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A novel decoupling method combining magnetic coupling and electric coupling is proposed in this paper to design a miniaturized two-element antenna array. Different from the traditional planar decoupling structure, a three-dimensional quasi-split resonant ring decoupling structure which can realize electric coupling is introduced. The quasi-split resonant ring is composed of two meandered antenna elements printed on the top and bottom of the substrate. The other decoupling structure is composed of two parasitic patches, which realize magnetic coupling with the open end of the dipole element in the opposite plane. By properly controlling the strength of magnetic coupling and electric coupling, the induced currents can cancel each other out, thereby enhancing the isolation between adjacent ports. Compared with the antenna array employing the planar decoupling method, the size of the antenna array in this paper is significantly reduced by half. In terms of $S$ -parameter and near-field radiation, the simulated results of the full-wave analysis are compared with the measured results. Essentially identical results successfully verify that the antenna achieves an isolation up to 27.5 dB and omnidirectional radiation mode in the resonant bandwidth of 1.76-1.80 GHz.

In this paper, a novel design of a near-field dipole antenna sensor array for breast tumor detection is presented. The proposed sensor consists of four electrically small dipole antennas fed by a single port. Due to the proven fact that breast tumors have higher dielectric properties than the surrounding normal tissues, the proposed sensor is utilized for detecting breast tumors by evaluating the variations of the sensor’s response of two cases, normal and abnormal, of the breast tissues. A simulation study is performed using both normal and abnormal numerical breast phantoms with different sizes of tumors inserted at different locations. Simulation results show the proposed sensor detected the inserted tumors at various locations inside the normal breast phantom due to an increased area of sensitivity of the sensor by using multiple sensors array. An experimental study is conducted on breast chicken meat that mimics a healthy breast and two cases of tumors including tumors made of oil and gelatin mixture and conductive spheres with different sizes inserted at different locations inside the chicken meat. Experimental results show that the proposed sensor has higher sensitivity for detecting different sizes of breast tumors placed at multiple locations.

In recent years, wireless power transfer (WPT) has become a widespread method for charging and powering devices, including but not limited to consumer electronics, industrial applications, electric vehicles, medical devices, and sensor nodes. This article provides an overview of the available WPT technologies, focusing on the near-field case, and highlights the main architecture and circuit-level challenges encountered in the implementation of magnetic-based near-field WPT systems while reviewing the proposed solutions in the literature, in order to identify the main research interests as well as the trends for the future.

The beneficial effect of using hybrid frames is realized in terms of the reduction of some desired engineering demand parameters (EDPs). However, this is achieved at the cost of increasing the values of some other EDPs as compared to the rigid frame. A good balance between the two can be achieved by selecting the optimum number of semirigid (SR) connections. In the present study, two schemes of the selection of the optimum number of SR connections are presented to obtain the desired benefit of the hybrid frame. One scheme provides the optimum number of SR connections which provides the desired reductions in the base shear (BS) and total number of plastic hinges formed (THmax) with the marginal increase in the maximum inter-story drift ratio (IDRmax). The other scheme provides the number of SR connections to be used for achieving the limiting drift allowed in the hybrid frame and accordingly, obtains the percentage reductions of the BS and THmax. Both schemes are developed using a graphical technique. Three illustrative examples are considered to demonstrate the efficacy of the two schemes using the nonlinear time history analysis under three types of earthquakes (i.e., near and far-field) at three peak ground accelaration (PGA) levels. The results of the study show that in both schemes of providing the optimum number of SR connections, significant reductions in the BS and THmax can be achieved as compared to the fully rigid frame. The corresponding IDRmax in the hybrid frames remains less than equal to the limiting value of the IDRmax prescribed in the literature. [ABSTRACT FROM AUTHOR]

In linear inverse scattering, the performance of the imaging system is sometimes evaluated in terms of its resolution, i.e., its capability to reconstruct a point-like scatterer. However, there is still a lack of analytical studies on the achievable resolution. To address this, we consider the point spread function (PSF) evaluation of the scattered near field for the single frequency and multi-view/multi-static case in homogeneous medium. Instead of numerically computing the PSF, we propose and discuss an approximate closed form under series expansions according to the angular ranges of both source and receiver location. In order to assess the effectiveness of the proposed approximation, we consider two cases including both full and limited view angles for the incident field and observation ranges. In addition, we provide a localization application to show the usefulness of the theoretical discussion. Numerical results confirmed the analytical investigations. [ABSTRACT FROM AUTHOR]

