Design of coils for millimeter- and submillimeter-sized biotelemetry

Biotelemetric systems, especially those that employ implanted devices, work with inductive links, where usually large circular external coils are separated by relatively large distances (dimensions of centimeters) from the small (millimeter- or submillimetersize) implanted coils. This paper shows that, under these conditions, a simplified method for calculation of the mutual inductance (M) between the coils, avoiding elliptic integrals, can be obtained. A procedure for coil design, with maximum M between them, is also described.