[ieee 2008 ieee international rf and microwave conference (rfm) - kuala lumpur, malaysia...

2008 IEEE INTERNATIONAL RF AND MICROWAVE 2008 IEEE INTERNATIONAL RF AND MICROWAVE 2008 IEEE INTERNATIONAL RF AND MICROWAVE 2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS CONFERENCE PROCEEDINGS CONFERENCE PROCEEDINGS CONFERENCE PROCEEDINGS December 2December 2December 2December 2----4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA

978-1-4244-2867-0/08/$25.00 ©2008 IEEE

R F

M 08

Measurement and Analysis of Temperature Rise caused by Handheld Mobile

Telephones using Infrared Thermal Imaging

Rusnani A.,

1 Norsuzila N.

2

1Faculty of Electrical Engineering, Universiti Teknologi Mara Pulau Pinang 2Telecom Malaysia Kuala Lumpur

[email protected],[email protected]

Abstract - With the increase in the number of

commercial mobile phones available and the longer

periods these products are used in close proximity

to the human body, concern has grown about the

possible health hazard from exposure to RF

electromagnetic radiation (EMR). Mobile phone

users often complain about burning sensations or

heating of the ear region. The increase in

temperature may due to thermal insulation by the

phone, conduction of the heat produced in the

phone by battery currents and running of the radio

frequency (RF) electronic circuits, and

electromagnetic field (EMF) energy absorbed by

the user’s head. This study investigates local

heating effects of the skin region including ear-

skull area that handheld mobile phones can cause

in humans. The goal is to visualize, quantify, and

compare these thermal effects in various

parameters condition and subjects using different

commercial mobile phones in the normal contact

position during standardized conversations.

Infrared thermal imaging was used in this

measurement and investigation. It is well suited to

investigate temperature rises of the side of the face

or the ear-skull region when using handheld mobile

phones because it is able to accurately measure

two-dimensional (2D) temperature fields with high

thermal, temporal, and spatial resolutions Thermal

imaging camera is capable of measuring local

temperatures directly, as opposed to other methods,

which can only derive temperatures if the

electromagnetic near-field pattern of the phone, the

energy-absorbing tissue properties, and the blood-

flow situation are exactly known. The strength of

local temperature rises is an indicator of the total

exposure related to radiofrequency electromagnetic

radiation from the mobile phone. Group of female

subjects were used as samples. These subjects were

requested to make a phone call on a standardized

tone. Two different time durations were allocated

to see the difference in the temperature rise. After

15 minutes of conversation, the mobile phone was

removed to acquire thermal image on the right and

left sides of ear-skull area. Then, the conversation

was continued for another 15 minutes and the

images for the same area were captured again.

The temperature for both, the ear-skull area and

temperature of the mobile front surface were

captured after 30 minutes exposure to see the

thermal equilibrium between these two

temperatures. The entire captured images were

collected and analyzed. It is shown in this study

that different commercially available handheld

mobile phones can cause very different thermal

effects under identical experimental conditions.

The measurement results are expected to help

consumers in choosing those phones that cause

the least thermal influences and biological

effects. They might also help change the phone

user’s behavior in order to minimize the

exposure to electromagnetic radiation.

Keywords: Infrared thermal imaging, mobile phones,

specific absorption rate, biological effects of RF

energy.

1.0 Introduction

The use of mobile and portable radio-

frequency (RF) transmitting equipment has

experienced explosive growth worldwide.

Specific absorption rate (SAR) is a dosimetric

quantity and is defined as the rate at which RF

power is absorbed per unit mass by any part of

the body. SAR measurements for the dosimetric

evaluation of mobile phones and similar RF

transmitting devices are carried out by

manufacturers and several independent

institutions Harmonization of RF safety

measurement standards is highly desirable,

particularly in light of the rapid development of

new wireless technologies. SAR values are

normally specified at the maximum transmission

power (when the phone’s display indicates very

low field strength of the received signals). SAR

values of different commercial phones vary by a

factor of about 10–20 (typical values 0.1–1.6

W/kg). The SAR limit for mobile phones used

268

by the public is 2.0 W/kg averaged over ten grams

of body tissue [3],[10].

Infrared thermal imaging is well suited to

investigate temperature rises of the side of the face

or the ear-skull region when using handheld mobile

phones, because it is able to accurately measure

two-dimensional (2D) temperature fields with high

thermal, temporal, and spatial resolutions [6].

Therefore, this measurement technique can derive

an indicator of the total exposure related to RF

radiation from mobile phones. Thermal imaging is

noninvasive and absolutely risk-free, easy to use,

and relatively inexpensive compared with RF and

microwave measurement equipment [6]. This study

does attempt to assess possible health risks of

specific biological effects, quantify thermal effects

due to normal commercial mobile phone use,

provide relative comparisons of overall exposure

from different mobile phones and identify those

phones that cause the smallest local heating and

interaction with the human body. The results might

sensitize mobile phone users and contribute to

behavioral changes, ultimately resulting in the

minimization of an individual’s risks [10].

