Showing papers on "Spatial filter published in 2010"

Switchable Frequency Selective Surface for Reconfigurable Electromagnetic Architecture of Buildings

Abstract: A frequency selective surface (FSS) that is electronically switchable between reflective and transparent states is tested. It can be used to provide a spatial filter solution to reconfigure the electromagnetic architecture of buildings. The FSS measurements show that the frequency response of the filter does not change significantly when the wave polarization changes or the angle of incidence changes up to ±45° from normal. The FSS is based on square loop aperture geometry, with each unit cell having four PIN diodes across the aperture at 90 degree intervals. Experiments demonstrated that almost 10 dB additional transmission loss can be introduced on average at the resonance frequency, for both polarizations, by switching PIN diodes to on from off state.

Dual Airy beam.

Abstract: We derive a general form of Airy wave function which satisfies paraxial equation of diffraction. Based on this, we propose a new form of Airy beam, which is composed of two symmetrical Airy beams which accelerate mutually in the opposite directions. This ‘dual’ Airy beam shows several distinguishing features: it has a symmetric transverse intensity pattern and improved self-regeneration property. In addition, we can easily control the propagation direction. We also propose ‘quad’ Airy beam, which forms a rectangular shaped optical array of narrow beams that travel along a straight line. We can control its propagation direction without changing transverse intensity patterns. These kinds of superposed optical beams are expected to be useful for various applications with their unique properties.

Defect Inspection Apparatus and Defect Inspection Method

Abstract: A defect inspection apparatus includes: stages each mounting an inspecting object on which a circuit pattern having a group of parallel lines is formed, and each running perpendicular or parallel to the group of lines; an illumination optical system which illuminating a surface of the inspecting object with a slit beam being slit light so that a longitudinal direction of the slit beam is substantially perpendicular to the running directions of the stages, and which has a first inclined angle formed by the direction of the group of lines and a projection line, of an optical axis of the slit beam, to the inspecting object; a spatial filter that shields or transmits reflected and scattered light of the inspecting object according to a difference in distribution of orientation; and a detection optical system that detects the reflected and scattered light transmitted through the spatial filter by image sensors. Moreover, the illumination optical system illuminates the inspecting object with another slit beam from a direction opposite to an incident direction of the slit beam on a plane.

Signatures of light-beam spatial filtering in a three-dimensional photonic crystal

Abstract: We report experimental evidence of spatial filtering of light beams by three-dimensional, low-refraction-index-contrast photonic crystals. The photonic crystals were fabricated in a glass bulk, where the refraction index has been periodically modulated using tightly focused femtosecond laser pulses. We observe filtered areas in the angular distributions of the transmitted radiation, and we interpret the observations by theoretical and numerical study of light propagation in index-modulated material in paraxial model.

Dynamic holography using pixelated light modulators

Abstract: Dynamic holography using spatial light modulators is a very flexible technique that offers various new applications compared to static holography. We give an overview on the technical background of dynamic holography focusing on pixelated spatial light modulators and their technical restrictions, and we present a selection of the numerous applications of dynamic holography.

Experimental characterization of periodic frequency-steerable arrays for structural health monitoring

Abstract: Beam steering through phased arrays is a well-established technique, used extensively in ultrasonic imaging for medical, NDE and SHM applications. Phased arrays typically need individual control of their elements, which involves hardware and software complexity. This paper presents the characterization of a novel frequency-steerable array for structural health monitoring. In the considered configuration, beam steering is achieved by exploiting interference phenomena generated by the spatial lay-out of the array elements, and their simultaneous activation at specific frequencies. Such frequencies correspond to wavenumbers which are associated with radiation in determined spatial directions. In essence, the array acts as a spatial filter, which preferentially radiates at wavenumbers defined by the spatial arrangement of the elements. As such, the array is also effective at tuning its radiation to specific wave modes. In this paper, a simple quadrilateral periodic topology illustrates the directional properties of the array and shows its tuning capabilities. The investigations are supported by a preliminary numerical analysis, which is used to design an experimental prototype. Tests successfully validate the numerical predictions and demonstrate the directional and tuning capabilities of the proposed array design.

