Maximum Incident Angle Research Articles

Damage assessment of fixed U-shaped stiffeners stiffened square plates subjected to close-in explosions

The aim of this study is to suggest an approach for evaluating the damage modes and damage levels of the U-shaped stiffeners stiffened plates exposed to close-in explosions. To achieve this objective, a numerical model was developed in LS-DYNA, and the numerical model was verified by experimental results of the authors. Using this validated model, various U-shaped stiffeners stiffened plates were examined under different blast loads. The study investigated the factors that influence the damage modes of the plates, including the strength and distribution of the blast loads, as well as the geometry of the stiffened plates. The results indicated that the small size stiffened plates exhibited overall damage mode while the large stiffened plate showed localized damage at the same blast load. The blast load distribution on the different size plate led to different damage modes. Additionally, this study found that the slenderness of the stiffened plate had a great influence on the support rotation angle of the tensile tearing threshold. The larger span to thickness ratio can result in larger tensile tearing threshold. Moreover, 400 numerical cases were included and used to classify the damage modes of stiffened steel plates. Based on the damage mechanism of the stiffened steel plate, the damage number (Φ1 and Φ2) which considering the blast loads and material parameters of plate, the maximum incident angle of the blast load(α), and the relative stiffness of the stiffeners and the flat steel plate (κ1 and κ2), and the thickness to span ratio of the stiffened plate (λ) were combined to identify the damage modes of stiffened plates. Furthermore, a flow chart was constructed for determining damage modes based on these considerations. Additionally, a curve surface fitting was performed using Φ1 and λ, the fitting formulas were then used to estimate the deformation characteristics of the stiffened plates with U-shaped stiffeners. The damage levels of the U-shaped stiffeners stiffened plates were then classified as low damage, medium damage, severe damage, and collapse by combining the nominal support rotation angle with the threshold of the global tensile tearing at boundaries. The study result can provide insight into the damage mode identification and damage level classification of stiffened steel plates under explosion. Additionally, this study was a base of damage evaluation of the structure elements (such as steel box girder) include stiffened steel plates under explosions.

Analysis of the Dihedral Corner Reflector’s RCS Features in Multi-Resource SAR

Artificial corner reflectors are widely used in the vegetated landslide for time series InSAR monitoring due to their permanent scattering features. This paper investigated the RCS features of a novel dihedral CR under multi-resource SAR datasets. An RCS reduction model for the novel dihedral corner reflector has been proposed to evaluate the energy loss caused by the deviation between the SAR incident angle and the CR’s axis. On the Huangtupo slope, Badong county, Hubei province, tens of dihedral CRs had been installed and the TSX–spotlight and Sentinel-TOPS data had been collected. Based on the observation results of CRs with more than ten deviation angles, the proposed reduction model was tested with preferable consistency under a real dataset, while 2 dBsm of systematic bias was verified in those datasets. The maximum incident angle deviation in the Sentinel data overlapping area is over 12°, which leads to a 2.4 dBsm RCS decrease for horizontally placed dihedral CRs estimated by the proposed model, which has also been testified by the observed results. The testing results from the Sentinel data show that in high, vegetation-covered mountain areas like the Huangtupo slope, the dihedral CRs with a 0.4 m slide length can be achieve 1 mm precision accuracy, while a side length of 0.2 m can achieve the same accuracy under TSX–spotlight data.

Maze-enclosed quad symmetric kite shaped SRR based metamaterial absorber for doppler navigation aids and earth exploration satellite remote sensing services

This paper represents a wide incident angle-polarization insensitive, stable in results, and compact-sized metamaterial absorber that can be used for Doppler navigation aids and remote sensing applications in Earth Exploration Satellite Services. The unit cell dimension was subwavelength-sized of 0.112λ X 0.112λ, with a good effective medium ratio (8.9), and achieved polarization insensitivity at a maximum incident angle up to 180°, making it more effective for proposed applications. The absorber resonated at 3.855 GHz, 5.13 GHz, 9.855 GHz, 13.335 GHz, and 16.02 GHz with single negative metamaterial properties due to negative permeability and absorptions of 99.7 %, 99.2 %, 98.6 %, 98.1 %, and 97.9 %, respectively. An RLC equivalent circuit on ADS was analyzed to validate the simulated results using the dipoles created by the surface currents. The absorber is cost-effective as no lumped elements or multilayer substrate materials were used, making fabricating less time-consuming and simple. The simulated results were validated by measuring data from a vector network analyzer after fabricating it. The proposed metamaterial absorber is suitable for use in Doppler navigation and Earth Exploration Satellite Services, and this research can further be extended to beamforming and sensing applications in the future.

