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Based on the principle of super-symmetric lens with quadratic phase gradient transformation, combined with the principle of digital coding of metasurface, we propose a wide-angle coded metalens for focusing control in two-dimensional space. This metalens achieves focus shift in the x-direction by changing the oblique incidence angle of the incident wave, and focus control in the y-direction by combining with the convolution principle of the digitally coded metasurface to achieve flexible control of light focusing in the two-dimensional plane. The metasurface unit is mainly composed of three-layer of metal structure and two layers of medium, and the transmission phase is obtained by changing the middle layer of metal structure, which in turn obtains the required phase distribution of the metalens. The design of the metalens realizes the function of the lens with a large viewing angle at the x-polarized incidence, and realizes two-dimensional focus control. Experimentally, we prepared the designed coding metalens and tested the focus control function of the wide-angle coding metalens. The experimental results are in good agreement with the design results.

In today's era of increasing energy constraints, harnessing the power of electromagnetic waves and converting them into directly usable energy has great potential in the field of renewable energy. This paper presents a highly efficient electromagnetic energy harvester with wide operation angles based on metasurface. The metasurface unit comprises four rotated copper rings plated on a Rogers RT5880 substrate. This unique design incorporates a 3.6 kΩ resistor within each of the four-cornered rotating metal rings, effectively emulating the input impedance circuit of a rectifier. Simulation results reveal that the metasurface achieves a remarkable electromagnetic wave harvesting efficiency of up to 92.3% at a frequency of 5.85 GHz. Additionally, it exhibits polarization insensitivity, enhancing its versatility and suitability for wide incident angles, which augments its practicality in various environments. The proposed metasurface energy harvester represents a significant advancement in electromagnetic energy collection technology, offering an efficient and reliable energy harvesting solution that contributes to addressing energy shortages and is applicable across multiple scenarios. [ABSTRACT FROM AUTHOR]

Designing dielectric absorber materials with wideband absorption, wide-angle performance, and lightweight characteristics remains a significant challenge. Inspired by the porous structure of volcanic rock, this study employed a simple one-step hydrothermal method and bubble assistance to synthesize micro/mesoporous Ni2P−Cu3P binary nanophosphides, which were then enhanced with CNTs to create a three-dimensional mesh structure. The porous structure of the Ni2P−Cu3P nanocomposite not only facilitates the formation of rich heterogeneous interfaces on the material surface, inducing lattice defects but also enhances interface polarization due to the uneven surface charge distribution of the pore structure. As a result, at a filling rate of only 10%, Ni2P−Cu3P/CNTs achieved an effective absorption bandwidth of 6.6 GHz with a thickness of 2.4 mm. Furthermore, this nanocomposite exhibited outstanding absorption performance within a wide oblique incidence range of 0−67° for transverse electrical (TE) mode and 0−75° for transverse magnetic (TM) mode. Notably, at reflection loss levels of −5 and −10 dB, the maximum effective oblique incidence angles reached 80° and 67° for TE and TM modes, respectively. These studies underscore the exceptional wide-angle and broadband absorption capabilities of Ni2P−Cu3P/CNTs nanocomposite materials even at extremely low filling rates, making them highly suitable for designing lightweight, broadband, and polarization-insensitive absorbers. [ABSTRACT FROM AUTHOR]

This work proposes and investigates a wide‐angle band‐pass frequency selective surface (FSS) with two sharp sidebands. The presented FSS element is made up of three metallic layers and two substrate layers in between, which are surrounded by a substrate‐integrated waveguide (SIW) cavity. The top metallic layer is identical to the bottom layer, composed of a square patch etched with a hexagonal groove, while the middle layer is a similar patch but with rectangular notch edges. This structure achieves a second‐order band‐pass response with highly frequency selectivity on either side of the passband. At the same time, this FSS demonstrates excellent stability for both transverse electric and transverse magnetic polarizations with incident angles between 0° and 60°. The electric current and field distributions are demonstrated for deep analysis. Furthermore, an equivalent circuit model is developed to further understand the operating mechanisms. To verify the validity of the design, we construct a prototype of the SIW‐based FSS (SIW‐FSS) and measured it. There is a fair degree of agreement between the measured and simulated results. Finally, we loaded it onto the horn antenna and tested its application in filtering antennas. [ABSTRACT FROM AUTHOR]

In today’s era of increasing energy constraints, harnessing the power of electromagnetic waves and converting them into directly usable energy has great potential in the field of renewable energy. This paper presents a highly efficient electromagnetic energy harvester with wide operation angles based on metasurface. The metasurface unit comprises four rotated copper rings plated on a Rogers RT5880 substrate. This unique design incorporates a 3.6 kΩ resistor within each of the four-cornered rotating metal rings, effectively emulating the input impedance circuit of a rectifier. Simulation results reveal that the metasurface achieves a remarkable electromagnetic wave harvesting efficiency of up to 92.3% at a frequency of 5.85 GHz. Additionally, it exhibits polarization insensitivity, enhancing its versatility and suitability for wide incident angles, which augments its practicality in various environments. The proposed metasurface energy harvester represents a significant advancement in electromagnetic energy collection technology, offering an efficient and reliable energy harvesting solution that contributes to addressing energy shortages and is applicable across multiple scenarios.

