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Liquid storage tanks are often arranged in rows with small spacing in practical applications, which may cause mutual influence under earthquake action and even aggravate the seismic damage of liquid storage tanks. Adding the vibration barrier (ViBa) into the foundation between the adjacent liquid storage tanks forms a new type of seismic control method. Considering important factors such as liquid–solid–soil coupling, liquid sloshing behavior, and structure–soil–structure interaction (SSSI), a refined 3D numerical calculation model of the adjacent liquid storage tanks with three ViBas is established by ADINA. The influence of seismic wave incidence angle on the seismic responses of the liquid storage tanks and the control effect of ViBa are studied, and the parameter influence analysis is carried out. The results show that the ViBa significantly control the seismic responses and liquid sloshing wave height of the adjacent liquid storage tanks, and the damping ratio of the liquid sloshing wave height is between 30% and 40%. When the seismic incidence angle is between 30 ∘ and 60 ∘ , the dynamic responses of the liquid storage tank is larger. With the increase of the seismic incidence angle, the control effect of the ViBa on the effective stress, hoop stress, axial compressive stress, and liquid pressure first increases and then decreases. When the liquid storage tank is close to full state, the control effect is most significant at an incidence angle of 60 ∘ , and the control effect of the ViBa on the liquid storage tank with medium height-diameter ratio is the best. [ABSTRACT FROM AUTHOR]

BackgroundThe 1.2 MeV/10 mA electron accelerator, as one of electron irradiation sources for comprehensive irradiation test chamber in Space Environment Simulation and Research Infrastructure (SESRI), can provide electron beams on the millimeter scale. However, the electron beam, as the electron irradiation source in space environment ground simulation experiment for aerospace, must be uniformly irradiated on large objects. Therefore, a well-suited irradiated technique is significant.PurposeThis study aims to obtain beam scanning with less than 10% of inhomogeneity for 0.6 MeV, 1.0 MeV, 1.2 MeV electron beam for SESRI.MethodsBased on the overall irradiation requirements, a specific beam-scanning system, including the scanning magnet with customized design, digital power supply and a dedicated apparatus for beam uniformity measurement, was developed. Particularly, in order to eliminate the influence of 45° incidence of electron beam upon scanning uniformity, an asymmetric and non-standard triangular waveform for the magnetic field excitation current was employed and implemented. The measurements for the beam non-uniformity were carried out on field experiments.ResultsExperimental results show that the scanning area of this electron accelerator reaches 1 000 mm×1 000 mm, and the scanning nonuniformity is less than 10% for variable beam energy from 0.6 MeV to 1.2 MeV, achieving the design goal and satisfying the irradiation requirements of SESRI.ConclusionsA specific beam-scanning system developed for SESRI is verified in this study, offering a good reference for any similar beam-scanning scenarios.

Based on the far field function of electric field, a new glass carbon fiber gradient-stitched structure is proposed and designed in the paper. In the frequency range of 8–28 GHz, the electric field distribution of transverse electric and magnetic field (TEM) waves incident obliquely on the surface of the structure by optimizing the glass fiber fabric units. It is confirmed that the surface has the function of suppressing electromagnetic wave reflection. The electrical performance simulation and testing results of the structure show that the radar cross section (RCS) is reduced by 90% in the frequency range of 12.3–26.5 GHz. In addition, a multi-scale analysis model is established to quickly predict the tensile modulus and strength of the composite material. The strength and modulus reached 26.9 GPa and 403 MPa, respectively. The simulating and testing results of mechanical properties are in good agreement. [ABSTRACT FROM AUTHOR]

A high‐efficiency polarization conversion metasurface (PCM) is proposed and applied to radar cross section (RCS) reduction. The PCM can achieve cross‐polarization conversion with a polarization conversion ratio of over 97% from 13.9 to 30.3 GHz, covering K‐band. The low‐RCS antenna is designed from a circularly polarized patch antenna loading with the PCM. The antennas with and without PCM are fabricated and measured. The results show that the radiation performance is well preserved and the scattering performance is greatly improved. The average monostatic RCS reduction value reaches 14.6 dB in an ultra‐wideband from 12.2 to 30.2 GHz under normal incidence. What's more important, bistatic RCS is researched in detail and evident RCS reduction is achieved at different incidence angles. This research has potential applications in the field of stealth platform. [ABSTRACT FROM AUTHOR]

The transmission and reflection of a pulse wave in a porous medium with a layer of a fractured porous medium under normal and oblique incidence is numerically investigated. The study was carried out using a two-velocity model of a porous medium and a three-velocity model of a fractured porous medium. "Opened pores" condition was used on the "porous medium–fractured porous medium" interface. The problem is considered in a two-dimensional formulation. The features of this wave process are revealed. [ABSTRACT FROM AUTHOR]

The boundary conditions of the moving layered medium are analyzed and the expressions of electromagnetic field are deduced. The reflection and transmission coefficients in fixed coordinates are obtained by using the covariance characteristic of Maxwell Equations. It is very complicated to apply boundary conditions many times in analyzing a multi-layer slab. In this paper, the results obtained from the boundary conditions of single-layer slab are analogous with those obtained by the transfer matrix method. Through improvement and generalization, the transfer matrix method can be used to calculate the moving multi-layer slabs. It can be applied to calculate the reflection and transmission coefficients of one-dimensional moving photonic crystal as well as deal with TM and TE polarization for the oblique incident. The zero reflection points of TM and TE polarization for layered slab are calculated. The results calculated in this study are matching well with the reference. It shows that the reflection oscillation enhances with the increase of β and layer number, while the changing rule of reflections about TM polarization is relatively complex. The reflections of both TE wave and TM wave are all related to the incidence angle. [ABSTRACT FROM AUTHOR]