Extremely large-scale multiple-input-multiple-output (XL-MIMO) at millimeter-wave (mmWave) and terahertz (THz) bands plays an important role in supporting extreme high beamforming gain as well as ultra-wideband spectrum resources. Unfortunately, accurate wideband XL-MIMO channel estimation suffers from a new challenge called the near-field beam split effect. Prior studies either neglect the accurate near-field channel model or fail to exploit the beam split effect, resulting in poor channel estimation accuracy for wideband XL-MIMO. To tackle this problem, this paper proposes a bilinear pattern detection (BPD)-based approach to accurately recover the wideband XL-MIMO channel. Specifically, by analyzing the characteristics of near-field wideband channels, we first reveal the bilinear pattern of the near-field beam split effect, which implies that the sparse support set of near-field channels in both the angle and the distance domains can be regarded as a linear function against frequency. Then, inspired by the classical simultaneously orthogonal matching pursuit technique, we use the bilinear pattern to estimate the angle-of-arrival (AoA) and distance parameters of each near-field path component at all frequencies. In this way, the entire wideband XL-MIMO channel can be recovered by compressed sensing algorithms. Moreover, we provide the computational complexity of the proposed algorithm compared with existing algorithms. Finally, simulation results demonstrate that our scheme can achieve the accurate estimation of the near-field wideband XL-MIMO channel in the presence of near-field beam split effect. [ABSTRACT FROM AUTHOR]

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling. [ABSTRACT FROM AUTHOR]

Hyperuniform disordered photonic structures are a peculiar category of disordered photonic heterostructures located between random structures and ordered photonic crystals. These materials, thanks to the presence of a photonic bandgap, exhibit the advantages of random and ordered structures since they have been shown to support in a small spatial footprint a high density of Andersonlocalized modes, which naturally occur at the bandgap edges with peculiar features like relatively high Q/V ratios. Different localization behaviors have been recently reported in hyperuniform disordered luminescent materials, with a well-established and widely studied design, based on disordered networks. Here, we explore an alternative design, based on circular holes of different sizes hyperuniformely distributed, that we investigate theoretically and experimentally by means of scanning near-field optical microscopy. We report that the spectral features of hyperuniform disordered networks can also be extended to a different design, which, in turn, displays pseudo-photonic bandgaps and light localization. The ability of generating different kinds of hyperuniform disordered photonic systems that share the same theoretical and experimental optical features can largely extend practical potentialities and integration in many optoelectronic applications. [ABSTRACT FROM AUTHOR]

The design of soft biomaterials requires a deep understanding of molecular self‐assembly. Here a nanoscale infrared (IR) spectroscopy study of a two‐component supramolecular gel is introduced to assess the system's heterogeneity and supramolecular assembly. In contrast to far‐field IR spectroscopy, near‐field IR spectroscopy revealed differences in the secondary structures of the gelator molecules and non‐covalent interactions at three distinct nano‐locations of the gel network. A β‐sheet arrangement is dominant in single and parallel fibres with a small proportion of an α‐helix present, while the molecular assembly derives from strong hydrogen bonding. However, at the crossing point of two fibres, only the β‐sheet motif is observed, with an intense π–π stacking contribution. Near‐field nanospectroscopy can become a powerful tool for the nanoscale distinction of non‐covalent interactions, while it is expected to advance the existing spectroscopic assessments of supramolecular gels. [ABSTRACT FROM AUTHOR]

A universal ultrahigh‐frequency (UHF) near‐field radio‐frequency identification (RFID) reader antenna with wide bandwidth and adjustable reading area is proposed in this letter. The antenna consists of an inverting power splitter base on double‐sided parallel stripline and adjustable traveling‐wave near‐field radiation units, which consists of two symmetrical meander microstrips and a complementary open resonant ring loaded on the ground plane. A design example with three radiation units is simulated, fabricated, and tested for verification. The result indicates that the proposed antenna has the 10‐dB impedance bandwidth of 128%, which completely covers the universal UHF RFID band from 840 to 960 MHz. The 100% read–write rate is achieved within the read–write distance of 10 mm according to the reading test. The reading area of 731 × 120 mm2 can be obtained for increasing the number of radiation units to 10. Moreover, the antenna features low far‐field gain, low‐cost, strong and uniform magnetic field distribution. Therefore, the proposed antenna and design method have good application prospects in the Internet of Things. [ABSTRACT FROM AUTHOR]

We model the effects of the photosensitive parameters of aerosols on their optical properties to provide a solid framework for further experimental and theoretical studies. A spherical dust particle is used to study the effects of the ambient medium, size, surface roughness, wavelength, and imaginary part of the complex refractive index. Five Gaussian random spheres with different aspect ratios are simulated to study the dependence of aerosol light scattering properties on particle shape distribution. To investigate the influence of composition, we model two typical kaolinite-like particles (pure and composite) collected from Southwest Sahara, with 0 and 2% hematite at different mixing states. Using the method of discrete-dipole approximation in DDSCAT, a comparative study is performed with the Mueller matrix elements, scattering, absorption, extinction efficiencies, single scattering albedo, and linear depolarization ratio as indicators. For single, microscopic dust particles, near-field calculations are carried out. The results show that the intensity of backscattering and the scattering efficiency decreases in water compared to dry air. Light in the visible range is more efficient for aerosol scattering experiments. A small number of impurities in the sample will increase its absorbing properties, but, in general, the scattering efficiencies strongly depend on the single-particle mixing state. Smaller particles with a diameter comparable to the wavelength of incident light show higher scattering efficiencies but lower backscattering intensities than larger particles, while surface roughness is shown to strongly alter the polarizability of the particle but has a negligible effect on its single-scattering albedo. Moreover, different shapes have a strong effect on the degree of linear polarization, but, in general, using the spherical over elliptic shape model can underestimate the scattering efficiencies by up to 4%. Finally, variation in the imaginary part of the complex RI can underestimate the single scattering albedo by up to 35.8%. [ABSTRACT FROM AUTHOR]

