Showing papers by "David R. Smith published in 2016"
TL;DR: In this paper, the authors investigate the imaging capabilities of a one-dimensional, dynamic, metamaterial aperture that operates at the lower part of K-band microwave frequencies (17.5-21.1 GHz).
Abstract: We investigate the imaging capabilities of a one-dimensional, dynamic, metamaterial aperture that operates at the lower part of K-band microwave frequencies (17.5–21.1 GHz). The dynamic aperture consists of a microstrip transmission line with an array of radiating, complementary, subwavelength metamaterial irises patterned into the upper conductor. Diodes integrated into the metamaterial resonators provide voltage-controlled switching of the resonant metamaterial elements between radiating and nonradiating states. Applying a series of on/off patterns to the metamaterial resonators produces a series of distinct radiation patterns that sequentially illuminate a scene. The backscattered signal contains encoded scene information over a set of measurements that can be postprocessed to reconstruct an image. We present a series of design considerations for the dynamic aperture, as well as a series of experimental studies performed using a dynamic aperture prototype. High-fidelity, real-time, diffraction-limited imaging using the prototype is demonstrated. The dynamic aperture suggests a path to fast and reliable imaging with low-cost and versatile hardware, for a variety of applications including security screening, biomedical diagnostics, and through-wall imaging.
110 citations
TL;DR: In this paper, a tunable metamaterial element that can serve as the building block for a dynamically reconfigurable aperture is presented, where the element is patterned into the upper conductor of a microstrip transmission line, providing both a means of exciting the radiating element as well as independent access for biasing circuitry.
Abstract: We present the design of a tunable metamaterial element that can serve as the building block for a dynamically reconfigurable aperture. The element-a complimentary electric-LC (cELC) resonator-is patterned into the upper conductor of a microstrip transmission line, providing both a means of exciting the radiating metamaterial element as well as independent access for biasing circuitry. PIN diodes are connected across the capacitive gaps of the cELC, and a dc bias current is used to switch the junction between conducting and insulating states. The leakage of RF signal through the bias line is mitigated by integration of a radial decoupling stub. The proposed design and operation of the element are demonstrated through full-wave electromagnetic simulations. We discuss the potential application of the cELC element as a building block for metamaterial apertures capable of dynamic beamforming, imaging, or security screening applications.
107 citations
TL;DR: The authors leverage this functionality to conduct volumetric computational imaging: a deformed cavity is outfitted with tailored, irregular surfaces, and its microwave resonant modes are projected into an imaging domain to retrieve the scene's spatial information.
Abstract: When coupled to a tuning mechanism, a disordered medium provides a powerful means for shaping electromagnetic waveforms. The authors leverage this functionality to conduct volumetric computational imaging: A deformed cavity is outfitted with tailored, irregular surfaces, and its microwave resonant modes are projected into an imaging domain to retrieve the scene's spatial information. This approach could be applied to biomedical imaging, security screening, or wireless power transfer or telecommunications.
97 citations
TL;DR: In this article, a frequency-diverse aperture for microwave imaging based on a planar cavity at K-band frequencies (18-26.5 GHz) is presented. But unlike the metamaterial apertures, the printed cavity imager does not require any mechanically moving parts or complex phase shifting networks.
Abstract: We demonstrate a frequency-diverse aperture for microwave imaging based on a planar cavity at K-band frequencies (18–26.5 GHz). The structure consists of an array of radiating circular irises patterned into the front surface of a double-sided printed circuit board. The irises are distributed in a Fibonacci pattern to maximize spatial diversity at the scene. The printed cavity is a phase-diverse system and encodes imaged scene information onto a set of frequencies that span the K-band. Similar to recently reported metamaterial apertures, the printed cavity imager does not require any mechanically moving parts or complex phase shifting networks. Imaging of a number of targets is shown; these reconstructed images demonstrate the ability of the system to perform imaging at the diffraction limit. The proposed printed cavity imager possesses a relatively large quality factor that can be traded off to achieve higher radiation efficiency. The general mode characteristics of the printed cavity suggest advantages when used in computational imaging scenarios.
