who is afraid of rf radiation

7/29/2019 Who is Afraid of RF Radiation

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November 2011

P.O. Box 85505605 KN Eindhoven

The Netherlandswww.imec-nl.nl

www.holstcentre.com

WHOS AFRAID OF RF RADIATION?Does Wireless Energy Transport Pose Health Risks?

By Hubregt J. Visser, PhD

A imec / Holst Centre White Paper


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November 2011

Contents

Introduction 2RF Radiation 2Heating Effects 4Long-Term Effects 4Implementing Wireless Energy

Transport 5Summary 6References 6

Introduction

For the general public - and even for people

with a science education - knowingto be

subject to Radio Frequency (RF) radiation

may arouse a feeling of uneasiness or evenfear. Those feelings are instigated by the fact

that you cannot see, hear, smell or feel RF

radiation. Furthermore, the term radiationin itself has become very sensitive from the

moment that the hazardous health effects of

excessive radioactive decay (ionizingradiation) have become apparent. Media

announcements of mostly unconfirmed

scientific studies add to the feeling of

uneasiness.

So, naturally, whenever a new Global

System of Mobile communications (GSM)base station is installed in an urban

environment, the people living in the

neighborhood may get worried. The sameapplies when we propose to use RF radiation

for powering wireless sensors in office and

home spaces [1].

In this paper we will outline the scientific

facts regarding RF radiation, the knowninteractions with human tissue and discusspast and present epidemiologic studies.

Finally, we will give recommendations on

how to implement wireless energy transportsystems.

RF Radiation

Whenever an electric current is changing1, it

will induce a changingmagnetic field

around this current. This changingmagnetic

field will create a changingelectric fieldaround the magnetic field lines. The

changingelectric field will create again a

changingmagnetic field around the electric

field lines and so on. What we describe here

1 Or on a microscopic level whenever a charged

particle accelerates or decelerates.


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is the propagation of electromagnetic

fields or radiation2.

Electromagnetic radiation may beordered according to an increasing

frequencyfor a decreasing

wavelength3. Going up in

frequency we encountersuccessively: radio waves,

microwaves, infrared radiation,

visible light, ultraviolet radiation, X-rays and gamma rays.

So, we see that RF radiation, visible

light and radioactive decay are allforms of the same physical

phenomenon.

In Table 1 we have ordered the

spectrum (roughly) in terms of

frequency and wavelength.

Table 1:Electromagnetic spectrum

Type of

radiation

f(Hz) (m)

RF and

microwave

0.0 - 0.3e12 >1.0e-3

Infrared 0.3e12 4.0e14

7.5e-7 1.0e-3

visible 4.0e14

7.5e14

4.0e-7

7.5e-7

ultraviolet 7.5e14 3.0e16

1.0e-8 4.0e-7

X-rays >3.0e16 1.0e20 3.0e16 >2.0e-17 >124

gamma >1.0e20 >6.6e-14 >4.1e5

When the quantum energy exceeds the level

of a few electronvolts (eV) - the thresholdlying somewhere in the ultraviolet region of

the electromagnetic spectrum - the energy is

high enough to eject an electron from an

atom, leaving behind a positively charged

particle; i.e. an ion. This ionizing radiation iscapable of mutating DeoxyriboNuclear Acid

(DNA) and may thus cause cancer.

We see that RF and microwave radiation

cannot directly be carcinogenic, no matter

the intensity of the radiation5. With respect

to indirect effects, current scientific

evidence has not conclusively linked RF and

microwave radiation to the development ofcancer. We will discuss past and present

epidemiologic studies, after discussing aknown effect of RF and microwave radiationon human tissue: heating.

4h=4.13566733e-15eV5 A higher intensity of non-ionizing electromagnetic

radiation means that more photons are emitted, but

the quantum energy of every photon remains the

same.


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Heating Effects

The effect of heating of tissue by RF

and microwave radiation is knownsince the 1930s and has become

well known since World War II with

the introduction of radar.

Microwave heating is caused by

dipole rotation. Molecules having an

electrical dipole moment (like water)will align themselves in an

electromagnetic field. When this

field alternates, the molecules will

reverse direction and in this processdistribute energy to adjacent

molecules in the form of heat. This

principle is used in microwaveovens.

The first exposure guidelines werealready developed by the US military

in the 1950s and have evolved in

todays exposure limits. These limitsare based on the fact that the human

body can handle heat up to 4W/kgwithout risking permanent damage

6.

The 4W/kgis for the whole body. For

limbs or parts of the body, the limit

may rise up to 80W/kgdue to the

cooling effect of blood circulation.The average exposure time is 6

minutes. For the eyes and males

testes the exposure limit is the sameas for the whole body due to the

limited blood flow in these organs.

Based on these limits and applying asafety factor of 10, the International

Commission on Non-Ionizing

6 The metabolic rate of a sleeping person is

about 1W/kg, increasing to about 2.5W/kg

during moderate exercise.

Radiation Protection (ICNIRP) has issued

guidelines for limiting exposure to time-

varying electric, magnetic andelectromagnetic fields up to 300GHz [2].

The ICNIRP exposure limits for frequencies

relevant for wireless power transmission arestated in Table 3.

Table 3:Exposure limits

Frequency

Range

Plane Wave Power Density, Wm-2

10-400MHz Occupational

exposure

10

General publicexposure

2

400-2000MHz

Occupationalexposure

f/40 f:frequency inMHz


f/200 f:frequency in

MHz

2-300GHz Occupationalexposure

50


10

When transmitting in the license-free

Industry Science and Medicine (ISM)

frequency bands, respecting the internationaland national legal transmit power

restrictions, these exposure limits will not beexceeded [1].

