A box coil for the stimulation of biological tissue and cells in vitro andin vivo by pulsed magnetic fields

An alternative coil system to the Helmholtz coil-pair is described for the stimulation of biological tissue and cells: a relatively large box coil mad e of copper or aluminum sheet stock. The design is based on the principal d eterminant of the induced electric field, namely the magnetic vector potent ial (A), in the equation, E = -partial derivative A/partial derivative t - del V, The second term in the equation is needed when boundaries of the con ducting medium are in close proximity to the region of interest, such as in a culture dish. An electric surface charge builds up on the boundaries to generate an electric field which cancels -partial derivative A/partial deri vative t at the surface. The effectiveness of the new coil is demonstrated in a study of the outgrowth enhancement of axons from rat embryonic dorsal root ganglia.