97 citations
TL;DR: A frequency diverse, multistatic microwave imaging system based on a set of transmit and receive, radiating, planar cavity apertures, with a detailed analysis of the Mills-Cross aperture design, with numerical simulations that predict the performance of the aperture as part of an imaging system.
Abstract: We demonstrate a frequency diverse, multistatic microwave imaging system based on a set of transmit and receive, radiating, planar cavity apertures. The cavities consist of double-sided, copper-clad circuit boards, with a series of circular radiating irises patterned into the upper conducting plate. The iris arrangement is such that for any given transmitting and receiving aperture pair, a Mills-Cross pattern is formed from the overlapped patterns. The Mills-Cross distribution provides optimum coverage of the imaging scene in the spatial Fourier domain (k-space). The Mills-Cross configuration of the apertures produces measurement modes that are diverse and consistent with the computational imaging approach used for frequency-diverse apertures, yet significantly minimizes the redundancy of information received from the scene. We present a detailed analysis of the Mills-Cross aperture design, with numerical simulations that predict the performance of the apertures as part of an imaging system. Images reconstructed using fabricated apertures are presented, confirming the anticipated performance.
88 citations
TL;DR: In this paper, a scheme for wireless power transfer (WPT) in the radiative near-field (Fresnel) region is presented, which is designed to focus microwaves to a diffraction-limited region where a detector can be positioned, achieving reasonably high power transfer efficiency over moderate distances.
Abstract: A scheme for wireless power transfer (WPT) in the radiative near-field (Fresnel) region is presented. The proposed Fresnel WPT scheme is designed to focus microwaves to a diffraction-limited region where a detector can be positioned, achieving reasonably high power transfer efficiency over moderate distances. The configuration consists of transmit and receive microstrip patch array antennas, with the receiving antenna connected to a power-harvesting half-wave rectifier (rectenna). Fresnel region operation enables the fields radiated by the transmitting aperture to be localized both in range and cross-range. Using Fresnel region focusing, we achieve an increase of 66.8% in the amount of received power when compared to the performance of a conventional beamforming array. We also demonstrate the efficiency improvement by powering an LED using the on-axis and off-axis focusing configurations.
83 citations
TL;DR: It is shown that antennas deliberately designed to produce many different radiation patterns as the frequency is varied can reduce the number of active components necessary while still capturing high-quality images.
Abstract: Radio imaging devices and synthetic aperture radar typically use either mechanical scanning or phased arrays to illuminate a target with spatially varying radiation patterns. Mechanical scanning is unsuitable for many high-speed imaging applications, and phased arrays contain many active components and are technologically and cost prohibitive at millimeter and terahertz frequencies. We show that antennas deliberately designed to produce many different radiation patterns as the frequency is varied can reduce the number of active components necessary while still capturing high-quality images. This approach, called frequency-diversity imaging, can capture an entire two-dimensional image using only a single transmit and receive antenna with broadband illumination. We provide simple principles that ascertain whether a design is likely to achieve particular resolution specifications, and illustrate these principles with simulations.
75 citations
TL;DR: It is shown that an in-house developed simulation code can be adapted and parallelized for the rapid design and optimization of a full-size, frequency-diverse aperture, and the potential of one aperture for threat object detection in security-screening applications is demonstrated.
Abstract: We present the design and simulation of a frequency-diverse aperture for imaging of human-size targets at microwave wavelengths. Predominantly relying on a frequency sweep to produce diverse radiation patterns, the frequency-diverse aperture provides a path to all-electronic operation, sampling a scene without the requirement for mechanical scanning or expensive active components. Similar to other computational imaging schemes, the frequency diverse aperture removes many hardware constraints by placing an increased burden on processing and analysis. While proof-of-concept simulations of scaled-down versions of the frequency-diverse imager and simple targets can be performed with relative ease, the end-to-end modeling of a full-size aperture capable of fully resolving human-size targets presents many challenges, particularly if parametric studies need to be performed during a design or optimization phase. Here, we show that an in-house developed simulation code can be adapted and parallelized for the rapid design and optimization of a full-size, frequency-diverse aperture. Using files of human models in stereolithography format, the software can model the entire imaging scenario in seconds, including mode generation and propagation, scattering from the human model, and measured backscatter. We illustrate the performance of several frequency-diverse aperture designs using images of human-scale targets reconstructed with various algorithms and compare with a conventional synthetic aperture radar approach. We demonstrate the potential of one aperture for threat object detection in security-screening applications.
