Reflector Design Research Articles

Design of an intermediate Bragg reflector within triple-junction solar cells for spectrum splitting applications

We investigate the use of distributed Bragg reflectors (DBRs) within triple-junction solar cells (TJSC) for spectrum splitting photovoltaics. An optical model of a lattice-matched (LM) GaInP/GaInAs/Ge TJSC with intermediate DBR is developed, in good agreement with measured reflectance. By modifying the DBR layer number, composition and thickness to broaden the reflectance band, we show that a DBR can provide suitable 900–1050 nm reflectance for spectrum splitting from the LM TJSC to a Si cell, resulting in a more efficient 4-junction receiver. For better practicality and cost effectiveness, we propose that the buffer layers in metamorphic (MM) TJSCs could additionally function as a DBR for spectrum splitting applications. We propose several DBR designs to achieve a suitable spectrum-splitting reflectance band from MM TJSCs to a Si cell, again resulting in a more efficient 4-junction receiver. Finally, we show that our intermediate DBR approach to spectrum splitting has the advantage of a greatly reduced angle-of-incidence dependence compared to a discrete dielectric filter.

Genetically optimized all-dielectric metasurfaces for visible perfect broadband reflectors

A design approach for flat metasurface devices is proposed and applied to design the broadband reflectors in the visible regime. Firstly, the geometry parameters of metasurfaces which comprise a monolayer amorphous titanium dioxide nanorod array in the air are optimized to achieve a broadband perfect reflector whose bandwidth is about 90 nm. Further, for practical application, the geometry parameters of a metasurface which is composed with a monolayer gallium phosphide nanoparticle (rod or cuboid) array on a glass substrate are optimized to achieve excellent reflection performance. Such all-dielectric metasurface near perfect reflectors can be used to protect surfaces against high power irradiation and create low loss mirrors in laser cavities. The design approach presented in this work is based on utilizing genetic optimization algorithm in order to determine the scatterers dimensions and lattice period within a unit-cell of the metasurface. The approach exhibits great superiority on the design of perfect reflectors and can be extended to design more complex flat components such as metalenses, holograms and deflectors. This approach is expected to provide a guideline for designing multifunctional photonic metamaterial devices.

Analysis and numerical simulation of a novel optical microcavity with the roof structure

We report a novel optical microcavity based on the Fabry–Perot (F–P) microcavity, which is a roof structure with two top reflectors that are symmetrical structure and proper inclined angle. The special design of the top reflectors increases the one-period-length for the mode light ray inside the microcavity and confines light in a smaller area effectively. The resonance principle of the microcavity is analyzed, and simple analytical expression of the resonant wavelength and resonant condition of the microcavity are given. The properties are numerically studied by the finite element method. Simulation results of the microcavity with small incline angle are almost consistent with theoretical analysis. Compared with the F–P microcavity, the result show that the proposed microcavity has outstanding advantages such as high quality factor, narrow spectrum, and small effective mode volume, which has a great potential in photonic devices and optoelectronic devices.

Development of LED-based illumination system for high-speed digital image correlation

The present work describes the design and development of a dedicated illumination system for application to high-speed digital image correlation. This type of application requires image acquisition to be performed with very short shutter times. This means that there is less time to integrate the incoming light and, as such, it is necessary to have significant light flux to acquire quality images. As such, illumination is usually the major concern in such high-speed imaging applications.The developed system uses a strobing high-power LED light source to tackle this issue, and illuminate the specimen with a large light flux during a very short period. This reduces the amount of heat that the specimen receives from the lighting source and has the advantage of enabling the use of cameras that would otherwise be unable to use such short shutter times effectively.In this paper, the whole design of the device is described. From the control electronics to the mechanical design, including the optical design of an appropriate reflector.

Calculation and experimental assessment of the strength and limit states of composite structures for spacecraft

Modern polymer composite materials with high specific characteristics of strength and stiffness allow creating strong, durable and geometrically stable space structures. To expand the scope of application of composite materials and increase the competitiveness of space structures, it is necessary to further improve design methods with the widespread use of multiscale computational modeling of deformation and fracture processes. The paper presents the results of analysis on the strength and dimensional stability of structures made of polymer composites. A metal-composite high-pressure tank for electric propulsion systems and the design of precision reflectors for space- and ground-based antennas are considered. The methods and results of experimental and computational studies on the stress-strain and ultimate states of structures are described. The methods and means of non-destructive testing, the results of the analysis on the stress-strain state and full-scale tests of the tank structure are described. Generalized estimates of the load-carrying capacity of reflector structures under given operating conditions are given.