Spatial filtering using dielectric photonic crystals at beam-type excitation

Abstract: Spatial filtering is demonstrated at beam-type excitations by utilizing finite thickness slabs of two-dimensional dielectric photonic crystals (PCs) showing exotic Fabry–Perot resonances that are preserved over a wide range of variation of the incidence angle. Bandstop and dual-bandpass filtering effects are illustrated theoretically and the corresponding filters are validated in the microwave experiments by using square-lattice PCs. It is shown that the basic transmission features that were observed earlier for a plane-wave illumination are also recognizable at beam-type excitations. The proposed spatial filtering mechanism exhibits directional beaming. The desired widths and the locations of the passbands and stopbands are attainable in the angle domain with a proper choice of the operating frequency for the given excitation characteristics.

Defect detection method and defect detection device and defect observation device provided with same

Abstract: The disclosed device, which, using an electron microscope or the like, minutely observes defects detected by an optical appearance-inspecting device or an optical defect-inspecting device, can reliably insert a defect to be observed into the field of an electron microscope or the like, and can be a device of a smaller scale. The electron microscope, which observes defects detected by an optical appearance-inspecting device or by an optical defect-inspecting device, has a configuration wherein an optical microscope that re-detects defects is incorporated, and a spatial filter and a distribution polarization element are inserted at the pupil plane when making dark-field observations using this optical microscope. The electron microscope, which observes defects detected by an optical appearance-inspecting device or an optical defect-inspecting device, has a configuration wherein an optical microscope that re-detects defects is incorporated, and a distribution filter is inserted at the pupil plane when making dark-field observations using this optical microscope.

The oriented spatial filter masks for electronic speckle pattern interferometry phase patterns.

Abstract: we propose the oriented spatial filter masks for filtering in electronic speckle pattern interferometry (ESPI) phase fringe patterns. We establish the oriented derivative operator that only highlights noise without edges of an image. The noise in the image can be removed while still preserving the edges simply by subtracting the oriented derivative image from original image, which can be implemented with one pass of the oriented spatial filter mask. Further, we make an improvement on the oriented spatial filter mask for enhancing the smoothness. The performance of the oriented spatial filter masks is demonstrated via application to a simulated speckle phase fringe pattern and an experimentally obtained phase fringe pattern and comparison with other directional filtering methods.

Experimental generation of Mathieu–Gauss beams with a phase-only spatial light modulator

Abstract: We present a novel method for the efficient generation of even, odd, and helical Mathieu-Gauss beams of arbitrary order and ellipticity by means of a phase-only spatial light modulator (SLM). Our method consists of displaying the phase of the desired beam in the SLM; the reconstructed field is obtained on-axis following a spatial filtering process with an annular aperture. The propagation invariance and topological properties of the generated beams are investigated numerically and experimentally.

Radio Frequency Interference Removal through the Application of Spatial Filtering Techniques on the Parkes Multibeam Receiver

Abstract: This paper addresses the first practical application of spatial filtering techniques to data taken with a multibeam receiver. Spatial filters make use of the relative arrival times of a signal at multiple sensors to identify and separate signals from different directions. The method is a consequence of the Karhunen-Loeve theorem and relies on the eigen decomposition of the covariance matrix formed from the multiple signal paths. The effectiveness of the spatial filtering techniques is demonstrated on observations of the Vela pulsar taken with the Parkes 20 cm Multibeam receiver. The experiment was highly successful, and the results show spatial filtering methods provide powerful tools for interference mitigation with an array feed receiver. Extensions of the algorithm to reduce computational requirements and allow application on short (submillisecond) timescales are also explored.

