The Influence of Piezoelectric Transducer Stimulating Sites on the Performance of Implantable Middle Ear Hearing Devices: A Numerical Analysis

Analysis of design parameters of round-window stimulating type electromagnetic transducer by a nonlinear lumped parameter model of implanted human ear

Round-window stimulating transducer is a new solution to treat mixed hearing loss. To uncover the factors affecting the round-window stimulation's performance, we investigated the influence of four main design parameters of round-window stimulating type electromagnetic transducer. Firstly, we constructed a human ear nonlinear lumped parameter model and confirmed its validity by comparing the stapes responses predicted by the model with the experimental data. Following this, an electromagnetic transducer's mechanical model, which simulates the floating mass transducer, was built and coupled to the human ear model; thereby, we established a nonlinear lumped parameter model of implanted human ear under round-window stimulation and verified its reliability. Finally, based on this model, the influences of the four main design parameters, i.e., the excitation voltage, the electromechanical coupling coefficient, the support stiffness, and the preload force, were analyzed. The results show that the change of excitation voltage does not alter the system's natural frequency. Chaotic motion occurs when the electromechanical coupling coefficient is small. Meanwhile, the stapes displacement appears to increase firstly and then decrease with the increase of the electromechanical coupling coefficient. The increase of the support stiffness enlarges the resonance frequency of the stapes displacement and reduces the stapes displacement near the resonance frequency, deteriorating the transducer's hearing compensation at low frequency. The preload force can improve the transducer's hearing compensation performance in mid-high frequency region.

[Numerical study on the effect of middle ear malformations on energy absorbance]

In order to study the effect of middle ear malformations on energy absorbance, we constructed a mechanical model that can simulate the energy absorbance of the human ear based on our previous human ear finite element model. The validation of this model was confirmed by two sets of experimental data. Based on this model, three common types of middle ear malformations, i. e. incudostapedial joint defect, incus fixation and malleus fixation, and stapes fixation, were simulated by changing the structure and material properties of the corresponding tissue. Then, the effect of these three common types of middle ear malformations on energy absorbance was investigated by comparing the corresponding energy absorbance. The results showed that the incudostapedial joint defect significantly increased the energy absorbance near 1 000 Hz. The incus fixation and malleus fixation dramatically reduced the energy absorbance in the low frequency, which made the energy absorbance less than 10% at frequencies lower than 1 000 Hz. At the same time, the peak of energy absorbance shifted to the higher frequency. These two kinds of middle ear malformations had obvious characteristics in the wideband acoustic immittance test. In contrast, the stapes fixation only reduced the energy absorbance in the low frequency and increased energy absorbance in the middle frequency slightly, which had no obvious characteristic in the wideband acoustic immittance test. These results provide a theoretical reference for the wideband acoustic immittance diagnosis of middle ear malformations in clinic.

Numerical analysis of the effects of ossicular chain malformations on bone conduction stimulation

To assess the effects of ossicular chain malformations on the performance of bone conduction hearing aids, a human ear finite-element model that includes an ear canal, a middle ear, and a spiral cochlea incorporating the third windows was established. This finite element model was built based on micro-computed tomography scanning and reverse modelling techniques, and the reliability of the finite element model was verified by comparison with reported experimental data. Based on this model, two main types of ossicular chain malformations, i.e., the incudostapedial disconnection and the ossicles fixation, were simulated, and their influences on bone conduction were analyzed by comparing the trans-cochlear-partition differential pressures. The results indicate that the incudostapedial disconnection mainly deteriorates the bone conduction response at mid frequencies. The stapes fixation has the largest effect among the ossicles fixation with the bone conduction stimulation, which also mainly decreases the mid-frequency response of the bone conduction, especially at 2 kHz. As the speech intelligibility has the most important frequency range at the range between 1 kHz and 2.5 kHz, the mid-frequency deterioration caused by ossicular chain malformations should be compensated in optimizing the design of the bone conduction hearing aids. For treating patients with the ossicular chain malformations, especially for the patients who suffer from the stapes fixation, the output of bone conduction hearing aids' actuator in the middle frequency band should be improved.