Showing papers on "Parabolic reflector published in 1977"

A new series representation for the radiation integral with application to reflector antennas

Abstract: Given the true or any approximate current on a reflector, the radiated far-field is determined from a rapidly convergent series representation of the radiation integral. The leading term is a well-shaped J_{1}(x)/x beam pointing in a desired direction. Higher order terms provide perturbations to the leading term. The coefficients of the series are independent of the observation angles. Hence, once they are computed, the field may be determined very rapidly at large numbers of points. Initially, a suitable small angle approximation is made that places the radiation integral in the form of a Fourier transform on a circular disk. The theory is then extended such that the results are valid in both the near and the wide angle regions. Application to a rotationally symmetric paraboloid is presented herein. Other applications include the offset and dual reflectors and near- to far-field integrations. A modified form of the series can also be used for Fresnel zone computations.

Solar energy collector system with cylindro-parabolic mirror

Abstract: A solar energy collector having concave mirrors shaped as troughs of parabolic cross-section with a longitudinal pivotal axis enabling them to be aimed at the sun and having, at intervals, connecting members for maintaining at the mirror focus a heat receiving tube of small diameter by comparison with the mirror aperture. A dusttight and moisturetight transparent chamber isolates both the receiving tube and the surface of the mirror from the surrounding atmosphere.

Sun tracking solar energy collector

Abstract: A parabolic reflector is supported so that it can track the sun The support for this reflector comprises an azimuth frame supported on two wheels and a central pivotal point which are positioned in a substantially triangular configuration The two wheels rotate on tracks On top of the azimuth frame, there is provided an elevation frame The elevation frame includes curved rails which define a portion of an arc and extend vertically The reflector rides on wheels captured within the curved rails The wheels of the azimuth frame are driven by an azimuth actuator The reflector structure is counterbalanced about its elevation axis by a pendulum cable system which is driven by a motor to change elevation At the focal point of the parabolic reflector, a heat engine or receiver is mounted independently on the reflector Suitable means are provided for moving the reflector about its two axes in order to track the sun

Electromagnetic field near the focus of wide-angular lens and mirror systems

Abstract: The time-averaged electric energy density near the focus of a parabolic mirror of wide-angular aperture is calculated and compared with that of an aplanatic lens system. The distributions exhibit great differences, the mirror showing a greater departure from circular symmetry, a more complicated structure and increased sidelobes. The vectorial integral representation of Wolf is derived from the Stratton-Chu formula.

Light reflector structure

Abstract: An elongated high intensity lamp which serves as a line-type of light source is placed at the focus of a generally shaped parabolic reflector which extends longitudinally with the light source. The reflector surface closest to the lamp is inwardly deformed toward the light source. The inwardly deformed section may itself be a concavely shaped parabolic or arcuate region; or inwardly angled flat sections; or a flat region extending squarely across the top of the reflector. The distortion of the parabolic reflector shape produces a more uniform intensity distribution across the area being illuminated by the lamp and the reflector. A plurality of parallel line-type sources are also disclosed.

Laser optical apparatus for operation under a microscope

Abstract: A laser optical apparatus for operation under a microscope comprises: a laser beam introducing 45° reflector arranged between two optical axes so as not to impair the range of vision frontwardly of a binocular telescope for operation, a parabolic mirror with a surface displaced from an axis for condensing introduced beams of laser and serving as an objective lens of the microscope, a plane reflector driven by motors to direct the condensed beams of laser and an optical axis of the microscope, and a maneuvering mechanism including a stick for operating said motor.

Solar energy collector

Abstract: A solar energy collector is shown which is comprised of an underlying support, a support surface, and a combined reflector and heat absorber. The combined reflector and heat absorber is formed from a continuous sheet of material to provide contiguous parabolic reflectors, each reflector having an upstanding heat absorber centrally located therein in the form of a fluid conduit. The absorber-fluid conduit is closed along one edge by the support surface or by a spacer between support surfaces. A pair of manifolds are operatively connected at the ends of the heat absorbers to enable heat-absorbing fluid to flow in from one manifold, through the absorber-conduits, and out the other manifold. The continuous formation of the parabolic reflectors and heat absorbers from one sheet provides production economies, manufacturing efficiencies and reduced weight and cost of the solar energy collector.

Spectral and Noise Characteristics of a 300-W Eimac Arc Lamp.

