• 제목/요약/키워드: Reduction of radiation noise

검색결과 148건 처리시간 0.023초

병원내 LED 조명기구의 전자파 저감대책 (Investigation on the EMI Noise Reduction of LED Lighting Module in Hospital)

  • 송민종;조현섭
    • 한국산학기술학회:학술대회논문집
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    • 한국산학기술학회 2011년도 춘계학술논문집 1부
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    • pp.385-388
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    • 2011
  • The electromagnetic wave occurs primarily LED lighting equipment in the interior medical imaging information a lot of high-frequency equipment environment installation. It generated by lighting fixtures mach damage to patients as well as non or no operation. It can be reduced through noise attenuation and filter change. It associated with the capacitors and inductors can reduce by are used frequency efficiently, Attenuation circuit does not significantly affect the radiation medical equipment devices

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난류 유동장 내 두께를 가지는 단일 에어포일의 음향파워 예측 (Prediction of acoustic power radiated from an airfoil with thickness in turbulent flow)

  • 김대환;정철웅
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2013년도 춘계학술대회 논문집
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    • pp.353-358
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    • 2013
  • Present paper deals with turbulence-airfoil interaction noise and mainly investigates the effects of airfoil thickness on the broadband noise spectrum. The acoustic power radiation from an airfoil is predicted using high-order time-domain method, which is based on the computational aeroacoustic technique solving the linear Euler equations. The homogeneous and isotropic turbulence is generated by utilizing the synthetic turbulence modeling based on random particle method. The airfoils taken into consideration are a flat-plate and a NACA0012 airfoil aligned with uniform mean flow. The effects of airfoil thickness on the radiated inflow turbulence noise are investigated by comparing acoustic power spectrum predicted for each airfoil. The comparison of acoustic power spectrum reveals that the airfoil thickness significantly contributes the high frequency noise reduction.

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단순지지 사각 접수 평판의 방사효율 근사식에 관한 연구 (A Study on the Approximate Formula for Radiation Efficiency of a Simply Supported Rectangular Plate in Water)

  • 김현실;김재승;김봉기;김상렬
    • 한국소음진동공학회논문집
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    • 제24권1호
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    • pp.21-27
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    • 2014
  • In this paper, an approximate formula for radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. By assuming an infinite plate, the fluid loading effect is derived in terms of an effective mass. Based on the observation that the fluid loading effect decreases as frequency increases, the radiation efficiency formula at high frequency, which was originally derived for a plate vibrating in the air, is modified as the approximate formula for a submerged plate. The fluid loading effect is taken into account in the wavenumber of the plate. Comparisons of the approximate formula with the numerical results shows that they match well except the mid-frequency range in which numerical results show many oscillations. In numerically solving the fully coupled equations of motion, fourfold integrals of the impedance coefficients are reduced to single nonsingular integrals, which results in substantial reduction in computing time.

디지털 래디오그라피의 신호 및 잡음 특성에 대한 방사선 영향에 관한 연구 (Investigation of Radiation Effects on the Signal and Noise Characteristics in Digital Radiography)

  • 김호경;조민국
    • 대한의용생체공학회:의공학회지
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    • 제28권6호
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    • pp.756-767
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    • 2007
  • For the combination of phosphor screens having various thicknesses and a photodiode array manufactured by complementary metal-oxide-semiconductor (CMOS) process, we report the observation of image-quality degradation under the irradiation of 45-kVp spectrum x rays. The image quality was assessed in terms of dark pixel signal, dynamic range, modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). For the accumulation of the absorbed dose, the radiation-induced increase both in dark signal and noise resulted in the gradual reduction in dynamic range. While the MTF was only slightly affected by the total ionizing dose, the noise power in the case of $Min-R^{TM}$ screen, which is the thinnest one among the considered screens in this study, became larger as the total dose was increased. This is caused by incomplete correction of the dark current fixed-pattern noise. In addition, the increase tendency in NPS was independent of the spatial frequency. For the cascaded model analysis, the additional noise source is from direct absorption of x-ray photons. The change in NPS with respect to the total dose degrades the DQE. However, with carefully updated and applied correction, we can overcome the detrimental effects of increased dark current on NPS and DQE. This study gives an initial motivation that the periodic monitoring of the image-quality degradation is an important issue for the long-term and healthy use of digital x-ray imaging detectors.

주변고정 장방형 평판에 있어서 임의점 가진에 의한 고체전파음의 예측 (An estimate of structure-borne sound by the excitation at an arbitrary point on the rectangular plate with fixed edges)

