Change Of Incident Angle Research Articles

Asymmetric Plasmonic Moth-Eye Nanoarrays with Side Opening for Broadband Incident-Angle-Insensitive Antireflection and Absorption.

Plasmonic absorbers with broadband angle-insensitive antireflection have attracted intense interests because of its wide applications in optical devices. Hybrid surfaces with multiple different sub-wavelength array units can provide broadened antireflection, while many of these antireflective surfaces only work for specific angles and require high complexity of nanofabrication. Here, a plasmonic asymmetric nanostructure composed of the moth-eye dielectric nanoarray partially modified with the top Ag nanoshell providing a side opening for broadband incident-angle-insensitive antireflection and absorption, is rationally designed by nanoimprinting lithography and oblique angle deposition. This study illustrates that the plasmonic asymmetric nanostructure not only excites strong plasmonic resonance, but also induces more light entry into the dielectric nanocavity and then enhances the internal scattering, leading to optimized light localization. Hence, the asymmetric nanostructure can effectively enhance light confinement at different incident angles and exhibit better antireflection and the corresponding absorption performance than that of symmetric nanostructure over the visible wavelengths, especially suppressing at least 16.4% lower reflectance in the range of 645-800 nm at normal incidence.Moreover, the reflectance variance of asymmetric nanostructure with the incident angle changing from 5° to 60° is much smaller than that of symmetric nanostructure, making our approach relevant for various applications in photocatalysis, photothermal conversion, and so on.

Reconfigurable angle sensitive metasurface for multibeam manipulation

AbstractAn angle sensitive transmission metasurface unit structure is designed in this paper. The metasurface unit presents a good transmission performance for the TE wave incidence, and has a linear phase response with the maximum phase difference up to 180° when the incidence angle changes in the range of −45° and +45°. Moreover, a reconfigurable design of the metasurface unit is realized by loading a varator, and the phase difference is extended to 270° to satisfy the demand of multibit metasurface. Based on the characteristics of angle sensitivity and reconfigurability of the metasurface unit, combined with the control of the varactor and the unit tilt angle, a new 1‐bit digital coding angle sensitive metasurface is proposed. The metasurface has a specification of 20 × 20 and a center frequency of 10 GHz. Both the simulation and measurement show that different transmission is realized for incident waves at different incident angles. It can form different beams, which can be used for multibeam modulation with the same frequency and same polarization.

Rotor Cascade Assessment at Off-Design Condition: An Aerodynamic Investigation on Platform Cooling

Off-design condition of a rotor blade cascade with and without platform cooling was experimentally investigated. The ability of the gas turbine to operate down to 50% to 20% of its nominal intake air flow rate has an important consequence in the change in the inlet incidence angle, which varied from nominal to −20°. Platform cooling through an upstream slot simulating the stator-to-rotor interface gap was considered. The impact of rotation on purge flow injection was simulated by installing fins inside the slot to give the coolant flow a tangential direction. Aerodynamic measurements to quantify the cascade aerodynamic loss and secondary flow structures were performed at Ma2is = 0.55, varying the coolant to main flow mass flow ratio (MFR%) and the incidence angle. The results show that losses strongly increase with MFR. A negative incidence allows a reduction in the overall loss even when coolant is injected with a high MFR. The more negative the incidence, the greater the loss reduction.

Optimization design of 3D-printed pyramid structure for broadband electromagnetic wave absorption

Aiming to improve the bandwidth of the absorber, which is more favorable for applications in military and civil fields, a novel FeSiAl/polylactic acid (PLA) composites pyramid was fabricated by fused deposition molding (FDM) 3D printing technology. The study investigated the impact of the geometric parameters of the unit structure on the absorption intensity and bandwidth of electromagnetic (EM) wave (EMW). The results show that the pyramid structure achieves a minimum reflection loss (RLmin) of − 37.2 dB. The cell structure of the pyramid structure features a period length of 22.5 mm, a base thickness of 0.5 mm, a cell thickness of 7.0 mm, and an upper surface edge length of 6.0 mm. These parameters result in a RL below − 10 dB within the frequency band of 6.7–18 GHz. Meanwhile, the effective absorption bandwidth (EAB, for RL below −10 dB) of TE polarization exceeds 11 GHz when the incident angle changes from 0° to 50°, and the EAB value of TM polarization still reaches 6.9 GHz at 70°. The broadband absorption properties of the proposed absorber are attributed to the synergistic enhancement effect of the structure and material.

