Wide Range Of Angles Research Articles

Solar Cell Detection and Position, Attitude Determination by Differential Absorption Imaging in Optical Wireless Power Transmission

In optical wireless power transmission, position, size, and attitude of photovoltaic device (PV) must be determined from light source. A method proposed in the previous report is based on selective absorption characteristics of PV, and it is detected by differentiating images of strongly absorbable wavelength and one not. In this study, using two infrared wavelengths, two kinds of targets were detected by differential absorption imaging. One was a GaAs substrate which simulates diffuse rear surface, and the other was a real GaAs PV. It was found that the substrate’s reflective characteristic was diffuse, and the solar cell’s was mainly non-diffuse and accompanied by small diffuse component supporting wide-angle reflection. Using this feature, the position of the GaAs solar cell could be determined within a wide range of angle. Its attitude could also be determined with an accuracy of ±10 degrees to its normal. The position of diffuse GaAs substrate could be determined within a wide range of angles, and its attitude determination was proposed by exploiting its varying apparent size with tilt angle. Broad reflection characteristics of the GaAs substrate enabled attitude determination for a wide-angle range, and determination around normal would be erroneous.

Multi-resonant tunable absorber of terahertz metamaterial based on GaAs and VO2

Based on the fact that the conductivity of photosensitive semiconductors can be regulated by external pump light, a metamaterial absorber with single-band and dual-band switchable in terahertz region is designed by replacing gallium arsenide (GaAs) within the nested cell ring structure. With the power increase of external pump light, the maximum absorptivity would be 99.9% when the conductivity of GaAs is setting as 5 × 105 S/m. Furthermore, based on the fact that the temperature can change the phase transition characteristic of vanadium oxide (VO2) and thus change the conductivity characteristic of VO2, the nested cell ring structure is extended, and a multi-resonant metamaterial absorber with tunable conductivity is proposed. When both GaAs and VO2 are in the metallic state, the absorption can be switched from triple-band to single-band, and when the conductivity of both is 5 × 105 S/m, the absorptivity is more than 99%. The GaAs is in the insulated state when there is no pump light irradiating and the conductivity of VO2 could be changed by temperature, or VO2 is in insulated state at room temperature and the conductivity of GaAs could be changed by pump light irradiation. After such supposed condition, the tunability from triple-band to dual-band shown in the proposed metamaterial absorber can be realized gradually. When the conductivity of VO2 or GaAs is 5 × 105 S/m, the maximum absorptivity of such multi-resonant tunable absorber is above 98%. Based on the controllability of GaAs and VO2 conductivity, the multi-resonant tunable absorber with arbitrary switching of single-band/dual-band/triple-band absorption state could be realized. At the same time, the designed absorber has excellent absorption characteristics about both transverse electric (TE) field and transverse magnetic (TM) one in the wide-angle incidence range, which is expected to be further applied in the research fields of modulator, frequency selector, detector, and so on.

3D printed propeller-like metamaterial for wide-angle and broadband microwave absorption

• A broadband wide-angle 3D meta-absorber was proposed based on the reciprocity theory. • The absorber was designed by characteristic mode analysis and dispersion engineering. • The absorber was fabricated of CB-PP composite by 3D printing technology. • Broadband and wide-angle absorption of the absorber was verified experimentally. It is a challenge to design an absorber which can simultaneously satisfy comprehensive demands of broad absorption band, wide incident angle range, and low-profile. In this work, we designed a metamaterial absorber (MMA) based on the antenna reciprocity theory to achieve the above goals. Firstly, a three-dimensional (3D) propeller-like structure with reference to a typical magneto-electric dipole (MED) antenna was proposed and analyzed by the characteristic mode (CM) theory to realize near-omnidirectional radiation. Then, the radiation-absorption conversion was realized by introducing lossy materials into this structure, and the absorption performance was further improved by optimizing the dispersion feature of the lossy materials. Finally, the propeller-like metamaterial absorber with a thickness of 0.113 λ L was manufactured efficiently and integrally through 3D printing technology. Simulation results showed that the proposed absorber can achieve broadband absorption with the efficiency more than 90% in the frequency band of 3.4-10 GHz. It also has excellent wide-angle absorption capacity, with Transverse Electric (TE) polarization of 0° to 50° and Transverse Magnetic (TM) polarization of 0° to 80°. With the increase of incident angle, the upper limit of absorption bandwidth can be gradually extended to 18 GHz. Moreover, the effectiveness in the range of 0° to 60° incident angle is verified by measuring the reflectivity of the 3D printed absorber.

