In this example XFDTD is used to compute the input impedance, radiation gain pattern, and SAR of a patch antenna embedded inside a human body.

---

• 
  Figure 1
• 
  Figure 2
• 
  Figure 3
• 
  Figure 4
• 
  Figure 5
• 
  Figure 6
• 
  Figure 7
• 
  Figure 8
• 
  Figure 9
• 
  Figure 10
• 
  Figure 11
• 
  Figure 12
• 
  Figure 13
• 
  Figure 14

The patch antenna is 19.2mm (across chest direction) by 32 mm (head to foot direction) with a substrate of lossless dielectric of permittivity 9.5. The patch is 2mm thick with the ground plane and patch radiator the same dimensions. The patch feed is offset from the center of the patch in the vertical (long) dimension.

Initial calculations are for the patch antenna in free space. In anticipation of using a 2mm human body mesh, the patch is initially meshed with 2mm FDTD cells. A slice through the mesh showing the feed location as a green dot is shown in Figure 1. All calculations are at 2.45 GHz.

Initial calculations made for the patch antenna in free space found an input impedance of 0.175 + j 11.8 Ohms with 100% efficiency. The radiation gain pattern with respect to an isotropic antenna for the horizontal plane is shown in Figure 2.

The green line is for E theta (vertical) polarization and the red line is for E phi (horizontal) polarization. The near zone transient electric fields in the plane of the patch antenna are shown in the Figure 3. Near zone steady state electric field is displayed in Figure 4.

Next a 2mm human body mesh obtained using VariPose is imported into XFDTD as a mesh object and the patch antenna is inserted into the body mesh. Figure 5 shows a slice through the body mesh with the patch antenna. The patch is located a few mm inside the chest close to the front of the body. In this figure the body is looking away from the reader, that is, into the page.

After the calculation is completed XFDTD finds the impedance of the patch antenna inside the human body to be 4.05 + j 15.61 Ohms with an efficiency of 0.23%. The far zone radiation pattern for the patch antenna inside the body in the following figure shows the reduction in gain due to the loss in the body tissues. The body is facing toward an angle of 270 degrees with the (left) shoulder containing the patch toward an angle of 0 degrees as shown in Figure 6.

Figure 7 shows a 3D view of transient electric fields external to the body mesh.

Figure 8, Figure 9, and Figure 10 show transient electric fields in various mesh slices for the patch antenna inside the body. For one figure the display of the body tissues and patch antenna is turned off to view the internal fields.

Figure 11 and Figure 12 show steady state electric fields in the plane of the patch antenna. Again, in one figure the body tissue display is turned off.

The final calculation is for Specific Absorption Rate, or SAR. In order to reduce calculation time only the chest portion of the mesh is used for the SAR calculations. A view of the chest only with near zone transient fields is shown in the following figure.

The SAR results are shown in Figure 13 adjusted to 1 Watt input power.

In Figure 14, the 1 gram average SAR is displayed in the plane of the patch antenna.

This example illustrates only the most basic application of XFDTD to this geometry. XFDTD could be used to improve the design the patch antenna in order to resonate at the desired transmission frequencies, to improve the radiation, and to reduce SAR. The effects on SAR and radiation resulting from moving the patch antenna to different locations in the body could also be investigated using XFDTD.