Nonsinusoidal in situ electric field caused by magnetic deactivator device for EAS labels—assessment of field strength inside a detailed anatomical hand model

Abstract

In order to evaluate the localised magnetic field (MF) exposure of the cashier’s hand due to a particular demagnetization device (deactivator) for single-use labels of an acoustomagnetic (AM) electronic article surveillance (EAS) system, comprehensive measurements of the MF near the surface of the deactivator, and numerical computations of the induced electric field strength E i, were performed in high-resolution anatomical hand models of different postures and positions with respect to the deactivator. The measurement results for magnetic induction B were assessed with respect to the action levels (AL) for limb exposure, and the computational results for E i were evaluated with respect to the exposure limit values (ELV) for health effects according to European Union (EU) directive 2013/35/EU. For the ELV-based assessment, a maximum of the 2 × 2 × 2 mm3 averaged E i (maxE i,avg) and the respective 99.9th, 99.5th, and 99.0th percentiles were used. As the MF impulse emitted by the deactivator for demagnetization of the AM-EAS labels was highly nonsinusoidal, measurement results were assessed based on the weighted peak method in the time domain (WPM-TD). A newly developed scaling technique was proposed to also apply the WPM-TD to the assessment of the (nonsinusoidal) E i regarding the ELV. It was used to calculate the resulting WPM-TD-based exposure index (EI) from frequency domain computations. The assessment regarding the AL for limbs yielded peak values of magnetic induction of up to 97 mT (measured with a 3 cm2 MF probe on top of the deactivator surface) corresponding to an EI of 443%. However, this was considered an overestimation of the actual exposure in terms of E i as the AL were intentionally defined conservatively. A WPM-TD-based assessment of E i finally led to the worst case EI of up to 135%, 93%, 78%, and 72% when using the maxE i,avg, 99.9th, 99.5th, and 99.0th percentiles, respectively.