Effects of gravity on natural oscillations of sessile drops

Natural oscillations of sessile drops with a free or pinned contact line in different gravity environments are studied based on a linear inviscid irrotational theory. The inviscid Navier–Stokes equations and boundary conditions are reduced to a functional eigenvalue problem by the normal-mode decomposition. We develop a boundary element method model to numerically solve the eigenvalue problem for predicting the natural frequencies. Emphasis is placed on the frequency shifts of modes due to gravity for a wide range of contact angles $\alpha$ and Bond numbers $Bo$ . Three types of $\alpha$ – $Bo$ diagrams reflecting how gravity shifts the frequency are identified. Specifically, the frequency of zonal modes shifts downwards (upwards) when $\alpha$ is smaller (larger) than a critical value, while the frequencies of most sectoral modes are shifted downwards regardless of $\alpha$ . As a result, gravity can transform the lowest mode from a zonal mode to a sectoral mode. The spectral degeneracy of hemispherical drops inherited from the Rayleigh–Lamb spectrum is also broken by gravity. However, we discover that gravity has no effect on the mode associated with the horizontal motion of the centre of mass, whose frequency is always zero regardless of $\alpha$ and $Bo$ . This implies that the ‘walking’ drop instability reported in previous literature does not exist.

An efficient underwater absorber using pentamode metamaterials for broadband frequency

To further design and develop broadband and efficient underwater sound absorption structure, we propose a hybrid acoustic structure composed of a rubber matrix layer, cylindrical cavity, pentamode metamaterial (PM) layer, impedance matching layer, and steel backing plate. Thanks to the special properties of the PMs, the hybrid acoustic structure obtains excellent broadband sound absorption performance (SAP) in the frequency range of 500–10000 Hz than that of the traditional cavity acoustic structure. To this end, we study the design principle of PM structure and its metal–water characteristics and analyze the sound absorption mechanism at the working frequency. In addition, the research shows that the material and geometric parameters of the structure have a significant impact on the SAP. By the optimization of structural material parameters, the average absorption coefficient at 500–10000 Hz can further increase to above 0.781. Finally, we also demonstrate that the structure still has good SAP under a wide range of oblique incidence angles. The research in this paper opens up bright perspectives for the design of underwater anechoic coatings for multifunctional applications.

Colorful Electrochromic Displays with High Visual Quality Based on Porous Metamaterials.

The introduction of metamaterials into electrochromic (EC) displays has recently inspired a great breakthrough in the EC field, as this can offer a variety of new attractive features, from a very wide gamut of colors to very fast switching times. However, such metamaterial-based EC displays still face significant constraints when developing from single electrodes to full devices, because other supportivecomponents in devices, such as counter electrodes and electrolytes, significantly affect light propagation and the subsequent perceived color quality in metamaterial-based EC devices. Herein, a new, cost-effective device design structured around a new type of porous metamaterial is reported to circumvent the critical problem in metamaterial-based EC displays. Owing to its unique design, the metamaterial-based EC device achieves good color quality with no drop in brightness or shift in color chromaticity when compared with a single electrode. Moreover, the porous-metamaterial-based EC device can exhibit non-iridescence and be viewed from a wide range of angles (5°-85°) and has fast switching response (2.4 and 2.5 s for coloration and bleaching, respectively), excellent cycling performance (at least 2000 cycles), and extremely low power consumption (4.0mWcm-2 ).

Improving the Angular Visibility of Photopolymer-Based Reflection Holograms for Sensing Applications.