One manifestation of light-Weyl fermion interaction is the emergence of chiral magnetic effects under magnetic fields. Probing real space magnetic responses at terahertz (THz) scales is challenging but highly desired, as the local responses are less affected by the topologically trivial inhomogeneity that is ubiquitous in spatially averaged measurements. Here, we implement a cryogenic THz microscopy instrument under a magnetic field environment—a task only recently achieved. We explore the technical approach of this system and characterize the magnetic field’s influence on our AFM operation by statistical noise analysis. We find evidence for local near-field spatial variations in the topological semimetal ZrTe5 up to a 5-Tesla magnetic field and obtain near-field THz spectra to discuss their implications for future studies on the chiral magnetic effect.

Phonon-polaritons (PhPs) in layered crystals, including hexagonal boron nitride (hBN), have been investigated by combined scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. Nevertheless, many of such s-SNOM-based FTIR spectra features remain unexplored, especially those originated from the impact of boundaries. Here we observe real-space PhP propagations in thin-layer hBN sheets either supported or suspended by s-SNOM imaging. Then with a high-power broadband IR laser source, we identify two major peaks and multiple auxiliary peaks in the near-field amplitude spectra, obtained using scattering-type near-field FTIR spectroscopy, from both supported and suspended hBN. The major PhP propagation interference peak moves toward the major in-plane phonon peak when the IR illumination moves away from the hBN edge. Specific differences between the auxiliary peaks in the near-field amplitude spectra from supported and suspended hBN sheets are investigated regarding different boundary conditions, associated with edges and substrate interfaces. The outcomes may be explored in heterostructures for advanced nanophotonic applications.

We present a new methodology that enables studies of the molecular structure of graphene-liquid interfaces with nanoscale spatial resolution. It is based on Fourier transform infrared nanospectroscopy (nano-FTIR), where the infrared (IR) field is plasmonically enhanced near the tip apex of an atomic force microscope (AFM). The graphene seals a liquid electrolyte reservoir while acting also as a working electrode. The photon transparency of graphene enables IR spectroscopy studies of its interface with liquids, including water, propylene carbonate, and aqueous ammonium sulfate electrolyte solutions. We illustrate the method by comparing IR spectra obtained by nano-FTIR and attenuated total reflection (which has a detection depth of a few microns) demonstrating that the nano-FTIR method makes it possible to determine changes in speciation and ion concentration in the electric double and diffuse layers as a function of bias.

Near-field optics is essential in many nanotechnology applications, such as implementing sensitive biosensing and imaging systems with extreme precision. Understanding optical near-fields at the nanoscale has so attracted the considerable research interest, which use a variety of analytical approaches, most notably near-field scanning microscopy. Here, we show defocused point localization mapped accumulation (DePLOMA), which can overcome many weaknesses of conventional analytical methods. DePLOMA is based on imaging fluorescence emitters at an out-of-focal plane. The acquisition, collection, and accumulation of the position and fluorescence intensity of emitters moving above nanostructures can generate three-dimensional near-field maps of light distribution. The idea enables super-resolution liquid-phase measurements, as demonstrated by reconstruction of near-field created by nanoslits with a resolution determined by emitter size. We employed fluorescent emitters with a radius of 50 and 100 nm for confirmation. The axial resolution was found to be enhanced by more than 6 times above that of diffraction-limited confocal laser scanning microscopy when DePLOMA was used.

Multichannel metasurfaces are becoming a significant trend in the field of optical encryption due to their excellent manipulation of optical wavefronts. However, existent multichannel metasurfaces for optical encryption mostly implement only two channels in the near-field, or three channels by combining the near- and far-field. In this paper, we propose and simulate a three-channel metasurface that works entirely in the near-field and uses the polarization state of the incident light, left circularly polarized (LCP) light, right circularly polarized (RCP) light, and linearly polarized (LP) light as the security key. The metasurface consists of two types of nanostructures that work as a polarizer and a quarter-wave plate, providing an additional degree of freedom for encoding that enables independent near-field display at 633 nm wavelength incident light. The proposed three-channel metasurface has the advantages of high information density and high security, which will pave the way for multi-channel applications such as ultracompact displays, optical encryption, and information storage. [ABSTRACT FROM AUTHOR]

