Wilhelm Helgesson Råbergh, MPBME

Evaluation of a novel and efficient transcutaneous energy transfer link for bone conduction devices

Examiner: Sabine Reinfeldt, Dept of Electrical Engineering
Supervisors: Erik Holgersson and Martin Johansson, Oticon Medical AB


Background: Implantable hearing devices of various designs, specifications and intended use are available today and are used to treat patients suffering from various types of hearing loss. Active transcutaneous bone conduction devices represents one such system, where sound is converted into vibrations that are transmitted to the skull and thus to the cochlea via bone conduction. In a transcutaneous system, the implant containing the transducer is placed under intact skin and the power is transferred through the skin via a transcutaneous energy transfer (TET) link. The efficiency of such a link is dependent on the skin thickness, which can vary from a few up to about 15 millimetres, resulting in a power transfer efficiency of approximately 10-30%. An improved link design would enable a higher sound output, opening up new possibilities for treating patients with severe hearing loss with these systems, while also increasing battery lifetime and reducing the size of the system. A novel link, the Open Toroid (OT) link is to be evaluated and optimized for efficiency. The solution consists of an external transmitting coil with a toroid ferrite core with a gap of 5 mm and an implanted receiving coil with an air core, electrically and dimensionally matched. The OT link has potentially a higher energy transfer efficiency compared with a TET link since the gap between the transmitting and receiving coils is constant and since the toroid core and windings concentrates the flux. The main objective of this thesis was to investigate the performance and the efficiency of a link based on a toroid and to compare it with a conventional TET link system in terms of efficiency of power transmission.

Materials & Methods: The influence of winding pattern, ferrite core material, wire diameter and misalignment between receiving and transmitting coils were systematically investigated. Evaluation was performed on a measurement system comprising a signal generator, a sound processor, a transducer, a skull simulator and a signal analyser. The energy transfer efficiency was evaluated for the OT link and compared that with a TET link using the same system level measurement setup.

Results: The OT link outperformed the TET link with regards to energy transfer efficiency. The power transfer efficiency was 2 to 10 times higher for the OT link compared with the TET link depending on the skin thickness and toroid parameters. More evenly distributed winding pattern, larger wire diameter up to 0.3 mm and more frequency specific ferrite core material improved the efficiency. The OT link showed robustness and stability as different alignments of the toroid in relation to the receiving coil resulted in only minor changes in efficiency. 

Conclusion: In conclusion, the present study demonstrate that the OT link provides an efficient alternative for transcutaneous energy transmission for bone conduction devices.

Keywords: Bone Conduction, Implant, Radio Frequency Link, Toroid, Transcutaneous Energy Transfer
Category Student project presentation
Location: https://chalmers.zoom.us/j/275223724
Starts: 31 March, 2020, 14:00
Ends: 31 March, 2020, 15:00

Published: Tue 24 Mar 2020.