Dynamic Response Analysis of Intake Tower-Hydrodynamic Coupling Boundary Based on SV Wave Spatial Incidence

In view of the insufficient analysis of the coupled joint seismic response of the intake tower–reservoir water–foundation boundary under the oblique incidence of SV wave space, a three-dimensional dynamic equation of the oblique incidence of SV wave space is established in this paper. The external wave input method of viscoelastic artificial boundary combined with equivalent load and the acoustic medium theory are used to simulate the action of reservoir water, and the angle change in the SV wave incidence is realized by controlling the incident vector. The dynamic response of the structure is analyzed and the dynamic response characteristics of the structure at different incidence angles are discussed. The results show that the dynamic response and damage degree of the intake tower decreases first and then increases with the change in angle. When the vertical incidence is 0°, the maximum displacement drop is 82.05%, and the displacement response of the intake tower is more sensitive to the change in SV wave incidence angle. When SV wave is vertically incident at 0° and 35° (near the maximum critical angle of incident), the dynamic response, dynamic water pressure, damage diffusion velocity, damage area, and damage degree of the intake tower are relatively large, which seriously affects the safety and stability of the intake tower. Therefore, the influence of the oblique incidence should be considered comprehensively in the aseismic stability design of the water intake tower to provide a new idea for the safety evaluation of the same type of engineering.

Terahertz broadband tunable chiral metamirror based on VO2-metal hybrid structure.

Aiming at the problems of narrow working bandwidth, low efficiency, and complex structure of existing terahertz chiral absorption, we propose a chiral metamirror composed of C-shaped metal split ring and L-shaped vanadium dioxide (VO2). This chiral metamirror is composed of three layers of structure, a gold substrate at the bottom, the first polyethylene cyclic olefin copolymer (Topas) dielectric layer and VO2-metal hybrid structure as the top. Our theoretical results led us to show that this chiral metamirror has a circular dichroism (CD) value greater than 0.9 at 5.70 to 8.55 THz and has a maximum value of 0.942 at f = 7.18 THz. In addition, by adjusting the conductivity of VO2, the CD value can be continuously adjustable from 0 to 0.942, which means that the proposed chiral metamirror supports the free switching of the CD response between the on and off states, and the CD modulation depth exceeds 0.99 in the range of 3 to 10 THz. Moreover, we discuss the influence of structural parameters and the change of incident angle on the performance of the metamirror. Finally, we believe that the proposed chiral metamirror has important reference value in the terahertz range for constructing chiral light detectors, CD metamirrors, switchable chiral absorbers and spin-related systems. This work will provide a new idea for improving the terahertz chiral metamirror operating bandwidth and promote the development of terahertz broadband tunable chiral optical devices.

Numerical simulation of efficient solar absorbers and thermal emitters based on multilayer nanodisk arrays

In this work, we design a solar absorber and thermal emitter with ultra-broadband perfect absorption and high thermal radiation efficiency. The solar absorber has a high absorption efficiency of 91.5 % in the full wavelength range (280–4000 nm), and the weighted average absorption efficiency (AM1.5) is as high as 99 % by the finite difference time domain method (FDTD) simulation calculation. And the absorption bandwidth with absorption efficiency greater than 90 % reaches 2929 nm (280–3209 nm), and the average absorption efficiency in this band is as high as 97.4 %. Such strong absorption is due to the plasmon resonance and near-field coupling of the multilayer nanodisks. In addition to being used in solar absorbers, the structure also has potential applications in thermal emitters. The novelty of this work is to explore the application of the structure in the field of thermal radiation, and the optimal working temperature of the structure for thermal radiation is obtained. Through calculation, we approximately consider that the optimal working temperature of the structure as a thermal emitter is 2000 K, and the thermal radiation efficiency at this temperature is 94.8 %. The structure proposed by us is polarization-independent, insensitive to incident angle changes, the absorption spectra of transverse electric (TE) mode and transverse magnetic (TM) mode are the same, and the absorption efficiency remains 80 % even when the incident angle is increased to 60°. The excellent performance makes the structure widely used in the fields of solar energy absorption and emission.

