共查询到20条相似文献,搜索用时 15 毫秒
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Homentcovschi D Miles RN Tan L 《The Journal of the Acoustical Society of America》2005,117(5):2761-2771
The paper contains an analysis of the transmission of a pressure wave through a periodic grating including the influence of the air viscosity. The system of equations in this case consists of the compressible Navier-Stokes equations associated with no-slip boundary conditions on solid surfaces. The problem is reduced to two hypersingular integral equations for determining the velocity components along the slits. These equations are solved by using Galerkin's method with some special trial functions. The results can be applied in designing protective screens for miniature microphones realized in the technology of micro-electro-mechanical systems (MEMS). In this case, the physical dimensions of the device are on the order of the viscous boundary layer so that the viscosity cannot be neglected. The microfluidic model of the screen consists of a periodic array of slits in a substrate. The analysis indicates that the openings in the screen should be on the order of 10 microm in order to avoid excessive attenuation of the signal. 相似文献
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Recurring to the characteristic of Bessel function, we give the analytic expression of the Fresnel diffraction by a circular aperture, thus the diffractions on the propagation axis and along the boundary of the geometrical shadow are discussed conveniently. Since it is difficult to embody intuitively the physical meaning from this series expression of the Fresnel diffraction, after weighing the diffractions on the axis and along the boundary of the geometrical shadow, we propose a simple approximate expression of the circular diffraction, which is equivalent to the rigorous solution in the further propagation distance. It is important for the measurement of the parameter of the beam, such as the quantitative analysis of the relationship of the wave error and the divergence of the beam. In this paper, the relationship of the fluctuation of the transverse diffraction profile and the position of the axial point is discussed too. 相似文献
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Analytical nonparaxial vectorial electric field expressions for both Gaussian beams and plane waves diffracted through a circular aperture are derived by using the vector plane angular spectrum method for the first time,which is suitable for the subwavelength aperture and the near-field region.The transverse properties of intensity distributions and their evolutions with the propagating distance,and the power transmission functions for diffracted fields containing the whole field,the evanescent field and the propagating field are investigated in detail,which is helpful for understanding the relationship between evanescent and propagating components in the near-field region and can be applied to apertured near-field scanning optical microscopy. 相似文献
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Jaroslav Pachner 《Czechoslovak Journal of Physics》1956,6(1):8-11
The problem of the diffraction of an arbitrarily polarized electromagnetic plane wave by a perfectly conducting plane screen of infinitesimal thickness is reduced to scalar problems by the method known from earlier papers. The wave field diffracted either by a screen of infinite extent which is perforated by an aperture of arbitrary size and shape or by a complementary screen is then described by means of the bra-vectors, ket-vectors and linear operators introduced by the present author in one of his preceding papers. 相似文献
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The rigorous electromagnetic theory of the diffraction of vector beams by an aperture is proposed and numerically evaluated by the diffraction of vector Gaussian beams by a circular aperture. The results are compared with those, by using the vector Rayleigh–Sommerfeld diffraction integrals and angular-spectrum expression theory, showing a good consistency. The numerical calculation shows that the result calculated by the rigorous theory is much more precise than those calculated by the integral method in diffraction near field, and a highly consistency reaches by the three methods in diffraction far field. A further extension of the theory is discussed. 相似文献
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Based on the vectorial Rayleigh–Sommerfeld diffraction integrals, analytical expressions for the transversal and axial field distribution of plane waves propagating through a thin lens followed by a small circular aperture are derived and used to study the focusing and diffraction properties of plane waves. Some special cases of our general result are discussed, and illustrative numerical calculation results are given. It is found that the vectorial nonparaxial approach should be applied if the aperture dimension is comparable with the wavelength or the focusing is strong. 相似文献
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V. P. Ivanov 《Acoustical Physics》2004,50(1):57-65
The three-dimensional problem of the active suppression of sound behind an aperture in a perfectly rigid screen is formulated and solved. 相似文献
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By using the vectorial Rayleigh diffraction integrals, a nonparaxial propagation equation of vectorial plane waves diffracted at a small rectangular aperture is derived analytically and some special cases are discussed. Numerical calculation results are given to illustrate the applicability and validity of our theoretical formulae. It is shown that for the apertured case the ratio of the aperture width and wavelength affects the beam nonparaxiality. The nonparaxial approach presented in this paper has to be used for diffracted plane waves if the aperture width is comparable with or less than the wavelength. 相似文献
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圆孔衍射光强分布的数值计算 总被引:24,自引:5,他引:19
利用数值积分的方法,计算了由点光源经圆孔衍射形成的光强分布,分别得到夫琅禾费及菲涅耳衍射图样,宽定量分析了满足夫琅禾费衍射的条件。 相似文献
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The near- and far-field diffraction due to a circular aperture illuminated with partially coherent light produced by a turbulent
medium has been theoretically studied. Formulations are developed for investigating the near- and far-field diffraction patterns.
The phase structure function, which is generated by the turbulent medium and determines the partially coherent condition of
a light beam passing through it, is assumed to take both the Gaussian form and the 5/3-power law. Numerical results concerning
the far-field intensity distribution and the axial intensity distribution in the near-field region are presented in diagrams
and discussed. 相似文献
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We present a formulation of the scalar diffraction of spherical waves through plane apertures that takes advantage of the importance of the critical points and the semiperiodic zones that are defined in the plane of the aperture. Our approach overcomes the intrinsic limitations of stationary-phase methods (when the critical points coalesce) and allows a direct implementation in terms of numerical algorithms for computations of any predefined accuracy. The method is illustrated with examples corresponding to a rectangular aperture. 相似文献
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Far-field divergence of a vectorial plane wave diffracted by a circular aperture from the vectorial structure 下载免费PDF全文
Based on the vectorial structure of an electromagnetic wave, the analytical and concise expressions for the TE and TM terms of a vectorial plane wave diffracted by a circular aperture are derived in the far-field. The expressions of the energy flux distributions of the TE term, the TM term and the diffracted plane wave are also presented. The ratios of the power of the TE and TM terms to that of the diffracted plane wave are examined in the far-field. In addition, the far-field divergence angles of the TE term, the TM term and the diffracted plane wave, which are related to the energy flux distribution, are investigated. The different energy flux distributions of the TE and TM terms result in the discrepancy of their divergence angles. The influences of the linearly polarized angle and the radius of the circular aperture on the far-field divergence angles of the TE term, the TM term and the diffracted plane wave are discussed in detail. This research may promote the recognition of the optical propagation through a circular aperture.vspace1mm 相似文献
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Fraunhofer diffraction field through an elliptical annular aperture is obtained for plane wave incidence when there is offset or tilt of the inner ellipse. The effects are observed through the field distribution. 相似文献
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The influence of circular aperture on the intensity of high-order harmonic generation (HHG) with intense femtosecond laser pulse was studied both experimentally and theoretically. The intensity variety of HHG with the diameter of circular aperture was observed in pulsed Ar gas. The result was discussed and interpreted in terms of the theory of Hankel transform. It is found that using the Gaussian beam truncated by an aperture could enhance the conversion efficiency of HHG at certain conditions. 相似文献