Array-Gain Constraint Minimum-Norm Spatial Filter With Recursively Updated Gram Matrix For Biomagnetic Source Imaging

Abstract: This paper proposes a novel spatial filter for biomagnetic source imaging. The proposed spatial filter is derived based on a modified version of the minimum-norm spatial filter and is designed to have a performance close to that of the adaptive minimum-variance spatial filter through the use of an estimated covariance matrix. In this method, the theoretical form of the measurement covariance matrix is estimated as an updated gram matrix in a recursive procedure. Since the proposed method does not use the sample covariance matrix, it is free of the well-known weaknesses of the minimum-variance spatial filter, namely, the proposed spatial filter does not require a large number of time samples, and it can even be applied to single-time-sample data. It is also robust to source correlation. We have validated the method's effectiveness by our computer simulations as well as through experiments using auditory-evoked magnetoencephalographic data.

Spatial filtering for image signal processing

Abstract: Systems and methods are disclosed for applying spatial filtering to raw image data. In one embodiment, a spatial filter may identify an n×n block of pixels from the current image frame, the n×n block including a plurality of neighboring pixels being centered about a current input pixel and being of the same color component as the current input pixel. The spatial filter may include a plurality of filter taps, with one filter tap corresponding to each of the pixels within the n×n block. A set of filtering coefficients for each filter tap, which may be based on a Gaussian function, may be determined. A pixel difference value between the current input pixel and each of the plurality of neighboring pixels in the n×n block are determined, and the pixel differences may be used to determine an attenuation factor for each filter tap. In one embodiment, the attenuation factor is based upon the pixel difference value between the raw input pixel and the neighboring pixel at the filter tap and brightness of the current input pixel. An attenuated set of filtering coefficients may be obtained thereafter by applying the attenuation factors to their respective filtering taps. Subsequently, the attenuated filtering coefficients may be applied to obtain a set of filtered pixel values. By normalizing the sum of the filtered pixel values using the sum of the attenuated filtering coefficients, a spatially filtered output value corresponding to the current input pixel (e.g., located at the center of the n×n block) may be determined.

Sound Source Separation Using Spatial Filtering and Regularization Phases

Abstract: Described is a multiple phase process/system that combines spatial filtering with regularization to separate sound from different sources such as the speech of two different speakers. In a first phase, frequency domain signals corresponding to the sensed sounds are processed into separated spatially filtered signals including by inputting the signals into a plurality of beamformers (which may include nullformers) followed by nonlinear spatial filters. In a regularization phase, the separated spatially filtered signals are input into an independent component analysis mechanism that is configured with multi-tap filters, followed by secondary nonlinear spatial filters. Separated audio signals are the provided via an inverse-transform.

Laser three-dimensional imaging device based on single-photon detector

Abstract: The invention discloses a laser three-dimensional imaging device based on a single-photon detector, belonging to the technical field of photoelectric instruments. A target to be detected is irradiated by the laser pulse emitted by a pulsed laser via a scanning system; the returning photons are received by a receiving/emitting co-axial optical system, i.e., the returning photons are received by a double-gating single-photon detecting module via a spectral filter and a spatial filter and an arriving pulse is outputted, so that the photon flight time of the target measuring point can be measured by combining the laser emission detection and the multi-photon arriving pulse time; and a data processing unit is used for carrying out the coordinate conversion based on the position and attitude data, scanning mirror targeting data, and photon flight time of the three-dimensional imaging device, de-noising and three-dimensional image construction and correction, so as to output the reliable target three-dimensional range image. The invention solves the problems that the existing laser three-dimensional imaging device is incapable of penetrating vegetation and camouflage and being miniaturized when conducting long-distance operations.

SVM for edge-preserving filtering

Abstract: In this paper, we propose a new method to construct an edge-preserving filter which has very similar response to the bilateral filter. The bilateral filter is a normalized convolution in which the weighting for each pixel is determined by the spatial distance from the center pixel and its relative difference in intensity range. The spatial and range weighting functions are typically Gaussian in the literature. In this paper, we cast the filtering problem as a vector-mapping approximation and solve it using a support vector machine (SVM). Each pixel will be represented as a feature vector comprising of the exponentiation of the pixel intensity, the corresponding spatial filtered response, and their products. The mapping function is learned via ∊-SVM regression using the feature vectors and the corresponding bilateral filtered values from the training image. The major computation involved is the computation of the spatial filtered responses of the exponentiation of the original image which is invariant to the filter size given that an IIR O(1) solution is available for the spatial filtering kernel. To our knowledge, this is the first learning-based O(1) bilateral filtering method. Unlike previous O(1) methods, our method is valid for both low and high range variance Gaussian and the computational complexity is independent of the range variance value. Our method is also the fastest O(1) bilateral filtering yet developed. Besides, our method allows varying range variance values, based on which we propose a new bilateral filtering method avoiding the over-smoothing or under-smoothing artifacts in traditional bilateral filter.

