A Principle Method for Mobile Handset Radiation Levels Tracking
JACOB GAVAN AND REUVEN ZEMACH
SCHOOL OF ELECTRICAL, ELECTRONICS & COMMUNICATION ENGINEERING
HOLON ACADEMIC INSTITUTE OF TECHNOLOGY
52 Golomb St., P.O.B. 305, Holon 58102, ISRAEL, Email: zemachr@barak-online.net
Abstract
The fast expanding use of mobile phones and their related applications call for configuring a
fundamental solution that will enable mobile communication radiation tracking and control
system. A principle method for Mobile Phone Radiation Levels Tracking (MPRT) shows that
basic electronic circuitry can solve the problem introducing either external or internal device
to the handsets in use. This principle method is basically general and could be reconfigured
in various modes to incorporate advanced user applications to the presented fundamental
framework. Such solution brings into consideration the varying public concern on nonionizing radiation exposure and the setting of regulations such as SAR and otherwise, so that
it presents an open environment that will adapt changing risk measures and perceptions. The
proposed electronic circuitry is general and dynamic to respond to newly electromagnetic
field (EMF) sensors and the advancements in DSP electronic technology.
1. Introduction
Mobile radio equipment and especially cellular units experience the highest growth in
the expanding communication field. In the seventies of the last century, for cellular
phones only, the global number of mobile units was a few thousands and increased
exponentially reaching about a bilion units in todays data. Indeed, mobile radio systems
can, sometime, save and protect human lives, and also serve as important mean for
enhancing economical and technological developments. However, due to their huge
numbers and the complexities of their networked layouts, there is an ongoing
misunderstanding of their potential random radiation effects to humans. Many
institutions, agencies, research centers and public groups are now highly aware of the
various hazardous risks in applying the cellular units, especially to the direct users’
heads. It is therefore recommended, for frequent users, to apply mobile phones with
accompanying novel devices functioning as Mobile Radiation Levels Tracker (MPRT),
following the the principle method introduced hereafter maintaining much of the
accumulated knowledge in the field [1, 2].
1
2. Radiation Intensities in Base Stations and Portable Phones
Base stations operate at higher power than portable phones, but distances between the
radiating antennas and the exposed people are quite large. Usually transmitted radiation
power density decreases at a rate greater than the square of the separating distance, and
in most cases people are located in the far-field electromagnetic zone of the radiating
base station antennas [3]. Thus, total human body exposure to base stations radiation
power density is at negligible levels in typical base station output confined by cellular
configuration layout in urban areas [3, 4].
For mobile phone the situation is significantly more complex and controversial. In spite
of the relatively low radiation transmitted power (usually less than 1 watt), mobile
phone users are exposed to higher levels of spatial density radiation than from base
station. The most radiating part of a mobile phone is situated at only a few centimeters
from the user head, which is the most sensitive area of the human body. In many cases,
the antenna base is even touching user ear or head, so that a mobile phone user is
exposed to the reactive near field of the phone-radiating antenna, where radiation effects
are complex for accurate determination and radiation hot spots are unpredictable.
Measurements data show that user head absorbs 30% up to 65% of the transmitted
phone radiated power, and only a small percentage can be absorbed by the less sensitive
user-hand, and in many cases less than half of the transmitted power is useful to the
wireless link [5,6].
Hence, it is far more important to control radiation exposure levels emitted by portable
phones than base stations. On the other hand radiation fields effects on users are
significantly more complex in portable phones than in base stations, due to the reactive
near field conditions [3,7]. The principle method of MPRT takes into consideration the
complexity and threats of human body exposure at the near field zone, where fields are
reactive. Such method could assist to monitor and alarm on excessive use of electromagnetic radiation towards the head and body of the users and also to economize energy
consumption thus extending mobile phone battery life.
2
3. Radiation Effects from Portables Phones
Standards of radiation intensity threshold limits of electromagnetic radiation are
relatively high, considering security factors and depending on mobile headset
transmission frequency range [8]. At resonance frequencies of the human body and
head, energy absorption is at maximum. This resonance frequency ranges from 30 MHz
for whole body radiation absorption, typical to tall men, up to about 600 MHz for head
resonance absorption in young children [9].
