• 대한기계학회논문집B
• /
• 제27권10호
• /
• pp.1472-1479
• /
• 2003

An attempt to reduce supersonic jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10 mm. Two micro-nozzles with an inside diameter of 1 mm each are installed on the exit plane at an angle of 45 relative to the main jet axis. Far-field noise was measured at 40 diameters off the jet axis. The angle between a microphone and the jet axis is 30 or 90$^{\circ}$. For an injection rate of 4-6% of the main jet, screech tones were completely suppressed by the microjets. The reduction in the overall sound pressure levels were 2.4 and 2.7 dB for 90 and 30 measuring directions, respectively. However, the enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or deformed large scale vortical structures by the microjets.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1499-1504
• /
• 2004

The effects of absorbing materials on the characteristics of supersonic jet noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. In order to investigate the effect of absorbing materials, baffle plates of different materials (metal, grass wool and polyurethane foam) were installed at the exit of the nozzle. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained show that the screech tone amplitude and the overall sound pressure level reduce by using the baffle plates of absorbing materials, compared with the metal baffle plate. It is also found that the characteristics of supersonic jet noise are strongly dependent on the size of baffle plate.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.747-750
• /
• 2002

An attempt to reduce supersonic Jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10mm. Two micro-nozzles with an inside diameter of 1mm each are installed on the exit plane with an off-axis angle of $45^{\circ}$. Far-field noise was measured at a location 40 diameters off the jet axis. The angles between a microphone and the jet axis are $45^{\circ}\;and\;90^{\circ}$. For an injection rate less than $1{\%}$ of the main jet, screech tones were completely suppressed by the microjets. The reduction in the ovelall sound pressure levels were $2.4\;and\;2.7\;dB\;for\;90^{\circ}\;and\;45^{\circ}$ directions, respectively. The enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or broken large scale vortical structures by the microjets.

• Journal of the Optical Society of Korea
• /
• 제5권3호
• /
• pp.93-98
• /
• 2001

In order to verify the performance of the two-stage iterative Fourier transform algorithm[Hankook Kwanghak Hoeji 11, 47 (2000)], a number of phase-only diffractive pattern elements which produce simple 16x16-pixel intensity patterns useful in the field of optical information processing have been designed and their performance has been compared with that from the nonlinear least-squares algorithm[Appl. Opt. 36, 7297(1977)] which is computationally intensive. for all intensity patterns, elements designed by the former algorithm show better overall signal-to noise ratio and uniformity, although they show essentially the same diffraction efficiency. In the case of continuous phase elements, they show far superior uniformity. Computationally,. the former algorithm is far more efficient than the latter.

• 소음진동
• /
• 제7권2호
• /
• pp.215-222
• /
• 1997

The flow and acoustic fields due to a vortex ring interaction with a rigid sphere are simulated numerically. The flow field is regarded as three-dimensional inviscid and incompressible. The vorticity is assumed to be concentrated inside the finite core of vortex filament. The vortex filament curve, described by parabolic blending curve function, is used to effectively solve the modified Biot-Savart equation. The interaction between a vortex ring and a rigid sphere using the parabolic blending curve is calculated. The trajectory of the vortex ring is obtained with several different initial positions between the ring and the sphere. The force variations acting on the sphere are calculated by using the boundary integral method. Finally, we can also obtain the acoustic signals at the far field observation positions from the force variations acting on the rigid surface. We can find that the dipole axis of the directivity patterns are rotated during the interacting phenomena.

• 한국음향학회지
• /
• 제2권1호
• /
• pp.35-40
• /
• 1983

수심 65m의 godutr에서 해면으로부터 10m 깊이에 수평 청음기 배열을 설치하여 수중소음의 상 관관계를 측정하였다. 분석은 FFT 방식을 이용하여 63Hz에서 315Hz 까지의 저주파 영역에서 True 상 관계수를 직접 얻었다. Buckingham의 천해모델과 비교한 결과 160 Hz 이하에서는 이론치와 거의 같았 으나 200Hz 이상에서는 이론치와 많은 차이를 보였다. 이는 200 Hz 이상에서 결과치의 Zero-Crossing point 가 이동된 것을 보보인면이나 Kuperman과 Ingenito의 천해 모델에서 NEAR-FIELD의 영향이 Zero-crossing point를 이동시킨다는 사실, 또 주파수가 높아질수록 해상상태의 영향을 받는다는 심해 수중소음의 상관관계에 대한 싫머결과등을 비교해 볼 Eio near-field 소음원의 영향을 무시한채 far-field 소음원의 영향만을 고려한 Buckingham의 천해모델이 갖는 제한성을 나타낸 것이라 볼 수 있다.