Abstract: : High-pressure xenon short-arc lamps have long been considered to be reliable, high intensity sources of radiation for the ultraviolet, visible, and near-infrared spectral regions. The Eimac illuminator series, which Varian began marketing in 1972, is a variant of the conventional short arc lamp, having an integral parabolic (or elliptical) reflector, which provides greatly improved light gathering efficiency over more simple arc lamps. The integral reflector also significantly simplifies lamp alignment.

Uniform illumination of spherical laser fusion targets

Abstract: Uniformity of illumination of spherical laser fusion targets is calculated for eight, twelve, and twenty beams arranged according to the symmetry of the Platonic solids. Uniformity is optimized by varying the f/no of ideal aberration-free lenses, amount of beam overlap, and the shape of the spatial beam profile. The numerical results show twenty-beam illumination to be slightly better than twelve-beam illumination, with eight beams running a poor third. Refractive energy losses due to nonorthogonal illumination and the implications for the design of a practical laser fusion reactor are discussed.

Experimental Evaluation of a Cylindrical Parabolic Solar Collector

Abstract: Results are presented for a series of solar collector experiments in which the incident solar flux was concentrated by a single-axis tracking parabolic trough mirror. The concentrated solar flux was directed onto an absorber tube whose axis coincided with the focal axis of the concentrator. The performance of the collector was evaluated using three different absorbers; a black painted tube designed to operate near ambient temperature, a heat pipe which had a selective solar absorber coating applied to its surface, and a heat pipe which had its surface coated with a nonselective black paint. The peak efficiency for the collector in the absence of heat losses is approximately 62 percent when the incoming solar energy is normal to the collector aperature. The heat losses which occurred at elevated temperatures (300degreeC) decreased the peak efficiencies to 50 and 30 percent, respectively, for the selectively coated and black painted tubes. The experimental results establish the technical feasibility of using parabolic trough collectors for applications requiring thermal energy at temperatures up to 300degreeC.

Stationary type solar energy collector apparatus

Abstract: A hybrid collector for collecting solar energy comprised of a plurality of parabolic reflectors cooperating with tube/fin type fluid carrying collector elements, selective ones of which are arranged at the focal points of the parabolas. Additional tube/fin elements are positioned at a spaced distance above the boundary line between adjacent parabolic reflectors. The exterior surfaces of the tube/fin collector elements are treated preferably with a selective coating to provide high absorptivity and low emissivity. The surface areas of the tube/fin elements are also reduced to further contribute to a reduction in emissivity to optimize total absorptance. Location of the tube/fin elements which are off the parabolic reflector focal points cooperate with those located at the focal points to absorb diffuse energy while the tube/fin elements at the focal points absorb beam energy providing for both absorption of beam energy on clear sunny days and absorption of diffuse energy on cloudy or overcast days. The positioning of the tube/fin collectors well above the reflectors takes advantage of convection currents to increase energy transfer by reduction of energy loss. The structure provides the above functions through a fully stationary mounting. The parabolic reflector structures comprise flexible reflector sheets mounted within supporting troughs which are adapted to slideably receive the reflective sheets and urge the sheets into perfect parabolic configurations due to the geometry and interrelationship of the troughs and the reflective sheets, yielding a perfect parabolic reflector produced in an inexpensive manner.

Bent Glass Optics

Abstract: The paper describes how a glass strip may be bent to match any curve of large radius of curvature, to a high degree of accuracy, so that it may be used as a glancing incidence X-ray or extreme ultraviolet optical element. The desired match is obtained by applying a suitable combination of end couples and adjusting the cross-sectional moment of inertia along the length of the strip by varying its breadth. Two applications are described; a parabolic reflector for use as a laboratory X-ray collimator for testing mechanical collimators to be used in space instruments, and an elliptical reflector for point-to-point focussing. The latter device has been used for testing gratings in the X-ray and extreme ultraviolet (EUV) regions and for concentrating radiation on the entrance slit of a spectrometer, with a resultant gain in speed and resolution. It is suggested that the technique may have other laboratory and space applications, which are briefly described.

Laser air-breathing jet engine

Abstract: A report is given of a theoretical and experimental study of the problem of vehicle propulsion in the earth's atmosphere under the action of shock waves produced as a result of CO2-laser-induced optical breakdown of air. It is shown that there are certain optimal conditions for the transfer of pressure impulses to receivers. Conical and parabolic receivers are used as an example to show that there are maximum values of the specific impulse (also known as the coupling coefficient). The experimentally obtained specific impulse values ~500 μNsecJ–1 are close to the maximum values deduced from the point explosion theory. Realization of motion of a parabolic reflector in a glass tube is reported for a pulse-periodic regime of laser emission with an average power of ~25W. The thrust obtained is reported.

