Abstract
Acoustic hearing aids generate amplified sound in the ear canal, and they are the standard of care for patients with mild to moderate sensorineural hearing loss. However, because of their limited frequency bandwidth, gain, and feedback, there is substantial room for improvement. Active middle ear implants, which directly vibrate the middle ear and cochlea, are an alternative approach to conventional acoustic hearing aids. They provide an opportunity to improve sound quality and speech understanding with amplification rehabilitation. For floating-mass type and direct-rod type (DRT) middle ear transducers, a differential floating-mass transducer (DFMT) and a tri-coil bellows transducer (TCBT), respectively, were fabricated to measure the output characteristics in four human temporal bones. Both were fabricated to have similar output forces per unit input and were placed in four human temporal bones to measure their output performances. The TCBT resulted in higher output than did the DFMT throughout the audible frequency range, and the output was more prominent at lower frequency ranges. In this study, we showed that DRT was a more effective method for round window stimulation. Because of its frequency characteristics and vibration efficiency, this implantation method can be utilized as a driving solution for middle ear implants.
Highlights
Active middle ear implants (AMEIs) are alternatives to conventional hearing aids, which are effective for sensorineural and mixed hearing loss[1,2,3,4,5,6]
The vibration transducers are classified into direct-rod type transducers (DRTs) and floating-mass type transducers (FMTs)[7]
Round-window (RW) vibroplasty with AMEI vibration transducers has been the focus of investigation because RW stimulation can be used to treat patients with middle ear diseases, such as otosclerosis[8,9,10,11,12,13,14,15,16,17]
Summary
Active middle ear implants (AMEIs) are alternatives to conventional hearing aids, which are effective for sensorineural and mixed hearing loss[1,2,3,4,5,6]. The first clinical AMEI was reported by Yanagihara in Japan in 1984 and was used to remove part of the ossicle chain to directly drive the stapes footplate[5] This device could only be applied to patients with middle ear malfunction, because patients cannot use a conventional hearing aid if the implant fails. The DFMT proposed by Kim et al.[18] consists of a differential magnet to which are glued two magnets with the same poles; these magnets focus the magnetic flux emitted in a radial direction from the center of the magnet and the three field coils, generating the driving force This modified FMT-type transducer is able to cancel the external environmental magnetic fields while remaining highly efficient. Some structures inside the transducer have been modified, its characteristic frequency is similar to the characteristic frequency of the FMT-type transducer because it operates in a floating-mass s tyle[19]
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