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Both multilayered (ML) and few-layered (FL) Ti3C2Tx nanosheets have been prepared through a typical etching and delaminating procedure. Various characterizations confirm that the dominant terminal groups on ML-Ti3C2Tx and FL-Ti3C2Tx are different, which have been assigned to O-related and hydroxyl groups, respectively. Such deviation of the dominant terminals results in the different physical and chemical performance and eventually makes the nanosheets have different potential applications. In particular, before coupling to Ag nanoparticles, ML-Ti3C2Tx can present stronger near-field enhancement effect; however, Ag/FL-Ti3C2Tx hybrid structure can confine stronger near-field due to the electron injection, which can be offered by the terminated hydroxyl groups. [ABSTRACT FROM AUTHOR]

Regarding wave scattering on a three-dimensional nonspherical obstacle, the Rayleigh hypothesis states that the scattered field can be expanded everywhere outside the obstacle using only outgoing eigensolutions of the underlying Helmholtz equation. However, the correctness of this assumption has not yet been finally clarified, although it is important for the near-field analysis of scattering processes and for multiple scattering. To circumvent this uncertainty, Waterman introduced the extended boundary condition to develop his T-matrix method. This approach leads to the restriction that, when modeling multiple scattering processes using this T-matrix, the smallest circumscribing spheres of the individual obstacles must not overlap. The purpose of this paper is to provide a justification of the correctness of Rayleigh's hypothesis and clarify its implications for modeling multiple scattering. We show that Waterman's T-matrix can in fact be used inside the critical region between the surface of the obstacle and its smallest circumscribing sphere to represent the near-field and that one does not necessarily have to exclude an overlap of these spheres in the multiple scattering modeling. The theoretical considerations in the first part of this paper are supplemented by a numerical study of a benchmark configuration for multiple scattering in the last part. [ABSTRACT FROM AUTHOR]

This article proposes and analyzes two possible methods to compensate the raw near-field data obtained with an array of near-field probes. The first method is based on the spatial compensation procedure for a single probe and is modified toward an array of probes. The second method is to use standard spectral (plane wave) single-probe compensation. To use the latter, guidelines on how to design an array and modify the overall measurement procedure such that mutual coupling and edge effects have less influence are given. The different methods are tested in simulation and compared with the performance of compensation on a single probe. It is shown that the standard spectral single-probe compensation, in combination with proper array design, will result in an error as low as the same compensation technique used on a single probe. It is also shown that the spatial compensation improves the results in comparison with regular calibration. However, the error is not low enough to be used for postprocessing due to ill-conditioning. This article shows the path to much needed, fast, and accurate near-field measurements. [ABSTRACT FROM AUTHOR]

We propose a thermal modulation structure made of two identical SiO2 slabs coated by Dirac semimetal (DSM) films and separated by a nanoscale vacuum gap. The energy transmission probability reveals that the coupled surface plasmon polaritons (SPPs) between the two DSM films, and the surface phonon polaritons (SPhPs) supported by the SiO2 substrate can vary sensitively with the Fermi level, the degenerate factor of 3D Dirac points and the thickness of the DSM film, thus providing the possibilities for modulating the radiative heat transfer by tuning these parameters. Based on Maxwell's equations incorporating fluctuational electrodynamics, the effects of these parameters on the heat transfer coefficient and the thermal modulation contrast are numerically analyzed. Under proper parameters, higher modulation contrasts are obtained by continuously tuning the Fermi level from 0.05 eV to 0.3 eV. The obtained results might be helpful in designing a DSM-based thermal modulator with higher modulation contrasts. [ABSTRACT FROM AUTHOR]

Investigation of the near field dynamics of a single and tandem array of three jets are provided by 2-D time-resolved particle image velocimetry (TR-PIV) measurements. Instantaneous velocity fields are examined in the transverse and spanwise planes with jet to crossflow velocity ratios in the range from 0.9 to 1.7. Previous studies have shown that for high ratios (≥ 2), the leading jet provides sufficient shielding to ensure that all jets downstream exhibit nearly identical flow characteristics. The current transverse plane measurements exhibit more unique and localized features as a result of the competing effects of pressure gradients and vortex mechanisms assessed via the jet exit profiles, first and second order turbulent statistics, streamline trajectories, recirculation areas and penetrations depths. Proper orthogonal decomposition (POD) is applied to the spanwise plane instantaneous velocity fields to determine the statistically dominant features of the single and tandem jet configurations at equivalent velocity ratios. The velocity fields are then reconstructed using the truncated POD modes to provide further insight into the shear layer and wake vortices that drive these configurations. Vortex identification algorithms are applied to the reconstructed velocity fields to determine the statistical characteristics of the vortices, including their centroids, populations, areas and strengths, each of which exhibit largely different dependencies on jet configuration and velocity ratio. Several of the investigated metrics are found to exhibit different behaviors below and above a velocity ratio of unity and also as a function of increasing velocity ratio between 1 and 2, implying that several transitions mechanisms are present in the low velocity ratio regime investigated herein. [ABSTRACT FROM AUTHOR]

We study how nanophotonic structures can be used for determining the position of a nearby nanoscale object with subwavelength accuracy. Through perturbing the near-field environment of a metasurface transducer consisting of nano-apertures in a metallic film, the location of the nanoscale object is transduced into the transducer's far-field optical response. By monitoring the scattering pattern of the nanophotonic near-field transducer and comparing it to measured reference data, we demonstrate the two-dimensional localization of the object accurate to 24 nm across an area of 2 × 2 μm. We find that adding complexity to the nanophotonic transducer allows localization over a larger area while maintaining resolution, as it enables encoding more information on the position of the object in the transducer's far-field response. [ABSTRACT FROM AUTHOR]

