Transcript Background & Historical review

SCIENTIFIC BASIS OF THE
COMPLIANCE ASSESSMENT
of
PORTABLE WIRLESS DEVICES
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________________
Jafar Keshvari
Chairman, International Electrotechnical Commission
IEC MT1 (IEC 62209-1 & IEC 62209-2)
Outline
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• Background & Historical review
• Ionizing and non-ionizing radiation
•
•
•
EMF exposure standards
•
Future of IEC wireless devices compliance standards
Why to develop RF compliance standards
RF measurement/assessment standards in International Electrotechnical Commission (IEC)
Background & Historical review
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• Along the history, philosophers and scientists have explored and
developed several natural phenomena that facilitated the life of the
humankind.
• The philosopher Thales of Milteus (640-546 B.C) is thought to have
been the first person who observed the electrical properties of amber
and explored the magnetic properties of lodestone.
• The twitch of the leg of a dead frog when dissected with a moisted metal
scapel that has been noticed by Galvani in 1786, had led Volta to invent
the electric battery .
• Armstrong demonstrated FM radio transmission in 1933.
• Advanced communications and telecommunications infrastructure have
reduced transportation needs, led to reduction of fuel consumption and
consequently reduction of air pollution from carbon monoxide, carbon
dioxide, nitrogen oxides, hydrocarbons and other pollutants.
Background & Historical review…
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• Electromagnetic Radiation: consists of waves of electric and
magnetic energy moving together through space.
• All electromagnetic radiation can be classified by frequency from
the extremely low to extremely high frequencies.
• Extremely high frequency radiation such as Ultraviolet (UV) and Xrays is called “Ionizing Radiation” because it is powerful enough to
effect changes in the atoms of matter it strikes, by breaking
chemical bonds (ionization) , thus altering their chemical and
biological nature .
• Electromagnetic radiation at those frequencies below the UV band
are generally classified as “Non-Ionizing Radiation” because they
typically lack the energy to effect changes in atomic structure.
The Electromagnetic Spectrum
Background & Historical review (Ionizing and
non-ionizing radiation
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•
Non-ionizing radiation, when incident on matter, is incapable of
liberating electrons (i.e. ionizing) from atoms and molecules.
•
There is a minimum quantum energy below which a radiation
would be unable to bring about ionization. The quantum energy,
E, of radiation is given by:
E = Ћf
where f and Ћ denote frequency of radiation and Plank’s constant
respectively.
• For minimum ionization energy of 12 electron volts (eV), since h =
4.1357e-15 eV.s, the minimum frequency of radiation would be
around 2.9e15 Hz (2900 TeraHz). This corresponds to a
wavelength of about 1.034e-07m or 103.4nm. This lies near the
lower wavelength-edge of the Ultraviolet (UV) spectrum
• Energy quanta of RF far below level needed to break chemical
bonds in DNA
Background & Historical review…
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Non-ionizing radiation wavelengths and frequencies
λ/ƒ
ULTRAVIOLET
VISIBLE
LIGHT
INFRA
RED
MW
&
RF
UVC**
UVB**
UVA**
(λ )
Wavelength,
200*
–
280
nm
280
–
315
nm
315 –
400
nm
400
–
780
nm
780nm
–
1mm
1mm
30km
(ƒ)
Frequency
1500
–
1071
THz
1071
– 952
THz
952 –
750
THz
750
–
385THz
385THz
300GHz
300GHz
10kHz
** WHO (World Health Organization) classification of the non-ionizing UV spectrum.
* 100nm as per the International Commission on Illumination.
Background & Historical review…
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• Wirless communication devices operates at frequencies 100-6000 MHz.
• Mobile phones operate at a variety of frequencies between about 800 and
2200 MHz.
• Mobile Phones base station antennas emit EMR in the range 1800 – 2000
MHz
• Computer monitors emit a broad range of EMR from 30 Hz up to 300
GHz.
• Electromagnetic waves may produce biological effects which may
sometimes, but not always, lead to adverse health effects. It is
important to understand the difference between the two:
• A biological effect occurs when exposure to electromagnetic waves
causes some noticeable or detectable physiological change in a
biological system.
• An adverse health effect occurs when the biological effect is outside
the normal range for the body to compensate, and thus leads to some
detrimental health condition.
Background & Historical review…
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• Does fast evolving Communications and Information Technologies has
negative Impacts on health and Environment:
•
•
The electromagnetic exposure associated with equipment use?
Equipment waste disposal?
Leave the answer to you, rather focus on:
•
How to evaluate the energy absorption in the human body caused by
electromagnetic expsoure
Wireless technology RF Sources
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Exposure to common EMF sources
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RF-human body Interaction analysis?
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• The quantification
challenge of RF interaction with human body?
• Micro and micro approach?
• The dimension of the wave is much larger than the human body.
• The dimension of the wave is much smaller than the human body.
• The dimension of the wave is about the same size as the human
body.
Low-frequency electric and magnetic fields
f = 0 - 30 kHz
 =  – 10 km
Electric field
Magnetic field
Surface
charge
Currents
Circulating
currents
Radio frequency electromagnetic fields
f = 30 kHz – 300 GHz
 = 10 km – 1 mm
Radiowave
Heating
Optical radiation
f = 300 GHz-1000 THz
 = 1 mm – 100 nm
Optical radiation
Heating,
photochemical
reactions
Epidermis
Dermis
How to quantify RF energy absorption, SAR
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The power absorbed per unit mass of tissue is referred to as
Specific Absorption Rate (SAR).
