• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.232-237
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• 2012

Transmission of unwanted vibration to sensitive systems can cause various problems including performance degradation and system malfunction. The most common approach to limit the transmission of harmful vibration disturbances to the sensitive system is adapting passive vibration isolator. The classical passive vibration isolator comprising a viscous damper and spring element in parallel, however, exhibits conflicting performance characteristics in that low amplification at the resonance, which is desirable, can only be achieved at the sacrifice of vibration isolation performance in high frequency region, which is undesirable. In this paper, vibration isolation characteristics of various passive isolator schemes in literature to circumvent this conflict are introduced and compared.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1048-1054
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• 2004

The Passive acoustic control is used in various fields, such as structures, automobiles, aircraft and so on. It is used in variety of acoustic field with the absorbing material, as one of the methods which can control the acoustic in optional space. In that case of passive control using this absorption material, it would be important to maximize the control performance of material property, numbers, geometry shape and the attached location of boundary area of the absorbing material. But realistically these variables, specially material Property, have no broad choice. Therefore, the position of absorbing material is the most important variable. In this study, we use the optimization method to minimize acoustic energy of optional space in the interest frequency attaching some absorbing materials to the boundary area. For analysis and optimization, this study uses the FEA and the conjugate gradient method. This optimization process is very efficient and useful in the passive acoustic control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.176-179
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• 2005

To control the vibration transmitted to the precision instruments from ground has always been of great interest among the researchers. This paper proposes a single axis vibration isolation system which can be used as a module far a table top six axis isolator for highly precise measurement and actuation system. The combined active-passive isolation principle is used for vertical vibration isolation by mounting the instrument on a passively damped isolation system made of Elastomer along with the active stage in series which consists of very stiff piezo actuator. The active stage works in combination with the passive stage for working as a very low frequency vibration attenuator. The active stage is isolated from the payload disturbance through the Passive stage and thus modularity in control is achieved. This made the control algorithm much easier as it does not need to be tuned to specific payload.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.13-20
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• 2001

The active noise cancellation system offers a better low frequency performance with a smaller and lighter system compared to a passive one. This paper presents an active noise control system capable of reducing the noise in a helmet after attenuating the external noise using the helmet as the passive noise reduction system, which consists of a controller for inverting and compensating the phase delay, a microphone for picking up the external noise, and a loudspeaker for radiating the acoustic anti-phase signal to reduce the external noise. In this paper, external noise can be reduced by noise controller by compensating the phase difference to be 180°in the frequency of maximun value in the amplitude response. The noise of the phase delay covered from 50°to 310°was reduced in this system and it is possible to obtain a noise reduction of up to approximately 20 dB at the ears in the enclosure.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.1069-1076
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• 2012

We use largely two methods, how to control the noise of the KTX, they are the passive noise control method and the active noise control method. The passive noise control has been used in a variety of ways since the KTX opening day, but lately it has shown the technical limitations by being dropped sharply. So, it is getting important to conduct the research about ANC that is able to reduce the ambient noise when the environmental-factor changes and be installed easily. To reduce a three-dimensional closed-space sound field like a car of a high-speed rail is hard to do using single channel ANC control system. Therefore we have to model the paths of the noise exactly for reducing the noise. And the control speakers and the error mics should be designed for optimal position. In this paper, we designed the transfer functions for modeling the noise paths under the influence of the distance between control speakers & error mics and primary noise speaker in TEST-BED where there is modeled as actual interior of KTX. We have made the modeling and the simulations of interior environment of KTX car by using three frequency bands of 120Hz, 280Hz, 360Hz. After the modeling, we compared the performance of active noise control and also we analyzed what to affect with difference in distance. After comparing of the performance using Pure Tone 120Hz, 280Hz, 360Hz at each modeling and then we simulated ANC for KTX's interior noise which we measured really and analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.510-518
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• 2008

