Ki Woong Seong

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.

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.

Wireless charing pillow for a fully implantable hearing aid: Design of a circular array coil based on finite element analysis for reducing magnetic weak zones.

Many types of fully implantable hearing aids have been developed. Most of these devices are implanted behind the ear. To maintain the implanted device for a long period of time, a rechargeable battery and wireless power transmission are used. Because inductive coupling is the most renowned method for wireless power transmission, many types of fully implantable hearing aids are transcutaneously powered using inductively coupled coils. Some patients with an implantable hearing aid require a method for conveniently charging their hearing aid while they are resting or sleeping. To address this need, a wireless charging pillow has been developed that employs a circular array coil as one of its primary parts. In this device, all primary coils are simultaneously driven to maintain an effective charging area regardless of head motion. In this case, however, there may be a magnetic weak zone that cannot be charged at the specific secondary coils location on the array coil. In this study, assuming that a maximum charging distance is 4 cm, a circular array coil-serving as a primary part of the charging pillow-was designed using finite element analysis. Based on experimental results, the proposed device can charge an implantable hearing aid without a magnetic weak zone within 4 cm of the perpendicular distance between the primary and secondary coils.

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.

Speech quality evaluation of subcutaneously implanted microphone using in vivo experiment

The microphone in a fully implantable hearing device (FIHD) is generally implanted under the skin covering the temporal bone. However, the implanted microphone can be affected by the skin, which causes both sound attenuation and distortion, particularly at high frequencies. As the degree of attenuation and distortion through the skin is severe, speech quality evaluation parameters are needed for the received signal when designing an implantable microphone. However, the performance of most implantable microphones is only assessed based on the sensitivity and frequency response. Thus, practical indicators based on human auditory characteristics are needed for an objective evaluation of the performance of implantable microphones. In this study, a subcutaneously implantable microphone was designed, and its frequency response investigated using an in vivo experiment. Plus, to evaluate the objective indicators, the speech quality of the signals measured by the implanted microphone was calculated using a MATLAB program, and the indicators compared before and after implantation.

Mastication noise reduction method for fully implantable hearing aid using piezo-electric sensor

BACKGROUND Fully implantable hearing devices (FIHDs) can be affected by generated biomechanical noise such as mastication noise. OBJECTIVE To reduce the mastication noise using a piezo-electric sensor, the mastication noise is measured with the piezo-electric sensor, and noise reduction is practiced by the energy difference. METHODS For the experiment on mastication noise, a skull model was designed using artificial skull model and a piezo-electric sensor that can measure the vibration signals better than other sensors. A 1 kHz pure-tone sound through a standard speaker was applied to the model while the lower jawbone of the model was moved in a masticatory fashion. RESULTS The correlation coefficients and signal-to-noise ratio (SNR) before and after application of the proposed method were compared. It was found that the signal-to-noise ratio and correlation coefficients increased by 4.48 dB and 0.45, respectively. CONCLUSION The mastication noise is measured by piezo-electric sensor as the mastication noise that occurred during vibration. In addition, the noise was reduced by using the proposed method in conjunction with MATLAB. In order to confirm the performance of the proposed method, the correlation coefficients and signal-to-noise ratio before and after signal processing were calculated. In the future, an implantable microphone for real-time processing will be developed.

3-POLES MAGNETIC COUPLER FOR INDUCTIVE LINK OF TRANSCUTANEOUS IMPLANTABLE DEVICE IN MR IMAGING

The number of patients who are implanted electronic medical devices has been rapidly increasing in recent years. However, for the patients of implanted electronic medical devices, scanning in the MRI bore has dangerous matter since the implantable electronic medical devices containing internal magnet would produce inevitable risk factors, such as, strong pulling force and torque generation, by strong base magnetic field. In this paper, an improved fixation magnet method which is applicable implantable medical device for MRI scanning of patient is proposed. This method can reduce risk factors during MRI scanning process by canceling the generated magnetic force of each permanent magnet in transcutaneous signal and power transmission coil of the implantable device. To effectively cancel out the generated magnetic force between implanted magnet and base magnetic field of MRI, the 3-poles magnet method is introduced. Using the proposed 3-poles magnet, in-vitro tests were performed in the 1.5 T MRI. As the result, risk factors were markedly diminished. So, if patients using implantable electronic medical devices including 3-poles magnet undergo a MRI scan, the possibility of magnet protrusion from implanted device can be avoided.

Proposition of a New Implantable Acoustic Sensor Based on Technology Evaluation of Fully Implantable Hearing Aids

Key components of implantable hearing aids are consist of an acoustic sensor that collect external sound by suppressing the body noise, a signal processor module for compensation algorithm of hearing loss, and a output transducer which has tiny size but have high efficiency, respectively. In the partial implantable hearing aids, technologies of transducer and signal processor are so matured that can be applied not too much difficulty. However, due to the difficulties in implantable acoustic sensor technology, such as minimization of masticatory sound and damage of sensor’s membrane from external impact, practical use of fully implantable hearing aids have not successful so far. In this paper, we have proposed a novel implantable acoustic sensor which has trans-tympanic structure, and is verified that the proposed method can be very useful for fully implantable hearing aids by cadaveric experiments.

Development of visible and NIR imaging equipment for small animals with smart pad.

The portable visible and near-infrared (NIR) imaging equipment for a pre-clinical test with small animals was designed and developed in this paper. The developed equipment is composed of a CCD camera, a focusing lens, an objective lens, a NIR band pass filter and a NIR filter driving motor. An NIR ray is mainly used for imaging equipment because it has high light penetration depth in biological tissue. Therefore, NIR fluorescent agents are available for chemical conjugation to targeting molecules in vivo. This equipment can provide a visible image, NIR image and merged image simultaneously. A communication system was specifically established to check obtained images through a smart pad in real time. It is less dependent on space and time than the conventional system.