We investigate the control mechanisms of the deep Pacific Ocean circulation by introducing updated methods for parameterizing tidal mixing. The column-integrated rates of dissipation in near- and far-fields are derived from the tidal energy conversion and dissipation rates estimated by a high resolution tide model. In the calculation of the far-field mixing, its dependency on stratification is taken into account based on theoretical and observational knowledge. Unlike previous studies that did not take the stratification dependence into account, the far-field mixing does not function to significantly enhance the deep Pacific Ocean circulation. The deep Pacific Ocean circulation is also found to be insensitive to the decay scale height of the near-field mixing. However, these factors affect the reproducibility of the radiocarbon distribution, especially its minimum in the upper deep layer, through their influence on the mixing with the shallower layers. [ABSTRACT FROM AUTHOR]

Excitation of novel graphene plasmons is examined using finite-element analysis via COMSOL RF module 5.6. The theoretical model is simulated with graphene grating on the glass substrate having fixed periodicity (Λ = 700 nm) by illumination with transverse magnetic (TM) polarized light through the substrate side. The effect of thickness variation on SPPs excitation has been acquired from transmission spectra while keeping the periodicity and slit width of grating structure constant via analyzing the trend followed by the resonance dips. The electric and magnetic field behavior has also been analyzed for each thickness, and a specific grating thickness of 10 nm was taken into consideration owing to the thickness constraints regarding graphene. Slit width variation of the grating structure has been investigated using far-field analysis to observe the formation of SPPs from transmission spectra and near-field analysis for understanding the underlying physics. These analyses resulted in SPP excitation more appreciable at slit widths in between 250 and 350 nm. The slit width range regarding the chosen periodicity supports the most efficient plasmonics mode and many applications of such devices are found in real life. [ABSTRACT FROM AUTHOR]

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This study investigates the transitional wake dynamics of a simultaneously pitching– heaving airfoil in the low Reynolds number regime. The transition from Kármán to reverse Kármán wakes and the subsequent wake deflection are known to take place entirely in the periodic regime as the dynamic heave velocity $\kappa h$ (proportionally, the amplitude-based Strouhal number $St_A$) is gradually increased. However, further increase in $\kappa h$ may result in the loss of dynamic stability of the deflected vortex street and an eventual transition to chaos. This phenomenon has largely remained unexplored in the existing literature. The present study attempts to fill this gap and aims to establish a dynamic link between the near- and far-field wake transitions. It is shown that the deflected jet undergoes a switching of deflection direction in the far-field as the near-field encounters a quasi-periodic transition with the increase in $\kappa h$. The quasi-periodic behaviour of the near-field is seen to get interspersed with intermittent aperiodic windows, resulting in a complete reversal of the deflection direction through flipping of the immediate vortex couple. Eventually, the wake topology becomes fully chaotic through a series of rapid aperiodic jet-switching. To the best of the authors' knowledge, this is the first study that investigates the role of this aperiodic jet-switching in ushering in chaos in the wake of a pitch–heave flapping system. The mechanism of jet-switching and the role of leading-edge vortex are also revealed. Flow field dynamics during these changes and the underlying vortex interactions are analysed using nonlinear dynamical tools. [ABSTRACT FROM AUTHOR]

• A multijunction thermophotovoltaic coupled with near-field radiation is proposed. • Hyperbolic metamaterial and surface coating are used to improve near-field radiation. • The new thermophotovoltaic system can achieve a conversion efficiency of 45.26%. A multi-junction thermophotovoltaic system based on near-field radiation and hyperbolic metamaterial was developed. The multilayer near-field system is studied through the fluctuational electrodynamics based on dyadic Green's function and a recursive calculation model, whereas the external quantum efficiency, open-circuit voltage and fill factor are considered to evaluate the performance of the photovoltaic cell. The system expands the available spectrum to 1720–3650 nm so that more photons can be recovered. The near-field radiative transfer is further improved owing to the infinite wavevector in the hyperbolic metamaterial. The results demonstrate that the multi-junction system generates 4.7236 × 106 W/m2 of electricity with a conversion efficiency of 45.26%, achieving 1.3 times (2.38 times) more electricity with 15.3% (25.95%) higher conversion efficiency than the single InGaAsSb (InAs) cell. The study further improves the performance of the multi-junction thermophotovoltaic and paves the way to design a more efficient near-field multi-junction thermophotovoltaic system. [ABSTRACT FROM AUTHOR]

The near and far fields of traditional loudspeakers are differentiated by whether the sound pressure amplitude is inversely proportional to the propagating distance. However, the audio sound field generated by a parametric array loudspeaker (PAL) is more complicated, and in this article it is proposed to be divided into three regions: near field, Westervelt far field, and inverse-law far field. In the near field, the audio sound experiences strong local effects and an efficient quasilinear solution is presented. In the Westervelt far field, local effects are negligible so that the Westervelt equation is used, and in the inverse-law far field, a simpler solution is adopted. It is found that the boundary between the near and Westervelt far fields for audio sound lies at approximately a2/λ – λ/4, where a is transducer radius and λ is ultrasonic wavelength. At large transducer radii and high ultrasonic frequencies, the boundary moves close to the PAL and can be estimated by a closed-form formula. The inverse-law holds for audio sound in the inverse-law far field and is more than 10 meters away from the PAL in most cases. With the proposed classification, it is convenient to apply appropriate prediction models to different regions. [ABSTRACT FROM AUTHOR]

The effect of delta-tabs with its apex leaning downstream on the jet mixing characteristics of a Mach 1.5 elliptic jet of aspect ratio (AR) 3.37 is reported in this paper. The delta-tabs were placed along the minor and major axes of the elliptic nozzle, referred to as tab configuration C1 and C2, respectively. For each tab configuration, four different orientation angles varying from θ = 90∘ to 150∘ were studied, where θ = 90∘ is the tab positioned normal to the nozzle exit and θ = 150∘ is the tab oriented in the downstream direction at the nozzle exit. The tab effects on jet manipulation were investigated via shadowgraph visualization, and the mean Pitot pressure was measured along the jet centerline and along the orthogonal planes of the jet. The non-dimensonalized supersonic core length L c * , average shock-cell spacing L s ¯ * , and the axis-switching location x a s * were examined in detail to understand the jet characteristics of the natural and manipulated jets. The mixing capability of the manipulated jets quantified based on the reduction in supersonic core length Δ L c * depends strongly on the ideally expanded jet Mach number Mj, tab configuration (C1 and C2), and θ. As such, the Δ L c * for the manipulated jet at θ = 135∘ is the largest, revealing the optimal tab orientation for jet mixing enhancement, as also observed for the circular jet [Zaman et al., "Control of an axisymmetric jet using vortex generators," Phys. Fluids 6(2), 778–793 (1994)]. The relationship between Δ L c * and Δ L s * is presented to understand the correlation between the jet mixing and noise characteristics of the manipulated jet. Discussion is conducted based on the dependence of Δ L c * and Δ L s * with θ, which provides useful insight into the jet flow physics. With suitable placement of tabs C1 and C2, the axis switching could be either stopped or augmented. The superior mixing characteristics of an elliptic jet relative to a circular jet, which were found in previous works on the supersonic over-expanded jet [Kumar and Rathakrishnan, "Characteristics of a supersonic elliptic jet," Aeronaut. J. 120(1225), 495 (2016)] prevail in the supersonic jet under-expanded jet as well. [ABSTRACT FROM AUTHOR]

