A tri-coil bellows-type round window transducer with improved frequency characteristics for middle-ear implants

Effectiveness of active middle ear implant placement methods in pathological conditions: basilar membrane vibration simulation

Active middle ear implants (AMEI) amplify mechanical vibrations in the middle ear and transmit them to the cochlea. The AMEI includes a floating mass transducer (FMT) that can be placed using two different surgical approaches: "oval window (OW) vibroplasty" and "round window (RW) vibroplasty." The OW and RW are windows located on the cochlea. Normally, sound stimulus is transmitted from the middle ear to cochlea via the OW. RW vibroplasty has been suggested as an alternative method due to the difficulty of applying OW vibroplasty in patients with ossicle dysfunction. Several reports compare the advantages of each approach through pre and postoperative hearing tests. However, quantitatively assessing the treatment effect is challenging due to individual differences in pathologies. This study investigates the vibration transmission efficiency of each surgical approach using a finite-element model of the human cochlea. Vibration of the basilar membrane (BM) of the cochlea is simulated by applying the stimulus through the OW or RW. Pathological conditions, such as impaired stapes mobility, are simulated by increasing the stiffness of the stapedial annular ligament. RW closure due to chronic middle ear diseases is a common clinical occurrence and is simulated by increasing the stiffness of the RW membrane in the model. The results show that the vibration amplitude of the BM is larger when the stimulus is applied to the RW compared to the OW, except for cases of RW membrane ossification. The difference in these amplitudes is particularly significant when stapedial mobility is limited. These results suggest that RW vibroplasty would be advantageous, especially in cases of accompanying stapedial mobility impairment. Additionally, it is suggested that transitioning to OW vibroplasty could still ensure a sufficient level of vibratory transmission efficiency when placing the FMT on the RW membrane is difficult due to anatomical problems in the tympanic cavity or confirmed severe pathological conditions around the RW.

Effects of design and coupling parameters on the performance of electromagnetic transducers in round-window stimulation

Many studies have investigated factors contributing to large variations in the outcomes of round-window (RW) stimulation but most have focused on the floating mass transducer (FMT). To determine whether results for the FMT hold for a fixed-type transducer (FTT), this study constructs two coupled finite element models of the transducer and the human ear that incorporate the cochlear third windows and inner structures of these two electromagnetic transducers. We use these FE models of the human ear and transducers to investigate the influence of four design parameters and coupling conditions for the transducers, i.e., the support's Young's modulus, the coupling layer's cross sectional area and Young's modulus, and the transducer's cross sectional area. The results show that an increase in the support's Young's modulus reduces the output of the FMT but increases that of the FTT. Reducing the cross sectional area and Young's modulus of the coupling layer significantly increases the low-frequency response of the FMT but slightly reduces that of the FTT. Reducing the cross sectional area of the transducer increases the output of the FMT but reduces that of the FTT. This shows that inner structures of electromagnetic transducers should be considered in the optimal design parameters and coupling conditions for RW stimulation.

Comparative study of efficiency and characteristics of FMT and DRT installed in human cadavers for round-window stimulation

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.

Effect of ossicular chain deformity on reverse stimulation considering the overflow characteristics of third windows

Stimulating the round window membrane via an active actuator of the middle ear implant, named the reverse stimulation, has become an option to help patients with ossicular chain deformity (OCD) to restore hearing. However, there is still no concise description of how OCD affects reverse stimulation considering the overflow characteristics of third windows. In the present study, an impedance model considering the vestibular and cochlear aqueducts was used to investigate the dynamic response of the cochlea to reverse stimulation under OCD. First, a finite-element (FE) model of the middle ear and the ear canal was used to estimate the changes in reverse middle-ear impedance caused by ossicular chain fixation and ossicular chain interruption. Then, the impedance model was used to predict the reverse transfer function, which characterizes the effect of OCD on the dynamic response of the cochlea. The results show that ossicular chain fixation reduces the reverse stimulation's performance. Moreover, the existence of the third windows complicates the effect of ossicular chain fixation on the reverse stimulation and boosts obviously the reverse stimulation's performance at low frequencies. In contrast, regardless of the existence of third windows, ossicular chain interruption enhances the effect of reverse stimulation.

