title: Reduction of eddy current losses in inductive transmission systems with ferrite sheets.
abstract: BACKGROUND
  Improvements in eddy current suppression are necessary to meet the demand for increasing miniaturization of inductively driven transmission systems in industrial and biomedical applications. The high magnetic permeability and the simultaneously low electrical conductivity of ferrite materials make them ideal candidates for shielding metallic surfaces. For systems like cochlear implants the transmission of data as well as energy over an inductive link is conducted within a well-defined parameter set. For these systems, the shielding can be of particular importance if the properties of the link can be preserved.
  
  
  RESULTS
  In this work, we investigate the effect of single and double-layered substrates consisting of ferrite and/or copper on the inductance and coupling of planar spiral coils. The examined link systems represent realistic configurations for active implantable systems such as cochlear implants. Experimental measurements are complemented with analytical calculations and finite element simulations, which are in good agreement for all measured parameters. The results are then used to study the transfer efficiency of an inductive link in a series-parallel resonant topology as a function of substrate size, the number of coil turns and coil separation.
  
  
  CONCLUSIONS
  We find that ferrite sheets can be used to shield the system from unwanted metallic surfaces and to retain the inductive link parameters of the unperturbed system, particularly its transfer efficiency. The required size of the ferrite plates is comparable to the size of the coils, which makes the setup suitable for practical implementations. Since the sizes and geometries chosen for the studied inductive links are comparable to those of cochlear implants, our conclusions apply in particular to these systems.
authors.affiliation: Institute of Mechatronics, University of Innsbruck, Technikerstrasse 13, 6020, Innsbruck, Austria.
authors.forename: Matthias
authors.initials: M
authors.lastname: Maaß
authors.affiliation: Institute of Mechatronics, University of Innsbruck, Technikerstrasse 13, 6020, Innsbruck, Austria. andreas.griessner@uibk.ac.at.
authors.forename: Andreas
authors.identifier: http://orcid.org/0000-0003-4628-3854
authors.initials: A
authors.lastname: Griessner
authors.affiliation: Institute of Mechatronics, University of Innsbruck, Technikerstrasse 13, 6020, Innsbruck, Austria.
authors.forename: Viktor
authors.initials: V
authors.lastname: Steixner
authors.affiliation: Institute of Mechatronics, University of Innsbruck, Technikerstrasse 13, 6020, Innsbruck, Austria.
authors.forename: Clemens
authors.initials: C
authors.lastname: Zierhofer
mesh_terms: D003300:Copper; D004553:Electric Conductivity; D005290:Ferric Compounds; D020342:Finite Element Analysis; D060526:Magnetic Fields
chemical_list: D005290:Ferric Compounds; C001215:ferrite; D003300:Copper
keywords: Cochlear implants; Eddy current losses; Ferrite shield; Inductive transmission systems; Series–parallel resonant converter