Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
1999-03-09
2001-12-18
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S858000, C359S859000, C359S850000
Reexamination Certificate
active
06331061
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to optical devices for altering the distribution of radiant energy and, more particularly, to optical devices for altering the spatial and/or angular distribution of electromagnetic radiation between an input plane and an output plane.
An energy concentrator is an optical device for increasing, between an input plane and an output plane, the energy density of radiant energy. One instance of a concentrator is a mirror or lens that focuses incident radiation to a relatively small area in the concentrator's focal or target plane. The resulting irradiance distribution often has a peaked shape. An energy concentrator generally is designed to maximize the amount of incident radiation that is directed onto a target area. By way of example, the irradiance distribution in the focal plane of a 10 kilowatt solar concentrator is shown in
FIGS. 15A and 15B
. The peaked distribution limits the possible applications of the concentrated irradiance.
In some applications, a uniform irradiance distribution over a specified target region is desired while simultaneously maintaining as high a mean irradiance level as possible. It has been found that defocusing the concentrator, by placing the target area of interest in front of or behind the focal plane, fails to provide a uniform irradiance distribution, as shown in
FIGS. 16A and 16B
. It will be observed that, although the irradiance distribution in the focal plane exhibits a well formed peaked distribution, the unfocused beam exhibits wide intensity differences across the target area. If the target area is an absorber of the concentrated energy, it must be able to withstand extreme thermal stresses in the various highly localized regions associated with the intensity peaks in the defocused irradiance distribution. At high irradiance levels, some absorbers of interest cannot withstand these high thermal stresses. Also, it is typically inefficient to configure an absorber to accommodate these stresses.
Theoretically, a long tube having a highly reflective inner surface, when a nonuniform irradiance distribution is input at one end, can output a uniform irradiance distribution at the other end. However, the use of such a tube is largely impractical because of the long length required and because of large reflective losses due to the multiple reflections occurring in the tube.
Accordingly, there is a need for a relatively compact device having a reflective surface that distributes, in a predetermined manner, the irradiance from a radiation source over a predetermined target area. The present invention satisfies this need.
SUMMARY OF THE INVENTION
The present invention provides a relatively compact reentrant optical guide that redistributes electromagnetic radiation to achieve a desired irradiance distribution. One embodiment of the invention is a method of altering the spatial and/or angular distribution of electromagnetic radiation. An optic is configured to have an input region, an output region, and a reflective surface. At least some electromagnetic energy incident at the optic's input region is output to the optic's output region. A portion of the output electromagnetic radiation has no interaction with the reflective surface. At the optic's output region, the energy distribution of the output electromagnetic radiation is determined in order to shape the reflective surface such that the distribution of output electromagnetic radiation having at least one interaction with the reflective surface overlays the distribution of output electromagnetic radiation having no interaction with the reflective surface to achieve, at the output region, a desired distribution of electromagnetic radiation.
In a more detailed feature of the invention, the output electromagnetic radiation interacting with the reflective surface is reflected at least once by the reflective surface. Further, the reflective surface may have a reentrant or a multiply reentrant shape.
In another more detailed feature of the invention, the input region is defined by an entrance aperture, the output region is associated with an exit aperture, and the reflective inner surface is an inner surface that is disposed between the entrance aperture and the exit aperture. Further, the reflective inner surface is rotationally symmetrical about a central longitudinal axis and may have a continuously varying cross-sectional radius.
In yet another more detailed feature of the invention, the step of determining is performed using a predetermined target area located in the output region and spaced away from the exit aperture, and the step of shaping the reflective surface achieves, across the target area, an arms irradiance deviation between 1% and 20%.
An alternative embodiment of the present invention is a reflective apparatus for receiving incident electromagnetic radiation from a radiation source providing a nonuniform irradiance distribution and redistributing the radiation onto a predetermined target area. The reflective apparatus has an entrance aperture configured to receive the incident radiation from the radiation source, an exit aperture configured to transmit radiation toward the target area, and a reflective inner surface disposed between the entrance aperture and the exit aperture and configured to increase the uniformity of the irradiance distribution in the target area.
In a more detailed feature of the present invention, the inner reflective surface is rotationally symmetrical about a central longitudinal axis and has a continuously varying cross-sectional radius. A substantial portion of the incident radiation received through the entrance aperture is transmitted through the exit aperture toward the target area such that, when compared with the arms irradiance deviation of the incident electromagnetic radiation, the rms irradiance deviation across the target area for any radiation received in the target area from the exit aperture is improved. More specifically, the rms irradiance distribution is improved by more than 10%.
In another more detailed feature of the invention, the entrance aperture has a radius that is greater than the radius of the exit aperture and at least a portion of the reflective inner surface has a radius that is greater than the radius of the entrance aperture. Additionally, a portion of the reflective inner surface may have a radius that is less than the radius of the exit aperture. Also, another feature is that the reflective inner surface can cause a portion of the radiation received by the entrance aperture to incur multiple reflections.
In yet another detailed feature of the invention, the reflective inner surface adjacent the entrance aperture has an increasing cross-sectional radius, in a direction along the axis from the entrance aperture to the exit aperture, providing that the entrance aperture with a flared opening. Also, the reflective inner surface adjacent the entrance aperture has an increasing cross-sectional radius, in a direction along the axis from the exit aperture to the entrance aperture, providing the entrance aperture with a flared opening. In operation, the irradiance redistribution guide, configured in accordance with the present invention, could be used with a target that is rotated about a longitudinal axis.
Other features and advantages of the present invention should become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
REFERENCES:
patent: 3899672 (1975-08-01), Levi-Setti
patent: 3923381 (1975-12-01), Winston
patent: 4270840 (1981-06-01), Cobble
patent: 5016995 (1991-05-01), Pullen
patent: 5237170 (1993-08-01), Shatz
patent: DD-0232561-A (1996-01-01), None
patent: WO-9007800 (1990-07-01), None
W.T. Welford & R. Winston; High Collection Nonimaging Optics; Dated 1989; pp. 47-88, 105-111,171-187.
Bortz John C.
Shatz Narkis E. I.
Science Applications International Corporation
Sidley Austin Brown & Wood
Sikder Mohammad
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