Change Of Incident Angle Research Articles

Broadband plasmon-induced transparency to an anapole mode induced absorption conversion Janus metastructure by a waveguide structure in the terahertz region.

A Janus metastructure (MS) assisted by a waveguide structure (WGS) resting on anapole modes and exhibiting direction-dependent behavior has been developed in the terahertz (THz) region. Ultra-broadband absorption is formed by the destructive interference through the anapole as well as Janus trait and is shaped by nested WGS. In this design, vanadium dioxide (VO2) is expected to attain functional transformation from plasmon-induced transparency (PIT) to absorption. The insulating nature of the VO2 results in the creation of the PIT, which is characterized by a wide and high transmission window ranging from 1.944 THz to 2.284 THz, corresponding to the relative bandwidth of 7.4% above 0.9. However, when the VO2 reaches the metallic state, a high absorptivity of 0.921 at 2.154 THz can be implemented in the -z-direction owing to the excitement of the toroidal dipole and electric dipole moments in the near-infrared region. And in the +z-direction, the broadband absorption above 0.9 in the 1.448-2.497 THz range takes shape in virtue of surface plasmon polariton modes, in which intensely localized oscillation of free electrons is confined to the metal-dielectric interface supported by the WGS. Noting that the MS is equipped with a favorable sensitivity to the incidence angle, we develop an ultra-broadband backward absorption in the TM mode from 0.7-10 THz nearly all above 0.9 when the incidence angle changes from 30°-70°. Moreover, owing to the highly symmetrical structure, the MS exhibits exotic polarization angular stability. All the awesome properties make this MS a good candidate for various applications such as in electromagnetic wave steering, spectral analysis, and sensors.

A tunable wide-angle narrowband perfect absorber based on an optical cavity containing hyperbolic metamaterials.

We demonstrate that wide-angle narrowband absorption can be achieved from a microcavity where a hyperbolic metamaterial and a dielectric layer are sandwiched between two metal reflectors. As the incident angle changes, the phase-shift variation in the hyperbolic metamaterial can compensate that in the dielectric layer and, consequently, result in the angle-insensitive Fabry-Perot resonance in the proposed cavity. Silicon, indium tin oxide (ITO), and gold layers are used to construct the microcavity to produce a narrow absorption band in the near-infrared region. Our device exhibits good absorption stability over a wide angle range of incidence from 0° to 70°. Moreover, the absorption wavelength can be tuned by changing the thickness of the resonator. The presented absorber may find potential applications in the design of narrowband thermophotovoltaic emitters, sensitive detectors, filters, etc.

Terahertz refractive index sensor based on tunable patterned graphene absorber

We introduce an ultrasensitive refractive-index sensor based on a patterned graphene dual-band absorber operating in the terahertz band. COMSOL Multiphysics software was employed to model and quantitatively assess the suggested micro-nano structure. The structure exhibits two perfect absorption peaks in the 1–9 THz band with theoretical absorptions of 99.4 % and 99.4 %. According to the properties of graphene, the positions of the absorption peaks can be adjusted using the applied bias voltage. Owing to the high symmetry of the proposed structure, it is insensitive to polarization and incident angle variations. Moreover, this study explored the effect of different parameters on the absorption peak by varying the structural parameters. Based on the simulation results, the refractive index sensor has a maximum sensitivity of 3 THz/RIU with a figure of merit (FOM) and can detect small refractive index changes. Therefore, we believe that this structure has promising applications in marine refractive index change determination. • The structure exhibits two perfect absorption peaks in the 1–9 THz band. • The positions of the absorption peaks can be adjusted using the applied bias voltage. • It is insensitive to changes in polarization and angle of incidence. • It has better sensitivity and FOM than most sensors of the same type.

