Topic

Determination of public exposure due to ultra-wideband technologies

Start

01.04.07

End

30.04.08

Project Management

ARC Seibersdorf research GmbH, Österreich

Objective

With upcoming Ultrawideband (UWB) a new technology will be introduced into the consumer market, that will cause exposures to electromagnetic fields covering outstanding broad frequency ranges - very much different to ordinary narrow-band transmission techniques used for civil radio transmission services so far. UWB technologies may be used for high data rate transmissions like e.g. video transmission over short distances.

The aim of this research project was to provide as early as possible a reliable data base for maximum and average exposures to be expected when using various ultra-wideband wireless applications. For this purpose existing measurement and calculation methods had to be examined with respect to their suitability and properly adjusted if necessary.

Results

With regard to the established measurement and calculation methods used in the project, please find detailed information in the interim reports and in the detailed final report respectively (for download see below).

Measurements carried out in close proximity (15 cm) of already available UWB devices yielded time-averaged power flux densities of up to about 0.32 mW/m². Temporal peak values measured at the same distance have been found to be less than 2.4 mW/m² in all analyzed scenarios. Measuring SAR values caused by UWB devices operated near the human body has been found not feasible at present because of the lack of tissue simulating liquids with dispersion properties that are comparable to those of human tissue over the entire frequency spectrum covered by UWB. Furthermore sensitivity of currently available SAR probes is too low.

For the computations based on the FDTD method an anatomical body model derived from the Visible Human Project data set with dispersive dielectric tissue properties was used. The numerical simulations of different exposure scenarios with an UWB source in close proximity to various regions of the human body (thigh, back of the head, chest, eye) yielded a 10 g averaged spatial peak SAR of up to 13 mW/kg, if a 100% spectral efficiency of the source with respect to the European UWB regulation was assumed. Devices for the U.S. market may cause somewhat higher SAR values (in the scenarios analyzed within the project about up to 22 mW/kg). In practice, it is assumed that the maximum of 10 grams of tissue mass averaged SAR will be even lower because of lower spectral efficiency and further reduction caused by duty-cycles (ratio of times of transmitting to those of receiving) well below 100%. Devices using DS-UWB will generate distinct pulses of HF, but it could be shown that the expected maximum of specific absorption SA_10g averaged over 10 grams is also well below the relevant recommendations, typically in the range of less than 10^-8 J/kg, i.e. below 0.0005% of the recommended basic restriction.

The first interim report contains information on technology, standardization, regulation and applications of ultra wideband technologies (UWB). The text is available as PDF-file (335 KB) in German.

The second interim report deals with exposure assessment by means of both measurements and computational techniques. Special attention was paid to the characteristics of UWB signals. The text is available as PDF-file (1,605 KB) in German.

The third and final interim report presents results of measurements carried out in the vicinity of currently available UWB devices as well as numerical calculations of the radiation absorption for different scenarios with UWB sources operated near the human body. The text is available as PDF-file (4,795 KB) in German.

The final report summarizes the project's results. The text is available as PDF-file (6,441 KB) in German.

A brief summary of the results can also be found in a presentation, which was prepared by the contractor for an internal project meeting at the BfS. The presentation is available as PDF-file (1,055 KB) in German.

Conclusions

UWB devices have been found to produce the lowest exposures among the wireless communication technologies investigated within the scope of the German Mobile Telecommunication Research Programme. UWB covers an extremely broad frequency band (up to 7.5 GHz bandwidth) but the resulting exposure is quite low. Due to their low transmitting power UWB devices for communication purposes can be inherently deemed compliant to the basic restrictions of current safety standards in terms of SAR_10g. The most likely dominating type of UWB devices that can be expected on the market in the near future will be utilizing the well-established modulation scheme OFDM. Pulsed signals can be expected from DS-UWB devices only. Exposure in terms of SA_10g will also be well below recommended basic restrictions for these type of devices.