title: Multi-coil approach to reduce electromagnetic energy absorption for wirelessly powered implants.
abstract: Near-field inductive coupling is a commonly used technique for wireless power transfer (WPT) in biomedical implants. Owing to the close proximity of the implant coil(s) with the tissue ( ∼1 mm) and high current ( ∼100-300 mA) in the magnetic coil(s), a significant induced electric field can be generated for the operating frequency (1-20 MHz). In this Letter, a multi-coil-based WPT technique is proposed to selectively control the currents in the external and implant coils to reduce the specific absorption rate (SAR). A three-coil WPT system, that can achieve 26% reduction in peak 1-g SAR and 15% reduction in peak 10-g SAR, as compared to a two-coil WPT system with the same dimensions, is implemented and used to demonstrate the effectiveness of the proposed approach. To achieve the seamless design for the external and implant electronics, the multi-coil system achieves the same voltage gain and bandwidth as the two-coil design with 46% improvement in the power transfer efficiency.
authors.affiliation: Department of Electrical and Computer Engineering , University of Utah , Salt Lake City , UT 84112 , USA.
authors.forename: Anil Kumar
authors.initials: AK
authors.lastname: RamRakhyani
authors.affiliation: Department of Electrical and Computer Engineering , University of Utah , Salt Lake City , UT 84112 , USA.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Lazzi
keywords: SAR; absorption; biological tissues; biomedical implant coils; coils; electromagnetic energy absorption reduction; implant electronics; induced electric field; inductive power transmission; magnetic coil; multicoil approach; multicoil-based WPT technique; near-held inductive coupling; power transfer efhciency; prosthetic power supplies; specific absorption rate; three-coil WPT system; tissue; two-coil WPT system; wireless power transfer; wirelessly powered implant