Metamaterial solar absorber based on titanium resonators for operation in the ultraviolet to near-infrared region

In this work, we design an ultra-broadband metamaterial solar absorber with near-unity absorption. The absorber’s structure is optimized by using the particle swarm optimization algorithm. A unit cell of the absorber consists of three T i / T i O 2 / T i square disks enclosed by a Ti square ring resonator, all superimposed on a thin stack of T i O 2 / T i films. The optimized structure shows high average absorption of 96.92% over the full wavelength range of 200–3200 nm. The over 90% absorption bandwidth is 3000 nm, which covers the ultraviolet, visible, and near-infrared regions. The solar absorption of the structure is 95.5% in the range of 280–3200 nm. The absorber is polarization independent and insensitive to incident angle changes. The absorption remains higher than 80% and 75% for TM and TE polarizations, respectively, even under oblique incidence radiation up to 55°. The structure possesses high thermal and chemical stability owing to the use of Ti and T i O 2 materials. Due to its outstanding features, the absorber has high potential to be used in solar energy harvesting, thermo-photovoltaics, and thermal emitting applications.

Evaluation of the design and optical errors for a parabolic trough collector field in an Algerian desert region: Gassi-Touil as a study area

Solar energy of its renewable nature is considered the best alternative for offering effective solutions to the energy and environmental challenges faced by the world. This study is carried out to optically model a parabolic trough collector (PTC) field and study the influence of Gassi-Touil climate on its optical and thermal efficiency. The study allowed the completion of the MATLAB code that allows the calculation of all design and optical parameters of the studied solar collector, taking into account the instantaneous change of incidence angle that has a direct impact on the change in design and optical errors. For the PTC efficiencies, its average optical performance found, is 75.15% and its average thermal efficiency is 70%. Besides, the average rate of total heat loss coefficient is 7.95 W/m2K, the average rate of local concentration ratio on the receiver tube surface is 40.65 and the average rate of heat flow intensity is 36823 W/m2. The obtained results are very encouraging to exploit this effective solar technology, which will help in preserving fossil resources and progress towards sustainable development in Algeria.

Study on Laser Parameter Measurement System Based on Cone-Arranged Fibers and CCD Camera.

This paper proposes a new laser parameter measuring method based on cone-arranged fibers to further improve the measurable spot size, allowable incident angle range, and spatial sampling resolution. This method takes a conical array composed of flexible fibers to sample and shrink the cross-section spot of the laser beam, facilitating low-distortion shooting with a charge-coupled diode (CCD) camera, and adopts homogenized processing and algorithm analysis to correct the spot. This method is experimentally proven to achieve high-accuracy measurements with a decimeter-level spot-receiving surface, millimeter-level resolution, and high tolerance in order to incite skew angle. Comparing the measured spot under normal incidence with the real one, the root mean square error (RMSE) of their power in the bucket (PIB) curves is less than 1%. When the incident angle change is between −8° and 8°, the RMSE is less than 2% and the measurement error of total power is less than 5% based on the premise that the fiber’s numerical aperture (NA) is 0.22. The possibility of further optimizing the measurement method by changing the fiber parameters and array design is also reported.

On the wake of a large depth ratio wall-mounted prism at a normal incident angle

The wake characteristics of a large depth-ratio (depth-to-height) prism at the incident angle of 90° is numerically examined at Reynolds number of 250. An arc type, symmetric vortex shedding is observed in the wake with periodicity of St=0.087. The flow periodicity reduced with increasing incidence angle to 90°. A Hexapole-type cross-sectional wake topology is observed in the wake, corresponding to the formation of two downwash inducing pairs and a single upwash inducing (base vortex) pair. The base-vortex dominate the wake, resulting in a strong upwash flow, while a relatively smaller tip-vortex induced downwash flow is limited to the near vicinity of the prism. The unsteady flow is attributed to fluctuations that arise from the lateral positioning of the prism by means of changing incidence angle, and consecutively increased projected width of the prism. The multiple downwash inducing vortices are formed due to the shear layer detachment from the side and top surfaces of the prism, which itself is attributed to the large depth-ratio in normal incident angle configuration and the base vortex that originated from the legs of the arc-type structure. This constitutes a new wake topology that differs with previous observations at lower incidence angles.

