• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.389-394
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• 2006

Mid-Frequency bistatic reverberation level is modeled using ray theoretic algorithms. The algorithm assumes multiple forward/backward scatter along with reciprocity in the Propagation paths. The environments modeled are assumed to be range independent in bathymetry, bottom scattering and surface scattering. Mid-Frequency bistatic scattering algorithm is used as a scattering model. A comparison of predicted reverberation versus time with measured data is presented to verify the bistatic reverberation model. The result demonstrates that it is possible to obtain reasonable reverberation Predictions in experimental site.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.679-685
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• 2002

Low-frequency mono-static reverberation model for shallow-water environment is presented. It is necessary to develop the transmission loss model to calculate the sub-bottom interaction because the ray-based transmission loss model is difficult to compute the pressure accurately which penetrates the bottom medium. In this paper reverberation level is calculated using the RAM (Range dependent Acoustic Model) to augment the multi-path expansion model because it does not estimate transmission loss accurately in shallow water. The signals generated by the L-HYREV and the GSM are compared with the observed signals and it is showed that the L-HYREV model provides a closer fit to the observed signals than those obtained using the GSM.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.216-225
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• 2020

In this paper, broadband underwater propagation channel modeling based on eigenray analysis is discussed. Underwater channels are often formulated in frequency domain time-harmonic signals, which are impractical for simulating broadband signals in time domain. In this regard, time domain modeling of the underwater propagation channel is required for the simulation of broadband signals, for which the eigenray analysis based on ray tracing, resulting in multipath propagation delays in time-domain, is used in this paper. For discrete time system application, the phase, frequency-dependent loss and non-integer sample delays for each eigenray, are approximated by the finite impulse response of the broadband propagation channel.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.16-24
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• 2011

The sound speed of seawater can be calculated by the empirical formula as a function of temperature, salinity and pressure. It is little affected by salinity because the average salinity is 34 psu and varies within a few psu seasonally and spatially in the ocean. Recently, low-salinity water of 24 psu flows into the western sea area of Jeju Island due to the flood of the Yangtze River in China during summer, affecting sound speed profile. In this paper, it was analyzed how environmental changes affected to the underwater communication - the sound speed of low-salinity water was calculated, and the communication channel was estimated by the simulated acoustic rays while the transmitting and receiving depth and the range were varied with and without the low-salinity layer. And The BER (Bit error rate) was calculated by BPSK(Binary phase shift key) modulation and the effects of the low-salinity water on the BER was investigated. The sound speed profile was changed to have positive slope by the low-salinity layer at the sub-surface up to 20 m of depth, forming acoustic wave propagation channel at the sub-surface resulting in the decrease of most of the BER Consequently, this paper suggests that it is important to consider changes of the ocean environment for correctly analyzing the underwater communication and the detection capability.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3
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• pp.154-162
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• 2008

Signals in an underwater channel get distorted by multipath propagation. In this paper, pre-coding method is suggested which helps comprehending the signals with minimum equalization. The signals are transformed based on the knowledge of the impulse response of the channel. Proposed pre-coding method is tested by simulations based on the ray theory and through water tank experiments. In weak multipath environment, in case of an SNR of about 20 dB, BER is $10^{-3}{\sim}10^{-4}$, while in strong multipath environment, similar BER is achieved with SNR of about 30 dB. In order for the pre-coding method to be used for underwater vehicles, channel prediction method utilizing the waveguide invariant is suggested and tested.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.3
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• pp.167-175
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• 2018

Despite the rapid development of IT technology, people with visual impairments still use simple forms of walking sticks and need more advanced walking aids. Smart Cane, which is developed based on Internet service and sensor, can provide high safety and convenience compared to existing sticks for visually impaired people by conveying peripheral information and walking situation to these visually impaired people through voice and vibration. In this paper, we propose and implement SmartKane to overcome lack of miniaturization, user friendly form, and sensing sensitivity, which have been pointed out as a problem of existing SmartKane.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2E
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• pp.83-91
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• 1994

Three components contribute to the acoustic field propagating in a wedge or over a ridge : a direct path arrival, an image component due to reflection from the boundaries and a component diffracted by the apex. All three contributions are included in a new, exact solution of the Helmholtz equation for the three-dimensional time harmonic field from a point source in a wedge(or over a ridge) formed by two intersecting, pressure-release plane boundaries. The solution is obtained by applying three integral transforms, and consists of and infinite sum of uncoupled normal nodes. The mode coefficients are given by a finite integral involving a Gegenbauer polynomial in the integrand, which may be computed relatively efficiently. Results of the theory for propagation over a 90 degree ridge is discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.297-297
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• 2010

이 논문에서는 음향 임피던스를 제어하는 능동형 소음 제어 방법을 연구하였다. 음향 임피던스 제어는 기존의 적응 제어 알고리즘 대신 임피던스의 크기 및 위상 최적화를 통하여 닫힌 관의 끝단에 음파의 반사를 최소화 하는 임피던스를 계산하고 제어함으로써 소음을 저감시킨다. 그리고 음향 임피던스 제어 방법을 끝단이 개방되어 있고, 중앙에 스피커가 있는 관에 적용시킨다. 이 경우에는 개방된 음장에서 음향 전달이 최소화하기 위한 임피던스를 계산하고, 음향 임피던스 제어를 통한 소음 저감을 확인한다. 이를 위해 스피커, 마이크로폰, 진동측정용 레이저 바이브로미터, 그리고 능동 소음 제어 하드웨어로 구성된 시스템을 구축하고 검증하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.245-248
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• 2000

해양음향 토모그래피 수행을 위해 필수적인 Forward 모의 알고리즘을 연구를 통해 Forward 문제에서의 선결문제(음파 전달경로의 안정성, 식별능력 및 분해능)를 고잘하였다. 이를 위해 동해의 기존 관측 자료를 이용하여 평균해양에 대한 음속구조 및 EOF 분석을 수행, 재현된 음속구조를 이용, 음선 모델에 의한 고유음선 정보를 파악하여 고유음선의 도달경로 및 도달시간의 비교를 시도하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.199-202
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• 2004

해양에서 연구목적으로 저주파 음원으로 사용하고 있는 폭발성 음원(SUS: Signals, Underwater Sound)의 신호특성을 파악하기 위해 1999년 9월에 동해의 대륙사면에서 1마일에서 80 마일까지 약 1에서 5마일의 정해진 간격으로 SUS를 투하하여 발생된 음향신호를 거리 및 수신수심별로 수신하였다. 주파수 필터를 사용하여 분석한 결과, 1 kHz이상의 고주파수 성분이 폭발시에 먼저 방출되며 저주파수 신호는 뒤이어 발생됨을 확인하였다. 이것은 폭약이 폭발시에 일어나는 메카니즘과 관련이 있는 것으로 사료된다. 거리의 증가에 따라 잔향의 영향을 받아 뒤이어 수신되는 파속(wave packet)들을 확인할 수 있었으며, 신호에 많은 영향을 주고 있었으나 잔향 분석은 여기서는 제외하였다. 본 연구는 실해역에서의 SUS신호에 관한 많은 자료를 분석한 것으로서 그 신호특성에 관한 이번 고찰은 해양음파전달시 사용하는 SUS 음향신호 해석에 많은 도움을 줄 것으로 기대한다.