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Measurements of the magnetic field strength generated by an Carstens Articulograph AG100 show that the field strength is approximately 150uT when measured at the surface of the coils (r=3.5cm), and decreases as 1/r² at greater distances from each coil. This field is below the 205uT maximum permissible exposure defined in ANSI/IEEE standard C95.1-1991. In normal use, the surface of a subject's head will typically be at least 5cm from the surface of any of the transmitter coils, or 7.5cm from the axis of any transmitter. At this distance, the field to which the subject is exposed will be less than or equal to approximately 35uT over the entire volume of the head, and the average exposure level will be considerably less.

ANSI standard C95.1-1991 is designed to prevent any possibility of accidentally stimulating excitable cells (such as neurons), or of heating tissue by any biologically significant amount. The standards committee notes that ``no reliable scientific data exist'' suggesting any health effect of VLF fields other than these two, or suggesting any effect of chronic exposure.

Mark Hasegawa-Johnson
Mon May 26 15:33:40 PDT 1997