Spatial Frequency Selection Research Articles

Особливості і розвиток технологій виявлення витоків трубопроводів тепло- та водопостачання в умовах зношеності та мілітарних впливів

The article is dedicated to analyzing the current state of underground heat and water supply pipelines in Ukraine, particularly under conditions of significant wear and tear and military impacts. The challenges associated with the operational detection of hidden leaks are exami¬ned, as well as the capabilities of known methods for identifying damaged sections and leak locations. The development of acoustic and correlation leak detectors is discussed as a promi¬sing direction for improving pipeline diagnostics in war conditions and amid network dete¬rioration. Several innovations are proposed, including a new parametric correlation method, spatial-frequency selection of useful leak signals, and other advancements to enhance the diag¬nostics of critical infrastructure. These measures aim to improve the effectiveness of leak de¬tection, ensure the continuity of essential services, and strengthen the resilience of the energy system in the face of current challenges.

Nonlinear regimes of spin wave propagation in a waveguide with a one-dimensional hole array

Purpose. Investigation of spin-wave signal passage in a system of magnetic microwaves separated from each other by a one-dimensional array of holes. Using numerical and experimental methods to show controlled spatial-frequency selection of the signal in linear and nonlinear modes of operation. Methods. Micromagnetic modeling of the spatial intensity distributions of spin waves. Obtaining S-parameters of spin waves propagating in a tangentially magnetized structure using a vector circuit analyzer. Results. The spatially selective properties of the structure in linear and nonlinear modes are demonstrated using micromagnetic modeling. A mechanism for controlling the frequency range of the Bragg zone is revealed using a vector analyzer. Conclusion. The proposed structure can be used as a functional element in planar topologies of magnon networks and parallel signal processing devices based on them.

Magnonic demultiplexer-switch based on the cluster of coupled ferrimagnetic Mach–Zehnder interferometers

Here we study the spin-wave propagation in a system of Mach–Zehnder interferometers (MZI) based on ferrimagnetic yttrium-iron garnet (YIG) thin film. The angular momentum transfer during the excitation of a surface magnetostatic spin wave and the coupling of the spin-waves inside the adjacent arms of MZIs is studied using the micromagnetic modeling method. The local variation of the YIG magnetization inside the arms of MZI manifests itself both in the phase shift of the propagating spin-wave signal and coupling efficiency in the region where the adjacent arms of MZI are placed in the close proximity to each other. The switching/demultiplexing performance which is reflected in the spatial frequency selection of the spin-wave signal upon dynamical local change of the magnetization in each of four arms of the interferometers is demonstrated. The proposed MZI demonstrates the basis for the realization of the set of logical operations and could serve the facility of add and drop frequencies (channels) to and from a magnonic data bus in frequency division multiplexed magnonic networks. The use of laterally coupled interferometers opens new possibilities for the formation of the logical magnon devices tuned by the local variation of magnetization which could be realized with the locally focused laser heating.

Spatial aliasing quantification and sampling frequency selection in imaging sensors.

Sampling, whether it be spatial or temporal, is a common occurrence. A result of this fact is the need for an anti-aliasing filter, which effectively limits high frequencies and prevents them from folding over and appearing as a low(er) frequency when sampled. In typical imaging sensors, such as optics plus focal plane detector(s), the optical transfer function (OTF) acts as a spatial anti-aliasing filter. However, decreasing this anti-aliasing cutoff frequency (or lowering the curve in general) via the OTF is tantamount to image degradation. On the other hand, the lack of high-frequency attenuation produces aliasing within the image, which is another form of image degradation. In this work, aliasing is quantified, and a method for sampling frequency selection is brought forth.

