A box coil for the stimulation of biological tissue and cells in vitro and in 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 made of copper or aluminum sheet stock. The design is based on the principal determinant of the induced electric field, namely, the magnetic vector potential (A), in the equation, E=-∂A/∂t-∇V. The second term in the equation is needed when boundaries of the conducting 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 -∂A/∂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.