The optical properties of a simple metallic nanomatryushka (nanosphere-in-a-nanoshell) with gain have been investigated theoretically. The spaser (surface plasmon amplification by stimulated emission of radiation) phenomena can be observed at two critical wavelengths in the active metallic nanomatryushkas. With increasing the gain coefficient of the middle layer, a similar super surface plasmon (SP) resonance is first found at the ω-+∣1 mode of the active nanoparticles and then breaks down. With further increasing the gain coefficient, another similar super-resonance occurs at the ω--∣1 mode. The near-field enhancements in the active nanomatryushkas also have been greatly amplified at the critical wavelengths for ω-+∣1 and ω--∣1 modes. It is further found that the amplifications of SPs in the active Ag-SiO2-Au nanoshell are strongest in four kinds of nanoshells and hence the largest near fields. The giant near-field enhancement can greatly enhance the Raman excitation and emission. [ABSTRACT FROM AUTHOR]

We show that the maximum work that can be obtained from the thermal radiation emitted between two planar sources in the near-field regime is much larger than that corresponding to the blackbody limit. This quantity, as well as an upper bound, for the efficiency of the process is computed from the formulation of thermodynamics in the near-field regime. The case when the difference of temperatures of the hot source and the environment is small, relevant for energy harvesting, is studied in detail. We also show that thermal radiation energy conversion can be more efficient in the near-field regime. These results open new possibilities for the design of energy converters that can be used to harvest energy from sources of moderate temperature at the nanoscale. [ABSTRACT FROM AUTHOR]

We provide an analytical solution for studying the near-field optical effect of a core-shell nanostructure in proximity to a flat surface, within quasi-static approximation. The distribution of electrostatic potential and the field enhancement in this complex geometry are obtained by solving a set of linear equations. This analytical result can be applied to a wide range of systems associated with near-field optics and surface plasmon polaritons. To illustrate the power of this technique, we study the field-attenuation effect of an oxidized shell in a silver tip in a near-field scanning microscope. The thickness of oxidized layer can be monitored by measuring the intensity of light. We also find a linear relation between resonant frequency and temperature in an Ag–Au core-shell structure, which provides insight for local temperature detection with nm scale resolution. Our results also show good agreement with recent finite element method results. [ABSTRACT FROM AUTHOR]

Near-field plates consist of non-periodically patterned surfaces that can overcome the diffraction limit and confine electromagnetic fields to subwavelength dimensions. Previous near-field plates experimentally demonstrated extreme field tailoring capabilities. However, their performance suffered from radiation/reflection in undesired directions, those other than the subwavelength focus. This issue can limit the practical use of near-field plates. In this paper, we address this issue by designing a unidirectional near-field plate that can form a subwavelength focal pattern, while suppressing the field radiated/reflected in other directions. The design and operation of the proposed unidirectional near-field plate are verified through full-wave simulation. The unidirectional nearfield plate may find application in high resolution imaging and probing, high density data storage, and wireless power transfer systems. As an example, its utility as a high resolution probe is demonstrated through full-wave electromagnetic simulation. [ABSTRACT FROM AUTHOR]

Bianisotropic metasurfaces have enabled highly efficient wavefront transformation. However, a passive and lossless bianisotropic metasurface must conserve local power at every point over the metasurface, hindering its application in handling complicated wavefields other than plane waves. In this paper, the power flow-conformal design methodology and bianisotropic unit cells are combined to comply with such a restriction. Our proposed approach provides a general recipe for arbitrary wavefront transformation with maximum power efficiency. As a demonstration, a transmission-type acoustic metasurface was designed to focus 3000 Hz plane wave airborne sound in the near field with theoretically unitary power efficiency. The metasurface was validated by both numerical simulation and experiment. [ABSTRACT FROM AUTHOR]

The chiral metasurface possesses wide applications in terahertz (THz) band. It is still an important issue to control the chiral properties of metasuface by a simple and effective method. We design a reflective chiral THz metasurface that reflection medium in bottom is based on monolayer graphene on low resistance Si substrate. This structure allows a more reasonable approach to tune Fermi level (E F) of graphene compared with previous report. THz reflection change in graphene as varying E F can control in a large dynamic range the chiral properties of metasurface, inducing the state switch between 'On' and 'Off'. The dynamic control is also effective for various further applications such as vortex focusing and near field imaging. Significantly, we report for the first time the variation rule of reflection amplitude for reflecting suppressed circularly polarized light, with the change in rotation angle of top metal ring of metasurface. Based on this, we develop an innovation application, called full grayscale near field imaging (FGNFI) that can show full grayscale details compared with traditional near field imaging that can only show two grayscale states. Image 1 We propose a new structure that using monolayer graphene on surface of low resistivity silicon substrate acts as a reflection medium in reflective chiral terahertz metasurface. When bias voltage is applied between graphene and silicon, electrons and holes in silicon can be injected into graphene to tune the chirality between 'On' and 'Off' states. An innovation near field imaging application is developed by using the regular amplitude change of reflection suppressed circular polarization with metal ring rotation. The new application we developed can theoretically achieve the imaging with a series of grayscale values between the brightest to the dimmest states, which give more color details and thus is called full grayscale near field imaging (FGNFI). The tunable chirality 'On' and 'Off' can be used not only for traditional applications, but also for our newly developed FGNFI application. • A new graphene tuned recflective chiral terahertz metasurface is proposed. • Monolayer graphene on surface of low resistivity Si acts as a reflection medium. • Appling voltage between graphene and Si obtains the chirality On and Off states. • New application called full grayscale near field imaging (FGNFI) is developed. • FGNFI can achieve full grayscale details. [ABSTRACT FROM AUTHOR]