Static and modal analysis of the construction of the precision large-sized antenna reflector from polymer composite materials

The article presents a design of a precision large-size antenna reflector that made of polymer composite materials (PCM) based on carbon fibers. Such reflectors are used for operation in high frequency ranges, since they have a low coefficient of linear thermal expansion and a high modulus of elasticity. Therefore, the main task of this work is to design the geometric accuracy of the reflector working surface from composite materials with a diameter of more than 10 meters and a frequency range of 42.5-45.5 GHz.The developed model of the reflector includes a power frame, segments of the reflecting surface and a hub. The power frame of the reflector consists of flat trusses supplemented with rods, so that during assembly a spatial construction with axial symmetry is formed. Segments are three-layer casings of polymer composite materials with filler.The proposed model of the reflector was analyzed using the finite element method with boundary conditions: a wind load of 20 m/s in the opening of the reflector; impact of gravity on the reflector, oriented to the zenith. The wind load was modeled as a uniformly distributed pressure applied to the segments. The obtained mean square deviation (SDE) of the geometry and natural oscillation frequency of a reflector made from polymer composite materials based on carbon fibers is sufficient for operation of the satellite earth station in high radio-frequency ranges Ka, Q and V.

Special aspects of modulation RCS measurement in Ka-band

Radar reflectors are used as standards for radioelectronic devices calibration, as navigation beacons for air and naval traffic control and for radar visibility increase. Controlled (parametric) reflectors change reflected signal characteristics. This leads to appearance of easily detectable additional frequency components on modulation frequency. Ka-band parametric reflector design, consisting of horn reflector and phase switch 0°/180° board, is suggested. Technique of parametric reflector modulation RCS measurement, using complex envelope of reflected signal in every phase switch state, is suggested. Measuring bench description is given. Comparative analysis of theoretical calculations and experimental results is carried out. Accuracy of modulation RCS measurement according to the said technique is obtained experimentally. Measurements accuracy constraints are detected.

Realization of the high-performance THz GaAs homojunction detector below the frequency of Reststrahlen band

High-performance terahertz (THz) detectors are in great need in the applications of security, medicine, as well as in astronomy. A high responsivity p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) detector was demonstrated for a specific frequency (5 THz) below the frequency of the Reststrahlen band. The experimental results indicate that the optimized detector shows significant enhancement of the response below the Reststrahlen band in contrast to the conventional detectors. With the bottom gold layer serving as a perfect reflector, nearly 50% increment of responsivity and quantum efficiency was obtained further due to the cavity effect. Though very simple, such reflector design shows a satisfactory effect and is easy to be realized in practical applications. The resultant peak responsivity of the detector with a bottom reflector could be as high as 6.8 A/W at 1 V bias. The noise equivalent power is 2.3×10−12W/Hz1/2. Due to the absorption ability to normal incident light and high responsivity, the p-GaAs HIWIP detector is promising for the focal plane array and large-scale pixelless imaging applications.

Design of a Reflector for LED Light Sources with Asymmetric Light Distribution

Design of a Reflector for LED Light Sources with Asymmetric Light Distribution

Integrated form finding method for mesh reflector antennas considering the flexible truss and hinges

Form finding plays an essential role in the design of deployable mesh reflectors (DMRs), and it concerns their electromagnetic performance. However, classic form finding methods ignore the compatible deformation between cable networks and supporting structures. Even though the finite element method can be adopted to compensate the deviations caused by the compatible deformation, many iterations have to be involved and the effects are usually not satisfied. In this paper, an integrated form finding method considering the flexibility of the truss and hinges is proposed. Firstly, the rod of the truss is modeled by Euler–Bernoulli beam and the hinge is described by the flexible joint with six degree of freedoms (DOFs) to form the integrated element. These elements are assembled according to the topology of the truss to obtain the equilibrium equation of the truss. Secondly, the boundary conditions are applied to condense the DOFs of beam nodes, so that the rods, hinges and cable networks can be combined by adopting the corresponding consistency conditions, and then the equilibrium equation of the coupled model is established. Finally, the integrated form finding method is formed by incorporating the gradient based optimization method into the coupled model. This method is further applied to the form finding of the ring truss DMR, and the corresponding case studies are provided. The stiffness coefficients of three kinds of hinges in six DOFs are measured and utilized. The obtained design parameters are imported into ABAQUS to calculate the actually formed reflective surface, so as to verify the result. The form finding results are also compared with those in previous literature. The proposed method is proved to be effective in the form finding of DMRs, and the deviations of the form and force distribution of reflective surfaces caused by the compatible deformation are totally avoided.