The total focusing method (TFM) has been increasingly applied to weld inspection given its high image quality and defect sensitivity. Oblique incidence is widely used to steer the beam effectively, considering the defect orientation and structural complexity of welded structures. However, the conventional TFM based on the delay-and-sum (DAS) principle is time-consuming, especially for oblique incidence. In this paper, a fast full-matrix imaging algorithm in the Fourier domain is proposed to accelerate the TFM under the condition of oblique incidence. The algorithm adopts the Chebyshev polynomials of the second kind to directly expand the Fourier extrapolator with lateral sound velocity variation. The direct expansion maintains image accuracy and resolution in wide-angle situations, covering both small and large angles, making it highly suitable for weld inspection. Simulations prove that the third-order Chebyshev expansion is required to achieve image accuracy equivalent to the TFM with wide-angle incidence. Experiments verify the algorithm's performance for weld flaws using the proposed method with the transverse wave and the full-skip mode. The depth deviation is within 0.53 mm, and the sizing error is below 15%. The imaging efficiency is improved by a factor of up to 8 compared to conventional TFM. We conclude that the proposed method is applicable to high-speed weld inspection with various oblique incidence angles. [ABSTRACT FROM AUTHOR]

A model of the acoustic scattering of a plane wave incident obliquely upon an infinite elastic bi-layered cylindrical shell is developed based on normal mode expansion technique. The far field backscattering form function for the composite copper/stainless steel cylindrical shell is calculated for reduced frequency range of k ⊥ a 1 = 0 – 70 and for different values of incident angles α (k ⊥ = k 1 cos ⁡ α , k 1 is the wave number in the fluid surrounding the shell and a 1 is the outer radius of the shell). Numerical calculations show the behaviour of the resonances of circumferential and helical guided waves as the angle of incidence increases. The obtained results are compared with those of copper and stainless steel one-layered cylindrical shells. The use of frequency-angle representation depicts the helical propagation of surface waves along the axis of the shell. This representation, along with the identification plan, enables to describe the evolution of acoustic scattering as a function of incidence angle and vibration mode n. Furthermore, a comparative analysis of the resonance trajectory evolution between mono-layered and composite cylindrical shells is performed. The evolution of the helical guided waves, the bifurcation of the A 0 wave into the A 0 − and A 0 + waves, and a region with high backscattering are investigated. The presented results show that the extension of the region with high backscattering depends on the thickness and physical properties of the bi-layered cylindrical shell. • Model of oblique acoustic scattering in bi-layered cylindrical shell (normal mode expansion). • Analysis of acoustic scattering in composite bi-layered shell. • Comparative study: mono-layered vs. bi-layered cylindrical shell. • Study resonance trajectory via frequency-angle & identification plan representations. • Estimation of cut-off angles, coupling angles & coincidence frequencies of guided waves. [ABSTRACT FROM AUTHOR]

In this article, an angle-independent wideband metamaterial microwave absorber (MMA) for C (4–8 GHz) and X (8–12 GHz) band frequency is presented. The unit cell of the proposed MMA consists of outer and inner structure associated with lumped resistors. The outer structure consists of rectangular split-ring resonator, whereas the inner structure consists of circular split-ring resonator. The structure is made up of three layers, in which top and bottom layers are made up of copper acting as a conducting material. The middle layer is made up of FR-4 acting as a dielectric substrate. The resonating structure at the top is designed in such a way that wideband absorption is achieved in the range from 6.11 to 13.52 GHz. The wideband absorption within the range approaches almost unity having a bandwidth of 7.41 GHz. Three different peaks are considered in the range of interest having maximum absorption of 0.94, 0.94, and 0.99 at frequencies of 6.76, 11.15, and 13.07 GHz, respectively. The structure is analyzed with respect to the effective parameters, i.e., effective permittivity (${\varepsilon _{{\textrm{eff}}}}$) and effective permeability (${\mu _{{\textrm{eff}}}}$), to prove that the structure acts as a metamaterial. Electric field and current distribution are plotted at three different peaks to prove the mechanism of wideband absorption. Normal and oblique incidence are plotted to determine that the structure is behaving as an angle independent. The simulated structure is fabricated on FR-4 substrate and measured inside an anechoic chamber. Finally, to prove the novelty of the work, the proposed structure is compared with the already reported MMA. The proposed MMA finds practical applications in radar cross section reduction, terrestrial communication, keyless entry system, space communication, radar, and baby monitor. [ABSTRACT FROM AUTHOR]

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption due to the programmable function of the LCoS-SLM and offer the ability to align the optical system. The oblique-incidence measurement theory and optical system adjustment method are established based on an off-axis paraboloid model. The ray-tracing program to calculate the compensation phase map in the measurement is proposed with math models. In the optical alignment step, the off-axis paraboloid model is used to apply the LCoS-SLM as a phase compensator to generate a focusing spot or light spot array to adjust the measured optical surface. And in the interferometric measurement step, the calculated compensation phase map from the ray-tracing calculation is loaded on the LCoS-SLM using the same optical setup as the optical alignment step without any mechanical adjustment. Two interference measurement experiments of typical optical surfaces were carried out to verify the accuracy of the measuring system. [ABSTRACT FROM AUTHOR]

