• Title/Summary/Keyword: 평면파

Search Result 166, Processing Time 0.064 seconds

Determination of Plane-wave Reflection Coefficient in Underwater Acoustic Pulse Tube Using Two-dimensional Fourier Filtering (이차원 푸리에 필터링을 이용한 수중음향 펄스 튜브에서의 평면파 반사계수 결정)

  • Kim, Wan-Gu;Kang, Hwi Suk;Yoon, Suk Wang
    • The Journal of the Acoustical Society of Korea
    • /
    • v.34 no.6
    • /
    • pp.493-498
    • /
    • 2015
  • Complex acoustic signals can be formed in a water-filled acoustic pulse tube under some exciting conditions. It makes difficult to measure plane-wave reflection coefficient with the pulse tube for low frequency bands. In this study, using COMSOL Multiphysics we show that the tube wall excitation generates complex acoustic field of nonplanar mode as well as planar one. From such field incident or reflected planar mode can be decomposed respectively with a modal decomposition method, two-dimensional Fourier filtering. It makes possible to more accurately determine the plane-wave reflection coefficient of acoustic specimen with time gating.

Analysis of Ultrasound Synthetic Transmit Focusing Using Plane Waves (평면파를 이용한 초음파 합성 송신 집속 기법의 해석)

  • Lee, Jong Pil;Song, Jae Hee;Song, Tai-Kyong
    • The Journal of the Acoustical Society of Korea
    • /
    • v.33 no.3
    • /
    • pp.200-209
    • /
    • 2014
  • In this paper, we present a general model for synthetic transmit focusing method using plane waves (STF-PW) of which the properties are investigated through mathematical analysis and compared with those of the conventional focusing method. The analysis results show that STF-PW produces non-diffracting beams in the sense that their main lobe widths do not change with depth. We also present a method for synthesis of plane waves to obtain a desired main lobe width while preventing grating lobe generation and a method for broadening the region over which the non-diffracting property is maintained. The proposed model and analysis results were validated through computer simulations.

Three-dimensional analysis of the mufflers by BEM (경계요소법에 의한 소음기의 3차원 해석)

  • 윤제원;임정빈;권영필
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 1995.10a
    • /
    • pp.19-24
    • /
    • 1995
  • 단순한 형상의 소음기는 평면파이론에 의해 비교적 간단하게 음향성능을 해석적으로 구할 수 있다. 그러나 소음기의 형상이 복잡해지거나 해석하고자 하는 주파수의 범위가 평면파의 차단주파수 이상이 될 경우 소음기 내부의 음장이 평면파에서 벗어나게 되어 평면파 이론에 의한 해석은 실제와 상당한 오차가 발생하게 되므로 음장에 대한 3차원 해석이 필요하다. 이론적으로 3차원 문제를 해석할 수 있는 경우는 형상이 극히 단순한 경우에 국한되므로 유한요소법(FEM), 경계요소법(BEM)과 같은 수치해석적인 방법이 이용되고 있다. 경계요소법은 적분 커넬(kernel)의 특이성(singularity) 문제가 있지만 대상 영역의 경계면만을 이산화함으로써 모델링에 소요되는 시간과 노력을 절약할 수 있으므로 음향문제 해석에 있어서 효율적인 방법이라고 할 수 있다. 본 연구의 목적은 3차원 경계요소법 프로그램을 개발하고 평면파이론에 의한 해석이 어려운 여러가지 형태의 소음기에 대한 음향성능을 예측하고 실험으로 검증하는것이다. 특히, 단일영역으로 해석이 불가능한 다공형 소음기에 영역분할법을 적용하여 계산하고 결과를 검토하였다.

  • PDF

Solution Comparisons of Modified Mild Slope Equation and EFEM Plane-wave Approximation (수정 완경사파랑식과 EFEM 평면파 근사식의 해 비교)

  • Seo, Seung-Nam
    • Journal of Korean Society of Coastal and Ocean Engineers
    • /
    • v.21 no.2
    • /
    • pp.117-126
    • /
    • 2009
  • In order to test the accuracy between the modified mild slope equation (MMSE) without evanescent modes and the plane-wave approximation (PA) of eigenfunction expansion method, various numerical results from both models are presented. In this study, analytical solutions of two models are employed, one based on the MMSE derived by Porter (2003) and the other on the scatterer method of PA by Seo (2008a). Judging from direct comparisons against existing results of rapidly varying topography, the PA model gives better predictions of the wave propagation than the MMSE model.

