Benchmark of different assessment methods for non-sinusoidal magnetic field exposure in the context of European Directive 2013/35/EU.

For the assessment of non-sinusoidal magnetic fields the European EMF Directive 2013/35/EU specified the Weighted Peak Method in Time Domain (WPM-TD) as the reference method. However, also other scientifically validated methods are allowed, provided that they lead to approximately equivalent and comparable results. In the non-binding guide for practical implementation of 2013/35/EU three methods alternative to the WPM-TD are described, i.e. the Weighted Peak Method in Frequency Domain (WPM-FD), the Multiple Frequency Rule (MFR), and an alternative Time Domain Assessment Method (TDAM). In this paper the results of a benchmark comparison of these assessment methods, based on 12 different time domain signals of magnetic induction, measured close to real devices and nine additional generic waveforms, are presented. The results demonstrated that assessments obtained with WPM-TD and WPM-FD can be considered approximately equivalent (maximum deviation 3.4 dB). The MFR systematically overestimates exposure, due to its inherently conservative definitions. In contrast, the TDAM significantly and systematically underestimates exposure up to a factor of 22 (26.8 dB) for the considered waveforms. The main reasons for this exposure underestimation by the TDAM are the introduction of an inappropriate time averaging, and the fact that the characteristic time parameter τ , describing the minimum duration of all field changes dB/dt of the waveform is derived independently from the extent of the field change in the definitions of the TDAM. Consequently, we recommend not to use the TDAM as presently published in the non-binding guide to 2013/35/EU, as its application would be in contradiction with the underlying aim of 2013/35/EU, i.e. a harmonised level of occupational safety with respect to exposure to electromagnetic fields.