Composite Reflector Research Articles

Development of Deployable Reflector Antenna for the SAR-Satellite: Part 1. Design and Analysis of the Main Reflector Using Honeycomb Sandwich Composite Structure

The deployable reflector antenna based on the synthetic aperture radar is a satellite component that consists of a unit structure in the form of a folded reflector. During the launch process, this satellite antenna is in the stowed condition to improve storage efficiency. It is then deployed to perform the space mission in the on-orbit condition. Due to these structural characteristics of the deployable reflector antenna, the reflector is possible to be loaded in the limited volume of the launch vehicle with the reduced size. Additionally, because the deployable reflector antenna is made by the lightweight material of the carbon fiber reinforced polymer and honeycomb core, it can reduce the launching cost and improve the revisit interval. In this paper, the conceptual design of the main reflector of the deployable reflector antenna was conducted. The main reflector was designed as the honeycomb sandwich composite structure. To design the main reflector, the stacking sequence of the composite material and honeycomb core was investigated to maximize the structural stiffness and minimize the antenna’s mass. Subsequently, finite element analyses including modal, quasi-static, structural–thermal coupling, and transient response were performed to numerically evaluate the structural performance of the lightweight composite reflector antenna.

Determination of Whole Field Strain in Composite Reflector Using Photogrammetry

Conventional strain measurement techniques cannot be used to obtain the strains in composite reflectors under thermal environment. Though photogrammetry can be used to measure the deformations it cannot provide information on strains. In this work a methodology is developed to determine the strains from the displacements obtained from photogrammetry coordinate measurement. The strains are determined by applying equilibrium conditions and not from the gradient of the displacements. The results are verified using simulated data as well as experiment. It is demonstrated for a composite reflector of a typical spacecraft when subjected to thermal load. The methodology developed in this work helps in obtaining the strain distribution without using expensive digital image correlation equipment. This methodology can be used on wide variety of applications like inflatable structures, flexible structures etc., where strain gauge measurements are not possible to be carried out.

Evolution of process-induced strain/stress field in plain woven composite antenna reflector by fusing multiscale numerical model and experimental data

This paper investigates the evolution of the process-induced strain/stress field in plain woven composite antenna reflectors by fusing the numerical simulation and the experimental data. In the numerical simulation, a new multiscale curing process model of plain woven composite reflectors is proposed for process-induced strain/stress prediction. Specifically, representative volume elements at three scales are established and solved to capture the effective properties of plain woven composites. Further, a novel interface layer with cure-dependent parameters is used to emulate the tool-part interaction. In the experiment, the fiber Bragg grating sensor network is embedded into the composite reflector to measure the process-induced strains. Some of the measurements are fused into the curing process model by the optimization-based fusion method. The fused model was used to predict the full-field strain and stress, and the results indicate that areas with larger curvatures experience greater strain and stress due to the interaction between the tool and the part.

Wavefront Control Strategies for Large Active Thin Shell Primaries with Unimorph Actuators

This paper presents various aspects of the wavefront control strategies for an ultra-lightweight composite reflector made of polymers for the large primary of a space telescope, and the shape control is made by a set of patterned unimorph strain actuators attached to the reflector. It starts with an analytical investigation of the mechanical behaviors of a strain-actuated curved shell, resulting in the accurate prediction of typical features, such as the damped wave deformation at the transition between electrodes and the limited morphing amplitude of a “print-through” actuation, which indicates that the curvature-induced rigidity deteriorates the performances of the forming accuracy of the active reflector and the morphing stroke of the actuators. The morphing capabilities are evaluated with both petal-like segmented and monolithic configured reflectors by numerical tests on forming target shapes of Zernike modes with various patternings of electrodes, and the structural dynamics are examined. Finally, a compound control strategy is proposed, which uses a deformable relay mirror to compensate for the residual surface error corrected partially by the active unimorph primary mirror, showing a great relaxation of the shape error budget of the thin-shell primary, especially for on-axis observation.

