CALCULATION OF INDUCED ELECTRIC-FIELDS BY DUALITY

This paper considers the prediction of induced electric fields for ner ve stimulation. Although functional electric stimulators have been in existence for many years, functional (site specific) magnetic stimulat ion is virgin territory. The problem of predicting localized electric fields from potential magnetic stimulators falls into a special class of eddy current problems. In this class, the currents do not themselve s effect the primary magnetic field responsible for the induced curren t; the medium conductivity is far too small for this secondary couplin g. A two stage static magnetic analysis is used to compute the induced electric fields accurately for a number of problems falling within th is category. The computations accurately the influence conductivity ju mps at interfaces, induced charges, and voltages between points, but u se conventional magnetic scalar potential boundary element solvers. Th e problems are solved as if they were magneto-quasistatic using dualit y. Comparisons to experiment validate the accuracy of this technique. The analysis is addressed to the induced bioelectric fields during mag netic stimulation, but the theory applies equally well to any problem where the induced eddy current has little bearing on the field because of its small amplitude.