Most planar absorbers are designed under normal incidence, leading to a sharp decline in absorber performance under oblique incidence, especially when the incidence angle exceeds 30°. Three‐dimensional structured absorbers ensure the performance of the absorber under oblique incidence, but they lack practicality due to their complex processing and assembly. In this letter, a tightly‐coupled planar absorber (TCPA) is proposed. Its design method combines the reciprocity principle and tightly‐coupled structure, incorporating a wide‐angle matching layer and interdigitated structures to improve planar absorber's performance under oblique incidence. A sample is fabricated and measured for verification. The measurement results show that the absorber has a fractional bandwidth of 102.0% with an absorption rate of at least 90% under normal incidence. When the incident angle reaches 50°, the absorber maintains good performance under both transverse electric and transverse magnetic polarization. [ABSTRACT FROM AUTHOR]

In this paper, a metasurface-based reflective polarization converter for multi-band multi-functional polarization conversion with high-efficiency and wide-angle in the terahertz region is presented. The proposed metasurface cell is formed by a hybrid resonator composed of a modified double V and a stepped cut-wire, and a single-layer polyimide backed with gold. In the frequency band of 0.7–1.1 THz and 1.72–1.92THz, a linearly y-/x-polarized (LP) incident EM wave is converted into its cross-polarized direction with a polarization conversion ratio greater than 0.9 (PCR > 0.9). Also, in the frequency band of 1.05–1.71THz, an LP incident EM wave is converted into a circularly polarized reflective wave with an axial ratio (AR) less than 3 dB (AR < 3 dB). The multi-functional polarization conversion performance stays stable even though the incident angle up to 40 ∘ . The numerical calculations, and physical insight analysis using surface currents distributions are studied. The results demonstrate that the proposed converter provides a new and efficient method to design high-efficient, incident angle insensitive, multi-band polarization converter for multiple polarization conversion in the terahertz frequency bands. The design can find potential applications in multi-band and multi-polarization THz communication, imaging, and sensing. [ABSTRACT FROM AUTHOR]

The rapid development of metamaterials offers a new avenue to achieve exotic electromagnetic properties, such as perfect absorption for important stealth engineering applications. So far, there are few demonstrations of wide-angle broadband absorption, due to the stringent impedance matching requirement. Here, inspired by the concept of log-periodic dipole antenna (LPDA) for broadband emission, we propose a wide-angle broadband absorption based on both indium tin oxide (ITO) material and judiciously engineered metapyramid geometry. The strip ITO arrays on the sidewalls of metapyramid follow the quasi-LPDA strategy for gradient impedance and expands significantly both angular and spectral operating bandwidth by a cascading of multiple electric and magnetic resonances, as revealed by the rigorous characteristic mode analysis. Our experimental results show that the exotic absorption reaches above 0.9 at 45° tilted incidence for both transverse electric and transverse magnetic polarizations across the band of 8 ∼ 18 GHz. Our strategy circumvents the issues of limited-angle operation, high costs and high weight raised by metal structures, providing a new paradigm toward wide-angle broadband metadevices.

Ultrathin metalenses are a revolutionary technology that have emerged in recent years, offering the potential for high‐resolution, wide‐angle imaging in a compact form factor. However, to eliminate imaging aberrations, multilayered structures are often required, which makes the thickness of these devices comparable to the focal length, negating their ultrathin advantage. Here, a novel methodology using a rear‐position wavevector filter is proposed as a solution to this problem, allowing for the necessary thickness to be achieved in subwavelength scale and independent of metalens parameters. Compared with the previous wide‐angle metalens with the minimum ratio of thickness to focal length, this approach has been shown to compress the ratio of thickness to focal length by 55 times compared to traditional metalenses and has been experimentally demonstrated in both the visible and near‐infrared with a maximum diffraction‐limited field of view of over 120°. In addition, this approach can also compress the system length by 50% and increase imaging resolution by more than 3 times. This methodology can be scaled to all spectral bands and has the potential to revolutionize the design paradigm of imaging systems for industrial and research applications. [ABSTRACT FROM AUTHOR]

Optical coherence tomography is a new promising chromatographic imaging technique with the advantages of noncontact and high resolution without damage, which is widely used in the field of biological tissue detection and imaging. As an important optical element in the system, the wide-angle depolarizing reflector plays a key role in the accurate acquisition of optical signals. Ta2O5 and SiO2 are selected as the coating materials for the technical parameter requirements of the reflector in the system. Based on the basic theory of optical thin film and combined with MATLAB and OptiLayer software, the design of 0~60° incident 1064 ± 40 nm depolarizing reflective film is realized by establishing the evaluation function of the film system. To optimize the oxygen-charging distribution scheme during film deposition, the weak absorption properties of the film materials are characterized by optical thermal co-circuit interferometry. According to the sensitivity distribution of the film layer, the optical control monitoring scheme with a thickness error of less than 1% is designed rationally. "Crystal control + optical control" is used to precisely control the thickness of each film layer and complete the preparation of resonant cavity film. The measurement results show that the average reflectance is more than 99.5%, and the deviation of P-light and S-light is less than 1% in the 1064 ± 40 nm wavelength band range from 0° to 60°, which meets the requirements of optical coherence tomography system. [ABSTRACT FROM AUTHOR]

Relaxation dynamics, as a key to understand glass formation and glassy properties, remains an elusive and challenging issue in condensed matter physics. In this work, in situ high-pressure synchrotron high-energy X-ray photon correlation spectroscopy has been developed to probe the atomic-scale relaxation dynamics of a cerium-based metallic glass during compression. Although the sample density continuously increases, the collective atomic motion initially slows down as generally expected and then counterintuitively accelerates with further compression (density increase), showing an unusual nonmonotonic pressure-induced steady relaxation dynamics cross-over at ~3 GPa. Furthermore, by combining in situ high-pressure synchrotron X-ray diffraction, the relaxation dynamics anomaly is evidenced to closely correlate with the dramatic changes in local atomic structures during compression, rather than monotonically scaling with either sample density or overall stress level. These findings could provide insight into relaxation dynamics and their relationship with local atomic structures of glasses. [ABSTRACT FROM AUTHOR]