• Applied Science and Convergence Technology
• /
• 제23권2호
• /
• pp.61-71
• /
• 2014

A field-effect transistor (FET) is one of the most commonly used semiconductor devices. Recently, increasing interest has been given to FET-based biosensors owing totheir outstanding benefits, which are likely to include a greater signal-to-noise ratio (SNR), fast measurement capabilities, and compact or portable instrumentation. Thus far, a number of FET-based biosensors have been developed to study biomolecular interactions, which are the key drivers of biological responses in in vitro or in vivo systems. In this review, the detection principles and characteristics of FET devices are described. In addition, biological applications of FET-type biosensors and the Debye length limitation are discussed.

• 한국전기전자재료학회논문지
• /
• 제22권3호
• /
• pp.248-251
• /
• 2009

We have investigated the effect of the quality of 1.3 um distributed feed back laser diode (DFB-LD) on the design of anti-reflection (AR) coatings. Optimal condition of AR coating to prevent internal feedback from both facets and reduce the reflection-induced intensity noise of laser diode was simulated with Macleod Simulator. Coating materials used in this work were ${Ti_3}{O_5}$ and $SiO_2$, of which design thickness were 105 nm and 165 nm, respectively. AR coating films were deposited by Ion-Assisted Deposition system. The electrical and optical properties of 1.3 um laser diode were characterized by Bar tester and Chip tester. Threshold current and slop-efficiency of DFB-LD were 27.56 mA 0.302 W/A. Far field pattern and wavelength of DFB-LD were $22.3^{\circ}(Horizontal){\times}24.4^{\circ}$ (Vertical), 1313.8 nm, respectively.

• 한국소음진동공학회논문집
• /
• 제17권7호
• /
• pp.596-604
• /
• 2007

이 논문은 후판 환형 디스크의 기하학적인 형상이 래디얼 방향 진동에 의해 방사되는 소음에 미치는 영향을 연구하였다. 디스크의 내경을 고정한 상태에서 두께와 외경을 주어진 범위내에서 변경하면서 이론적인 해를 이용하여 래디얼 모드의 고유진동수와 진동모드의 변화를 검토하였다. 이 결과를 이용하여, 해당 형상을 가진 디스크의 래디얼 방향 고유진동에 의해 발생되는 원격음장, 음향파워 및 방사효율을 계산하였다. 이 결과로부터 고유진동에 의한 음향파워와 방사효율을 최소화할 수 있는 기하학적인 형상을 선택하였다. 마지막으로, 최적화된 디스크의 임의 위치에 단위 하모닉 가진을 가했을 경우에 발생되는 음향파워 및 방사효율 스펙트럼을 구하였으며, 전산해석을 통해 그 정확성을 검증하였다. 이 논문에 소개된 방법을 적용하면 주어진 제한 조건을 만족하면서 목표 주파수 범위내에서 래디얼 진동에 의해 발생되는 소음을 최소화할 수 있는 기하학적인 형상을 간편하고 논리적으로 구할 수 있다.

• 한국자기학회지
• /
• 제5권3호
• /
• pp.165-170
• /
• 1995

자기적으로 분극 되어 큰 자화를 지닌 상태로 흐르는 물속 양성자의 핵스핀을 측정자장 영역에서 섭동자장을 인가하여 전이시키고, 이로부터 떨어진 지점의 고자장 하에 설치된 분리형 감지기를 이용한 양성자의 핵자기 공명신호 측정에 관한 연구를 수행하 였다. 감지기의 변조자장 크기, 변조자장 주파수 및 고주파 자장의 크기와 물 속도 및 측정자장 영역에서의 섭동 자장의 크기에 대한 핵자기 공명신호의 최적조건을 구하였다. 수 ${\mu}T$에서 mT 수준의 저자장 하에서 반치폭이 320 nT이고 신호 대 잡음비가 10.5인 Lorentz형 공명신호를 측정하였으며, 핵자기 공명신호의 크기 및 형태는 측정 자장의 크기 및 균일도와 무관하였다.