Optical features of linear Fresnel collectors with different secondary reflector technologies

This paper is devoted to the analysis of different secondary reflector designs for linear Fresnel collectors. A number of authors have proposed alternative shapes of secondary reflectors in order to enhance the efficiency and the flux intensity at the absorber tube. In this work the primary mirrors layout has been maintained constant for all designs. Thus, only secondary concentrators that do not require a change in the primary mirrors field have been studied. In order to carry out the study a validated Monte Carlo ray trace code has been used, where three optical properties are considered: annual optical efficiency, mean flux intensity and circumferential flux intensity homogeneity. The maximum efficiency reached by each technology, for given optical flux specifications, is obtained. Finally, the optical performance of linear Fresnel collectors with secondary reflector is compared with that of state-of-the-art parabolic trough collectors. It is concluded that the efficiency of Fresnel collectors is around 23% than that of parabolic troughs, although with mean flux intensities around 46% higher and circumferential flux intensities notably more homogeneous (top to bottom flux intensity ratios five times higher).

Heuristic driven inverse reflector design

This paper presents a global optimization algorithm specifically tailored for inverse reflector design problems. In such problems, the goal is to obtain a reflector shape that produces a light distribution as close as possible to a user-provided one. The optimization is an iterative process where each step evaluates the difference between the current reflector illumination and the desired one. We propose a tree-based stochastic method that drives the optimization process, using some heuristic rules, to reach a minimum below a user-provided threshold that satisfies the requirements. When we are close to the solution, we resort to the Hooke and Jeeves method, to reach the minimum faster. Extending our previous work Mas et al. (2010), we show that our method reaches a solution in fewer steps than most other classic optimization methods, and also avoids many local minima. The method has been tested on a real case study based on European road lighting safety regulations.

A study on the design of ensemble reflector in a concert hall

A study on the design of ensemble reflector in a concert hall

Optimized design of a Linear Fresnel reflector for solar process heat applications

Abstract Heat demands in industrial processes represent a high rate of the thermal energy consumption that could be directly delivered by a concentrated solar thermal technology. Linear Fresnel reflectors are a promising example of this kind of technology. This paper presents an innovative and optically optimized design of linear Fresnel collector for solar process heat applications. An in-house ray trace code was employed to evaluate different geometrical options of the solar collector over conventional concepts, aiming to maximize its optical performance and tackle the inherent weakness of this concentrating solar technology when it is compared to other type of concentrators. Geometrical modifications accomplished in the optimization process include the tilt of the concentrator and receiver, the receiver displacement and the concentrator rotation along with the optimization of other relevant parameters. As a result, a significant upgrade of the monthly power on the receiver was achieved, with an average enhancement ranging from 2% to 61%, compared to a standard linear Fresnel collector without the proposed modifications. This result provides a more homogenous thermal power profile delivered along the year, which is an important requirement to place the technology in the spotlight.

Acoustic anomalous reflectors based on diffraction grating engineering

We present an efficient method for the design of anomalous reflectors for acoustic waves. The approach is based on the fact that the anomalous reflector is actually a diffraction grating in which the amplitude of all the modes is negligible except the one traveling towards the desired direction. A supercell of drilled holes in an acoustically rigid surface is proposed as the basic unit cell, and analytical expressions for an inverse diffraction problem are derived. It is found that the the number of holes required for the realization of an anomalous reflector is equal to the number of diffracted modes to cancel, and this number depends on the relationship between the incident and reflected angles. Then, the "retrorreflection" effect is obtained by just one hole per unit cell, also with only two holes it is possible to change the reflection angle of a normally incident wave and five holes are enough to design a general retroreflector changing the incident and reflected angles at oblique incidence. Finally, the concept of Snell's law violation is extended not only to the incident and reflected angles, but also to the plane in which it happens, and a device based on a single hole in a square lattice is designed in such a way that the reflection plane is rotated $\pi/4$ with respect to the plane of incidence. Numerical simulations are performed to support the predictions of the analytical expressions, and an excellent agreement is found.

