Saturday, March 14, 2015

Infant exposures to electronic article surveillance systems

Dosimetry for infant exposures to electronic article surveillance system: Posture, physical dimension and anatomy


Li C, Wu T. Dosimetry for infant exposures to electronic article surveillance system: Posture, physical dimension and anatomy. Bioelectromagnetics. 2015 Mar 10. doi: 10.1002/bem.21901. [Epub ahead of print]

The use of electronic article surveillance (EAS) systems has become popular in many public sites. As a consequence, concern has risen about infant exposure to magnetic fields (MFs) from this kind of device.

To evaluate infant exposure to MFs of an EAS system (operating at 125 kHz and 13.56 MHz), we numerically compared dosimetric results among adult, child and infant models.

Results revealed that postures insignificantly influenced dosimetric results if there was a similar cross-sectional area under exposure. Although safety limits are unlikely to be exceeded, the infant has higher SAR values for brain and central nervous system tissues compared with adult (1.5x at 125 kHz and 112x at 13.56 MHz), which deserve further investigation. Infant's specific anatomy (e.g., non-proportionally large head and high fat content) did not induce higher SAR values. The numerical models developed in the study (stroller and postured infant models) could be freely used for nonprofit academic research.

Electronic article surveillance (EAS) systems have been widely installed in stores and libraries to prevent pilferage of merchandise or books. One major component of a typical EAS system is a detection system, which includes one or multiple coils with alternating driving currents to generate magnetic fields (MFs). Its operational frequency varies from several Hertz to 20 MHz.

Recently, EAS systems were reported to have been used in hospitals, nurseries and maternity wards to track children, infants and neonates [Saito et al., 2013]. Particular concerns regarding the minors' EMF safety evoked keen discussions on the standards' conservativeness [Gandhi and Kang, 2001; Martinéz-Búrdalo et al., 2010; Fiocchi et al., 2011a,b; Fiocchi et al., 2013]. Neonate and child models age of 5 or older were used in the studies. Some studies observed overexposure for the minor's brain in terms of current density (J). However, analysis on the infant (defined as a young child between the ages of several weeks and 24 months) has never been reported due to lack of numerical model ...

In conclusion, exposure of postured infant models to MF of an EAS system did not induce significant dosimetric variability for torso and PNS tissues if the CSA under exposure was similar. Infant brain and CNS tissues had much higher dosimetric results compared to the adult; the infant head was in the intensified MF region due to its particular height. Although basic restrictions were unlikely to be exceeded when current reference levels and product compliance measurement methods were applied (Table 1), further attention to head exposure of shorter models is needed. At higher frequencies, calculating pSAR10g for torso and head together will conceal higher values in infant brain/CNS tissues. Infant anatomy (e.g., disproportionally large head and high fat content) would not certainly induce higher dosimetric results. In this study, we evaluated exposure cases at 125 kHz and 13.56 MHz, two typically lower and higher operational frequencies of the EAS system. Results depended on the relative heights of the model and EAS coil rather than on specific frequency. Thus, results were representative for other frequencies.

EAS and stroller models in this study were not representative of any commercial products to protect proprietary interests of manufacturers. However, parameters were typical and similar protocols applied in many peer-reviewed papers relating to exposure to EAS systems [Gandhi and Kang, 2001; Martinéz-Búrdalo et al., 2010]. In our simulations, distance between the EAS gate and human/stroller model was 20 cm, consistent with the measurement standard [CENELEC, 2001a]. The height of the EAS installation was selected so that the infant head fell in the central intensified MF region, which could be regarded as the worst case for the head exposure. In all, we kept generality in selecting simulation parameters.

Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley

Electromagnetic Radiation Safety

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