rexresearch1
Richard STEENBLIK
Fresnel Spiral Reflector
Fresnel Spiral Reflector
Popular Science, 1981
Masonite and aluminum foil – that’s all Rick Steenblik, a research engineer at the Georgia Institute of Technology, needs to bring the sun into focus. Conventional point-focusing solar concentrators are paraboloid dish types. Made of metal, these complex-shape reflectors must be prcisely molded and machines – therefore they’re expensive.
Steenblik’s simple design begins with a computer program that prints a spiral pattern. This pattern is transferred onto a flat material already covered with a reflective medium, then cut out on a band saw. By lining up mounting points (also printed by the program) along a straight frame member, the proper twist is given to each segment of the spiral to concentrate sunlight at the selected focal point. The computer program can vary the focal length of the spiral or even alter the design to focus light behind the reflector.
Nine Georgia Tech Spiral Concentrators have been built thus far. For such simple applications as solar cookers Steenblik has used as materials aluminum foil and hardboard. Other models have been made with sheet aluminum. Steenblik believes his reflector can replace parabolic concentrators in some present applications at much lower cost.
https://www.researchgate.net/publication/311475268_Numerical_modeling_of_the_conformational_transition_of_a_spiral_focusing_surface
April 1990ACM SIGSIM Simulation Digest 20(4):127-134
Numerical modeling of the conformational transition of a spiral focusing surface
Authors: Richard Steenblik, Dar-Veig Ho
Abstract
A new class of focusing reflectors was created by modeling the conformational transitions between a wound spiral focusing surface and its planar, non-focusing, unwound spiral state. Two solutions to the problem were found; one by modeling the process of unwinding the focusing spiral surface, the other by modeling the winding of the planar spiral surface. Both the mathematical derivations and the resulting equations relating the two states of the spiral surface proved markedly different for the two approaches. Implementation of each solution was accomplished by specifying the locations of marker points and tracking them through the conformational transitions. Although the mathematics and the algorithms employed are completely different between the two solutions, both result in identical sets of marker points for a given spiral. However, the solution based on the winding conformational transition is completely general, while the solution based on unwinding is limited to a narrow set of focusing geometrie
https://omnivorenz.wordpress.com/tag/steenblik/
Spiral Fresnel Reflector (a simple solar concentrator)
Tobin Fricke has posted a PostScript program for computing the spiral:
http://nibot-lab.livejournal.com/13319.html
Tobin Fricke's Lab Notebook
spiral fresnel reflector [Apr. 9th, 2004|10:14 am]
%!
% Postscript program to draw a planar spiral that may be developed into a
% spiral fresnel lens, as described in U.S. Patent 4,350,412.
% Tobin Fricke <tobin@splorg.org> April 2004
72 72 scale % coordinate system is inches,
8.5 2 div 11 2 div translate % with the origin in the center of the page
1 setlinecap
0.001 setlinewidth
/pi 3.14159 def
/radians{180 mul pi div}def % convert to degrees
/degrees{pi mul 180 div}def % convert to radians
/x 0.75 def % these parameters define the spiral
/f 42.75 def
/max_theta 20 2 pi mul mul def
newpath
0 0 moveto
0 0.1 max_theta { % this loop does polar plotting
/theta exch def
/r % equation 1 from the patent, expressed
x theta mul % in postfix notation
x theta mul
2 pi f mul mul
atan degrees
0.5 mul
cos
2 pi mul mul
div
def
r theta radians cos mul
r theta radians sin mul lineto
} for
stroke
showpage % that's all, folks!
Now one possibility is to print this on a transparancy and then project it onto a big piece of cardboard, tracing out the projection with a sharpie. Another possibility is to print out a grid of 8"x11" sheets that can be reassembled into a giant spiral. (I could do this easily in postscript by having a loop go over each of the pages, using 'translate' to put each page at the appropriate coordinates in the plane). ..
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to Fresnel reflectors and more specifically to spiral Fresnel reflectors.
2. Description of the Prior Art
There is a great need, particularly in the poor third world countries, for an inexpensive solar cooker which can cook food without the necessity of using valuable fuel. Traditionally, solar cookers have been in the form of paraboloids or hemispheres. However, such shapes are difficult to manufacture and in order to keep their shape they must be formed from metal, fiberglass or hard plastic. All of these materials are expensive and the forming processes for these materials are expensive. As a result, the finished cooker is also expensive. Further, such shapes are bulky and require a disproportionate amount of space when shipped. Since shipping volume is expensive, the cost is again increased.
