Showing papers on "Parabolic reflector published in 2016"

High efficiency near diffraction-limited mid-infrared flat lenses based on metasurface reflectarrays

Abstract: We report the first demonstration of a mid-IR reflection-based flat lens with high efficiency and near diffraction-limited focusing. Focusing efficiency as high as 80%, in good agreement with simulations (83%), has been achieved at 45° incidence angle at λ = 4.6 μm. The off-axis geometry considerably simplifies the optical arrangement compared to the common geometry of normal incidence in reflection mode which requires beam splitters. Simulations show that the effects of incidence angle are small compared to parabolic mirrors with the same NA. The use of single-step photolithography allows large scale fabrication. Such a device is important in the development of compact telescopes, microscopes, and spectroscopic designs.

Generation of scalable terahertz radiation from cylindrically focused two-color laser pulses in air

Abstract: We demonstrate scalable terahertz (THz) generation by focusing terawatt, two-color laser pulses in air with a cylindrical lens. This focusing geometry creates a two-dimensional air plasma sheet, which yields two diverging THz lobe profiles in the far field. This setup can avoid plasma-induced laser defocusing and subsequent THz saturation, previously observed with spherical lens focusing of high-power laser pulses. By expanding the plasma source into a two-dimensional sheet, cylindrical focusing can lead to scalable THz generation. This scheme provides an energy conversion efficiency of 7 × 10−4, ∼7 times better than spherical lens focusing. The diverging THz lobes are refocused with a combination of cylindrical and parabolic mirrors to produce strong THz fields (>21 MV/cm) at the focal point.

Design, simulation and optimization of a solar dish collector with spiral-coil thermal absorber

Abstract: The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.

A 100-GHz Metal-Only Reflectarray for High-Gain Antenna Applications

Abstract: A 100-GHz metal-only reflectarray antenna is designed, fabricated, and tested. The required phase shift is achieved by simply tuning the metal block height, aiming to eliminate dielectric losses at high frequencies. An equivalent circuit model is employed to analyze the element reflection performance. A prototype reflectarray with a 30-mm square aperture is then fabricated and tested using near-field measurement setup. The measured results show an aperture efficiency of 50.1% at 100 GHz, and the measured radiation patterns agree very well with the full-wave simulation results. To compare the radiation performances, a parabolic reflector, a Fresnel zone plate reflector, and an unwrapped reflectarray of same size are also evaluated. The full-wave simulation results demonstrate that the proposed design not only achieves good radiation performance, but also exhibits advantages such as low profile, easy fabrication, and low cost.

Modified optical fiber daylighting system with sunlight transportation in free space

Abstract: We present the design, optical simulation, and experiment of a modified optical fiber daylighting system (M-OFDS) for indoor lighting. The M-OFDS is comprised of three sub-systems: concentration, collimation, and distribution. The concentration part is formed by coupling a Fresnel lens with a large-core plastic optical fiber. The sunlight collected by the concentration sub-system is propagated in a plastic optical fiber and then collimated by the collimator, which is a combination of a parabolic mirror and a convex lens. The collimated beam of sunlight travels in free space and is guided to the interior by directing flat mirrors, where it is diffused uniformly by a distributor. All parameters of the system are calculated theoretically. Based on the designed system, our simulation results demonstrated a maximum optical efficiency of 71%. The simulation results also showed that sunlight could be delivered to the illumination destination at distance of 30 m. A prototype of the M-OFDS was fabricated, and preliminary experiments were performed outdoors. The simulation results and experimental results confirmed that the M-OFDS was designed effectively. A large-scale system constructed by several M-OFDSs is also proposed. The results showed that the presented optical fiber daylighting system is a strong candidate for an inexpensive and highly efficient application of solar energy in buildings.