Achieving high aspect ratio in plasmonic lithography for practical applications with sub-20 nm half pitch

Plasmonic lithography, which exploits a bowtie nanoaperture (BNA) for the purpose of subwavelength near-field focusing, has the capability of high-resolution patterning. However, the ultra-small feature size is achieved at the price of sharply decay of the surface plasmon waves (SPWs) in the photoresist (PR) layer, which directly leads to some unfavorable patterning issues, such as non-uniformity and shallow pattern depth even over small exposure areas. In this work, a special hybrid plasmonic waveguide (HPW) patterning system, which is composed of the plasmonic BNA-PR layer-silver reflector, is designed to facilitate high spatial frequency selection and amplify the evanescent field in the PR layer. Theoretical calculations indicate that the antisymmetric coupled SPWs and plasmonic waveguide modes excited by the HPW structure can remove the exponential decay and ensure uniform exposure over the entire depth of the PR layer. Importantly, the hyperbolic decaying characteristic of the SPWs in the PR layer plays a noticeable role in the improvement of achievable resolution, depth-of-field, and line array pattern profile. It is worth to note that the uniform periodic patterns in sub-20 nm feature can be achieved with high aspect ratio. Additionally, further numerical simulation results are presented to demonstrate the achievement of spatial frequency selection of high-k mode in HPW structure by controlling the PR thickness and gap size. Our findings may provide a new perspective on the manufacture of surface nanostructures and broaden the potential promising applications of plasmonic lithography in nanoscale patterning.

Surface Spin-Wave Propagation in the Orthogonal Transverse Junction of YIG-Based Magnonic Stripes

In this article, we experimentally demonstrate the propagation of magnetostatic surface spin wave (MSSW) in the orthogonally joined yttrium iron garnet stripes in the form of T-shaped connection. By the means of microwave spectroscopy technique, we show how the transmission is affected by the distance between orthogonal yttrium iron garnet stripes. Micromagnetic modeling demonstrates the presence of nonreciprocal propagation of spin waves (SWs) between all three ports of the T-junction. A mechanism for controlling the spatial-frequency selection of a propagating signal by variation of the air gap in the area of connected orthogonal sections is shown. The proposed structure can act as a magnonic splitter for 3-D topology of multilevel magnonic networks (MNs). The transition to a multilayer topology of MNs opens the possibility of increase of the packing density of computational units based on the principles of magnonics.

Frequency selective surface with complex topology elements

Relevance: The solution of specific problems in modern technology of microwave and UHF ranges, such as the implementation of reducing the radar signature of objects, spatial frequency-selective filters, reflectors requires the development and creation of a special class of electrodynamic structures - frequency-selective surfaces. Due to the uniqueness of their electrodynamic characteristics, it is possible to solve quite technically complex problems - suppression of excited surface waves, the creation of "forbidden" zones in the amplitude-frequency characteristics. The purpose of the work is numerical modeling and experimental study of electrodynamic characteristics of plane frequency-selective surfaces with slotted elements of complex topology. Evaluation of the influence of the geometric parameters of the slot inhomogeneity and the material constants of the dielectric substrate on the reflection and transmission coefficients of the frequency-selective surface. Materials and methods: The paper presents the results of numerical simulation of the electrodynamic characteristics of a cell of an infinite 2D frequency-selective surface with the topology of a structural element -shaped and experimental studies of the prototype parameters. Modeling was performed within the framework of the finite element method (FEM) using the ANSOFT HFSS / ANSYS software product. Characteristic measurements are performed in free space by direct measurement of attenuation values. Results: In the course of numerical experiments, it was found that two types of resonances can arise in the structure, associated both with the ratio of the geometric dimensions of the structural element and with the presence of double-sided shielding. The influence of the thickness of the dielectric substrate and the values ​​of the dielectric constant on the reflection and transmission coefficients is investigated. The frequency dependences of the reflection value are established with a change in the spatial orientation of the structure relative to the incident wave front. The dependence of the magnitude of the radio transparency of a two-layer frequency-selective surface on the angle of rotation of the structure around a given axis has been established experimentally. Conclusion: The presented results of numerical simulation of the electrodynamic characteristics of a cell of an infinite 2D frequency-selective surface with the topology of a structural element -shaped and experimental studies have shown the possibility of spatial frequency selection. The totality of the results obtained makes it possible to predict the creation of sufficiently technological and highly efficient frequency-selective surfaces in the microwave range.