Volume reflection hologram-based sensors are designed to visibly change colour in response to a target stressor or analyte. However, reflection holograms fabricated in thick photopolymer films are highly angularly selective, making these sensors challenging to view and interpret by non-experts. Here, the use of speckle holography to improve the visibility of reflection holograms is presented. A novel recording approach combining speckle recording techniques with Denisyuk reflection recording geometry is described. The recorded speckle reflection grating operates as a series of multiplexed reflection gratings with a range of spatial frequencies, capable of reflecting light at a wider range of angles. A comparative study of the angular and wavelength selectivity of speckle and standard reflection gratings was conducted. The FWHM of the angular selectivity curves of the speckle reflection gratings is doubled (4°) in comparison to standard 4500 lines/mm reflection gratings (2°). The wavelength selectivity FWHM is also doubled from 4.2 to 8.6 nm. The comparative ability of the speckle and standard reflection gratings to act as colour-changing compressional pressure sensors in the 0.88-5.31 MPa range is described. Finally, we present a prototype reflection hologram viewer which enables the easy observation of angularly specific reflection holograms by non-experts.

Design of All‐Metal 3D Anisotropic Metamaterial for Ultrabroadband Terahertz Reflective Linear Polarization Conversion

Herein, a novel and simple design of all‐metal 3D anisotropic metamaterial (3DAMM) is proposed and investigated numerically, which can achieve a high‐efficient and wide‐angle ultrabroadband reflective linear–linear and dual‐band linear–circular polarization conversion in the terahertz (THz) region. The 3DAMM is composed of a periodic array of copper stand‐up split ring resonator (SRR) adhered on a copper film ground plane. Incident ultrabroadband linear polarization waves can be converted to its orthogonal counterpart after reflection due to the three neighboring plasmon resonances of the 3DAMM structure. The proposed design demonstrates a high conversion efficiency of over 90% within a relative bandwidth of 88.7% in the range of 0.62–1.61 THz, and its efficiency is validated for both transverse electric and transverse magnetic modes and a wide range of incident angles (0°–50°). This ultrabroadband and high‐efficient linear polarization conversion of the 3DAMM is attributed to multiple plasmon resonances within the operating frequency range. The surface current distributions on the unit cell show that the ultra‐broadband conversion behaviors result from the decomposed electric field components coupling with different resonance modes. Further simulation results suggest that the polarization conversion properties of the 3DAMM can be adjusted by changing the geometric parameters of the unit cell. The proposed 3DAMM‐based reflective linear polarization convertor can find potential applications in remote sensors, imaging systems, and reflector antennas at THz frequencies.

Strategically constructed high-reflectivity multiple-stack distributed Bragg reflectors for efficient GaN-based flip-chip mini-LEDs

Full-angle distributed Bragg reflectors (DBRs) consisting of numerous sub-DBRs with discrete central wavelengths have been developed to enhance performance of GaN-based flip-chip mini light-emitting diodes (FC mini-LEDs). However, relatively low reflectivity of full-angle DBRs at large angle incidence restricts further enhancement in performance of FC mini-LEDs. Here, we introduce a reflectivity optimization strategy for constructing high-reflectivity multiple-stack DBRs by rationally engineering the number of sub-DBRs and adjusting central wavelength distribution of sub-DBRs. Based on the reflectivity optimization strategy, we devise a Ti3O5/SiO2 quintuple-stack DBR which is composed of five sub-DBRs. Our quintuple-stack DBR maintains a high reflectivity (>97.5%) over a wide range of incident angles of light. Notably, compared with the full-angle DBR, our quintuple-stack DBR exhibits higher reflectivity at large angle incidence and thinner multilayer thickness. Furthermore, we demonstrate two types of GaN-based blue FC mini-LEDs with indium-tin oxide (ITO)/quintuple-stack DBR and ITO/full-angle DBR p-type ohmic contacts. Benefiting from superior reflection performance, blue FC mini-LED with ITO/quintuple-stack DBR achieves an enhancement of ∼5.8% in light output power at 10 mA, in comparison with blue FC mini-LED with ITO/full-angle DBR. Our work signifies an advancement towards high-reflectivity DBRs, which enables higher-performance FC mini-LEDs.