Wideband reflective half- and quarter-wave plate metasurface based on multi-plasmon resonances

In this article, a single-layer reflective anisotropic metasurface (MS) is proposed, which presents both half- and quarter-wave plate operation in different microwave frequency regimes. The unit cell of the proposed metasurface consists of a tilted rectangular plane with triangular ends accompanied by an equidistant-filled triangle on both sides. The unit cell is printed on a dielectric substrate backed by a metallic plane. The proposed meta-plate transforms horizontal polarization into vertical and vice versa in two wide frequency bands, 7.1-15.3 GHz and 19.8-21.7 GHz. Similarly, a linearly polarized (LP) wave is transformed into a circularly polarized (CP) wave and vice versa at 7.9 GHz and 21.8 GHz. The wide bandwidth is acquired through three plasmonic resonances occurring at 8.2 GHz, 12.7 GHz and 20.8 GHz, where the cross-polarization conversion ratio reaches almost 100%. Moreover, quarter and half-wave plate operations occurring at 7.9 GHz and 7.1-15.3 GHz, respectively, are robust to changes in oblique incidence angle (up to 45°) both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The physical mechanism behind polarization conversion is also explained through surface current distribution. The proposed meta-plate structure is fabricated and validated through experimental measurements. The wide bandwidth, high efficiency, angular stability, and simple structure make the proposed metastructure incredible for numerous microwave applications such as antennas, radars, and satellite communication.

A THz-OAM Wireless Communication System Based on Transmissive Metasurface

With the development of various emerging technologies, the capacity of current wireless communication system is gradually saturated, and terahertz (THz) and orbital angular momentum (OAM) have hereby attracted much attention as two key technologies to increase the communication capacity. In this paper, a THz-OAM wireless communication system operating at 100 GHz based on a transmissive metasurface is proposed for the first time to the best of our knowledge. The operation principle of multiplexing metasurface which allows simultaneous generation of two coaxial OAM beams at different modes of l = 1 & –1 is studied. To meet the requirements of wireless communication and OAM multiplexing, a C-shaped transmissive unit is designed with characteristics of broad bandwidth, low transmission loss and insensitive to the change of incident angle. Experimental measurements show that the generated two OAM beams feature high mode purity, providing the excellent orthogonality of modes. The generated two OAM modes are also employed as two OAM channels to transmit two independent communication signals with on-off keying (OOK) modulation, and a data rate of 10 Gbit/s is achieved at a transmission distance of 300 mm (100 λ of 100 GHz) with bit error rates (BERs) below 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . This work verifies the feasibility of the multiplexing metasurface supporting wireless communication, and makes THz-OAM wireless communication systems potential for future large capacity wireless services.

Dynamically tunable single-/dual-band of the graphene absorber with a resonant asymmetric grating based on lithium niobate on insulator

We propose a tunable single-/dual-band of graphene absorber with a resonant asymmetric grating based on lithium niobate on insulator (LNOI). The single-/dual-band of the absorber can be dynamically switched by changing the incident angle, and the increase of the spacing between the two peaks reduces the crosstalk in adjacent channels as the incident angle increase. Meanwhile, the resonant wavelength is adjusted by applying a voltage to lithium niobate (LN), changing the refractive of LN. The wavelength shifts caused by a slight change in incident angle can be regulated back through the electro-optical effect of LN. Furthermore, the effects of the structural parameters and the incident angle on the bandwidth are investigated by the finite element method (FEM). This structure has promising applications in optical filters, sensors, thermal emitters, and spatial optical measurements.