Reflective gradient metasurfaces for polarization-independent light focusing at normal or oblique incidence

Abstract: Reflective gradient metasurfaces are reported as flat, ultra-thin light focusers using a cross-resonator array with spatially varied geometric parameters atop a continuous gold ground plane spaced by a layer of SiO2. The sub-wavelength cross-shaped building element offers polarization-independent performance and full 2π phase tuning range by varying its width and length, which is explained by an analytical model based on harmonically oscillating dipole antenna. With a radial phase gradient, a metasurface is demonstrated to function as a parabolic reflector at 1.47 μm wavelength with the measured efficiency of 44%. In addition, by elaborately engineering the planar distribution of different building elements, another two focusing reflectors are designed and experimentally verified to anomalously reflect and concentrate light along normal direction but with oblique incident angles of 30° and 60°, respectively.

Circular paraboloid reflection cell for laser spectroscopic trace gas analysis.

Abstract: Absorption cells with circular geometry are a class of multipass reflection cells consisting of a single, circular mirror. They can be particularly favorable for trace gas measurements because of their mechanical robustness, simplicity, and their optical versatility. In this article, we present detailed theoretical considerations and ray tracing simulations for the optimization of the optical design of circular multipass reflection cells. A parabolic mirror shape in a confocal arrangement is found to be most suitable for long optical paths in a small volume. We experimentally demonstrate more than 12 m optical path in a 14.5 cm diameter gas cell and NO2 concentration measurements in ambient air with a measurement precision better than 0.1 ppb.

High-Order Vortex Beams Generation in the Radio-Frequency Domain

Abstract: A novel technique for generating high-order vortex beams in the radio-frequency domain is reported. Vortex beams with non-null radial index are generated by means of a dielectric mask, mounted upon either a twisted parabolic reflector or a conventional one. The far-field intensity pattern is compared to analytical models and numerical simulations, thus illustrating how diffraction and illumination can affect the generated fields.

Fast and low-cost beam steering using an agile mechanical feed system for exciting circular arrays

Abstract: A novel feed system for circular arrays enabling beam steering over 360° in the azimuth plane with a stable scanned beam is proposed. It consists of rotating and fixed parts. The rotating part is a two-dimensional offset fed parabolic reflector which is inside a circular parallel plate waveguide. The power coming from the rotating part is coupled with the elements of the circular array through a fixed coupling structure. The rotating part is light and its moment of inertia is significantly less than the conventional rotating antenna systems for beam scanning. Therefore, the beam can be steered much faster than the current rotating antenna systems. The details of the structure including the rotating and the fixed parts are presented and a design procedure for the fixed coupling section is suggested. The performance of the feed system is investigated by simulations and measurements. It is shown that the simulations and experimental results are in good agreement.

Optical analysis and performance evaluation of a solar parabolic dish concentrator

Abstract: In this study, the optical design of a solar parabolic dish concentrator is presented. The parabolic dish concentrator consists from 11 curvilinear trapezoidal reflective petals made of polymethyl methacrylate with special reflective coating. The dish diameter is equal to 3.8 m and the theoretical focal point distance is 2.26 m. Numerical simulations are made with the commercial software TracePro from Lambda Research, USA, and the final optimum position between absorber and reflector was calculated to 2.075 m; lower than focus distance. This paper presents results for the optimum position and the optimum diameter of the receiver. The decision for selecting these parameters is based on the calculation of the total flux over the flat and corrugated pipe receiver surface; in its central region and in the peripheral region. The simulation results could be useful reference for designing and optimizing of solar parabolic dish concentrators as for as for CFD analysis, heat transfer and fluid flow analysis in corrugated spiral heat absorbers.