A Fresnel Reflector is a reflector made from a flat sheet of material and having concentric rings which have an identical focal point. The use of a Fresnel reflector as a solar cooker would be advantageous since all of the parts of the Fresnel reflector could be cut from one sheet of material and there would be no complex three dimensional shapes to manufacture; the Fresnel reflector could be made out of inexpensive materials such as aluminized cardboard or aluminized plastic; and the assembled reflector would have a very low profile and would be easy to transport and store. A concentric ring Fresnel reflector is disclosed in "Compact Solar Energy Concentrator" by Robert W. Hosken in Electro-Optical Systems Design, January 1975, pages 32-35. However, the Fresnel reflector described in this article provides rings which are machined into a blank of solid material. Therefore, a high degree of precision is necessary is machining the rings into the blanks with a resulting relatively high cost of manufacture.
A Fresnel reflector using separate concentric rings has been proposed in the past (for example, "EVALUATION OF SOLAR COOKERS" by Volunteers for International Technical Assistance for the U.S. Department of Commerce, Office of Technical Services). However, such a Fresnel reflector using concentric rings has several disadvantages. Each ring of the Fresnel reflector must be assembled and mounted separately, a time consuming task. Further, each reflector is composed of many separate parts. Since each ring is a separate part, there are many parts which can be misplaced or damaged.
An inexpensive, easily transportable, Fresnel reflector would also be advantageous in other areas of solar energy. For example, it could be used for low to medium temperature steam generation for producing power. It could also be used for the production of electric power by use of a Brayton or Sterling cycle generator located at the focus of the reflector. Further, direct electric power production by photovoltaic conversion would also be possible by the placement of solar cells at the focal point of the reflector. Accordingly, an inexpensive, easily transportable, Fresnel reflector would be advantageous in all areas of solar energy production.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a Fresnel spiral reflector.
It is a further object of the present invention to provide a method for making a Fresnel spiral reflector.
It is a further object of the present invention to provide a Fresnel spiral reflector having a negative focal length.
It is yet a further object of the present invention to provide a Fresnel spiral reflector which may be assembled in one simple and fast operation.
It is a final object of the present invention to provide a Fresnel spiral reflector whose reflector is composed of a single piece of material.
If a mathematically defined spiral is developed on a piece of flat material and the spiral is cut along its spiral line and "wound up" the arms of the spiral will have an angle of inclination with respect to the plane of the original sheet. The angle of inclination is proportional to the distance of the arm from the center of the spiral. It has been found that the angle of inclination of this spiral would be continuously changing so that the point on the spiral would have the proper angle of inclination so as to reflect sunlight through a focal point. The present invention therefore involves the calculation of a spiral which can be formed on a sheet of flat reflecting material and which, when "wound up" will have a predetermined focal point. The spiral can be formed so that the resulting reflector will have either a positive or a negative focal length.
Such a Fresnel spiral reflector will have all of the advantages of a concentric circle Fresnel reflector and will have the additional advantages of being quickly and simply assembled and of being composed of a single piece.
The developed spiral can be formed by using a computer program to calculate a spiral which, when wound up, will provide a predetermined maximum diameter, focal length, concentration ratio, estimated blockage, reflectivity and number of mounting rods. The computer program can then be used to plot the developed spiral which can be transferred to a sheet of reflecting material, cut out, and wound up to result in the desired reflector. The wound up arms of the reflector can be held in place by radial mounting rods whose positions can be determined by the computer program.
Alternatively, a cam can be used to plot a developed spiral on a rotating sheet, this developed spiral then being transferred to a sheet of reflecting material as with the spiral developed by the computer program.
As a further alternative, the cam could be used to plot a developed spiral on the sheet of reflecting material itself. In further alternatives, the computer program could be used to generate a tape which could be used to direct a numerically controlled machine to cut out the spiral, or a stencil could be made from the spiral pattern and the stencil could be used to mass produce identical spiral patterns.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic plan view of the spiral Fresnel reflector;
FIG. 2 is a schematic cross-sectional view of the spiral reflector of FIG. 1;
FIG. 3 is a schematic plan view of a positive focal length developed spiral;
FIG. 4 is a detail of a portion of the reflector of FIG. 2;
FIG. 5 is a schematic cross-sectional view of a negative focal length spiral Fresnel reflector;
FIG. 6 is a schematic plan view of a negative focal length developed spiral;
FIG. 7 is a schematic elevational view of a spiral Fresnel reflector reflecting coverging light rays from a plurality of mirrors;
FIG. 8 is a schematic representation of an apparatus for plotting a spiral on a sheet of material.