65 citations
Patent•
29 Jan 2016
TL;DR: Modulation patterns for surface scattering antennas provide desired antenna pattern attributes such as reduced side lobes and reduced grating lobes as mentioned in this paper, which can be used to obtain desired antenna characteristics.
Abstract: Modulation patterns for surface scattering antennas provide desired antenna pattern attributes such as reduced side lobes and reduced grating lobes.
61 citations
TL;DR: The range migration algorithm is adapted for use with dynamic metasurfaces and a preprocessing step is proposed that ultimately allows for expression of measurements in the spatial frequency domain, from which the fast Fourier transform can efficiently reconstruct the scene.
Abstract: Dynamic metasurface antennas are planar structures that exhibit remarkable capabilities in controlling electromagnetic wavefronts, advantages that are particularly attractive for microwave imaging. These antennas exhibit strong frequency dispersion and produce rapidly varying radiation patterns. Such behavior presents unique challenges for integration with conventional imaging algorithms. We adapt the range migration algorithm (RMA) for use with dynamic metasurfaces and propose a preprocessing step that ultimately allows for expression of measurements in the spatial frequency domain, from which the fast Fourier transform can efficiently reconstruct the scene. Numerical studies illustrate imaging performance using conventional methods and the adapted RMA, demonstrating that the RMA can reconstruct images with comparable quality in a fraction of the time. The algorithm can be extended to a broad class of complex antennas for application in synthetic aperture radar and MIMO imaging.
58 citations
TL;DR: In this article, a periodic array of planar nanoparticles coupled to a metal film can act as an absorbing metasurface with an angle-dependent impedance, and the perfect absorbing condition is equivalent to balancing the Ohmic and radiative losses of the nanoparticles at normal incidence.
Abstract: A metasurface that absorbs waves from all directions of incidence can be achieved if the surface impedance is made to vary as a function of incidence angle in a specific manner. Here we show that a periodic array of planar nanoparticles coupled to a metal film can act as an absorbing metasurface with an angle-dependent impedance. Through a semi-analytical calculation based on coupled-mode theory, we find the perfect absorbing condition is equivalent to balancing the Ohmic and radiative losses of the nanoparticles at normal incidence. Absorption over a wide range of incidence angles can then be obtained by tailoring the scattered far-field pattern of the individual planar nanoparticles such that their radiative losses remain constant. The theory provides a means of understanding the behavior of perfect absorbing structures that have been observed experimentally or numerically, reconciling previously published theories and enabling the optimization of absorbing surfaces.
TL;DR: In this paper, a multistatic imaging system at microwave frequencies based on arrays of planar cavity sub-apertures, or panels, is presented, which produces distinct radiation patterns as a function of frequency.
Abstract: The authors present a multistatic imaging system at microwave frequencies based on arrays of planar cavity sub-apertures, or panels. The cavity imager consists of sets of transmit and receive panels, loaded with radiating irises distributed over the sub-apertures in an aperiodic pattern. This frequency-diverse aperture produces distinct radiation patterns as a function of frequency that encode scene information onto a set of measurements; images are subsequently reconstructed using computational imaging approaches. Similar to previously reported computational imaging systems, the cavity-based imager presents a simple system architecture, minimising the number and expense of components required in traditional microwave imaging systems. The cavity imager builds on previous frequency-diverse approaches, such as the recently reported metamaterial and air-filled cavity systems, by utilising frequency-diverse panels for both the transmit and receive sub-apertures of the imaging system. Though the panel-to-panel architecture has greater sensitivity to calibration error, this implementation nevertheless increases mode diversity and, in the context of a computational imaging system, results in improved image reconstructions.