The preparation of the vast majority of nonlinear optical metal metasurfaces currently relies on complex top-down methods such as electron beam or ion beam etching, which are expensive and difficult to meet the requirement of large area preparation. In this paper, an easily prepared quasi-periodic silver dendritic metasurface model with high Q factor is established in the near-infrared band based on a simple and easy-to-operate electrochemical deposition method. The simulations prove that the silver dendritic metasurface has a high Q factor (exceeds 104) because of its strong electric field localization ability, which is analogous to the superposition of multiple split-ring resonators. It is demonstrated that the second harmonic generation (SHG) intensity of the dendritic metasurface at a large incident angle (such as 85°) is about 30 times that of the metasurface at a small incident angle when the x -polarized pump light is incident obliquely to break the centrosymmetry of the metasurface. The influences of the incident angle or dendritic structure's dimensions on the Q factor and SHG efficiency have also been researched through a lot of simulation. This easily prepared quasi-periodic silver dendritic metasurface SHG device may provide a new avenue for the development and application of miniature, integratable nonlinear optical devices. [ABSTRACT FROM AUTHOR]

In this work, the design of broadband, wide-angle, direction-independent metamaterial (MM) electromagnetic wave (EM) absorber for K-band frequency application is investigated and validated experimentally. The unit cell of the metamaterial absorber consists of four 90° rotated L-shaped metallic patches imprinted on a dielectric substrate backed by a metallic sheet. The structure yield absorption in the broad frequency ranges from 22.5 to 29.3 GHz for both TE and TM polarized waves with more than 90 % absorptivity having a wide fractional bandwidth of (6.8 GHz) 25.8 %. The structure is four-fold symmetric and hence yields polarization insensitivity for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80 % absorptivity holds up to 45° incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonance in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. Measured results are showing good agreement with the simulated responses. The novelty of the proposed absorber lies in its unique metallic pattern on a λ0/8 (concerning the canter frequency of absorption bandwidth) thin FR-4 substrate while showing the wide absorption bandwidth and direction independence to normal and oblique incidence. The compact nature of the absorber and broadband response with good polarization insensitivity at normal and oblique incidence makes it commercially suitable for the reduction of radar cross section (RCS) in stealth applications at the K-band. [ABSTRACT FROM AUTHOR]

This paper presents a mantle cloak structure to provide a wideband capability to hide a metallic cylinder over a broad span of angles of obliquely impinging plane waves. A bi-layered dielectric structure and a sheet of metasurface are used to enclose the object to be hidden. At first, the scattered field, including co- and cross-polarized components, is analytically formulated using circumferential waves for a multilayer wrap around the cylinder. A tensor description is also applied to model the impedance of the metasurface for TE and TM waves. Then, a metasurface made of rectangular patches is considered, and its related parameters are optimized to hide a perfect electric conductor (PEC) cylinder. Moreover, a double-layered mantle cloak is presented and numerically investigated using a software package to enhance its cloaking bandwidth. The numerical results show that the clocking bandwidth is enhanced by up to 33% compared to that of a single-layered structure. [ABSTRACT FROM AUTHOR]

ObjectivesIn order to explore the feasibility of replacing steel trusses with composite reinforcements, this study proposes a composite reinforcement design for the near-field acoustic scattering characteristics of stiffened plates, and conducts the requisite experiments. MethodsFirst, based on the hydroacoustic material testing standards, a test protocol for the sound transmission performance of stiffened plates is established; second, the feasibility of the test environment and conditions is verified through the free field calibration of an anechoic pool and comparisons between the sound transmission performance of flat steel and steel trusses; finally, the sound transmission performance law of stiffened plates under the conditions of positive and oblique incidence is analyzed through experiments. ResultsThe results show that the sound transmission performance of stiffened plates under the conditions of positive and oblique incidence is basically the same, and in the order of bare plate > steel truss > composite stiffened plate. The sound transmission performance of composite stiffened plates is influenced by the cross-sectional area of the incident surface, and the smaller the cross-sectional area, the better the performance. ConclusionsCombined with experimental analysis to explore the future development direction of high sound transmission composite stiffened plates and ensure equal bending stiffness, the design of composite reinforcements should try to use a hollow structural form and reduce the cross-sectional area of the incident surface as far as possible; in addition, the types of material used should be minimized so as to reduce the number of different material interfaces in reinforcements.

The propagation of acoustic waves in the periodic structure of phononic crystals has energy band effects, and phononic crystals containing defects can form new defect modes in the original forbidden band. In this study, the omnidirectional transmission spectra of phononic crystals with and without defects in obliquely incident acoustic waves are calculated respectively by the transfer matrix method, and the defect modes caused by solid defects are found by comparative analysis. On this basis, the influence of the thickness and position of the defect layer on the transmittance of the defect state is studied in this study. The existence of defect modes caused by solid defects and their angle-dependent characteristics are verified by underwater acoustic transmission experiments. The experimental results show that there is a new transmission passband in the first Bragg forbidden band of the omnidirectional transmission spectrum of the defect-containing structure, and with the increase of the incident angle within a certain range, the frequency corresponding to this passband is shifted to the high frequency direction. This study improves the propagation characteristics of obliquely incident acoustic waves in one-dimensional phononic crystals containing defects, and provides a theoretical and experimental basis for the practical application of defect states. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To improve the photoelectric test accuracy of moving objects, in this study, the speed attenuation caused by air resistance was introduced into the double-N six-light-screen test system, and the test system was theoretically analyzed through oblique incidence with field experiment for verification. It was found in the study that the optimal test values for yaw angle, pitch angle, axial speed, and distance could be obtained by selecting the pulse time origin at the center of two light screen groups. In addition, mud pellets were used for field experiments to effectively verify the simulation results. In a new model, the test accuracy of yaw angle and pitch angle was greatly improved when compared with traditional processing methods, but the laws of error distribution remained almost unchanged. The error of axial speed showed monotonicity as affected by the pitch angle. At the same time, the error of test distance remained symmetric with the improved accuracy, thereby meeting the statistical test requirements for small-volume moving objects.

