Eui-Sung Jung

Study on frequency response of implantable microphone and vibrating transducer for the gain compensation of implantable middle ear hearing aid

ACROSS device, which is composed of an implantable microphone, a signal processor, and a vibrating transducer, is a fullyimplantable 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 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 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.

In vivo evaluation of mastication noise reduction for dual channel implantable microphone.

Input for fully implantable hearing devices (FIHDs) is provided by an implantable microphone under the skin of the temporal bone. However, the implanted microphone can be affected when the FIHDs user chews. In this paper, a dual implantable microphone was designed that can filter out the noise from mastication. For the in vivo experiment, a fabricated microphone was implanted in a rabbit. Pure-tone sounds of 1 kHz through a standard speaker were applied to the rabbit, which was given food simultaneously. To evaluate noise reduction, the measured signals were processed using a MATLAB program based adaptive filter. To verify the proposed method, the correlation coefficients and signal to-noise ratio before and after signal processing were calculated. By comparing the results, signal-to-noise ratio and correlation coefficients are enhanced by 6.07dB and 0.529 respectively.

Intelligent Pillow Type Wireless Charger for Fully Implantable Middle Ear Hearing Device with a Function of Electromagnetic Emission Reduction

Recently, implantable middle ear hearing devices have been developed as full implant by several countries for hearing impaired people. These devices will be surgically implanted in human temporal bone, a rechargeable battery is employed for long-term implant. To charge the battery, a pillow type wireless charger using electromagnetic coupling has been developed in South Korea. In the previous device, several primary coils are used, which can surround head considering heads movement in sleep. However, this device should unnecessarily consume power to drive the uncoupled primary coil. Especially, users must expose themselves to electromagnetic field generated from all primary coils during the charge process. In order to solve these problems, an intelligent pillow type wireless charger, which can recognize the implanted coilpsilas position using hall effect sensors and which can drive the only primary coil among primary coils array, has been proposed to reduce potential risks from the electromagnetic field emission.

A method for reducing body exposure to electromagnetic field of pillow type wireless charger in fully implantable middle ear hearing device

Implantable middle ear hearing devices (IMEHDs) have been developed at several countries. Some devices can be selected rechargeable battery for long-term implant. In South Korea, a kind of IMEHD with rechargeable battery and a pillow type wireless charger have been developed. The charger includes several coils surrounding users head in sleep. However, this device should excessively consume power due to driving all primary coils. Especially, needless exposure to magnetic field generated from uncoupled primary coils may induce bio-hazards. Therefore, a method reducing the body exposure to electromagnetic field was proposed as decreasing the emitted total magnetic flux during charge process.

Vibration characteristic analysis of differential floating mass transducer using electrical model for fully-implantable middle ear hearing devices

A differential floating mass transducer has been developed in Korea for fully implantable middle ear hearing devices (F-IMEHDs). In particular, the performance of a differential floating mass transducer (DFMT) is very important among the parts of the F-IMEHDs because the mechanical vibration generated by DFMT is delivered to the inner ear directly. In this paper, the electrical model is proposed to analyze the DFMT vibration characteristic using the mechanical model of the DFMT. The electrical model enables the simple analysis of DFMT vibration characteristics using a computer program. The proposed electrical model is simulated through PSpice as changing the values of passive elements in the electrical model. To verify the proposed model, the DFMT has been implemented on the basis of the simulated results and the experiment for vibration measurement has been carried out. Through the comparison, it is verified that the proposed model is useful to analyze the vibration characteristics of the DFMT.

Measurement of transmitted vibration to stapes and tympanic membrane by DFMT`s vibration in implantable middle ear hearing devices

The implantable middle ear hearing devices(IMEHDs) have been developed to overcome the conventional hearing aid`s problem(ringing effect caused by the acoustic feedback, cosmetic problem, etc.). In the IMEHDs, the vibrating transducer is a key component because its vibration enables to hear for hearing impaired people. The vibrating transducer is implanted on ossicular chain by surgical operation. The coupling status between implanted transducer and ossicular chain has an effect on delivering vibrating force from transducer to stapes. Noninvasive method is required to investigate the output characteristics of IMEHDs after implementation. Recently, emitted sound pressure measuring method of tympanic membrane is proposed to investigate the output characteristics of IMEHDs. However, the relationship between displacement of stapes and sound pressure by tympanic membrane was not cleared. In this paper, displacement of stapes and sound pressure by tympanic membrane were measured using the differential floating mass transducer(DFMT) that implanted on the ossicular chain of the human temporal bone and physical ear model. Through the experiments results, the relationship between displacement of stapes and sound pressure by tympanic membrane was investigated.

Fitting System Based on Base-Etation and Fitting Software for Fully Implantable Middle Hearing Device

We announced that fully implantable middle ear hearing device (F-IMEHD) has been researched in several papers. The F-IMEHD requires proper fitting process reflected properties of each device like other hearing aids. The F-IMEHD uses vibration transducer attached on ossicles for a sound transmission to humans inner ear. The F-IMEHD is implanted under the skin. Therefore, the fitting process for F-IMEHD has to consider properties of the microphone and transducer. In this paper, fitting system which consist of basestation and fitting software, have been designed and implemented for fitting and control of F-IMEHD. We calculate proper parameters according to hearing threshold level of each patient using the fitting software, and the parameters are transmitted to implanted system from the base-station. The base-station has all control function for F-IMEHD using a wireless communication. Moreover the base-station is a relay station which fitting parameters send to implanted system from fitting software on a PC.