This paper presents recent development of (semi)-active steering bogies for railway vehicles and introduce the state-of-art of related technologies. Steering bogies have been studied in various researchers since they can offer high ride quality for passengers and reduce the maintenance costs of wheel and rail wear. Especially, they are considered to be a fundamental solution to dramatically reduce the squeal noise on tight curves. However, passive steering bogies such as self-steering bogies and forced steering bogies have shown their limits to cope with the various running conditions. Therefore, (Semi)-active steering bogies have been studied to overcome the drawbacks of the passive steering bogies. As a result, an active steering bogie, so called mechatronic bogie, is developed successfully in Europe and it has shown remarkable performance in test line.

• Journal of KIISE:Information Networking
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• v.37 no.1
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• pp.27-34
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• 2010

In this paper, we examine a long-range dependence in an active measurement of a network traffic which has been a well known characteristic from analyses of a passive network traffic measurement. To this end, we utilize RTT(Round Trip Time), which is a typical active measurement measured by PingER project, and perform a relevant analysis to a time series of both RTT and its volatilities. The RTT time series exhibits a long-range dependence or a 1/f noise. The volatilities, defined as a higher-order variation, follow a log-normal distribution. Furthermore, volatilities show a long-range dependence in relatively short time intervals, and a long-range dependence and/or 1/f noise in long time intervals. From this study, we find that the long-range dependence is a characteristic of not only a passive traffic measurement but also an active measurement of network traffic such as RTT. From these findings, we can infer that the long-range dependence is a characteristic of network traffic independent of a type of measurements. In particular, an active measurement exhibits a 1/f noise which cannot be usually found in a passive measurement.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.392-399
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• 2014

The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.98-103
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• 1986

The passive acoustic system only has generally used in fish detection. But the passive acoustic system has not been tried in fishing since Freytag has proposed a possibilities of the passive detection of fishes in 1963. This paper describes the .feasible aspects of fish detection by listening of the sound they make. The passive acoustic system accompanied the active acoustic system may expand the range of detection and compensate for lack of capabilities each other, but there are some difficulties in noise rejection because the fre9uency range of ship noises covers the whole range vf biological sounds. The attempt to collect useful informations from underwater would be greatly contributed in fisheries.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2006.02a
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• pp.1-14
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• 2006

[ $\blacklozenge$ ] PCB에 있어서 Embedded passive 는chip을 직접 내장하는 방법과 특별한 특성을 갖는 재료 및 공법을 사용하여 chip 응 대치하는 방법이 있다. $\blacklozenge$ Embedded passive PCB가 적용될 수 있는 유력한 적용 분야는 소형화가가 요구되는 분야와 고속 특성이 요구되는 분야를 들 수 있고, 따라서, Module, SOP/SIP, Package substrate 등이 우선적으로 적용될 수 있는 분야다. $\blacklozenge$ Embedded capacitor를 적용한 경우, 일반적인 chip capacitor를 적용한 경우보다 더 좋은 전기적인 특성(SRF, Q)을 얻을 수 있으며, solder joint 등의 영향을 포함하면 더욱 좋은 특성이 얻어질 수 있다. $\blacklozenge$ Embedded passive 의 상용화를 위해서, 공차를 관리하는 방법의 개발과 공차에 대한 합리적인 규격을 설정하는 것이 우선 과제이다. $\blacklozenge$ Embedded resistor 의 경우, Laser trim을 적용하여 ${\pm}\;5\%$ 또는 그 이하의 공차를 실현할 수 있고, $30\;K\Omega/sq$. 의 고저항의 적용까지 가능하다. $\blacklozenge$ 고속 신호에서의 noise 감소, module, SIP/SOP 의 소형화를 실현하는데 Embedded passive(혹은 active)PCB 가 기여 할 수 있을 것이고, 이를 위하여 Set 업체, PCB 업체, 재료 업체간의 지속적인 협조가 필요할 것이다.