Improving radiation performance of the cylindrical dielectric reflector sandwiched by thin resistive layer illuminated by a complex line source

We studied two-dimensional (2-D) thin dielectric parabolic reflector, sandwiched by thin resistive layer from both sides. It is illuminated by an E-polarized electromagnetic plane wave from front side. It is expected to observe the radiation performance of such a composite reflector depending on the electrical and geometrical parameters. We applied two-sided generalized boundary conditions which are modified for a thin multilayer structure. The electromagnetic boundary value problem is formulated and it finally produced a set of two coupled singular integral equations (SIEs). They are handled with the analytical regularization method based on the Riemann-Hilbert Problem solution. The final numerical results are in the Fredholm second-kind matrix equation form and any desired accuracy can possibly be obtained. Also the solution procedure guarantees the convergence. It is observed that the proper selection of the electrical resistivity of the thin resistive layer produces wider bandwidth in the aperture efficiency and the directivity variation approaches to the perfect electric conductor (PEC) reflector case for higher dielectric constants. This selection can increase the allowable frequency band in the applications by coating dielectric layer from both sides. We demonstrate these statements in the numerical results section in the microwave frequency range.

Evaluation of the E‐polarization focusing ability in Thz range for microsize cylindrical parabolic reflector made of thin dielectric layer sandwiched between graphene

We consider two-dimensional (2-D) thin dielectric parabolic reflector, covered with graphene from both sides, illuminated symmetrically by an E-polarized electromagnetic plane wave. Our aim is to estimate the focussing ability of such a composite reflector depending on the graphene parameters. We use a version of the two-side generalized boundary condition, modified for a thin multilayer case. The scattering is formulated as an electromagnetic boundary-value problem; it is cast to a set of two coupled singular integral equations that are further subjected to analytical regularisation based on the known Riemann–Hilbert problem solution. Thanks to this procedure, the numerical results are computed from a Fredholm second-kind matrix equation that guarantees convergence and provides easily controlled accuracy. In the lower part of the THz range, high values of the focusing ability are observed even for a thin reflector; they are greater than for a purely dielectric reflector and a free standing graphene reflector. On the other hand, a regime of almost full transparency, intrinsic for the dielectric layer, can spoil focusing ability. Novel aspect is that the location in frequency of this effect can be controlled, in wide range, by changing the chemical potential of graphene.

ЭКСПЕРИМЕНТЫ ПО ИССЛЕДОВАНИЮ ПРОХОЖДЕНИЯ НЕЙТРОНОВ ЧЕРЕЗ СЛОИ ГИДРИДА ЛИТИЯ-7 В УРАНОВОЙ РАЗМНОЖАЮЩЕЙ СИСТЕМЕ С ПРИМЕНЕНИЕМ МЕТОДА НЕЙТРОННО-АКТИВАЦИОННОГО АНАЛИЗА

The paper provides the precision experimental results on fission spectrum neutrons transmission through lithium hydride layers-7 with neutron activation analysis. The experiments were performed in Zababakhin All-Russia Research Institute of Technical Physics” on a critical assembly stand FKBN 2. A cylindrical multiplying system (MS) made of high enriched uranium was used as a source of fission spectrum neutrons. Activation integrals of neutron activation detectors (NADs) located at different points of the composite lithium-7 hydride reflector face-mounted on the cylindrical uranium MS were determined in the experiments. NADs based on nickel, indium, titanium, aluminum and copper were used. NADs of different types were exposed to radiation at power ~25-30 W during 1-1,5 hours. Nickel NAD was used as a monitor. Activation integrals absolute measurement error was determined by a certified technique and ranged from ~4 to ~8 % (2σ). Relative measurement error was determined by statistical accuracy, instrument peaks software processing correctness and was found not to exceed 5,4 % (2σ). Using the data obtained, spectral indices (the ratio of the normalized values of the activation integrals of various detectors types to the one of nickel detector), which provide information on the neutron spectrum were determined.

