Electromagnetic Midsagittal Articulography (EMMA) is a technique for obtaining real-time data about the motion of points on the surface of the tongue and other articulators using relatively low-cost, lightweight, and non-invasive equipment (Perkell, 1992). EMMA relies on alternating magnetic fields to measure the distance between fixed transmitter coils and movable receiver coils fixed to the surfaces of the articulators. The Carstens Articulograph AG100 is, at the time of this writing, the only commercially available EMMA system capable of correcting for small misalignments of the receiver coils using a redundant third transmitter (Hoole and Nguyen, 1996). Because of its light weight and relative low cost, the Articulograph offers small laboratories a unique opportunity to collect large amounts of articulatory data.
Alternating magnetic fields generate electric current in any conducting medium, including human bones and blood. Fields of moderate strength at the frequencies used in the Articulograph have not been conclusively linked to any health risk, but caution dictates that unnecessary exposure should be minimized. In particular, the American National Standards Institute has endorsed a standard which limits exposure to magnetic fields at frequencies above 3kHz (IEEE, 1992). The purpose of this article is to very briefly review the relevant safety considerations, and to describe measurements which show that the Articulograph AG100 meets the maximum permissible exposure standards endorsed by the American National Standards Institute.