Two-dimensional bidirectional principal component collaborative projection feature for SAR vehicle target recognition

With the continuous improvement in the resolution of synthetic aperture radar (SAR), there are many problems in the interpretation of high-resolution SAR images, such as a large amount of data and low efficiency of target recognition. In this paper, a novel SAR target recognition method based on a two-dimensional bidirectional principal component cooperative representation projection feature ((2D)2PCA-CRP) is proposed. First, (2D)2PCA is used to project the image into the low-dimensional feature space, and the redundant information in the high-resolution SAR image is filtered while considering the spatial structure. Then, the spatial global separability feature and local structure feature of the target in the high-resolution SAR image are extracted by CRP to form the (2D)2PCA-CRP feature. Finally, based on this feature, the nearest neighbour classifier is used to complete the target recognition experiments on MSTAR data. The experiments of this study are divided into three parts using standard operation condition (SOC) samples, type change samples and radar incidence angle change data. The experimental results show that the proposed feature achieves better target recognition performance in high-resolution SAR images.

Terahertz angle-independent photonic bandgap in a one-dimensional photonic crystal containing InSb-based hyperbolic metamaterials.

According to the Bragg scattering theory, terahertz (THz) photonic bandgaps (PBGs) in all-dielectric one-dimensional (1-D) photonic crystals (PhCs) are strongly dependent on the incident angle. Such a strongly angle-dependent property of the PBGs not only limits the widths of omnidirectional PBGs, but also causes the strongly angle-dependent property of defect modes and optical Tamm states in multilayer structures containing all-dielectric 1-D PhCs. Until now, ways to achieve a THz angle-independent PBG have been an open problem. Herein, according to the existing phase-variation compensation theory, we achieve a THz angle-independent PBG in a 1-D PhC containing indium antimonide (InSb)-based hyperbolic metamaterials for transverse magnetic polarization. Different from conventional strongly angle-dependent PBGs, the angle-independent PBG remains almost unshifted as the incident angle changes. The relative frequency shifts of the upper and the bottom edges of the angle-independent PBG are only 1.4% and 0.4%, respectively. Besides, the angle-independent property of the PBG is robust against the disturbance of the layer thickness. The proposed 1-D PhC composes only two frequently used materials: silicon (Si) and InSb. Such a Si/InSb multilayer can be fabricated by the current ion-assisted electron beam coating or spin coating techniques. This THz angle-independent PBG would be utilized to design THz omnidirectional filters or absorbers.

Estimation of the Induced Incidence of a High Reaction Axial Turbine Bucket

This paper describes the effect of the incidence angle of the bucket on the performance of the axial turbine stage. The off-design operating conditions of the turbine stage result in a change in the velocity diagrams. This results in a positive or negative incidence. One of the basic objectives in turbine stage design is to estimate the flow behaviour of the turbine stage during off-design operation as accurately as possible and to quantify the corresponding decrease in efficiency. The available loss prediction models allow the estimation of the loss distribution when the incidence angle changes in the preliminary design phase. However, the incidence angle is actually affected by the velocity of circulation, which changes the input velocity vector (induced incidence). Thus, the blade row angle of attack is different from the angle based on the velocity diagram calculations. The result of our paper is a relation for estimating the angular difference of the input flow angle to the bucket defined as a function of the turbine operation mode.

