Due to the fact that measurements in true biological heads typically cannot be carried out, SAR norms for mobile phones or EMI problems are commonly defined in terms of standardized phantom models. In the easiest case, only spherical structures are considered. To predict the SAR behavior of a new product already during the design stage, it is desirable to include the phantom head in the EM simulations.
The following examples investigate two spherical phantom models, a basic one that only contains of tissue material inside a glass sphere and a more complex one that has two additional layers of bone and tissue. A dipole antenna is used for the excitation and is displayed as a yellow line in the following picture:
Figure 1: Basic spherical phantom head containing tissue material in glass. The yellow lines represent the exciting dipole antenna....
The SAR distribution is simulated at 835 MHz and visualized in the figure below. A comparison of the SAR values over a radial line shows good agreement with the measurement of the same structure.
Figure 2: SAR values in a 2D cutplane inside the phantom model.
Figure 3: Comparison of simulation and measuremant results along the orange arrow in the previous figure.
For the following simulation a more complex model including a simplified skull is used.
Figure 4: Inhomogeneous phantom model including a simplified skull.
A comparison of the SAR values at 1.95 GHz on an off-axis path shows a significant difference between the basic homogeneous model and the more complex one. Since the values are higher, the simplified model may not be sufficient in all cases.
Figure 5: Comparison of the SAR values at 1.95 GHz for the basic and the inhomogeneous model.