The physiological thermal effects of radiation power density penetration and absorption
in human head or body are measured in Specific Absorption Rate (SAR) units expressed
in
W
, the transmitted electrical field strength in E
kg
V 
  and power density in S
m
W 
 2 ,
m 
represented in far field conditions by:
S=
E2
Zo
(1).
In this case, H is the magnetic field intensity given by:
H=
in
E
Zo
(2),
A
units, with air characteristic impedance  0 ~
 377 [3]. The equivalent specific
m
absorption rate is given by:
SAR 

Et
2. 
2
(3),
where  is the conductivity in mho/m, ρ is the volumetric weight density in
kg
of
m3
characteristic human tissues and E(t) is the tangential electric field intensity peak
penetrating human tissues skin. This absorbed energy power determine the change in
human tissue temperature so that:
SAR =
c . T
t
(4),
where c is the specific heat, T is the difference of temperature change due to radiation
energy absorbed and t is the time of exposure to the absorbed radiating source [7,8].
For near field and especially reactive near field conditions the equations become
complex and numerical, statistical and semi-empirical 3D computation methods must be
applied. Also, both E and H components must be measured, since Zo in this case is not
3
constant [10. 11]. The weight ρ in SAR indicates that radiation physiological effects
should to be stricter for small thin children than for big fat adults [9].
Non-ionizing radiation power density threshold and SAR levels standards as function of
the radio frequency are presented in [12, 13] for the occupational case and for the
general public. Environmental general public standard threshold limits are 5 times lower
in comparison to the occupational ones due to the higher sensitivity given to public
health, inhibiting the lack of awareness of the general public to radiation threats. Threats
of cellular phone radiation effects are usually higher for teenagers than for adults due to
their lightweight (SAR), the longer life-years of exposure to handset radiation and the
tendency to talk frequently at longer times. Therefore, radiation effects have complex
statistic distribution features, and the probability of exceeding threshold levels is
function of exposure time to cell phones [8, 14].
Non-ionizing radiation may have also physiological effects that are not thermal, which
may indicate a need for threshold radiation level reduction. Some factors are changes in
biological cell growth control mechanisms, indirect induced DNA mutations and
changes in calcium efflux, which may occur at even low-level radiation intensity [14].
These generated non-thermal weak power effects resemble for e.g. the emergence of
relatively high currents at low power excitation levels in Tunnel Diodes applied in
electronic circuits. Scientists stress a concern that low frequency modulation and pulsed
peak power applied in modern digital cellular methods increase the probability of nonthermal radiation effects [7, 15]. On the other hand, Digital Signal Processing (DSP) of
headsets power control can be arranged in many cases to decrease power density
applied and hence lower probability of harmful radiation effects [8]. Recently countries
such as Australia, Italy and Switzerland have decided to lower threshold radiation
intensity limit standard, e.g. to 4 W2 RF power density at 900 MHz instead of
cm
450 W2 in ICNIRP standards, in effect in Switzerland since February 2000 [16].
cm
Due to the stricter threshold radiation levels in the mentioned countries the problem of
threshold standard radiation intensity levels become more serious especially for heavy
use of cellular phones. Therefore efficient, compact and low cost non-ionizing radiation
monitoring devices could be useful to warn and protect users of portable headphones. A
principle method for MPRT system can help to monitor exposure to RF power density
generated by the transmitting mobile cell phone as function of frequency range and
time.
4
4. Concepts of the Principle Method for MPRT.
Measurement and monitoring of non-ionizing radiation in far field conditions are
complex considering multiple paths and shadowing effects [3, 9]. Still, these are much
less complex than near field considerations, especially for reactive near field conditions,
typical to the cases of mobile headset equipments [8, 11]. In far field conditions it is
V 
 A
enough to measure E in   to obtain the H in   , the power density S and the SAR
m
m
as shown in equations 1 to 4 if  and ρ are known. Several relative simple monitoring
equipments for far field radiation effects are available (see Web [17]). However for near
field radiation conditions, radiation power density and SAR are significantly high,
unpredictable and require multiple measurements of E, H, S and SAR in three
dimensions due to the complexity of the Electro-Magnetic fields. Today, very complex,
costly and bulky equipments are available, applying in some case 6 probes to measure
and monitor radiation fields intensity and the physiological effects of portable headset
radiation
[10, 18-21].