Spectral bandpass filters serving as crucial signal processing components are widely applied in various electromagnetic/optical systems. However, the filtering of reflection signal always faces problems of notably accompanied transmission or strict angular limit. Here, we propose novel transmissionless metagratings for specular-reflection bandpass filtering under wide oblique incidence angles. The metagratings are composed of metallic groove gratings and high-refractive-index dielectric particles, which of them respectively provide continuum of localized cavity mode and discrete magnetic dipole resonance under oblique transverse magnetic waves, and produce broadband and narrowband anomalous reflection. Their destructive interference gives rise to a Fano-type narrow bandpass filter in the specular reflection. By integrating CaTiO3 ceramic particles with metallic groove gratings, we experimentally demonstrate a single-bandpass metagrating filter at microwave frequency which exhibits a low insertion loss and narrow bandwidth under wide-angle oblique incidence, and agrees with simulations well. Furthermore, by arranging two different sized CaTiO3 ceramic particles or changing the temperature, the metagrating filter is endowed with dual-bandpass or thermally tunable feature, respectively. Finally, the design is extended to terahertz frequencies by improving the structure to a double-groove configuration. The proposed composite metagratings with novel bandpass filtering function and angular insensitivity not only enrich the category of spatial filter but have promising applications in microwave communication systems and optical devices. [ABSTRACT FROM AUTHOR]

According to the Fraunhofer diffractive formula, the expression of the complex amplitude of diffractive light for the ultrasonic grating of travelling wave in water for the case of oblique incidence of plane wave is obtained, the expression of the diffractive intensity is obtained and the expression contains a Bessel function, the values of Bessel function affect the diffractive intensity, the factors which affect the value of Bessel function are presented and discussed, the characteristics of the frequency of the diffractive light is discussed. [ABSTRACT FROM AUTHOR]

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption due to the programmable function of the LCoS-SLM and offer the ability to align the optical system. The oblique-incidence measurement theory and optical system adjustment method are established based on an off-axis paraboloid model. The ray-tracing program to calculate the compensation phase map in the measurement is proposed with math models. In the optical alignment step, the off-axis paraboloid model is used to apply the LCoS-SLM as a phase compensator to generate a focusing spot or light spot array to adjust the measured optical surface. And in the interferometric measurement step, the calculated compensation phase map from the ray-tracing calculation is loaded on the LCoS-SLM using the same optical setup as the optical alignment step without any mechanical adjustment. Two interference measurement experiments of typical optical surfaces were carried out to verify the accuracy of the measuring system.

The total focusing method (TFM) has been increasingly applied to weld inspection given its high image quality and defect sensitivity. Oblique incidence is widely used to steer the beam effectively, considering the defect orientation and structural complexity of welded structures. However, the conventional TFM based on the delay-and-sum (DAS) principle is time-consuming, especially for oblique incidence. In this paper, a fast full-matrix imaging algorithm in the Fourier domain is proposed to accelerate the TFM under the condition of oblique incidence. The algorithm adopts the Chebyshev polynomials of the second kind to directly expand the Fourier extrapolator with lateral sound velocity variation. The direct expansion maintains image accuracy and resolution in wide-angle situations, covering both small and large angles, making it highly suitable for weld inspection. Simulations prove that the third-order Chebyshev expansion is required to achieve image accuracy equivalent to the TFM with wide-angle incidence. Experiments verify the algorithm’s performance for weld flaws using the proposed method with the transverse wave and the full-skip mode. The depth deviation is within 0.53 mm, and the sizing error is below 15%. The imaging efficiency is improved by a factor of up to 8 compared to conventional TFM. We conclude that the proposed method is applicable to high-speed weld inspection with various oblique incidence angles.

A new analytical approach to optimize the thicknesses of a two-layer absorbing structure constituted by a graphene-based composite and a polymer dielectric spacer backed by a metallic layer acting as perfect electric conductor (PEC) is proposed. The lossy sheet is made by an epoxy-based vinyl ester resin filled with graphene nanoplatelets (GNPs) characterized by known frequency spectra of the complex permittivity. The optimal thicknesses are computed at the target frequencies of 26, 28, and 39 GHz in order to obtain a –10 dB bandwidth able to cover the 5G frequency bands between 23.8 and 40 GHz. The resulting absorbing structures, having a total thickness lower than 1 mm, are excited by transverse magnetic (TM) or electric (TE) polarized plane waves and the absorption performances are computed in the 5G high frequency range. [ABSTRACT FROM AUTHOR]

