• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.22-28
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• 2001

This paper describes the implementation of a robust speaker position location system using the voice signal received by microphone array. To be robust to the reverberation which is the major factor of the performance degradation, low-frequency phase restoration algorithm which eliminates the influence of reverberations using the low-frequency information of the CPSP function is proposed. The implemented real-time system consists of a general purpose DSP (TMS320C31 of Texas instruments), analog part which contains amplifiers and filters, and digital part which is composed of the external memory and 12-bit A/D converter. In the real conference room environment, the implemented system that was constructed by the proposed algorithms showed better performance than the conventional system. The error of the TDOA estimation reduced more than 15 samples.

• The Journal of the Acoustical Society of Korea
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• v.31 no.4
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• pp.205-213
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• 2012

Active acoustic array signal was measured in the East Sea and the South sea and spatial coherence was analyzed. The measurement of ambient noise, target reflection signal, sea surface backscattering signals took place including environmental measurements of sea wind, and vertical temperature profiles. The spatial coherence of ambient noise was lower than that of target reflection signal in the South Sea. The spatial coherence of target reflection signal was above 0.5 over all array length. The spatial coherence of sea surface backscattering signal was higher in high incident angle. The maximum non-dimensional array length was 3.0 ($26^{\circ}$) and 3.5 ($32^{\circ}$) to have spatial coherence above 0.5 in the East Sea. To find a design criteria for array configuration and array performance, more measurements of temporal and spatial coherence will be needed continuously in the future.

• Journal of radiological science and technology
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• v.26 no.2
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• pp.49-56
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• 2003

The purposes of this study are to improve the ultrasound resolution of various nylon and metallic mono-filament wires, therefore, it was tested that it analyze on nylon mono-filament wire of 0.1 mm in A Co.'s ultrasonic phantom and synthesis of C15 g tissue mimicking materials(TMM), analyze resolution of nylon and metallic mono-filament wires in water and TMM. The results obtained were summarized as follows: 1. Metallic mono-filament wire of 0.1 mm and nylon mono-filament wire of 0.12 mm, 180 denier showed that it cleared dot echo pattern. 2. Metallic and nylon mono-filament wire of 0.2 mm showed that it cleared comet tail echo by reverberation artifact. 3. Nylon and metallic mono-filament wire of 0.1 mm showed that it can used for dead zone and axial resolution test. 4. Nylon mono-filament wire compared with metallic mono-filament wire showed that it satisfy elasticity and construction. 5. Degree of hardness of na not changed mono-filament's echo textures.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.29-38
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• 1989

Detection of an underwater target by acoustic wave raises various difficulties due to unpredictable noise interference which originates from clutter, reverberation, and variations of medium characteristics with time and location. The SNR and the range resolution of conventional SONAR systems using a matched filter are generally poor, since the latter is optimum only in the additive white noise case. Furthermore, it cannot compensate for variations of the detection level which are responsible for the resultant detection errors. In this paper, the unpredictable interferences are compensated for by using an adaptive filter. It recursively estimates the channel impulse response based on the received echo signal. In the low noise environments, the estimated impulse response is close to the true one, providing a good range resolution, and a matched filter is used subsequently for the purpose of detection. It is shown through computer simulation that good performance can be achieved via the two steps of filtering. Also, the detection level remains unchanged without any additional provisions. Finally, we present the characteristics of the employed adaptive filter parameters.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.444-454
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• 2015

Measurements of bottom backscattering strengths in a frequency range of 6-14 kHz were made on the shallow water off the southern Gyeonggi Bay in Yellow Sea in May 2013, as part of the KIOST-HYU joint acoustics experiment. Geological surveys for the experimental area were performed using multi-beam echo sounder, sparker system, and grab sampling to investigate the bottom topography, sub-bottom profile and composition of surficial sediment, respectively. In this paper, the backscattering strengths as a function of grazing angle (in range of $28^{\circ}{\sim}69^{\circ}$) were estimated and compared to the predictions obtained by Lambert's law and APL-UW scattering model. Finally, the effects of geoacoustic parameters corresponding to the experimental area on the backscattering strengths are discussed.