Metasurfaces attracted extensive interests due to their outstanding ability to manipulate the wavefront at a subwavelength scale. In this study, we demonstrated quasi-freeform metasurfaces in which the radius, location, and height of the nanocylinder building blocks were set as optimized structure parameters, providing more degrees of freedom compared with traditional gradient metasurfaces. Given a desired wavefront shaping objective, these structure parameters can be collectively optimized utilizing a hybrid optimized algorithm. To demonstrate the versatility and feasibility of our method, we firstly proposed metasurfaces with deflecting efficiencies ranging from 86.2% to 94.8%, where the deflecting angles can vary in the range of 29°–75.6°. With further study, we applied our concept to realize a variety of high-efficiency, wide-angle, equal-power beam splitters. The total splitting efficiencies of all the proposed beam splitters exceeded 89.4%, where a highest efficiency of 97.6%, a maximum splitting angle of 75.6°, and a splitting uniformity of 0.33% were obtained. Considering that various deflecting angles, and various splitting channels with different splitting angles, can be realized by setting the optical response of metasurfaces as the optimization target, we believe that our method will provide an alternative approach for metasurfaces to realize desired wavefront shaping. [ABSTRACT FROM AUTHOR]

Beam steering plays a vital role in light detection and ranging (LiDAR). However, the scanning speed is below megahertz (MHz) in current LiDAR systems. Frequency‐gradient metasurface has been reported to achieve gigahertz (GHz) beam steering with 25° scanning angle in two dimensions. However, the fabrication of millions of form‐varying nanoscale meta‐atoms poses challenges in operation efficiency, massive production, and overall cost‐effectiveness when the size goes beyond millimeter scale. Here, a dynamic beam steering comprising periodic grating nanostructures fabricated through nanoimprint lithography with an ultrafast scanning rate up to GHz (≈81 ps) and ultra‐wide three‐dimensional (3D) fields of view up to 53° × 23° is reported, which shows the powerful acquisition of 3D space data. The detection distance of object reaches to ≈230 m. This work demonstrates a wide‐angle and high‐speed beam steering, and paves a robust way to realize cost‐efficient, high‐volume manufacturing, and powerful 3D all‐solid‐state LiDAR for next‐generation intelligent vision and self‐driving technologies. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: The purpose of this study was to test for superiority of wide-angle digital breast tomosynthesis plus synthetic mammography (Insight 2D) in comparison to full-field digital mammography (FFDM).Materials and Methods: In this study, twenty readers interpreted 350 screening and diagnostic cases of wide-angle digital breast tomosynthesis (DBT) plus Insight 2D and FFDM in two separate reading sessions separated by at least a 6-week washout period. Breast-level estimates of the area under the curve and sensitivity along with subject-level recall rate were measured and compared between wide-angle DBT plus Insight 2D and FFDM. The same measures were also assessed for dense breasts. A hierarchical analysis plan was used to control the study's type I error rate at 0.05.Results: The mean breast-level area under the curve for distinguishing breasts with cancer from non-cancer breasts was 0.893 with DBT plus Insight 2D versus 0.837 with FFDM, showing superiority of DBT plus Insight 2D (p < 0.001). Breast-level sensitivity was significantly superior for DBT plus Insight 2D in comparison to FFDM (0.852 vs. 0.805, p = 0.043). Subject-level recall rate for DBT plus Insight 2D was significantly lower in comparison to FFDM (0.344 vs. 0.473, p < 0.001). For dense breasts, the readers' accuracy with DBT plus Insight 2D was superior to their accuracy with FFDM (0.875 vs. 0.830, p = 0.026), and their recall rate was significantly lower for DBT plus Insight 2D in comparison to FFDM (0.338 vs. 0.441, p = 0.003).Conclusion: Reader performance with wide-angle DBT plus Insight 2D is superior to that with FFDM, showing significantly higher breast-level accuracy and sensitivity and significantly lower recall rates. [ABSTRACT FROM AUTHOR]

Conventional Dammann gratings control the phase profiles of light by varying the etching depths of the DOEs, suffering from a contradiction between the fabrication complexity and the output performance. Due to the advantage of the single-step fabrication procedure, the ability to locally manipulate light at a subwavelength resolution, and the possibility of vertical integration, metasurfaces have attracted extensive interest. Here, we propose polarization-independent metasurface-based Dammann gratings that can redistribute a collimated light into high efficiency wide-angle spot arrays with desired intensity distributions. We combine a hybrid optimization algorithm with the finite-difference time-domain method to optimize the supercells of the metasurfaces. To illustrate the effective control over the power distributions among the desired diffraction orders, we first optimize metasurfaces with uniform intensity distributions. As an extension of the finding, we furthermore demonstrate metasurfaces with an intensity proportion of 1: 1.5: 2 and 1: 2. The diffraction efficiency errors are 4.67 %, 3.85 %, 1.7 %, and 9.16 % with an overall efficiency reaching 89.9 %, 85 %, 90.2 %, and 77.6 % in the four designed metasurfaces. The maximal diffraction angles for 3 × 3 and 5 × 5 diffractive spot arrays are 43.2° and 49.3° from the center. The bandwidth performance analysis demonstrates that the proposed metasurfaces show high diffraction performance in the C-band fiber telecommunications window (1530–1565 nm). Owing to the accurate modulation over intensity distributions, high diffraction efficiency, large diffraction angle, wideband characteristics, polarization-insensitive property, and single-step fabrication procedure with high etching depth tolerance, the proposed gratings may have potential applications in various regions, including optical information processing, beam shaping, and depth detection.