Performance Evaluation of Novel Concentrating Photovoltaic Thermal Solar Collector under Quasi-Dynamic Conditions

Concentrating Photovoltaic Thermal (CPVT) collectors are suitable for integration in limited roof space due to their higher solar conversion efficiency. Solar sunlight can be used more effectively by CPVT collectors in comparison to individual solar thermal collectors or PV modules. In this study, the experimental investigation of a novel CPVT collector called a PC (power collector) has been carried out in real outdoor conditions, and the test set-up has been designed based on ISO 9806:2013. A quasi-dynamic testing method has been used because of the advantages that this method can offer for collectors with a unique construction, such as the proposed collector, over the steady-state testing method. With a quasi-dynamic testing method, it is possible to characterize the collector within a wide range of incidence angles and a complex incidence angle modifier profile. The proposed novel collector has a gross area of 2.57 m2. A maximum power output per collector unit area of 1140 W is found at 0 °C reduced temperature (1000 W/m2 irradiance level), while at a higher reduced temperature (70 °C), it drops down to 510 W for the same irradiance level. The data have been fitted through a multiple linear regression method, and the obtained efficiency curve coefficients are 0.39, 0.192, 1.294, 0.023, 0.2, 0, −5929 and 0 for Kθd, b0, c1, c2, c3, c4, c5 and c6, respectively. The experimental characterization carried out on the collector proved that the output powers calculated by using the obtained parameters of the quasi-dynamic testing method are in good agreement with experimental points.

Absorption properties and mechanisms of metallic moth-eye structures

The antireflection and absorption properties of non-metallic moth-eye structures have been intensively studied, however the research on those of metallic moth-eye structures, especially their absorption mechanisms, is far from enough. In this paper, the absorption properties and mechanisms of a metallic Au moth-eye structure are studied in detail. The results show that broadband perfect absorption covering the entire visible to the near infrared range with polarization independence and in a wide incident angle range can be easily realized using a single-layer single-material Au moth-eye structure. As for the absorption mechanism, in the short wavelength range of 300 nm–550 nm, due to the high loss of the Au material, the antireflection effect plays a main role. While in the long wavelength range of 550 nm–1000 nm, the widely accepted absorption mechanisms (the antireflection effect as well as the cascaded multiple plasmonic resonances, and even the combination of them) cannot completely account for the broadband perfect absorption. We found that the adiabatic nanofocusing effect of the plasmonic resonances enabled by the ultra-sharp air grooves plays a key role in the absorption. It is the nanofocusing effect that effectively increases the absorption to nearly 100% in a broad wavelength band. These findings provide a deeper insight into the absorption mechanisms of metallic moth-eye structures and offer an effective guide to explore demanded excellent absorption performance.

Time-reversal even charge hall effect from twisted interface coupling

Under time-reversal symmetry, a linear charge Hall response is usually deemed to be forbidden by the Onsager relation. In this work, we discover a scenario for realizing a time-reversal even linear charge Hall effect in a non-isolated two-dimensional crystal allowed by time reversal symmetry. The restriction by Onsager relation is lifted by interfacial coupling with an adjacent layer, where the overall chiral symmetry requirement is fulfilled by a twisted stacking. We reveal the underlying band geometric quantity as the momentum-space vorticity of layer current. The effect is demonstrated in twisted bilayer graphene and twisted homobilayer transition metal dichalcogenides with a wide range of twist angles, which exhibit giant Hall ratios under experimentally practical conditions, with gate voltage controlled on-off switch. This work reveals intriguing Hall physics in chiral structures, and opens up a research direction of layertronics that exploits the quantum nature of layer degree of freedom to uncover exciting effects.

Light nurtures plants: The picosecond laser-induced lithops-like microstructures on titanium alloy surface with broad-band ultra-low reflectivity

Micro-nanostructures on metal surfaces have received significant attention due to their widespread applications. Although ultrafast laser processing was a feasible method to fabricate micro-nanostructures, some issues involving the formation and application of novel micro-nanostructures still exist. Here, we proposed the unique lithops-like microstructures on titanium alloy (Ti-6Al-4V) by ultraviolet picosecond (UV-ps) laser treatment. These structures were either separate tomb-like bumps or bump clusters consisting of several interconnected bumps, which were similar in appearance to lithops. Due to nanoparticle deposition, these bumps were also covered with nanostructures. Titanium alloy was oxidized to form Ti2O3 and TiO2 during treatment. The formation of lithops-like microstructures involved the laser-induced physical/chemical processes of melting, flowing, vaporization, oxidation, solidification, and deposition of material. As laser energy increased, the smooth surface gradually evolved into lithops-like microstructures under the synergistic effects of electromagnetic interference, the Marangoni effect, preferential valley ablation, and thermal effects. By combining geometric light trapping within microstructures with surface plasmon resonance (SPR) absorption within nanostructures, these structures exhibited ultra-low reflectivity (0.02%∼2.31%) in the ultraviolet–visible-near-infrared band (200 ∼ 2500 nm). They also showed ultra-low reflectance (<3%) over a wide range of incidence angles (5°∼70°). The anti-reflection properties of lithops-like microstructures were superior to those of some typical micro-nanostructures.