Calculation of the interaction between an overlapping spherical lens and a pin-type second optical element for spherical lens microtracking concentrator photovoltaic with a wide angle of incidence

Concentrator photovoltaics (CPV) can efficiently convert light into electricity; however, conventional CPVs require large and heavy tracking systems. Microtracking CPVs (MTCPVs) can solve this significant problem. Most MTCPV systems have a limited angle of incidence (AOI). If diffuse light was used, MTCPV required traveling light from top to bottom. In this study, a spherical-lens-based microtracking CPV (SMTCPV) with a pin-type second optical element (SOE) was developed. In SMTCPV, the light travel light from above to below. Pin-type SOEs were inserted between the spherical lenses, thus increasing the acceptable wide AOI. Optical analysis and calculations of the interaction between overlapping spherical lenses and pin-type SOEs were performed. An optical efficiency of 59% was maintained at any angle when the gap was considered. The maximum AOI was 64.7° in the direction of adjacent spherical lenses and 90° in the gap direction.

Ultrawide and unidirectional enhancements of a photonic spin Hall effect in a tilted uniaxial crystal.

Since the enhancement of the photonic spin Hall effect (PSHE) is limited around the Brewster's angle, the scientific problem of how to extend the range of incident angles and to keep them unidirectional for the enhanced PSHE remains open. Here, we propose an effective method to achieve the ultrawide angle and unidirectional enhancement of PSHE via the omnidirectional Brewster's effect in a tilted uniaxial crystal. By properly setting the permittivity and the optical axial angle of the uniaxial crystal, the omnidirectional Brewster's effect can be obtained to realize an ultrawide angle enhancement of the PSHE. Then, by appropriately deviating the optical axial angle, the ultrawide enhancement of the PSHE can be achieved within the maximum incident angle range of 60° with unchanged direction. These findings inspire an unprecedented route to facilitate the applications in precision measurement and spin-dependent devices.

EURADOS IC2019exteye- a self-funded intercomparison for extremity and eye lens dosemeters organised by EURADOS working group 2.

The European Radiation Dosimetry Group (EURADOS) has been organising regular, self-funding, external dosimetry intercomparisons (ICs) since 2008. IC2019exteye, for extremity and eye lens dosemeters, attracted 113 systems (68 extremity and 45 eye lens) from 60 institutes with participants from 26 countries around the world. Irradiations were carried out in accredited European irradiation facilities in terms of Hp(0.07)/or Hp(3) in the ranges: photon energy: 16-662keV, beta mean energy 250-1000keV, dose: 0.5mSv to 1Sv, maximum angle of incidence: ±60°. This paper describes the IC2019exteye set-up, irradiation plan and coordination with an overview of the main conclusions. Out of the total of 113 systems, 57 reported results for photons only and 56 reported both photon and beta. In general, the participants showed very satisfactory performances with the medians of all Hp(0.07) and Hp(3) response values very close to unity.

Luminous Flux Utilization of Static Birefringent Fourier Transform Imaging Spectrometer with Zoomable Spectral Resolution

The optical displacement calculation formula for the dual Wollaston prism is derived for any incident plane and angle using the wave normal tracing method. The validity of the calculation is confirmed by comparing it with captured photographs. The relationship between the maximum incident aperture, incident angle, and incident surface angle is given when plane and spherical waves incident on the prism group. The aperture utilization of a novel static birefringent Fourier transform imaging spectrometer based on dual Wollaston prisms is also analyzed. The relationship of aperture utilization with the incident surface angle, incident angle, and prisms’ air gap thickness is given. The results provide a theoretical foundation for fully describing the optical transmission characteristics of the dual Wollaston prism group and developing a high-performance spatio-tempo hybrid modulated birefringent spectral zoom Fourier transform imaging spectrometer.

Measurement of the diffuse field sound absorption using a sound field synthesis method

A method for measuring the diffuse field sound absorption coefficient of a material using sound field synthesis is proposed. A planar loudspeaker array is first used to generate acoustic plane waves with variable incidence angle on the surface of a material under test. Using a two-microphone probe positioned closely to the sample’s surface, the angle-dependent sound absorption coefficients are then estimated. Finally, the diffuse field absorption coefficient is computed following Paris formula. Numerical simulations are used to evaluate the respective effects of the maximum incidence angle value and the number of individual incidence angles that are required for a robust calculation of the diffuse sound field absorption. Measurements are conducted on three different materials and compared with either simulation results obtained using the Johnson-Champoux-Allard theory, or with measurement results obtained using the standard reverberation chamber method. For all considered materials and over a wide frequency range, the proposed method leads to results that are in better agreement with theoretical predictions than those obtained using standardized methods.

