共查询到20条相似文献,搜索用时 109 毫秒
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菲涅尔平板天线由于其具有宽频带、重量轻、馈电简单和易于共形等优点,可替代透镜天线用于毫米波成像或用作微波移信通信中的接收天线单元等。同时,其作为聚焦器件,通过与馈源阵列组合,可以构成一种新型的自适应天线应用于蜂窝移动通信的基站智能天线等领域,基于其良好的工程应用前景,本文在对有关研究工作简要回顾的基础上,深入分析其去相关机理,应用极大似然估计算法实现了相干信号源在大角度入射的情形下,菲涅尔平板天线对来波方向的有效估计,避免了应用MUSIC算法进行来波方向估计所遇到的观察区域的限制问题,仿真计算和有关文献数值分析结果的比较表明,菲涅尔平板天线具有良好的空间谱估计性能。 相似文献
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针对基于白光LED室内可见光无线光通信技术的应用需求, 设计了等齿距平面菲涅尔透镜. 相比常规透镜光接收天线, 菲涅尔透镜具有聚焦能力强、焦距短、透镜厚度薄、重量轻、成本低等优点. 利用Trace pro软件对设计进行了模拟仿真, 分析了透镜不同设计参数对接收天线光学增益、光学效率及光斑尺寸的影响, 讨论了透镜在平行光斜入射时的会聚情况. 结果表明, 平面点聚焦菲涅尔透镜的光学效率可达92.1%, 适用于小视场、高增益接收光学系统前端. 相似文献
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该文提出了一种基于菲涅尔区域的乳腺三维超声成像技术,可实现病变组织早期的定性诊断与定量监测。主要研究内容包括:采用透射方式,以慢度作为反演参量,将正演与反演的透射时间差作为迭代判据,基于菲涅尔区域法实现乳腺组织的二维反演成像;根据柱面传感阵列的分布特点,将乳腺三维超声成像问题转为二维成像问题,进而实现乳腺三维超声成像;计算三维病变成像声速及尺寸误差,并分析菲涅尔区域法的成像分辨率以及入射频率对成像分辨率的影响。该文研究结果证明基于柱面传感阵列的菲涅尔区域法可实现乳腺三维超声成像并有效实现病变早期监测与诊断。 相似文献
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基于菲涅尔原理及卡塞格伦天线设计方法,设计了一种口面直径为200 mm的卡赛格伦菲涅耳相位修正平面天线。天线采用连续相位修正方式,由一组同心菲涅耳相位修正圆环组成,与传统卡赛格伦抛物面天线相比,该天线具有平面化结构,大大减小了天线自身重量,天线辐射性能较离散相位衍射天线有大幅度提高。在95 GHz频率下,采用物理光学法进行仿真计算,并采用近场扫描系统进行了天线性能测试,天线3 dB波束宽度分别为0.95及1.05,天线实测增益为44.1 dB,天线口面效率为65%。 相似文献
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介绍了一种全新的轴向线聚焦方案.采用菲涅尔波带片,在实验中产生了沿轴向长为5mm,宽 100μm的线聚焦.光学测量表明,线聚焦轴向强度分布比较均匀.这些参数基本上可以满足激 光等离子体实验的要求.