Special complex head phantom measurement systems are
available only in special laboratories for measuring accurately the SAR affecting the
head of mobile phone users [20, 21].
5. Technical Description of the Principle MPRT Method
The basic synoptic diagram of prescribed principle MPRT method is presented in
figures 1. The principle MPRT method is demonstrated in an embedded Very
Large Scale Integration (VLSI) hybrid unit. The final dimensions of a typical
embedded package should be of the order of 2x1x1.5 cm and its weight a few
grams only.
The generated MPRT unit should in principle be positioned on the edge of cellular
headset box in the direction of the user head as shown in figure 2. The position of
the MPRT unit is fixed in relation to the headset radiating source antenna.
Therefore the absorbed radiated energy in the MPRT unit will depend on the
radiated power of the headset and on the position of user head, hand and body
which will load, and modify radiation intensity at the MPRT unit. As mentioned
earlier, both E and H field components must be measured in 3 dimensions due to
5
the reactive near field conditions between the mobile headset, user head and the
MPRT system.
PART A
TX
(*)
Antenna Probes
(Sensors)
Frequency Range
Protection
Unit
E - Field
DC
Amplifier
Buffer
Adaptive
Filter &
Terminator
Detector
Filter
Regulator
X
Antenna
X
Full
Rectifier
LPF
Charging
Unit
X
Counter
+
Memory
Units
Multiplier
PART B
Z
X
Y
Protection
Unit
H - Field
Buffer
Adaptive
Filter &
Terminator
Z
DC Amplifier
Detector
Filter
PART B
Threshold
Level
LCD
X
y1
Amplifier
VCO
Audible
Alarm
Amplifier
X
X
X
(Buzzer)
X
Threshold
Level
Memory
Unit
Counter
y2
X
to outside
computer
Fig. 1 Basic MPRT Unit Scheme
The E and H field probes (sensors’ circuitry), shown in figure 1 can be very simple and
low cost due to the following reasons:
1.
The proximity of the headset antenna provides high-level radiation intensity to
the MPRT unit during transmitting periods.
2.
The principle MPRT method is not configured to monitor low radiation
intensity levels requiring sensitive equipment, and only field intensity in the
6
range from 0.1 ET to 10 ET and 0.1 HT to 10 HT (T-required thresholds), which
require a low dynamic range of only 40 decibels.
Fig 2. Mobile Phone Headset and MPRT Unit
These reasons enable the use of simple low cost and robust detector diodes in the MPRT
unit instead of expensive sensitive diodes.
ADAPTIVE
FILTER
Fig 3. E Field Probe
The E field probe should be composed of very thin and short 3 wires as shown in figure
3 and the H field probe should be made of 3 short and thin wired-loops using 2 simple
adders whose output is connected to and adaptive filter as shown in figure 4a. It may be
sufficient to apply 2 loops and one adder since the MPRT unit is at fixed position
related to the headset antenna radiation source as shown in figure 4b. The adaptive
filters include a tuned circuit with variable (trimmer) capacitances and (attenuators)
resistances. The adaptive filter trimmers are used to calibrate radiation intensity
threshold limits as a function of frequency range according to the applied radiation
security standards [12, 13, 16].
Fig. 4a
Fig. 4b
7
H field Probe Optional Configurations
Variable attenuator protects the detector diode from excessive intensity and keeps linear
relations between detector output and E , H intensity variations during headset
transmitting time. A third probe should be a simple thin and short wire (shot) monopole
which couple maximum RF radiation from the (transmitting) radiating headset antenna
to the MPRT unit in order to charge a capacitor via a full wave rectifier circuit including
2 diodes as shown in figure 5. The charged capacitor supplies DC bias to all MPRT
circuitry units.
A low cost buffer circuits operational amplifiers should be included to protect the
detector circuits from loading and keep the MPRT output intensity level proportional to
the real radiated parameters E, H and S from the transmitting headset antenna.