Numerical simulation study on the influence of artificial reefs on the instantaneous collision with seabed based on the explicit finite element method

The deposition of artificial reef (AR) is a complicated systematic project. The instantaneous impact and subsidence between ARs and seabed will reduce the effective volume of AR. This study presents the effects of ARs on seabed subsidence based on explicit finite element method. The cut-opening ratio on reef bottom, weights and incident angles of ARs were used as the influencing factors, and the respective terminal velocities were used as the initial conditions to simulate the instantaneous collision process. The research results showed that the subsidence effect of ARs with a larger volume ratio (0.50) and material density (7896 kg/m3) in the seabed will be more obvious, and the rate of effective facility volume can be reduced to 79.1%. The change of incident angle affected the deformation region after AR subsidence. The indexes of the subsidence ratio and the rate of effective facility volume should be used simultaneously to measure the extent of subsidence. In addition, the maximum stress monitoring results of AR in subsidence process verified that the current strength standard of 25 MPa can meet the safety needs of AR deposition. This study aims to provide a scientific reference for the structural design and release scheme of AR.

Modeling of evacuated tube solar collector involving longitudinal fins and nanofluids

In this research, the thermal characteristic of a thermosyphon evacuated tube collector for domestic application was examined, and the structure of the collector was modified by employing longitudinal fins within the absorber to raise the thermal efficiency. The efficacy of water-based Cu and MWCNT nanofluids in different volume fractions on the collector’s performance was investigated using computational fluid dynamics. Moreover, the alteration in the fluid flow structure and average tank temperature for various solar radiation incidence angles on the absorber surface was also discussed. A comparison has been made for distributions of velocity and temperature of the modified model and the conventional type along the different cross-sections of the absorber during the one-hour time period. Regarding the solar radiation incidence angle, the fluid flow pattern undergoes an alteration while the incidence angle changes to 30° and 60° in relative to the y-axis. However, tank mean temperature possesses the highest value, and the heat transfer improves when solar radiation is normal to the absorber surface. Moreover, the thermal analysis demonstrated the increment of the system’s thermal efficiency up to 65.21 % when longitudinal fins were employed along the evacuated tube. The comparison of simulated cases using nanofluids in different volume fractions revealed that applying 5 % MWCNT nanofluid for the finned case shows the greatest heat transfer improvement with the useful heat gain of 116.11 kJ and the optical efficiency of 67.61 % compared to unfinned, and finned cases using Cu nanofluids.

Conformal Miniaturized Angular Stable Triband Frequency Selective Surface for EMI Shielding

This article presents single-layer conformal high angle stable miniaturized triband bandstop frequency selective surface (FSS) for microwave shielding. This new FSS is supported on an ultrathin dielectric substrate and has stable response with change in polarization and incidence angle. Via-less convoluted geometry is adopted in the unit cell design to increase spatial efficiency with a unit cell size of 0.091 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> , where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> is the wavelength at lowest resonance. The proposed FSS exhibits three transmission zeros at 4, 6.95, 11.3 GHz with stopband bandwidth (BW) founds application for shielding the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> band frequencies for satellite communication. A prototype of the proposed FSS is fabricated. The filter response is measured on normal and on curved surfaces. Simulated and measured transmission coefficients confirm the operating principle of the FSS. Unit cell periodicity of the triband FSS is further reduced by using two layers based 2.5-D geometry. The modified unit cell has a periodicity of 0.038 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> and exhibits stopband BWs center at 0.8, 1.4, and 2.36 GHz.

Ultrafast Laser Texturing of Stainless Steel in Water and Air Environment

Ultrafast laser texturing allows the generation of micro- and nanostructures on steel substrates. Laser-ablated textures show a wide range of structure geometries, from the micro to the nanoscale, which can enable plastic product functionalization. Polymer processing technologies are used to replicate mold textures on a large manufacturing scale. To enable new product functionalities, developing novel texture geometries is critical. The laser-ablated texture dimensions are primarily linked to the laser light properties, such as the laser wavelength, thus limiting the achievable structure shapes. This work uses ultrafast laser to manufacture textures in air and water environments. The effect of the different mediums on structures formation is characterized. The irradiation is performed over a wide range of fluence values. The texture geometry and characteristics are evaluated by scanning electron microscopy. For decreasing fluence values, the structures transitioned from micro bumps, to LIPSS, to nanostructures, regardless of the irradiation environment. Conversely, structure morphology is affected by the irradiation environment. The LIPSS pitch is lower for the underwater environment due to the change in the laser angle of incidence, which changes with the refraction index ratio of the air and water. A novel nano-lamellae texture was generated when irradiating the steel surface underwater at relatively low fluence. The dynamics of different LIPSS generations are discussed, considering the irradiation medium’s optical, thermal, and physical properties.