So, respecting (inter)national legal power

restrictions will prevent adverse heatingeffects of human tissue by RF and

microwave radiation. Furthermore, RF and

microwave radiation is non-ionizing andthus cannot directly cause cancer. What

remains to be discussed are possible long-term adverse health effects of RF andmicrowave radiation.

Long-Term Effects

With long-term adverse health effects we

mean an increased risk of developing cancer

other than by ionizing radiation.


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With the widespread use of cell

phones, a growing public concern

about possible long-term adversehealth effects has grown and several

(epidemiologic) studies have been

undertaken. Studies thus far have notshown a consistent link between cell

phone use and cancers of the brain,

nerves, or other tissues of the head or

neck. Considering the very lowexposure levels and research results

collected to date there is no

convincing scientific evidence that

RF and microwave radiation causeadverse health effects.

We do know that the human body

absorbs about five time more of the

signals from FM radio and televisionbroadcasting stations than it does

from a GSM base station. Broadcast

stations have been in use for over 50

years now. Up to date no adversehealth effects originating from these

broadcasting stations have beenestablished.

The largest, most prominent and

scientifically sound epidemiologicstudy to date, i.e. the Interphone

Study [3], concluded that Biases

and errors limit the strength of the

conclusions that can be drawn fromthese analyses and prevent a causal

interpretation.

A problem in the study was that dataon mobile phone use was obtainedthrough questioning the users. This

lead to inaccurate reporting, recall

bias, participation bias and so on.

Notwithstanding these conclusions,

the International Agency for

Research on Cancer (IARC), part of the

World Health Organization (WHO), recently

classified radiofrequency electromagneticfields as possibly carcinogenic to humans

7.

This classification paves the way for furtherresearch.

A large study of cell phone use and its

possible long-term effects was launched inEurope in March 2010. The COSMOS study

will enroll about 250000 cell phone users

aged 18 years or older and will follow them

amongst others through their mobile phonerecords - for 20 to 30 years [5].

Implementing Wireless EnergyTransport

Considering the above, we see that using RFand microwave radiation do not pose an

immediate or mid-term risk to health. The

long-term effects are not known. Regardlessof personal views and interpretations of

conducted (epidemiologic) studies

concerning these long-term effects, it wouldbe wise to apply the As Low As TechnicallyAchievable (ALATA) principle concerning

transmitting powers. This ALATA principle

needs to be applied on top of the (inter)national legal transmit power limits.

For wireless energy transport systems it willbe beneficial to place the RF base station

7 The Classification is Group 2B. The different

classifications are:Group1: The agent is carcinogenic to humans.

Group 2A: The agent is probably carcinogenic to

humans.

Group 2B: The agent is possibly carcinogenic to

humans.

Group3: The agent is not classifiable as to its

carcinogenicity to humans.

Group 4: The agent is probably not carcinogenic to

humans.


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and the wireless sensor nodes on the

ceilings of office and house spaces

and direct the electromagneticradiation along the ceiling. Thus the

energy transmission will not be

blocked by humans and humans willnot be subject to (low intensity, non-

ionizing) electromagnetic radiation.

Summary

A general public concern does exist

about health effects of RF andmicrowave radiation. A large group

of people perceive risks of RF andmicrowave exposure as likely and

even possible severe.Through explaining the physics of

electromagnetic radiation and

ordering the electromagneticspectrum with respect to photon or

quantum energy, it is shown that

ionizing radiation a cause of cancer cannot be associated with RF and

microwave radiation. These types of

radiation cannot be directlycarcinogenic, no matter the intensityof the radiation.

Furthermore, it is shown that RF

heating caused by molecule dipolerotation in an electromagnetic field

is well controlled by (inter)national

power restrictions and exposure limitrecommendations.

We see that using RF and microwave

radiation do not pose an immediate

or mid-term risk to health. The long-term effects are not known and

research concerning possible effectsin ongoing. Awaiting these resultswe propose to use the As Low As

Technically Achievable (ALATA)

principle concerning transmitpowers.

For wireless energy transport we

furthermore propose to place RF base station

and wireless sensor nodes on the ceiling ofoffice and home spaces and direct the

electromagnetic radiation along the ceiling.

The benefit of this configuration is two-fold:Humans are not subject to electromagnetic

radiation and energy transport is not blocked

by humans.

References

[1] Hubregt J. Visser, No More DeadBatteries, Opening the Gateway to

Smart Building Integration through RFWireless Battery Charging, imec /

Holst Centre White Paper, October2011. Available at:

http://www.iwweth.org/downloads

[2] International Commission on Non-Ionizing Radiation Protection

(ICNIRP), Guidelines for Limiting

Exposure to Time-Varying Electric,Magnetic, and Electromagnetic Fields

(up to 300GHz),Health Physics, Vol.

74, No. 4, April 1998, pp. 494-522.[3] International Agency for Research on

Cancer, Interphone Study Reports on

Mobile Phone Use and Brain Cancer

Risk, World Health Organization,Press Release No. 200, 17 May 2010.

[4] International Agency for Research on

Cancer, IARC ClassifiesRadiofrequency Electromagnetic

Fields as Possibly Carcinogenic to

Humans, World Health Organization,

Press Release No. 208, 31 May 2011.[5] Available at:

http://www.ukcosmos.org

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