FIG. 9 is another embodiment of the apparatus of FIG. 8;
FIG. 10 is a plan view of a connecting rod arrangement;
FIG. 11 is a detail of the connection between one of the connecting rods and the spiral;
FIG. 12 illustrates one embodiment of the centerpiece for the connecting rods of FIG. 10;
FIG. 13 is a plot of a developed spiral produced by a computer;
FIG. 14 illustrates a frame defining an equilateral triangle grid;
FIG. 15 illustrates a frame defining a square grid;
FIG. 16 is a cross-sectional view of a type A-B conic reflector;
FIG. 17 is a cross-sectional view of a type A conic reflector;
FIG. 18 is an isometric view of the reflector of FIG. 17;
FIG. 19 is a cross-sectional view of a type P-B conic reflector; and
FIG. 20 is a cross-sectional view of a type P-A conic reflector.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a plan view of a wound up Fresnel reflector. The reflector has a projected arm width of x and the spiral is at a distance d from the center of the polar coordinate system, d varying with the angle .beta. of the spiral. The same reflector is shown in cross-sectional elevation in FIG. 2. As can be seen, the angle of inclination .phi. of each portion of the spiral reflector arm varies with the distance d of that portion of the arm from the center of the polar coordinate system. It can also be seen that the focal length of a reflected light ray which is reflected from the base of the arm portion, that base corresponding to the plotted spiral, is equal to f.
FIG. 3 is a plan view of the spiral which is developed on a flat sheet of reflecting material in such a manner that, when cut along the spiral line and wound up, the Fresnel spiral reflector of FIGS. 1 and 2 results. The developed spiral of FIG. 3 has a distance D from the center of the polar coordinate system for any angle .PSI. of the spiral. In order to develop a spiral on a flat sheet of reflecting material having a desired projected arm width x and diameter d, it is therefore necessary to calculate what D and .PSI. corresond to a wound Fresnel spiral reflector having a projected arm width x, and a diameter d at a wound angle .beta.. ##EQU1##
The above equation (1) relates the distance D of the developed spiral to the desired focal length and the desired arm width at a wound up angle .beta.. ##EQU2##
In the above equations, (2) relates the angle .PSI. of the developed spiral to the desired projected arm width and the desired focal length for any wound up spiral angle .beta.. Therefore, a developed spiral can be plotted for any desired resulting spiral Fresnel reflector having a predetermined projected arm width, focal length and wound up maximum diameter.
The above equations, however, only relate to the inner most edge of a portion of the spiral arm since it is that edge which is defined by the spiral according to the above equations. However, the maximum concentration ratio is not located at the focal point of light striking the bottom of each portion of the arm but at the focal point ff of the light striking the radial center of each portion of the spiral arm. As can be seen in FIG. 2, it is at the focal length ff that the focal area is at a minimum (mw) and it is at this minimum focal width that the concentration of energy is greatest. Therefore, it is desirable to relate a developed spiral to the concentration ratio within the minimum focal width at the focal length ff. The relation between f and ff is found from equation (3). ##EQU3##
The minimum width (mw) from equation 3 can be found according to equation (4): ##EQU4## G is percentage of blockage .rho. is reflectivity of the material
CR is concentration ratio
The percentage of blocking (G) from equation (4) is most easily understood from FIG. 4. FIG. 4 shows a close up of the cross-sections of two portions of a spiral arm. It can be seen from FIG. 4 that the light rays 1 reflected from each portion of the spiral arm 2 may be partially blocked by an adjacent portion of the spiral arm. The percentage of the blocked area 4 is represented by (G). The concentration ratio (CR) of equation 4 is simply the ratio, expressed in terms of "suns" by which the energy of the sun is multiplied within the minimum focal width (mw).
Further, the projected arm width is not a parameter which one would normally be initially aware of in order to produce a reflector having certain characteristics. The projected arm width can be found from equation (5) once (mw) and (ff) are found: ##EQU5##
Therefore, the above equations provide a complete description of a developed spiral given an input of the maximum desired diameter, the desired focal length, the desired concentration ratio, the desired estimated blockage and the reflectivity of the reflector. An appropriate computer program can then find the minimum focal width (mw) for the outermost point of the spiral from equation (4), the projected arm width x from equation (5) and the focal length of the inner edge of each point in the spiral f from equation (3). From these parameters, the developed spiral can be plotted from equations (1) and (2).
