SAR of A Human Head Next To A Wi-Fi Antenna: Created in COMSOL Multiphysics 5.5
SAR of A Human Head Next To A Wi-Fi Antenna: Created in COMSOL Multiphysics 5.5
SAR of A Human Head Next To A Wi-Fi Antenna: Created in COMSOL Multiphysics 5.5
This model is licensed under the COMSOL Software License Agreement 5.5.
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Introduction
Users of consumer electronics with radiating devices are exposed to radio frequency (RF)
emission. The amount of exposure is defined as the specific absorption rate (SAR). That
is, the SAR value represents the radio frequency (RF) energy rate absorbed by a body. This
model computes local SAR values over a simplified human head and brain mock-up when
a microstrip patch antenna operating in the Wi-Fi frequency range is placed close to the
head.
Lumped port
Figure 1: Human head phantom next to a microstrip patch antenna resonant around the Wi-
Fi frequency range. The surrounding air domain and perfectly matched layer are removed
from the figure for visualization purposes.
Model Definition
The human head geometry is the same as the specific anthropomorphic mannequin (SAM)
phantom provided by IEEE, IEC, and CENELEC from their standard specification of
SAR value measurements. The geometry is imported into COMSOL Multiphysics after
minor adjustments and scaling down to 60 % of the original geometry to reduce the
problem size. The shape of brain is simplified using an ellipsoid geometry. This model
Other parts of the human head is characterized using the properties of cortical bone tissue
(Ref. 2), as displayed below.
This example is an introductory model showing how to analyze SAR. It is assumed here
that all materials are homogeneous, which is an oversimplification. For more realistic brain
material characterization, see another application library example, Specific Absorption
Rate (SAR) in the Human Brain in which material parameters based on the imported MRI
image data with a volumetric interpolation function characterize the variation of tissue
type inside the head.
The microstrip patch antenna next to the human head is composed of a thin layer of metal,
a rectangular FR4 dielectric block, and a ground plane. The microstrip feed line, antenna
radiator and ground plane are modeled as perfect electric conductor (PEC) surfaces. The
antenna is fed by a 50 lumped port, representing a feed from the power source.
The human head phantom and antenna are enclosed by a spherical air domain which is
truncated by perfectly matched layers. This mimics the antenna testing in infinite free
space. The perfectly matched layers work like an anechoic chamber in reality preventing
unwanted reflection from the outer walls.
References
1. G. Schmid, G. Neubauer, and P.R. Mazal, “Dielectric properties of human brain tissue
measured less than 10 h postmortem at frequencies from 800 to 2450 MHz,”
Bioelectromagnetics, vol. 24, pp 423–430, 2003.
NEW
In the New window, click Model Wizard.
MODEL WIZARD
1 In the Model Wizard window, click 3D.
2 In the Select Physics tree, select Radio Frequency>Electromagnetic Waves,
Frequency Domain (emw).
3 Click Add.
4 Click Study.
5 In the Select Study tree, select General Studies>Frequency Domain.
6 Click Done.
STUDY 1
GEOMETRY 1
The head geometry has been created outside COMSOL Multiphysics, so you import it
from an MPHBIN-file. Then create the PML, air, simplified brain, and antenna domains
manually.
Import 1 (imp1)
1 In the Home toolbar, click Import.
2 In the Settings window for Import, locate the Import section.
3 Click Browse.
4 Browse to the model’s Application Libraries folder and double-click the file
sar_wifi_antenna.mphbin.
Ellipsoid 1 (elp1)
1 In the Geometry toolbar, click More Primitives and choose Ellipsoid.
2 In the Settings window for Ellipsoid, locate the Size and Shape section.
3 In the a-semiaxis text field, type 0.035.
4 In the b-semiaxis text field, type 0.045.
5 In the c-semiaxis text field, type 0.025.
6 Locate the Position section. In the y text field, type -0.005.
7 In the z text field, type 0.04.
Build a geometry for a microstrip patch antenna operating in the Wi-Fi frequency range.
