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Cited by 16Wireless Power Transfer SystemsInduction Heating and Inverter TechnologyWireless Body Area Networks

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Reduction of eddy current losses in inductive transmission systems with ferrite sheets

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Maaß, Matthias, Griessner, Andreas, Steixner, Viktor, Zierhofer, Clemens·2017·BioMedical Engineering OnLine
DOI 10.1186/s12938-016-0297-4PMC PMC5234259
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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.

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Fig. 1 Functional principle of the ferrite shield. The figure shows the investigated coil configurations with the corresponding magnetic field lines drawn schematically. Air Air-cored coil-system without substrate. Cop The single layer of copper substrate represents a detrimental metallic surface where substantial eddy current losses arise. Fer + Cop An additional ferrite layer is used to minimize the eddy current losses
Fig. 1 Functional principle of the ferrite shield. The figure shows the investigated coil configurations with the corresponding magnetic field lines drawn schematically. Air Air-cored coil-system without substrate. Cop The single layer of copper substrate represents a detrimental metallic surface where substantial eddy current losses arise. Fer + Cop An additional ferrite layer is used to minimize the eddy current lossesCC BY · PubMed Central
Fig. 2 3D and cross-sectional view of two single windings on an infinite double-layer substrate
Fig. 2 3D and cross-sectional view of two single windings on an infinite double-layer substrateCC BY · PubMed Central
Fig. 3 Cross-sectional view of two planar coils on an infinite double-layer substrate
Fig. 3 Cross-sectional view of two planar coils on an infinite double-layer substrateCC BY · PubMed Central
Fig. 4 Top: Cross-sectional view of the used prototype coil system on a finite double-layer substrate. The number of turns in the secondary coil b is fixed to N b = 3 while N a varies between 1 and 24 for different experiments. Bottom: Setup for the experimental measurements
Fig. 4 Top: Cross-sectional view of the used prototype coil system on a finite double-layer substrate. The number of turns in the secondary coil b is fixed to N b = 3 while N a varies between 1 and 24 for different experiments. Bottom: Setup for the experimental measurementsCC BY · PubMed Central
Fig. 5 Setup for inductance and coupling measurements. In a the connection of the device under test (DUT) to the network analyzer is shown. The specific configurations for measuring the inductance L and the coupling k are shown in b and c
Fig. 5 Setup for inductance and coupling measurements. In a the connection of the device under test (DUT) to the network analyzer is shown. The specific configurations for measuring the inductance L and the coupling k are shown in b and cCC BY · PubMed Central
Fig. 6 Dependence of the primary inductance L a on the substrate radius for four substrate configurations obtained from the analytical model, FEM simulations and experimental measurements. Error bars indicate the measurement uncertainty due to the limited precision of the instruments
Fig. 6 Dependence of the primary inductance L a on the substrate radius for four substrate configurations obtained from the analytical model, FEM simulations and experimental measurements. Error bars indicate the measurement uncertainty due to the limited precision of the instrumentsCC BY · PubMed Central
Fig. 7 Analytical, FEM and experimental results for the primary inductance L a are shown as a function of N a for three substrate configurations. Measurement uncertainties are represented via error bars for the experimental results. Three examples of the used PCB planar spiral coils are shown on the right
Fig. 7 Analytical, FEM and experimental results for the primary inductance L a are shown as a function of N a for three substrate configurations. Measurement uncertainties are represented via error bars for the experimental results. Three examples of the used PCB planar spiral coils are shown on the rightCC BY · PubMed Central
Fig. 8 Dependence of the self- and mutual inductances on the coil separation distance d for the air-cored coil system (a), the copper-layered coil system (b) and the double-layer ferrite-shielded coil system (c). Error bars indicate the measurement uncertainties. Please note the different scale in the center plot
Fig. 8 Dependence of the self- and mutual inductances on the coil separation distance d for the air-cored coil system (a), the copper-layered coil system (b) and the double-layer ferrite-shielded coil system (c). Error bars indicate the measurement uncertainties. Please note the different scale in the center plotCC BY · PubMed Central
Fig. 9 Coupling coefficient k as a function of the coil separation distance d for three substrate configurations. Error bars indicate the measurement uncertainty and are obtained from error propagation calculations
Fig. 9 Coupling coefficient k as a function of the coil separation distance d for three substrate configurations. Error bars indicate the measurement uncertainty and are obtained from error propagation calculationsCC BY · PubMed Central
Fig. 10 Circuit diagram of the inductive transmission system in series–parallel resonant topology
Fig. 10 Circuit diagram of the inductive transmission system in series–parallel resonant topologyCC BY · PubMed Central
Fig. 11 Series resistance R s of planar coils on finite substrates as a function of the operating frequency f
Fig. 11 Series resistance R s of planar coils on finite substrates as a function of the operating frequency fCC BY · PubMed Central
Fig. 12 a Voltage gain v and b power transfer efficiency η as a function of the separation distance d at 11.7 MHz for three substrate configurations. Error bars indicating measurement uncertainties are shown for the experimental results
Fig. 12 a Voltage gain v and b power transfer efficiency η as a function of the separation distance d at 11.7 MHz for three substrate configurations. Error bars indicating measurement uncertainties are shown for the experimental resultsCC BY · PubMed Central

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Metadata

Authors
Maaß, M., Griessner, A., Steixner, V., & Zierhofer, C.
Affiliations
Universität Innsbruck (AT)
Corresponding author
Griessner, Andreas
ORCID
Venue
BioMedical Engineering OnLine
Publisher
Springer Science and Business Media LLC
Published
2017-01-05
Volume
16
Issue
1
Pages
3-3
ISSN
1475-925X (ISSN-L)
DOI
10.1186/s12938-016-0297-4
PMC
PMC5234259
OpenAlex
W2574893335
Cited by
16
References
23
Citations by year
2026: 3 · 2024: 3 · 2023: 2 · 2022: 1 · 2021: 2 · 2020: 1 · 2019: 1 · 2018: 2 · 2017: 1
FWCI
0.57
Type
journal article
Language
en
Open access
Licence
cc-by
Locations
  • BioMedical Engineering OnLine (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Digital Library of the University of Innsbruck (University of Innsbruck) (submittedVersion, cc-by)
Funders
  • Universität Innsbruck
  • MED-EL Medical Electronics
Topics
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Wireless Power Transfer Systems
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Induction Heating and Inverter Technology
  • Physical Sciences › Engineering › Biomedical Engineering › Wireless Body Area Networks
Keywords
eddy current loss, ferrite sheet, inductive power transfer, cochlear implants, active implantable medical devices, planar spiral coil, magnetic shielding, transfer efficiency, inductive coupling, coil inductance, copper substrate
MeSH terms
Copper, Electric Conductivity, Ferric Compounds, Finite Element Analysis, Magnetic Fields

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CoChat. (2026). Citation check: Reduction of eddy current losses in inductive transmission systems with ferrite sheets. https://app.cochat.ai/papers/10.1186/s12938-016-0297-4
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Maaß, M., Griessner, A., Steixner, V., & Zierhofer, C. (2017). Reduction of eddy current losses in inductive transmission systems with ferrite sheets. BioMedical Engineering OnLine. https://doi.org/10.1186/s12938-016-0297-4