Leading edge erosion detection for a wind turbine blade using far-field aerodynamic noise

In this paper, the feasibility of using far-field acoustic measurements as a non-contact monitoring technique for wind turbine blade leading edge erosion is assessed. For this purpose, a DU96 W180 airfoil with several eroded leading edge configurations of different severities is experimentally investigated. The eroded leading edges are designed with pits, gouges and coating delamination scaled from a real eroded blade. To assess the feasibility of the technique in quasi-realistic configurations, experiments are carried out under clean and turbulent inflow conditions. Acoustic measurements are performed with a phased microphone array. In the absence of inflow turbulence, because of the low Reynolds number at which the experiments are carried out, the case with minor erosion severity shows similar far-field noise spectra as the clean leading-edge cases, i.e., the presence of tonal peaks caused by laminar boundary layer instability noise through a self-sustained feedback loop but with higher tonal amplitudes. Increasing the damage level (considered as moderate erosion), the spectra of the noise scattered from the suction side show that the tonal peaks shift to higher frequencies and have lower amplitudes, thus suggesting that the damage alters the flow features responsible for the acoustic feedback loop; whereas, the spectra from the pressure side show a broadband noise distribution. For heavy erosion, the far-field noise spectra show broadband features from both airfoil sides, thus suggesting that the damage has fully forced the transition to turbulent flow; in which case, an increase in the low-frequency content is observed. Conversely, in the presence of turbulent inflow, when comparing the noise scattered at the trailing edge, no difference is found. However, leading edge impingement noise decreases at medium–high frequency compared with the baseline case at a chord-length-based Strouhal number StC∼10. The experimental results also suggest that the delamination feature is the one which is the most easily detectable and the approach is valid for a wide range of angles of attack and inflow velocity.

Direct pre-stack inversion of elastic modulus using the exact Zoeppritz equation and the application in shale reservoir

Young’s modulus and Poisson’s ratio are important for reservoir characterization and rock brittleness prediction in unconventional resource exploration and development. Conventional methods can estimate Young’s modulus and Poisson’s ratio by indirect calculations and direct inversion using approximate expressions, which have cumulative errors and limited accuracy of the estimated results, especially at large incident angles. In this study, we derived a new form of the Zoeppritz equation and P-to-P wave reflection coefficient in terms of density and Young’s modulus, Poisson’s ratio. It has the same accuracy as the original Zoeppritz equation over a wide range of incident angles. A robust non-linear inversion method based on the iteratively regularized Levenberg Marquardt (IRLM) algorithm, is used to invert all three parameters based on the new equation directly and simultaneously. Synthetic data and field data are used to test and verify the proposed direct inversion method, ensuring the feasibility and effectiveness of the proposed method and the high accuracy and stability of the inversion results. This study has a great potential and valuable guidance for “sweet spot” evaluation and subsequent horizontal well deployment and hydraulic fracturing.

A 3D dislocated re-entrant structure with compression-twist coupling effect

Compression-twist metamaterials are artificially designed materials which can realize transformation from axial compressing to twist loading. In this study, a new dislocation design of the 2D re-entrant hexagonal structure is proposed with the compression-shear coupling effect. Through orthogonal assembling, its 3D dislocation re-entrant structure is successfully obtained that exhibits compression-twist coupling effect. A theoretical model is built to clarify the deformation mechanisms of the novel structures, and relevant analyses indicate that the compression-twist coupling effects can be tuned by tailoring structure’s geometric parameters with a wide range of adjustable twist angles. Besides, the experiments and numerical simulations are also performed to verify our developed theoretical model, and finally more feasible structure designs are extended with compression-twist coupling effect based on the re-entrant structure. The novel 3D material structure with excellent compression-twist coupling effects provides new ideas for the design of compression-twist metamaterials.