Optical displacement meter

Abstract: An optical displacement meter includes: a spatial filter configured to extract light under measurement of a wavelength focused on a measurement target and to specify the wavelength of the light under measurement; a polarizer configured to divide the light collimated and caused to propagate in one direction into linearly polarized beams in two directions orthogonal to a propagating direction; a wavelength plate that allows passage of the linearly polarized beams to produce elliptically polarized light having a phase difference commensurate with a light wavelength; a polarized light separator configured to divide the elliptically polarized light into polarized light components in the two directions; and a computing circuit configured to perform computation of (A−B)/(A+B) by use of light quantity signals A and B, which respectively correspond to the two polarized light components.

Spatial Filtering of Sound Beams by Sonic Crystals

Abstract: We propose and numerically demonstrate an efficient cleaning of spatial structure (spatial filtering) of sound beams by propagating them through at least twodimensional sonic crystals, i.e. through acoustic structures periodically modulated in longitudinal and in transversal direction with respect to the sound propagation direction. We show the spatial filtering in two configurations: with- and without the angular band-gap. We also show that besides the spatial filtering the beams can be additionally focalized at a particular distance behind the sonic crystal in both configurations.

Laser light source device and image display apparatus

Abstract: A laser light source device has a laser light source for emitting a laser beam, a laser driver for driving the laser light source, a light-collecting lens for collecting the laser beam and reflecting a part of the laser beam, an optical sensor for receiving a reflected laser beam which has been reflected by the light-collecting lens and outputting a detection signal corresponding to intensity of the reflected laser beam, and a controller for controlling driving of the laser light source by the laser driver in accordance with the detection signal, and the light-collecting lens is disposed in a eccentric-rotated state so that an optical axis of the light-collecting lens has a tilt with respect to a central ray of the laser beam being incident on the light-collecting lens.

Improved interferometric tracking of trapped particles using two frequency-detuned beams.

Abstract: For most optical tweezer applications, precise and reliable tracking of the trapped particle is an important requirement. Backfocal-plane interferometry is the fastest and most accurate tracking technique if the particle displacements are limited to half of the focal width. Especially for positive axial displacements, the nonlinear detector response can lead to incorrect tracking results. Here we show how the linear detection range around the trap center can be extended by a factor of 2 to 4 in the axial direction using a second frequency-detuned tracking focus that is generated by the same laser as the optical trap. Additionally, we show how the noise in the axial signal can be decreased significantly using a second detector.

Space-Time-Frequency Processing of Acoustic Wave Fields: Theory, Algorithms, and Applications

Abstract: Consider a nonparametric representation of acoustic wave fields that consists of observing the sound pressure along a straight line or a smooth contour L defined in space. The observed data contains implicit information of the surrounding acoustic scene, both in terms of spatial arrangement of the sources and their respective temporal evolution. We show that such data can be effectively analyzed and processed in what we call the space-time-frequency representation space, consisting of a Gabor representation across the spatio-temporal manifold defined by the spatial axis L and the temporal axis t. In the presence of a source, the spectral patterns generated at L have a characteristic triangular shape that changes according to certain parameters, such as the source distance and direction, the number of sources, the concavity of L, and the analysis window size. Yet, in general, the wave fronts can be expressed as a function of elementary directional components-most notably, plane waves and far-field components. Furthermore, we address the problem of processing the wave field in discrete space and time, i.e., sampled along L and t, where a Gabor representation implies that the wave fronts are processed in a block-wise fashion. The key challenge is how to chose and customize a spatio-temporal filter bank such that it exploits the physical properties of the wave field while satisfying strict requirements such as perfect reconstruction, critical sampling, and computational efficiency. We discuss the architecture of such filter banks, and demonstrate their applicability in the context of real applications, such as spatial filtering, deconvolution, and wave field coding.

