Hyung Gyu Lim

Implantable microphone with acoustic tube for fully implantable hearing devices

Fully Implantable hearing devices consist of a microphone that is implanted under the human skin. However after the implantation, the gain characteristics of the microphone are attenuated at the high frequencies because of the sound filtering effect of the skin and tissue. To solve this problems, we proposed an implantable microphone with an acoustic tube, which generates a resonance effect between the diaphragm and the acoustic transducer inside a case. By performing several experiments in water, it has been confirmed that the frequency response of the implantable microphone at high frequencies can be improved by use of the acoustic tube.

Measurement of stapes vibration in Human temporal bones by round window stimulation using a 3-coil transducer

Round window placement of a 3-coil transducer offers a new approach for coupling an implantable hearing aid to the inner ear. The transducer exhibits high performance at low-frequencies. One remarkable feature of the 3-coil transducer is that it minimizes leakage flux. Thus, the transducer, which consists of two permanent magnets and three coils, can enhance vibrational displacement. In human temporal bones, stapes vibration was observed by laser Doppler vibrometer in response to round window stimulation using the 3-coil transducer. Coupling between the 3-coil transducer and the round window was connected by a wire-rod. The stimulation created stapes velocity when the round window stimulated. Performance evaluation was conducted by measuring stapes velocity. To verify the performance of the 3-coil transducer, stapes velocity for round window and tympanic membrane stimulation were compared, respectively. Stapes velocity by round window stimulation using the 3-coil transducer was approximately 14 dB higher than that achieved by tympanic membrane stimulation. The study shows that 3-coil transducer is suitable for implantable hearing aids.

The Design of Temporal Bone Type Implantable Microphone for Reduction of the Vibrational Noise due to Masticatory Movement

Abstract A microphone for fully implantable hearing device was generally implanted under the skin of the temporal bone. So, the implantedmicrophone’s characteristics can be affected by the accompanying noise due to masticatory movement. In this paper, the implantablemicrophone with 2-channels structure was designed for reduction of the generated noise signal by masticatory movement. And anexperimental model for generation of the noise by masticatory movement was developed with considering the characteristics of humantemporal bone and skin. Using the model, the speech signal by a speaker and the artificial noise by a vibrator were suppliedsimultaneously into the experimental model, the electrical signals were measured at the proposed microphone. The collected signals wereprocessed using a general adaptive filter with least mean square(LMS) algorithm. To confirm performance of the proposed methods, thecorrelation coefficient and the signal to noise ratio(SNR) before and after the signal processing were calculated. Finally, the results werecompared each other.

A Physical Cochlear Model for Transducer Performance Evaluation of Implantable Hearing Aid with Round Window Driver

Recently, various hearing aids are developed to overcome hearing loss. There are available hearing aids, such as air conduction hearing aid, implantable middle ear hearing aid and so on. But air conduction hearing aid is inconvenience caused by howling, and ossicle chain driving type implantable middle ear hearing aid has some week point due to problem of possible nercobiosis of coupling spot along incus long process. In recent years, in order to improve these shortcomings round window (RW) driving hearing aid has been paying attention. In this paper, the physical cochlear model is proposed for a performance evaluation of the RW driving hearing aids of a transducer. In order to verify an experiment proposed on a performance of physical cochlear model, the transducer which has ossicles characteristics is used. By measuring and comparing the frequency characteristics of transducer with ossicles and human temporal bone, performance of physical cochlear model was verified. As from the result of experiment, it is expected that an implemented cochlear model is useful for evaluating characteristics of RW transducer.

Membrane design of vibration transducer to drive round window to increase vibration displacement

Many kinds of hearing aids have been developed to overcome hearing loss. Each hearing aid has their own method to improve hearing threshold level of the patient. In case of vibration transducer to drive round window, a part of implantable hearing aid, uses the vibration displacement to compensate the hearing level. However, the vibration displacement is limited by membrane size made of metal, when it has been fixed dimensions. In this paper, several form of vibration transducer membrane to drive round window to increase vibration displacement has been proposed. It is calculated using finite element analysis. It is confirmed the vibration displacement can be higher in limited size.

Development of Fitting Program for Fully Implantable Middle Ear Hearing Device

A fully implantable middle ear hearing device (F-IMEHD) has been investigated in Korea. Generally, F-IMEHD is implanted under the skin at human temporal bone and it uses implantable microphone and vibrating transducer. Therefore, F-IMEHD must require a different fitting process from conventional hearing aids. In this paper, a fitting program for the F-IMEHD has been developed using Lab VIEW. We calculate proper fitting parameters based on FIG6 fitting rule. And also, it takes account of frequency characteristics of F-IMEHD’s components. Through experimental results, it can be confirmed that the proposed fitting program is suitable to F-IMEHD.

Body temperature predicting Patch-Type telemedicine system

The aim of this study was implementation of a wireless patch system that can predict a patients body temperature. The proposed patch can predict the body temperature from the skin temperature and sweat rate by using a modified Pennes bio-heat transfer equation. The proposed patch was small and lights enough to be attached to the patients skin, and a small skin temperature transducer was built-in the patch. Further, the sweat rate was measured by using humidity sensors while the sweat was evaporating. The proposed patch was compared with commercial body temperature measuring device, and the results were found to be correlated.

Verification of Vibration Characteristic of Hermetically Sealed Differential Floating Mass Transducer for Implantable Middle Ear Hearing Device Using Mock-Up of Ear

Several types of implantable middle ear hearing devices (IMEHDs) have been developed to overcome disadvantages of the conventional hearing aids. IMEHDs are divided into three parts which are a microphone, a signal processing unit, and a vibration transducer. In particular, the vibration transducer is very important component because it directly generates the mechanical vibration in the ossicles so that the input sound can be delivered to the inner ear. As one of the vibration transducer for IMEHDs, a differential floating mass transducer (DFMT) has been developed in Korea. However, the study for the DFMT has focused on the improvement in vibration efficiency until now. In this paper, the hermetically sealed DFMT for implantation is implemented and its vibration characteristic is measured. Then, the vibration characteristic of the DFMT is also compared with that of the stapes displacement defined by ASTM. Through the comparison, it is verified that the implemented DFMT has proper vibration displacement.