Although various nonreciprocal thermal emitters have been suggested to break the balance between absorption and emission, the majority can only achieve nonreciprocal effect at one certain angle, and the angular range in which these structures exhibit nonreciprocal effect is heavily restricted. In this work, the scheme to realize extremely wide-angle nonreciprocal thermal radiation effect is proposed and investigated. It is achieved by placing a dielectric grating atop a Weyl semimetal film backed with a metal mirror. The results show that the emitter exhibits strong nonreciprocal radiation at the wavelength of 15.98 μm when the incident angle is 30°. What's more, the strong nonreciprocal radiation can be achieved in a wide angular range. Such behavior results from the guided mode resonance, which is revealed by investigating the distribution of electromagnetic field at the resonant wavelength and is also confirmed by the dispersion relation of guided mode. This work provides a new approach to the design of novel nonreciprocal thermal emitters.

With the rapid development of laser medicine, there are higher requirements placed on the performance of optical components in various medical systems. This paper is aimed at exploring the critical optical devices of medical equipment for treating periodontitis and gingivitis. The cathode sputtering method was used to produce the wide-angle short-wave pass filter, and a hundreds grid fastness test was conducted to detect the occurrence of film peeling. Considering the results of SEM, transmission spectrum, and stress test of the sample, an analysis was conducted as to the cause of poor bonding force for the film. By increasing the amount of argon gas and adjusting the baking temperature, the problem of film peeling was resolved. Besides, a short-wave pass filter film with good bonding and low roughness was obtained to meet the requirements of laser medical equipment. [ABSTRACT FROM AUTHOR]

This paper proposes a double layer of gold multipattern swastika (DLMP) resonator based on SiO2 substrate. The average absorption of 95% is achieved for the DLMP metasurface‐based solar absorber in the spectrum (0.1–3 μm) covering the ultraviolet, visible, near‐infrared (NIR), and some range of mid‐infrared regions which makes proposed solar energy absorber ultra‐wideband. The absorptance rate of more than 90% is achieved for the bandwidth of 2516 nm, in absorptance spectrum of 0.314 to 2.830 μm. Shape analysis is also carried out for proposed structure with simulations of five variations and comparative analysis in terms of absorptance response under solar radiation is also presented to check the effect of shape variation on absorption. Furthermore, the influence of several structural parameters on absorptance spectra is also investigated. It is also observed that the absorptance spectrum of proposed solar absorber is angle insensitive for the range of 0° to 70° and is also polarization insensitive. General regression neural network is used to build regression models which can learn and predict the behavior of absorbers in assorted conditions. Experimental results prove that these models can predict the absorber behavior with high accuracy and can reduce the simulation time, resource requirements by 80%. [ABSTRACT FROM AUTHOR]

In this study, a low-profile ultra-thin metasurface-based reflection-type polarization converter with enhanced bandwidth for X-band (8.2–12.4 GHz) applications is proposed. The designed converter, which has a cell topology above a substrate (FR-4) material terminated in a metal conductor with overall thickness of 1.2 mm corresponding to a thickness of 0.042 λ in terms of wavelength (ultra-thin), indicates the cross polarization performance with a polarization converter ratio (PCR) value of 90% in a wide (9–12 GHz) frequency range (normal incidence) and linear to circular polarization performance with left-handed circular polarization between 8.44 and 8.58 GHz and between 12.74 and 13.14 GHz. It is observed that the converter has a PCR value of 80% for incidence angles up to 60 ∘ . Simulations of the designed converter performed by a commercial electromagnetic simulation program (CST Microwave Studio) were validated by free-space measurements. [ABSTRACT FROM AUTHOR]

• A simple and easy-to-fabricate Ag-NPs/SiO 2 /MXene plasma model is proposed. • The average absorption with a maximum absorption of 99.99 % in the visible and near-infrared can be realized in the proposed Ag-NPs/SiO 2 /MXene structure. • The wide-angle absorption can be realized in the proposed Ag-NPs/SiO 2 /MXene structure. • The ultra-high thermal emissivity was realized at 1200 K for the proposed Ag-NPs/SiO 2 /MXene model. n this paper, we presented an Ag-NPs/SiO 2 /MXene plasma model consisting of an MXene layer, a silicon dioxide (SiO 2) layer with silver nanoparticles (Ag-NPs) as well as an indium tin oxide (ITO) substrate. The light absorption and thermal radiation of the Ag-NPs/SiO 2 /MXene plasma model were investigated by finite-difference time-domain (FDTD) and experimental methods. The results showed that due to the localized surface plasmon resonance (LSPR) generated on the surface of Ag-NPs, the maximum absorption of the Ag-NPs/SiO 2 /MXene plasma model in the visible and near infrared could reach 99.99 %, and the ultra-high wide-angle absorption from 0° to 60° was achieved, and the simulated data were in good agreement with the experimental data. Finally, we calculated that the Ag-NPs/SiO 2 /MXene model was 93.0 % ultra-efficient thermal emissivity at 1200 K using Planck's law theory. Broadband absorption and thermal emission of the Ag-NPs/SiO 2 /MXene structure of importance in the field of light absorption. [ABSTRACT FROM AUTHOR]

A 2-bit wide-angle coding metasurface is proposed to decrease the bistatic radar cross section (RCS) in this study. Each meta-atom of the designed coding metasurface is composed of a wide-beamwidth microstrip antenna whose feeding port is loaded with an open stub. There are globally four phase-coding states, namely, “00,” “01,” “10,” and “11,” which are achieved in a wide-angle range through an elaborate design of the lengths of the open stubs. Simulation results indicate that, for each meta-atom, the reflective amplitude is above −1 dB, and the reflective phase difference between two adjacent coding states is limited in the range of 90° ± 25° at 8 GHz at incident angles, 0°, 20°, 40°, and 60°. In addition, the generalized Rudin–Shapiro (RS) polynomial is applied to design the coding sequence of the metasurface array to reduce bistatic RCS. A 16 × 16 metasurface array is simulated, manufactured, and measured to validate the bistatic RCS reduction. The simulated results perfectly agree with the experimental results when the incidence angle of the 8 GHz plane wave is within 60°, which shows that the coding metasurface is practical and valid.

