Research project on the charging of electric vehicles

The energy storage devices of battery-electric and plug-in hybrid electric vehicles are usually charged with a cable. As is the case whenever an electric current flows, a magnetic field is formed around the conductor. However, the cables can be manufactured so that the field strengths outside the cable are lower.

Another, less widespread, option is wireless charging. Vehicles equipped for this charging method are parked over a coil located on or in the ground – in a garage or parking space, for example. The generated magnetic field induces a current in the vehicle coil, and this current charges the battery. The ground coil generates powerful magnetic fields that far exceed the EU's recommended reference values, but these fields become significantly weaker with increasing distance from the coil.

Compared to those into low- and high-frequency fields, there are relatively few studies into the effects of the intermediate frequency range that are relevant to electric vehicles. As part of the Federal Environment Ministry's departmental research plan, there are therefore plans to launch further projects aimed at investigating the influence that intermediate-frequency magnetic fields generated during inductive charging could have in animal models. The BfS also intends to invite tenders for additional measurements on newer vehicle models and thereby to obtain data relating to other vehicles and exposure during the charging process.

Influence of intermediate-frequency magnetic fields from inductive power transfer during the charging of electric vehicles on the behaviour of laboratory rodents

Project management: Fraunhofer ITEM, Hanover
Start: 1 May 2021
End: 28 February 2025

Background

The wireless charging of electric vehicles is carried out using the frequencies 20 kHz, 85 kHz and 140 kHz, which lie within the intermediate frequency range. So far, this range has been the subject of relatively little research into potential biological and health effects.

The BfS commissioned a literature study in order to determine the current state of knowledge ^[1]. As well as identifying the currently used technologies that emit intermediate-frequency fields, this included a search of specialist literature on biological effects. Despite an increasing number of corresponding devices, such as induction hobs or wireless charging systems, biological effects are the subject of a relatively small number of studies ^[2].

Most of these studies focused on reproduction and development, including a number of high-quality studies from Japan that found no negative impacts. Other studies focused on the brain, cognition and behaviour and failed to reach a consistent conclusion. A small number of in vitro studies found no evidence of genotoxic effects. A study of mice at a frequency of 20 kHz found no indications of carcinogenic effects ^[3]. Another study, of female mice at 20 kHz, found no influence on development or tumour incidence. In the same study, effects suggesting improved agility and alertness were observed in two out of three behavioural tests ^[4].

Objective

The behavioural tests that revealed effects in the event of exposure to 20 kHz in the aforementioned study ^[4] are to be repeated at 85 kHz and 140 kHz. In addition, a potential toxicological or carcinogenic effect at these two frequencies is to be investigated.

Implementation

The study will be carried out on mice of the strain C57BL/6J, which is an established mouse model for the investigation of various endpoints. Over a period of 300 days, 80 animals will be permanently exposed to fields with frequencies of 80 kHz and 140 kHz respectively and a magnetic flux density of 200 µT. Two equally sized groups will be sham exposed in parallel. The study will be blinded, i.e. the personnel carrying out the experiments and analysing the results will not be informed of which animals are exposed or sham exposed.

After 200 days, three behavioural tests will be carried out on 20 animals from each exposure group in order to obtain insights into motor behaviour (Rotarod), memory and spatial orientation (eight-arm maze), and exploratory behaviour or anxiety (open field test).

After 300 days, histopathological examinations will be performed on 39 organs from each of the animals and the tumour incidence will be determined in accordance with the OECD Guideline.

References

[1] Hirtl R et al. (2018) Exposition und Wirkungen der elektromagnetischen Felder neuartiger Technologien im Zwischenfrequenzbereich – systematischer Review - Vorhaben 3616S82437
[2] Bodewein et al. (2019). Systematic review on the biological effects of electric, magnetic and electromagnetic fields in the intermediate frequency range (300Hz to 1MHz). Environ Res 171: 247-259.
[3] Nishimura I et al. (2019). Carcinogenicity of intermediate frequency magnetic field in Tg.rasH2 mice. Bioelectromagnetics 40: 160-169.
[4] Lerchl A et al. (2021) Effects of long‐term exposure of intermediate frequency magnetic fields (20 kHz, 360 μT) on the development, pathological findings, and behavior of female mice. Bioelectromagnetics 42: 309-316.