복합 소재 곡면 반사판 안테나 패널의 반사 특성 분석을 위한 측정법 정확도 개선

Conventionally, to measure the electrical characteristics of a reflector antenna panel made of a composite material, a flat sample was separately manufactured with the same material as the panel or a part of the antenna panel was cut to make it flat. In this study, it was confirmed that the electrical characteristics of the curved sample can be accurately analyzed without deformation by performing measurements using an electromagnetic interference shielding foam adapter and a vertical-type measurement device. It is possible to efficiently analyze the electrical characteristics of the composite reflector panel by manufacturing a measurement device for curved panels to overcome the size limit of the vertical-type measurement device and enable measurement by angle at an arbitrary position.

Measuring Spectral Indices in a Critical Cylindrical Uranium System with a Lithium Hydride End Reflector

The results of precision experiments concerning neutron passage through the layers of lithium-7 hydride are reported. Activation integrals for neutron activation detectors positioned at various points of the composite lithium-7 hydride reflector mounted at the end of the uranium breeder system have been determined. Spectral indices have been calculated on the basis of the data obtained.

Comprehensive design and simulation of a composite reflector for mode control and thermal management of a high-power VCSEL

We propose a composite top reflector composed of a distributed Bragg reflector (DBR) and a subwavelength high-contrast grating (HCG) for a high-power 808-nm vertical-cavity surface-emitting laser (VCSEL). The DBR and HCG in the reflector are connected by an indium tin oxide (ITO) surrounding layer, which makes it possible for the reflector to improve current injection uniformity and reduce heat generation while providing high reflectivity. The angle-dependent reflectivity of the composite reflector is optimized to suppress the high-order transverse modes of VCSEL while ensuring sufficient fundamental mode feedback. The number of top DBR periods and the thickness of the ITO surrounding layer are optimized to reduce the loss and provide high out-coupling efficiency. The double resonator coupled by top DBR is designed to provide optimal resonant wavelength stability, longitudinal optical confinement factor, and thermoelectric characteristics. Optical simulation results demonstrate that the well-designed configuration can provide a highest fundamental mode reflectivity of 99.7%, an out-coupling efficiency of 65%, a wavelength stability rate of 0.011 with the thickness of the ITO layer, and a confinement factor of 0.05. The transverse modes with order greater than 2 are effectively suppressed. The result of the thermoelectric model shows that the composite reflector-based VCSEL has low operating temperature and uniform current injection; thermal resistance of 0.87 K/mW is realized. In this context, devices with high emission efficiency and beam quality can be expected.

3D printing of composite reflectors for enhanced light collection in scintillation detectors

Abstract The present study deals with the fabrication of light-reflecting materials used in pixelated scintillator detectors. For the first time the reflecting surfaces for pixels of different sizes (from 0.8 to 3.2 mm) were obtained via low-cost DLP 3D printing technique. The material for the reflectors was the new composite of transparent ultraviolet light-cured resin and TiO2 as a light-scattering filler. It was observed that TiO2 showed better performance compare to other pigments such as BaSO4, hBN or cubic zirconia. The reflectors formation rate was about 1 cm per hour with the possibility to produce several units simultaneously that simplifies the wrapping procedure. It was found that the regular pattern of the fabricated reflectors (stair-steps effect) could increase a light collection from a scintillator. The reflective properties of such surfaces were comparable to conventional reflection coating (e.g., Teflon wrapping).

FOUCAULT KNIFE-EDGE METHOD APPLICATION FOR ADAPTATION OF THE MILLIMETRON OBSERVATORY MIRROR SYSTEM

In the process of space telescopes development there is an increase in the diameter of their reflector.In this case, composite reflectors are used more often. So the main mirror of the Millimetron observatory consists of 96 elements, each of which can deviate from the calculated position during the transition to the transport position and back to the working position when the telescope is put into orbit. In this paper, we consider the possibility of using Foucault knife-edgemethod to solve the problem of adapting the mirror system of the Millimetron observatory. An optical scheme for solving the adaptation problem is proposed. It was simulated in the Zemax software package. In the process of modeling, the effects arising from the deviation of all the components of the reflector in 6 degrees of freedom were studied. The advantage in the approach to the digital matrix in the telescope is highlighted.

