Alistair Ruddle, a computational electromagnetics specialist at Horiba MIRA, considers the challenges presented by the assessment of electromagnetic field exposure:
The race to develop intelligent, connected and autonomous vehicles (ICAV) and intelligent transport systems (ITS) is driving the deployment of a widening range of ADAS and increasing levels of wireless connectivity. The latter includes both intra-vehicle and vehicle-vehicle/infrastructure (V2X) communications, as well as personal communications devices that may be used on-board. Typical personal communications services include cell phones – operating at frequencies in the range 0.9GHz to 2.1GHz – as well as Bluteooth and wi-fi at 2.4GHz. The V2X applications operate at 5.8GHz, supporting applications such as toll collection and transmission of warnings between vehicles. In addition, many ADAS functions are also reliant on RF transmissions. For example, radar systems operating at frequencies from 24GHz to 77GHz are used for applications such as collision warning and blind-spot detection. Thus, the electromagnetic environment in and around modern vehicles is becoming increasingly complex.
Electromagnetic fields produce a number of well-established acute physiological effects on body tissues. The most notable of these at RF frequencies is tissue heating, an effect that is widely exploited in microwave ovens. A number of national and international bodies have therefore recommended limits for human exposure to electromagnetic fields (for example, 1999/519/EC), which also include methods for assessing the risks associated with exposure to multiple sources. Although these limits are often interpreted as requirements on the characteristics of individual equipment, they in fact apply to the overall electromagnetic environment that humans may be exposed to. Consequently, the exposure levels that can be tolerated from any specific equipment are not absolute values, but depend on the levels due to other sources that can be expected to be present in its intended operating environment.
Assessing the field exposure of vehicle occupants at frequencies up to 77GHz is not a trivial task. Measurements are not easy, and simulations bring their own challenges. Although deterministic 3D numerical modeling of such scenarios has been carried out for frequencies up to 2.4GHz, very significant computing resources would be required in order to go to higher frequencies. A preliminary assessment of potential in-vehicle field exposure due to radar and communications systems has therefore been carried out using a statistical approach. This allows the average electric field strengths over the passenger compartment to be estimated, which are then compared with the field limits of 1999/519/EC.
The resulting exposure estimates indicate that while none of the sources considered are likely to be problematic in isolation, there may in future be a large enough number of sources present in the vehicle environment that could produce sufficiently high individual exposure levels to warrant more careful scrutiny of their cumulative effects. The use of light-weight materials in vehicle construction will also have significant implications for occupant exposure to electromagnetic fields.
As ICAV technologies and ITS applications mature, detailed investigation and further research will be required to identify the best ways to achieve reliable field exposure estimates to ensure passenger safety. As these technologies continue to be developed, each bringing another layer of complexity to the safety mix, such investigation into their physiological effects will be critical to ensuring future vehicle technology delivers the safety and efficiency enabled by autonomy while managing the field exposure risks inevitable with ICAV technology.
Alastair R Ruddle is an electromagnetics expert working primarily on computational electromagnetics techniques to support applications relating to electromagnetic compatibility, electromagnetic metrology, antennas, and human exposure to electromagnetic fields. He is a leading international expert in these areas and has published more than 150 papers in scientific conferences and journals, as well as a number of book chapters, and acts as a reviewer for leading international electromagnetics journals and conferences.