Tremors are a type of slow earthquake with long‐duration signals compared to ordinary earthquakes. The long signals have been considered to solely reflect their long source process. However, here, we provide evidence suggesting that the source processes of tremors are not always long. We refer to these observations as short‐duration tremors. They were recorded by ocean‐bottom seismometers placed very close to the source. Although these tremors exhibit a short‐duration signal when recorded near the source, they exhibit a typical long‐duration signal elsewhere. Our numerical simulations demonstrate that the features can be captured by considering a strongly scattering medium around their source. One such structure could be small low‐velocity inclusions distributed around the seismic source. The inclusions may represent the seismic expression of geologically detected aquifers in tremor source regions. Furthermore, this medium could be embedded along the slow earthquake fault zone and play a critical role in their source process. Plain Language Summary: At least two types of earthquakes occur in shallow subduction zones: ordinary earthquakes and tremors. Tremors are known to exhibit long signal duration compared to ordinary earthquakes. To date, tremors' long‐duration signal has been solely interpreted by their source process. Here, we discovered tremors that exhibit short duration signals when recorded close from the source which we referred to as "short‐duration tremors". They suggest that tremors' source process is not always long and structural effects may partially form the typical long‐duration signals. We performed numerical simulations on elastic wave propagation and demonstrated that the observations can be qualitatively reproduced by assuming a strongly scattering material surrounding the seismic source. On the other hand, it has been reported based on ocean bottom drilling project that tremor source region may consist of patchily distributed aquifers. The inclusions in our model may be the seismic expressions of the geologically detected aquifers. Further, such a structure could be embedded along the slow‐earthquake fault zone and play a key role in their source process. Key Points: Short‐duration tremors in ocean‐bottom seismometer records suggest that the source process of tremors is not always longShort‐duration tremors can be interpreted by placing a strongly scattering medium around their sourceSuch a medium embedded along the slow earthquake fault zone could play a key role in the tremor source process [ABSTRACT FROM AUTHOR]

In the authors' previous research, a new method for partial discharge detection in the switchgear based on near-field detection was proposed. The content of this paper is the continuation of the authors' previous research. In order to realize the reasonable layout of the near-field magnetic field probe for partial discharge detection in the switchgear, this paper simulates and analyzes the influence of the internal structure of the switchgear on the near-field propagation characteristics of the electromagnetic wave signal generated by partial discharge, and determines the installation position of the near-field probe in the switchgear. Firstly, the propagation characteristics of electromagnetic wave signals in the different media of the switchgear are analyzed, and the switchgear model is established. Then, based on the finite difference time domain method, the influence of different devices in the switchgear on the near-field propagation of the partial discharge electromagnetic wave signal is simulated. The simulation results show that the current transformer, insulator, busbar and cabinet all obviously attenuate the amplitude of the near-field electromagnetic wave signals generated by partial discharge, and the insulator causes obvious signal distortion. Finally, it is determined that the near-field probe can be installed on the inner wall or the right wall near the bottom plate of the switchgear. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two β -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like α -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions. [ABSTRACT FROM AUTHOR]

This paper introduces a localized masked thermal therapy method for only the breast through the Fresnel region. A pyramidal horn antenna has been used as a hyperthermia system applicator. The antenna is fed by a Yagi array and resonates at 4.74 GHz. A metal plate with a square slot masked the breast phantom. The antenna irradiates the breast phantom for 5 and 10 minutes with input power of 10 and 20 watts (W). Thermal and specific absorption rate (SAR) distributions are studied under the same conditions for a fair comparison between masked and unmasked system performance. The square slot dimensions are altered, and their effects are studied considering the phantom heated area. Moving from unmasked to masked hyperthermia scenarios, a heated area size reduction of 99.87 % is achieved along with a very considerable SAR value reduction. The masked scenario elevates the breast temperature to 43 °C in a very concentrated area. The proposed system can elevate only an area of 2×2 mm2 of the breast tissue to a temperature of 40 °C in 5 minutes, and that is a very promising result in hyperthermia therapy applications. [ABSTRACT FROM AUTHOR]

Terahertz (THz) communication has a large available bandwidth, which is expected to be deployed in future communication networks. As THz wave suffers from severe propagation loss in wireless transmission, we consider a THz near-field scenario where a base station (BS) is equipped with a large-scale antenna array with a low-cost hybrid beamforming architecture to serve mobile users nearby. However, the large-scale array and the user mobility incur difficulty in channel estimation. To tackle this issue, we propose a near-field beam training scheme that can align a beam to the user in a fast way by searching the codebook. Specifically, the BS employs a uniform circular array (UCA), and the radiation pattern of the beams in our proposed codebook appears as ellipsoids. To cover the serving zone with the minimum codebook size, we develop a near-field codebook by tangent arrangement approach (TAA). To reduce the time overhead, we leverage the hybrid beamforming architecture to realize multi-beam training concurrently since each RF chain can enable a codeword whose element has a constant magnitude. Numerical results validate that our proposed UCA near-field codebook achieves less time cost while achieving a comparable coverage performance compared to the conventional near-field codebook. [ABSTRACT FROM AUTHOR]