Microstrip feed with reduced aperture blockage

Abstract: A parabolic reflector is fed by a microstrip antenna supported at the focusy a tube aligned along the focal axis of the reflector. The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

Ultrasonic antenna assembly

Abstract: In an ultrasonic antenna assembly specifically adapted for use in a material level control system and of the type which includes a parabolic reflector and an ultrasonic energy source mounted at the parabolic focus and directed to radiate energy toward the reflector surface from the direction of the parabolic axis, the improvement comprising a sonic absorber of low-density fiberglass disposed at the reflector surface opposite the energy source to absorb energy directed onto said surface from said source, such that multiple reflections between the energy source and the reflector surface are inhibited. In a modified embodiment the parabolic reflector and energy source are adapted to be mounted in the upper portion of a storage tank such that the parabolic axis is substantially horizontal, and a plane reflector is disposed adjacent the parabolic reflector at an angle of forty-five degrees with respect to the parabolic axis.

Principles Of The Fixed Mirror Solar Concentrator

Abstract: A new concept for a fixed-mirror solar concentrator is described. The fixed, stepped surface of the proposed cylindrical mirror is designed to produce a sharply focused line image regardless of the incident sun direction. This is in contrast with the severe off-axis aberration (hence, poor concentration factor) of a parabolic mirror for all sun directions other than on-axis. It is shown that 1) the heat absorber follows a circular path to remain in the focus as the sun moves, 2) the annual light losses from self-shadowing of the "stepped structure of the mirror surface can amount to less than %in for appropriate mirror orientation, 3) by facing the mirror in a southerly direction in the northern hemisphere) , the winter deficit in sun input can be significantly compensated, and 4) practical concentration factors of around 50 can be achieved with a single stage of concentration, 80 with a second stage of concentration.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Equipment for detecting buried non metallic objects - uses cross correlation technique on echoes from loudspeaker at focus of parabolic reflector

Abstract: The apparatus detects inhomogeneities using echo and cross correlation technique. A loudspeaker is mounted above a microphone at the focal point of a parabolic reflector. A number of microphones and loudspeakers may be mounted in a row in a single elongated reflector, or the reflector may be of rectangular section with a resonating membrane across its face. The signal processing network produces a timed pulse modulated signal from the loudspeaker. The timing circuit gates out the directly received pulse from the detection networks which include a logarithmic amplifier. It applies a cross correlation algorithm to the transmitted and reflected signals to display any results on a display unit.

Cross-polarization in satellite and earth-station antennas

Abstract: Cross-plarization in axially symmetric reflector antennas can be reduced, theoretically, to zero by use of special feeds like the Huygens' source. Alternatively, paraboloidal reflectors with large f/D ratio do not deteriorate further the cross polarization level relative to the value due to the feed itself. The Cassegrainian optics is equivalent to a large f/D paraboloid. The reflector of linearly polarized off set fed antennas contribute more cross-polarization than symmetrical reflectors fed by the same feed. With symmetrical reflectors the cross-polarized component generated by the reflector vanishes in the principal planes and is confined to four main lobes that have peak values in planes at 45° to the principal planes. In the case of offset fed reflectors cross-polarization vanishes in the plane of symmetry and has its peak in the plane of asymmetry. The reflector generated cross-polarization with offset fed antennas may be reduced by use of small offset angles and large f/D ratios. Feed offsetting has but little effect on the peak level of cross-polarization. This is usually accompanied with an asymmetry in the cross-polarization radiation pattern. Feed offsetting also results in spatial tilt in the copolarized and cross-polarized lobes with the cross-polar minimum always coinciding with the main beam peak. The effect of surface errors on the antenna cross-polarization is to partly fill the cross-polar along boresight. The peak cross-polarization, however, changes but slightly.

Device for measuring the width of timber

Abstract: The width of a piece of timber, such as a board is measured with a device including a laser tube emitting laser beam to be reflected by a rotatable mirror polyhedron and a parabolic reflector into a direction along the board, mirror rasters being provided at intervals along the board so as to reflect laser beam pulses onto the board, each raster including a group of mirrors reflecting the beam pulses onto spots of the board that are spaced apart laterally across the board, and detecting means being provided for receiving the pulses reflected from the board surface in order to obtain information about the board width. Preferably, the pulses received by the detectors are transferred to a computer which calculates, in a manner known per se, the optimal sawing width for the board. Instead of the reflector, lens means may be used for directing the beam along the board.

