Abstract
Implantable assembly components that are biocompatible and highly miniaturized are an important objective for hearing aid development. We introduce a mechanical transducer, which could be suitable as part of a prospective fully-implantable hearing aid. The transducer comprises a sensor and an actuator unit in one housing, located in the joint gap between the middle ear ossicles, the incus and stapes. The setup offers the advantage of a minimally invasive and reversible surgical solution. However, feedback between actuator and sensor due to mechanical coupling limits the available stable gain. We show that the system can be stabilized by digital control algorithms. The transducer is tested both in a finite elements method simulation of the middle ear and a physical model of a human middle ear. First, we characterize the sensor and actuator elements separately. Then, the maximum stable gain (MSG) of the whole transducer is experimentally determined in the middle ear model. With digital feedback control (using a least mean squares algorithm) in place, the total signal gain is greater than 30 dB for frequencies of 1 kHz and above. This shows the potential of the transducer as a high frequency hearing aid.
Highlights
We aim to show how well the device can be stabilized with digital feedback suppression, determine its dynamic working range as a hearing aid and predict a possible medical indication for its application
The finite elements method (FEM) simulation model of the human middle ear used in this study has been described in [5]
If the actuator is excited with U = 1 V, the measured movement of the stapes footplate is up to 3 × 10−1 mm s−1 V−1, which conforms to an equivalent sound pressure level of 120 decibel sound pressure level (dB SPL) for this model
Summary
The role of implantable hearing aids as a treatment for hearing loss is increasing. Besides visual advantages, they provide the benefit of a free ear canal and a more natural signal acquisition. Several active implants for the treatment of intermediate hearing loss have been developed to serve as an alternative for conventional hearing aids. The references [1,2,3] give an overview of existing middle ear implants. It should be noted that for severe inner ear pathology, the current state-of-the-art treatment is the cochlear implant, which applies an electrical stimulus directly on the auditory nerve. In this study, we will focus on the acoustic or mechanical amplification type of implantable hearing aid
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