Pollution Worse Than Air Pollution? Part 3
Home Radiation Protection
3. Cell Phones Radiation
In order to estimate the dangers coming from the use of
mobile phones, I present you a few things about it.
In the top picture on the left, you see a "classic" FDTD
simulation of electromagnetic absorption inside a model
“human head” made by a composite material for a mobile phone
working at 915 MHz with power 1 W (SAR is the Specific
Absorption Rate to electromagnetic radiation).
In the following graph on the left, you can see the change
of safety limits by frequency for Electric Field, Magnetic
Field and Energy Flux. In the case of the previous
simulation the safety limits are not achieved.
The maximum magnetic field has been found 1.04 A/m against
0.1 A/m, which is the safety limit at frequency 915 MHz.
Also, the maximum SAR has been found 1.87 W/kg against 1.6
W/kg, which is the safety limit for the same frequency.
The relation of electric field E and magnetic field H in the
air is given by the formula: H = E / 376.8, with Η measured
in (Α/m) and E in (V/m). This relation does not depend on
In the above graph of safety limits, the previous relation
does not go along with frequencies smaller than 1 MHz.
Except of that, this relation sets us a question about the
need of existence of two kind of devices to measure electric
and/or magnetic field in the market of electromagnetic
pollution measurements devices.
3.1. SAR - measurement methods
a) MRI (Magnetic Resonance Imaging) known also as “magnetic
tomography” is one precise technique to measure – in real
time - SAR inside real human head to the radiation of a
b) In the picture on the right, you can see a less
sophisticated method of measuring SAR by using a model human
head made from composite material and an antenna located in
the opposite direction.
3.2. Temperature change inside human head during a
In the top picture on the left, the calculated change of
temperature at different sections of a model “human head”
made by composite materials is shown, after solving
arithmetically a set of electromagnetic and thermal
differential equations, supposing a mobile phone-head 5 mm
A temperature change about 0.5 - 1.5 °C has been found.
In the bottom picture on the left, two MRI images of the
brain of a user with his cell phone at On and Off state are
The existene of more expanded and more dense yellow color
areas inside the curves A and B of each MRI image, verified
the expected from calculation higher brain electromagnetic
absorption of radiation from a cell phone at the On state.
The red arrow shows some exttra absorption phenomena ought
to metalic teeth implants of the user!
It is useful to know the value of SAR of your mobile phone,
which must not overpassed the safety limit of its working
frequency. You can find it inside its manual.
4. Microwave Oven Radiation
A common microwave oven is made basically by a a magnetron
source (2.45 GHz), a stirrer, a cooking cavity, and a
control system. In the picture on the left, the structure of
a microwave furnace is presented.
Microwaves are produced from the magnetron source and
propagate with waveguides inside the cooking cavity. These
microwaves are absorbed from the water, which exists inside
the food and they heat it. The metallic parts of the cavity
act as reflectors of the microwaves. The stirrer is used to
homogenize spatially the power distribution of microwaves
inside the furnace.
The window of the oven is used for the reflection of
microwaves, for the heat isolation and also for a direct
safer observation of the food. It is usually double glazed
with a metallic net inside it. The metallic net has special
coating against the oxidation and appropriate geometry to
create band gaps in different angles and to increase the
number of reflections. The geometry of such a net is shown
in the picture on the right.
By using FDTD electromagnetic simulation with typical values
of physical constants of materials used in the coating of
nets, the reflection and transmission coefficients (known as
S - parameters) are calculated for vertical incidence of
microwaves on the window of the furnace.
Our results are presented in the picture on the left, in the
form of two curves (red color for transmission and blue
color for reflection). These curves do not show a big
reflection at 2.45 GHz (resonance peak) as it should be.
In the same picture two more curves have been designed by
hand, which correspond to the expected S-parameters of a
well designed window.
In conclusion, the coating which is used to protect the net
from oxidation actually iterrupts its reflection ability.
This is a usual phenomenon which can be observed to the
common microwave ovens used at homes and contributes to
Is Electromagnetic Pollution Worse Than Air Pollution? Part
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