two nodes on opposing corners of a rectangle.
14. 
    For example,
    efield_output 0 0 0 10 10 0 example.out
    will cause EMAP4 to write the fields at the nodes within the rectangle area specified by the two diagonal nodes (0, 0, 0) and (10, 10, 0) to the file example.out. This node information is obtained by averaging the field values along the two edges in each direction that meet at this node.
15. default_out : The keyword "default_out" causes EMAP4 to print electric fields along all the edges to the file specified in the parameter list. For example,
16. 
    default_out default.out
    prints the values of the electric field along all edges to the file default.out. To use the information in this file, knowledge of the global edge numbering (see Section 4) is necessary.

This section describes how to write a typical input file using an example. All it takes to write an input file is a simple text editor. All the coordinates are specified in the file itself. The point to note here is that the coordinates are based on the number of cubes (see Section 4) rather than the actual dimensions. If the mesh density has to be changed, all the coordinates have to be changed. A simple setup is shown in Figure 1 and the corresponding input file is also given.

 

Figure 1: A simple setup.
 

# 8x4x5 waveguide half filled with a dielectric
# Default output written to file "default.out"
# Electric fields along axis written to "center.out"
# Electric fields along shifted axis written to "off_axis.out"
celldim 1 cm
box 0 0 0 8 4 5
dielectric 0 0 3 8 4 5 3.0
esource 4 0 2 4 4 2 1000 y 1.000 0
default_output default.out
efield_output 4 2 0 4 2 5 center.out
efield_output 2 2 0 2 2 5 off_axis.out
 

The first four statements are comment statements. The "celldim" statement initializes all the brick lengths to 1 cm. The "box" statement specifies that the outer shell is a conductor. The "dielectric" statement specifies the dielectric location and properties. The "esource" statement specifies the source location and properties. The "default_output" causes EMAP4 to write out all the electric field values to the file default.out. The "efield_output" statements cause EMAP4 to write out the values of the electric field at all the nodes within the volume specified by the given coordinates to the files specified.