• Journal of electromagnetic engineering and science
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• v.15 no.3
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• pp.151-157
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• 2015

The increasing use of mobile phones has raised public concern about the possible biological effects of radiofrequency electromagnetic field (RF-EMF) exposure on the human brain. To investigate the potential effect of RF-EMF exposure on the brain, we examined the behaviors and hippocampal morphology of C57BL/6 mice after sub-chronic exposure to RF-EMFs with a relatively high SAR level (5.0 W/kg). We applied a 2-hour daily exposure of WCDMA 1,950 MHz using a reverberation chamber that was designed for whole-body exposure for 60 days. In the behavioral tests, RF-EMF did not alter the physical activity or long-term memory of mice. Moreover, no alteration was found in the neuronal and glial cells in the hippocampus by RF-EMFs. In this study, we showed that sub-chronic whole body RF exposure did not produce memory impairment and hippocampal morphological alteration in C57BL/6 mice.

• Journal of electromagnetic engineering and science
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• v.15 no.3
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• pp.173-180
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• 2015

To explore the effects of radiofrequency electromagnetic field on the fate of neuronal cells, we investigated whether exposure to 915 MHz radiofrequency identification (RFID) caused morphological changes in neuronal cells in rat hippocampal dentate gyrus (DG). A reverberation chamber was used as a whole-body RFID exposure system. Rats were assigned to two groups: sham- and RFID-exposed groups. Rats in the RFID-exposed group were exposed to RFID at 4 W/kg specific absorption rate (SAR) for 8 hours daily, 5 days per week, for 2 weeks. Morphological evaluation of DG was performed using immunohistochemistry with doublecortin (DCX) as a neuronal precursor cell marker and neuronal nuclei (NeuN) as a mature neuronal cell marker. No significant morphological changes in DCX+ or NeuN+ cells in the DG of RFID-exposed rats were observed. These results suggest that RFID exposure induces no significant change in DCX+ neuronal precursor or NeuN+ neuronal cells in DG of rats.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.237-245
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• 2012

This paper describes an acoustic echo canceller with double-talk by the blind signal separation. The acoustic echo canceller is deteriorated or diverged in the double-talk period. So we use the blind signal separation to estimate the near-end speech signal and to eliminate the estimated signal from the residual signal. The blind signal separation extracts the near-end signal with dual microphones by the iterative computations using the 2nd order statistical character. Because the mixture model of blind signal separation is multi-channel in the closed reverberation environment, we used the copied coefficients of echo canceller without computing the separation coefficients. By this method, the acoustic echo canceller operates irrespective of double-talking. We verified performances of the proposed acoustic echo canceller by simulations. The results show that the acoustic echo canceller with this algorithm detects the double-talk periods thoroughly, and then operates stably in the normal state without the divergence of coefficients after ending the double-talking. And it shows the ERLE of averagely 20dB higher than the normal LMS algorithm.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.5
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• pp.1-8
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• 2010

In this paper, a sound externalization method is proposed for out-of-the-head localization in a headphone listening environment. In order to reduce timbre distortion by the conventional methods using a measured a head-related transfer function (HRTF) or early reflections, the proposed method integrates a model-based HRTF with reverberation. In addition, for improving frontal externalization performance, techniques such as decorrelation and spectral notch filtering are included. To evaluate the performance of the proposed externalization method, subjective listening tests are conducted by using different types of sound sources such as white noise, sound effects, speech, and music. It is shown from the test results that the proposed externalization method can localize sound sources farther away from out of the head than the conventional method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.426-435
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• 2013

In this paper, we propose the MIMO circular polarization feed network to enhance the communication performances from the previous $2{\times}2$ MIMO channel to $4{\times}4$ channel for Land Mobile Satellite communication system. The only possibility to extend the communication channel is to use the additional satellite because of the limitation of satellite spaces to install additional antennas. For overcoming this problems, we propose the MIMO circular polarization feed network to secure the isolation characteristics without the distant antenna space. The port isolation characteristics and each port impedance matching conditions are numerically verified and we suggest the $4{\times}4$ MIMO channel model of the proposed system and the performances are verified. The fabricated circular polarization patch antennas with the proposed feed network are measured in the reverberation chamber and 7~10 dB of diversity gain and 80 % increasement of channel capacity are obtained.