Fig. 5 Antenna Supply Probe
In the presented principle method the DC amplifiers, shown in figure 2, enhance the
power level from the detector output in order to provide enough (energy) power to
operate the Voltage Controlled Oscillator (VCO) and Multipliers Units, counters,
memory circuits, visual and audible alarms. The counters and memory units integrate
the radiation intensity received from the transmitting headset over the operation talking
time. The Multiplier Unit provides a signal proportional to E x H , which is also
proportional to the power density generated by the headset antenna during transmitting
periods. The VCO Unit is activated when one of the input values proportional to E , H
and S amplitude exceed a fixed threshold value related to the security standard limits.
The activated VCO unit operates Liquid Crystal Diodes (LCD) or Light Emitting
Diodes (LED), which will flash, and a buzzer audible alarm. Rules for applying the
principle method could be fitted according to various parameters. e.g. if one diode will
be flashing the headset user may continue to speak, but moderately, whereas when all
diodes will be flashing and the audible buzzer operated, then it will be recommended
that the user will stop talking for a while. In this principle method, a buzzer alarm will
be activated from the VCO Unit via a low frequency amplifier providing enough
(energy) signal to operate a small speaker which loudness will be proportional to the
8
MPRT input energy. Thus the MPRT audible and visual alarm indicators will warn the
headphone users on excessive electromagnetic radiation levels.
The alarm indicators can also operate via the memory units if the average radiation
energy exceeds a threshold value during a measured continuous time. The MPRT
memory unit output can also be connected to a mini-plug which can be connected to a
personal computer to analyze the amount of radiation, E and H average and peak
values in relation to the security threshold standards and E x H power density
transmitted by the headset.
The described principle method for MPRT unit can be a suitable black box for
monitoring a mobile headset radiation effects only if the headset internal circuits are
correctly grounded and shielded so that during the transmitting periods most of the
radiation is generated via the antenna and not via the whole headset box. Thus, in such a
method it is required that the user mobile headset is of good quality grounding and
shielding in order to obtain satisfactory real performances and security from the MPRT
system.
6. Different Options of the MPRT Unit
The MPRT principle method may be designed in hardware at various levels, where
some of them are presented herein:
6.1 A simple low cost option of MPRT system can be developed as shown in
figure 6.
The proposed MPRT principle method may be manifested by an option that will not be
accurate and will only flash a LED or LCD when the peak value of radiation intensity
exceed a threshold value. Still MPRT unit will operate a simple audible alarm buzzer
when the average intensity of radiation exceeds higher-level threshold limit, which will
require limiting or stopping to talk for a while.
Fig. 6 Simpler Option of the MPRT unit.
9
This simple configuration of the MPRT principle method is not planned to yield data
output to a computer. However, it can be constructed with significantly low cost (using
LSI instead of VLSI technology) and its physical dimensions can be smaller than the
main basic option, for instance (1x0.5x0.5) cm.
6.2 An internal mini battery or fuel cell can be added to the main basic MPRT system in
order to increase reliability and to reduce the required RF supply from the mobile
headset unit.
6.3 The principle method for the MPRT unit can be designed so that its output could be
fed to the mobile headset itself, or even maybe integrated with the mobile phone devices
electronic circuitry if cooperation with the manufacturing company is reached. This
option could employ headset internal artificial intelligent circuit to provide verbal
warning to the user applying the headset loudspeaker and control transmitter power
level at lower edge levels for a while. This option can include plugging connection to
external monitoring computer devices and the interface or inclusion within the mobile
phone will enable integrated counter and memory circuits required for the basic MPRT
operation.
7. Summary
The basic and improved options of employing the principle method for MPRT system
can warn mobile phone users about excessive radiation exposure and fulfill the function
of a black box to control and monitor headset users security. The basic implementation
options for the principal method of MPRT are accurate, safe and manufacturer
independent, though may be limited in the available spectrum of options. In case of
manufacturer collaboration having MPRT unit inclusion within mobile phone electronic
circuitry, performances may be far improved and cost may significantly reduced (see
section 6.3).
Thus, in all described cases, the use of the principle MPRT method in production units
either external or internal for headsets is useful for enhancing user security and attention
of mobile phone utilization as required in the natural expansion of mobile
communication and application market.
