Specific Anthropomorphic Mannequin (SAM) geometry is placed in different orientations relative to the coordinate system to perform SAR calculations.

While anatomically correct head and body meshes, such as the Remcom High Fidelity meshes, provide more accurate and realistic results, many standards involving Specific Absorption Rate (SAR) limits use head phantoms for testing. A widely accepted phantom head is the Specific Anthropomorphic Mannequin (SAM).

The CAD files for the inner and outer portions of SAM are first imported into XFdtd^® as separate objects with different materials. The shell file is the outer insulating shell of the SAM including the ear spacers. The inner file corresponds to the interior of SAM which is filled with a conducting dielectric to approximate brain tissue. The result of importing the SAM cad files into XFdtd is shown in Figure 1.

To illustrate using XFdtd for a SAR calculation for a phone, a CAD file of a phantom phone was obtained and also imported into XFdtd. It is easy to orient the phone relative to the SAM head using the move function. Repeated applications allow the user to “walk” the phone to the correct position using the lines marked on the SAM head Figure 2 to locate the phone at the correct location relative to the ear.

Once the phone is correctly positioned at the ear, the head is rotated so as to provide the correct tilt relative to the phone while allowing the phone to remained aligned with the coordinate system and thus with the eventual mesh. The result is shown in Figure 3.

Next step is another rotation of the head to put the phone into either “touch” or “tilt” position. Using the XFdtd rotation function again, and if necessary moving the phone position, the head can quickly be located in the correct position relative to the phone as in Figure 4 .

Next step is meshing the phone-head. This is extremely fast in XFdtd. Just click on the Mesh tab, set and lock the desired cell size, set a boundary of free space and generate the mesh. For this example the result for a 1mm mesh is shown in Figure 5 .

Once the mesh is generated mesh viewing and editing can be used to check that the mesh is correct and place ports. In Figure 6 the region at the base of the antenna has been edited so as to disconnect the antenna from the surrounding phone case, and the feed port (green dot) added to drive the antenna. From this point the SAM head and phone are ready for specification of waveform and desired output. For this example a 900 MHz sine wave voltage source with 50 Ohm source resistance was specified, and a sequence of vertical SAR calculation planes including 1 and 10 gram averages were also specified. After the calculation is complete the SAR results are available and can be scaled to any desired input power as shown in Figure 7.

Color displays of both SAR and Electric Field are available. An SAR display is shown in Figure 8 and Electric Fields are shown in Figures 9 and 10.

The CAD file for the SAM model, based on the original data from the IEEE Standard 1528, was generated and provided by Dr. Wolfgang Kainz from the U.S. Food and Drug Administration - Center for Devices and Radiological Health.