Light funneling determines how enhanced energy flows into subwavelength slits. In contrast to the previous research on oblique incident light, this study reveals that light funneling in the slits can be highly asymmetric, even at small angles. This mechanism is explained by polarized fields and charges, which are induced using Poynting vectors. It is shown that when light is obliquely incident to the slits perforated in a perfect electric conductor, asymmetrical fields and charges accumulate at the upper apex corners of the left (right) sides. When light is incident from the left (right) side, more (less) induced fields and charges accumulate in the left (right) slit corner so that the funneling width, area, and energy flow at the left (right) side increases (decreases). [ABSTRACT FROM AUTHOR]

This study derives the expression of dynamic stress components of the soil element in the semi-infinite elastic space under obliquely incident P- and SV-waves, and obtained the corresponding dynamic stress path. The effects of some factors including the incidence angle, Poisson's ratio, frequency, wave velocity, phase difference, and soil depth on the dynamic stress path are analyzed. It is found that the dynamic stress path in the (σy − σx)/2 − τxy plane is an oblique ellipse, and the above factors have significant effects on that. The maximum dynamic stress level for Poisson's ratio of 0.3 is about twice that for 0.48. The maximum dynamic stress level for 2.5 Hz is about six times that for 1 Hz. In general, the maximum dynamic stress level is about 40 kPa, no matter how the wave velocity changes. Compared with other phase difference, the dynamic stress level for the phase difference of 60° is largest with a value of 43 kPa. The dynamic stress level becomes greater as the soil depth increases, and the maximum value at 30 m depth is about 40 kPa. The variation trend of the three characteristic parameters with the incident angle exhibits the double-peak or triple-peak curves for different influencing factors. The research findings can provide some guidance for the site seismic dynamic response analysis and structural seismic design. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Asymmetric gratings can be designed to support quasi-bound states in the continuum. • Quasi-bound states in the continuum can serve as a surface refractive index sensor. • Ridge-, groove-, and dual-asymmetric gratings are designed and compared for sensing. • Oblique incidence plays a critical role in improving sensitivity and figure of merit. • Resonance-trapped phenomenon is observed in three gratings at oblique incidence. Asymmetric nanostructures that support quasi-bound states in the continuum (quasi-BIC) are known to exhibit an extremely sharp and sensitive optical resonance, making them attractive platforms for optical sensing applications. In this work, we numerically propose an asymmetric grating based on quasi-BIC for surface refractive index sensing with enhanced sensitivity and figure of merit. The gratings are realized by three asymmetric types: ridge-asymmetry, groove-asymmetry, and dual-asymmetry. Numerical simulations of the proposed structure were conducted by using the rigorous coupled wave approach and finite-difference time-domain method. At normal incidence, the three asymmetric gratings support a single quasi-BIC at 910.3 nm, a single quasi-BIC at 1067 nm, and double quasi-BICs at 910.4 nm and 1067.1 nm, respectively. The single quasi-BIC at 910.3 nm, achieved through ridge-asymmetry, and the quasi-BIC at 910.4 nm, achieved through dual-asymmetry, exhibit almost the same electric field distribution and high sensitivity of about 444 nm/RIU. At oblique incidence, another quasi-BIC can be induced in ridge-asymmetry or groove-asymmetry types, which has the same resonance wavelength as the quasi-BIC in dual-asymmetry type. As the incident angle increases, the sensitivity of the quasi-BICs at longer wavelengths consistently increases in three types. Remarkably, as the angle approaches approximately 28°, these quasi-BICs collapse into resonance-trapped BICs, leading to an extremely sharp resonance. Therefore, it is possible to achieve high resolution at this angle while maintaining high sensitivity simultaneously. Our study represents the first attempt to enhance the sensing performance of BIC sensors by using oblique incidence, which has significant implications for the design and application of such sensors. [ABSTRACT FROM AUTHOR]

• The response of expansion tube structure (ETS) under the coupled loading of blast wave and detonation products is investigated. • The deformation mode of ETS transitions from expansion to one-end buckling, and then to both-ends simultaneous buckling as the scaled distance decreases. • The energy absorption (EA) of ETS exhibits distinct trends for different explosive masses in the scaled distance range of 0.4–0.5 m/kg1/3. • Under oblique impact, the percentage decrease in EA within the near-field range is higher than that at mid-to-far range. Expansion tube structures (ETSs) are extensively employed as energy-absorbing components in protective structures, yet their dynamic response under near-filed explosion remains inadequately understood, which limits their applications in anti-explosion devices. This paper investigates the response of ETS through explosion experiments, testing both the overpressure history of blast loading and the propagation process of detonation products. Following experimental verification, finite element models are established to obtain the characteristics of explosive loading and the response of ETS. The findings demonstrate that as the velocity of slider increases, the embedding displacement of ETS exceeding its limit induces a local buckling transformation in thin-wall tubes from one end buckling to simultaneous buckling at both ends. In the scaled distance range of 0.4–0.5 m/kg1/3, the energy absorption (EA) of ETS under different explosive masses exhibits distinct trends as the scaled distance increases, despite the decrease in peak pressure of blast loading. This is due to the coupling effect between blast shock waves and detonation products, resulting in diverse alterations in specific impulse with increasing scaled distance for varying explosive masses. In the case of oblique impact of blast loading, the percentage decrease in EA within the near-field range (Z < 0.8 m/kg1/3) is higher than that at mid-to-far range due to the uneven and random ejection of detonation products. The study elucidates the dynamic response of ETS under the coupled loading of blast wave and blast products, and provides valuable insights for optimizing designs of ETS utilized in near-field blast-resistant structures. [ABSTRACT FROM AUTHOR]