Anapole modes of all-dielectric nanostructures hold great promise for many nanophotonic applications. However, anapole modes can hardly couple to other modes through far-field interactions, and their near-field enhancements are dispersed widely inside the nanostructures. These facts bring challenges to the further increasing of the response of an anapole mode. Here, we theoretically show that an anapole mode response in a dielectric nanostructure can be boosted through electromagnetic interactions with the coupling distance of a wavelength scale, which is beyond both the near-field and far-field limits. The all-dielectric nanostructure consists of a disk holding an anapole mode and a ring. Both analytical calculations and numerical simulations are carried out to investigate the electromagnetic interactions in the system. It is found that the electric dipoles associated with the fields of the anapole mode on the disk undergo retardation-related interactions with the electric dipoles associated with the ring, leading to the efficiently enhanced response of the anapole mode. The corresponding near field enhancement on the disk can reaches more than 90 times for a slotted silicon disk-ring nanostructure, where the width of the slot is 10 nm. This enhancement is about 5 times larger than that of an individual slotted disk. Our results reveal the greatly enhanced anapole mode through electromagnetic couplings in all-dielectric nanostructures, and the corresponding large field enhancement could find important applications for enhanced nonlinear photonics, near-field enhanced spectroscopies, and strong photon–exciton couplings. [ABSTRACT FROM AUTHOR]

The near-field coupling between closely placed metallic structures has been utilized to cope with the dilemma of a normal-mode helical antenna (NMHA) design. For small NMHAs, the impedance-matching difficulty is mitigated by designing appropriated coupling feeds, either electrically or magnetically. For long NMHAs, the radiation pattern distortion is rectified by dividing the complete helix into properly designed small sections. With mutual section coupling, the currents on all of the sections can be nearly in-phase, dictating an omnidirectional radiation pattern. The design principle has been described as twoelement models and a corresponding equivalent circuit analysis. The simulated and measured results show that, compared to conventional NMHAs, it is possible to design an NMHA of simultaneous good matching and radiation properties but with a much more flexible helix length and size. [ABSTRACT FROM AUTHOR]

Background: Networks of tower-based CO2 mole fraction sensors have been deployed by various groups in and around cities across the world to quantify anthropogenic CO2 emissions from metropolitan areas. A critical aspect in these approaches is the separation of atmospheric signatures from distant sources and sinks (i.e., the background) from local emissions and biogenic fluxes. We examined CO2 enhancements compared to forested and agricultural background towers in Indianapolis, Indiana, USA, as a function of season and compared them to modeled results, as a part of the Indianapolis Flux (INFLUX) project. Results: At the INFLUX urban tower sites, daytime growing season enhancement on a monthly timescale was up to 4.3–6.5 ppm, 2.6 times as large as those in the dormant season, on average. The enhancement differed significantly depending on choice of background and time of year, being 2.8 ppm higher in June and 1.8 ppm lower in August using a forested background tower compared to an agricultural background tower. A prediction based on land cover and observed CO2 fluxes showed that differences in phenology and drawdown intensities drove measured differences in enhancements. Forward modelled CO2 enhancements using fossil fuel and biogenic fluxes indicated growing season model-data mismatch of 1.1 ± 1.7 ppm for the agricultural background and 2.1 ± 0.5 ppm for the forested background, corresponding to 25–29% of the modelled CO2 enhancements. The model-data total CO2 mismatch during the dormant season was low, − 0.1 ± 0.5 ppm. Conclusions: Because growing season biogenic fluxes at the background towers are large, the urban enhancements must be disentangled from the biogenic signal, and growing season increases in CO2 enhancement could be misinterpreted as increased anthropogenic fluxes if the background ecosystem CO2 drawdown is not considered. The magnitude and timing of enhancements depend on the land cover type and net fluxes surrounding each background tower, so a simple box model is not appropriate for interpretation of these data. Quantification of the seasonality and magnitude of the biological fluxes in the study region using high-resolution and detailed biogenic models is necessary for the interpretation of tower-based urban CO2 networks for cities with significant vegetation. [ABSTRACT FROM AUTHOR]

Plasmonic nanoantennas have been widely explored for boosting up light-matter interactions due to their ability of providing strongly confined and highly enhanced electric near fields, so called 'hot-spots'. Here, we propose a dielectric-loading approach for hot-spots engineering by coating the conventional plasmonic nanoantennas with a conformal high refractive index dielectric film and forming dielectric-loaded plasmonic nanoantennas. Compared to the conventional plasmonic nanoantennas, the corresponding dielectric-loaded ones that resonate at the same frequency are able to provide an extra enhancement in the local electric fields and meanwhile spatially transfer the hot spots to the dielectric surfaces. These findings have important implications for the design of optical nanoantennas with general applications in surface enhanced linear and nonlinear spectroscopies. As a demonstration application, we show that the maximum achievable fluorescence intensity in the dielectric-loaded plasmonic nanoantennas could be significantly larger than that in the conventional plasmonic nanoantennas. [ABSTRACT FROM AUTHOR]

Near-field engineering is considered a significant strategy in constructing plasmonic nanostructures for efficient plasmonic chemistry. We demonstrate interfacial near-field engineering on a Au-NP/TiO2/Au-film (ATA) photoanode to improve the water oxidation efficiency. To tailor the near-field distribution, postdeposited Au on an ATA electrode (Au@ATA) is implemented using a facile constant potential electrolysis technique. As a result, the average photocurrent conversion efficiency of Au@ATA is approximately 1.3-fold higher than that of ATA. [ABSTRACT FROM AUTHOR]