关键词:
菲涅尔波带片
轴向线聚焦 相似文献
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为研制适用于太阳光直接泵浦激光器的聚能系统,在分析菲涅尔透镜聚光原理及缺陷的基础上,提出抛物面环形阵列聚光器的设计方法。完成了由抛物面环形阵列聚光器、菲涅尔透镜及复合抛物面聚光器(CPC)组成的太阳光泵浦激光器二级聚能方案,并与传统菲涅尔透镜方案进行了对比。光线追迹仿真分析表明:新型聚光器能够克服传统菲涅尔透镜的色散、小棱镜面像差及光线遮挡的缺陷,从而提高聚能效,使用抛物面环形阵列聚光器的多级聚能方案较传统菲涅尔透镜的多级聚能方案聚光比提高约18.5%,更适合于大相对孔径、高聚光比聚光场合的应用。 相似文献
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The applicability of different types of Fresnel acoustic lenses as antenna array systems in acoustic brightness thermometry of biological tissues is theoretically and numerically analyzed. On the basis of the technical feasibility criterion formulated for these systems, the wavelength suitable for the use in acoustic thermographs with arrays in the form of Fresnel lenses is determined. The focusing properties of different Fresnel lenses are analyzed. A method for constructing Fresnel lenses that is based on varying the focusing distances is proposed. The method provides an opportunity to design trifocal antenna systems with improved focusing properties. 相似文献
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Kang HC Maser J Stephenson GB Liu C Conley R Macrander AT Vogt S 《Physical review letters》2006,96(12):127401
We report on a type of linear zone plate for nanometer-scale focusing of hard x rays, a multilayer Laue lens (MLL), produced by sectioning a multilayer and illuminating it in Laue diffraction geometry. Because of its large optical depth, a MLL spans the diffraction regimes applicable to a thin Fresnel zone plate and a crystal. Coupled wave theory calculations indicate that focusing to 5 nm or smaller with high efficiency should be possible. Partial MLL structures with outermost zone widths as small as 10 nm have been fabricated and tested with 19.5 keV synchrotron radiation. Focal sizes as small as 30 nm with efficiencies up to 44% are measured. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the framework of the quasi-optical approximation. It is shown theoretically and experimentally that when a Gaussian beam illuminates such a type of bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The diffractive method proposed allows the focusing of wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensity and high-power radiation. 相似文献
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A. Gürtler J.J. Gilijamse A.A.R. Wetzels L.D. Noordam E. Sali M. Bellini 《Optics Communications》2007,270(2):1457-339
We propose focusing by a Fresnel zone plate into a pinhole as a cost-efficient, rugged component for wavelength selection in femtosecond pulses. We show measurements of the frequency selectivity of a Fresnel zone plate for an ultra-broadband supercontinuum pulse. We verify that our zone plate does not considerably stretch the 65 fs laser pulses in time. 相似文献
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X射线Bragg-Fresnel元件是近十年发展起来的一种用于X射线波段的新型光学元件。本文介绍一种具有二维聚焦效能的Bragg-Fresnel元件的设计理论和方法。设计中采用衍射理论并用C语言编制计算机程序系统对衍射图形进行设计。对于使用波长13.8nm,入射角5°,使用焦距200mm的使用条件,设计结果为35Mo/Si双层多层膜,周期厚度7.14nm,理论反射率约为60%;衍射图形共400个环带,最内环半宽度52.5μm,最外环宽度1.3μm。 相似文献
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A conical configuration plasmonic zone plate based on Fresnel zones made up of Au thin film slits is proposed for focusing in the free space with visible illumination. The surface plasmons enable propagation of radiating modes to distances equal to several wavelengths of the illumination field. Through numerical simulations, the conical structure found to yield focal spot beating the diffraction barrier encountered by conventional focusing elements. The focal spot size measured as full-width at half-maximum (FWHM) is observed to be as small as 0.31 times the illumination wavelength at the focal distance of 8 wavelength. Moreover, the simple design rules make it possible to predict and control the focal distances accurately. 相似文献
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为获得高功率、波长量级尺寸的聚焦光斑,提出利用紧聚焦方式实现阵列光束相干合成的新方案.通过建立阵列光束经紧聚焦方式相干合成的物理模型,分析了阵列光束的排布方式、偏振态、束宽、间距和紧聚焦系统数值孔径等参数对合成光束特性的影响及规律.结果表明,阵列光束经紧聚焦方式合束时,线偏振及圆偏振阵列光束均能获得较好的合成效果,径向偏振阵列光束次之,而角向偏振阵列光束则不能有效地合成.通过优化阵列光束的排布方式、束宽和间距,以及合理选择紧聚焦系统的数值孔径,能在保持较好光束质量和较高合成效率的前提下获得能量集中度高的焦斑. 相似文献
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Using the WKB approximation and assuming that the spatial spectrum of modes excited by a vertical array is sufficiently narrow, a quasi-optical theory is developed to describe the fundamental regularities manifesting themselves in the formation, propagation, and focusing of multimode acoustic beams in oceanic waveguides. Functional dependences on the parameters of both the transmitting array and the oceanic waveguide are obtained for horizontal distances at which ordinary beams form refraction focusing zones. Conditions ensuring the formation of a beam with the minimum wave front divergence are formulated for the distribution of the source excitation factor over the array aperture. 相似文献