Programmable metasurfaces have the powerful capability of controlling electromagnetic (EM) waves by coding the digital state of each meta-atom. However, conventional programmable metasurface units are difficult to maintain stable controllability under wide-angle incidence conditions, which limits the application of 1-bit programmable metasurfaces in single-beam scanning. A 1-bit dual-polarized programmable metasurface that allows oblique incidence at large angles is presented in this article. Inspired by the principle of reciprocity in the antenna theory, a wide-angle patch antenna which operates in the receiving mode and is loaded by a PIN-diode–based load circuit is designed as the basic structure of the meta-atom. Numerical simulations show that the 1-bit coding state maintains good angular stability within ±70 degrees of the incident angle for both orthogonally polarized EM waves, and single-beam scanning can be achieved at large oblique incident angles for any polarization.

Abstract Background Recent advances in material science and electronics led to the rapid development of communication devices and radar detection techniques resulting in an ever-increasing demand for improved stealth performance of air vehicles during scouts. Absorber design employing metastructure concept has recently become a popular approach to improving radar stealth performance. Metastructure permits the realization of desired absorption characteristics by careful design of geometrical structures and material compositions. In this study, a metastructure designed based on graphite SLS composite for radar absorption has been demonstrated. The unit cell of the proposed structure is simulated by COMSOL Multiphysics to determine the frequency-dependent absorption characteristic of the structure. It is fabricated by using a low-cost selective laser sintering technique of additive manufacturing technology. Results The prototype, while measured, shows effective absorption bandwidth of 1.04 GHz that is in reasonable agreement with the simulated response of 2.08 GHz. The optimized structure exhibits ≤ − 10 dB reflectivity within a broad frequency range extending from 7.60 GHz to 18.00 GHz under normal incidence in both TE and TM polarizations. Furthermore, the absorption performance under different polarizations and incident angles has been investigated. Results indicate that the absorber displays polarization indifference and exhibits a wide-angle of incidence tolerance of up to 45° in TE polarization and 30° in TM polarizations. Conclusion In this paper, the feasibility of using graphite SLS material to design and 3D print a metastructure design for radar absorbing has been established as confirmed by the simulation and the measurement results. The advantages of low cost, ultra-broad operating band, wide-angle of incidence feature, and polarization insensitivity qualifies the proposed absorber for stealth and electromagnetic shielding applications.

In this paper, a wide-angle frequency-scanning array antenna is presented for three-dimensional (3D) radar. Initially, a modified composite right/left-handed (CRLH) unit cell based on a dual-layer finger-connected interdigital capacitor (FCIDC) is analyzed. Compared with its conventional counterpart, the proposed unit cell eliminates the undesired high-order resonances and has a lower right/left-handed passband. Then, a broadband frequency-scanning feeding network, which has a large scanning angle, is designed using the proposed CRLH unit cell. The responses of the four output ports indicate that the network can offer desired amplitude and phase difference to scan towards both negative and positive elevation angles. To validate its performance, a tightly coupled planar quasi-Yagi antenna array is fed to synthesize an array antenna. The measured results show that the designed array antenna has an impedance bandwidth ($\vert \text{S}_{11}\vert

This paper proposes a broad-band linear-to-circular polarization converter based on a multi-layer stripline metasurface. The structure is constructed of three stripline metallic layers stacked with two dielectric plates, and it has different electromagnetic response characteristics in two orthogonal directions. Based on this, the amplitude of the two orthogonal components of the transmitted wave is equal, and the phase difference is 90°. To better understand the working principle of the proposed converter, a detailed equivalent circuit model is presented. The simulation results indicate that the converter can convert linearly polarized incident waves into circularly polarized transmitted waves in the frequency range of 4.96–12.44 GHz. For an increased incident angle of 50°, the device can still maintain an axial ratio bandwidth of 53.7% in the x-z and y-z planes. Because of its broadband, small size, and wide-angle, the proposed converter can be integrated into a linearly polarized antenna system to generate circularly polarized waves without significantly affecting antenna performance.

A novel back-to-back microstrip antenna is proposed to cover 2G/3G/4G/5G communication bands and ISM-2.4 GHz, ISM-5.8 GHz to simultaneously realize broadband wide-angle ambient wireless energy harvesting and dedicated wireless power transfer. The ground mode radiation is introduced by the limited-sized ground, with the loading of the patches and shorting vias, to form a broadband resonance from 2 GHz to 4 GHz. Furthermore, a resonance at ISM-5.8GHz is also excited with high-directivity. On the basis of ensuring miniaturization (e.g. $0.28\lambda _{0} \times 0.22\lambda _{0} \times 0.05\lambda _{0}$ for 2 GHz) and compactness, omnidirectional radiation in broadband resonance and bi-directional radiation at 5.8 GHz are realized by the `back-to-back' combination of two antenna elements. Measured results show that an over 67.2% impedance bandwidth (2.03 GHz~4.08 GHz) is obtained. Through the wireless power transmitting and receiving test, the angular stability of above ±60° for wireless energy harvesting is achieved at the mainstream operating frequencies. At ISM-2.4 GHz RF power of up to -8.5 dBm can be harvested at a distance of 0.5 m from the transmitter with the transmitting power of 12.5 dBm, while it is -8.9 dBm at ISM-5.8 GHz, which validates the effectiveness for WEH/WPT.