2.0 Scope of Works

This measurement and analysis were done

to investigate the temperature rise caused by

different commercial mobile phone using infrared

thermal imaging camera. Group of female subjects

were used as samples. These subjects were

requested to make a phone call on a standardized

tone. Two time duration were allocated to see the

different in the temperature rise. After 15 minutes

of conversation, the mobile phone was removed to

acquire thermal image on the right and left side of

head area. Then, the conversation was continued

for another 15 minutes. Both the ear area

temperature and mobile front surface were

captured after 30 minutes exposure to see the

thermal equilibrium between these two

temperatures for both sides of the head. The entire

captured images were analyzed. The results were

analyzed and compared to the SAR standards as to

relate to biological effect.

3.0 Methodology

3.1 Subjects

The subjects were 10 adult female (age

range 24-26 years, height range 145-165 m, weight

range 45-70 kg). All subjects were in excellent

health.

3.2 Experimental Setup

To investigate the temperature of the

ear-skull region, the subjects sat in a comfortable

chair about 0.5 m in front of IR camera with

constant room temperature. Thermal images

were acquired after 15 minutes and 30 minutes

of exposure immediately after the phone was

removed from the head. The unexposed side

images also captured for comparison. The

temperatures of the front surface of mobile

phone used were captured for every sample and

after 30 minutes duration of conversation.

3.3 Mobile Phones

For this study, three different sets of

GSM mobile phones with different SAR values

were chosen. The SAR limit for mobile phones

used by the public is 2.0 watts/kilogram (W/kg)

averaged over ten grams of body tissue. The

mobile phones used were Samsung SGH300 (the

highest SAR value when tested at the ear was

1.14 W/kg), Sony Ericson T230 (the highest

SAR value when tested at the ear was 0.74

W/kg) and Nokia 3610 (the highest SAR value

when tested at the ear was 0.60 W/kg). The

phones all operated at exactly the same location

in a GSM 900 MHz [7]. Therefore, all phones

experienced the same field strength of the

received signals from the base station. More

important is a relative comparison of different

phone models under exactly the same realistic

condition [5]. It was used at maximal power

during emission and their batteries were at full

capacity.

3.4 Measurement Protocols

Upon pre-measurements, the phones’

batteries were fully charged. For reason of

comparison, the phones’ surface temperature was

captured before conversation. The subjects were

asked to sit down on comfortable chair and to

hold and place the phone on the right side of

head. The only restriction imposed on the

subjects was to position their heads

approximately perpendicular to the camera’s

fixed viewing direction just before the thermal

images were taken so that the side of the face

with the phone could be imaged.

Pictures of right and left side of head

were taken first immediately before the exposure

for references. After 15 minutes of exposure, the

images of subjects for right and left sides were

captured. Then, the conversation was continued

for another 15 minutes exposure. Both side of

269

the head and mobile front surface temperature were

captured.

For relative comparisons, it is also

important to keep influences of psychological

origin as constant as possible. Thus, the

conversations on the phone were standardized by

using the same, emotionally neutral text in all

sessions. This was also necessary in order to

guarantee the same speech-to-pause ratios because

a few phone models slightly decrease their

transmitted RF power during speech pauses.

Different loudness levels of individual subjects do

not influence the transmitted RF power since all

phones have automatic gain control circuits in the

audio signal processing path and frequency

modulation. Since the target captured is human

being, neither active nor passive infrared markers

were attached to the subjects’ head. Once the target

was captured, the image will appear on the screen

of IR Snapshot and being stored at the memory

card. The images then download to PC using

RS232 cable.

3.5 Image Processing and Data Analysis

The task of image processing is to analyze

the acquired thermal image sequences and to

calculate temperatures as a function of time. By

using Snapview software programs it is easy to

determine the average temperature within a

manually selected region of interest (ROI) inside

the target in a single image. In all these cases, the

ROI must be chosen smaller than the target

because background pixels must not contribute to

the calculated mean temperature inside the target,

consequently leading to a loss of information.

The temperatures of head areas and

mobile temperature were analyzed. Each area was

defined to have rectangular shape. The

corresponding areas of the unexposed side were

used as temperature references. The points were

manually identified for each image, and Snapview

software was used to position the rectangles.

Differences between images caused by tilting the

head upward or downward and by variations in the

distance to the subject were compensated for by the

software so that the rectangles covered the same

skin areas in all pictures.

Snapview software was used to generate

report from the images. The maximum, mean,

minimum temperature and standard deviation of

the two regions were developed. The changes in

these temperatures and standard deviations of each

ROI were determined at three different stages, one

at initial stage, second after 15 minutes and third

after 30 minutes of exposure. These were

calculated for both exposed and unexposed sides.