Near-infrared narrow-band minus filter based on a Mie magnetic dipole resonance.

The traditional minus filter is composed of many layers of thin films, which makes it difficult and complicated to manufacture. It is sensitive to incident light angle and polarization. Here, we propose a near-infrared narrow-band minus filter with a full width at half maximum around 5 nm made of all-dielectric Si-SiO2 structures without any ohmic loss. The stop band transmittance of the proposed filter is close to 0, while its broad pass band transmittance is as high as 90% in the work wavelength range. Theoretical analysis shows that the transmission dip originated from magnetic dipole resonance: Its position can be tuned from 1.3 µm to 1.8 µm by changing the thickness of Si structure, and the proposed structure is insensitive to changes in incident light angle and polarization angle. We further studied its potential applications as a refractive index sensor. The sensitivity of dip1 and dip2 are as high as 953.53 nm/RIU and 691.09 nm/RIU, while their figure of merit is almost unchanged: 59.59 and 115.18, respectively.

Numerical characterization of 1D-Photonic crystal waveguide for female reproductive hormones sensing applications

The current work investigates the detection of a wide range of estradiol and progesterone hormone concentrations by the use of a defective 1D photonic crystal. The suggested structure consists of repeating layers of PbS and SiO2, with a central cavity layer. The transfer matrix technique is manipulated to examine the transmission spectrum of the proposed structure. The mainstay of the present work is to analyse the shift in the wavelength of the defect mode concerning the changes in different concentrations of hormones that are infiltrated into the cavity layer. In the course of a simulation, various geometrical parameters such as the thickness of the cavity layer and incident angle are properly optimized to envisage high performance. The colour map plot is investigated to convey a clear view of the shift of defect mode position concerning the change in incident angle. Moreover, all the sensing parameters like sensitivity, figure of merit, quality factor, signal-to-noise ratio, sensor resolution, and limit of detection are evaluated for each hormone at different incident angles. The main application behind this study is that it is important to sense the levels of estradiol and progesterone hormones for balanced needs in a women's reproductive system as well as to monitor the overall health systems. This proposed structure is suitable for bio-sensing applications due to their cost-effective fabrication and high performance.

Influence of stealth aircraft dynamic RCS peak on radar detection probability

For modern stealth aircraft, it is important to analyze the influence of Radar Cross Section (RCS) peak exposure on penetration for guiding stealth design and penetration trajectory planning, which needs to reflect the RCS statistical uncertainty and the RCS difference with the change of incident angle. Based on the RCS characteristics of typical stealth aircraft, this paper established a simplified RCS dynamic fluctuation statistical model with the parameters log mean and log standard deviation. According to the detection probability algorithm in radar signal processing field, this paper built the algorithm of radar detection probability based on the RCS dynamic fluctuation statistical model. The analysis of examples concluded that the key to successful penetration is to shorten the RCS peak exposure time, which can be reduced by decreasing the RCS peak width or increasing velocity. Based on the conclusion, this paper proposed the method of turning maneuvering to reduce RCS peak exposure time dramatically.