An additional equation which may be useful in plotting the developed spiral is the equation relating the change of the diameter of the wound up spiral to the angle .beta.. Such a relationship is expressed by equation (6): ##EQU6##
The above equations describe a spiral Fresnel reflector having a positive focal length as seen in FIG. 2. FIG. 5 schematicaly illustrates a spiral Fresnel reflector having a negative focal length while FIG. 6 illustrates a developed negative focal length spiral which may be plotted on a flat sheet of reflective material. As can be seen from FIG. 5 which is a cross-sectional view through a wound up spiral, the focal point of the reflected light in a negative focal length spiral Fresnel reflector is on the opposite side of the reflector from the incoming light. Further, the angles that the spiral arms 2 make with the horizontal plane are much greater than those of a positive focal length reflector. Further, as can be seen from FIG. 6, a negative focal length reflector must be wound in a direction opposite to that of a positive focal length reflector so that the outer coils of the developed spiral become the inner most coils of the wound spiral reflector. The developed spiral for the negative focal length Fresnel spiral reflector can be developed in a method similar to that for the positive focal length reflector except that equations 1, 2 and 6 are respectively replaced by equations 7, 8 and 9 below: ##EQU7##
Although the spiral Fresnel reflector will typically be used to concentrate the direct rays of the sun, and the above equations provide a spiral reflector for so concentrating parallel rays, the spiral Fresnel reflector can also be used as a secondary reflector for concentrating converging rays, as for example the rays reflected from a field of mirrors. FIG. 7 is a schematic representation of a spiral Fresnel reflector 2 located between a field of reflecting mirrors 6 and the apparent focal point F of the field of mirrors. The Fresnel spiral reflector 2 is located at a height H from the field of mirrors and the apparent focal point F of the field of mirrors is at a height F from the field of mirrors 6. A spiral Fresnel reflector which will concentrate the converging rays at desired focal point DFP can be formed from a developed spiral plotted from the above equation (2) where f is found from the following equations (10) and (11): ##EQU8## Therefore, using equations (10) and (11), one need only preselect the desired heights H and F as well as the other desired parameters such as the maximum desired diameter, focal length, concentration ratio, estimated blockage and the reflectivity of the reflector in order to plot a developed spiral which may be wound up to form a spiral Fresnel reflector usable with converging light rays.
An alternative method of plotting the developed spiral for the spiralFresnel reflector is by use of the apparatus shown in FIG. 8. FIG. 8 illustrates a schematic representation of a mechanical device for plotting a developed spiral. A piece of flat reflective material 10, or a stencil, is position for rotation about axis 12. The axis 12 is supported for rotation on rigid guide 14 and includes a pinion 16. The pinion 16 meshes with a rack 18 connected to cam 20 which guides pin 22 against the reaction force of spring 24. Therefore, when material 10 is rotated in the direction 26, or when cam 20 is moved in the direction 28, the rotation of the material and the movement of the pin 22 due to the cam 20, cause the pin to describe the spiral 30 on the material 10. The shape of the cam 20 can be predetermined based upon the equations. This method for developing the spiral is useful when a large number of identical spirals are to be produced.
Once the developed spiral is plotted, the developed spiral may be transferred to a sheet of flat reflective material such as aluminized flexible plastic or aluminized mylar bonded to low molecular weight polyethylene or any other reflective sheet material. The developed spiral can also be plotted directly onto the reflective material. Once the developed spiral is plotted on the reflective material, the reflective sheet is cut along the spiral line.
Other material which may be usable for the spiral Fresnel reflector are masonite (such as 1/8" thick masonite) having aluminum foil glued to one side, thin aluminum sheet and cardboard having an aluminum foil reflective surface.
Once the developed spiral has been cut, it is necessary to wind up the developed spiral in order to result in the spiral reflector. In the case of a positive focal length Fresnel spiral reflector, the outermost portion of the spiral arm of the developed spiral is placed at a fixed distance from the center of the spiral and the center of the spiral is wound up. In the case of a negative focal length spiral Fresnel reflector, the innermost end of the developed spiral is placed at a fixed distance from the center of the spiral reflector and the outermost end of the developed spiral, which is the innermost end of the spiral Fresnel reflector, is wound up. The degree of winding determines the angle of inclination of the arms of the spiral, and therefore determines the focal length of the resulting reflector. It is therefore possible to make minor changes in the focal length by performing minor adjustments upon the degree of winding up the arms of the spiral reflector.
