Coupling enhancement of planar spiral coils using planar ferrite for biomedical implants

The application of biomedical implants is far reaching, encompassing biological monitoring, as well and diagnosis, treatment, and therapeutic treatment applications. Delivering electrical power to biomedical implants wirelessly has many advantages, and is extensively researched at this time. The basis for the current wireless power transfer technology (WPTT) is inductive coupling. Thus, enhancing the inductive coupling efficiency plays an important role to improve the efficacy of WPTT. Planar Spiral Coils (PSCs) are widely used in biomedical implants for inductive coupling because they can be easily optimized and reliably batch-fabricated. In this paper, an innovative and easy-to-implement method is demonstrated to dramatically improve the coupling efficiency of PSCs. By incorporating a ferrite layer under the PSC, its induced open-circuit voltage is improved by up to 48% in a low frequency rotating-magnet based WPTT system. At radio frequencies, the mutual inductance between two PSCs using a layer of ferrite material is improved by 50%. Because adding a ferritic layer in the PSC is still a planar fabrication process, the described method could be widely used to enhance the inductive coupling efficiency of PSCs that are used in biomedical implants.