• 한국소음진동공학회논문집
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• 제25권6호
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• pp.391-398
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• 2015

The swing noise of an excavator is reduced in this study. When an excavator is under a swing motion, it produces the annoying noise which is required to be reduced. To identify the characteristics of the swing noise, the signals of noise and vibration from an excavator are measured during the swing motion. From the variation of the driving motor speed, the noise and vibration signals are picked up and plotted in the waterfall plots. From the waterfall plots, we identify the frequency components corresponding to the driving motor frequency, the gear mesh frequency of the planetary gear, and their harmonics. In addition, the natural frequencies and modes of the center frame are extracted by using the experimental modal test. It is found that the swing noise is amplified when the gear mesh frequencies coincide with the natural frequencies of the center frame. To reduce the swing noise, the structural modification is performed to the center frame. Finally, it is observed that the noise is considerably reduced by the structural modification.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.614-619
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• 1997

The hydraulic pressure pulsation has on the effected on the acoustic nosie and control performance of the hydraulic-servo system. The Helmholtz attenuator introduction on the hydraulic line is an efficient device to reduce the hydraulic pulsation. The salient feature of causing hydraulic pulsation and the frequency characteristics of Helmholtz attenuator are studied. The hydraulic filter design parameters such as the locating position, connecting orifice area and accumulator volume are mathematically analyzed. The instrumental works are carried out with the remarkable reduction of the hydraulic pressure pulsation magnitude and the acoustic noise level.

• 한국소음진동공학회논문집
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• 제14권11호
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• pp.1107-1114
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• 2004

Axial fans are widely used for automotive engine cooling device due to their ability to produce high flow rate to keep engine cool. At the same time, the noise generated by these fans causes one of the most serious problems. Especially, engine cooling fan noise in idle condition of a car is noticeable. Therefore. the high efficient and low-noise fan is seriously needed. When a new fan system is designed, system resistance and non-uniform inflow are the key factors to get the high performance and low noise fan system. In this study, aerodynamic and acoustic calculations are carried out on the automotive cooling fan and system. Effects of various design parameters are studied through the free wake analysis and experiments. Better performance and noise characteristic are obtained for the new design fan using the methodology. Furthermore through the modification of the fan system geometry parameters, the fan system produce more flow rate and become less noisy.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.75-78
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• 2014

MLCC is one of the most frequently used component in high-tech device like smart phone. Because of dynamic characteristic of piezoelectric materials which is main ingredient of MLCC, its vibration leads to acoustic noise from pcb. To solve this problem at minimal cost, company has to change only the main noise-generating MLCC to low noise-generating MLCC. To find the main noise source, this study approached to solution from a vibration point of view. From mode shapes of pcb at particular frequencies, two groups can be obtained; MLCCs soldered at where maximum deformation occurs and where anti-phase with respect to the other group appears. When the MLCC belongs to 1st group does not working, amplitude at where maximum deformation occurs decreases compared to when all MLCCs are working. This tendency also appears in noise measurement. This analysis can be put to use in various fields where require noise reduction or noise source identification.

• 한국소음진동공학회논문집
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• 제25권9호
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• pp.593-598
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• 2015

In this paper, the silencer for large caliber gun to reduce the propagation of gun-generated noise was studied. The results of structural analysis and firing test were described. Structural analysis was conducted by using a commercial program, ANSYS, and showed that there was not any structural problem. The sound pressure level was diminished about 10 dB by the silencer adapted in front of the gun and the soundness of the material was verified from the internal pressure measurement. The reduction of weight, improvement of durability and speed-up of actuating device have to be studied later to improve the usability of silencer for large caliber gun.

• The Journal of the Acoustical Society of Korea
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• 제18권2E호
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• pp.45-52
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• 1999

This paper presents the integrated speech enhancement system for hands-free mobile communication. The proposed integrated system incorporates both acoustic echo cancellation and engine noise reduction device to provide signal enhancement of desired speech signal from the echoed plus noisy environments. To implement the system, a delayless subband adaptive structure is used for acoustic echo cancellation operation. The NLMS based adaptive noise canceller then applied to the residual echo removed noisy signal to achieve the selective engine noise attenuation in dominant frequency component. Two sets of computer simulations are conducted to demonstrate the effectiveness of the system; one for the fixed acoustical environment condition, the other for the robustness of the system in which, more realistic situation, the acoustic transmission environment change. Simulation results confirm the system performance of 20-25dB ERLE in acoustic echo cancellation and 9-19 dB engine noise attenuation in dominant frequency component for both cases.