This work presents, for the first time, a generalized bimode Foster’s equivalent circuit for characterization of 2-D planar periodic structures (PPSs) with arbitrary geometry at oblique incidence. It considers the interactions between the fundamental TE and TM modes without any restriction within the bimode bandwidth of the geometry. The proposed circuit is only composed of frequency-independent LC elements, which can be extracted systematically from electromagnetic (EM) simulations. The reactive immittances obtained in the process fulfill Foster’s theorem, enabling the design process of PPS-based devices using standardized synthesis techniques from the circuit theory. To demonstrate its viability and general nature, equivalent circuits are extracted for different single-layer and multilayer PPS composed of rotated dipoles under oblique incidence $\theta $ = 20° and $\varphi $ = 30° and including dielectrics. Excellent agreement is found between the response of the circuit model and the EM simulation in all cases. Finally, to validate experimentally the proposed equivalent circuit and highlight its applicability, a 90° reflective linear-polarization (LP) rotator centered at 25 GHz and under oblique incidence, $\theta $ = 30° and $\varphi $ = 0° (TE), is designed, manufactured, and tested. The agreement between the circuit response, the EM simulation, and the measurement underlines the potential of the new equivalent circuit for PPS design under oblique incidence. [ABSTRACT FROM AUTHOR]

Recently, reconfigurable intelligent surface (RIS) has attracted continuous attention in wireless communications. Because the normal incidence condition of electromagnetic waves cannot always be satisfied in practical applications, the angular insensitivity in RISs has become an important issue. The angular sensitivity in RISs may lead to the failure of RIS-assisted wireless communication networks that rely on the reciprocity of wireless channels. In this work, an angle-insensitive 3-bit RIS meta-atom is proposed. By introducing metallic vias in the substrate of programmable meta-atoms, the interference induced by multiple reflections in the multilayered structure is restrained, and the decoupling between adjacent meta-atoms makes the metasurface insensitive to the incident angle. Hence the angular insensitivity can be achieved. An RIS is fabricated using the proposed angle-insensitive programmable meta-atom with metallic vias, which is capable of maintaining stable phase and amplitude responses at oblique incidences. Both simulated and measured results show stable angle performance. A maximum of 315° phase range and eight digital coding states with 45° stable interval are obtained for wide incidence angles from 0° to 60°. Finally, numerical simulations and experimental results of anomalous reflections are performed to verify the angular reciprocity of the proposed RIS, which is important in wireless communications. [ABSTRACT FROM AUTHOR]

A complex cylindrical structure consisting of a group of parallel stratified circular lossy dielectric cylinders, embedded in a dielectric circular cylindrical region and surrounded by unbounded dielectric space, is considered in this paper. The scattering of electromagnetic (EM) plane waves by the aforementioned configuration was studied; the EM waves impinged obliquely upon the structure and were arbitrarily polarized. The formulation used was based on the boundary-value approach coupled with the generalized separation of variables method. The EM field in each region of space was expanded in cylindrical wave-functions. Furthermore, the translational addition theorem of these functions was applied in order to match the EM field components on any cylindrical interface and enforce the boundary conditions. The end result of the analysis is an infinite set of linear algebraic equations with the wave amplitudes as unknowns. The system is solved by the truncation of series and unknowns and then matrix inversion; thus, we provide a semi-analytical solution for the scattered far-field and, as a consequence, for the scattering cross section of the complex cylindrical structure. The numerical results focus on calculations of the electric- and magnetic-field intensity of the far-field as well as of the total scattering cross section of several geometric configurations that fall within the aforementioned general structure. The effect of the geometrical and electrical characteristics of the structure on the scattered field was investigated. Specifically, the cylinders' size and spacing, their conductivity and permittivity as well as the incidence direction were modified in order to probe how these variations are imprinted on scattering. Moreover, comparisons with previously published results, as well as convergence tests, were performed; all tests and comparisons proved to be successful. [ABSTRACT FROM AUTHOR]

In this communication, a novel metasurface with multiple unit cells of different thicknesses based on optimized multielement phase cancellation (OMEPC) is proposed for extremely wideband, omnidirectional, and polarization-independent radar cross section (RCS) reduction under wide-angle oblique incidence. Omnidirectional characteristic refers to the capability of RCS reduction under all azimuth angles ($\varphi ^{i}$) at certain elevation angles ($\theta ^{i}$). The equivalent circuit model of the square patch unit cell is analyzed under both normal and oblique incidences. Unit cells of multiple thicknesses are adopted to solve the in-phase reflection at certain frequencies. The scattered fields of the proposed multiple-element metasurface under different frequencies, polarizations, and incident angles are jointly optimized and simultaneously suppressed by OMEPC. When the range of incident angles is increased from 0° to 40°, the proposed multiple-element metasurface can achieve the 10 dB specular RCS reduction from 7.34 to 64.85 GHz with a ratio bandwidth of 8.84:1 for both TE and TM polarizations, and the 8 dB RCS reduction bandwidth is approximately 6.76–83.70 GHz. The measurement results are in agreement with the theoretical analysis and simulation results. [ABSTRACT FROM AUTHOR]