TL;DR: In this article, the authors present an analysis of a slotted waveguide antenna (SWA) whose directivity has been enhanced by using metamaterial parasitic elements, and apply an adapted form of the discrete dipole approximation (DDA) as a modeling tool and verify the accuracy and versatility of this method for different configurations, including matched and shorted SWAs, with and without parasitic elements.
Abstract: We present an analysis of a slotted waveguide antenna (SWA) whose directivity has been enhanced by using metamaterial parasitic elements. We apply an adapted form of the discrete dipole approximation (DDA) as a modeling tool and verify the accuracy and versatility of this method for different configurations, including matched and shorted SWAs, and with and without parasitic elements. The results presented in this letter demonstrate the capabilities of the DDA for the fast and accurate simulation of aperture antennas composed of small radiators, and its further application for the design of complex metamaterial structures.
TL;DR: The metamaterial element is an electrically-small, complimentary electric-LC (cELC) resonator designed to exhibit large radiated power while maintaining low ohmic losses in a waveguide-fed metasurface antennas.
Abstract: We present a metamaterial element designed as an efficient radiator for waveguide-fed metasurface antennas. The metamaterial element is an electrically-small, complimentary electric-LC (cELC) resonator designed to exhibit large radiated power while maintaining low ohmic losses. The shape of the element is tapered to simultaneously achieve broadband operation and suppression of cross polarization radiation. Full-wave numerical studies at the K-band are conducted to examine its performance when etched into a microstrip line. In this configuration, the element shows a radiation efficiency of 90.2% and a fractional bandwidth of 8.7%. To investigate the potential benefits of the proposed element in two-dimensional platforms, the radiative characteristics of the element are calculated when the element is embedded in a dielectric-filled parallel-plate waveguide. This efficient metamaterial element has potential application as a building block for metasurface devices used in imaging, sensing, wireless power transfer, and wireless communication systems.
TL;DR: In this paper, the authors derived simple analytical expressions to model the electromagnetic response of an electrically large printed cavity, which is then used to develop printed cavities for microwave imaging purposes.
Abstract: We derive simple analytical expressions to model the electromagnetic response of an electrically large printed cavity. The analytical model is then used to develop printed cavities for microwave imaging purposes. The proposed cavity is excited by a cylindrical source and has boundaries formed by subwavelength metallic cylinders (vias) placed at subwavelength distances apart. Given their small size, the electric currents induced on the vias are assumed to have no angular dependence. Applying this approximation simplifies the electromagnetic problem to a matrix equation which can be solved to directly compute the electric current induced on each via. Once the induced currents are known, the electromagnetic field inside the cavity can be computed for every location. We verify the analytical model by comparing its prediction to full-wave simulations. To utilize this cavity in imaging settings, we perforate one side of the printed cavity with radiative slots such that they act as the physical layer of a comput...
TL;DR: Major anatomic resection with lymphadenectomy for pulmonary metastasectomy can be considered in selected CRC patient with sufficient functional reserve to improve the DSS and DFS.
TL;DR: A calibration scheme is proposed that compares the measured versus simulated scattered field from a cylinder and calculates a compensating phase difference to be applied at each of the panels comprising the system, avoiding a more laborious manual calibration step.
Abstract: We demonstrate a technique for calibrating a frequency-diverse, multistatic, computational imaging system. A frequency-diverse aperture enables an image to be reconstructed primarily from a set of scattered field measurements taken over a band of frequencies, avoiding mechanical scanning and active components. Since computational imaging systems crucially rely on the accuracy of a forward model that relates the measured and transmitted fields, deviations of the actual system from that model will rapidly degrade imaging performance. Here, we study the performance of a computational imaging system at microwave frequencies based on a set of frequency-diverse aperture antennas, or panels. We propose a calibration scheme that compares the measured versus simulated scattered field from a cylinder and calculates a compensating phase difference to be applied at each of the panels comprising the system. The calibration of the entire system needs be performed only once, avoiding a more laborious manual calibration step for each transmitting and receiving path. Imaging measurements performed using the system confirm the efficacy and importance of the calibration step.
