The Balanced Electromagnetic Separation Transducer for Bone Conduction Audiometry and Hearing Rehabilitation
Doktorsavhandling, 2017

Hearing via air conduction (AC) and bone conduction (BC) are attributed to be the natural ways of conducting sound to the cochlea. With AC hearing, air pressure variations are transmitted to the cochlea via the ear canal, whereas with BC hearing, sound vibrations are transmitted through the skull bone to the cochlea. Patients with a hearing loss in the cochlea or auditory nerve are commonly rehabilitated with conventional AC hearing aids in the ear canal, but also using cochlear implants. If the pathway for AC sound to reach the cochlea is obstructed, patients can often benet from bone conduction devices (BCDs). In order to determine the type and degree of hearing loss, the BC hearing thresholds are measured using a bone conduction vibrator, and then analyzed together with the AC hearing thresholds for the diagnosis and to suggest an appropriate rehabilitation alternative. The motor unit in conventional BCDs and bone vibrators are known to generate high amount of distortion at low frequencies where the Balanced Electromagnetic Separation Transducer (BEST) principle may oer a new era in BC hearing rehabilitation and audiometry. This thesis combines two BC hearing related topics, where the rst topic is an evaluation of a new audiometric bone vibrator, Radioear B81, which is assumed to oer more accurate BC hearing threshold measurements. The second topic is related to a new type of active transcutaneous BCD, called the Bone Conduction Implant (BCI), which leaves the skin intact by using a wireless solution that does not require a permanent skin penetration. Even though the applications are dierent, both devices use the BEST principle as motor unit in their design. The audiometric bone vibrator Radioear B81 was found to have an improved performance at low frequencies where it can produce higher output levels with less harmonic distortion than the conventional Radioear B71. In a clinical study of the rst six patients, the BCI was found as ecient as already commercially available BCDs, and with the advantage of not needing a skin penetration. In a technical evaluation of the BCI, it was shown to be a mechanically robust design and to tolerate magnetic resonance imaging at 1.5 Tesla.

retention magnet

bone vibrator


bone conduction

balanced electromagnetic separation transducer

magnetically induced torque

image artifact

magnetic resonance imaging

Room EB, Hörsalsvägen 11, Chalmers University of Technology
Opponent: Associate Professor Daniel Rowan


Karl-Johan Fredén Jansson

Chalmers, Signaler och system, Signalbehandling och medicinsk teknik

The bone conduction implant: Clinical results of the first six patients.

International Journal of Audiology,; Vol. 54(2015)p. 408-416

Artikel i vetenskaplig tidskrift

MRI Induced Torque and Demagnetization in Retention Magnets for a Bone Conduction Implant

IEEE Transactions on Biomedical Engineering,; Vol. 61(2014)p. 1887-1893

Artikel i vetenskaplig tidskrift

Electro-acoustic performance of the new bone vibrator Radioear B81: A comparison with the conventional Radioear B71

International Journal of Audiology,; Vol. 54(2015)p. 334-340

Artikel i vetenskaplig tidskrift

Magnetic resonance imaging investigation of the bone conduction implant - a pilot study at 1.5 Tesla.

Medical Devices: Evidence and Research,; Vol. 8(2015)p. 413-23

Artikel i vetenskaplig tidskrift

Fredén Jansson, K-J., Håkansson, B., Reinfeldt, S., Fröhlich, L., Rahne, T. Vibrotactile thresholds on the mastoid and forehead position of deaf patients using Radioear B71 and B81

Fredén Jansson, K-J., Håkansson, B., Reinfeldt, S., Rigato, C. Robustness and lifetime of active transcutaneous bone conduction devices


Medicinsk laboratorie- och mätteknik

Medicinsk apparatteknik

Medicinsk bildbehandling



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4249



Room EB, Hörsalsvägen 11, Chalmers University of Technology

Opponent: Associate Professor Daniel Rowan

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