Conventionally, mixed near-field (NF) and far-field (FF) source localization is performed using a symmetric uniform linear array (ULA). Recently, two symmetric nonuniform linear arrays (NLAs), symmetric nested array (SNA) and compressed SNA (CSNA), have been developed to enhance the positioning performance by their advantages in the degrees of freedom and the array aperture over symmetric ULAs. In this article, we devise a new symmetric NLA, termed symmetric displaced coprime array (SDCA), to locate the NF and FF sources simultaneously. The SDCA configuration consists of three sparse ULAs with a certain displacement, implying there are two displaced coprime arrays with one common subarray. For a given number of sensors, the SDCA configuration is solely determined by a closed-form expression and its consecutive coarray ranges can also be analytically computed. In addition, we derive two optimum SDCA configurations by maximizing the number of the unique and consecutive lags in the difference coarray. Compared with the SNA and the CSNA, the SDCA provides more unique and consecutive virtual sensors, as well as a larger physical array aperture. Numerical experiments are presented to verify the superiorities of the SDCA configuration over the existing symmetric NLAs. [ABSTRACT FROM AUTHOR]

The direct numerical simulation of the acoustic wave scattering created by very small obstacles is very expensive, especially in three dimensions and even more so in time domain. The use of asymptotic models is very efficient and the purpose of this work is to provide a rigorous justification of a new asymptotic model for low-cost numerical simulations. This model is based on asymptotic near-field and far-field developments that are then matched by a key procedure that we describe and demonstrate. We show that it is enough to focus on the regular part of the wave field to rigorously establish the complete asymptotic expansion. For that purpose, we provide an error estimate which is set in the whole space, including the transition region separating the near-field from the far-field area. The proof of convergence is established through Kondratiev's seminal work on the Laplace equation and involves the Mellin transform. Numerical experiments including multiple scattering illustrate the efficiency of the resulting numerical method by delivering some comparisons with solutions computed with a finite element software. [ABSTRACT FROM AUTHOR]

Featured Application: In-line implementation of microwave nondestructive testing and evaluation (MNDT&E) based on continuous wave radar operating in monostatic mode. A free-space microwave nondestructive testing and evaluation module is developed for the low-power, non-ionizing, contactless, and real-time characterization of doped composite thin-film materials in an industrial context. The instrumentation proposed is built up with a handled vector network analyzer interfaced with corrugated horn antennas to measure the near-field complex reflection S11 of planar prepreg composite materials in a roll-to-roll in-line production line. Dedicated modeling and calibrations routines are developed to extract the microwave conductivity from the measured microwave signal. Practical extraction of the radiofrequency (RF) conductivity of thin film prepreg composite materials doped with nano-powders is exemplary shown at the test frequency of 10 GHz. [ABSTRACT FROM AUTHOR]

Empirical methods are commonly employed to predict the PGA distribution of an earthquake and are widely used. However, current empirical methods assume the seismic source to be a point source, a line source, or a plane source, where the energy is concentrated and released uniformly. An empirical attenuation model of the near-field peak ground acceleration (PGA) was proposed that considers a nonuniform spatial distribution of seismic fault energy and its 3D scale. Then, this model was used to reconstruct the PGA distribution of the 2008 Wenchuan, China, Mw7.9 earthquake based on the data of a seismic fault model and ground acceleration records of the mainshock and aftershocks collected by seismic stations. The predicted PGA values show similar attenuation characteristics to the interpolated map of the PGA recorded by seismic stations. A comparison with the results of a finite-fault model developed by the USGS indicates that the proposed model can provide more details and give a more precise result in the near field. The analysis of landslides triggered by the Wenchuan earthquake demonstrates that the PGA distribution estimated by this model can be used to validate the findings of other researchers. [ABSTRACT FROM AUTHOR]

Central Chile is exposed to tsunami hazard, and large earthquakes and tsunamis have occurred over the last 500 years. Tsunami hazard analysis in Chile has been traditionally implemented by means of a deterministic approach, which is based on historical events and uniform slip distribution. The objective of the present study is to improve tsunami hazard analysis in central Chile (30°S to 38°S). To encompass the purpose, stochastic earthquake scenarios of magnitude M w 8.8 to 9.2 were generated. Two different sets of stochastic tsunami scenarios were selected by means of the Stochastic Reduced Order Model (SROM), which were applied to Quintero bay to perform a Probabilistic Tsunami Hazard Analysis (PTHA). The results showed that PTHA of Quintero bay from stochastic tsunami scenarios agrees with paleotsunami records in the bay, while a deterministic tsunami scenario underestimated the hazard. Two sets (50 and 100 scenarios, respectively) give similar results when smaller return periods are analyzed. However, for larger return periods ( > 2000 yr) the set of 100 scenarios show better results consistent with previous paleoseismological findings. The methodology implemented here can be replicated in other seismic regions in Chile as well as in other active subduction zones, thus, both near field and far field events can be analyzed. [ABSTRACT FROM AUTHOR]

A hexagonal shaped six‐port multiple‐input‐multiple‐output (MIMO) antenna array comprising of six printed circular monopole antennas with wideband characteristics is presented. Based on the measured data, −10 dB impedance bandwidth of the antenna is found to be from 3.44 GHz to 4.68 GHz. The isolation between the adjacent antenna elements is enhanced by self‐cancelation of the induced near field currents by printing a microstrip neutralization line between them. Isolation among antenna elements are greater than 15 dB with an inter‐element spacing of 0.076 times the free space wavelength at 3.44 GHz. The maximum gain of the antenna is noted to be 5.1 dBi with an envelope correlation coefficient ≤ 0.4 and channel capacity loss ≤0.0328 bits/S/Hz in its entire operating bandwidth. [ABSTRACT FROM AUTHOR]