Finally, the change in the temperature at the

exposed side relative to the unexposed side was

used to determine the thermal effect from

different mobile phone models.

4.0 Results

Figure 1 shows thermal image of

sample 6 immediately before exposure. Figure 2

shows thermal image of sample 6 after 30

minutes exposure to three different models of

mobile phones. Figure 3 displays thermal image

of mobile phones after 30 min standardized

conversation. Maximum values of temperatures

on right and left sides of head after 15 minutes

and 30 minutes exposure to Nokia were tabulated

in Table 1. Maximum values of temperatures on

right and left sides of head after 15 minutes and

30 minutes exposure to Samsung were tabulated

in Table 2 and maximum temperature values for

exposure to Sony Ericson were tabulated in

Table 3. Figure 4 shows the comparison between

right side of head and Nokia temperatures after

30 minutes exposure. Figure 5 shows the

comparison between right side of head and

Samsung temperatures after 30 minutes

exposure. Figure 6 shows the comparison

between right side of head and Sony Ericson

temperatures after 30 minutes exposure. Table 4

shows the tabulated data for temperatures

increase of different mobile phone for every

sample after 30 minutes exposure. Table 5 shows

the temperature rise of exposed (right) side

relative to unexposed (left) side after 15 minutes

exposure.

(a) (b) Figure 1: Thermal image of sample 6 immediately

before exposure. (a): Right side of the subject.(b) Left

side of the subject.

(a) (b)

270

(c) Figure 2: Thermal image of sample 6 after 30 minutes

exposure to different mobile phone. (a) Nokia 3610 (b)

SamsungSGH300 (c) Sony Ericson T230

(a) (b)

(c) Figure 3: Thermal image of mobile phone after 30 min

standardized conversation. (a) Nokia 3610 (b) Samsung

SGH300 (c) Sony Ericson T230.

Table 1& Table 2: Max values of head temperature after

15 and 30 min exposure to Nokia and Samsung

Table 3: Max values of head temperature after 15 and

30 min exposure to Sony Ericson.

Comparison Between Head and Nokia

Temperature After 30 Min Exposure

30

32

34

36

38

40

1 2 3 4 5 6 7 8 9 10

Samples

Temp (Celcius)

Skin

Nokia

Figure 4: Comparison between head and Nokia

temperatures after 30 min standardized conversation.

Maximum temperatures for every sample after

30 minutes exposure to Nokia lies between

34.8 to 36 ºC while maximum temperatures for

the phone itself is between 34.4 to 37.9 ºC.

Comparison Between Head and Samsung


3132

3334

3536

37

1 2 3 4 5 6 7 8 9 10

Samples

Temp (Celcius)

Skin

Samsung

Figure 5: Comparison between head and Samsung

temperatures after 30 min standardized

conversation.

Maximum temperatures for every sample after

30 minutes exposure to Samsung lies between

33.7 to 35.5 ºC while maximum temperatures for


References 15 min

exposure

30 min

exposure

Samples

Right Left Right Left Right Left

1 33.1 33.0 34.0 33.8 34.7 34.4

2 34.3 34.4 35.1 34.8 35.4 34.5

3 32.9 33.5 33.3 33.3 33.3 33.3

4 34.9 34.4 35.0 34.1 35.3 34.3

5 33.4 34.7 35.2 35.3 35.4 35.3

6 34.2 33.8 34.2 34.3 35.8 34.5

7 34.2 33.9 34.2 34.1 34.6 34.2

8 33.9 34.0 35.1 34.6 34.6 34.5

9 33.8 34.0 34.4 33.7 34.2 33.7

10 34.1 33.9 34.8 33.9 34.9 34.5

References 15 min

exposure

30 min

exposure

Samples


1 33.1 33.0 33.7 33.3 36.0 36.0

2 34.3 34.4 35.5 35.8 35.3 35.2

3 32.9 33.5 34.0 33.8 35.3 35.3

4 34.9 34.4 35.5 35.5 35.6 35.6

5 33.4 34.7 34.7 33.5 35.3 34.6

6 34.2 33.8 34.9 34.0 35.6 34.9

7 34.2 33.9 34.8 34.0 34.9 34.2

8 33.9 34.0 34.1 33.8 34.8 34.1

9 33.8 34.0 34.6 33.8 34.9 34.5

10 34.1 33.9 34.8 33.6 36.1 35.7

References 15 min

exposure

30 min

exposure

Samples


1 33.1 33.0 33.4 33.8 33.7 33.7

2 34.3 34.4 34.6 34.7 34.6 34.5

3 32.9 33.5 32.9 33.3 34.0 33.8

4 34.9 34.4 35.5 35.2 35.5 35.5

5 33.4 34.7 33.4 34.7 35.2 33.6

6 34.2 33.8 34.5 34.3 35.3 34.5

7 34.2 33.9 34.4 33.9 34.7 34.7

8 33.9 34.0 34.1 33.8 34.3 34.0

9 33.8 34.0 33.9 33.2 34.1 33.9

10 34.1 33.9 34.1 33.9 34.6 34.1

271

Comparison Between Head and Sony Ericson


32

33

34

35

36

1 2 3 4 5 6 7 8 9 1

Samples

Temp (Celcius)

Skin

Sony Ericson

Figure 6: Comparison between head and Sony Ericson

temperatures after 30 min standardized conversation.