10
8. References
[1]. Kuster, N., Balzano, Q., Lin, J.C., “Mobile Communications Safety” Chapman
&Hall 1997
[2]. Balzano, Q., “EMC Metrology Issues in Wireless Communications” Modern
Radio Science 1999, pp 79-90.
[3]. Gavan. J., J. Perez, R. Editor., “Electromagnetic Compatibility Handbook” Chapter
19, Academic Press 1995.
[4]. Faraone, A., R.Y.S, Tag., K.H, Joyner., Q, Balzano., “Estimation of the Average
Power Density in the Vicinity of Cellular Base Station Collinear Array Antennas”
IEEE Trans. on V.T. Vol 49 No 3 May 2000 pp 984-996.
[5]. Jensen, M.A., Rahmat-Samii, Y., “Interaction of Handset Antennas and a
Human in Personal Communications” Proceedings of the IEEE Vol. 83 No 1,
Jan 1995
pp 7-17
[6]. Okoniewski, M., M.A. Stuchly., “A Study of the Handset Antenna and Human
Body Interaction” IEEE Trans. on MTT. Vol.44 October 1996. pp 1855-1864.
[7]. Chesworth, E.T., “Near Field Energy Densities of Hand Held Transceivers”
IEEE Int. Symposium on EMC Digest 1989 pp.182-185.
[8]. Moulder, J.E., “Cell Phones and Cancer: what is the Evidence for a Connection
“ Radiation Research, May 1999, Vol. 151 No 5, pp 513-531.
[9] Carlo, G.L. Editor ., “Wireless Phones and Health Scientific Progress” Kluver
Academic Pub. 1998.
[10]. Bucci, O.H., D’ Elia, G., Nigliore, M.B., “A New strategy to Reduce the
truncation Error in Near Field/Far Field Transformations” Radio Science
February 2000 , pp 3-17.
[11]. Faraone, A. Mc Coy D.O. Chou, C.K., Balzano, Q., “Characterization of
Miniaturized E-Field Probes for SAR Measurements” IEEE/EMC
International Symposium Digest, August 2001, pp 749-754.
[12]. EN 50360 CENELEC, European Standard : Product Standard to
Demonstrate the compliance of Mobile Phones with the Basic Restrictions
Related to Human Exposure to Electromagnetic Fields 300 MHz to 3GHz,
July 2001.
11
[13]. ICNIRP Guidelines., “Guidelines for limiting Exposure to Time Varying
Electric, Magnetic and Electromagnetic Fields up to 300 GHz, Health
Physics Vol 74, No 4, 1998, pp494-522.
[14] Adey, W. R., “Frequency and Power Widowing in Tissue Interactions with
Weak Electromagnic Fields” Proc. IEEE Vol. 68, 1980, pp 119-125.
[15] Byus, C.V., et al (Royal Society of Canada) “ A Review of the Potential
Health Risks of Radiofrequency Fields form Wireleess Telecommunication
Devices” Biological Effects of EMR Conference in Roma, Nov. 1999 pp 2934.
[16]. Microwave News “Switzerland Adapts Strict Limits for Cell Towers and
Power Lines” Jan/Feb 2000 . www.microwavesnews.com/strict limits.
[17] . Web Adresses
1) www.narda microwave.com
2) www. radhaz.com
3) www. trifield.com
4) www. enertech.net
5) www. enviromentor.se
6) www. techintl.corp.com
7) www. milligauss.com
[18]. Brown, J. “Personal Monitor Checks RF Safety Levels” Microwaves & RF,
June 2001, P.128.
[19]. Brishoual, M., C, Dale., J, Wiart., J, Citerne., “ Methodology to Interpolate
and Extrapolate SAR measurements in Volume in Dosimetric Experiment “
IEEE trans. on EMC, Vol. 43 No 5; August 2001 pp 382-389.
[20]. Bolomey. J.C. , Lassere, J.L., “Characterization of EMC Sensors in a
spherical Near Field Facility” IEEE EMC Symposium Montreal August 2001
pp 356, 363-367.
[21].Bucci, O.M., et al., “Phaseless Near-Field Measurements” IEEE EMC
International Symposium Digest Montreal. August 2001. pp.389-394
12