Distillate Yield Improvement using a Parabolic Dish Reflector Coupled Single Slope Basin Solar Still with Thermal Energy Storage using Beeswax

Abstract: A single slope solar still, integrated with latent heat thermal energy storage system coupled to a parabolic concentrator was designed with the aim of improving productivity. 14 kg of beeswax was used as phase change material (PCM) beneath the absorber plate to keep the operating temperature of the still high enough to produce distilled water even during the sunset hours. The underside of the still is covered by 0.2 m aluminum sheet painted black on the side facing the parabolic concentrator to help in absorbing solar radiation reflected from the parabolic concentrator and conducting same to the PCM. To determine the performance of single slope solar still, it was tested without the PCM effect and then with the PCM effect. The temperature of water, temperature of PCM, air temperature, inner surface glass temperature and outer surface glass temperature were measured. Experimental results show that the effect of thermal storage in the parabolic concentrator-coupled single slope solar still increased the productivity by 62%.

Design of parabolic solar concentrator to improve the optical efficiency for thermal engine generator using dual reflector Gregorian method

Abstract: Parabolic Dish Solar Concentrator (PDSC) are commonly used to generate electricity from thermal energy employing Stirling engine, steam, photovoltaic and thermoelectric generator. Heat concentrator of Parabolic Dish (PD) is used for focusing radiation of the sun into the receiver that connected to the generator system. The conventional generator system is located above the focus of the primary reflector parabolic dish. This paper presents a new design of the parabolic dish solar concentrator using dual reflector Gregorian method. The design applies an additional reflector to place the engine generator in the bottom of the primary reflector parabolic dish. The design was verified using “SolTrace”, a software package for tracing the solar ray. It found that the heat flux collected was 0.73 MW/m2 for the designed parabolic with 300 cm primary diameter. This parabolic have obtained 594.65x geometry concentration ratio and 84.27% optical efficiency.

Efficient autonomous solar energy harvesting system utilizing dynamic offset feed mirrored parabolic dish integrated solar panel

Abstract: This paper presents the design and performance analysis of an efficient solar energy harvesting single axis sun tracking system employing dynamic offset parabolic mirrored reflector dish to increase the efficiency of solar energy harvesting system. The performance of proposed solar energy harvesting system has been analyzed by comparing the output of proposed system with static solar panel and solar panel with static mirrored reflector system. It has been observed that proposed system is capable of harvesting more energy than static solar panel system and solar panel with static offset mirrored parabolic dish. The parabolic mirrored reflector dish is capable of reflecting the light radiations and focusing the reflected light at its focal point where solar panel has been placed to harvest the light energy efficiently. The clocked tracking system has been used to rotate the dish in the direction of motion of sun. The Arduino UNO controller has been employed to rotate the dish by step angle of 6.25 degree at periodic interval of 30 minutes during daytime between 6 AM to 6 PM. The energy harvesting system is autonomously operating the motor driven dish by harnessing a portion of harvested solar energy which is stored in rechargeable lead acid battery. The proposed solar energy harvesting system is capable of generating average output voltage of 7.822 volts and 6.144 mA. The proposed system is 81 percent more efficient than static solar panel system and 48.26 percent more efficient than solar panel with static reflector system. The proposed energy harvesting system can be efficiently employed for various applications like water heating, etc.

Theoretical Study of a Broadband Quasi-Optical Mode Converter for Pulse Gyrotron Devices

Abstract: Theoretical investigation of a broadband quasi-optical mode converter for 330-GHz TE62 mode gyrotron application is presented. The converter consists of a Vlasov launcher and three reflector mirrors. Special considerations, including a Vlasov launcher with reasonably large aperture radius and optimized combination of two elliptic reflectors and a bifocal parabolic reflector, are the keys to achieve broadband mode converting. The optimized internal converter is well compatible with the gyrotron electron-optical system and generates Gaussian beam with efficiency higher than 80% in an extraordinary broadband range between 310 and 340 GHz. The principle of the broadband converter can also be applied to gyrotron amplifiers.

A study of orbital angular momentum generated by parabolic reflector with circular array feed

Abstract: This paper discusses the generation of orbital angular momentum (OAM) produced by a parabolic reflector with a circular array (CA) feed. Simulated electromagnetic (EM) field verifies the behavior of OAM. Design parameters are numerically optimized for both the parabolic reflector and the circular array feed, in term of beam divergence associated with different OAM modes. Primitive estimations suggest that a few low-order-OAM modes can be transmitted simultaneously up to 100 meters in the mm-wave bands.

