Optimal frequency for powering millimeter-sized biomedical implants inside an inductively-powered homecage.

This paper presents the optimal design and operation frequency (f) of an inductively-powered homecage for powering biomedical devices with millimeter (mm) dimensions, implanted inside the body of freely-behaving small animal subjects, for longitudinal behavioral neuroscience and electrophysiology experiments. In order to improve the power transmission efficiency (PTE) for powering mm-sized implants, the geometry of the multi-coil inductive links in the form of 3- and 4-coil links as well as fp need to be co-optimized. A simplified equation for the PTE of 3-coil inductive links for powering mm-sized implants has been derived, based on which the optimal geometries and fp of a 3-coil link have been found using a commercial field solver (HFSS). In simulations, the optimized 3-coil inductive link achieved a significant PTE of 2.56% at the optimal fp of 40 MHz for powering a 1 mm3 implant coil at the nominal height of 7 cm, thanks to the link and fp optimization as well as an intermediate coil in the receiver side with 18 mm diameter.