Another version of the apparatus for plotting the developed spiral of FIG. 8 may be seen in FIG. 9. This device is useful for forming large reflectors of varying diameters. The blank sheet 10 is fixed for rotation on axis 32 which includes bevel gear 34. Bevel gear 34 meshes with bevel gear 36 which is mounted on splined shaft 38 for axial movement only. Bevel gear 40 is mounted on the other end of splined shaft 38 and meshes with bevel gear 42 which is mounted on axis 44 together with pinion 46. The axis 44 is fixed by guide pin 48. Pinion 46 meshes with rack 50 attached to cam 52. Cam follower 54 of linkage 56 is guided by cam 52 against the reaction force of spring 58 as the cam 52 is moved. This results in the movement of pin 60 which describes spiral 62 in a manner similar to the device of FIG. 8. The pinion gears 36 and 40 can move along splined shaft 38 so as to accommodate spirals of different sizes.
Once the developed spiral is wound into the resulting spiral Fresnel reflector, it is necessary to stabilize the arms and maintain them in their proper position with the desired amount of winding. Preferably, this may be done by the use of radial connecting arms which radiate from the center of the spiral and attach to the arms of the spiral at radial points. Such radial arms 70 may be seen in FIG. 10. The spiral arms 2 may be attached to the connecting arms 70 at attachment points 72. Although four connecting arms are shown in FIG. 10, any number can be used.
According to a preferred method, the attachment points may be plotted on the developed spiral and the Fresnel spiral reflector may be wound up from the developed spiral simply by the attachment of the attachment points 72 to their appropriate connecting arms 70. The plotting of the appropriate attachment points on the developed spiral may be done by determining the number of connecting arms to be used, calculating the angle .beta. between the connecting arms, and utilizing equation 2 or 8 to calculate the angle .psi. on the developed spiral for each connecting point.
The connection of the spiral arms 2 to the connecting rods 70 at the connecting points 72 must be done in such a way that the spiral arms are not distorted at the connection points. According to a preferred embodiment, this may be done by creating two holes 74 in the innermost portion of the spiral arms at each connecting point. A U shaped length of aluminum or stainless steel wire may then be slid through the holes so that the base of the U connects the two holes as shown in FIG. 11. The arms of the U which extend past the bottom of the connecting rod may then be bent inwards as shown at 76 in FIG. 11. This provides a pivot for the spiral arm to pivot about its innermost edge.
FIG. 10 shows the connecting rods as being formed of a single piece of material. Alternatively, the connecting rods may be fixedly attached to a separate center piece 80 at 82 as shown in FIG. 12. The center piece may include a central bore 84 in which may be positioned a dowel plug 86 and turning handle 88. The end of the developed spiral may be placed in the dowel plug 86 and the dowel plug 86 turned for winding up the developed spiral into the spiral Fresnel reflector. Using such a technique, one end of the developed spiral is fixed a predetermined diameter from the dowel plug while the other end is inserted into the dowel plug and wound until the fixing points 72 are aligned with their appropriate connecting rods 70.
The center piece need not include a central bore and dowel. In such a case, the spiral may be wound up by first attaching the outermost point of the spiral to one of the connecting rods. The spiral is then wound at its next innermost strip until its fixing point falls into line with the connecting rod and this fixing point is then fixed to the connecting rod. The winding is continued and succeedingly inner arms of the spiral are attached to the connecting rod along a radial line reaching the center of the spiral, and then outwards to the opposite edge. Once a full diameter of the spiral has been fixed to the connecting rods, the other fixing points are mounted.
The frame for stabilizing the wound spiral need not be in the form of radial connecting arms but, rather, may be in the form of a frame defining a grid. Such a grid would be easier to manufacture and have greater strength the the radial arm frame arrangement.
One form of such a grid is shown in FIG. 14. This is a grid compose of equilateral triangles. The arms of some of the equilateral triangles form intersecting rods 90 which could be the primary mounting points for the spiral. The spiral could also be attached at other mounting points where it crosses the grid.
A second form of grid is illustrated in FIG. 15. This is a grid composed of a plurality of squares. The grid has a center point 100 from which radial rods 102, which are defined by the arms of some of the squares, extend. The spiral could be mounted at fixing points 104 to these radial arms, as well as to other points on the grid where the edge of the spiral crosses the grid. Other grid shapes are, of course, also possible.