Bilateral filter-based adaptive nonuniformity correction for infrared focal-plane array systems

Abstract: In scene-based nonuniformity correction (NUC) methods for infrared focal-plane array cameras, the problem of ghosting artifacts widely affects the sensitivity of the imaging system and visibly decreases the image quality. Ghosting artifacts can also degrade the performance of several applications, such as target detection and tracking. We carried out a detailed analysis of the problem using a well-established NUC technique: the least mean square Scribner's algorithm. In order to solve some drawbacks of the original Scribner's algorithm, we introduced in the scheme a new technique that mitigates ghosting. Such technique relies on the employment of an edge-preserving spatial filter for the purpose of computing reliable spatial estimates. We tested the effectiveness of the new technique applying the improved NUC method to an experimental IR sequence of frames acquired in the laboratory. Finally, the performance of the proposed method was discussed and compared to that yielded by a well-established deghosting technique.

Method, medium, and apparatus of filtering depth noise using depth information

Abstract: A depth noise filtering method and apparatus is provided. The depth noise filtering method may perform spatial filtering or temporal filtering according to depth information. In order to perform spatial filtering, the depth noise filtering method may determine a characteristic of a spatial filter based on depth information. Also, in order to perform temporal filtering, the depth noise filtering method may determine a number of reference frames based on depth information. The depth noise filtering method may adaptively remove depth noise according to depth information and thereby enhance a noise filtering performance.

Spatial filter for near field modification in a wireless communication device

Abstract: A spatial filter is developed for specific absorption rate (SAR) reduction in a wireless device. A conductive element is designed to modify the near field distribution of an antenna operating in a wireless device. This reduces SAR while minimizing degradation of antenna efficiency at one or several frequency bands that the antenna is designed to operate over. Lumped reactance can be designed into the conductive element to generate low pass, band pass, and/or high pass frequency characteristics. Distributed reactance can be designed into the conductive element to replace or to work in conjunction with the lumped reactance. Active components can be designed into the conductive element to provide dynamic tuning of the frequency response of the conductive element.

Flexible contrast for low-coherence interference microscopy by Fourier-plane filtering with a spatial light modulator.

Abstract: We propose a full-field low-coherence interference (LCI) microscope that can provide different contrast modes using Fourier-plane filtering by means of a spatial light modulator. By altering the phase and spatial frequencies of the backreflected wavefront from the sample arm of the interferometer, we are able to change the contrast in the depth-resolved LCI images. We demonstrate that different types of contrast modes, such as, e.g., spiral phase contrast, can successfully be emulated to provide specific enhancement of internal structures and edges and to reveal complementary details within the samples under investigation.

Automatic spatial filtering to obtain the virtual image term in digital holographic microscopy

Abstract: The main factor that limits the quality of an image reconstructed by the process of spatial filtering in digital holographic microscopy is discussed. A spatial filter determined by the distribution of the spectrum of the virtual image is designed automatically for real time dynamic analysis of a micro-object, and an optimal reconstructed phase image can be obtained. An experiment of a holographic image with an onion specimen is presented to prove the validity of this approach. Comparing the numerical reconstruction of the hologram by employing different spatial filters with the automatic spatial filtering shows the superiority of the automatic spatial filtering method, and it is suitable for dynamic and automatic analysis.

Crosswind sensing from optical-turbulence-induced fluctuations measured by a video camera

Abstract: We present a novel method for remote sensing of crosswind using a passive imaging device, such as a video recorder. The method is based on spatial and temporal correlations of the intensity fluctuations of a naturally illuminated scene induced by atmospheric turbulence. Adaptable spatial filtering, taking into account variations of the dominant spatial scales of the turbulence (due to changes in meteorological conditions, such as turbulence strength, or imaging device performance, such as frame rate or spatial resolution), is incorporated into this method. Experimental comparison with independent wind measurement using anemometers shows good agreement.