Flexible Dual-Band Dual-Beam Radiation of Reflector Antennas by Embedding Resonant Phase Alignment Elements for Power Refocusing

This article presents a dual-band composite reflector antenna by embedding an array of metallic phase alignment elements (PAEs) on a selected area of reflector. As a result, this phase-configurable reflector may radiate two relatively arbitrary beams at two widely separated frequency bands, respectively. In this concept, a conventional parabolic surface is first created for ordinary field radiation by a focal feed in the low-frequency band. Afterward, a feed of high-frequency band is offset from the focal point to result in defocused radiation due to the phase distortion of reflection from the parabolic reflector. Metallic PAEs are subsequently implemented on the reflector to configure their phases of reflections for distortion compensation, and thus to refocus the radiation power along a desired direction. Here, the resonance of PAEs also specifies a valid high-frequency range. In this article, the methodology is first presented with radiation discrepancy evaluated to validate the design concept, which is further validated by full-wave simulations. Numerical examples are presented to demonstrate the feasibility.

Experimental study of the functional and mechanical properties of shape memory polymer composites for a reflector of the space antenna

Experimental study of the shape memory polymer composite is carried out as a part of scientific and technological work aimed at development of the new promising reflectors for space antenna. The studied material consists of three-layered carbon biaxial fabric St 12073 impregnated with a polyurethane-based Diaplex MP5510 polymer matrix. This material is intended for manufacturing a frame used in the construction of a precise composite reflector of space antenna. When opening the reflector to the transport position, the rim activated by heating recovers a previously specified shape thus increasing the rigidity of the reflector at the periphery and enhancing the accuracy of the reflecting surface. To study the functional and mechanical properties of the rim material in manufacturing and operating conditions, experimental tests were carried out on the samples with different schemes of reinforcement: [03], [0/±60] and [0/±45]. The main goal of the study is to determine the degree and rate of the shape recovery, reinforcement angles, deformation rate and exposure time in the strained state. The developed test program included several stages. At the first stages, tests were carried out for fixing and restoring the shape upon three-point bending of flat samples at a strain rate of 1, 5, and 10 mm/sec and exposure of the specimens in deformed state for 24, 48, and 96 h. According to the results the material with the reinforcement angles [03] was accepted as optimal for the rim design, as it has maximal shape recovery parameters. For the selected material at the final stage of the study, the elastic modulus and tensile strength were determined at operating temperatures –50, +20, and +60°C. The tests showed that the studied polymer composite material has the desired shape memory properties and is promising for the rim manufacturing provided the heat insulation during operation.

Broadband and wide angle perfect reflection by super periodic cubes metamaterials in terahertz region

We present three kinds of broadband terahertz perfect reflectors by using all-dielectric metamaterials. Based on the principle of Mie resonances of resonators with high refractive index, the perfect reflection with wide spectrum and wide angle can be achieved. For the first kind of metamaterial, the common type of reflector with one cube in unit cell is demonstrated. For the second kind of reflector, there are two resonators with different geometric parameters in super periodic unit cell. For the third kind of reflector, there are four resonators with different geometric parameters in super periodic unit cell. Importantly, in order to enhance the response of angle for the perfect reflection, we propose the pyramidal composite microstructure metamaterial to realize the broadband reflection at oblique incidence. For the pyramidal composite reflector with four resonators in one super unit cell, the perfect reflection can be obtained from 0.75THz to 1.15THz with the decreased Fano resonant effect at oblique incidence.

Research and optimization of production cycle of high-precision composite spacecraft antenna reflector

The article presents a finite element model of CFRP (carbon fiber reinforcement material) reflector polymerization in autoclave for prediction of its shape after removing from the tool. The simulation was performed in the FEM software environment. The technique has developed in this work provides an opportunity to predict a shape and values of the production deformation of the reflector prior to its manufacture, and, if necessary, to introduce design and technological modifications. Successful verification of the finite-element modeling results of the reflector polymerization was performed using a full-scale experiment. Tool from CFRP has been created to forming the composite antenna reflector. This tool is cheaper than the Invar tool currently used. Also, the CFRP tool requires less time to manufacture. Recommendations for improving the technological process of composite contour antenna reflectors production manufactured on CFRP-tool are developed in the paper. The optimum curing mode of the composite reflector is determined. The research results were used in the performance of experimental design work and in the manufacture of reflectors for the spacecraft.