In the analysis of most circuit analog (CA) absorbers, it is only the absorption performance under normal incidence that is taken seriously, leading to a much worse absorption with the increase of incident angle, especially when it is larger than 30°. In this communication, a novel absorber, which consists of a conductive square-loop (SL) array embedded with lumped resistors and a well-designed wide-angle impedance matching (WAIM) layer, is proposed. Equivalent circuit (EC) and strict formula derivations are introduced to present a great insight into the deterioration of absorption performance under oblique incidence and the effect of WAIM layer. An absorber sample is further fabricated and measured for verification. It is shown through measurement that the structure has a fractional bandwidth of 137.1% for at least 10 dB reflection reduction under normal incidence. When the incidence angle is increased to 45°, the overlapped bandwidth for both transverse electrical (TE) and transverse magnetic (TM) polarizations is still measured to be 110.5%. [ABSTRACT FROM AUTHOR]

Consider the scattering of electromagnetic waves by a penetrable homogeneous cylinder at oblique incident. The Maxwell equations are then reduced to a system of a pair of the two-dimensional Helmholtz equations for 푧-components of the electric and magnetic field through coupled oblique boundary conditions. This paper studies an inverse problem of recovering the penetrable obstacle from the far-field pattern of the electric field. The well-known linear sampling method is used to solve this problem. Compared with the usual inverse scattering problem, the coupled system and the oblique derivative boundary condition bring difficulties in theoretical analysis. Some numerical examples are presented to illustrate the validity and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

An efficient discontinuous Galerkin time-domain (DGTD) method with an implementation of generalized periodic boundary conditions (PBCs) is proposed to analyze the electromagnetic scattering from arbitrary skewed periodic structures. The transformed field variable approach and the discontinuous Galerkin technique with nonconformal mesh are presented to implement the generalized PBCs for arbitrary skewed periodic structures under both normally and obliquely incident illuminations. The arbitrary high-order time-stepping scheme, which retains the DGTD feature of high-order accuracy and breaks the Butcher barrier, is extended to a transformed version of Maxwell’s equations introduced by the generalized PBCs implementation. The proposed method enables an efficient modeling of arbitrary skewed arrays with a fixed unit-cell mesh. Numerical examples for skewed periodic structures, such as an infinite gold film, 1-D and 2-D staggered dipole frequency-selective surfaces (FSSs), mechanically reconfigurable FSSs, and skewed nanohole arrays, are presented to demonstrate the accuracy and applicability of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, the significant radar cross section (RCS) reduction of curved surfaces in the low microwave frequency band is reported. The design method of partition layout loading of frequency selective surface (FSS) absorbers to control the surface current is put forward. Comparison of the scattering field intensities of different zones on the curved surface clearly shows that surface current should be suppressed in a large zone to effectively reduce the RCS of the curved surface at these frequencies. FSS absorbers under normal and 45° angle of incidence are designed and placed on the different zones of the curved surface to realize the partition layout loading, and remarkable RCS reduction has been obtained. Specifically, more than 15-dB RCS reduction is achieved in 1.05–1.45 GHz, and absorption above 90% is obtained from 0.95 to 1.5 GHz for TE polarization. The great agreement between the simulated and measured results validates the proposed design method. [ABSTRACT FROM AUTHOR]

Most previous circuit analog absorbers only considered absorption performance under normal incidences, leading to bad absorption for large incident angles, particularly those > 30°. With the advancement in modern bistatic radar detection technology, radar electromagnetic waves may come from different spatial directions, thereby necessitating radar absorbers with high absorption performance under normal and oblique incidences. Thus, in this paper, we present a novel wideband absorber comprising a conductive square-loop array embedded with lumped resistors and a well-designed Wide-Angle Impedance Matching (WAIM) layer. Results show that the WAIM layer can significantly improve absorption under oblique incidences. To make the absorber design clear and simple, an Equivalent Circuit (EC) and strict calculating formulas are proposed under normal and oblique incidences. Fractional bandwidth is increased into 137.1% through measurement under normal incidence, and the structure has a common fractional bandwidth of at least 110.5% for at least 10 dB reflection reduction when the incidence angle < 45°. The similarity among EC calculated, simulated, and measured results proves the validity of the designed absorber.

The spectral finite-difference time-domain method is combined with the discrete-time time-domain vector fitting (TD-VFz) algorithm to analyze three-dimensional (3-D) periodic structures excited by oblique incident plane waves over a wide frequency band. The time signal reconstruction with TD-VFz produces an untruncated response over an infinite time window allowing an accurate spectral result, especially near the cutoff frequency separating the spectrum propagating wave region of the evanescent wave region. [ABSTRACT FROM AUTHOR]

This work proposes a health care monitoring method of femoral fractured bone healing as a novel application, based on the oblique incidence case and transmission of electromagnetic waves. The difference between the transmitted average power densities of normal and fractured bone cases is used to monitor the bone healing status. The study demonstrates the in-to-out body channel characteristics regarding the electromagnetic wave propagation and angle of incidence on a multi-layered human tissue in the range of frequencies from 100 MHz to 10 GHz. The monitoring method is presented by the analysis of electromagnetic wave propagation through a multilayer model and simulated by the CST Microwave studio. Fully insulated planar and meander half-wave dipole antennas are designed and used to simulate both types of bone fracture healing. Results show good monitoring of common types of fractures. Verification is carried out by experimental measurements on non-living animal tissues. [ABSTRACT FROM AUTHOR]

We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occur due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms’ angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point dipole models are used which incorporate different aspects of the meta-atoms’ angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modeling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations. [ABSTRACT FROM AUTHOR]