Electromagnetic forces in nanoparticles made of multilayer hyperbolic metamaterials

We theoretically study the electromagnetic forces (optical gradient force, optical torque and vacuum friction) acting on a spherical anisotropic nanoparticle, which can be characterized by multilayer hyperbolic metamaterials (mHMMs). We find three important results about these forces: (i) Firstly, we theoretically demonstrate that the optical gradient force produced on a mHMMs nanoparticle can be flexibly tuned, from pushing the particle to pulling it, just via changing incident angle of illuminating plane light wave. (ii) Secondly, we find the optical torque acting on the mHMMs nanoparticle (its filling factor is around 0.3) can be tuned between positive and negative via changing the incident angle of circularly polarized plane light. Therefore, the rotating mHMMs nanoparticle with designed filling factor can be accelerated or decelerated by the optical torque. (iii) Finally, due to the large fluctuations of dipole polarizability of mHMMs nanoparticle with appropriate filling factor, we propose a new method to obtain the large enhancement of vacuum friction torque by designing the filling factor of the rotating mHMMs nanoparticle.

Stall Behavior in an Ultrahigh-Pressure-Ratio Centrifugal Compressor: Backward-Traveling Rotating Stall

AbstractThis paper describes the stall mechanism in an ultrahigh-pressure-ratio centrifugal compressor, composed of a double-splitter impeller, radial diffuser, and axial diffuser. A model comprising all impeller and diffuser blade passages is used to conduct unsteady simulations that trace the onset of instability in the compressor. Backward-traveling rotating stall waves appear at the inlet of the radial diffuser when the compressor is throttled. Six stall cells propagate circumferentially at approximately 0.7% of the impeller rotation speed. The detached shock of the radial diffuser leading edge and the number of stall cells determine the direction of stall propagation, which is opposite to the impeller rotation direction. Dynamic mode decomposition is applied to instantaneous flow fields to extract the flow structure related to the stall mode. This shows that intensive pressure fluctuations concentrate in the diffuser throat as a result of changes in the detached shock intensity. The diffuser passage stall and stall recovery are accompanied by changes in incidence angle and shock wave intensity. When the diffuser passage stalls, the shock-induced boundary–layer separation region near the diffuser vane suction surface gradually expands, increasing the incidence angle and decreasing the shock intensity. The shock is pushed from the diffuser's throat toward the diffuser leading edge. When the diffuser passage recovers from the stall, the shock wave gradually returns to the diffuser throat, with the incidence angle decreasing and the shock intensity increasing. Once the shock intensity reaches its maximum, the diffuser passage suffers severe shock-induced boundary–layer separation and stalls again.

Employing the Defective Photonic Crystal Composed of Nanocomposite Superconducting Material in Detection of Cancerous Brain Tumors Biosensor: Computational Study

The present research is focused on the externally tunable defect mode properties of a one dimensional (1D) defective photonic crystal (DPhC) for fast detection of cancerous brain tumors. The proposed design has utilized conventional 1D DPhC whose cavity is coated with SiO2 nanoparticles embedded in a superconducting material layer called a nanocomposite layer. The purpose of a nanocomposite superconducting layer is to induce temperature dependent external tuning of the defect mode inside PBG, in addition, to changing in the angle of incidence. The inclusion of a nanocomposite layer also improves the interaction between light and different brain tissue samples under examination. In order to investigate the transmission properties of the proposed structure the transfer matrix formulation in addition to the MATLAB computational tool has been used. First, we have chosen the optimized internal parameters at normal incidence to obtain the maximum performance of the design. Secondly, the effect of change in angle of incidence has been studied to further increase the performance by means of sensitivity, quality factor, the figure of merit and limit of detection to ensure external tuning of defect mode. After achieving a maximum value of sensitivity (4139.24 nm/RIU) corresponding to a sample containing a wall of brain tissues at θ = 63° we have further investigated the effect of change in temperature of nanocomposite layers on the position and intensity both of the defect mode inside PBG. We have found that the increase in temperature results in minute changes in sensitivity but a significant increase in the intensity of defect mode which is highly required in any photonic biosensing design. The findings of this study may be very useful for designing various bio-sensing structures which could have a significant and decisive role in the field of biomedical applications.