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Presentation on EMF

U. K. SrivastavaDDG (Radio)Telecom Engineering CentreNew Delhi

26 July 2010, ALTTC, Ghaziabad26 July 2010, ALTTC, Ghaziabad

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Electromagnetic Fields

• Exposure of human beings to EMF raises concerns of possible health effects.

• Radio transmitters used for telecommunication are proliferating.

• ITU-T began to study a question on health effects in 1996.

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EMF exposure standards

• International Commission on Non Ionizing Radiation Protection (ICNIRP) guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic field up to 300 GHz.

• Adopted in many countries.• Fundamental reference for K.52• Should be used unless a national

standard takes precedence.

Relevant ITU-T standards

• K-52: Guidance of complying with limits for human exposure to electromagnetic field.

• K-61: Guidance on measurement and numerical prediction of electromagnetic fields for compliance with human exposure limits for telecommunication installations.

• K-70: Mitigation techniques to limit human exposure to EMFs in the vicinity of radiocommunication stations.

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Exposure fundamentals

• Two tier exposure limits– Controlled/ occupational exposure– General population/ uncontrolled

exposure, also called general public exposure.

• Formulas for multiple exposures

• Formulas for short term exposures

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ICNIRP reference levelsType of

exposureFrequency

rangeElectric field

Strength (V/m)Magnetic fieldStrength (A/m)

Equivalent PlaneWave power

Density Seq (W/m2)

General public

Up to 1 Hz - 2x104 -

1-8 Hz 10 000 2x104 /f2 -

8-25 Hz 10 000 5 000/f -

0.025-0.8 kHz 250/f 4/f -

0.8-3 kHz 250/f 5 -

3-150 kHz 87 5 -

0.15-1 MHz 87 0.73/f -

1-10 MHz 87/f ½ 0.73/f -

10-400 MHz 28 0.073 2

400-2000 MHz 1.375f ½ 0.0037f½ f/200

2-300 GHz 61 0.16 10

Summary of ICNIRP exposure guidelines

Summary of exposure limits

General Public

S (Power density)

W/m2

E (Electric field intensity)

V/m

900 MHz 4.5 41.3

1800 MHz 9.0 58.3

S=ExH, E/H= 377 ohm, S= E2/377

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Achieving compliance

• Identify appropriate compliance limits• Perform exposure assessment for

intentional transmitters only• If needed, perform by calculations or

measurement.• If the EMF exposure assessment

indicates pertinent exposure limits may be exceeded in areas where people maybe present, mitigation/ avoidance measures should be applied.

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Exposure classification

• Compliance zone– Potential exposure to EMF is below the

applicable limits

• Occupational zone– Potential exposure to EMF is below the limits

for occupational exposure but exceeds the limits for general public exposure

• Exceedance zone– Potential exposure to EMF exceeds the limits

for both, occupational and general public exposure

Exposure zones

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Mitigation techniques

• Occupational zone– Restrict access to general public

• Physical barriers, lock out procedures or adequate signs can accomplish the access restriction.

– Workers may be permitted to enter the area• Workers entering the occupational zone

should be informed

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Mitigation techniques

• Exceedance zone– Restrict access to workers and the

general public• If workers need to enter the area, take

steps to control the exposure– Temporarily reduce the power of the emitter,– Controlling the duration of the exposure so that

time averaged exposure is within safety limits,– Use shielding or protective clothing

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Specific Absorption Rate (SAR)

• SAR is a dosimetric quantity that is widely adopted to quantify the radiation from mobile phones.

• SAR is used to measure the amount of RF energy absorbed into the head during the use of mobile phone.

• SAR values are a measure of the maximum absorption of energy per unit of tissue mass of a person exposed to RF radiation over a given period of time; or in simple terms, the power absorbed per unit mass.

• The unit for SAR is watts per kilogram (W kg-1). This measurement is made over 10 g of tissue.

Installation Compliance Scheme

• Inherently compliant- complies with limit a few centimeter away.

• Normally compliant- exceedance zone is not normally accessibly to public.

• Provisionally compliant- require special measure to achieve compliance.

