Showing papers on "Reflector (antenna) published in 2006"

Efficiency enhancement in Si solar cells by textured photonic crystal back reflector

Abstract: An efficient light-trapping scheme is developed for solar cells that can enhance the optical path length by several orders of magnitude using a textured photonic crystal as a backside reflector. It comprises a reflection grating etched on the backside of the substrate and a one-dimensional photonic crystal deposited on the grating. Top-contacted crystalline Si solar cells integrated with the textured photonic crystal back reflector were designed and fabricated. External quantum efficiency was significantly improved between the wavelengths of 1000 and 1200nm (enhancement up to 135 times), and the overall power conversion efficiency was considerably increased.

Robust estimates of 3D reflector dip and azimuth

Abstract: Much of seismic stratigraphy is based on the morphology of seismic textures. The identification of reflector terminations and subtle changes in dip and azimuth allows us to infer coherent progradational and transgressive packages as well as more chaotic slumps, fans, and braided-stream complexes; infill of karsted terrains; gas seeps; and, of course, faults and angular unconformities. A major difficulty in estimating reflector dip and azimuth arises at discrete lateral and vertical discontinuities across which reflector dip and azimuth change. The smearing across these boundaries produced by traditional dip and azimuth estimations is avoided by using temporally and spatially shifted multiple windows that contain each analysis point. This more robust estimation of dip and azimuth leads to increased resolution of well-established algorithms such as coherence, coherent amplitude gradients, and structurally oriented filtering. More promising still is the analysis of high-resolution dip and azimuth through vol...

Spurious multiples in seismic interferometry of primaries

Abstract: Seismic interferometry is a technique for estimating the Green’s function that accounts for wave propagation between receivers by correlating the waves recorded at these receivers. We present a derivation of this principle based on the method of stationary phase. Although this derivation is intended to be educational, applicable to simple media only, it provides insight into the physical principle of seismic interferometry. In a homogeneous medium with one horizontal reflector and without a free surface, the correlation of the waves recorded at two receivers correctly gives both the direct wave and the singly reflected waves. When more reflectors are present, a product of the singly reflected waves occurs in the crosscorrelation that leads to spurious multiples when the waves are excited at the surface only. We give a heuristic argument that these spurious multiples disappear when sources below the reflectors are included. We also extend the derivation to a smoothly varying heterogeneous background medium.

Millimeter-wave indoor wireless personal area network with ceiling reflector and methods for communicating using millimeter-waves

Abstract: Embodiments of an indoor millimeter-wave wireless personal area network and method are described. In some embodiments, a directional antenna (103) and a diffusive reflector (106) are used to increase throughput and reduce multipath components.

All-metamaterial-based subwavelength cavities (λ/60) for ultrathin directive antennas

Abstract: In this letter, we present the characterization and modeling of a metamaterial-based resonant cavity for ultrathin directive printed antennas. A planar artificial magnetic conductor is used for the two reflectors of the Fabry–Perot-type resonant cavity. One reflector behaves as a high impedance surface, and serves as a substrate for the printed antenna. The other reflector is a partially reflective surface used as a transmitting window. The cavity is operated on subwavelength modes, the smallest cavity thickness being of the order of λ∕60. A drastic enhancement of the antenna directivity and gain is obtained over a relatively wide band from 7.5to10.1GHz, corresponding to a range of cavity thicknesses from ∼λ∕3 to ∼λ∕60. The cavity resonance is seen to be correctly predicted from the standard ray theory approach.

Satellite ground station antenna with wide field of view and nulling pattern using surface waveguide antennas

Abstract: The present invention is applicable to satellite ground station antennas having a wide field of view in comparison to the satellites with which the antenna connects One embodiment includes a parabolic reflector having a size that corresponds to a beam with an angular half-width larger than the spacing between neighboring interfering satellites It also has a feed comprising at least two dielectric rod-based surface waveguides coupled to the parabolic reflector configured to have a high sensitivity for a target satellite within the angular half-width of the reflector beam and a low sensitivity for neighboring interfering satellites within the angular half-width of the reflector beam

Antenna with Shaped Asymmetric Main Reflector and Subreflector with Asymmetric Waveguide Feed

Abstract: A low-profile antenna system includes a main reflector (102) formed as a shaped main reflector surface that is approximately, but not precisely, parabolic. The main reflector (102) has a main reflector edge configuration (103) that is asymmetric. A feed system (104) for the main reflector includes a subreflector (106) formed as a shaped subreflector surface that is approximately, but not precisely, elliptical. The subreflector has a subreflector edge configuration (107) that is also asymmetric. An RF feed horn (108) associated with the feed system 104 has an aperture profile which also has an asymmetric shape.