Two-shaped Au nanorod structures are used to create the optical chiralities at the surface plasmon resonances (SPRs) from visible to near-infrared wavelength range, which is theoretically explored by using the 3D finite difference time-domain method. To understand the effects of the middle horizontal Au nanorod on the optical energy coupling between the upper inverted L-shaped Au nanorods and the bottom regular L-shaped Au nanorods, the near-field distributions of the asymmetric and symmetric 2-shaped Au nanorod structures are discussed. The simulation results show that the three horizontal Au nanorods can effectively harvest the x-directed electric field of incident lightwaves and generate the z-directed electric field near the corners of Au nanorods and thereby result in the local optical chiralities at the three SPRs. In addition, the optical energy coupling from the horizontal Au nanorods to the vertical Au nanorods can contribute to the total optical chirality. The understanding of local and total optical chiralities of Au planar nanostructures at nanoscales helps us find the best way to optimize the metallic chiral nanostructures. [ABSTRACT FROM AUTHOR]

The characteristics of square twin surface jets at various offset heights from the free surface were studied using a particle image velocimetry technique. The offset heights were varied from 1 to 4 nozzle widths at a fixed Reynolds number of 3890. The entrainment and mixing characteristics were examined using the potential core length, merging point, combined point, maximum velocity decay, half-velocity width and were found be nearly independent of offset height in near field. The jet–surface interaction was examined by surface velocity, vorticity thickness and surface turbulence intensities. The growth rate of the vorticity thickness reduced in the interaction region; and was more severe for shorter offset height. Turbulent structures were examined using weighted joint probability density function and two-point cross-correlations between swirling strength and velocity fluctuations. Weaker turbulent events were observed for deeper jet close to a free surface at the streamwise location beyond the attachment point. [ABSTRACT FROM AUTHOR]

Zero-mode waveguides have become important tools for the detection of single molecules. There are still, however, serious challenges because large molecules need to be packed into nano-holes. To circumvent this problem, we investigate and numerically simulate a novel planar sub-wavelength 3-dimension (3D) structure, which is named as near-field spot. It enables the detection of a single molecule in highly concentrated solutions. The near-field spot can produce evanescent waves at the dielectric/water interface, which exponentially decay as they travel away from the dielectric/water interface. These evanescent waves are keys for the detection of fluorescently tagged single molecules. A numerical simulation of the proposed device shows that the performance is comparable with a zero-mode waveguide. Additional degrees-of-freedom, however, can potentially supersede its performance. [ABSTRACT FROM AUTHOR]

The use of high resistivity amorphous solids as photodetectors, especially amorphous selenium, is currently of great interest because they are readily produced over large area at substantially lower cost compared to grown crystalline solids. However, amorphous solids have been ruled out as viable radiation detection media for high frame-rate applications, such as single-photon-counting imaging, because of low carrier mobilities, transit-time-limited photoresponse, and consequently, poor time resolution. To circumvent the problem of poor charge transport in amorphous solids, we propose unipolar time-differential charge sensing by establishing a strong near-field effect using an electrostatic shield within the material. For the first time, we have fabricated a true Frisch grid inside a solid-state detector by evaporating amorphous selenium over photolithographically prepared multi-well substrates. The fabricated devices are characterized with optical, x-ray, and gamma-ray impulse-like excitations. Results prove the proposed unipolar time-differential property and show that time resolution in non-dispersive amorphous solids can be improved substantially to reach the theoretical limit set by spatial spreading of the collected Gaussian carrier cloud. [ABSTRACT FROM AUTHOR]

We show how to obtain the correct electronic response of a large system by embedding; a small region is propagated by TDDFT (time-dependent density functional theory) simultaneously with a classical electrodynamics evolution using the Near-Field method over a larger external region. The propagations are coupled through a combined time-dependent density yielding a common Coulomb potential. We show that the embedding correctly describes the plasmonic response of a Mg(0001) slab and its influence on the dynamical charge transfer between an adsorbed H2O molecule and the substrate, giving the same spectral shape as full TDDFT (similar plasmon peak and molecular-dependent differential spectra) with much less computational effort. The results demonstrate that atomistic embedding electrodynamics is promising for nanoplasmonics and nanopolaritonics. [ABSTRACT FROM AUTHOR]

The wide range of interesting electromagnetic behavior of contemporary materials requires that experimentalists working in this field master many diverse measurement techniques and have a broad understanding of condensed matter physics and biophysics. Measurement of the electromagnetic response of materials at microwave frequencies is important for both fundamental and practical reasons. In this paper, we propose a novel near-field microwave sensor with application to material characterization, biology, and nanotechnology. The sensor is based on a subwavelength ferrite-disk resonator with magnetic-dipolar-mode (MDM) oscillations. Strong energy concentration and unique topological structures of the near fields originated from the MDM resonators allow effective measuring material parameters in microwaves, both for ordinary structures and objects with chiral properties. [ABSTRACT FROM AUTHOR]

We use dynamic near field scattering to measure the dynamics of concentration non equilibrium fluctuations at the steady-state of Soret separation. The analysis reveals that above a threshold wave vector qc, the dynamics is governed by diffusion while at smaller wave vectors, gravity dominates. From the measurements, we extract both the mass diffusion and the Soret coefficients. Comparing our results with literature data, we find good agreement confirming that the proposed experimental technique can be considered a sound approach for the study of thermodiffusion processes. [ABSTRACT FROM AUTHOR]

Plasmonic surface lattice resonances (SLRs) supported by metal nanoparticle arrays have a range of appealing characteristics such as extremely narrow linewidths and greatly enhanced near fields, and thus are attractive in diverse applications. Improving the quality factor of SLRs is important for many applications and thus it has been the focus in this field. In this work, we report high quality out-of-plane SLRs supported by two-dimensional metal nanohemisphere arrays embedded in a symmetric dielectric environment. These SLRs, excited under oblique incidence with TM polarization, can have an ultra-narrow resonant linewidth (∼ 0.9 nm) at visible wavelengths around 715 nm. This corresponds to an exceptionally high quality factor of 794, which is ten times that of the widely-adopted nanorods. We attribute this striking performance to the nanohemisphere geometry, which greatly relaxes the stringent requirement on the height of nanoparticles for supporting out-of-plane SLRs, reducing the absorption loss, and in which the out-of-plane oscillations are much stronger than in-plane ones, leading to stronger inter-particle coupling. The tuning of the resonance wavelength and the quality factor can be explained by a qualitative approach based on the detuning between the Rayleigh anomaly and the localized surface plasmon resonance of an isolated nanoparticle. We expect this work will advance the engineering and applications of high quality SLRs. [ABSTRACT FROM AUTHOR]

