Ensuring the safety of wireless power transfer systems
Challenge
Non-ionizing radiation in the radiofrequency range from 600 MHz to 300 GHz provides the basis for connectivity in mobile communication applications. Additionally, electromagnetic fields (EMFs) generated by inductively coupled coils at low frequencies (typically below 10 MHz) are widely used for contactless charging of household appliances and electric vehicles.
Exposure to EMFs can have adverse health effects, however, as EMFs penetrate the body and can cause tissue heating and, below 10 MHz, may also cause unintended stimulation of nerves.
International safety guidelines set ‘basic restrictions’ in terms of body-induced field levels to prevent health hazards as well as permissible exposure levels measured outside the body, known as ‘reference levels’, that ensure that basic restrictions are met.
Yet, reference levels only account for exposure to uniform fields, whereas WPT systems show a strong gradient in proximity to the coils that decays with distance, meaning reference levels greatly overestimate the exposure in case of WPT.
Hence exposure measurements and estimates must be accurate to ensure the general public’s safety without greatly overestimating the exposure as this would hinder technological advances.
Solution
The MICEV project addressed this challenge by developing a Best Practice Guide (BPG) to implement precise measurements in electric vehicle charging systems and by significantly contributing to the new specification IEC PAS 63184 that was published in 2021 and will soon become a definitive standard.
As part of the MICEV project, Schmidt and Partner Engineering AG (SPEAG) developed a mathematical model that transforms the ‘incident’ magnetic fields into body-internal basic restriction quantities.
Simulations were performed examining the effects of EMFs from 3 kHz to 10 MHz on a ‘virtual population’ of humans of different height, age (children to adults), sex, and body-mass index.
The method was validated by numerical analysis of human exposure to actual WPT sources at various locations and distances from a human phantom. It was then compared to the existing compliance test methods using incident fields.
As a result of the work, SPEAG was able to establish a novel compliance testing method that mitigates the overestimation of EMF exposure while maintaining the simplicity of the testing procedure.
Impact
SPEAG, based in Switzerland, is the world leader in instrumentation and numerical tools for evaluating EMFs in complex environments, with customers including leading mobile device manufacturers, governments, and regulatory agencies.
The metrology developed in the MICEV project – the first in the world – for the assessment of the body-induced EMFs by measurement below 4 MHz – has been integrated into SPEAG’s measurement capabilities, which now cover the frequency range from 3 kHz to 300 GHz.
Two new instruments have been developed. The Magnetic Amplitude and Gradient Probe System (MAGPy) is a handheld device for in situ evaluation of inductive WPT systems from 3 kHz to 10 MHz. It is capable of real-time 3D electric and magnetic field and field gradient measurements, and its small sensors (< 1 cm2) can overcome the inaccurate estimations of non-homogenous fields made by larger sensors.
For laboratory testing, SPEAG now offers the DASY8 Module WPT for high precision robotbased evaluations, allowing manufacturers of WPT devices to demonstrate full compliance with the new IEC standard.
These instruments and capabilities will help to introduce future WPT systems in Europe and ensure that already existing systems are safe to use.
- Category
- EMPIR,
- Energy,
- EMN Advanced Manufacturing,