Graded elastic metasurface for enhanced energy harvesting

In elastic wave systems, combining the powerful concepts of resonance and spatial grading within structured surface arrays enable resonant metasurfaces to exhibit broadband wave trapping, mode conversion from surface (Rayleigh) waves to bulk (shear) waves, and spatial frequency selection. Devices built around these concepts allow for precise control of surface waves, often with structures that are subwavelength, and utilise Rainbow trapping that separates the signal spatially by frequency. Rainbow trapping yields large amplifications of displacement at the resonator positions where each frequency component accumulates. We investigate whether this amplification, and the associated control, can be used to create energy harvesting devices; the potential advantages and disadvantages of using graded resonant devices as energy harvesters is considered. We concentrate upon elastic plate models for which the A0 mode dominates, and take advantage of the large displacement amplitudes in graded resonant arrays of rods, to design innovative metasurfaces that trap waves for enhanced piezoelectric energy harvesting. Numerical simulation allows us to identify the advantages of such graded metasurface devices and quantify its efficiency, we also develop accurate models of the phenomena and extend our analysis to that of an elastic half-space and Rayleigh surface waves.

Reconfigurable Lateral Spin-Wave Transport in a Ring Magnonic Microwaveguide

Features of spin-wave dynamics in a ring magnonic microwaveguide that appear at change in the direction of the equilibrium magnetization with respect to the axis of symmetry of the structure have been studied by micromagnetic simulation based on the numerical solution of the Landau–Lifshitz–Gilbert equation. Mechanisms of control of lateral spin wave transport in yttrium iron garnet stripes located along the parallel sides of the ring magnonic microwaveguide have been considered. The possibility of the inversion of the group velocity of a spin wave with the simultaneous selection of transverse spin-waveguide modes in the lateral structure has been demonstrated. It has been shown that the method proposed to control the direction of transfer of the spin wave power can be used to fabricate controllable integrated units of functional magnonic circuits with the simultaneous spatial–frequency selection of an information signal.

Diffuse and nonlinear imaging of multiscale vascular parameters for in vivo monitoring of preclinical mammary tumors.

Diffuse optical imaging (DOI) techniques provide a wide-field or macro assessment of the functional tumor state and have shown substantial promise for monitoring treatment efficacy in cancer. Conversely, intravital microscopy provides a high-resolution view of the tumor state and has played a key role in characterizing treatment response in the preclinical setting. There has been little prior work in investigating how the macro and micro spatial scales can be combined to develop a more comprehensive and translational view of treatment response. To address this, a new multiscale preclinical imaging technique called diffuse and nonlinear imaging (DNI) was developed. DNI combines multiphoton microscopy with spatial frequency domain imaging (SFDI) to provide multiscale data sets of tumor microvascular architecture coregistered within wide-field hemodynamic maps. A novel method was developed to match the imaging depths of both modalities by utilizing informed SFDI spatial frequency selection. An in vivo DNI study of murine mammary tumors revealed multiscale relationships between tumor oxygen saturation and microvessel diameter, and tumor oxygen saturation and microvessel length (|Pearson's ρ| ≥ 0.5, P < 0.05). Going forward, DNI will be uniquely enabling for the investigation of multiscale relationships in tumors during treatment.

Optical property uncertainty estimates for spatial frequency domain imaging.

Spatial frequency domain imaging (SFDI) is a wide-field diffuse optical imaging modality that has attracted considerable interest in recent years. Typically, diffuse reflectance measurements of spatially modulated light are used to quantify the optical absorption and reduced scattering coefficients of tissue, and with these, chromophore concentrations are extracted. However, uncertainties in estimated absorption and reduced scattering coefficients are rarely reported, and we know of no method capable of providing these when look-up table (LUT) algorithms are used to recover the optical properties. We present a method to generate optical property uncertainty estimates from knowledge of diffuse reflectance measurement errors. By employing the Cramér-Rao bound, we can quickly and efficiently explore theoretical SFDI performance as a function of spatial frequencies and sample optical properties, allowing us to optimize spatial frequency selection for a given application. In practice, we can also obtain useful uncertainty estimates for optical properties recovered with a two-frequency LUT algorithm, as we demonstrate with tissue-simulating phantom and in vivo experiments. Finally, we illustrate how absorption coefficient uncertainties can be propagated forward to yield uncertainties for chromophore concentrations, which could significantly impact the interpretation of experimental results.