Few-Layers Graphene (FLG) are able to improve the performance of materials, due to their chemical-physical properties. Engineered amorphous silica nanoparticles (SiO2NPs) are among the most widespread nanomaterials (NMs) in the world. Such nanomaterials are two case studies of the research project 'NanoKey' that integrated the exposure assessment through personal measurements and sampling in the workplace, as described in the present work (part I), with the biomonitoring of exposed workers (reported in part II). Measurement campaigns were conducted according to OECD and WHO harmonized approach in two production sites. The set of instruments included real-time devices for high-resolution measurements at the nanoscale and time-integrated samplers for the off-line gravimetric analysis and chemical and morphological (SEM-EDS) characterization of exposure in order to identify the contribution of production compared to the background. Values of particle number concentration (PNC) and lung deposited surface area (LDSA) within the FLG production resulted higher than the background far field (FF), even if they are always similar to the near field (NF) ones: the average diameter (Davg) during the production was higher than the NF background but always lower than the FF values. SEM-EDS analysis highlighted the presence of structures comparable to those produced. During the SiO2NPs production, the PBZ values showed PNC and LDSA levels higher than the background, with a decrease in the Davg probably due to NPs emission. SEM-EDS confirms the presence of rare silica nanoparticles. Since the exposure to airborne NMs cannot be excluded in both production sites, a prevention-through-design approach to mitigate the potential risk for workers has been recommended. [ABSTRACT FROM AUTHOR]

This paper presents a characteristic mode(CM) analysis of polarization conversion metasurface (MTS) placed in the near field of an exciting antenna. CM analysis has been carried out for three different MTS configurations with respect to excitation slot antenna. A systematic design approach has been adopted by identifying the orthogonal modes with 90 o phase difference. The orthogonal modes with broadside radiation patterns are identified and optimized to have 90 ∘ excitation phase difference. Simulated, as well as, the measurement results at the designed frequency are presented to validate the analysis. [ABSTRACT FROM AUTHOR]

For microwave power transmission (MPT), the transmitting (Tx) array with a tapered amplitude distribution can achieve a maximum beam collection efficiency, but it needs a feeding network with an arbitrary power division ratio; thus, it is complicated and costly in practical applications. This work explores realizing high transmission efficiency by a Tx array with the equal-ratio steps amplitude distribution (ERSAD). By using the ERSAD, the amplitude value of the central units of the Tx array is uniform, and the amplitude feeding of the edge units only needs equal power divisions. Thus, the amplitude feeding is greatly simplified. Besides, a compensated phase distribution is used to focus the radiating beam on the receiving aperture. To validate the proposed design, a Tx antenna consisting of 8 × 8 units with a total aperture size of 1 × 1 m2 is designed. The operating frequency and the focused distance are 5.8 GHz and 10 m, respectively. A 64-way microwave power source is used to adjust the amplitude and the phase of the Tx array, and an MPT experiment is conducted. The measurement shows that, compared with the 10 dB Gaussian amplitude array, the proposed array nearly has the same transmission efficiency against different receiving apertures. [ABSTRACT FROM AUTHOR]

To identify sound source locations and strength by using near-field acoustical holography (NAH), many microphones are generally required in order to span the source region and to ensure a sufficiently high spatial sampling rate. It is often the case that hundreds of microphones are needed, so such measurements are costly, which has limited the application of NAH in industrial settings. Recently, however, it has been shown that it is possible to accurately identify concentrated sound sources with a limited number of microphones based on compressive sampling theory. Here, the theory of the four NAH methods that were studied in the present work, that is, statistically optimized near-field acoustical holography (SONAH), wideband acoustical holography (WBH), l1-norm minimization, and a hybrid compressive samplingmethod, is briefly reviewed. Note that the latter three procedures incorporate elements of compressive sampling. Then, a simulationwith one monopole as the sound source was conducted to illustrate some basic characteristics of these algorithms. In the experimental portion of the work, a multi-element loudspeaker was used as the sound source. A near-field intensity scan was conducted to measure both the true intensity spatial distribution and the sound power generated by the loudspeaker to provide a basis against which the values obtained from the holography reconstructions could be compared. The sound field was reconstructed by using both near- and far-field measurements, and the number of microphone measurements used to reconstruct the sound field was systematically decreased by increasing the spacing between microphones. Both in the simulation and experiment, the sound field was reconstructed by using the four NAH methods mentioned above. Then, the reconstruction resultswere comparedwith the measured intensity results in terms of spatial localization and sound power, and the benefits of the compressive sampling approach are illustrated. [ABSTRACT FROM AUTHOR]

In a hardware-in-the-loop simulation system, the insertion of an asymmetric layout beam combiner will seriously affect the near-field uniformity. In this study, the effects of the aperture shape, transverse distance and size of the beam combiner on the near-field uniformity were analysed. The square beam combiner with a transverse distance of 0.51 m and a size of 1.05 m × 1.05 m was regarded as the optimal design, but it still cannot meet the test requirements. In order to obtain excellent near-field uniformity, an asymmetric Uniform + Linear taper compensation method was proposed. The maximum values of the amplitude fluctuation (Epv) and phase ripple (φpv) decreased dramatically from 2.62 dB and 16.79° to 0.78 dB and 7.42°, respectively. Asymmetric Uniform + Linear taper was achieved through serrating the edge of the beam combiner. When the number of serrations N was 22, Epv and φpv were <0.83 dB and 7.50°, respectively, which indicated that the near-field uniformity can be significantly improved by asymmetric Uniform + Linear taper. [ABSTRACT FROM AUTHOR]