Stepped-reflector antenna for satellite communication payloads

Abstract: A stepped reflector for being illuminated by at least one multiple-band feed is provided. The reflector includes a central region and a first annular region with an annular width of w. The first annular region is axially stepped a height h above the central region, where h is approximately equal to m x [ϕ ± (ϕ (Θ = 0)- ϕ (Θ=Θ0))]x π/180 xλ/2π x 1/2, where m is a positive odd integer, Φ is a desired amount of phase shift of an outer region of a phase front for reflecting off of the reflector, φ is a feed phase contribution for an angle θ, and Θo is an angle formed between an axis of the at least one feed and a line connecting a phase center of the at least one feed and an inner edge of the at least one annular region. The central region and the annular region of the reflector may be parabolically curved or may alternately be shaped. The reflector may be fed by one or more multiple-band horn antennas.

Vertical beaming of wavelength-scale photonic crystal resonators

Abstract: We report that $g80%$ of the photons generated inside a photonic crystal slab resonator can be funneled within a small divergence angle of $\ifmmode\pm\else\textpm\fi{}30\ifmmode^\circ\else\textdegree\fi{}$. The far-field radiation properties of a photonic crystal slab resonant mode are modified by tuning the cavity geometry and by placing a reflector below the cavity. The former method directly shapes the near-field distribution so as to achieve directional and linearly polarized far-field patterns. The latter modification takes advantage of the interference effect between the original waves and the reflected waves to enhance the energy directionality. We find that, regardless of the slab thickness, the optimum distance between the slab and the reflector closely equals one wavelength of the resonance under consideration. We have also discussed an efficient far-field simulation algorithm based on the finite-difference time-domain method and the near- to far-field transformation.

Design and fabrication of planar multilayer structures with coherent thermal emission characteristics

Abstract: A large number of recent publications dealt with enhanced emission properties of micro/nanostructures by the excitation of surface plasmon or phonon polaritons. Some used grating structures to demonstrate coherent thermal emission in a narrow spectral band and towards a well-defined direction. Others suggested that planar layers could also be used to achieve coherent emission. In the present paper, we describe two alternative designs with fewer layers for the application as coherent emission sources in planar multilayer structures. One design is a composite of several unit cells of one-dimensional photonic crystal atop a highly reflective material. Coherent emission can be obtained by the excitation of surface waves between the photonic crystal and the reflector. The other design employs a Fabry-Perot resonance cavity constructed by coating a dielectric layer onto the reflector and then a thin metallic film on the dielectric layer. When standing waves exist in the cavity, the emissivity plots show sharp s...

Transmissive optical imaging device with micromirror array

Abstract: We propose a new imaging optics called the Transmissive Mirror Device (TMD). It consists of numerous micromirrors placed perpendicular to the surface of a flat, thin metal plate. The micro-mirror array is implemented by the inner walls of minute square holes, which are densely pitted on the device. The basic mode of operation is based on two reflections by a pair of adjacent mutually perpendicular mirrors, i.e., a dihedral corner reflector. Although the principal of operation is based on reflection by mirrors, the device is also transmissive and deflects light. Since this imaging system forms a real image at a plane symmetric point, the depth of the 3D image is inverted. Its optical defects are low optical transmittance and stray light caused by non-reflected light and that reflected once. We manufactured the device experimentally with nano-precision machining technology and also evaluated it.

A New End-effector for On-orbit Assembly of a Large Reflector

Abstract: In Earth orbit, astronomical observations are possible free from any absorption or disturbances by the Earth's atmosphere. Therefore, some large space telescopes and large space radio telescopes are planned for the future. We discuss the design of a radio telescope reflector which can be assembled in orbit by a space robot arm, with its networks and connecting mechanisms suitable for robot tasks. The characteristics of the new end-effector of robot arm and their suitability for onboard assembly tasks were confirmed by testing using a prototype end-effector and a two dimensional ground test arm. The test results are also described in this paper.