Spatial polarization variation in terahertz electromagnetic wave focused by off-axis parabolic mirror

Abstract: We have investigated the spatial distribution of the polarization state of a terahertz electromagnetic wave focused by an off-axis parabolic mirror (OPM) in the focal plane. We employed polarization-resolved terahertz time-domain spectroscopy and found that a steep spatial variation in the polarization state appears slightly distant from the focus when a linearly polarized terahertz wave is focused. The spatial variation includes an abrupt change in the polarization state (states change between circular and linear polarizations) within a wavelength. The observed phenomena are confirmed by numerical calculations and are shown to be intrinsic to the reflection from the OPM.

Optimization of heat flux distribution on dual parabolic dish for Stirling engine applications

Abstract: This research giving up new concept for heat flux distribution improvement to SOLO 161 Stirling engine receiver. Stirling engine receiver need some stable heat flux, so the system could operate optimally until 9–10 kW el . Eurodish system operated stirling engine with single parabolic dish, located above the parabolic reflector. This paper developed a new design using dual parabolic dish with Gregorian method in order to be able place the Stirling engine below the parabolic reflector or on the ground. Geometry design from dual parabolic used mathematical calculations with intersecting line method done with Delphi software. The heat flux were evenly distributed with receiver diameter of 0.272 m could be achieved with parabolic design with primary diameter of 8.65 m and secondary diameter of 2.67 m with rim angle 71°. The geometrical calculations were verified by simulations using Geogebra software. We used solar ray tracing simulations from SolTrace software, were acquiring the optimal peak and average of heat flux are 1608 kW/m2 and 660 kW/m2 when the DNI 1100 W/m2.

Multi-panel antenna system

Abstract: A multi-panel antenna system may be disassembled and packaged into a container with substantially smaller dimensions than the assembled antenna system. The antenna system may include two or more reflector panels, such that a respective reflector panel can include a curved surface that may form a portion of a parabolic reflector, and can include an inter-panel fastener operable to align a side surface of the respective reflector panel with a side surface of another reflector panel. The antenna system may also include a mounting assembly that may be used to fasten a convex side of the two or more reflector panels to a surface external to the antenna system, and a feed assembly that may be attached to the mounting assembly.

Emissivity measuring device based on tri-off-axis parabolic mirrors and double reference black bodies

Abstract: The invention discloses an emissivity measuring device based on tri-off-axis parabolic mirrors and double reference black bodies.The emissivity measuring device comprises a spectrograph (1), a high-temperature black body heating device (2), a sample heating device (3), the high-temperature reference black body (4), the low-temperature reference black body (5), a horizontal displacement platform (6), an electronic control rotary table (7), a displacement control system (8), a computer (9), a diaphragm (10), a low-temperature black body heating device (11), the off-axis parabolic mirror I (12), the off-axis parabolic mirror II (13) and the off-axis parabolic mirror III (14).Material normal spectral emissivity is measured within the spectral region of 1-14 micrometers and the temperature range of 50-800 DEG C, influence on measuring results by instrument short-term drifting and environment changes is reduced by means of the device, and measurement efficiency and measurement uncertainty are improved.

Wide-angle scanning reflector configuration for focal plane arrays

Abstract: A mathematical analysis of reflector shaping for wide-angle scanning is presented. Parabolic, hyperbolic and spherical reflectors are defined based on geometrical optics method in order to have the smallest deviation of the focused beam (Fig. 1) during wide-angle scanning. It is shown that it is possible to expand the illuminated region of the array by a factor 3 for parabolic reflectors with axial displacement based on an estimated 80 % aperture efficiency at 30 GHz, D/λ=80. Moreover, it is demonstrated that spherical reflector have the smallest deviation from the axis of revolution during wide-angle scanning.