A Study on the Realization of Transmit and Receive Focusing Using Linited-Diffraction Beam in Ultrasound Imaging (초음파 영상에서 제한회절빔을 이용한 송수신 집속의 구현에 관한 연구)

  • 정목근;권성재;안영복
    • The Journal of the Acoustical Society of Korea
    • /
    • v.17 no.4
    • /
    • pp.67-71
    • /
    • 1998
  • 초음파 선형트랜스듀서에서 제한회절음장은 영상깊이에서 다른 방향으로 진행하는 평면파들의 선형적인 중첩으로부터 구한다. 제한회절음장을 구현하기 위한 송신음장은 영상 깊이를 지나가는 평면파들의 공간적인 확장으로부터 구해지는데 실제의 하드웨어로 구현하 기 어렵다. 본 논문은 진행방향이 다른 pulsed mode 평면파를 각각 송신한 후, 얻어진 데이 터로부터 합성집속 방법에 의하여 제한회절빔을 구현하였다. 제안한 방법은 모든 송신소자 에서 발사되는 음장의 크기가 동일하므로 송신전력이 증가하여 신호대잡음비와 명암비를 증 가시키며 간단한 하드웨어로 구현이 가능하다. 시뮬레이션 결과는 송신은 한점집속, 수신은 동적집속을 사용하는 기존의 방법과 비교하여 주엽(mainlobe)의 폭과 부엽(sidelobe)의 크기 관점에서 우수함을 증명하였다.

  • PDF

A Study of Power Absorption in Human Head Exposed to Plane Wave (평면파에 노출된 인체 두부의 전력흡수 해석)

  • 이애경;조광윤;이혁재
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.8 no.6
    • /
    • pp.665-680
    • /
    • 1997
  • The specific absorption rate (SAR) distributions in various models of the human head have been analyzed when the models are exposed to 350 MHz and 900 MHz plane waves. The numerical analysis is performed with the finite-difference time-domain (FDTD) method. A homogeneous sphere including a cylinderical neck, a homogeneous head shaped model, and a heterogeneous realistic model are used as models of human head. The incident plane wave used for these calculations is propagating from the front to the back or from the back to the front of the head model, with its E-field vector orientation being parallel to the major length of the body. The specific findings are: 1) the average SARs of the three models are similar mutually but the local SARs of them differ greatly mutually; 2) the power is deposed more deeply in the head at 350 MHz, which is roughly the resonant frequency of a human head, than at 900 MHz; 3) for a plane wave propagating from the back, "hot spot" is found in the neck region, not in the head; 4) for a plane wave propagating from the front, "hot spot" is found in the nose at 900 MHz, and in the upper part of the lip and the jaw region at 350 MHz.

  • PDF

Nearfield Eigenvector Method for Array Shape Estimation (어레이 형상 추정을 위한 근거리 고유벡터 기법)

  • 신원민;도경철;강현우;윤대희;이충용;박희영
    • The Journal of the Acoustical Society of Korea
    • /
    • v.23 no.4
    • /
    • pp.282-287
    • /
    • 2004
  • This paper proposes the nearfield eigenvector method for array shape estimation using reference signals basted on the nearfield signal modeling. Generally. direction finding methods assume the reference signals to be plainwave. However, in case of the reference signals in nearfield, this assumption is inadequate for array shape estimation. In this paper. the nearfield reference signals are modeled. and we propose the nearfield eigenvector method. The numerical experiments indicated that the proposed method shows good performance for array shape estimation regardless of the ranges of the reference signals.

Analytic solution of TE plane-wave scattering from rectangular grooves (네모난 금속홈에 의한 TM 평면파 산란의 해석적 해)

  • Cho, Yong-H.
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
    • /
    • 2005.11a
    • /
    • pp.175-178
    • /
    • 2005
  • TM plane-wave scattering from finite rectangular grooves in a conducting plane is systematically analyzed with the overlapping T-block method. Multiple rectangular grooves are divided into several overlapping T-blocks to obtain the fast CPU time, CAD applicability, and wide versatility. The scattered fields are obtained in simple closed forms including a fast-convergent integral.

  • PDF