TL;DR: In this article, the authors evaluate to what extent, flow generation and water storage within shallow, degraded peatland catchments may be controlled by the spatial attributes of the contributing area of the peat land, the drainage ditch size, morphology and geometry.
TL;DR: This work demonstrates the viability of the resonant metamaterial approach with a single layer, co-polarized holographic metasurface that produces an image at millimeter wavelengths (92.5 GHz) despite the elements' limited phase range and coupled amplitude dependency.
Abstract: Holographic optics are an essential tool for the control of light, generating highly complex and tailored light field distributions that can represent physical objects or abstract information. Conceptually, a hologram is a region of space in which an arbitrary phase shift and amplitude variation are added to an incident reference wave at every spatial location, such that the reference wave will produce a desired field distribution as it scatters from the medium. Practical holograms are composed of materials, however, which have limited properties that constrain the possible field distributions. Here, we show it is possible to produce a hologram with continuous phase distribution and a non-uniform amplitude variation at every point by leveraging resonant metamaterial elements and constraining the hologram’s pixels to match the elements’ resonant behavior. We demonstrate the viability of the resonant metamaterial approach with a single layer, co-polarized holographic metasurface that produces an image at millimeter wavelengths (92.5 GHz) despite the elements’ limited phase range and coupled amplitude dependency.
TL;DR: In this article, the authors investigated how vegetation composition and CO2 fluxes vary spatially in response to the pattern of drainage features in Molinia caerulea-dominated peatlands.
Abstract: Peatlands are recognized as important carbon stores; despite this, many have been drained for agricultural improvement. Drainage has been shown to lower water tables and alter vegetation composition, modifying primary productivity and decomposition, potentially initiating peat loss. To quantify CO2 fluxes across whole landscapes, it is vital to understand how vegetation composition and CO2 fluxes vary spatially in response to the pattern of drainage features. However, Molinia caerulea-dominated peatlands are poorly understood despite their widespread extent.
Photosynthesis (PG600) and ecosystem respiration (REco) were modelled (12 °C, 600 µmol photons m−2 s−1, greenness excess index of 60) using empirically derived parameters based on closed-chamber measurements collected over a growing season. Partitioned below-ground fluxes were also collected. Plots were arranged ⅛, ¼ and ½ the distance between adjacent ditches in two catchments located in Exmoor National Park, southwest England.
Water table depths were deepest closest to the ditch and non-significantly (p = 0·197) shallower further away. Non-Molinia species coverage and the Simpson diversity index significantly decreased with water table depth (p < 0·024) and increased non-significantly (p < 0·083) away from the ditch. No CO2 fluxes showed significant spatial distribution in response to drainage ditches, arguably due to insignificant spatial distribution of water tables and vegetation composition. Whilst REco showed no significant spatial variation, PG600 varied significantly between sites (p = 0·012), thereby controlling the spatial distribution of net ecosystem exchange between sites. As PG600 significantly co-varied with water table depths (p = 0·034), determining the spatial distribution of water table depths may enable CO2 fluxes to be estimated across M. caerulea-dominated landscapes. © 2015 The Authors. Ecohydrology published by John Wiley & Sons, Ltd.
TL;DR: In this article, the authors considered a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region.
Abstract: Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function (PSF). Near-zone focusing can be achieved by generating different amplitude or phase profiles over the aperture, which can be realized using traditional architectures, such as phased arrays. Alternatively, metasurface guided-wave apertures can achieve dynamic focusing, with potentially lower cost implementations. We present an initial tradeoff analysis of the near-zone WPT concept, relating key parameters such as spot size, aperture size, wavelength, focal distance, and availability of sources. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed using numerical calculations.
TL;DR: A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval, and a comparison of the estimated images from both complex valued and phaseless measurements is presented, verifying the fidelity of Phaseless computational imaging.