Maximum temperatures for every sample after 30

minutes exposure to Sony Ericson lies between

33.3 to 35.8 ºC while maximum temperatures for


Table 4: Temperature increase of different mobile phone

for every sample after 30 minutes exposure.

Model (ºC) Samples

Nokia Samsung Sony Ericson

1 3.7 2.0 2.8

2 4.2 2.7 2.8

3 2.9 2.1 2.0

4 4.2 3.8 2.4

5 4.9 5.1 2.9

6 6.4 3.2 3.5

7 2.9 2.0 2.0

8 3.0 2.3 3.1

9 3.3 3.0 3.4

10 4.0 3.7 2.7

The average temperature increase for Nokia is in

range 2.9 to 6.4 ºC. The maximum temperature rise

obtained for all subjects lies between 2.0 to 5.1ºC

for Samsung and 2.0 to 3.5 ºC for Sony Ericson.

Table 5: Temperature rise of exposed (right) side relative

to unexposed (left) side after 15 min exposure.

Nokia Samsung Sony Ericson Samples

Righ

t

Left Righ

t

Left Righ

t

Left

1 2.9 3 0.6 0.7 1.6 1.4

2 1.0 0.8 0.3 0.1 1.1 0.1

3 2.4 1.8 1.1 0.3 0.4 -0.2

4 0.7 1.2 0.6 1.1 0.4 -0.1

5 1.9 -0.1 1.8 -1.1 2.0 0.6

6 1.4 1.1 1.1 0.7 1.6 0.7

7 0.7 1.5 0.5 0 0.4 0.5

8 0.9 0.1 0.4 -0.2 0.7 0.7

9 1.1 -0.2 0.3 -0.8 0.3 -0.3

10 2.0 0.3 0.5 0 0.8 0

Average temperature increase on right side of

head after 15 minutes exposure lies between 0.3

to 2.9 ºC. While temperature increase on left side

of head after 15 minutes exposure lies between -

1.1 to 3 ºC.

5.0 Discussion And Conclusion

The result of this study showed that

most of the mobile phones temperatures were

stayed well below the head temperature. These

indicate that the heat insulation was not the main

reason for the increase in head temperature for

both at 15 minutes and 30 minutes exposure.

Temperature on right side of head with an

average rise of 0.3 to 2.9 ºC is higher than the

temperature of the mobile phone itself (average

rise 2.0 to 6.4 ºC). The temperatures for mobile

phones were lower than the temperatures for the

right side of the heads for all brands of mobile

phones. It proves that the rise in temperature in

the head is not due to the phone battery heating.

There were significant increases in temperature

at unexposed side after 15 minutes exposure with

and average rise up to 3 ºC.

After 30 minutes of exposure to Nokia,

the samples experienced temperature increase

0.7 to 2.9 ºC. When Samsung were used, their

temperature increases approximately from 0.3 to

1.1 ºC. The average temperature rise for every

sample when Sony Ericson was used was 0.4 to

2.0 ºC.

Non-ionization radiation is a type of RF

and microwave radiation. Biological effect can

result from human exposure to RF energy.

Biological effects results from heating of tissue

by RF energy are often referred as thermal

effects. In accord to Magras [1997], the process

of ionization can produce molecular changes that

can lead to damage in Deoxyribonucleic Acid

(DNA), genetic material [11]. DNA is a chemical

at the centre of cells of the living things which

controls the structure and purpose of each cell

and carries the genetic information during

reproduction. Zotti-Martelli L [2000] reported

that once the DNA is damage, the cell of tissue

formation will be disturbed. It is generally

accepted that chromosome and nucleus damage

can be the initiator in a process of mutagenic

transformation, cancer [12].

From this study, it can be concluded

that by using a mobile telephone, the user is

exposed to electromagnetic radiation and the

radiation can affect the rise in temperature of the

ears and head side. The longer the usage of the

272

telephone, the higher the temperature rise. Nokia

3610 has produced the highest increase in

temperature compared to Samsung SGH300 and

Sony Ericson T230. Sony Ericson has lowest

increase in temperature.

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[14] http://www.energyfields.org/

[15] http://www.microwavenews.com/

[16] http://www.emrnetwork.org/

[17] http://www.wave-guide.org/

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