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三维测量中一种新的自适应窗口傅里叶相位提取法 总被引:2,自引:1,他引:1
针对多尺度窗口傅里叶变换中,窗口尺寸的自适应选取及提取基频时的频谱混叠等问题,提出基于希尔伯特-黄变换(HHT)的自适应窗口傅里叶相位提取法。对变形条纹信号进行HHT后,通过谱分析,自适应确定能够准确描述条纹信号变化情况的瞬时频率及条纹图的背景分量。根据所得的瞬时频率,给出自适应定位条纹信号局部平稳区域的步骤,进而确定窗口尺寸。不需额外计算,可有效去除背景分量以减少基频提取过程中零频频谱的干扰。与现有的用最大脊法确定窗口尺寸的方法相比,本方法不受被测相位必须线性逼近且变化缓慢的前提约束。实验证明本方法有效、可行,且对测量携带陡峭边缘或面形复杂的物体也能进行较为精确有效的测量。 相似文献
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S变换引导的窗口傅里叶变换相位提取 总被引:3,自引:0,他引:3
提出了一种基于S变换引导的自适应窗口傅里叶变换相位提取方法.通过连续S变换,得到局部条纹的最佳变换窗口,可以保证窗口尺寸随变形条纹的频率变化而自动调整,适合复杂物体的面形测量.计算机模拟和实验验证表明,该方法克服了传统窗口傅里叶变换窗口大小固定的缺点,相位提取的误差由-2~8rad降低为-1~1rad,而且还可以得到被... 相似文献
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对比研究了CCD非线性对小波变换轮廓术和傅里叶变换轮廓术的影响,并从信号频域角度分析推导出考虑CCD非线性时,变形条纹的小波变换的频谱描述形式,得到了"脊"处小波系数的解析表达式。处理由CCD非线性引起的非完善的条纹图时,采用小波变换轮廓术提取相位,实质是采用最佳的加权滤波窗口,这样能减弱CCD非线性引起的频谱混叠对测量的影响,可以得到比傅里叶变换轮廓术更稳定的恢复效果。计算机模拟验证了此结论的正确性。 相似文献
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傅里叶变换轮廓术中滤波窗方位选择研究 总被引:1,自引:0,他引:1
在傅里叶变换轮廓术频域滤波过程中通常采用不对称的汉宁窗滤波窗来提取基频信号,当投影呈二维变化的光栅条纹时,采用的滤波窗长短轴方向和载频方向不吻合,会导致被测物体的部分高频信息丢失,从而影响相位展开的难易程度和系统测量的精度。分析比较物体高度的分布与频谱的关系,通过旋转滤波窗使其短轴方向与载频方向一致,可以保留物体的高频信息,降低相位展开的复杂度,提高测量的精确度。计算机模拟和实物实验结果表明滤波窗旋转滤波可以避免相位展开在物体高度突变处的出错,有效地提高测量精度。 相似文献
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窗口傅里叶变换轮廓术中窗口尺度选取的改进 总被引:1,自引:0,他引:1
多尺度窗口傅里叶变换法根据条纹信号的瞬时频率梯度来确定信号的局域平稳长度,再由局域平稳长度来控制窗口的尺度,即窗口的尺度和局域平稳长度成正比。使用多尺度窗口傅里叶变换法来使条纹信号的频谱局域化,可以在条纹信号的频率分辨率和空间分辨率之间达到一种较佳的调和。针对多尺度窗口傅里叶变换三维形貌测量技术中局域平稳长度提取算法的不足进行了改进,使窗口尺度的选取更具合理性,对变形光栅基频提取更精确,进一步减小了位相测量的误差。给出了理论分析、计算机模拟以及实验结果。 相似文献
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Ugeda MM Fernández-Torre D Brihuega I Pou P Martínez-Galera AJ Pérez R Gómez-Rodríguez JM 《Physical review letters》2011,107(11):116803
Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in freestanding graphene layers. 相似文献
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A. H. Taub 《General Relativity and Gravitation》1979,10(12):1009-1009
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In this note we use some of the results of [3] to derive a general duality theorem for the cohomologies of foliated structures on a manifold. The result is applied to the special case of a symplectic manifold M on which the foliation is given by a complex polarization F in the sense of geometric quantization. We obtain, for example, a rigorous proof of the fact that for a smooth function ƒ on M whose Hamiltonian vector field leaves F invariant, the spectrum of the corresponding prequantization operator v(ƒ) coincides with the spectrum of its transpose, under the above duality. This latter result was obtained by Simms in [12] under certain hypotheses. Proofs of the validity of those hypotheses are now available in the literature; cf. [3] and [7]. 相似文献
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Valfells A. Verboncoeur J.P. Lau Y.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(3):529-536
Analyzes the effects of space charge shielding on the steady state of a multipactor discharge on a dielectric. Analytic methods are used to obtain an exact function for the potential in the discharge, assuming a Maxwellian distribution of emitted electrons. An equation for the amount of power deposited on the dielectric by the multipactoring electrons, for a given saturation level, is given. A simple method for obtaining the saturation level, for a given material, is obtained 相似文献
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Kopeikin SM 《Physical review letters》2007,98(22):229001; discussion 229002