Triple-Band Surface Plasmon Resonance Metamaterial Absorber Based on Open-Ended Prohibited Sign Type Monolayer Graphene.

This paper introduces a novel metamaterial absorber based on surface plasmon resonance (SPR). The absorber is capable of triple-mode perfect absorption, polarization independence, incident angle insensitivity, tunability, high sensitivity, and a high figure of merit (FOM). The structure of the absorber consists of a sandwiched stack: a top layer of single-layer graphene array with an open-ended prohibited sign type (OPST) pattern, a middle layer of thicker SiO2, and a bottom layer of the gold metal mirror (Au). The simulation of COMSOL software suggests it achieves perfect absorption at frequencies of fI = 4.04 THz, fII = 6.76 THz, and fIII = 9.40 THz, with absorption peaks of 99.404%, 99.353%, and 99.146%, respectively. These three resonant frequencies and corresponding absorption rates can be regulated by controlling the patterned graphene's geometric parameters or just adjusting the Fermi level (EF). Additionally, when the incident angle changes between 0~50°, the absorption peaks still reach 99% regardless of the kind of polarization. Finally, to test its refractive index sensing performance, this paper calculates the results of the structure under different environments which demonstrate maximum sensitivities in three modes: SI = 0.875 THz/RIU, SII = 1.250 THz/RIU, and SIII = 2.000 THz/RIU. The FOM can reach FOMI = 3.74 RIU-1, FOMII = 6.08 RIU-1, and FOMIII = 9.58 RIU-1. In conclusion, we provide a new approach for designing a tunable multi-band SPR metamaterial absorber with potential applications in photodetectors, active optoelectronic devices, and chemical sensors.

Preparation and Properties of Broadband Terahertz Absorbing Coatings

This study designs and prepares broadband terahertz absorbing coatings. The electromagnetic simulation software is used to simulate and analyze the influence of permittivity, thickness of the coatings and incident angle of terahertz wave on the reflectivity of the absorption coatings within the range of 0.25 THz ~ 3 THz. Results show that as the real part of the dielectric constant and thickness increase, the low-reflection peak moves to lower frequencies. When the imaginary part of the dielectric constant and incident angle change, the intensity of the reflectivity peak changes relatively vastly. Terahertz absorption coatings with different thicknesses are prepared, and the reflectivity test results are consistent with the simulation results. The coatings have excellent absorption performance within the range of 0.25 THz ~ 3 THz, and the absorption exceeds 2.5 THz when the bandwidth is lower than -10dB.

A coupled ray-tracing based CFD and cellular automaton model for predicting molten pool formation and microstructure evolution in narrow gap laser welding

Laser beam reflection plays a significant role in the temperature development history during various laser material processes. Different from other processes where laser beam reflection main happens inside the keyhole, in narrow gap laser welding (NGLW), the laser beam would interact with the sidewalls multiple times before existing the narrow groove, which would have a great impact on the defect formation as well as the grain structure development. However, the underlying mechanism of this process remains unknown in multi-pass NGLW. In this study, an integrated ray-tracing based CFD and cellular automaton (CA) modelling framework is established to investigate the impact of laser beam reflection on molten pool formation and microstructure evolution in multi-pass NGLW. From the CFD simulation, it is found that the overall laser beam absorption of NGLW is greater than laser metal deposition (LMD) while smaller than laser powder bed fusion (LPBF) process. Besides, the overall absorptivity in NGLW is increased 28% when considering the ray reflection during the first welding pass. The absorptivity would increase and then stabilise through the multi-pass welding process, which is attributed to the change in incident angle and number of reflections. Additionally, it is found that the undercut defect is more likely to occur with ray reflection due to the excessive temperature rise on the sidewalls, while lack of fusion is observed in the case without ray reflection. By incorporating the thermal history of each welding pass with CA, the impact of laser beam reflection on grain structure development is evaluated. Columnar grains would govern the microstructure evolution in the case with ray reflection, which grow epitaxially from the fusion line to the molten pool centre. Grain coarsening would occur around the lack of fusion region in the case without ray reflection. Moreover, the analysis on grain size distribution is conducted and a greater maximum grain size is obtained in the case without ray reflection as a result of lower cooling rate caused by lack of fusion. However, a higher grain size increase is obtained in the case with ray reflection during multiple welding passes, and larger grains are expected to form if more welding passes are to be conducted. The simulated molten pool morphology and grain structure are compared with the experimental observation, and a good agreement is achieved.