EXAMPLE
It was desired to construct a spiral Fresnel reflector having a radius of 22.5", a focal length of 42.75", a maximum theoretical concentration ratio of 1000 and 8 mounting arms. These parameters were introduced into equations 1-6 which provided an arm width of 1.078", a flat radius of 23.175" and a minimum focal width of 1.21". A computer was used to plot the above developed spiral as shown in FIG. 13. The spiral was cut along its spiral line and holes for the mounting wire were cut into the spiral. The connecting arms were then constructed which were made from square tubing connected at a central point to a plywood center piece by square nuts and washers. The spiral arms were then connected to the connecting rods by the wires 76 as described above. The resulting apparatus was tested at 5:00 in the afternoon on a sunny day and a concentration ratio of 500 suns was measured.
The wound spiral need not be in the form of a flat plane. The wound Fresnel reflector can also be in the form of a hollow cone or a hollow truncated cone. This may be done by providing a frame in the form of a hollow cone or the frustum of a cone. As with the flat spiral Fresnel reflector, the spiral could be cut from a single sheet of flat material and wound up onto the conical frame. The angle of inclination of any point on the wound conic spiral would be set so as to reflect light through a chosen focal point f.
There are at least four different types of conical spiral Fresnel reflectors possible. A first type of conical reflector has an entirely conic support frame having a frame angle .tau. which is greater than the angle of inclination of the spiral arm at a given radial point. This is referred to as a type (A) reflector. Such a type (A) reflector is shown in FIG. 17. As seen in FIG. 17, which is a cross-sectional view through the reflector, the angle of inclination of the arms at any point is less than the angle of inclination .tau. of the frame up to the transitional point T. Therefore, the arms are fixed to the frame at their outermost radial point. If the reflector were to continue radially outwards beyond the transitional point T, the angle of inclination of the arms would be greater than the angle .tau.. This portion of the reflector would be a type (B) reflector.
FIG. 16 shows a conical spiral Fresnel reflector which is a combined type (A) and type (B) reflector. As can be seen in FIG. 16, the reflector extends radially outward beyond the transitional point T where the angle of inclination of the spiral arms is greater than the angle .tau.. In such a type (B) portion of the reflector, the arms are fixed to the frame at their radially innermost edges.
It should be noted that in a pure type (A) conical reflector, the transitional point T need never be reached. That is, the reflector may terminate radially at a point short of the point where the angle of inclination of the reflector arms equals the angle .tau.. In the case where the outermost arm of the spiral does have an angle of inclination which equals the angle .tau., so that the transitional point is reached, the outermost arm may be fixed flat to the support arm. Such an arrangement is shown in FIG. 18. In this Figure, the frame is in the form of a plurality of radially extending rods 112 having a quadrilateral cross section. The arms of the spiral are secured at fixing points 114 located at the outermost edges of the spiral arms. As can be seen at 116, the outermost arm of the spiral, which is at the transition point, is secured at both its innermost and outermost edges.
The type (A) reflector will have no blockage or shadowing of one portion of the reflector arm by the radially inwardly adjacent portion of the arm. However, since the effective focal length of the strips decreases as the strips move out from the center and up the conical support frame, the light reflected from the outer strips impinges on the focal plane at shallower angles. This increases the focal spot diameter, thereby reducing the concentration ratio obtained.
Where a portion of a conical spiral Fresnel reflector is planar (that is, in the truncated portion of a truncated cone), this planar type is referred to as a type (P) reflector. FIG. 19 illustrates a combined type P-B reflector in which the radially innermost portion of the frame is planar and the remainder of the frame is conical but with an angle .tau. which is less than the angle of inclination of the spiral arms at the radial distance of the conical frame. In such a P-B reflector, the support frame changes from the planar support to the conic support at the transition point T. As seen in FIG. 19, the angle .tau. is equal to the angle of inclination of the spiral arm at the transition point T.
A fourth type of conical spiral Fresnel reflector is the type "P-A" shown in FIG. 20. In this type of reflector, the angle T is such that the transition point is not where the planar frame changes to the conic frame, but at, or beyond, the outermost radial point of the spiral arm. A second type of transition point T1 occurs where the planar frame intersects with the conic frame section. As can be seen from FIG. 20, in the (P) portion of the reflector, the spiral arms are fixed to the frame at their innermost edges. At the (A) portion of the reflector, the spiral arms are fixed to the frame at their outermost edges. This second type of transitional point T1 occurs where both the innermost edge and the outermost edge of the spiral arm contact the frame adjacent the intersection of the planar and conic sections thereof.
