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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TL;DR: A new photoelectric device for measuring blood vessel diameters is described, and the elimination of the light by the vessel due to reflection, refraction, diffraction, or scattering is achieved with the aid of a lens and pinhole representing a spatial filter.
Abstract: A new photoelectric device for measuring blood vessel diameters is described. The principle of this device consists in locating the vessel within a beam of parallel light at right angles to the beam direction, and eliminating all light striking the vessel. Thus only the light passing by the side of the vessel determines the signal strength of a photocell. The elimination of the light by the vessel due to reflection, refraction, diffraction, or scattering, is achieved with the aid of a lens and pinhole representing a spatial filter. This arrangement is effective irrespective of whether the vessel is opaque or transparent. The resolving power of the device in measuring changes of outside diameter is better than 0.5 μm for vessels up to 3 mm in diameter. The upper frequency limit is 300 Hz (−3 dB). The application of the method is demonstrated by two examples of measurements obtained on a small muscular artery.
26 citations
ENEA1
TL;DR: In this paper, a generalization of the self-filtering unstable resonator (SFUR) is presented, where the resonator is no longer confocal, and in principle, may have a shorter cavity length, while the other properties remain almost the same.
Abstract: Calculations on a generalization of the self-filtering unstable resonator (SFUR) are presented. The resonator is no longer confocal, and in principle, may have a shorter cavity length, while the other properties remain almost the same. >
26 citations
TL;DR: Measurements of the relative optical collection efficiency are presented for two optical collection systems used in the authors' laboratory for single molecule detection and absolute measurements of the peak collection efficiencies for the two collection systems are presented.
Abstract: The sensitive flow cytometric detection of fluorescent species in liquid sample streams requires efficient collection of light from small [approximately 1 picoliter (pl)] sample volumes. This is often accomplished with high numerical aperture (NA) imaging collection optics used in combination with a spatial filter. A method to measure the spatial variation of the optical collection efficiency within the sample volume, using a submicrometer light source, is described. Measurements of the relative optical collection efficiency are presented for two optical collection systems used in our laboratory for single molecule detection. The measurement are in qualitative agreement with relative optical collection efficiency calculations using a simple geometrical optics model. Absolute measurements of the peak collection efficiencies for the two collection systems are also presented. These absolute collection efficiency measurements are in good quantitative agreement with ideal collection efficiencies calculated using measured transmissions and rated NAs of the collection optics. The utility of this information for the characterization and optimization of sensitive fluorescence detection apparatus is discussed.
26 citations
TL;DR: This work proposes a fully data-dependent spatial filtering framework for extraction of speech signals that originate from a SOI that is applicable in challenging multitalk situations, without requiring any prior information, except the geometry, location, and orientation of the arrays.
Abstract: Hands-free capture of speech often requires extraction of sources from a certain spot of interest (SOI), while reducing interferers and background noise. Although state-of-the-art spatial filters are fully data-dependent and computed using the power spectral density (PSD) matrices of the desired and the undesired signals, the existing solutions to extract sources from a SOI are only partially data-dependent. Estimating the time-varying PSD matrices from the data is a challenging problem, especially in dynamic and quickly time-varying acoustic scenes. Hence, the spot signal statistics are often pre-computed based on a near-field propagation model, resulting in suboptimal filters. In this work, we propose a fully data-dependent spatial filtering framework for extraction of speech signals that originate from a SOI. To achieve position-based spatial selectivity, distributed arrays are used, which offer larger spatial diversity compared to arrays of closely spaced microphones. The PSD matrices of the desired and the undesired signals are updated at each time-frequency bin by using a minimum Bayes risk detector that is based on a probabilistic model of narrowband position estimates. The proposed framework is applicable in challenging multitalk situations, without requiring any prior information, except the geometry, location, and orientation of the arrays.
26 citations
TL;DR: A common-path interferometer with a tri-window built using a 4f optical system with Ronchi ruling as a spatial filter and reconstructed from the three patterns using just one interferogram is proposed.
Abstract: A common-path interferometer is proposed with a tri-window. It is built using a 4f optical system with Ronchi ruling as a spatial filter. The input rectangular aperture is formed by three windows; the central window supports a phase object, and the other two are used for reference beams. Using an appropriate grating period relative to input aperture size, an interferogram containing three patterns can be obtained in the output plane. The object phase can then be reconstructed from the three patterns using just one interferogram. The experiments are carried out to demonstrate the feasibility and reliability of the proposed scheme.
26 citations