Abstract: Computational imaging modalities support a simplification of the active architectures required in an imaging system and these approaches have been validated across the electromagnetic spectrum. Recent implementations have utilized pseudo-orthogonal radiation patterns to illuminate an object of interest---notably, frequency-diverse metasurfaces have been exploited as fast and low-cost alternative to conventional coherent imaging systems. However, accurately measuring the complex-valued signals in the frequency domain can be burdensome, particularly for sub-centimeter wavelengths. Here, computational imaging is studied under the relaxed constraint of intensity-only measurements. A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval. In this paper, the methodology associated with this novel principle is described, studied, and experimentally demonstrated in the microwave range. A comparison of the estimated images from both complex valued and phaseless measurements are presented, verifying the fidelity of phaseless computational imaging.
TL;DR: This paper proposes and investigates a single hybrid FSO/RF antenna that could be used in high-speed access networks, and outlines the design procedures based on the concept of Cassegrain antenna, and shows how the FSO transceiver is incorporated into the original design.
Abstract: The concept of hybrid free space optical/radio frequency (FSO/RF) communications has been considered for the last mile access network applications. The existing schemes mostly use two separate transceiver antennas for outdoor terrestrial links of few kilometres long. In this paper, we propose and investigate a single hybrid FSO/RF antenna that could be used in high-speed access networks. We outline the design procedures based on the concept of Cassegrain antenna, and show how the FSO transceiver is incorporated into the original design. The proposed antenna is fabricated and extensive measurements are carried out for the radiation pattern, return loss, RF signal-to-noise ratio and the FSO received power. By performing link budget analysis and the results obtained from experiments, we demonstrate the operation of proposed hybrid antenna with 1 × 3 single-input multiple-output configuration and an equal gain combining at the receiver under moderate regime turbulence regime.
TL;DR: The aim of Moosh is to provide a complete set of tools to compute all the optical properties of any multilayered structure: reflection, transmission, absorption spectra, as well as gaussian beam propagation or guided modes.
Abstract: The aim of Moosh is to provide a complete set of tools to compute all the optical properties of any multilayered structure: reflection, transmission, absorption spectra, as well as gaussian beam propagation or guided modes. It can be seen as a semi-analytic (making it light and fast) solver for Maxwell’s equations in multilayers. It is written in Octave/Matlab, available on Github and based on scattering matrices, making it perfectly stable. This software is meant to be extremely easy to (re)use, and could prove useful in many research areas like photovoltaics, plasmonics and nanophotonics, as well as for educational purposes for the large number of physical phenomena it can illustrate.
TL;DR: In this paper, a novel 3D imaging system is conceived based on "phaseless" and compressed measurements, with benefits from recent advances in the field of phase retrieval, which is described, studied, and experimentally demonstrated in the microwave range.
Abstract: Computational imaging modalities support a simplification of the active architectures required in an imaging system and these approaches have been validated across the electromagnetic spectrum. Recent implementations have utilized pseudo-orthogonal radiation patterns to illuminate an object of interest-notably, frequency-diverse metasurfaces have been exploited as fast and low-cost alternative to conventional coherent imaging systems. However, accurately measuring the complex-valued signals in the frequency domain can be burdensome, particularly for sub-centimeter wavelengths. Here, computational imaging is studied under the relaxed constraint of intensity-only measurements. A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval. In this paper, the methodology associated with this novel principle is described, studied, and experimentally demonstrated in the microwave range. A comparison of the estimated images from both complex valued and phaseless measurements are presented, verifying the fidelity of phaseless computational imaging.
10 Apr 2016
TL;DR: A metal waveguide feed chain in a Ku-band scanning lens array antenna comprises five parts: two iris polarisers, two bend-feeds, and a central power combiner.
Abstract: A metal waveguide feed chain in a Ku-band scanning lens array antenna comprises 5 parts. These are: two iris polarisers, two bend-feeds, and a central power combiner. The combiner comprises a pair of septum polarisers and tee junctions. The feed chain generates a controllable, linear polarised E-field at each of two hemispherical lenses. Additive manufacturing was used to produce a copy of the power combiner and each bend-feed in copper plated plastic. In satellite receive-only trials at 10.7–12 GHz the plastic parts and metal parts performed equivalently.