Disc antenna feed for parabolic reflector

Abstract: A generally paraboloidal shaped reflector with a coaxial feedline extending outwardly along the axis thereof and a disc antenna feed mounted in spaced relation from the reflector, said feed including a first disc forming a ground plane mounted coaxially on the feedline and a second disc forming a disc radiator mounted coaxially on the feedline. The center conductor of the coaxial feedline extends outwardly through the end thereof and back through an opening in the ground plane disc to a feedpoint on the disc radiator.

Railroad crossing signal lamp

Abstract: An improved railroad crossing signal includes a deep dish parabolic reflector and an essentially flat plastic lens angled forward at the top relative to the axis of the reflector. The lens includes prism elements for laterally dispersing parallel light from the reflector more toward the crossing highway at near and far distances than toward the adjacent land. The lens also includes prism elements for vertically dispersing a portion of the light to produce uniform brightness before the signal.

Incandescent bar display module

Abstract: A bar-type display utilizing incandescent lamps stacked in a linear array in a metallic lamp block preferably of aluminum shaped to form a parabolic reflector configuration along its length and a tongue and groove configuration for attachment to an insulating connector block. Fins are provided on each side of the block for heat dissipation and grooves are formed transversely of the block through the parabolic reflector configuration at intervals into which barrier plates are inserted to sectionalize the block into separate reflectors for each lamp. To disperse the radiated and reflected light, a plastic diffuser is placed across the top of the reflector configuration, which may be colored to color the transmitted light, and to provide anti-reflective qualities for non-glare viewing. The insulator connecting block is molded to the lamp block and the lamp pins are arranged so that alternate lamps may be powered by separate power supplies for redundancy purposes.

Solar heat collector - with parabolic mirror swivelled by photocell controlled motor, around focal axis

Abstract: A solar heat collector is fitted with a cylindrical parabolic mirror in a frame which can be swivelled around the focal axis of the mirror by a photocell-controlled motor. The centre of gravity of the moving part lies in the middle of this axis. A tube, made of heat conductive material (e.g. copper) and pref. enclosed in an evacuated glass tube, which is mounted along the focal axis, has inlets and outlets for a heat absorbing fluid. The design requires very little energy for the mirror adjustment to follow the sun. Limit switches can automatically return the mirror after sunset.

Surveillance radar aerial with altitude determination - has cylindrical parabolic reflector supplied from linear source

Abstract: Azimuth scanning is carried out by rotation of the aerial, and elevation scanning is done by electronic swinging of the radiation beam produced by the linear source parallel to the cylinder axis. The linear source consists of a series of radiators. Individual radiators (4) in the radiator series are supplied by radiation from a primary radiator (2). electronically controlled phase shifters are allocated to individual radiators and they are used to focus and deflect the beam in the vertical direction.

Solar heating system

Abstract: A system for collection of solar energy by one or more reflectors which concentrate the suns rays on liquid circulating pipes which is part of a collecting and storing system for solar heated liquid to replace or supplement usual sources of heat in heating systems. More specifically, the system comprises one or more bent, preferably parabolic reflectors pivotly mounted on black heat absorbing pipes through which liquid circulates to absorb heat energy from the sun. The reflectors and the pipes are mounted in an open space such as a building roof with adjusting mechanism to pivot and fix the reflectors in different positions. Transparent plates bridge the space between the edges of the reflectors with hooked cross straps to hold the assembly together.

Projection of distributed-collector solar-thermal electric power plant economics to years 1990-2000

Abstract: A preliminary comparative evaluation of distributed-collector solar thermal power plants was undertaken by projecting power plant economics of selected systems to the 1990 to 2000 time frame. The selected systems include: (1) fixed orientation collectors with concentrating reflectors and vacuum tube absorbers, (2) one axis tracking linear concentrator including parabolic trough and variable slat designs, and (3) two axis tracking parabolic dish systems including concepts with small heat engine-electric generator assemblies at each focal point as well as approaches having steam generators at the focal point with pipeline collection to a central power conversion unit. Comparisons are presented primarily in terms of energy cost and capital cost over a wide range of operating load factors. Sensitvity of energy costs for a range of efficiency and cost of major subsystems/components is presented to delineate critical technological development needs.