A multifunctional broadband polarization rotator based on reflective anisotropic metasurface

In this paper, both linear cross-polarization conversion (CPC) and linear-to-circular or circular-to-linear polarization conversion based on a single reflective anisotropic metasurface are realized and experimentally demonstrated. The multifunctional CPC metasurface in the frequency range of 5.9-6.4 GHz and 8.7-17.7 GHz has a fractional band of 68.2%, and the efficiency reaches almost 100% under plasma resonance. In addition, the metasurface acts as a high efficiency circular-polarizer in the range of 6.7–8.4 GHz. Moreover, the polarization transforming functionality of the structure is stable for the change of incident angle for both x-polarized or transverse-electric (TE) and y-polarized or transverse-magnetic (TM) illumination up to 45∘. It can be seen that the anticipated hypersurface has potential applications in reflector antenna, satellite communication and radar.

Impedance matching characteristic parameters of microwave absorbing materials for specular reflection and non-specular scattering suppression

The impedance matching characteristic parameters (IMCPs) of microwave absorbing materials for specular reflection under oblique incidence and surface wave attenuation are first proposed and defined. A microwave absorbing sheet was fabricated and its electromagnetic parameters were measured. The specular reflection suppression characterized by reflection loss and non-specular scattering suppression described by surface wave attenuation constants were studied with the change in thickness, polarization, and incident angle. The present results demonstrate that the definition of IMCPs for both specular reflection and non-specular scattering is effective. Meanwhile, the curves of IMCPs share the same shape and have the same peak frequency in specular reflection and non-specular scattering cases. In addition, Brewster angle properties are also consistent with the IMCPs under oblique incidence. Thus, this work develops a pathway for the design of microwave absorbing sheets suppressing both the specular reflection and non-specular scattering by adjusting the IMCPs.

Numerical study of the interaction between an internal solitary wave and a submerged extended cylinder using OpenFOAM

To investigate the impacts of cylinder extended length, rotation angle and wave incidence angle on hydrodynamic characteristics, the numerical simulation of an internal solitary wave (ISW) interaction with a submerged extended cylinder is conducted by using OpenFOAM. The accordance between the experimental data and numerical simulation forces on the isolated cylinder shows that the OpenFOAM-based numerical model can deal with the ISW-submerged cylinder interaction. The distributions of forces, maximum dynamic pressure forces and flow field around the submerged extended cylinder are discussed to reveal the hydrodynamic characteristics of submerged cylinder under the ISW action. The horizontal forces on an extended cylinder are found to change from increasing to decreasing with the increase in extended length when the extended length is 2.5 times the cylinder diameter. The forces on the cylinder are sensitive to the change in the rotation angle. Both the horizontal loads and the evolution of the wave profile are easily affected by the change in incidence angle. The vortices shedding around the cylinder varies with the change of wave incidence angle. Investigation of the ISW and a submerged cylinder interactions can help to understand the mechanism of structural damage in internal wave ocean environment.

Bloch surface wave-atom coupling in one-dimensional photonic crystal structure.

Considering efforts for hot atomic vapor-nanophotonics integration as a new paradigm in quantum optics, in this paper, we introduce 1D photonic crystal-Rb vapor cell as structure with miniaturized interaction volume. The Bloch surface wave (BSW) excited on surface of a photonic crystal as electromagnetic hosting photonic mode, and altered the optical response of Rb atoms in the vicinity of surface. Coupling of atomic states with BSW confined modes would lead to quantum interference effects and results in nonlinearities in resonant coupling of atoms with BSW. We show Bloch surface wave induced transparency is highly stable under a change of incidence angle. Our results show slight changes in transitions detuning's due to nonlinear interactions like the Casimire-Polder effect under change of localized density of optical states.