TL;DR: In this article, the authors show that arrays of very narrow and shallow metallic slits have an optical response that is influenced by the spatial dispersion in metals arising from the repulsive interaction between electrons.
Abstract: In the framework of the hydrodynamic model describing the response of electrons in a metal, we show that arrays of very narrow and shallow metallic slits have an optical response that is influenced by the spatial dispersion in metals arising from the repulsive interaction between electrons. As a simple Fabry-Perot model is not accurate enough to describe the structure's behavior, we propose to consider the slits as generalized cavities with two modes, one being propagative and the other evanescent. This very general model allows to conclude that the impact of spatial dispersion on the propagative mode is the key factor explaining why the whole structure is sensitive to spatial dispersion. As the fabrication of such structures with relatively large gaps compared to previous experiments is within our reach, this work paves the way for future much needed experiments on nonlocality.
TL;DR: The correlation was very accurate in patients with single radiologic nodules, however, half of the patients with more nodules showed discrepancies, and the two independent predictors of discordance between computed tomography and the number of pathologic metastases were the bilateral involvement and thenumber of radiologic nods.
05 May 2016
TL;DR: In this article, a volumetric approach is proposed to control the wake in a stationary flow past cylindrical and spherical objects, coupled with rigid, fluid-permeable structures prescribed by a macroscopic design approach.
Abstract: Wake reduction is a crucial link in the chain leading to undetectable watercraft. Here, we explore a volumetric approach to controlling the wake in a stationary flow past cylindrical and spherical objects. In this approach, these objects are coupled with rigid, fluid-permeable structures prescribed by a macroscopic design approach where all solid boundaries are parameterized and modeled explicitly. Local, gradient-based optimization is employed which permits topological changes in the manifold describing the composite solid component(s) while still allowing the use of adjoint optimization methods. This formalism works below small Reynolds number (Re) turbulent flow (–10,000) when simulated using small Reynolds-averaged Navier-Stokes (RANS) models. The output of this topology optimization yields geometries that can be fabricated immediately using fused deposition modeling (FDM). Our prototypes have been verified in an experimental water tunnel facility, where the use of Particle Image Velocimetry (PIV) described the velocity profile. Comparisons with our computational models show excellent agreement for the spherical shapes and reasonable match for cylindrical shapes, with well-understood sources of error. Two important figures of merit are considered: domain-wide wake (DWW) and maximum local wake (MLW), metrics of the flow field disturbance whose definitions are described.
01 Nov 2016
TL;DR: In this paper, a meshed patch antenna for two-way satellite internet and TV applications at remote areas, covering the communications frequency range from 11.7GHz to 12.22GHz (downlink) and 14.0GHz to 14.5GHz (uplink) bands allocated by the ITU to the Regions 1 and 2.
Abstract: In this paper, a design of broadband compact microstrip meshed patch antenna integrated with solar cells for Ku-band satellite applications is presented. A Plexiglas transparent substrate is also employed to enable the light to pass through with high efficiency to illuminate the solar panel cells while the RF performance is maintained with minimal degradation. This meshed patch antenna for two-way satellite internet and TV applications at remote areas, covering the communications frequency range from 11.7GHz to 12.22GHz (downlink) and 14.0GHz to 14.5GHz (uplink) bands allocated by the ITU to the Regions 1 and 2. The effect of replacing the solid elements of a microwave suspended patch antenna with meshed element is examined. A compact flat meshed element is obtained and simulated in CST Microwave Studio and achieved the broadband width of 500 MHz in both portions and the nominal element gain is 7.47dBi downlink and 8.51 dBi uplink, suffering only by 0.23 dBi and 0.14 dBi respectively, comparing to the original suspended solid patch antenna design. The visible light transmission is found at normal incidence and an oblique angle to be approximately 87% and 80%, respectively.