In the design of ultra-high-frequency (UHF) radio frequency identification (RFID) near-field antennas, realising an antenna with electrically large size, wide frequency band, and far read range has always been a challenge. To solve these problems, a planar hexagonal broadband near-field antenna for UHF RFID applications is proposed and investigated. The antenna structure is composed of six dipoles (resembles three sets of double-arrow structures) that are printed on the top and bottom surfaces of an FR4 substrate, forming a dual-layer (inner and outer layers) broken hexagonal loop. The 10 dB return loss bandwidth of the proposed antenna can reach up to 20.8% (856–1055 MHz), thus able to cover the entire European Telecommunication Standards Institute and Federal Communication Commission system operating bands. Since the current distribution along the loop is kept in a single direction and the length of each dipole is ∼1/2 wavelength (λ), strong and uniform z-component magnetic field distribution with an 18 cm read range can be obtained in the near-field zone of the antenna. As the proposed near-field antenna has a planar size of 175 mm × 175 mm, it is suitable for multi-system and wide-range RFID applications. [ABSTRACT FROM AUTHOR]

The interaction of monocycle terahertz (THz) fields with metal nanostructures such as nanotips is attracting a lot of interest for the development of new applications such as THz-scanning tunneling microscopy and ultra-fast field emission. New methods have been introduced to measure the enhanced THz near field waveform in the vicinity of a nanotip surface. Here, we present results obtained by electron field emission in the multiphoton emission regime. The nanotip mimics the behavior of an antenna with a simplified equivalent circuit. We show that the electrical characteristics can be calculated using the nanowire geometry approximation and taking into account a conduction shell with a thickness smaller than the material skin depth. The results introduce a method to predict the antenna response of the nanotip and thus the near THz field waveform. [ABSTRACT FROM AUTHOR]

A new theory is presented for the generation of two-dimensional internal wave beams, including the effects of viscosity and unsteadiness on the propagation of the waves, and extending to the near field the classical theory of Lighthill for the far field. For this, the forcing is assumed to be of compact support. Several equivalent expressions of the waves are obtained, each associated with the choice of a support of simple shape embedding the actual support of the forcing. When the two match, the expression of the waves is valid everywhere in the fluid. For an oscillating body, the existence of critical points where the waves rays are tangential to the body is correctly accounted for, an essential requirement with regard to later inclusion of nonlinear effects and boundary layer eruption into the analysis, both of which take their origin at the critical points. Embedding supports in the shape of a circle, an ellipse and a strip are considered. Line forcing is also considered, on a weaker assumption of rapid decrease at infinity. The analysis reduces to the classical analysis of Hurley & Keady in the isotropic case of an oscillating circular cylinder, and is otherwise applied to four anisotropic oscillating bodies: an elliptic cylinder, a vertical plate, a vertical wave generator and a thin Gaussian bump. [ABSTRACT FROM AUTHOR]

Recently introduced self-tuning RFID tags are capable to dynamically modify the input impedance of the embedded microchip transponder in order to compensate the possible impedance mismatch with the antenna, thus making the communication performance rather insensitive to the nearby environment. A general method for the design of this new class of tags is presented with the purpose to master the complex configuration, where the tag is placed at a close distance from the interrogating antenna, and the free-space assumption is not valid. A two-port system is introduced, and the network-oriented reformulation of self-tuning action permits to derive an optimization problem for the minimization of the interrogation power for a wide range of boundary conditions. The method is demonstrated, both numerically and experimentally, through the application of a finger augmentation device, which aimed to achieve a smart interaction with touched objects. [ABSTRACT FROM AUTHOR]

Deep‐sea ecosystems are fragile yet diverse habitats that are sensitive to disturbance. In the northern Gulf of Mexico deepwater extraction of hydrocarbons led to the accidental release of four million barrels of oil from the Macondo wellhead in 2010. The release of oil combined with the addition of dispersant at depth and the resulting delivery of oiled "marine snow" led to dramatic disruptions of diversity and ecosystem services within the near field deep‐sea benthic communities. Analysis of the biological trait diversity of the surrounding megabenthos reveals notable loss of traits that may explain the stunted recovery of communities within 2 km of the wellhead. The present megafauna show complete loss of some traits relating to tier, motility, and feeding mechanisms. Functional evenness was higher than in surveyed unaffected sites, highlighting some loss of trait space, reflecting increasing abundances of scavengers and the loss of sessile invertebrates. Loss of biological traits that aid in ecosystem resilience has impeded recovery of benthic communities severely impacted by the Deepwater Horizon oil spill. [ABSTRACT FROM AUTHOR]

A handy method of calculating far-field gain based on the magnitude of the power transmission in a Fresnel region is presented, which can be applied to the phaseless near-field measurement. Due to the short range inside an anechoic chamber, the probe antenna is often placed in the Fresnel region of the antenna under test (AUT). It is well-known that far-field gain of an antenna gradually reduces when one antenna moves to the other one placed in a proximity distance. This fact can be advantageously applied to estimate the far-field gain in a far-field region. The proposed method offers rapid estimation of the far-field gain based on the simple input knowledge such as the probe antenna gain and the magnitude of the power transmission and the separation distance between AUT and probe antenna. The proposed method can be applicable to a wide range of microwave antennas. This feature makes it possible to offer preliminary measurement results and reference parameters of the measurement for the various types of microwave antennas. [ABSTRACT FROM AUTHOR]

The inverse scattering problem for anisotropic media with data measured inside a cavity is considered. We aim to introduce the exterior Steklov eigenvalues (ESEs) and the modified exterior Steklov eigenvalues (MESEs) to detect changes in the material properties of the medium from a knowledge of a modified near field operator each. First, a connection between a modified near field operator and the exterior Steklov eigenvalue problem is established. Then the ESEs are proved to be discrete and lie in the lower half-plane. Since the existence of the ESEs is unknown due to non-self-adjointness, we propose the modified exterior Steklov eigenvalue problem for which infinitely many eigenvalues exist. Based on the factorizations of both the modified near field operator and the auxiliary near field operator, a nonsymmetric version of generalized linear sampling method (GLSM) is employed to compute the ESEs. This method also allows for the computation of the MESEs by adjusting the definitions of some associated operators. Numerical examples are presented to demonstrate the viability of this method and show the potential use of these eigenvalues as new classes of target signatures in nondestructive testing. [ABSTRACT FROM AUTHOR]