It is important to note that the outer arms of the type (P), or planar, spiral Fresnel reflector experience the greatest blockage and contribute the most to the total area of the reflector. The type P-A reflector eliminates blocking entirely for those spiral arm portions which are attached to the conic frame portion, that is, the outermost arms. This will tend to increase the concentration ratio obtained by the type P-A reflector over that obtained by a type (P) reflector having the same diameter, focal length and projected arm width. On the other hand, the outermost strips of the P-A reflector will be at a higher angle of inclination than those of similar type P reflector. This will tend to enlarge the minimum focal width for the type P-A reflector, reducing the concentration ratio obtainable. Therefore, the type P-A conic Fresnel reflector includes aspects which increase the obtainable concentration ratio as well as other aspects which decrease the obtainable concentration ratio. With the proper selection of design parameters, it is possible for one skilled in the art to optimize the type P-A reflector so that the obtainable concentration ratio is maximized.
Related:
Light-guide solar energy concentrator -- US8885995B2/
[ PDF ]
Abstract
A light-guide solar concentrator that requires less precision to assemble and manufacture than some other two-layer solar concentrators has a light-condensing layer and an optical waveguide layer. The light-condensing layer includes a plurality of focusing elements for focusing incident sunlight and a plurality of corresponding collimating elements for collimating the light for output to the optical waveguide layer. The optical waveguide layer receives the collimated light and has a plurality of deflectors for redirecting the light for lateral transmission through the optical waveguide layer toward an exit surface. A secondary optic optically coupled to the exit surface can also be provided to redirect the light toward a light collection area where a solar energy collector can be placed to harvest the concentrated sunlight.
https://history.gtri.gatech.edu/files/media/ees-report/EES_Report_1980_11.pdf
https://history.gtri.gatech.edu/innovations/adding-three-dimensions-innovation
Adding three dimensions to innovation
Former Engineering Experiment Station Research Engineer Richard Steenblik developed a three-dimensional vision technique in the late 1970s and early 1980s. This technique is used today in the production of a popular commercial optical film product used in certain 3D glasses.
ChromaDepth 3D uses pieces of microptic film to selectively shift the points at which different colors of light are focused. Known as chromostereoscopy, the technique makes objects of different colors appear to be at varying distances from the viewer.
Steenblik's discovery came after he noticed slight three-dimensional effects produced by a video game. The effect was caused by an imperfection called chromatic aberration in the lenses of the eye. Also, Steenblik knew the brain expects that red color often comes from objects close to the viewer, while blue tends to come from objects far away.
He worked to enhance the effect and concluded that passing light through two different liquids would provide the necessary shifting or refraction. In his first prototype, he used two liquids of Chinese cinnamon oil and glycerin. The liquids provided the opposing refraction needed to produce right-eye and left-eye views from the same two-dimensional image.
Steenblik patented the discovery in 1983. He soon thereafter founded Atlanta-based Chromatek Inc. with New York businessman Frederick Lauter. The company owners then developed 3D glasses based on double prisms rather than liquids, but they did not work as well as Steenblik hoped.
Collaboration with binary optics scientists at the Massachusetts Institute of Technology (MIT) led to the inexpensive manufacture of the complex prism patterns needed to produce the three-dimensional effect. The new product debuted in 1992. Georgia Tech licensed the technique to Chromatek, while MIT licensed the binary optics technology to the company.