Broadband Bi-Directional All-Dielectric Transparent Metamaterial Absorber.

Water-based absorbers have shown great development potential in the past few years. In this paper, an all-dielectric transparent bi-directional water-based broadband metamaterial absorber is designed. The simulation results indicate that absorptance of the absorber is over 90% in 5.7-41.6 GHz, and its fraction bandwidth is 151.8%. The experimental results are greatly consistent with the simulations. The designed absorber has excellent performances of polarization insensitivity, oblique incidence stability and thermal stability. When the absorptance is more than 0.8, the maximum incident angle reaches 40° in TE mode and is over 60° in TM mode. In 0-80 °C, absorptance of the absorber is hardly changed. Because of the optical transparency of the designed absorber, it can be extensively used in stealth window weapons and electromagnetic compatibility equipment.

Damage mechanism of U-shaped ribs stiffened steel flat plates subjected to close-in explosion

The U-shaped ribs stiffened plates are widely used in civil and marine engineering structures for their high bending resistance performance. Moreover, these structures may be exposed to blast scenario especially terrorist and accidental explosions. Based on this background, this investigation carried out a study on the damage modes and the damage mechanisms of the U-shaped ribs stiffened plates subjected to close-in blast loads. The work used both field experimental and numerical methodologies. In this investigation, field blast tests were conducted on two flat plates and a stiffened plate. Furthermore, a fine numerical model was developed on the LS-DYNA platform and validated by the experimental results. Numerical analysis was conducted follow the validated model, and three typical damage modes (five detailed damage modes) of the single U-shaped stiffener stiffened plates subjected to blast loads were revealed through the numerical calculation of 40 specimens. Furthermore, a new damage number (Φ) was proposed for the classification of the damage modes. Meanwhile, maximum incident angle (α) and relative stiffness (κ) were put forward for further identification of the damage modes. It is proven that the damage modes of the single U-shaped stiffener can be well identified by the combination of damage number, maximum incident angle, and relative stiffness. Damage mode I occurred when Φ is less than Φ1 (0.042). And while the Φ is more than Φ2 (0.071), the stiffened plates exhibited mode IIIb damage. For Φ is between Φ1 and Φ2, the damage modes can be classified as mode IIa (κ < 0.0032) and IIb (κ≥ 0.0032) when α is less than 45°. While α is greater than 45°, the damage modes can be classified as mode IIa (κ < 0.001), IIIa (0.001 ≤κ < 0.0032) and IIIb (κ≥ 0.0032).

Polarization insensitive dual band metamaterial with absorptance for 5G sub-6 GHz applications

A couple ring enclosed circular geometric resonator (CRECGR) based dual-band polarization insensitive metamaterial (MM) with high effective medium ratio (EMR), and excellent absorptance is proposed in this study, which can be utilized as a sensor and absorber in the 5G sub-6 GHz frequency range. A circular geometry-based unique patch has been introduced in the proposed unit cell to achieve high polarization insensitive properties with excellent absorption for the 5G sub-6 GHz spectrum. The distinctive feature of this proposed CRECGR unit cell is its simple and unique structure with a high EMR of 11.13, polarization insensitive up to 180°, and epsilon negative (ENG) properties, including a negative refractive index and near-zero permeability for 5G sub-6 GHz applications. Furthermore, this designed unit cell yields excellent absorption properties with high quality factor. The designed MM unit cell is fabricated on low loss Rogers RT5880 printed media with an electrical dimension of 0.089λ × 0.089λ × 0.017λ. The performance of the designed CRECGR metamaterial is determined using Computer Simulation Technology (CST), Advanced Design Software (ADS), and measurements. The CRECGR unit cell offers dual resonances at 3.37 GHz and 5.8 GHz, covering the 5G sub-6 GHz band with ENG, near-zero permeability and negative index. The polarization insensitive properties of the unit cell were also investigated for maximum angle of incidence, which confirmed the identical response. The simulated outcome is verified by experiment with excellent accordance. Moreover, the unit cell performance with a complete backplane is explored, noting a maximum absorption of 99.9% for all normal and oblique incidence waves, suitable for sensing and antenna systems. In addition, the suggested unit cell sensing performance is evaluated using the permittivity-based sensing model. The proposed MM outperforms recent related studies in terms of polarization insensitivity up to 180°, high insensitive absorptivity, high EMR, and sensing applications. These features prove that the proposed CRECGR metamaterial is perfect for 5G Applications.

An Ultraminiaturized Frequency Selective Surface With Angular and Polarization Stability

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> × 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> with a thickness of 0.006 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems.

