Hearing impaired people with noise-induced hearing loss or age-related hearing loss have been increased due to industrialization, urbanization, and the growth of portable multimedia device. In order to compensate their hearing loss, conventional hearing aids which can generate acoustic output genera...
Hearing impaired people with noise-induced hearing loss or age-related hearing loss have been increased due to industrialization, urbanization, and the growth of portable multimedia device. In order to compensate their hearing loss, conventional hearing aids which can generate acoustic output generally have been used. Although the performance of conventional hearing aid was enhanced with advancement of digital technology, hearing impaired people did not satisfy because of several defects such as howling effect, occlusion effect, foreign body sensation, and social discriminations. To overcome these disadvantages, many kinds of implantable hearing devices such as cochlear implant, auditory brainstem implant, bone anchored hearing device, or implantable middle ear hearing device (IMEHD) have been studied for the hearing impaired people. IMEHDs, which can transfer vibrational output to the ossicular chain, have been actively studied because of high sound fidelity and low acoustic feedback. IMEHDs have been usually implemented for oval window drive by means of vibrating the ossicular chain. But, this method may induce ossicular chain’s necrosis or the loading effect of vibrator. In 1995, Spindel et al. proposed the first method for round window drive to solve demerits of oval window drive. Since Colletti et al. presented successful results of clinical test using MED-EL’s floating mass transducer (FMT) in 2005, round window drive has been widely investigated because the loading effect of vibrator cannot be considered. Especially, this method is applicable to hearing impaired people without ossicular chain. Otologics Inc. and MED-EL Inc., which already possess an IMEHD for oval window drive, lead in the development of IMEHD for the round window drive. The fixed type round window driving method proposed by Otologics Inc. contacts round window using a spherical tip which was connected at an end of electromagnetic vibrator. But, the vibrator of Otologics must be implanted at inside wall of temporal bone because of the large sized vibrator. Thus, surgical procedure must be complicated due to long distance between round window and a vibrator. The floating mass type round window driving method suggested by MED-EL Inc. inserts a floating mass transducer which was surrounded by fascia at round window niche. Generally, to study the theory of round window drive, this method has been preferred to the Otologic’s method because of simple implant. However, the FMT may fall out from round window and lead wire may affect the vibrational output of FMT. Besides, the FMT with a permanent magnet may be induced noise due to the external electromagnetic field. As mentioned above, exclusive vibrators for round window drive have not been designed until now. Thus, new structures of round window vibrator are necessary. In this paper, a new type round window vibrator has been proposed to remove defects of the round window vibrators so far. The proposed vibrator can facilitate the surgical approach to round window because the proposed vibrator will be implanted at middle ear cavity on the basis of anatomic information. And differential electromagnetic method using two permanent magnets was introduced to maintain the vibrational characteristics regardless of external electromagnetic field. Because most magnetic flux of two magnet must be crossed with coil to maximize the vibrational force, the electromagnetic vibrator using two magnets and three coils has been finally suggested. The proposed vibrator can be designed by means of electromagnetic analysis and mechanical vibration analysis using finite element method. After experiments that measure vibrational characteristics of the fabricated vibrator using laser Doppler vibrometer, the validity about design procedure of the suggested round window vibrator was confirmed by means of comparison between the measured results and the analytic results. To verify performance of the proposed vibrator as hearing aid, two kinds of experiments were executed. The first is verification using the proposed vibrator and the physical cochlear model similar to human temporal bone’s characteristics. The next is evaluation by means of measuring auditory brainstem response of animal according to sound stimulation or round window stimulation using the proposed vibrator.
Hearing impaired people with noise-induced hearing loss or age-related hearing loss have been increased due to industrialization, urbanization, and the growth of portable multimedia device. In order to compensate their hearing loss, conventional hearing aids which can generate acoustic output generally have been used. Although the performance of conventional hearing aid was enhanced with advancement of digital technology, hearing impaired people did not satisfy because of several defects such as howling effect, occlusion effect, foreign body sensation, and social discriminations. To overcome these disadvantages, many kinds of implantable hearing devices such as cochlear implant, auditory brainstem implant, bone anchored hearing device, or implantable middle ear hearing device (IMEHD) have been studied for the hearing impaired people. IMEHDs, which can transfer vibrational output to the ossicular chain, have been actively studied because of high sound fidelity and low acoustic feedback. IMEHDs have been usually implemented for oval window drive by means of vibrating the ossicular chain. But, this method may induce ossicular chain’s necrosis or the loading effect of vibrator. In 1995, Spindel et al. proposed the first method for round window drive to solve demerits of oval window drive. Since Colletti et al. presented successful results of clinical test using MED-EL’s floating mass transducer (FMT) in 2005, round window drive has been widely investigated because the loading effect of vibrator cannot be considered. Especially, this method is applicable to hearing impaired people without ossicular chain. Otologics Inc. and MED-EL Inc., which already possess an IMEHD for oval window drive, lead in the development of IMEHD for the round window drive. The fixed type round window driving method proposed by Otologics Inc. contacts round window using a spherical tip which was connected at an end of electromagnetic vibrator. But, the vibrator of Otologics must be implanted at inside wall of temporal bone because of the large sized vibrator. Thus, surgical procedure must be complicated due to long distance between round window and a vibrator. The floating mass type round window driving method suggested by MED-EL Inc. inserts a floating mass transducer which was surrounded by fascia at round window niche. Generally, to study the theory of round window drive, this method has been preferred to the Otologic’s method because of simple implant. However, the FMT may fall out from round window and lead wire may affect the vibrational output of FMT. Besides, the FMT with a permanent magnet may be induced noise due to the external electromagnetic field. As mentioned above, exclusive vibrators for round window drive have not been designed until now. Thus, new structures of round window vibrator are necessary. In this paper, a new type round window vibrator has been proposed to remove defects of the round window vibrators so far. The proposed vibrator can facilitate the surgical approach to round window because the proposed vibrator will be implanted at middle ear cavity on the basis of anatomic information. And differential electromagnetic method using two permanent magnets was introduced to maintain the vibrational characteristics regardless of external electromagnetic field. Because most magnetic flux of two magnet must be crossed with coil to maximize the vibrational force, the electromagnetic vibrator using two magnets and three coils has been finally suggested. The proposed vibrator can be designed by means of electromagnetic analysis and mechanical vibration analysis using finite element method. After experiments that measure vibrational characteristics of the fabricated vibrator using laser Doppler vibrometer, the validity about design procedure of the suggested round window vibrator was confirmed by means of comparison between the measured results and the analytic results. To verify performance of the proposed vibrator as hearing aid, two kinds of experiments were executed. The first is verification using the proposed vibrator and the physical cochlear model similar to human temporal bone’s characteristics. The next is evaluation by means of measuring auditory brainstem response of animal according to sound stimulation or round window stimulation using the proposed vibrator.
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