Optimizing a CATR quiet zone using an array feed

Abstract: The efficiency of use of the parabolic reflector of a single offset reflector compact antenna test range (CATR) is affected largely by the illumination provided by the range feed and the reflector edge treatment. Thus, when these factors are taken together it is commonly found that the realized quiet zone (QZ) diameter is typically as little as 30% of the diameter of the reflector for the commonly encountered case of a single offset CATR. Furthermore, single offset CATR performance is known to degrade as the wavelength of the illuminating fields becomes more comparable with the physical dimensions of the reflector because the physical optics (PO) assumption needed for collimation of the reflected field becomes less effective. Different reflector edge treatments such as rolled or serrated edges are commonly employed to taper the intensity of the reflected fields at the reflector aperture boundary, seeking to minimize the level of diffracted fields in the quiet-zone (QZ). Such strategies mean that at higher frequencies the transverse dimensions of the QZ are unnecessarily reduced thereby decreasing the spatial efficiency of the CATR and limiting the effective bandwidth of the antenna test system. In this paper we report preliminary results that begin to investigate the alternative strategy for controlling the signal illuminating the CATR reflector by utilising a shaped beam feed antenna. Building on our previously reported work of efficient CATR computational electromagnetic simulation, we report the use of an array feed whose excitation is optimized to achieve maximum QZ size. We illustrate the concept by employing the technique with a sector-shaped, reflector single offset CATR having no edge treatment and then using the same reflector with an edge treatment and by examining the impact that this has on the amplitude taper and the amplitude and phase peak-to-peak ripple.

Absorber Tube with Internal Pin-Fins for Solar Parabolic Trough Collector

Abstract: Solar parabolic trough collectors exploit solar energy for power generation in solar thermal power stations. These systems require long arrays of reflective troughs with absorber tube running along the axis of parabolic dish. A successful attempt to reduce the length of arrays was accomplished by experimentally analysing the modifications done in absorber tube. Two out of three tubes were fabricated and they were employed to obtain the performance parameters through experimentation conducted at VIT University, Vellore, India. Distilled water was used as the working fluid. Maximum efficiency of 39.12% was obtained at 451.6 W/m 2 of direct normal irradiance (DNI) for absorber tube with internal pin-fins and without glass tube (AFWG t ) compared to 8.15% obtained at same value of DNI and other conditions for simple absorber tube without glass cover (AWG t ). Cylindrical parabolic trough available at the university was utilized, providing the basis for designing and fabrication of the tubes. Plots for varying mass flow rate at interval of 10 minutes were made against instantaneous thermal efficiency and heat utilized, for direct normal irradiance vs. temperature difference across the tubes and instantaneous thermal efficiency. Through the experimentation conducted, better performance was procured compared to earlier works. Thus, the proposal infers that absorber tube with internal fins has good scope for its application, both domestically as well as industrially. It also calls for further research and development of proposed techniques so as to achieve better performance curves.

Design, Construction and Testing of Parabolic Solar Oven

Abstract: The work is on the Design, Construction and Testing of Parabolic Solar Oven with focused reflector. Heat from the sun was concentrated on a transparent glass located at the focal point; to the black casted Aluminum plate (absorber) which was located in an enclosed insulated space (Oven). The heat was absorbed by the Aluminum plate which could be utilized for baking or cooking. The sun tracking was made to be manual tilt of the parabolic reflector and a booster was mounted on top of the Oven which would focus the sun rays into the enclosed oven through the top glass layer. The frame was made using 50 mm×3 mm angle iron. The holder and its support were constructed out of 3 mm×12 mm flat bar and shaped round to accommodate the receiver holder. The principles of heat transfer were carried out to ascertain the efficiency of the oven. The system was tested in average sunny/cloudy conditions; the test results gave a higher temperature of 104°C