A 2.5D miniaturized low-profile ultra-wideband band-stop frequency selective surface

This paper proposes a miniaturized UWB band-stop frequency selection surface based on metalized via technology, aiming at the problem of the large cell size and thick profile of the UWB band-stop frequency selection surface. By studying the principle of miniaturization of 2.5D frequency selective surface, a 2.5D ultra-wideband band-stop miniaturized frequency selective surface with high angular stability and low profile is designed. The simulation and test results show that the designed structure can cover the ultra-wideband frequency range of 2.36 GHz ∼ 11.36 GHz, the −10 dB percentage bandwidth is 161.9%, the unit size is , and the thickness is , where represents the resonance wavelength in free space. The maximum incident angle can reach 60 degrees for TE and TM polarization. Compared with the existing literature, the designed ultra-wideband band-stop miniaturization frequency selection surface miniaturization is better, and the profile is lower.

Investigating the absorption performance of a monolayer-coated absorber at oblique incidence

There is a widely observed phenomenon in the microwave absorption field that an absorber always exhibits good oblique incidence absorption capacity if it has high performance at normal incidence. However, if a certain angle is exceeded, this kind of effective absorptive capacity will no longer be maintained. Besides, an absorber performs differently for incident transverse electric (TE) and transverse magnetic (TM) waves: for the TE case, the absorber can no longer obtain effective absorption; for the TM case, another efficient absorption region was observed at higher frequencies even when the incident angle exceeded 80°. These phenomena are widely found in the literature, which demonstrates that they are caused by physical laws rather than material properties. To demonstrate the underlying reason, in this study, the common spherical carbonyl iron-polyurethane composite absorbers were fabricated as a typical example. Their absorbing performance was investigated via both simulation and experiment. All the phenomena mentioned above were observed, studied in detail by employing the multiple reflection model, and explained quantitatively. Further, along with establishing the underlying mechanism of electromagnetic wave transmission in the absorber, two formulas were deduced to predict: (a) the maximum incident angle for efficient absorption of the TE polarized wave; and (b) the required absorber thickness for obtaining efficient absorption for a large incident angle of the TM polarized wave.

Non-uniform illumination in low concentration photovoltaic systems based on small-scale linear Fresnel reflectors

Low concentration photovoltaic systems improve performance by absorbing and concentrating more sunlight than non-concentration ones. However, they require uniform illumination of the PV cells, as their electrical performance can decrease dramatically otherwise. A thorough analysis of the design causes of non-uniform illumination in small-scale linear Fresnel reflectors (SSLFR) is carried out, yielding the main parameters to be optimized. Then, such an optimized SSLFR guaranteeing uniform illumination is designed, and an optimum operation interval is estimated during which, furthermore, neither shading nor blocking on the mirrors happens. The study requires computing the maximum optimal transverse incidence angle, θt0, whose influence on the time-span of optimum operation, width of the SSLFR, annual solar irradiation, width of the mirrors, and position of the mirrors is also studied. We include a detailed example showing the accuracy of our calculations, using Monte Carlo Ray Tracing.

Angle-insensitive co-polarized metamaterial absorber based on equivalent circuit analysis for dual band WiFi applications

A novel and systematic procedure to design a co-polarized electromagnetic metamaterial (MM) absorber with desired outputs and resonance frequencies for dual-band WiFi signal absorption is presented. The desired resonance frequencies with expected S parameters' values were first designed as an equivalent circuit with extensive analysis and then implemented into frequency-selective MM absorber by numerical simulation with precise LRC elements, satisfying least unit cell area (0.08λ), substrate thickness (0.01λ) and maximum effective medium ratio (12.49). The absorber was simulated for the maximum angle of incidence for both the normal and oblique incidences at co-polarization. The absorptions at the desired resonance frequencies were found at a satisfactory level by both simulation and practical measurement along with a single negative value to ensure metamaterial characteristics. The proposed equivalent circuit analysis approach can help researchers design and engineering co-polarization insensitive MM absorbers using conventional split-ring resonators, with perfection in output and desired resonance frequencies without the necessity of lumped elements or multilayer substrates. The proposed metamaterial can be utilized for SAR reduction, crowdsensing, and other WiFi-related practical applications.