Achieving pattern uniformity in plasmonic lithography by spatial frequency selection

Abstract The effects of the surface roughness of thin films and defects on photomasks are investigated in two representative plasmonic lithography systems: thin silver film-based superlens and multilayer-based hyperbolic metamaterial (HMM). Superlens can replicate arbitrary patterns because of its broad evanescent wave passband, which also makes it inherently vulnerable to the roughness of the thin film and imperfections of the mask. On the other hand, the HMM system has spatial frequency filtering characteristics and its pattern formation is based on interference, producing uniform and stable periodic patterns. In this work, we show that the HMM system is more immune to such imperfections due to its function of spatial frequency selection. The analyses are further verified by an interference lithography system incorporating the photoresist layer as an optical waveguide to improve the aspect ratio of the pattern. It is concluded that a system capable of spatial frequency selection is a powerful method to produce deep-subwavelength periodic patterns with high degree of uniformity and fidelity.

Spatial–frequency selection of magnetostatic waves in a two-dimensional magnonic crystal lattice

Features of the propagation of magnetostatic waves in a tangentially magnetized magnonic crystal structure based on iron–yttrium garnet with a two-dimensional array of grooves on the surface are studied. Numerical simulation is performed by the finite element method and the dispersion characteristics and the spatial distribution of fields of eigenmodes of surface magnetostatic waves propagating in this structure are calculated. The characteristics of waves in the magnonic crystal structure are experimentally studied by means of Brillouin scattering. It is shown that the formation of waveguide channels is possible when the frequency of the input signal is close to the frequency of the band gap of the structure.

Jones-matrix mapping of complex degree of mutual anisotropy of birefringent protein networks during the differentiation of myocardium necrotic changes.

The azimuthally stable method of Jones-matrix mapping of histological sections of myocardium tissue biopsy using spatial-frequency selection of the mechanisms of linear and circular birefringence is proposed. Correlation parameter-the complex degree of mutual anisotropy-and its diagnostic application are analytically substantiated. The method of measuring the complex degree of mutual-anisotropy coordinate distributions using spatial filtration of their high- and low-frequency components is developed. The interconnections between such distributions and parameters of linear and circular birefringence of myocardium tissue histological sections are defined. The comparative investigations of coordinate distributions of the complex degree of mutual anisotropy formed by fibrillar networks of myocardium tissues of different necrotic states (dead due to coronary heart disease and acute coronary insufficiency) are performed. The values and ranges of change of the statistical (moments of the first-fourth order) parameters of coordinate distributions of the complex degree of mutual anisotropy are defined. The objective criteria of cause of death differentiation are determined.

Spatial frequency selection and integration of global and local information in visual processing: A selective review and tribute to Shlomo Bentin

Previous research has suggested a relationship between processing lower versus higher spatial frequencies (SFs) and global/local perception, respectively. Here we honor Shlomo Bentin by reviewing the work we conducted with him regarding this issue. This work was aimed at investigating the mechanisms by which selective attention to spatial frequency (SF) mediates global and local perception in general and how these perceptual levels are integrated with the shapes that define them. The experiments demonstrate that attention to global and local aspects of a hierarchical display biases the flexible selection of relatively lower and relatively higher SFs during image processing. Additionally, attentional selection of SF allows for the shapes in a hierarchical display to be integrated with the level (global/local) at which they occur. The studies reviewed here provide strong evidence that the flexible, top-down selection of low-level SF channels mediates the perception of global and local elements of visual displays. The studies also support a hemisphere asymmetry in this process, with right hemisphere functions biased toward global perception and left hemisphere functions biased toward local.

Model-based analysis on the influence of spatial frequency selection in spatial frequency domain imaging.

Frequency variation in spatial frequency domain imaging is a powerful tool for adjusting the penetration depth of the imaging signal and the parameter sensitivity toward absorption and diffusive and subdiffusive scattering. Through our computational analysis, using an analytical solution of the radiative transfer equation, we add quantitation to this tool by linking the different spatial frequency regimes to their relative information content and to their absolute depth sensitivity. Special focus is placed on high spatial frequencies by analysis of the phase function parameter γ and its significance and ambiguity in describing subdiffusive scattering.

Optically-sectioned two-shot structured illumination microscopy with Hilbert-Huang processing.