Comparison between different solar cells based on perovskite types

Perovskite solar cells (PSCs) are getting popular as promising photovoltaic technology due to their high efficiency and economical manufacturing costs. PSCs' effectiveness and stability have continuously improved in recent years, and research into minimizing lead leakage and creating environmentally acceptable lead-free perovskites is advancing the commercialization of PSCs step by step. The goal of this paper is to design a solar cell model based on getting higher light transmission and lower light reflection. Three-layer solar cell structure containing perovskite, titanium dioxide, and metal Nano layer sandwich between a silicon substrate and glass cover. The Maple 17 software is used to create the numerical results for the Transfer matrix, which determines the transmission and reflection of the incident light for various physical parameters of the structure. The results showed that the cell with aluminum cell has an excellent transmittance for a wide range of incident angles, perovskite thickness, and effective layer thickness. The short circuit current density reaches the most significant value at (𝛼 = 0), and it has zero value for parallel incidents. The cell of CH3NH3PbI3perovskite type and the aluminum metal nanolayer has the highest current density and a non-zero value for a wide range of incident angles.

A simulator for charged particle guns and lenses

An algorithm is presented that extends the application of ray optics to charged particle guns, where particles are emitted with a wide range of angles and relative energies. The extension is made possible by replacing the ray tangent as a coordinate with the directional sine, which remains finite for all take-off angles, and if necessary, by simulating the ray optics for multiple segments of the energy distribution. Consequently, an electron gun comprising a cathode, an extractor, and an anode, for example, may be characterized by its focal length, the location of its image plane, the magnification of the emission spot at this plane, and the primary and higher-order aberrations of the module, which reshape this spot. This description is realized by modeling the particle trajectories as a power series in their initial conditions and by using standard algebraic techniques, namely, the binomial and Taylor expansions, to transform the relativistic Newton’s equation, which describes the evolution of the trajectories in the electromagnetic fields of the gun, into a differential equation for the evolution of the series coefficients. In addition to providing the optical parameters, the series coefficients produce an algebraic map between the particle coordinates along the gun axis and their initial values at the plane of emission, thereby circumventing the need to launch a multitude of trajectories in a particle simulator to model the source that the gun presents to the optical elements downstream. The algorithm may be enhanced in the future by incorporating some effects of space charge from the emission current.

Adaptive overcurrent relay (AOCR) based on Fano Factors of current signals

AbstractA Fano Factor‐based adaptive overcurrent protection scheme, that automatically adjusts the protection settings in response to the prevailing conditions of the power system, is presented. Both phase and ground overcurrent relays are based on the same mathematical algorithm to calculate the operating time using Fano Factors (FFs) estimated for phase and ground current signals, respectively. Effectiveness of the proposed adaptive overcurrent method is validated for various fault types under a plethora of loading current levels, besides a wide range of fault inception angles and fault resistance. Simulation results confirm that the proposed algorithm can detect series and shunt faults, differentiate between grounding and phase faults, and adapt the relay operating time settings using the FF for all conditions examined. The relay algorithm speed and sensitivity are controllable using both the FF setting values and moving data window size. Moreover, it is characterized by being simple, reliable, accurate, and can be implemented practically as a base of digital protective relay for use in substation automation systems and phasor measurement units.

Multi-band and wide-angle nonreciprocal thermal radiation

Violating Kirchhoff's radiation law through magneto-optical materials or spatiotemporal (Floquet) metamaterials can open a new door for engineering thermal radiation by breaking the widely-accepted equal constraint of spectral absorptivity (α) and emissivity (ϵ). Most existing work only reports the unequal α and ϵ spectra in one or two bands and within limited angles. This significantly limits the practical applications like the nonreciprocal thermophotovoltaics. In this work, we present a general machine-learning-kernel-based algorithm framework, based on which we achieve four-band nonreciprocal thermal radiation via the magneto-optical (MO) materials. The realization of multi-band nonreciprocity is mainly attributed to the coupling effect of magneto-optical effect and the excitation of cavity modes with different orders, which can be confirmed by investigating the magnetic field distribution. In addition, it is found that dual-band/multi-band strong nonreciprocal thermal radiation can be realized in a wide range of incident angles (15°-85°). The number of bands and range of angle can be further enhanced by modulating the number of layers, structures, materials, and applied magnetic field. The present work offers a general design roadmap for nonreciprocal thermal radiation, and can be extended for designing metamaterials beyond thermal metamaterials.