When reinforced with conductive fibers, woven composites can exhibit interesting shielding properties. This paper focuses on their response for obliquely incident plane waves in the high-frequency range (500 MHz to 40 GHz). A two-step homogenization technique is carried out. First, the composite response (shielding effectiveness and reflection coefficient) is computed using a 3D finite element simulation, then the effective properties are estimated by implementing an optimization process to solve the inverse problem. Results show that composites effective properties are independent of the angle of incidence and wave configuration. This suggests that oblique incidence scenarios can be studied by homogenizing the material based on the case of normal incidence. [ABSTRACT FROM AUTHOR]

Metasurfaces, as two-dimensional (2-D) metamaterials, show great potentials in electromagnetic wave manipulation. Here, an angular nondispersive transmission-type Huygens’ meta-atom, made up of an I-shaped metal patch and a square split ring, is proposed for wide incidence angle holographic metasurfaces. Nine varieties of the Huygens’ meta-atom with high transmission amplitude (higher than 0.9) and stable transmission phase (vary less than 10°) under transverse magnetic wave illumination from 0° to 60° are selected. To verify the performance of the meta-atoms proposed, two holographic metasurfaces are simulated and fabricated to reconstitute identical holographic images under normal and oblique linearly polarized wave illuminations, respectively. The experimental demonstrations show imaging efficiencies higher than 48.28% with signal-to-noise ratio as high as 22.57. Our designs provide a solution for angular nondispersive metasurface designs, which suggest great practical applications in beamforming, and information storage systems. [ABSTRACT FROM AUTHOR]

A transparent frequency selective surface (FSS) on a glass window is proposed for signal selectivity of 5G millimeter-wave communication, based on a transparent and low loss material cyclic olefin copolymer (COC). The proposed FSS based on dual-loop units is designed on both sides of COC, which helps to realize the band-pass filtering effect under both normal and oblique-incident conditions in the desired frequency range from 27.5 to 29.5 GHz. The metal-meshed technology is employed to enhance the light transmission of the circuits, and the measured performances with traditional glass show that our proposed concepts can be a potential solution for signal filtering at millimeter wave on glass windows. [ABSTRACT FROM AUTHOR]

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In this paper, a broadband double-layer metamaterial absorber (MMA) based on carbon fibers (CFs) is proposed, which consists of three basic elements. Firstly, the reflectivity of CFs double-layer MMA in normal incidence is analyzed, and compared to the copper double-layer MMA with same size, the simulated results show that it obtains better absorbing effect. With the increase of incident angle, the multi-frequency resonance is activated, leading to larger effective bandwidth. Moreover, when incident angle is between 55 and 70 degrees, the continuous absorption band above 85% can totally cover X and Ku microwave band. Meanwhile, when the EM frequency is at 6-7.5GHz, the change of incident angle hardly affects the absorbing performances of CFs double-layer MMA. A specimen of the CFs double-layer MMA was fabricated by the vacuum bag molding process to verify its effectiveness and the measured results fitted well with the simulated results. In order to discuss the mechanism of EM absorption, the distribution of E-fields and power loss density were monitored. The results indicate that incident angle effects the distribution of E-fields and the way of absorption to change the absorbing performances. The proposed MMA has potential application prospects in the structural and functional integration design of CFs.

We consider the effects of oblique incidence of a wave on the creation of a 3-D image of a planar interface with an array-type directional borehole radar. In this study, we focus on the situation where the radar probe is close to the planar interface. In such circumstances, the reflected wave from the planar interface may be incident on the receiving array antenna at very steep elevation angles. As a result, borehole effects cause differences in the arrival times of the wave at the array elements, and consequently some errors emerge in imaging the planar interface. Observing the arrival time differences, we present an algorithm to compensate those errors in creating a 3-D image of a planar interface. Computer simulations predict that the errors may occur when the circular dipole array antenna is in an air-filled borehole in rock. Numerical simulations show that our proposed algorithm generates a 3-D image of an interface around an exact position, whereas conventional methods produce some spurious images opposite to the correct position (i.e., out of position by 180°). We then applied the proposed method to analyze reflected waves from a real-world fault in rock. A 3-D image of the fault could be successfully created, which was not possible using the conventional method.

Laser-ultrasonic waves are used in nondestructive inspections because they can be excited on arbitrarily shaped surfaces by irradiation of a pulsed laser from a distance. During the non-contact scanning of a laser, the waveform of excited ultrasonic wave is changed because the incident angle varies substantially. The change of the waveform will be more obvious for carbon fiber reinforced plastics (CFRP) laminates that have anisotropic properties. In order to guarantee the inspection, in this paper, we investigated the generation of ultrasonic waves in CFRP laminates by a laser irradiation with various incident angles and azimuth angles. Firstly, we constructed a simulation model: the thermal force field caused by the laser absorption is derived from a heat conduction equation, and it is introduced into an FEM software for analyzing the propagation behavior of generated ultrasonic waves. Then, the simulation result is compared with an experiment result. Through the FEM analysis, we found that the amplitude of the excited waves has an obvious directivity because of the strong anisotropy in the thermo-elastic property of the CFRP. In addition, the change in propagation behavior in the case of a small incident angle of 30° was found to be inconspicuous. However, when the incident angle of the laser beam is larger than 60°, the directivity pattern changes depending on the azimuth angle. Thus, it is important to control the incident angle and direction when a laser ultrasonic inspection is applied to CFRP structures.