EMF evaluation techniques

A. Calculation methoda. Prediction of RF fields

b. Calculation to determine EIRPth

B. Software simulation

C. Field measurement

Prediction for RF field

2 m

222 xhR

x

h1–tan

22)(

4

56.2

hx

EIRPFS

To simplify the foregoing, define h' = h – 2 [m]. Using trigonometry,

Taking into account reflections from the ground, the power density becomes:

2.56 may be replaced by 4, for 100% reflection

)()(

22 hx

EIRPFS

Procedure to determine installation class

• Define antenna types.• Define set of accessibility conditions.• Define threshold EIRP for given antenna type and

accessibility condition.• For each site, an installation is normally compliant if

following criteria is met:

1,

i ith

i

EIRP

EIRP

Antenna directivity categories

• Half wave dipole

• Broad coverage antenna (omnidirectional or sectoral)

• High-gain producing a pencil beam

Accessibility categories

h

Accessibility category 1

Accessibility category 2

Accessibility category 3

Access. Cat. 4 a

Access. Cat. 4 b

Measurement

•SAR measurement human head phantom and automatic

system very important for the hand sets

manufacturers

•Electric field strength measurement broad band – cheap but with

overestimation frequency selective – more

expensive and time consuming, require post processing

•On site and laboratory

Measurementadvantages

•It takes into account all radiating sources with real parameters

•It takes into account real environment (reflections, antenna supporting hardware, obstacles)

•Takes into account simultaneous exposure in the real way

(phase differences of the different waves are taken into account)

Measurementadvantages

•It can be done with little knowledge about radiating sources (initial measurement of the occupied spectrum is required only)

•Good quality measurement equipment is accessible on the market

•A live demonstration of the measurement to the interested people is possible

Measurementdisadvantages

•Measurement is not possible for the radiating

sources that do not exist yet•It is difficult to take into account

the time variation of the EMF (for example mobile communication)

•The effect of the presence of staff and equipment on the

EMF distribution has to be avoided

•SAR measurements have to use phantoms that are

approximations only of the human body

Measurementdisadvantages

•It is difficult to confirm and check that all the sources are operating with maximum ERP

•In the multiple sources environment a post processing is required because of different limits for different operating frequencies

•Out of band emissions may lead to overestimation in the in-band measurement

Calculationsadvantages

•Non existing radiating sources can

be considered

•The possibility to take into account

the maximum possible radiation levels

(ERP’s) that lead to the maximum

possible exposure levels

•There are many calculation

methods with different level of

accuracy

•The calculation with high level of

overestimation is very easy to use

ITU-T Technical Session on EMFGeneva, 27 May 2009

Calculationsadvantages

•Calculation costs are lower then the cost of measurements•It gives an opportunity to use mitigation technique if required•It is possible to make calculation in areas with no access

Calculationsdisadvantages

•Very accurate results require detailed description of the radiating antennas

•In most cases do not take into account the influence of reflections

•Require good knowledge of the software used

•Require at least basic knowledge concerning transmitting antennas

FEKO software

Measurement vs. Calculations

•Human exposure assessment

may be done by measurement or

calculations

•Both methods have advantages

and disadvantages

•Both methods have similar level

of uncertainty and accuracy

depending on the method and

equipment or software used

Mitigation techniques• Decrease in transmitter power

• Increase in antenna height

• Decrease in the Vertical Radiation Pattern (VRP) downtilt

• Increase in antenna gain (directivity)

• Change in VRP

• Change in HRP

• Multiple methods applied simultaneously

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Indian scenario• Existing BTS to be guidelines compliant and self

certified.• New BTS to radiate only after self certificate.• TERM cell to test up to 10% of BTS.• Old BTS audit in case of public complaint.• Testing charge Rs. Ten thousand.• Tools and equipment by service provider.• Penalty of Rs. 5 lakh.• Testing status on website.• Total testing by TERM cells on payment.

Status so far

• TEC has developed the following documents-

– Testing procedure for SAR measurement system

– Generic Requirement for EMF strength measuring system

– The test procedure for EMF measurement is likely by August 2009, after consulting all the stakeholders.

– TEC is setting up a SAR lab35

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WHO observations

Fact sheet N°304May 2006…ConclusionsConsidering the very low exposure levels and research results collected to date, there is no convincing scientific evidence that the weak RF signals from base stations and wireless networks cause adverse health effects.

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THANKS

Rough calculation for exclusion zoneRough calculation for exclusion zone

1. Output power per carrier is 20W, sectoral antenna gain about 16-18 dbi in cities and 33 dbi on highways.

2. Neglect cable loss, and assume 4 carriers, the worst case for main lobe in city will be:

20W=43 dbm

EIRP per carrier= 43dbm+ 18dbi= 61dbm=1258.925W

Total EIRP= 4 x 1258.925= 5037.7W

Using K.70 formula, D=6.38 x √ (EIRP/f)= 15.1m

This is the worst case value as cable loss is neglected and also main lobeassumed.