Topic
Spatial filter
About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.
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Papers
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TL;DR: In this paper, the effects of spatial filtering on the streamwise spectrum function of wall-bounded flows were investigated using a grid-generated turbulence as a benchmark flow, and it was shown that spatial filtering significantly attenuates the attenuation of the Reynolds stress due to spatial filtering.
Abstract: We use grid-generated turbulence as a benchmark flow to test the effects of spatial resolution on turbulence measurements with hot wires. To quantify the spatial filtering, measurements of the turbulence statistics and spectra downstream of the grid were made using hot wires of varying length and compared to the results from a new nanoscale thermal anemometry probe, which has a sensing length of the order of, or smaller than, the Kolmogorov scale. In order to separate the effects of temporal and spatial filtering, a study was performed to ensure that the data were free of the artifacts of temporal filtering so that differences in the measurements could be wholly attributed to spatial filtering. An empirical correlation for the attenuation of the streamwise Reynolds stress due to spatial filtering is constructed, and it is shown that these grid turbulence results relate directly to the near-wall region of wall-bounded flows, where the effects of spatial filtering are most acutely felt. The effect of spatial filtering on the streamwise spectrum function is observed to extend to almost all wavenumbers, even those significantly lower than the length of the hot wire itself. It is also shown that estimates of the Kolmogorov scale are affected by spatial filtering when wires longer than the Kolmogorov length are used.
41 citations
Patent•
01 Sep 1999
TL;DR: In this paper, a method and system for recording diffractive high resolution text, pictorial, and/or other graphical information is provided which is particularly suited to recording information that would be difficult to reproduce by typical counterfeiting methods.
Abstract: Device, method, and system for recording diffractive high resolution text, pictorial, and/or other graphical information is provided which is particularly suited to recording information that would be difficult to reproduce by typical counterfeiting methods. The information recorded may be used to authenticate the recorded item, or indirectly, an item to which the recording is attached. Such items may include legal, financial and commercial instruments, credit cards, and packaging for such items as software, art, and other items where forgery of the item may be a concern. In one embodiment of the invention light is selectively passed by a shutter, and a spatial filter then cleans the beam to remove undesirable frequency components. A liquid crystal display (LCD) dynamically receives a data stream from a computer where each of the displayed data values presents an optical characteristic (for example density, phase, or polarization) to the filtered beam and causes diffraction into a plurality of diffracted beams, the character of which is dependent on the data displayed. A mask selectively passes only predetermined ones of the beams so that only frequency components that will generate the desired optical interference fringes are allowed to pass. Additional optical components receive the passed beams and redirect them to overlap at an output plane to form interference fringes. These interference fringes can have a very high spatial frequency so that extremely fine lines or small objects, including text and graphics, can be recorded.
41 citations
TL;DR: A holographic lens has been made that utilizes some of the earlier work on holographic aberration correction, and the lens properties are obtained by interferometrically recording a plane wave and a pinhole generated spherical wave.
Abstract: A holographic lens has been made that utilizes some of our earlier work on holographic aberration correction [ J. E. Ward D. C. Auth F. P. Carlson , Appl. Opt.10, 896 ( 1971)]. The lens properties are obtained by interferometrically recording a plane wave and a pinhole generated spherical wave. The theoretical analysis is followed by the results of the Ronchi lens test, Fourier transformation of a grating, and imaging of a test picture.
41 citations
TL;DR: This study uses a Bessel-like beam in-conjugation with an orthogonal detection system to achieve depth imaging and demonstrates a penetration depth that extends up to 650 µm, which will advance the field of fluorescence imaging and deep nano-particle tracking.
Abstract: Monitoring and visualizing specimens at a large penetration depth is a challenge. At depths of hundreds of microns, several physical effects (such as, scattering, PSF distortion and noise) deteriorate the image quality and prohibit a detailed study of key biological phenomena. In this study, we use a Bessel-like beam in-conjugation with an orthogonal detection system to achieve depth imaging. A Bessel-like penetrating diffractionless beam is generated by engineering the back-aperture of the excitation objective. The proposed excitation scheme allows continuous scanning by simply translating the detection PSF. This type of imaging system is beneficial for obtaining depth information from any desired specimen layer, including nano-particle tracking in thick tissue. As demonstrated by imaging the fluorescent polymer-tagged-CaCO3 particles and yeast cells in a tissue-like gel-matrix, the system offers a penetration depth that extends up to 650 mu m. This achievement will advance the field of fluorescence imaging and deep nano-particle tracking.
41 citations
TL;DR: A method based on an optical Fourier transform technique during the weaving process is described that recognises significant variations in the Fourier pattern occurring in the presence of defective fabric with a CCD sensor joined to an electronic hardware system performing a simple algorithm.
41 citations