Metasurfaces attracted extensive interests due to their outstanding ability to manipulate the wavefront at a subwavelength scale. In this study, we demonstrated quasi-freeform metasurfaces in which the radius, location, and height of the nanocylinder building blocks were set as optimized structure parameters, providing more degrees of freedom compared with traditional gradient metasurfaces. Given a desired wavefront shaping objective, these structure parameters can be collectively optimized utilizing a hybrid optimized algorithm. To demonstrate the versatility and feasibility of our method, we firstly proposed metasurfaces with deflecting efficiencies ranging from 86.2% to 94.8%, where the deflecting angles can vary in the range of 29°–75.6°. With further study, we applied our concept to realize a variety of high-efficiency, wide-angle, equal-power beam splitters. The total splitting efficiencies of all the proposed beam splitters exceeded 89.4%, where a highest efficiency of 97.6%, a maximum splitting angle of 75.6°, and a splitting uniformity of 0.33% were obtained. Considering that various deflecting angles, and various splitting channels with different splitting angles, can be realized by setting the optical response of metasurfaces as the optimization target, we believe that our method will provide an alternative approach for metasurfaces to realize desired wavefront shaping.

In this communication, a phased array antenna with an integrated metasurface is designed to achieve wideband and wide-angle scanning. Generally, the coupling between adjacent elements changes significantly as the scanning angle increases, resulting in limited scanning coverage. Two mutually perpendicular metasurface slabs are designed to achieve wide-angle scanning. The mutual coupling is reduced by properly tuning the dimension of the metasurface. Two perpendicular linear arrays were fabricated to verify the design. The measured 3 dB beamwidth of the active element pattern (AEP, in the array environment) with the integrated metasurface is about 150° in the E-plane and 109° in the H-plane, which is suitable for wide-angle scanning. The simulated and measured results indicate that the beam can scan from −78° to 78° with a 3 dB gain fluctuation in the E-plane array and a wide frequency range from 10 to 12.5 GHz (22.2%). In the H-plane array, the scan angle ranges from −69° to 69° with a 3 dB gain fluctuation and a relative bandwidth of 11%. [ABSTRACT FROM AUTHOR]

This article focuses on the design of super compact, polarization insensitive with wide angular stability, ultrathin triple‐band metamaterial absorber. The unit cell comprising patches achieves almost perfect absorption (close to 100%) at C, X, and Ku band thereby justifying the term perfect metamaterial absorber. The structure provides 99.96%, 99.98%, and 99.62% absorptivity at the 4.75 GHz (C‐band), 9.47 GHz (X‐band), and 14.40 GHz (Ku‐band), respectively. The dimension of the structure is super compact of the order of 7.2 × 7.2 × 0.8 mm3 along with the ultrathin profile. The unit cell thickness is 0.012 λlowest (where λlowest is at a lowest cut‐off frequency). The proposed absorber comprises an outermost ring, split ring, innermost ring and square line with triangle patches at the boundary. The combinational effect of rings and internal patch provides perfect absorption at designated frequencies. Further, equivalent circuit is explained for the proposed design. The absorptivity remains insensitive towards transverse electric and transverse magnetic polarized wave and exhibits matched absorption. Moreover, the stability of the proposed design is validated with the different incident (for TE and TM modes) and polarization angles. The results are found close to perfect absorption. Finally, the simulated results are validated with measured results and found in close agreement. [ABSTRACT FROM AUTHOR]

In this paper, a wideband and wide-angle transmissive linear-to-circular polarization converter (LCPC) working in the C, X and Ku bands is proposed, which is based on a single-layer dielectric substrate. In order to increase the axial ratio bandwidth of the single-layer LCPC, a method of combining infinite length metal strips and horizontal strips is proposed, which cannot only improve the passband, but also realize large phase difference conversion. The single-layer LCPC with small size is designed and optimized, which can maintain axial ratio stability in the ultra-wide band over large incident angles. When the linear polarized (LP) wave is normal incident, the 3 dB axis ratio bandwidth of LCPC is 6.41–15.07 GHz (relative bandwidth 80.63%). When LP wave oblique incident along the yoz plane, the axial ratio bandwidth will increase with the increase of the incident angle, it is worth noting that when the incident angle reaches 45°, its 3 dB axial ratio bandwidth can reach 100.6%. Moreover, when LP wave oblique incident along the xoz plane, the insertion loss is always less than 3 dB within the working bandwidth, and the incident angle can even reach more than 70°. The measured results are in good agreement with the simulated ones. The LCPC can be widely used in multi-beam antenna, beam scanning antenna and satellite communication. [ABSTRACT FROM AUTHOR]

Digital retinal imaging is at the core of a revolution that is continually improving the screening, diagnosis, documentation, monitoring, and treatment of infant retinal diseases. Historically, imaging the retina of infants had been limited and difficult to obtain. Recent advances in photographic instrumentation have significantly improved the ability to obtain high quality multimodal images of the infant retina. These include color fundus photography with different camera angles, ultrasonography, fundus fluorescein angiography, optical coherence tomography, and optical coherence tomography angiography. We provide a summary of the current literature on retinal imaging in infants and highlight areas where further research is required. [ABSTRACT FROM AUTHOR]