Experimental limitations such as design complexity and low optical throughput have prevented photonic nanojet (PNJ) and photonic hook (PH) measurements from demonstrating and characterizing the implementation of narrow intense electromagnetic beams generated from dielectric microelements with circular symmetry. Near-fields optical microscopy can mitigate these limitations and still present a capability of detecting a highly localized electromagnetic beam for applications in step-index media. Here we model a localized PNJ and PH formation in step-index media. We show that despite negligible refractive index contrast between the water ( n w a t e r = 1.33 ) and silica microcylinder (∼1.1), a formation of PNJ and PH is observed with equivalent performance compared to that of silica microcylinder embedded in air ( n a i r = 1 ). This model features a practical fiber source and silica microcylinder as an auxiliary structure. Simultaneously, we performed experimental characterization of a photonic nanojet generated from an optical fiber and studied the resulting near-fields. Our electromagnetic simulation results are in good agreement with the experimental ones, demonstrating a full width at half maximum (FHWM) with a relative error of 0.64%. This system will make fiber-based nanojet realization and characterization accessible and practical for optics and laser engineering applications, super-resolution imaging, and nanolithography. [ABSTRACT FROM AUTHOR]

The initial dilution generated by the final disposal of untreated wastewater through a submarine outfall in Santa Marta was examined with a near-field dilution model. Northward and eastward seawater velocity, salinity, and temperature profiles from a 3D hydrodynamic model were used to provide the oceanic conditions to calculate the dilution. The upwelling phenomenon occurs two times a year at the wastewater discharge site, the major from December to March and the minor in July, eliminating the stratification condition of seawater. The results of the dilution model showed that in these periods the plume reaches the water surface, achieving dilutions greater than 100. In addition, the external wave effect on the initial dilution of submarine outfall discharge in Santa Marta was determined. Surface waves increase dilution during the dry period of the year, when trade winds increase the surge and start the upwelling phenomenon. The dilution with/without waves factor is up to 1.90 for the center of the plume on the water column. [ABSTRACT FROM AUTHOR]

Abstract As we all know, the non‐uniform array is widely used in the mixed near‐field (NF) and far‐field sources localization. The nested array contains a uniform linear array, it is easy to be affected by mutual coupling, so we propose a symmetric thinned coprime array (STCA) to reduce the mutual coupling effect of mixed source localization. In this paper, the STCA configuration consists of two sparse uniform linear arrays, the first subarray is composed of 2N − 1 sensors, and the sensor element spacing is Md. The second subarray is composed of 2M+2⌊M2⌋ sensors, and the sensor element spacing are Nd and Md respectively. The two subarrays form the symmetric coprime array, which shares a reference sensor. Under the same number of physical array sensors, compared with the latest symmetric nested array, although STCA has lower consecutive lags, the array sensors have larger inter‐sensor spacing and larger physical array aperture, which can significantly reduce the mutual coupling effect between physical sensors, and better estimation performance of direction‐of‐arrival (DOA) estimation can be achieved. Finally, simulation results show that STCA can achieve better performance than other symmetric nested arrays under the same array sensors and mutual coupling effects.

We demonstrate the formation of the near field with non-trivial phase distribution using surface plasmon interference devices, and experimental quantitative imaging of that phase with near-field phase microscopy. The phase distribution formed with a single device can be controlled by the polarization of the external illumination and the area of the device assigned to the object wave. A comparison of the experimental data to a numerical electromagnetic model and an analytical model assigns the origin of the near-field phase to the out-of-plane electric component of surface plasmon polaritons, and also verifies the predictive power of the models. We demonstrate a formation of near-field plane waves with different propagation directions on a single device, or even simultaneously at distinct areas of a single device. Our findings open the way to the imaging and tomography of phase objects in the near field.

Thermal modulators based on phase change materials have gained attention due to their ability to self-adaptively tune the heat flux. However, achieving a large positive modulation ratio with increasing temperature remains challenge. In this work, we present a near-field thermal modulator with a large modulation ratio and heat transfer coefficient. The thermal modulator consists of two identical VO 2 metasurfaces placed on planar Au substrates. The thermal modulator can achieve three stages, corresponding to three different combinations of phase states of VO 2. An extremely large heat transfer coefficient with value exceeds 20000 W/m2 K is achieved at a room temperature of 300 K, and the largest modulation ratio is about 12. The underlying mechanism involved in the modulator is the construction of cavity surface plasmon polaritons for the metallic state and the suppression of surface phonon polaritons for the dielectric state. Meanwhile, we numerically demonstrate the excellent modulation performance of the proposed modulator as a contact filling in the spacecraft applications. This work can accelerate the utilization of near-field thermal modulators in thermal management and thermal circuit applications. • Three-stage modulation of near-field radiative heat transfer is achieved by one PCM. • Achieve an extremely large heat transfer coefficient with value exceeds 20000 W/m2 K. • An excellent modulation property is demonstrated with ratio excess 12. • Underlying mechanism involves constructing the cavity SPPs and suppressing SPhPs. • Excellent modulation performance is illustrated for the spacecraft application. [ABSTRACT FROM AUTHOR]

This paper addresses an inverse scattering problem in a near-zone setting under a multi-monostatic multi-frequency configuration. The main goal is to design a sampling scheme for collecting the data to be convenient and efficient. Accordingly, the considered approach to achieve this goal is a non-uniform sampling strategy which functions based on approximation of the point-spread function via a migration-like inversion algorithm. This scheme benefits from a convolutional scattering operator which can capture the most significant singular values of the continuous operator. However, this scheme leads to a complicated measurement grid due to the influence of different frequencies. To overcome this problem, we exploit an iterative optimal strategy, which optimizes the sampling grid with respect to frequency samples and spatial points. This solution results in an efficient, simple and convenient grid in which the data points are distributed uniformly. We will support the theoretical findings by numerical results. [ABSTRACT FROM AUTHOR]

