이식형 마이크로폰과 진동체를 갖는 인공중이의 이득 보상을 위한 주파수 특성 고찰
정의성
*
·성기웅**
·임형규*
·이장우*
·김동욱*
·이정현***
·김명남***
·조진호* , ** †
Study on frequency response of implantable microphone and vibrating transducer for the gain compensation of implantable middle ear hearing aid
EuiSung Jung * , KiWoong Seong ** , HyungGyu Lim * , JangWoo Lee * , DongWook Kim * , JyungHyun Lee *** , MyoungNam Kim *** , and JinHo Cho * , ** †
Abstract
ACROSS device, which is composed of an implantable microphone, a signal processor, and a vibrating transducer, is a fully- implantable middle ear hearing device(F-IMEHD) for the recovery of patients with hearing loss. And since a microphone is implanted under skin and tissue at the temporal bones, the amplitude of the sound wave is attenuated by absorption and scattering.
And the vibrating transducer attached to the ossicular chain caused also the different displacement from characteristic of the stapes.
For the gain control of auditory signals, most of implantable hearing devices with the digital audio signal processor still apply to fitting rules of conventional hearing aid without regard to the effect of the implanted microphone and the vibrating transducer.
So it should be taken into account the effect of the implantable microphone and the vibrating transducer to use the conventional audio fitting rule. The aim of this study was to measure gain characteristics caused by the implanted microphone and the vibrating transducer attached to the ossicle chains for the gain compensation of ACROSS device. Differential floating mass transducers (DFMT) of ACROSS device were clipped on four cadaver temporal bones. And after placing the DFMT on them, displacements of the ossicle chain with the DFMT operated by 1 mA peak current was measured using laser Doppler vibrometer. And the sensitivity of microphones under the sampled pig skin and the skin of 3 rat back were measured by stimulus of pure tones in frequency from 0.1 to 8.9 kHz. And we confirmed that the microphone implanted under skin showed poorer frequency response in the acoustic high-frequency band than it in the low- to mid- frequency band, and the resonant frequency of the stapes vibration was changed by attaching the DFMT on the incus, the displacement of the DFMT driven with 1 mA rms was higher by the amount of about 20 dB than that of cadaver's stapes driven by the sound presssure of 94 dB SPL in resonance frequency range.
Key Words : fully-implantable middle ear device(F-IMEHD), differential floating mass transducer(DFMT), implantable microphone
1. 서 론
인간의 귀는 외부 음향신호를 집음하는 외이 , 집음된
음향신호를 기계적 진동으로 변환하는 중이 , 그리고 진 동을 전기적 생체신호로 변환하는 내이로 이루어져 있 다 [1] . 이 중 사람들이 겪고 있는 청각 이상에서 전음성
난청은 음을 전달하는 외이나 중이에 이상이 생겨서 나 타나고 , 감각 신경성 난청은 내이 속의 음을 감지하는 기관이나 청각 중추에 이상이 생겨서 발생한다 . 그리고 혼합성 난청은 이 두 가지가 동시에 이상이 생겨 발생한 경우이다 . 그 중 난청을 겪고 있는 대부분의 경우는 내
이의 이상에 의해 발생하는 감각 신경성 난청자이다 [2] .
난청 인구수는 미국의 경우 전체 인구의 약 16%, 65 세
이상 인구의 30% 가 난청을 겪고 있으나 , 약 1500 만 명
* 경북대학교 대학원 전자전기컴퓨터학부 (Graduate School of Electrical Engineering and Computer Science, Kyungpook National University)
** 경북대학교 첨단감각기능회복장치연구소 (Advanced research center for recovery of human sensibility, Kyungpook National University,)
*** 경북대학교 병원 의공학과 (Dept. of Biomedical Engineering, Kyungpook National University Hospital)
†