Sisto R, Casciardi S, Giliberti C, Moleti A
ISPESL, Dipartimento Igiene del Lavoro, Rome, Italy.
Am Ind Hyg Assoc J. 1999 Jan-Feb;60(1):111-5. doi: 10.1080/00028899908984429.
Measurements of extremely low frequency electromagnetic fields and low frequency magnetic fields emitted by a set of video display terminal (VDT) units are reported. The field values measured at the position normally occupied by the user are below the safety limits. This is because the field amplitudes decrease rapidly (following a 1/R3 law) with the distance from the source, as has been verified in this work. Measurements with a commercial shielding device consisting of small plastic balls filled with a water solution of rare earth elements were also performed. The only physical mechanism that could be hypothesized to produce an active suppression of the VDT field is that rare earth atoms, which probably were chosen due to their large magnetic moment, behave as oscillating magnetic dipoles capable of emitting a secondary magnetic field that, along some particular directions, has a phase that is opposite to that of the exciting field. Unfortunately, if one analyzes this mechanism quantitatively, it is easy to show that the secondary magnetic field is absolutely negligible, as was confirmed by experimental measurements performed in this study.
报告了一组视频显示终端（VDT）设备发出的极低频电磁场和低频磁场的测量结果。在用户正常占据的位置测量的场值低于安全限值。这是因为场强幅度随着与源的距离迅速减小（遵循1/R³定律），正如本研究中所验证的那样。还使用了一种由填充有稀土元素水溶液的小塑料球组成的商用屏蔽装置进行了测量。唯一可以假设能对VDT场产生有效抑制作用的物理机制是，稀土原子（可能因其大磁矩而被选用）表现为振荡磁偶极子，能够发射一个二次磁场，该二次磁场沿某些特定方向的相位与激励场的相位相反。不幸的是，如果对这一机制进行定量分析，很容易表明二次磁场绝对可以忽略不计，本研究进行的实验测量证实了这一点。