The design of a lightweight and ultra‐wideband absorber for C and X bands is still a challenge as the dimension of the absorber is relatively large in such a relatively low‐frequency band. Herein, an ultra‐wideband and lightweight metamaterial absorber (MMA) is presented for C‐ and X‐band applications. The unit cell of the proposed MMA consists of four copper sectors loaded by lumped resistors and a continuous copper ground plane, which is printed on two FR‐4 substrates. Furthermore, an airgap separating the FR‐4 layers is used as the active substrate medium of the MMA to achieve both ultra‐wideband absorption spectra and lightweight design. The MMA is investigated by simulation and measurement, showing that a good agreement is achieved. The result indicates that the absorptivity of the MMA under both transverse electric (TE) and transverse magnetic (TM) polarizations is greater than 90% in a wide range from 3.7 to 13.6 GHz for all polarization angles. Compared to other reported broadband absorbers, the proposed MMA shows an ultra‐wide absorption bandwidth and a lightweight design, which demonstrates a great potential for C‐and X‐band applications. [ABSTRACT FROM AUTHOR]

• We numerically show that an ultra-thin Weyl semimetal film can achieve an excellent performance of a high polarization extinction ratio (more than 40 dB) and a low insertion loss (less than 0.07 dB). • Monolayer polarizer shows that the optimum insertion loss is not achieved in the band with the highest PER. An isotropic substrate has little effect on the TM mode, while effectively adjusts the position of TE mode transmission peak. Thus, the proposed sandwich structure can further reduce insertion loss (from 0.06 dB to 0.03 dB) and obtain wider acceptances range of angle (from 49. 5 ∘ to 71 ∘). • Due to the high reflectivity of the two interfaces inside the WSM layer, the incident light is reflected several times in the single-layer structure, forming a structure similar to the Fabry-Perot cavity, which seriously affects the polarizer's performance. To overcome the challenges above, the proposed a gradient Fermi level structure eliminates the interference peak, thus resulting a wider bandwidth (approximately 60 % improvement). This method can be generalized to larger thickness cases. • With the increasing demand for on-chip integrated devices, our work can be helpful for the integration of a range of potential optical applications in optical communication and omnidirectional polarization detectors. Recently, Weyl semimetals have been extensively studied due to their unique optical responses, especially in the mid-infrared region. However, the possibility of developing optical polarizers based on Weyl semimetals remains unexplored. In this paper, under the Voigt geometry, we numerically show that an ultra-thin Weyl semimetal film with thickness L = 100 nm can achieve an impressive polarization extinction ratio (more than 40 dB) with a wide acceptance angle. Further, the proposed sandwich structure can effectively adjust the position of the TE mode transmission peak alone, thus obtaining lower insertion loss (from 0.06 dB to 0.03 dB) and wider acceptance range of angle (from 49. 5 ∘ to 71 ∘). The proposed gradient Fermi level structure eliminates the Fabry-Perot cavity resonance, thus resulting a wider bandwidth (approximately 60 % improvement). Our proposed ultra-thin and wide-angle polarizer may have potential applications in optical communication and omnidirectional polarization detectors. [ABSTRACT FROM AUTHOR]

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Since it is designable, metasurface was widely used in various fields, especially the design of polarization converters. However, most of the polarization converters currently designed can only work under normal incidence or small angle incidence, which hugely limits the application of the device. In this paper, a chiral metasurface based on the z-shaped unit cell, which can manipulate circular polarization wave, is proposed. The simulation result shows that this converter can maintain the polarization state of circular polarization after reflection from 8.18 to 13.988 GHz with a polarization conversion ratio of more than 90%. Moreover, the structure is insensitive to the incidence angle, which can keep a stable performance both for left-handed circularly polarized wave and right-handed circularly polarized waves as the incident angle increase to 75°. The proposed metasurface with simple structure and angular stability can be used in communication and polarization manipulating devices.

A novel dual-band wide-angle ultra-thin absorber composed of dual closed-concentric ten-point stars with polarization independence is presented in this article. The ten-point stars formed resonators are engraved on low cost FR4 substrate. The EM absorber performance is studied in terms of electrical and physical parameters. The polarization independence is practically demonstrated using waveguide measurement method. The measured results are in good agreement with simulated results. The absorbance values of 99.37% and 97.18% are achieved at 2.13 GHz and 2.52 GHz, respectively. The presented absorber design is wide-angle RF absorber with high absorbance values of about 80% up to 60° under TE mode and 87% up to 75° of oblique incidence angle for TM mode excitations. The experimental results demonstrate the absorption effectiveness of the proposed design to be utilized in RF energy harvester modules for capturing ambient UMTS band signals and in RF absorber applications for S band radar systems. The presented absorber unit cell is ultrathin and compact with the thickness and size less than λ/56 mm and λ/5 mm, respectively, at lowest absorption frequency.

A novel 1 bit reconfigurable transmitarray antenna (RTA) using an equivalent magnetic dipole element for wide-angle beam scanning at Ku-band is presented. The RTA element consists of a rectangular patch and a side-shorted patch with an equivalent magnetic dipole radiation. A 1 bit phase difference is achieved by controlling two p-i-n diodes on the side-shorted patch based on the current reversal mechanism. The half-power beamwidth of the presented antenna element is 142° in E-plane, which is significantly larger than other conventional elements. A RTA prototype with $16\times16$ elements is designed, fabricated, and tested. The measured results show good beam scanning capabilities of the 1 bit RTA. The measured gain in the broadside direction is 21.4 dBi, and the scan gain loss is 3.6 dB for the 60° scanned beam in E-plane. [ABSTRACT FROM AUTHOR]