This paper presents a hyperspectral microscopy system that offers two-dimensional (2D) measurement of the spectral phase and amplitude information of terahertz (THz) radiation without the need for raster scanning. To achieve this, a new THz imaging method is introduced, wherein the distribution of the THz electric field is spatially measured using the electro-optic effect with a commercial polarization image sensor. This method enables the direct measurement of polarization components, eliminating the need for the polarization optics usually required in conventional electro-optical imaging. The performance of this imaging method is compared with a conventional 2D imaging system based on a standard visible camera. Finally, the sub-wavelength resolution capabilities of this new sensor are demonstrated by imaging a sample in the near field.

Direction of arrival (DOA) estimation of mixed near‐field (NF) and far‐field (FF) signals is one of the key issues in the study of array signal processing. For more precise localisation performance, sparse arrays have drawn the attention of an increasing number of academics. Excitingly, sparse arrays enable larger array apertures and higher degrees of freedom (DOFs) than traditionally used uniform linear arrays. Consequently, this study proposes a transformed symmetric nested array (TSNA) for the passive localisation application regarding mixed NF and FF. There are three processes that go into building the proposed array. In the first step, we swap the positions of the uniform linear arrays and the sparse linear arrays in the nested array. In the second step, we place the corresponding array sensors extracted from the uniform linear array behind the uniform linear array to form a new subarray. In the last step, the TSNA is constructed by folding the formed array in half. Furthermore, we give the formula of the largest consecutive lags of the TSNA and its corresponding constructor. Finally, through theoretical analysis and computer performance simulation, this study illustrates the proposed array's numerous advantages over currently used symmetric sparse arrays. [ABSTRACT FROM AUTHOR]

Purpose: The efficiency and robustness of tuned mass dampers (TMDs) are the two main criteria in the optimum design and evaluation of their seismic performance. In this study, a framework is presented for optimum seismic design and assessment of TMD performance in frequency and time domains based on efficiency and robustness. Material and methods: Two 10- and 20-story linear shear buildings have been studied, which represent mid- and high-rise buildings, respectively, with two inherent damping ratios (2% and 5%) to evaluate the performance of TMDs in this framework. The TMD design has also been investigated for seven different mass ratios. The Particle Swarm Optimization method has been used to determine the optimal parameters of each damper, and the objective function is considered as minimizing the largest singular value of the inter-story drift transfer function to ensure the seismic performance and robustness of the TMD. In addition, three sets of seven earthquake records have been applied with different characteristics to evaluate the robustness of the TMD regarding the stochastic nature of the earthquake. Finally, to explicitly assess the robustness of optimally designed TMD with other uncertainties in the dynamic properties of the building and TMD, two sensitivity analyses have been performed in the frequency and time domain to achieve an unbiased seismic evaluation of optimally designed TMDs. Conclusion: The results show the good performance of the damper with optimum parameters but its high sensitivity to the uncertainty of frequency ratio, especially in the time domain, can significantly reduce the seismic performance of the damper. [ABSTRACT FROM AUTHOR]

To support more users and higher data rates in future communication networks, the extremely large-scale massive multiple-input multiple-output (XL-MIMO) is considered a promising technique. The booming research on XL-MIMO necessitates a reconfigurable XL-MIMO testbed that can be used to validate new research ideas in real wireless environments and collect data for XL-MIMO channel characteristics analysis. To provide such a reliable and convenient testbed, we designed a multi-beam XL-MIMO testbed based on the hybrid CPU-FPGA architecture and channel calibration schemes. The ability to customize modules makes our testbed a convenient verification platform for future communication systems. Moreover, numerous trial measurement results in the indoor near-field scenario with moderate user equipment (UE) mobility are presented, and the excellent performance indicates that our testbed is an ideal platform for the evaluation of XL-MIMO-related algorithms. [ABSTRACT FROM AUTHOR]

• Near-field acoustic range estimation. • Spherical harmonics decomposition of acoustic signal. • Spherical harmonics intensity vectors for rigid sphere. • Spherical harmonics intensity vector based range estimation. • Convolution neural network based classification. Near-field acoustic range estimation is considered one of the least explored research problems in digital signal processing under noise and reverberant conditions. This letter develops a new learning-based range estimation technique utilizing the spherical harmonics intensity (SH-INT) coefficients. The conventional range estimation in the spherical harmonics (SH) domain relies on the pressure coefficients. However, at high frequencies, these coefficients of different order and range overlap and hinder the accuracy of range estimation. On the contrary, the SH-INT coefficients are well distinguished at high frequencies for various orders and ranges, making these features favorable for accurate range estimation using learning algorithms. Since the SH-INT coefficients in the radial direction are independent of the source signal and vary with range, a convolutional neural network (CNN) model has been adopted to map the SH-INT coefficients with the range classes. The performance of the proposed spherical harmonic intensity (SH-INT) features in the context of near-field range estimation is validated by conducting exhaustive experiments on simulated and real data. Further, the error in near-field source range estimates is characterized using root mean square error (RMSE) criteria. The results are impactful and encourage the use of this method for practical near-field source range estimation applications. [ABSTRACT FROM AUTHOR]