We introduce a fast, simple, adaptive and experimentally robust method for reconstructing background-rejected optically-sectioned images using two-shot structured illumination microscopy. Our innovative data demodulation method needs two grid-illumination images mutually phase shifted by π (half a grid period) but precise phase displacement between two frames is not required. Upon frames subtraction the input pattern with increased grid modulation is obtained. The first demodulation stage comprises two-dimensional data processing based on the empirical mode decomposition for the object spatial frequency selection (noise reduction and bias term removal). The second stage consists in calculating high contrast image using the two-dimensional spiral Hilbert transform. Our algorithm effectiveness is compared with the results calculated for the same input data using structured-illumination (SIM) and HiLo microscopy methods. The input data were collected for studying highly scattering tissue samples in reflectance mode. Results of our approach compare very favorably with SIM and HiLo techniques.

Attending to global versus local stimulus features modulates neural processing of low versus high spatial frequencies: an analysis with event-related brain potentials.

Spatial frequency (SF) selection has long been recognized to play a role in global and local processing, though the nature of the relationship between SF processing and global/local perception is debated. Previous studies have shown that attention to relatively lower SFs facilitates global perception, and that attention to relatively higher SFs facilitates local perception. Here we recorded event-related brain potentials (ERPs) to investigate whether processing of low versus high SFs is modulated automatically during global and local perception, and to examine the time course of any such effects. Participants compared bilaterally presented hierarchical letter stimuli and attended to either the global or local levels. Irrelevant SF grating probes flashed at the center of the display 200 ms after the onset of the hierarchical letter stimuli could either be low or high in SF. It was found that ERPs elicited by the SF grating probes differed as a function of attended level (global versus local). ERPs elicited by low SF grating probes were more positive in the interval 196–236 ms during global than local attention, and this difference was greater over the right occipital scalp. In contrast, ERPs elicited by the high SF gratings were more positive in the interval 250–290 ms during local than global attention, and this difference was bilaterally distributed over the occipital scalp. These results indicate that directing attention to global versus local levels of a hierarchical display facilitates automatic perceptual processing of low versus high SFs, respectively, and this facilitation is not limited to the locations occupied by the hierarchical display. The relatively long latency of these attention-related ERP modulations suggests that initial (early) SF processing is not affected by attention to hierarchical level, lending support to theories positing a higher level mechanism to underlie the relationship between SF processing and global versus local perception.

Fourier-domain Jones-matrix mapping of a complex degree of mutual anisotropy in differentiation of biological tissues' pathological states.

This article presents the theoretical background of an azimuthally stable method of Jones-matrix mapping of histological sections of a uterine wall biopsy on the basis of spatial-frequency selection of the mechanisms of linear and circular birefringence. The diagnostic application of a new correlation parameter--a complex degree of mutual anisotropy--is analytically substantiated. The method of measuring coordinate distributions of a complex degree of mutual anisotropy with further spatial filtration of their high- and low-frequency components is developed. The interconnections of such distributions with linear and circular birefringence parameters of the uterine-wall-endometrium histological sections are found. The comparative results of measuring the coordinate distributions of a complex degree of mutual anisotropy formed by fibrillar networks of myosin and collagen fibrils of uterus wall tissue of different pathological states--pre-cancer (dysplasia) and cancer (adenocarcinoma)--are shown. The values and ranges of change of the statistical (moments of the first to fourth orders) parameters of complex degree of mutual-anisotropy coordinate distributions are studied. The objective criteria of diagnosing the pathology and differentiation of its severity degree are determined.

Spatial-frequency selection of complex degree of coherence of laser images of blood plasma in diagnostics and differentiation of pathological states of human organism of various nosology.

The theoretical background of correlation and phase analysis of laser images of human blood plasma with the spatial-frequency selection of the manifestations of mechanisms of linear and circular birefringence of albumin and globulin is presented. The comparative results of measuring the coordinate distributions of the module of complex degree of coherence (CDC) of laser images of blood plasma taken from the patients of three groups--healthy patients (donors), the patients suffering from the rheumatoid arthritis, and those with stomach cancer (adenocarcinoma)--are shown. The values and ranges of change of the statistical (moments of the first-fourth orders), correlation (excess of autocorrelation functions), and fractal (slopes of approximating curves and dispersion of the extremes of logarithmic dependencies of power spectra) parameters of CDC coordinate distributions are studied. The objective criteria of diagnostics of the pathology and differentiation of the inflammation and oncological state are determined.