In this article, a coding optimized metasurface is proposed for linear polarization conversion in broadband and wide‐angle. Using an improved coding method, the geometry of the metallic structure and the size of the unit cell are encoded with a code sequence. The code sequence is optimized by genetic algorithm, considering bandwidth, efficiency, and angular stability. In this way, a coding optimized metasurface was obtained for polarization conversion in broadband and wide‐angle. It can convert linear polarized incidence to its orthogonal polarized reflection in 8 to 18.9 GHz and 0° to 45°, with the polarization conversion ratio larger than 80%. Both simulated and measured results demonstrated the effectiveness of the proposed metasurface. Hence, our method offers an effective strategy to design high‐performance polarization conversion metasurfaces. [ABSTRACT FROM AUTHOR]

A glide-symmetry Goubau line leaky-wave antenna for achieving both high scanning rate and wide scanning angle range is introduced. The novelty of the design is its combination of glide symmetry and a single-layer Goubau line. This combination leads to performance enhancement in both scanning rate and scanning angle range. Utilizing a corrugated Goubau line in a glide-symmetry fashion closes its stopband at the cutoff frequency while slowing down its group velocity. As the dispersion around the closed stopband is shifted to the fast-wave region by periodic profile modulation, the space harmonics exhibit high-scanning-rate radiation. In conjunction with this, the single-layer nature of the Goubau line allows the beam to scan from nearly endfire to backfire directions, leading to a wide scanning angle range. Numerical examples and experimental validation are provided to validate the proposed design. These show that the proposed antenna exhibits dual-band operation, where one band scans 152° within 2.2 GHz (corresponding to scanning rate of 69°/GHz) with 67% efficiency, while the second band scans 145° within 0.7 GHz (corresponding to scanning rate of 207°/GHz) with 26% efficiency. A tradeoff between scanning rate and efficiency always exists in high-scanning-rate leaky-wave antennas. One is able to freely choose the preferred scanning rate in this single antenna. A comparison with other related works shows that the proposed antenna exhibits the best performance. [ABSTRACT FROM AUTHOR]

A compact wideband wide-angle polarization-free metasurface lens (MSL) antenna array is proposed for a multibeam base station operating over the band of 1.71–2.2 GHz. The MSL element comprises of a planar wideband wide-angle polarization-free reflectionless MSL and three feeding sources of ±45° polarized cross-dipole antennas. With the shared lens aperture, the antenna achieves the three beams in the directions of 0° and ±30° in a horizontal plane. A five-layer patch-based metasurface loaded with metal poles are introduced to achieve consistent performance for wide-angle response. To reduce spillover loss, the feeding antennas are loaded with a metasurface and four directors for narrow beamwidth and low profile. With the optimized feeding antennas and MSL, a section of array with $1\,\,\times \,\,4$ MSL elements is prototyped for validation. The measured results show that an impedance bandwidth for return loss ≥ 10 dB is 1.63–2.24 GHz with the isolation larger than 22.3 dB. The measured gain ranges for 0° and 30° beams are 11.8–13.5 and 10–12.2 dBi with the sidelobe levels less than −22.6 and −13.6 dB, respectively. [ABSTRACT FROM AUTHOR]

A wideband and wide-angle linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The converter element consists of a metal strip cross backed by a strip horizontally and centrically located on the other metallic layer. The vertical arm of the strip across the whole surface performs as a high- pass filter with a wide passband above a low cutoff frequency. Meanwhile, the horizontal strip resonates at a high out-of-band frequency and also offers a wideband response below the resonant frequency. Another two short strips vertically and horizontally placed around the crosses increase the phase shift caused by the crosses and improve both the passbands. Using equivalent circuit models and ANSOFT HFSS, an example of LCPC is designed with the overall element size of only $0.11\lambda _{0}\times 0.21\lambda _{0}$ for a 90° phase difference and wide-angle stability over the wide operation band. The prototype shows the simulated / measured axial ratios (ARs) below 3 dB over the bandwidth of 69%/74% for a normal incidence wave and 54% for the oblique incident angle of 55° in yz plane, respectively. With the insertion loss of less than 3 and 2 dB, the measured 3 dB AR bandwidth keeps 70% and 55%, respectively. [ABSTRACT FROM AUTHOR]

Excellent broadband absorption features have broad applications such as photoelectric conversion, optical communication, and photovoltaic cells. In the work, the absorption for a simple and easily fabricated all-MXene grating metamaterial absorber is investigated by using finite-difference time-domain (FDTD) method. The results show that the maximum absorption of the all-MXene grating absorber is higher than 98.5%, and the average absorption up to 90% in the range of 400 nm–2500 nm. The mechanism of broadband absorption is analyzed through using the electric field, magnetic field, and impedance theories. Furthermore, the absorption spectra of the all-MXene grating metamaterial absorber in different polarization states and incidence angles are investigated, and the results show that the wide-angle absorption from 0 to 70° can be realized by the proposed all-MXene grating metamaterial absorber, and the absorption was also independent on the polarization of the light. Lastly, we can apply the advantages of the all-MXene grating metamaterial to solar metamaterial absorbers, which have almost the same absorption spectra as the AM1.5 solar spectra, indicating the all-MXene grating metamaterial absorber have high absorption efficiency and low energy loss. These findings suggest potential applications of the all-MXene grating metamaterial absorber in many fields, including solar batteries, photovoltaics, and solar thermal conversion. • The ultra-broadband and wide-angle absorber from 400 nm to 2500 nm, 0° to 70°can be realized in a simple, low cost and easy to be fabricated all-MXene grating metamaterials. • The absorber has no dependence on polarization of the input light wave. • The proposed absorber can be well applied in the field of solar energy with the advantage of high absorption efficiency and low energy loss. [ABSTRACT FROM AUTHOR]