In this work, we present a 2 × 2 near-field multi-input multiple-output (MIMO) prototype for bit-error-rate (BER) and error vector magnitude (EVM) measurements in a metal enclosure. The near-field MIMO prototype was developed using software-defined-radios (SDRs) for over-the-air transmission of QPSK modulated baseband waveforms. We checked the near-field MIMO BER and EVM measurements in three different scenarios in a highly reflecting metal enclosure environment. In the first scenario, the line-of-sight (LOS) communication link was investigated when the mode stirrer was stationary. In the stationary channel conditions, near-field MIMO BER and EVM measurements are performed. In the second scenario, BER and EVM measurements were performed in dynamic channel conditions when the mode stirrer was set to move continuously. In the third scenario, LOS communication near-field MIMO BER and EVM measurements were performed in stationary channel conditions but now in the presence of MIMO interference. In three different scenarios, near-field MIMO BER and EVM measurements were investigated at different Tx USRP gain values and in the presence of varying levels of MIMO interference. [ABSTRACT FROM AUTHOR]

Point source excitation and point detection in the near-field provides new perspective to study the near-field optical phenomena of plasmonic nanostructures. Using the automated dual-tip scanning near-field optical microscope (SNOM), we have measured the optical near-field response of a dipolar emission near the edge of a monocrystalline gold platelet. The image dipole method was used to analytically calculate the interference pattern due to surface plasmon polaritons excited at the position of aperture tip and those reflected from edges of the gold platelet. The near-field enhancement was observed on the edges of the gold platelet. Our results verify that automated dual-tip SNOM is an intriguing technique for quantum plasmonic studies where deterministic coupling of quantum emitters and the detection of the near-field enhancement are of great interest. [ABSTRACT FROM AUTHOR]

A compact antenna test range (CATR) system based on a planner stepped‐edged reflectarray antenna is proposed in this article. The parameters of the reflectarray antenna are determined by the design method of a single reflector system. Physical Optics (PO) method is used to calculate the unit phase of the reflectarray. The performance of the quiet zone is improved by optimizing the array shape. A 4320‐element reflectarray antenna with a dual‐ring structure is proposed and fabricated. The measured results show that the amplitude distribution of the designed reflectarray compact range is within ±1 dB, the phase distribution is within ±10°, and the cross‐polarization isolations are greater than 24 dB in the region of 50% at 10 GHz. The performance of the quiet zone is favorable for the usage of CATR systems. [ABSTRACT FROM AUTHOR]

The 2022 MS 6.9 (MW 6.6) Menyuan earthquake occurred in the northeastern Tibetan Plateau and was recorded by a large number of recently installed micro-electro-mechanical system (MEMS) stations within 100-km fault distance. By comparing the pre-event noises and earthquake signals in time domain and frequency domain, it is found that the records are feasible to be used to analyze ground motion parameters. These records provide a database for analyzing the main features of the ground motions recorded by MEMS stations, in terms of ground motion models (GMMs), near-field impulsive characteristics, and seismic intensities. The observed ground motion parameters are compared with the predicted values by Boore et al. (Earthq Spectra 30(3):1057–1085, 2014) GMM model, and it is found that the GMM model predicts higher shaking at the short and medium periods and lower shaking at the long periods. However, the shaking intensities at the short periods for Central Italy 2016 earthquake sequence are well predicted by the GMM model. The observed Chinese seismic intensity (CSI) by instruments is compared with modified Mercalli intensity (MMI) and surveyed macroseismic intensity (SMI), and it is found that CSI values are 0.73 intensity unit greater than MMI values and high SMI can be well predicted by CSI. Ground motions at three stations are classified as pulse-like based on the methodology by Baltzopoulos et al. (Bull Seismol Soc Am 110(4):1495–1505, 2020), and whether the pulses have been caused by forward directivity or fling step is discussed, and only one station may be directivity related and the other two are still inconclusive. Finally the earthquake damage of a high-speed railway bridge in the intensity IX area is presented. [ABSTRACT FROM AUTHOR]

Millimeter-wave SAR (Synthetic Aperture Radar) imaging is widely studied as a common means of RF (Radio Frequency) imaging, but there are problems of the ghost image in Sparsely-Sampled cases and the projection of multiple targets at different distances. Therefore, a robust imaging algorithm based on the Analytic Fourier Transform is proposed, which is named mmSight. First, the original data are windowed with Blackman window to take multiple distance planes into account; then, the Analytic Fourier Transform that can effectively suppress the ghost image under Sparsely-Sampled is used for imaging; finally, the results are filtered using a Mean Filter to remove spatial noise. The experimental results show that the proposed imaging algorithm in this paper, relative to other algorithms, can image common Fully-Sampled single target, hidden target, and multiple targets at the same distance, and solve the ghost image problem of single target in the case of Sparsely-Sampled, as well as the projection problem of multiple targets at different distances; the Image Entropy of the mmSight is 4.6157 and is on average 0.3372 lower than that of other algorithms. Compared with other algorithms, the sidelobe and noise of the Point Spread Function are suppressed, so the quality of the image obtained from imaging is better than that of other algorithms. [ABSTRACT FROM AUTHOR]