A device of XOR logic gate and multiscale sensing based on layered topology

In this paper, a multiscale non-reciprocity device based on the layered topology of one-dimensional (1-D) photonic crystals is studied, which can meet the functions of XOR logic gate, magnetic field sensing and refractive index sensing. Modulating by the external magnetic fields, sharp transmission peak (TP) is obtained in the terahertz (THz) range (the value of TP is more than 0.9), by changing the two different magnetic fields applied to the particular medium layers, TP enables XOR logic phenomena at the same frequency point. Simulation shows that with the detection of physical quantities changes, the frequency point of TP will vary. Therefore, through the location of TP, the sensing functions of magnetic field and refractive index can be realized, moreover the optimum performances of quality factor (QF), sensitivity (S), the figure of merit (FOM), and the detection limit (DL) belonging to them are 1323.45, 0.01 (2πc/d 0)/T, 35.93 T−1, 1.39 × 10−3 T and 1381.88, −0.0061 (2πc/d 0)/RIU, 13.57 RIU−1, 3.7 × 10−3 RIU. Additionally, the device also realizes the non-reciprocity of electromagnetic waves (EWs) via the introduction of magneto-optical media InSb and the change of EWs incident angle, which means that XOR logic gate, magnetic field, and refractive index sensing detection respectively have positive and negative scales.

Improved topographic reconstruction of turbid media in the spatial frequency domain including the determination of the reduced scattering and absorption coefficients.

The separation of scattering and absorption is of great importance for studying the radiative transfer in turbid media. Obtaining the corresponding coefficients for non-flat objects is difficult and needs special consideration. Building on our previous work [J. Opt. Soc. Am. A39, 1823 (2022)JOAOD60740-323210.1364/JOSAA.464007], we present an approach that takes the changing incident and detection angles relative to the surface normal of curved surfaces into account to improve the determination of the reduced scattering and absorption coefficients with measurements in the spatial frequency domain (SFD). The optical coefficients are reconstructed using a pre-calculated lookup table generated with Monte Carlo simulations on graphical processing units. With the obtained values, the error in the captured surface geometry of the object, which is due to the volume scattering, is compensated and reduced by 1 order of magnitude for measurements in the SFD. Considering the approximate surface geometry, the absorption and reduced scattering are accurately resolved for moderate object curvatures, with very low dependence on the tilt angle. In contrast to models that only correct the amplitudes of the SFD signal, our approach, in addition to the optical properties, predicts the phase values correctly, which is the reason why it can be used to correct the surface geometry.

Surface morphology and carbon structure effects on sputtering: Bridging scales between molecular dynamics simulations and experiments

Experiments report large scatter in the sputtering yield of carbon materials under the bombardment of low-energy noble gas ions. Here, we conduct scale-bridging molecular dynamics (MD) simulations on the xenon bombardment of carbon substrates across ion energies of 75 eV to 2 keV, and at ion incidence angles of 0°–75°, to resolve uncertainties in the sputtering data. Results show rapid amorphization of the carbon subsurface with ion bombardment, but the structural characteristics (sp/sp2/sp3 bond proportion, atomic density) eventually plateau once steady-state sputtering is achieved. In addition, we obtain virtually indistinguishable “steady-state” amorphous structures across the range of ion energies and ion incidence angles, as well as for several different carbon structures, which suggests that the steady-state sputtering yield data is independent of the initial carbon structure and prior sputtering history. By accounting for changes in the local incidence angle, surface shielding, and redeposition of the sputterants associated with surface morphology effects, we demonstrate that the sputtering predictions from MD are in perfect agreement with prior experiments across the range of ion energies and incidence angles. Using a Bayesian approach based on the MD data, we calibrate the parameters of a semi-empirical sputtering model for different surface morphologies.