Polarization Insensitive and Transparent Frequency Selective Surface for Dual Band GSM Shielding

This article proposes a single-layer, dual-band, optically transparent frequency-selective surface (FSS) for GSM shielding. The design evolves from a fractal cross dipole to achieve dual-band response, polarization insensitivity, and wide angle of incidence stability with a miniaturized size. A two-axis symmetric structure helps to provide a stable frequency response for incident waves with different polarization angles up to 60°. Capacitive loading further reduces the unit size and extends the maximum stable incident angle. The working mechanism of the design has been explained through an equivalent lumped element circuit model (ECM), which provides a generic approach to retune or optimize the design for another frequency band. Both the full-wave EM and circuit simulations are in good agreement. A prototype has been realized by screen printing a custom silver nanowire (Ag NW)-based transparent ink on a flexible polymer substrate. A decent reflection performance has been achieved from 0.71 to 1.25 GHz and from 1.73 to 2.16 GHz in measurements, which are consistent with the simulations. Optical measurements reveal a transparency of 81.6%. Printed FSS is completely flexible, and the performance does not deteriorate after bent or rolled up conditions. Field testing on a glass box demonstrates decent shielding from the incoming GSM signals. The highly transparent and flexible nature of the FSS structure makes it suitable for mounting on glass windows of cars or home environments for EM shielding purposes.

Numerical Study of an Ultra-Broadband and Polarization Independence Metamaterial Cross-Shaped Fractal Absorber

A three-dimensional cross-shaped fractal metamaterial absorber with ultra-wide wavelength band, polarization-independence and wide-angle, is numerically investigated by the finite-difference time-domain method. In this absorber, the solar energy is trapped by the cross-shaped fractal of the upper layer, and the Si-ring filled with iron in the middle layer and the wavelength band can be broadened by the self-similarity of fractal structure. The absorber exhibits absorptivity higher than 91% for the wavelengths from 400 to 2000 nm and an absorption bandwidth of about 133%. Furthermore, the proposed absorber realizes polarization independence, and the maximum incident angle is 76°. However, as the iron material applied in the nano-metamaterial absorber (NMA) can be easily oxidized and rusted, it is replaced by nickel with characteristics such as corrosion resistance and high-temperature resistance; thus, an improved NMA is obtained. The improved absorber not only eliminates the corrosion-prone defects of the above proposed structure but also maintains polarization independence and high absorption and widens the angle of incidence up to 79° and thereby can be applied in many areas, such as solar energy harvesting.

Portable Body-Attached Positioning Mechanism Toward Robotic Needle Intervention

This article presents a robotic needle positioning approach with a novel 4-DoF parallel positioner, two back-driveable 2-channel linear/rotational driver, and a machine–body interface. Being more compact and flexible, Ni–Ti alloy wire-based Bowden cable transmission is introduced to connect the positioner and the drivers. For this new mechanism, forward and inverse kinematics are derived, and the workspace is analyzed. The mechanism’s maximum incidence angle is 45 $^{\circ }$ , and the stroke of the slider is 41 mm. The structural size of one positioner is $\varnothing$ 70 mm × 45 mm. The compact size and lightweight of the positioner make it readily mountable on the skull or attached to other parts of the body. We fabricated a 3D printed proof-of-concept prototype of the system and tested its performance. The open-loop positioning accuracy of the slider and rotor is within $\pm$ 1 mm and from $-0.8^{\circ }$ to 1.5 $^{\circ }$ , respectively. The trajectory tracking error of the system is within 1.71 mm. The stiffness of the positioner in the x - and y -directions can be calculated as 9.03 and 11.91 N/mm, respectively. Finally, an image-guided navigation framework based on electromagnetic tracking demonstrates the feasibility of the proposed system on a phantom study.

Seismic inversion for fluid bulk modulus based on elastic impedance

Beginning with the simplification of Gassmann's fluid substitution equation, we propose a simplified bulk modulus of saturated rock in terms of fluid bulk modulus and porosity. Using relationship between reflection coefficients and scattering function, we derive a linearized PP-wave reflection coefficient as a function of fluid bulk modulus and modified porosity, and we also present the corresponding elastic impedance, which is useful for modeling how fluids affect seismic reflection amplitudes. The accuracy of derived reflection coefficient is confirmed in the case of maximum incidence angle being around 30°. Using the derived reflection coefficient and EI, we establish an inversion approach to estimate fluid bulk modulus and porosity from observed seismic data, which involves 1) the estimation of EI from partially stack seismic data, and 2) the extraction of fluid bulk modulus from estimated EI datasets. The extraction of fluid bulk modulus is implemented using a nonlinear inversion approach. Using the derived elastic impedance we compute the gradient of energy residual with respect to model vector directly, which allows us to implement the nonlinear inversion stably. Synthetic tests confirm the stability and robustness of the proposed inversion approach, and applying the inversion approach to a real dataset we obtain meaning results of fluid bulk modulus that are valuable for fluid identification in reservoirs.