For sinusoidal EM fields, the time rate of energy deposited in a small
volume is defined as Specific Absorption Rate:
2
E
SAR  (σ  ωε')
(W/kg)
ρ
σ and ε’ indicate how much energy will be absorbed by the material
Permittivity
ε:
Describes how much induced polarization and partial
alignment of permanent electric dipoles occures for a given
applied electric field E
Conductivity
σ:
How much conduction current density will be
given applied E.
produced by a
EMF EXPOSURE STANDARDS
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•
ICNIRP
• guidelines developed by a committee of appointed experts, no
industry members
• ICNIRP’s guidance is equally applicable to both base stations,
phones and other radio transmitting equipments
• closed meetings
• Endorsed by WHO
Rationale behind limits for human RF
exposure in International Commission for
Non-Ionizing Radiation Protection (ICNIRP)
guidelines
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• A biological effect occurs when exposure to electromagnetic fields
causes some noticeable or detectable physiological change in a
biological system.
• An adverse health effect occurs when the biological effect is outside
the normal range for the body to compensate.
• In the RF region thermal effects are the stablished harmfull effect
• Only replicated studies can be a scietific basis of expsoure standards.
• Identified behavioural changes i.e. a rise in whole body temperature in
excess of 1°C at a Specific Energy Absorption Rate (SAR) of 1- 4w/kg.
RF exposure limits and safety margins
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•
Limits are given for whole body SAR and localized SAR to prevent
excessive tissue heating due to RF exposure
•
Limit for whole body SAR is based on a threshold of 4W/kg
(corresponds to about 1°C body temperature rise). Safety factors 10 and
50 are used for occupational and general public exposure respectively
•
The rationale for local SAR limit and averaging mass is implicitly based
on exposure effects (thermal) on eye with a safety factor of 50
Exposure from mobile phone
• SAR non-uniform (local
SAR value usually below 1
W/kg in 10 g tissue mass)
• Temperature more uniform
• Equilibrium local
temperature increase is
<0.2 °C at maximum
T in head
(10 g average mass, antenna average emitted power of 0.25 W)
ICNIRP: threshold-based
Exposure
high
low
Established health effects
Threshold of established health effects
Reduction factors
“Safe” exposure
Exposure
limit
Source: ICNIRP
ICNIRP basic restrictions on exposure on the
frequency range 10MHz to 10GHz
Tissue
Region
SAR Limit
W/kg
Average
Parameters
Occupational General
Public
Mass
(g)
Time
(mins)
Whole
Body
0.4
0.08
-
6
Head and
Trunk
10
2
10
6
Limbs
20
4
10
6
Flux of electromagnetic energy
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EMF source
Approximate energy flux
(watts/square meter)
Sunlight at the earth's surface at noon
1350 W/m2
Infrared heat radiation from a living person
20 W/m2
Mobile base station
70 W/m2 – 3 mW/m2 a)
Microwave emission from a living person
3 mW/m2
a)
30 – 2000 MHz, Göteborg and various sites, Sweden
ICNIRP limit 4.5 W/m2 at 900 MHz
(Uddmar T, Thesis, Chalmers U., 1999)
Introduction: Measurement and Computational
standards
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• All portable wireless devices have to comply with RF exposure limits before
putting them in the market.
• Compliances standards for the portable RF wireless devices were
developed by International Electrotechnical Commission IEC and IEEE
mainly relevant to the mobile phones [IEC-62209-1 2005, IEEE-1528, 2003].
• The merge of new technologies and different usage positions of the mobile
devices led to development of relevant compliance standard to cover the
exposure evaluation of the other parts of the body other than the head [IEC62209-2, 2010].
• Although the SAR was established at the highest certified level, the actual
SAR level for the mobile phone during use is generally much lower than the
maximum values. In fact, since mobile phones are designed to operate at
many different power levels, they only use the minimum level of power
required to provide a connection to the network. In theory, the closer you
are to a base station antenna, the lower the power level required by the
mobile phone.
RF compliance assessment standards
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• Compliance can be assessed through measurements or
calculations.
• There is no meaning for existence of exposure
Guidelines/standards if it is not possible to measure it.
• Practically it is not possible to measure the energy absorption in
the body of living humans!
• In order to assess the exposure limits there has to be
standardized procedures to evaluate those limits.

There is a need to develop phantoms head/body phantoms
• Advanced instrumentation is needed for this purpose
• Accurate procedure with well defined and quantified uncertainty is
needed.
International Electro-technical Commission (IEC)
Wireless devices RF Assessment Standards
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• IEC-MT62209,
- Part 1, SAR for handsets. To revise the standard
IEC62209-1: “Procedure to Measure the Specific
Absorption Rate (SAR) for Hand-Held Mobile
Telephones in the Frequency Range of 300 MHz to 3
GHz” by the end of 2011.
- Part 2, SAR for other handheld and body worn
devices. To revise the IEC62209-2: “Procedure to
determine the specific absorption rate (SAR) for
wireless communication devices used in close
proximity to the human body (frequency range of 30
MHz to 6 GHz) standard by 2013.
- To unify IEC62209 part 1 & 2 standards by 2013.
Field measurement unit
SAM
Head phantom
SAM head phantom
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• the Standard Anthropomorphic Model - is a head shell phantom
intended primarily for use in the measurement of exposure from
mobile phones (or other hand-held transmitters)
• SAM is defined as standard phantom allowing a conservative measure
of the radio exposure of people of all origins and all ages. The ear
region is defined with reference points and planes to facilitate
reproducible positioning of telecommunications devices.
• The dimensions of a 90th percentile male head were selected for the
phantom.
• IEC, CENELEC, and IEEE have developed standard procedures for
assessing exposures from mobile phones which specify the use of a
SAM phantom.
•
Device under test
Tissue simulating liquid
Mobile phone exposure assessment
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Thank you!
Questions?