PHASE-ISOTROPIC CORNER REFLECTOR FOR FIBER-OPTIC CONVERTER

The article is devoted to the design of optical device ‒ phase isotropic corner reflector, which may find application as a mirror in the fiber-optic converter. The use of phase-isotropic elements will reduce the effect of a light signal phase shift on reflection from the mirror mounted on the end of the fiber sensor. The work analyzes the existing phase devices and suggests a device using real film-forming materials, the angle of incidence of radiation, and the materials of the prism.

Experimental studies on the mechanical properties of a woven composite material for space antenna reflector

In this paper the results of mechanical tests of a biaxial woven composite are presented. This material was used for a new design of deployable precision space antenna reflector of large aperture. The experiments included standard tensile tests at low, normal and high temperatures, compression and shear tests. An additional nonstandard bending test was performed to determine the smallest radius of curvature that a specimen could withstand without fracture. The experiments showed the perspectives for the use of the studied composite in the reflector structure. The determined mechanical properties can be used for numerical modeling of the reflector behavior.

Rapid design and modelling of wideband sinuous antenna reflector feeds through blended rational interpolation

AbstractThis paper describes the design of sinuous antenna reflector feeds using blended rational interpolation. The blended rational interpolation method is developed to interpolate a sparse set of high‐fidelity (HF) data while following the trends of a denser set of low‐fidelity (LF) data. The HF data are obtained by full‐wave computational electromagnetics simulations of the input impedance of a pyramidal sinuous antenna above a ground plane, while the LF data are obtained, at a significantly reduced computational cost, through simulations of a truncated version of the same antenna. Comparisons with other interpolation schemes, both for HF as well as for multifidelity data sets, are presented. It is shown that the blended rational interpolation scheme presented herein yields improved accuracy in most cases. A design example is also presented where a global model of the maximum input reflection coefficient over frequency is built over the design space and thus used to identify the region of acceptable performance. Comparisons with a validation set of HF data resulted in similar results, with the blended rational interpolation model requiring significantly shorter computer simulation time.

Hydrogen‐Bonded Liquid Crystals in Confined Spaces—Toward Photonic Hybrid Materials

AbstractA series of hybrid materials based on chiral nematic mesoporous organosilica (CNMO) films infiltrated with liquid crystalline hydrogen‐bonded assemblies is prepared and characterized with respect to the mutual manipulation of the photonic properties of the host and the liquid‐crystalline behavior of the guest. Detailed differential scanning calorimetry studies reveal the impact of confinement on the mesomorphic behavior of the liquid crystalline assemblies in the pores of the CNMO films. The photonic properties of the chiral nematic mesoporous host can be controlled by changing the temperature or irradiating the films with UV light. These stimuli‐induced phase transitions are accompanied by changes in the orientational order of the mesogens as revealed by 19F NMR spectroscopy. The combination of confinement and changes in the molecular orientation in a unique hybrid material based on hydrogen‐bonded liquid crystals and a porous host with a chiral nematic mesostructure is an interesting concept for the design of optical sensors, reflectors, or filters.

Doubly Curved Reflector Design for Hybrid Array Fed Reflector Antennas

This communication discusses a generalized analytical formulation for the design of doubly curved reflectors fed by line sources of any shape, including straight, circular, and even elliptical profiles. The proposed hybrid array fed reflector antenna configuration produces pencil beams from line sources which may be either passive multiple beam line sources or reconfigurable linear phased arrays. The proposed formulation, based on parabolic strips derived from geometrical optics considerations, reduces significantly phase aberrations which were responsible for beam squint and sidelobes imbalance with the previous simpler formulation. Numerical results are presented at Ka-band. This doubly curved reflector design is considered of interest in combination with linear phased arrays to introduce some level of coverage reconfigurability (one-axis beam steering) for on-board broadband satellite communication payloads with a much simpler focal array design when compared to existing planar phased array fed reflector antennas.