Theoretical demonstration of enhancement of light extraction of flip-chip GaN light-emitting diodes with photonic crystals

Abstract: The authors demonstrate, using finite-difference time-domain modeling, an enhancement in the extraction efficiency of flip-chip GaN light-emitting diodes (LEDs) using photonic crystals. The authors compare the extraction efficiencies of four configurations of a flip-chip GaN LED: with and without photonic crystal (PhC) layers, with a perfect reflecting mirror, and a bottom PhC reflector on GaN in combination with a top PhC extractor on sapphire. The authors show that, by using a photonic crystal layer as a bottom reflector, they can enhance the extraction efficiency similar to that of a mirror, yet the PhC reflector has the advantage that the metallic mirror loss can be avoided.

Stepped-reflector antenna for dual-band multiple beam Satellite communications payloads

Abstract: A novel stepped-reflector antenna (SRA) suitable for dual-band multiple beam satellite payloads is introduced in this paper. The SRA system produces "flat-top" radiation patterns for receive beams and highly efficient Gaussian patterns for transmit beams over a geographic coverage region as seen by the geo-synchronous satellite. It combines the reflector improvements through the use of SRA with the feed horn advancements through the use of dual-band "high-efficiency horns" in order to realize an efficient multiple beam antenna (MBA) system supporting both downlink transmit and uplink receive signals of communication satellites. It is shown that the SRA provides a congruent set of spot beams on ground for both transmit and receive frequencies with the benefits of significantly improved edge-of-coverage gain, improved co-polar isolation among beams that re-use the same frequency channels, receive beam patterns that are less sensitive to satellite pointing error, and reduced number of reflector antennas when compared to conventional MBAs

Reflection properties of coupled-ring reflectors

Abstract: The reflection properties of a coupled-ring reflector (CRR) are analyzed using the transfer matrix method. The CRR is composed of two coupled rings that are coupled to a bus waveguide. Depending on the combination of the cross-coupling ratios of the couplers, the reflection spectrum shape changes greatly. In the lossless case, the reflection spectrum has four peaks when the ring-bus coupling ratio is small. When the ring-bus coupling ratio is more than half and the ring-ring coupling is very small, the four peaks broaden, forming a single peak with still considerably narrow reflection spectrum, which makes the CRR attractive in applications requiring compact reflectors such as for single-mode laser diodes. The dependence of the propagation and insertion losses of the couplers on the reflection spectrum is also investigated, and the design guidelines are presented.

Measurement of Temperature Distribution Using Acoustic Reflector Array

Abstract: We propose an ultrasonic measurement of temperature distribution. Using the system, we aim to measure temperature distribution to be used for a sophisticated air-conditioning system. The system consists of a loudspeaker (SP), a microphone (MIC) and an acoustic reflector array. Sound velocity is dependent on air temperature along the propagation path, and is measured from the time of flight (TOF) of sound. A measurement area is partitioned into a 1×3 grid. The sound velocities in each partitioned grid square were obtained by arranging the SP, MIC and three reflectors appropriately. We created a temperature gradient in a grid square of the measurement area using an electrical heat source to confirm that the system detects an area of heat concentration. The product of area length (m) and area temperature (°C) corresponds to the amount of heat (m°C) in that area. The amount of heat measured by the system showed good agreement with the amount of heat estimated using thermocouples, which were installed as reference. The method has the advantages of noncontact sensing, a quicker response and a simpler composition, over conventional temperature measurement systems.

Security Device Based on Customized Microprism Film

Abstract: A security device comprises at least two regions, each region comprising a prismatic surface structure defining an array of substantially planar facets. Each region forms a reflector due to total internal reflection when viewed at least one first viewing angle and is transparent when viewed at at least one second viewing angle. The said at least one first viewing angle of one region is different from the at least one first viewing angle of the other region.