The 3D indoor localization of low-cost standard mobile devices represents an important research topic. Since the implementation of ultra-wideband localization systems requires elaborated hardware, a localization concept based on phase-difference-of-arrival (PDOA) evaluation of narrow band communication signals at spatially distributed antennas is favorable in many applications. Typically, PDOA measurements are used to estimate the angle-of-arrival (AOA) at several receivers, which are then combined via multiangulation. However, AOA estimation requires far field conditions, thereby limiting measurement sensitivity, and distorts measurements in a non linear fashion. To overcome these limitations, this paper proposes the iterative holographic extended Kalman filter (IHEKF), which directly evaluates the phase differences between spatially distributed antenna pairs. The IHEKF requires neither a specific waveform nor emitter–receiver synchronization and, therefore, represents a good candidate for localization within communication systems such as 5G/6G. Since the evaluation of phase differences is affected by phase ambiguity, the IHEKF is designed so that closely spaced antenna pairs are evaluated first and then more distant antennas are included successively to improve accuracy. The IHEKF’s capabilities are demonstrated via a 24 GHz narrow band measurement setup with strong multipath propagation, providing outstanding localization accuracy in the millimeter range without consuming any notable RF signal bandwidth.

When intense laser fields interact with nanoscale targets, strong-field physics meets plasmonic near-field enhancement and subwavelength localization of light. Photoemission spectra reflect the associated attosecond optical and electronic response and encode the collisional and collective dynamics of the solid. Nanospheres represent an ideal platform to explore the underlying attosecond nanophysics because of their particularly simple geometry. This review summarizes key results from the last decade and aims to provide the essential stepping stones for students and researchers to enter this field.

Electromagnetic waves possessing orbital angular momentum, namely, vortex beams, have attracted considerable attention in the fields ranging from optical communications to quantum science, due to their extraordinary information encoding capabilities. Vortex beams are traditionally exhibited with a doughnut‐shaped intensity distribution, where a null intensity center surrounded by a bright ring, caused by the phase singularity. Herein, geometric metasurface devices that can generate near‐field vortex beams with variable intensity profiles are proposed and experimentally demonstrated. The generation of a vortex beam with tailored intensity profile is realized by integrating the azimuthal nonlinear phase and spiral phase into ring‐shaped anisotropic air‐slit arrays. As proof‐of‐principle examples, multiple geometric metasurfaces that generate vortex beams with CN−fold rotational symmetric or asymmetric intensity profiles in the near‐field are demonstrated in the terahertz domain. This unique capability for terahertz near‐field vortices with variable intensity distributions based on geometric metasurface approach opens an avenue to develop multifunctional integrated systems and system‐on‐chip devices, leading to potential applications in microscopy, integrated photonics, quantum information processing, and optical communication.

Metamaterial-based quarter-wave plates (QWPs) have emerged as promising candidates for advanced polarization control in a variety of optical applications, owing to their unique properties, such as ultra-thin profiles and tailored spectral responses. We design an ultra-thin, high-efficiency, and broadband QWP in transmission mode based on a TiO2/Au grating structure. We show that multiple reflections and the near-field effects associated with the integration of these devices pose challenges that must be considered when combining multiple metamaterials. We present insights that facilitate improved design methodology and the optimization of integrated metamaterial QWPs and other metadevices. Our results contribute to the development of miniaturized and high-density advanced lightwave and polarization control devices in optical systems.

A chiral near‐field with a highly contorted electromagnetic field builds a bridge to match chiral molecules and light wavelengths with large size differences. It significantly enhances the circular dichroism of chiral molecules and has great prospects in chirality sensing, detection, trapping, and other chirality‐related applications. Surface plasmons feature outstanding light‐trapping and electromagnetic‐field‐concentrating abilities. Plasmonic chiral nanostructures facilitate light manipulation to generate superchiral near‐fields. Meanwhile, the nanophotonic structures have attracted significant interest to obtain strong chiral near‐fields due to their unique electromagnetic resonant properties. During the interaction of light and chiral materials, the chiral near‐field not only bridges the light and chiral molecules but is also responsible for the optical activities. This paper reviews state‐of‐the‐art studies on generating or enhancing chiral near‐fields using plasmonic and photonic nanostructures. The principle of chiral near‐fields and the development of chiral near‐fields with plasmonic and photonic nanostructures are reviewed. The properties and applications of enhanced chiral near‐fields for chiral molecule detection, spin‐orbit angular interaction, and the generation of the chiral optical force are examined. Finally, current challenges are discussed and a brief outlook of this field is provided. [ABSTRACT FROM AUTHOR]