Topic

Determination of the specific absorption rate (SAR values) occurring during day-to-day mobile phone use

Start

01.12.2003

End

31.05.2005

Project Management

Engineering Firm Telecom Consult

Objective

In June 2002, a jury put forth 'Environment Marks', which are criteria regulating the awarding of the 'Blue Angel' for mobile phones. Specification for the limitation of SAR values is, among other things, also included. At the moment, these specifications are oriented towards maximum SAR values for devices. However, in order to evaluate aspects of preventive radiation protection for mobile phones, the actual SAR value occurring during use is particularly relevant. Currently no method exists to determine this value nor its temporal and, if applicable, local variability. Very rudimentary indications of expected burden to the user can be found in scientific papers.

In order to protect the public form the possible health risks of electromagnetic fields when using mobile phones, besides the knowledge of the effects of such fields on man, the actual exposure needs to be characterised precisely. Such detailed knowledge is currently not available. Furthermore, harmonised methods for determining the actual exposure from mobile phones do not exist. In order to make solid recommendations for preventive radiation protection, the results aspired in this project are urgently needed. The objective of this project is to discuss possible methods to determine the actual exposure of mobile phone users. Furthermore, the project will point to variability over time and the relationship between burden and mobile phone use, network structure and environmental influences.

Results

To cover most of every-day usage scenarios of mobile phones, journeys by car and train as well as walks inside or outside a building have been investigated. Stationary phone calls inside a room without handovers with a duration of half an hour performed by several volunteers complete the data collection. Up to now, the exposure level within such scenarios has only been investigated in particular cases. The results of this study make it possible to link the changes of the SAR with output power and receiving signal level of the phone as well as with movements of the test person or changes in the environment.

As the SAR-value cannot be measured inside the user’s head, the measuring head by Maschek was used to determine the absorbed radiation inside a simulated human head. Furthermore, the actual mobile phone’s output power was read out. Based on this power value, the field computation programme FEKO was used to calculate the related SAR. Typical positions of the handwere derived from video recordings.

Within a GSM network, at the beginning of a phone call and when a handover takes place, the mobile phone uses its maximum power. This suggests the SAR to be lower in cases with less or no handovers, bearing in mind the additional importance of the receiving signal level.

The following values of the mean output power and mean SAR-values of mobile phones were observed under GSM at different scenarios:

• during journeys by car with many handovers and varying signal level
• 25 % of the max. output power and 13 % of the SAR limit value,
• during journeys by train with many handovers and poor signal level
• 50 % of the max. output power (the SAR-value was not calculated),
• inside a room without any handover and with a good signal level
• 10 % of the max. output power and 5 % of the SAR limit value,
• inside a room without handover but with poor signal level
• 20 % of the max. output power and 10 % of the SAR limit value,
• during valking within a room with avery good signal level (CeBIT)
• 13 % of the max. output power and 5 % the SAR limit value,
• during valking outside at varying or poor signal levels
• 70 % of the max. output power and 25 % of the SAR limit value.

In addition to the work reported above we also carried out some investigations on an UMTS network and the results were compared to GSM. The nature of UMTS makes it obligatory that every device uses the minimum power which is sufficient to hold the connection. Together with the fact that maximum power at the beginning of a call or at a handover is not used, it can be assumed that radiation exposure should be lower than for GSM. Investigations under comparable situations show that presently the exposure is about 1000 times lower in UMTS than in GSM, which leads to the result that the SAR is far below the established limits.

The final report, which also contains all interim reports, is available as PDF-file in German (5.365 KB).

References

• Baumann J, Landstorfer FM, Geisbusch L, Georg R. (2006) Evaluation of radiation exposure by UMTS mobile phones. Electronics Letters 42(4): 225-226

Conclusions

The results of the presented study show that under GSM the maximum output power of a mobile phone is reached in fraction of about 5% to 30% of the total calling time. During this time the resulting SAR-value is close to the maximum SAR-value reported by the producer. The receiving signal level has a large influence on the real exposure - at good signal level the exposure can be strongly reduced. Frequent handovers can cause an increased exposure. The comparison between GSM and UMTS shows that as a result of different regulatory modes UMTS causes a considerably lower exposure than GSM. The maximum SAR-value of a mobile phone is by far not reached in UMTS.

Considering the minimalizing of the exposure of the population by electromagnetic fields of mobile phones a good receiving signal and the introduction of the UMTS technology should be supported. Especially under GSM phone calls should be made at good signal quality and with few handovers. At poor signal level, a headset can be used to reduce the exposure.