Models of the uniformity of electro-magnetic fields generated for biological experiments by Merritt coils

Electromagnetic field (EMF) producing wire coils were described by Merritt et al, Rev. Sci. Instrum. 54 (7), 1983. Merritt coils produce large volume EMFs in which statistical numbers of biological experiments are performed. We build and use Merritt coils for cell/animal studies and are developing therapeutic EMF systems. Here we present models illustrating the EMFs produced by our coils and discuss the criteria that should be applied to the use of Merritt and other coils to achieve valid experimental results. In a companion paper at this meeting Nindl et al, describe biological experiments, using these Merritt coils, showing that EMFs may be useful in treating many inflammatory disease states. Although the large-volume EMFs produced by Merritt coils are convenient for biological experiments the EMFs are not perfectly uniform and the deviations can be a significant source of experimental error. The orientation and size of experimental objects are key contributors to these deviations. To evaluate our Merritt coils we solved the Biot-Savart law explicitly for ideal 3-coil and 4-coil Merritt systems and compared these theoretical EMFs with those of our systems. We present a detailed examination of deviations in magnetic field amplitude, as well as magnetic field direction, as a function of location within the coils. We find that spherically shaped experimental sets minimize these deviations. We developed simple formulae for accurately predicting deviations associated with Merritt coils.