Block 1 (blk1)
1 In the Geometry toolbar, click Block.
2 In the Settings window for Block, locate the Size and Shape section.
3 In the Width text field, type 0.004.
4 In the Depth text field, type 0.05.
5 In the Height text field, type 0.05.
Plane Geometry
In the Model Builder window, click Plane Geometry.
Plane Geometry
In the Model Builder window, click Plane Geometry.
Sphere 1 (sph1)
1 In the Geometry toolbar, click Sphere.
2 In the Settings window for Sphere, locate the Size section.
3 In the Radius text field, type 0.18.
DEFINITIONS
3 In the Settings window for Perfectly Matched Layer, locate the Geometry section.
4 From the Type list, choose Spherical.
The metal parts of the antenna substrate are defined as perfect electric conductors,
assuming that the conductivity of copper is high enough to have negligible loss.
Lumped Port 1
1 In the Physics toolbar, click Boundaries and choose Lumped Port.
2 Select Boundary 63 only.
The Far-Field Domain feature defines a wave number for use by its subfeature - the Far-
Field Calculation feature.
The specific absorption rate feature defines the SAR postprocessing variable. It is
calculated from the electromagnetic dissipation density and the specified density for the
human head.
MATERIALS
In the Home toolbar, click Windows and choose Add Material from Library.
ADD MATERIAL
1 Go to the Add Material window.
2 In the tree, select Built-in>Air.
3 Click Add to Component in the window toolbar.
4 In the tree, select Built-in>FR4 (Circuit Board).
5 Click Add to Component in the window toolbar.
2 In the Home toolbar, click Add Material to close the Add Material window.
Material 3 (mat3)
1 In the Model Builder window, right-click Materials and choose Blank Material.
2 In the Settings window for Material, type Brain in the Label text field.
4 Locate the Material Contents section. In the table, enter the following settings:
Material 4 (mat4)
1 Right-click Materials and choose Blank Material.
2 In the Settings window for Material, type Head in the Label text field.
4 Locate the Material Contents section. In the table, enter the following settings:
DEFINITIONS
View 1
Some domains and boundaries can be removed from the view. This may help when
inspecting the mesh quality.
MESH 1
1 In the Model Builder window, under Component 1 (comp1) right-click Mesh 1 and choose
Build All.
RESULTS
Multislice
1 In the Model Builder window, expand the Electric Field (emw) node, then click Multislice.
2 In the Settings window for Multislice, locate the Multiplane Data section.
3 Find the Y-planes subsection. In the Planes text field, type 0.
4 Find the Z-planes subsection. In the Planes text field, type 0.
5 Locate the Coloring and Style section. From the Color table list, choose HeatCamera.
6 Select the Reverse color table check box.
The default polar plot shows the far-field norm on the xy-plane.
Radiation Pattern 1
1 In the Model Builder window, expand the Results>3D Far Field (emw) node, then click
Radiation Pattern 1.
2 In the Settings window for Radiation Pattern, locate the Evaluation section.
3 Find the Angles subsection. In the Number of elevation angles text field, type 90.
4 In the Number of azimuth angles text field, type 90.
5 Locate the Coloring and Style section. From the Color table list, choose Twilight.
The far-field radiation pattern of the microstrip patch antenna is distorted due to the
reflection from the human head.
Filter 1
1 In the Model Builder window, expand the Results>Specific Absorption Rate (sar1) node.
2 Right-click Volume 1 and choose Filter.
3 In the Settings window for Filter, locate the Element Selection section.
4 In the Logical expression for inclusion text field, type z<0.04 && x>0.
The computed SAR values are plotted over the entire SAR domain. By adding a filter
subfeature, the values inside the domain can be visualized.
5 In the Specific Absorption Rate (sar1) toolbar, click Plot.
6 Click the Zoom In button in the Graphics toolbar.
Compared the SAR plot with Figure 2.