• Current Optics and Photonics
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• 제5권5호
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• pp.506-513
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• 2021

An arrayed diffractive optical element design for the beam-shaping of a multi-array light source is proposed. This is an essential device for recent optical security and face recognition applications. In practice, we devise a DC noise reduction technique featuring high fabrication error tolerance regarding the multi-array light source diffractive optical elements, as a necessary part of the proposed design method. The spherical diverging illumination leads to DC-conjugate noise spreading. The main idea is tested experimentally, and the multi-array light source diffraction pattern is investigated numerically.

• ETRI Journal
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• 제27권6호
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• pp.685-690
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• 2005

DC and RF characteristics of $0.15{\mu}m$ GaAs power metamorphic high electron mobility transistors (MHEMT) have been investigated. The $0.15{\mu}m{\times}100{\mu}m$ MHEMT device shows a drain saturation current of 480 mA/mm, an extrinsic transconductance of 830 mS/mm, and a threshold voltage of -0.65 V. Uniformities of the threshold voltage and the maximum extrinsic transconductance across a 4-inch wafer were 8.3% and 5.1%, respectively. The obtained cut-off frequency and maximum frequency of oscillation are 141 GHz and 243 GHz, respectively. The $8{\times}50{\mu}m$ MHEMT device shows 33.2% power-added efficiency, an 18.1 dB power gain, and a 28.2 mW output power. A very low minimum noise figure of 0.79 dB and an associated gain of 10.56 dB at 26 GHz are obtained for the power MHEMT with an indium content of 53% in the InGaAs channel. This excellent noise characteristic is attributed to the drastic reduction of gate resistance by the T-shaped gate with a wide head and improved device performance. This power MHEMT technology can be used toward 77 GHz band applications.

• 대한의용생체공학회:의공학회지
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• 제43권4호
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• pp.280-289
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• 2022

In this paper, we present a QRS-complex detection algorithm to calculate an accurate heartbeat and clearly recognize irregular rhythm from ECG signals. The conventional Pan-Tompkins algorithm brings false QRS detection in the derivative when QRS and noise signals have similar instant variation. The proposed algorithm uses amplitude differences in 7 adjacent samples to detect QRS-complex which has the highest amplitude variation. The calculated amplitude is cubed to dominate QRS-complex and the moving average method is applied to diminish the noise signal's amplitude. Finally, a decision rule with a threshold value is applied to detect accurate QRS-complex. The calculated signals with Pan-Tompkins and proposed algorithms were compared by signal-to-noise ratio to evaluate the noise reduction degree. QRS-complex detection performance was confirmed by sensitivity and the positive predictive value(PPV). Normal ECG, muscle noise ECG, PVC, and atrial fibrillation signals were achieved which were measured from an ECG simulator. The signal-to-noise ratio difference between Pan-Tompkins and the proposed algorithm were 8.1, 8.5, 9.6, and 4.7, respectively. All ratio of the proposed algorithm is higher than the Pan-Tompkins values. It indicates that the proposed algorithm is more robust to noise than the Pan-Tompkins algorithm. The Pan-Tompkins algorithm and the proposed algorithm showed similar sensitivity and PPV at most waveforms. However, with a noisy atrial fibrillation signal, the PPV for QRS-complex has different values, 42% for the Pan-Tompkins algorithm and 100% for the proposed algorithm. It means that the proposed algorithm has superiority for QRS-complex detection in a noisy environment.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.377-381
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• 2006

본 논문에서는 노즐출구 단면에 설치된 메쉬 스크린을 이용하여 초음속 제트 소음 제어하기 위한 실험을 수행하였다. 메쉬 스크린은 미소 직경을 가진 스테인레스 철사들로 만들어졌으며 철망 형태이다. 노즐 압력비는 과팽창에서 부족팽창된 초음속 제트를 얻기 위해 다양하게 변화시켰다. 초기 제트 전단층을 교란하기 위해, 메쉬 스크린의 중앙 부분에 구멍을 만들었으며 그 구멍크기는 메쉬 스크린의 소음 저감효과를 조사하기 위해 변화시켰다. 유동장을 가시화하기 위해 쉴리렌 광학 장치를 사용하였고 OASPL과 소음 스펙트럼을 얻기 위해 음향을 측정하였다. 본 실험으로부터 얻어진 결과는 메쉬 스크린이 스크리치 톤을 상당히 억제하였으며, 메쉬 스크린의 구멍크기는 초음속 제트 소음을 저감하는 중요한 인자였다. 과팽창된 제트인 경우, 소음 저감효과는 적정팽창과 부족팽창된 제트에서의 저감효과보다 매우 크게 나타났다.