Design Study of a Round Window Piezoelectric Transducer for Active Middle Ear Implants

This report describes the design of a new piezoelectric transducer for round window (RW)-driven middle ear implants. The transducer consists of a piezoelectric element, gold-coated copper bellows, silicone elastomer (polydimethylsiloxane, PDMS), metal cylinder (tungsten), and titanium housing. The piezoelectric element is fixed to the titanium housing and mechanical resonance is generated by the interaction of the bellows, PDMS, and tungsten cylinder. The dimensions of PDMS and the tungsten cylinder with output characteristics suitable for compensation of sensorineural hearing loss were derived by mechanical vibrational analysis (equivalent mechanical model and finite element analysis (FEA)). Based on the results of FEA, the RW piezoelectric transducer was implemented, and bench tests were performed under no-load conditions to confirm the output characteristics. The transducer generates an average displacement of 219.6 nm in the flat band (0.1–1 kHz); the resonance frequency is 2.3 kHz. To evaluate the output characteristics, the response was compared to that of an earlier transducer. When driven by the same voltage (6 V_p), the flat band displacement averaged 30 nm larger than that of the other transducer, and no anti-resonance was noted. Therefore, we expect that the new transducer can serve as an output device for hearing aids, and that it will improve speech recognition and treat high-frequency sensorineural hearing loss more effectively.

Research on coupling effects of actuator and round window membrane on reverse stimulation of human cochlea

An active actuator of a middle-ear implant coupled to the round window membrane (RWM), which transmits vibration to the cochlea, has been used to compensate for hearing loss in patients. However, various factors affect the coupling condition between the actuator and the RWM, resulting in coupling leakage. In this study, a coupling impedance model of the human ear and the actuator was used to investigate the effect of inefficient coupling during reverse stimulation. First, the three-port circuit network model of the actuator was coupled with the acoustic impedance model of human ear reverse sound transmission. Meanwhile, the inefficient coupling impedance was estimated. Then, the effect of the actuator's coupling on reverse stimulation was studied by comparing the reverse pressure transfer function. Furthermore, the inefficient coupling's influence in the ear with middle-ear disorder was also investigated by simulating two typical forms of middle-ear disorder: otosclerosis and ossicular chain disarticulation. The results show that the change of the inefficient coupling impedance plays a significant role during reverse stimulation. Inefficient coupling of the actuator and the RWM deteriorates the cochlear response of reverse stimulation over the entire frequency range. Additionally, the coupling effect of the actuator does not change the influence tendency of middle-ear disorder on reverse stimulation's performance, but changes the response amplitude of the reverse stimulation.

Implementation of a fully implantable middle-ear hearing device chip

BACKGROUND AND OBJECTIVE

Recently, with the increase in the population of hearing impaired people, various types of hearing aids have been rapidly developed. In particular, a fully implantable middle ear hearing device (F-IMEHD) is developed for people with sensorineural hearing loss. The F-IMEHD system comprises an implantable microphone, a transducer, and a signal processor. The signal processor should have a small size and consume less power for implantation in a human body.

METHODS

In this study, we designed and fabricated a signal-processing chip using the modified FFT algorithm. This algorithm was developed focusing on eliminating time delay and system complexity in the transform process. The designed signal-processing chip comprises a 4-channel WDRC, a fitting memory, a communication 1control part, and a pulse density modulator. Each channel is separated using a 64-point fast Fourier transform (FFT) method and the gain value is matched using the fitting table in the fitting memory.

RESULTS AND CONCLUSION

The chip was designed by Verilog-HDL and the designed HDL codes were verified by Modelsim-PE 10.3 (Mentor graphics, USA). The chip was fabricated using a 0.18 μm CMOS process (SMIC, China). Experiments were performed on a cadaver to verify the performance of the fabricated chip.