Development of Elastic Memory Composite Stiffeners for a Flexible Precision Reflector

Abstract: Harris Corpor ation is currently developing a next -generation, large -deployable, solid surface radio frequency reflector, called the Flexible Precision Reflector (FPR). The FPR will significantly advance satellite communication systems by enabling very -large -aperture an tennas to be stowed within existing launch vehicle shrouds at a relatively low cost and part count. Additionally, by replacing traditional mesh surfaces with a furlable composite laminate, the FPR antenna will be capable of operating at radio frequencies a bove 40GHz. To realize the full potential of the FPR design, Harris Corporation is considering the use of Composite Technology Development’s TEMBO ® Elastic Memory Composite materials for critical components within the FPR system. This paper present s the de sign, development, fabrication, and testing of a FPR breadboard model that demonstrates the benefits of incorporating TEMBO ® materials in the design.

Design Evaluation of a Large Aperture Deployable Antenna

Abstract: Large aperture on-axis antennas for space based and terrestrial applications are of interest to NASA. The NEXRAD in Space (NIS) antenna concept is a large deployable spherical reflector that will provide accurate measurements of the earth’s atmosphere, ocean winds and other environmental parameters at much higher spatial resolutions than currently feasible. This paper presents a study conducted to evaluate the feasibility of developing a large aperture, deployable spherical antenna that meets the needs of NASA science missions requiring large (up to 35-meter) apertures for monitoring earth’s atmosphere. Several conceptual design concepts are considered for this application. The candidate concepts include inflatable reflectors, rigidizable reflectors, hybrid systems, and a deployable electrostatically tensioned reflector. An initial screening of these concepts based on mass, stiffness, and shape controllability was performed. Out of the several design concepts evaluated in this study, the electrostatically figured deployable mesh design concept is proposed as the preferred LDA design. A more detailed evaluation of this concept is performed to address the feasibility of achieving the desired surface shape accuracy using active electrostatic control to correct for on-orbit shape errors introduced by orbital heating. The concept is based on combining a proven lightweight deployable mesh antenna structure and a high precision polymer membrane reflector. The key features of this design are light weight, ability to support active shape control, ability to package well, and the concept is scalable to larger diameters.

Light-emitting diode

Abstract: A light-emitting diode includes a substrate having a main surface, a light-emitting diode device arranged on the main surface, a translucent sealing resin portion sealing the light-emitting diode device so that the light-emitting diode device is implemented as an independent convex portion projecting from the main surface, and a reflector arranged on the main surface so as to surround an outer perimeter of the sealing resin portion with an inclined surface at a distance from the outer perimeter

Enhancing cholesteric liquid crystal laser performance using a cholesteric reflector

Abstract: A high performance dye-doped cholesteric liquid crystal (CLC) laser is demonstrated by incorporating a passive CLC reflector to the active cell. The polarization-conserved CLC reflector effectively increases the distributed feedback cavity length which, in turn, results in a significant enhancement in lasing efficiency and a dramatic reduction in beam divergence. The lasing characteristics are still dominated by the circularly polarized light with the same sense as the cholesteric helix.

Reflector based optical design

Abstract: A novel optical design based on a faceted conical or curved reflector centered within an upward facing circular array of light emitting diodes (LED) and protected by a transparent cover.

High reflectivity air-bridge subwavelength grating reflector and Fabry-Perot cavity in AlGaAs/GaAs

Abstract: We present a novel air-bridge subwavelength grating reflector with very high reflectivity be used as a top mirror in a VCSEL structure. We explain the design method, model the structure using both RCWA and FDTD, and predict the characteristics of a Fabry-Perot structure built with this reflector. We describe the fabrication of the suspended grating.

Global Optimization and Antenna Synthesis and Diagnosis, Part Two: Applications to Advanced Reflector Antennas Synthesis and Diagnosis Techniques

Abstract: The paper presents the application of the hybrid global optimization algorithm, introduced in the companion paper Part I, to reflector antenna power pattern synthesis and reflector antenna surface diagnosis from only amplitude data. The synthesis algorithm determines both the reflector surface and the excitation coefficients of the array of primary feeds to meet the designing specification on the far-field pattern expressed by means of two couple of masks bounding the squared amplitude of both the copolar and crosspolar components. The diagnosis technique allows to find the reflector surface profile from the measurement of the far field power pattern by a proper formulation of the corresponding inverse problem. In both cases we take advantage of the exploring capability of an evolutionary algorithm and of the solution refinement capability of an efficient, quasi-Newton based, local search procedure. The numerical analysis shows that Global Optimization can outperform the standard local approach, by significantly improving the performance of the synthesized antenna in the first case and by enhancing the reliability of the diagnosis procedure in the second one.