An ADS irradiation facility for fast and slow neutrons

We studied a flexible ADS-based irradiation facility with fast neutrons inside the core and slow neutrons in the composite reflector containing light materials. The fast reactor core has been designed using MCNP-6 code with a mixed reflector formed by three concentric cylindrical layers (lead+graphite+lead) in order to have different neutrons spectra to perform various types of measurements without perturbing the ADS core fast characteristics. We also included in the ADS design three irradiation points external to the core, in positions such to have different neutron spectra, for measurements to be performed out of the ADS system. Moreover, we performed a thermal-hydraulic assessment of the behavior of target and core cooling systems. In order to investigate the capabilities of the system, we studied different kinds of possible measurements that could be performed in various positions, both inside and outside the ADS.

Solid state additive manufacture of highly-reflective Al coatings using cold spray

This research presents the results of an investigation into the additive manufacture of reflective Al coatings using cold spray (CS). This work is the first time that CS technology has been used to fabricate highly reflective surfaces. The coatings were characterised with respect to total reflectivity within the wavelength range of 400–1800 nm, surface roughness, particle deformation levels, and density. The experimental results indicate that raising the gas heating temperature increased the porosity and that the lowest gas heating temperature delivered the highest spectrally average reflectivity of 93.4% which was within 1% of bulk Al. This investigation demonstrates that CS can be used to coat thin layers of Al onto various materials, which can be subsequently polished to create composite reflectors. Hence, a reflector with the reflectivity of Al and the structural and thermal properties of the substrate material can be fabricated, allowing for greater design flexibility and the rapid manufacture of multi-material reflectors.

Suppressing high-order surface errors of an active carbon fiber reinforced composite reflector using two types of actuators

Active feedback control is a feasible approach for maintaining the desired shape of a reflector. An architecture for an active reflector is presented in which both piezoelectric ceramic transducer (PZT) and macrofiber composite (MFC) actuators are introduced to reduce both the global and local (high-order) surface errors. An electromechanical finite element model with two types of actuators is developed using the Hamilton principle. An optimal shape controller is then developed to minimize the reflector surface error. Lower-order orthogonal Zernike polynomials are derived in a unit hexagon. The polynomials are considered to be the basic error modes of a reflector and are used to optimize the length of the PZT actuators. The arrangement of MFC actuators can be optimized in a single triangular component of the reflector because the deflections they induced are very local. An experiment is conducted to verify the performance of MFC actuators in a triangular component. The improvement in the control efficiency of the active reflector is demonstrated by two numerical examples.

Numerical and experimental investigation on nonlinear dynamic behavior of satellite antenna reflector mechanism considering geometrical nonlinear effect and laminated composite material

A nonlinear dynamic modeling method for a satellite antenna system composed of laminated composite shell reflector undergoing large rotation considering its geometrically nonlinear effect and material nonlinearity effect is proposed in this paper. The present model treats flexible appendages of a spacecraft mechanism as laminated composite material and takes into account the coupling relations between nonlinear constitutive relation of laminated material characteristics and large-angle maneuver. Then, the corresponding efficient formulations for laminated paraboloidal reflector based on higher order shear deformation theory and Hamilton's principle are developed to capture the correct dynamic response. Furthermore, the experiment for evaluating the dynamic behavior of laminated composite reflector is conducted; the vibration of the laminated composite material is smaller than that of isotropic material. Numerical results are in good agreement with those obtained from experiment to validate the correctness of the present modeling formulation. Finally, numerical simulations demonstrate that nonlinear stiffness terms and elastic force resulting from with different curvature and different laying angle have significant effect on the dynamic characteristics. The larger curvature of the reflector and the larger laying angle of the laminated composite material will induce the larger deformation of the reflector. The conclusion has important theoretical value and practical significance for the study of controlling the pointing behavior of satellite antennas.