Finite element analysis of round-window stimulation of the cochlea in patients with stapedial otosclerosis

An active actuator coupled to the round window (RW) can transmit mechanical vibrations into the cochlea and has become a therapeutic option of hearing rehabilitation for patients with stapedial otosclerosis. A finite-element model of the human ear that includes sound transmission effects of the vestibular and cochlear aqueducts of the inner ear is adopted in this study for investigating the cochlear response to RW stimulation under stapes fixation. There are two effects due to otosclerosis of the stapes: the fixation of the stapedial annular ligament (SAL) and the increase of the stapes mass. The frequency responses of the middle ear and cochlea with normal and otosclerotic stapes are calculated under sound and RW stimulations. The results show that changes in the material property of the stapes have different effects on the cochlear responses under sound and RW stimulations. Because of the vestibuli aqueduct, the reduction in the low-frequency magnitude of the pressure difference across the cochlear partition due to SAL fixation is much smaller under RW stimulation than under sound stimulation. The results of this study help understand sound transmission during RW stimulation in patients with stapedial otosclerosis.

Piezoelectric Actuator with Frequency Characteristics for a Middle-Ear Implant

The design and implementation of a novel piezoelectric-based actuator for an implantable middle-ear hearing aid is described in this paper. The proposed actuator has excellent low-frequency output characteristics, and can generate high output in a specific frequency band by adjusting the mechanical resonance. The actuator consists of a piezoelectric element, a miniature bellows, a cantilever membrane, a metal ring support, a ceramic tip, and titanium housing. The optimal structure of the cantilever-membrane design, which determines the frequency characteristics of the piezoelectric actuator, was derived through finite element analysis. Based on the results, the piezoelectric actuator was implemented, and its performance was verified through a cadaveric experiment. It was confirmed that the proposed actuator provides better performance than currently used actuators, in terms of frequency characteristics.

Feasibility of Round Window Stimulation by a Novel Electromagnetic Microactuator

Introduction

Most implantable hearing aids currently available were developed to compensate the sensorineural hearing loss by driving middle ear structures (e.g., the ossicles). These devices are successfully used in round window (RW) stimulation clinically, although this was initially not the intended use. Here, a novel microactuator, specifically designed for RW stimulation, was tested in human temporal bones to determine actuator performance and applicability.

Methods

Stapes footplate response to RW stimulation was determined experimentally in human temporal bones and the obtained sound pressure output level was estimated.

Results

The actuator had a flat displacement response between 0.125 and 4 kHz, a resonance between 4 and 7 kHz, and a roll-off above. At increasing contact force, the stapes footplate displacement decreased by 5–10 dB re μm for forces ≥ 2 mN. The equivalent sound pressure level between 0.125 and 4 kHz amounted to 87–97 eq dB SPL and increased to 117 eq dB SPL for frequencies of 4–7 kHz. The total harmonic distortion (THD) of the actuator ranged within 15–40% for static forces of 5 mN.

Conclusion

The feasibility of an electromagnetic actuator that may be placed into the RW niche was demonstrated but requires further optimization in terms of THD and static force sensitivity.

Concept and Evaluation of a New Piezoelectric Transducer for an Implantable Middle Ear Hearing Device

Implantable middle ear hearing devices (IMEHDs) have been developed as a new technology to overcome the limitations of conventional hearing aids. The piezoelectric cantilever transducers currently used in the IMEHDs have the advantages of low power consumption and ease of fabrication, but generate less high-frequency output. To address this problem, we proposed and designed a new piezoelectric transducer based on a piezoelectric stack for the IMEHD. This new transducer, attached to the incus body with a coupling rod, stimulates the ossicular chain in response to the expansion-and-contraction of its piezoelectric stack. To test its feasibility for hearing loss compensation, a bench testing of the transducer prototype and a temporal bone experiment were conducted, respectively. Bench testing results showed that the new transducer did have a broad frequency bandwidth. Besides, the transducer was found to have a low total harmonic distortion (<0.75%) in all frequencies, and small release time (1 ms). The temporal bone experiment further proved that the transducer has the capability to produce sufficient vibrations to compensate for severe sensorineural hearing loss, especially at high frequencies. This property benefits the treatment of the most common sloping high-frequency sensorineural hearing loss. To produce a 100 dB SPL equivalent sound pressure at 1 kHz, its power consumption is 0.49 mW, which is low enough for the transducer to be utilized in the IMEHD.