https://worldwide.espacenet.com/searchResults?compact=true&page=0&AB=&ST=advanced&PR=&IN=Steenblik+Richard&rnd=1740011760292&locale=en_EP&AP=&PA=&PD=&TI=&CPC=&IC=&DB=EPODOC&PN=
44 results found in the Worldwide database for: Steenblik Richard as the inventor
1. MICRO-OPTIC SECURITY AND IMAGE PRESENTATION SYSTEM -- ES2946765 (T3) 2023-07-25
2. A TAMPER INDICATING OPTICAL SECURITY DEVICE -- ZA201200509 (B) 2022-03-30
3. SINGLE LAYER IMAGE PROJECTION FILM -- ES2860910 (T3) 2021-10-05
4. IMAGE PRESENTATION AND MICRO-OPTIC SECURITY SYSTEM -- ES2794076 (T3) 2020-11-17
5. MICRO-OPTICS FOR ARTICLE IDENTIFICATION -- DK1476782 (T3) 2020-08-17
6. OPTICAL SYSTEM DEMONSTRATING IMPROVED RESISTANCE TO OPTICALLY DEGRADING EXTERNAL EFFECTS -- ES2731671 (T3) 2019-11-18
7. Sistemas de imagenes opticas sinteticos, sistema de presentacion de imagen y sistema micro-optico para formar imagenes de elementos de icono de microestructuras. -- CL2007003350 (A1) 2009-07-03
8. MICRO-OPTIC SECURITY AND IMAGE PRESENTATION SYSTEM -- BRPI0713906 (B1) 2018-06-05
9. sistema de apresentação de imagem e de segurança microóptica ---= BRPI0520898 (B1) 2017-09-12
10. Micro-optic security and image presentation system -- TW200643469 (A) 2006-12-16
11. SINGLE LAYER IMAGE PROJECTION FILM -- US2016101643 (A1) 2016-04-14
12. Micro-optic security and image presentation system -- AU2015207918 (A1) 2015-08-20
13. MICRO-OPTIC SECURITY AND IMAGE PRESENTATION SYSTEM -- CA2812971 (A1) 2005-06-09
14. Micro-optic security and image presentation system -- AU2013204903 (A1) 2013-05-16
15. Micro-optic security and image presentation system -- AU2013204884 (A1) 2013-05-16
16. Image presentation and micro-optic security system -- AU2013204845 (A1) 2013-05-16
17. Micro-optic security and image presentation system -- AU2013204869 (A1) 2013-05-09
18. A tamper indicating optical security device -- TW201206721 (A) 2012-02-16
19. Micro-optic security and image presentation system -- TW200902339 (A) 2009-01-16
20. Image presentation and micro-optic security system -- ZA200710725 (B) 2008-12-31
21. Merchandising Systems, Methods of Merchandising...
-- US2009173654 (A1) 2009-07-09
22. Merchandising Systems, Methods of Merchandising... -- US2009173653 (A1) 2009-07-09
23. Merchandising Systems, Methods of Merchandising... -- US2009172978 (A1) 2009-07-09
24. MERCHANDISING SYSTEMS, METHODS OF MERCHANDISING, AND POINT-OF-SALE DEVICES COMPRISING MICRO-OPTICS TECHNOLOGY -- WO2007081862 (A2) 2007-07-19
25. Lenses and uses, including microscopes -- US2005063049 (A1) 2005-03-24
26. Apparatus for providing autostereoscopic and dynamic images -- US5359454 (A) 1994-10-25
27. Microstructured Taggant Particles, Applications and Methods of Making the Same -- US2008130018 (A1) 2008-06-05
28. Stereoscopic process and apparatus using diffractive optical elements -- US4717239 (A) 1988-01-05
29. Method and apparatus for selectively controlling the quantum state probability distribution of correlated quantum objects -- US6057541 (A) 2000-05-02
30. PLANAR OPTICAL WAVEGUIDE -- US2008019652 (A1) 2008-01-24
31. Stereoscopic process and apparatus -- US4597634 (A) 1986-07-01
32. Stereoscopic process and apparatus using different deviations of different colors -- US5002364 (A) 1991-03-26
33. Microstructured taggant particles, applications and methods of making the same -- US2004067360 (A1) 2004-04-08
34. Method and apparatus for selectively controlling the quantum state probability distribution of entangled quantum objects -- US6473719 (B1) 2002-10-29
35. Light control material -- US5503902 (A) 1996-04-02
36. Optical image encryption and decryption processes -- US5715316 (A) 1998-02-03
37. Fresnel spiral reflector and method for making same -- US4350412 (A) 1982-09-21
38. Apparatus for enhancing the brightness of an image and method of making the same -- US5475533 (A) 1995-12-12
39. CONTROLLING CORRELATED QUANTUM STATE PROBABILITY DISTRIBUTIONS -- WO9735388 (A1) 1997-09-25
40. LIGHT CONTROL MATERIAL AND METHOD FOR MAKING SAME -- WO9523710 (A1) 1995-09-08
41. Device for attaching rain shields to motor vehicle windows -- US4685718 (A) 1987-08-11
42. MEJORAS EN METODO PARA FORMAR UN REFLECTOR TIPO FRESNEL -- MX154161 (A) 1987-05-15
43. DEVICE FOR ATTACHING RAIN SHIELDS TO MOTOR VEHICLE WINDOWS -- CA1283146 (C) 1991-04-16
44. sistema de apresentação de imagem de segurança micróptica -- BRPI0503224 (A) 2007-01-23