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

Doctoral thesis, 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.