Enhanced light-extraction in GaInN near-ultraviolet light-emitting diode with Al-based omnidirectional reflector having NiZn∕Ag microcontacts

Abstract: Enhancement of light extraction in a GaInN near-ultraviolet light-emitting diode (LED) employing an Al-based omnidirectional reflector (ODR) consisting of GaN, a SiO2 low-refractive-index layer perforated by an array of NiZn∕Ag microcontacts, and an Al layer is presented. A theoretical calculation reveals that a SiO2∕Al ODR has much higher reflectivity than both a SiO2∕Ag ODR and a Ag reflector at a wavelength of 400nm. It is experimentally shown that GaInN near-ultraviolet LEDs with GaN∕SiO2∕Al ODR have 16% and 38% higher light output than LEDs with SiO2∕Ag ODR and Ag reflector, respectively. The higher light output is attributed to enhanced reflectivity of the Al-based ODR in the near-ultraviolet wavelength range.

Multi-tower Line Focus Fresnel Array Project

Abstract: As an alternative to conventional tracking solar thermal trough systems, one may use line focus Fresnel reflector systems. In a conventional Fresnel reflector design, each field of reflectors is directed to a single tower. However, efficient systems of very high ground utilisation can be setup if a field of reflectors uses multiple receivers on different towers. This paper describes a line focus system, called the compact linear fresnel reflector system and a project to produce an initial 95 MWth solar array. The array will be used as a retrofit preheater for a coal fired generating plant.

Light Extraction in GaInN Light-Emitting Diodes using Diffuse Omnidirectional Reflectors

Abstract: A theoretical and experimental analysis of light extraction in GaInN light-emitting diodes LEDs employing diffuse omnidirectional reflectors is presented. The diffuse omnidirectional reflector consists of GaN, a Ni/Au current spreading layer, a SiO2 layer roughened by Ar ion etching, and a Ag layer. Randomly distributed polystyrene spheres are used as an etch mask. The diffusely reflected power is enhanced by two orders of magnitude for a roughened reflector surface compared with a planar surface. The GaInN LEDs with diffuse omnidirectional reflectors show a higher light output 3.3% and a lower angular dependence of emission than LEDs with specular reflectors. The enhancement is attributed to reduced trapping of light within the high-index GaN semiconductor.

Integrated monitoring and feedback designs for external cavity tunable lasers

Abstract: An integrated structure includes front and rear facets (201, 203) optically- coupled by a waveguide (220) passing through the integrated structure. The integrated structure includes a gain section (202) and a reflector (208) optically coupled to the gain section by the waveguide, the reflector to emit an optical output. A modulator (214) is optically coupled to the reflector by the waveguide, the modulator to modulate the optical output. And a control section (216) disposed along the waveguide.

Geodetic Target Object and Surveying System

Abstract: Disclosed is a geodetic target object comprising at least one reflector surface, a receive channel with a detector (18) for receiving electromagnetic radiation (ES) transmitted by a measuring unit (2″), and a transmit channel with a radiation source (13′). The associated transmission port and/or reception port is/are integrated into the reflector surface or is/are embodied so as to adjoin the reflector surface such that radiation (RS) that is modulated for transmitting data can be transmitted in the direction of the measuring unit (2″) within the cross section (5″) of the radiation (ES) generated by the measuring unit (2″).

Illumination Light Unit and Optical System Using Same

Abstract: The present disclosure provides an illumination light unit including an array of LEDs disposed on a substrate, a controlled transmission mirror positioned to receive illumination light from the array of LEDs, and a reflector sheet positioned between the substrate and the controlled transmission mirror. The reflector sheet includes an array of reflectors each having an aperture. Respective LEDs of the array of LEDs protrude through respective apertures of the reflectors. Each reflector is operable to direct at least a portion of illumination light from its respective LED to the controlled transmission mirror.