  • 김의간
    • Journal of Advanced Marine Engineering and Technology
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    • 제12권2호
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    • pp.21-34
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    • 1988
  • Machinery enclosures are widely adopted to reduce the noise emission in various fields of application. Emitted noise, which is due to the vibration of enclosure's outer surface, is composed of two kinds of sound with different path of propagation. One is the "structure-borne sound", while the other is "air-borne sound". In order to get a most efficient machinery enclouser a prudent consideration upon the above structure-borne and air-borne sound is required, as the guiding principle of contermeasure for each noise is quite different. The controlling of input vibration and its isolation are major subjects for the structure-borne sound, and the specifications of absorbing members and damping panels are the major related matters for the air-borne sound. Hence, it seems very efficient to separate the total sounds into two categories with a great accuracy when one think of further reduction of noise from the existing enclosure, although its separating methods have not been made clear for many years. Author proposes an application method of experimental modal analysis to extract the structure-borne sound from the measured total radiation sound, as the air-borne sound is deduced by the vectorial difference between the measured total radiation sound and the calculated structure-borne sound. In order to calculate the correct structure-borne sound by the excitation at an arbitrary point on the enclosure structure, it is important to decide 1) how to estimate the enclosure's surface vibration velocity and 2) how to compute the radiation sound which is considered as the effect of vibration modes of enclosure surface. The former can be solved with total frequency response function calculated by the application of experimental modal analysis. The latter is to be solved by the author's new approaches for radiation sound computation by means of the Rayleigh's integral equation and the boundary-element method applied complex surface vibration velocity. As a first step, structure-borne sound by the excitation at an arbitry point on the rectangular plate with fixed edges, has been calculated to verified the reliability of the developed computation methods. The results of calculation show good agreements with those of the actual measurements.actual measurements.

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복합재료 유연 프로펠러의 재료 및 구조적 특성 연구 (Material & Structural Characteristics of Composite Material Flexible Propeller)

  • 이상갑;황정오;변준형
    • 대한조선학회논문집
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    • 제46권2호
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    • pp.203-217
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    • 2009
  • The researches on the development of composite material propeller with outstanding damping effects have been actively attempted for the reduction of radiation noise of underwater vehicle propeller. Composite material suitable for the flexible propeller has the following advantages, such as high specific strength and specific stiffness, low thermal expansion coefficient, high resistance against environmental deterioration, low possibility of corrosion due to cavitation, nonoccurrence of rapid fracture due to fatigue, easy molding of complicated shape, easy repair maintenance and low production costs, etc. For the confirmation of optimal fiber array structures of composite material for the production of the flexible propeller blades, in this study, mechanical characteristics of its specimens according to materials were obtained and structural characteristics of propeller blade were also examined according to materials and stacking fiber arrays.

BLDC 모터의 소음 저감을 위한 로터부 구조 최적설계 (An Optimal Design of the Rotor of BLDC Motors for Noise Reduction)

  • 김지훈;고강호;김민수;허승진
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2004년도 추계학술대회논문집
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    • pp.972-975
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    • 2004
  • In order to reduce the noise of BLDC motor, a systematic optimization procedure for rotor structure is presented. The noise index is defined as the sum of volume velocity of FE-model that are calculated at the dominant frequencies during dehydration process, which is based on the principle of radiation simple volume source. Then, the five design variables are selected to represent the shape and layout or rotor structure. This discrete design optimization problem for minimizing the noise index is solved by 3-level orthogonal array based effect analysis. Finally, the response surface method (RSM) combined optimization approach is employed for more refining the approximate optimum.

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An adaptive nonlocal filtering for low-dose CT in both image and projection domains

  • Wang, Yingmei;Fu, Shujun;Li, Wanlong;Zhang, Caiming
    • Journal of Computational Design and Engineering
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    • 제2권2호
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    • pp.113-118
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    • 2015
  • An important problem in low-dose CT is the image quality degradation caused by photon starvation. There are a lot of algorithms in sinogram domain or image domain to solve this problem. In view of strong self-similarity contained in the special sinusoid-like strip data in the sinogram space, we propose a novel non-local filtering, whose average weights are related to both the image FBP (filtered backprojection) reconstructed from restored sinogram data and the image directly FBP reconstructed from noisy sinogram data. In the process of sinogram restoration, we apply a non-local method with smoothness parameters adjusted adaptively to the variance of noisy sinogram data, which makes the method much effective for noise reduction in sinogram domain. Simulation experiments show that our proposed method by filtering in both image and projection domains has a better performance in noise reduction and details preservation in reconstructed images.

자기감응 액추에이터를 이용한 능동소음제어 (Active Noise Control Using Sensory Actuator)

  • 고병식
    • 대한기계학회논문집A
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    • 제20권5호
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    • pp.1573-1581
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    • 1996
  • This paper present as experimental demonstratio of DSP and a sensory actuator that is used to actively control sound transmission/radiation through a vibrating plate. A plane acoustic wave incident on a clamped, thin circular plate was used as a noise source, and a sensory actuator bounded to the plate was used to control and sense vibration of the plate. The sound transmission reduction problem was tranformed as a structural vibration control problem that actively control the structural vibration modes coupled to acoustic modes. The results show that the first structural vibration mode is controlled with a reduction of 78 percent in the displacement and velocity of the plate. This corresponds to a 13dB reduction in the acoustic response. These experimental results indicate that a sensory actuator bounded to the plate can be employed to attenuate the sound transmitted to radiated from the plate.

저선량 핵의학 감마카메라 영상장치의 최근 발전 (Recent Development in Low Dose Nuclear Medicine Gamma Camera Imaging)

  • 황경훈;이병일;김용권;이해준;선용한
    • 대한의용생체공학회:의공학회지
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    • 제36권4호
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    • pp.123-127
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    • 2015
  • Recently, new gamma camera systems enabling low radiation dose imaging have been developed. We reviewed the recent development of these low dose gamma camera systems including high sensitivity detectors, device structures, noise reduction filters, efficient image reconstruction algorithms, low dose protocols, and so on. It is expected that further technological advances reduce both radiation dose and imaging time in gamma camera imaging especially for radiation-sensitive patients such as pediatric patients.