How Electric and Magnetic Fields are Measured
are Measured
How Electric and Magnetic Fields are Measured
Electric and magnetic fields are measured using metallic antennas. Electric fields (remember, these are open lines that travel from positive to negative charges) are picked up by straight antennas, li
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which are oriented parallel to the electric field lines. These straight antennas have a space in the middle that is left open to create a measurable voltage difference. An example is shown in Figure 1. This miniature electric field probe antenna was designed for assessment of compliance of electromagnetic devices with RF exposure guidelines.(Smith, 1983) Measurement of this value is difficult, because it requires measuring the localized electric field. Large metal objects (such as a )p
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measurement antenna) perturb the fields. This small dipole antenna was specifically designed to receive the localized fields being measured without perturbing them. Because this probe is inherently sensitive to the direction (polarization) of the electric field, three perpendicular probes are used in practice, as shown in the SPEAG probe in Figure 2. Each probe picks up the electric field parallel to its major axis. The three perpendicular electric field vectors can be measured independently or combined to give total electric field.
The magnetic field has closed field lines These are picked up using a loop antenna The loop is
The magnetic field has closed field lines. These are picked up using a loop antenna. The loop is oriented so that the magnetic field line passes through the loop. As with the electric field, three separate perpendicular loops can be used to pick up the three components of the magnetic field, as shown in Figure 2.
Figure 1 Miniature Printed Dipole Antenna for measurement of electric
fields to determine cell phone RF exposure compliance. (from (Smith,
1983) © 1983 IEEE)
ctric and
gnetic Field
obes from
EAG
printed with
mission,
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Experimental Setup for Testing Cell Phones
Dr. Om Gandhi’s Research Group
University of Utah
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Department of Electrical and Computer Engineering
Radiation Pattern Measurement System
Radiation Pattern Measurement System
The University of Utah
mm-resolution
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Head
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Model
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Furse, Lazzi, Gandhi, “FDTD Computation of Power Deposition in the Head for Cellular
Telephones,” Proc. 1996 IEEE APS Symposium
Power Deposition in the Human Head
915 MHz Cellular Telephone
Adult
10 year old
5 year old
O.Gandhi, G.Lazzi, C.Furse, "Electromagnetic Absorption in the Human Head and Neck for Mobile Telephones at 835 and 1900 MHz," IEEE
Transactions on Microwave Theory and Techniques, Vol. 44, No. 10, Part 2, Oct. 1996, pp. 1884-1897
Cellular Telephone Simulation
835 MHz / 1900 MHz
/4 Antenna
Plastic-coated handset:
2.96 x 5.73 x 15.5 cm
FDTD Resolution:
1.974 x 1.974 x 3mm
G. Lazzi, C.M. Furse, O.P. Gandhi, Optimization and De
of Conductivity Profiles for the PML Boundary Condi
and Its Application
pp
to Bioelectromagnetic
g
Problems,,
Presented at IEEE AP-S International Symposium and
URSI Radio Science Meeting,
Montreal, Canada, July 13-18, 1997
Applications: Cellular
Telephones
SAR
Distribution
in Adult
- 835 MHz
p
- Simplified
Phone
Model
  /4
antenna
Pandit,McDermott,Lazzi,Furse,Gandhi, “Electrical Energy Absorption in the
Human Head,” presented at IEEE Visualization ‘96, S.F., CA 1996
Pandit,McDermott,Lazzi,Furse,Gandhi, “Electrical Energy Absorption in the
Human Head,” presented at IEEE Visualization ‘96, S.F., CA 1996
Realistic Positioning of the
Phone
Vertical
Tilted 30
Lazzi & Gandhi, IEEE Trans. EMC, 39(2), 1997
Tilted
Tilt
d 30
Rotated 9
Incorporating CAD Models in
FDTD Simulations
CAD (ProEngineer)
BioEM Research Lab Annual Report 1997
Om Gandhi, Dept. of Electrical Engineering
FDTD Model
Internal Structure of the Telephone
Accurately Described
Internal Metal Parts
BioEM Research Lab Annual Report 1997
Om Gandhi, Dept. of Electrical Engineering
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Truncated
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Expanding
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Grid
id (TEG)
TEG
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