OPTICAL REFLECTOR ARRAYS AND APPARATUS USING SUCH ARRAYS

Abstract: An energy directing device, for use with all forms of energy having a wave-like propagation mode, consists of an array of reflecting elements. The reflecting elements are either planar reflecting strips (12, 52, 92) or channels (32) with an internal surface (or internal surfaces) which is (are) reflecting. A surface called the "surface of curvature" of the array - which may differ from the enveloppe of corresponding points on the elements of the array - is orthogonal to the plane of each reflecting strip, or to the axis of each internally reflecting channel. The arrays may be used to concentrate, to deflect, or to otherwise direct incident radiation. Applications of the invention include solar radiation concentrators, light wells for buildings, beam splitters, and ultrasonic lenses.

Description: TITLE: "OPTICAL REFLECTOR ARRAYS AND APPARATUS USING SUCH ARRAYS" Technical Field This invention concerns arrays of reflecting elements for focusing, collimating or directing wave-structured energy, such as electromagnetic radiation and acoustic radiation. It also concerns various forms of apparatus which utilise such arrays of reflecting elements, including (but not limited to) improved solar energy collectors, skylights for buildings, desk-illuminators, beam splitters, radar receivers and transmitters, ultrasonic lenses, and underwater sonic energy detectors or hydrophones. Background Art Reflecting surfaces, or mirrors, have been used for many years to focus, or to direct, radiant energy which has a wave-like structure. Parabolic mirrors, for example, have been used in solar water heaters. Examples of such solar energy concentrating arrangements are found in the specifications of US patents Nos 4,137,897 and 4,195,620. It is also known to use arrays of mirrors or reflectors, collectively aimed, to simulate a large aperture collector (examples being the "Mills Cross" Molonglo Radio Telescope, near Canberra, Australia, the Californian mirror-field of part-parabolic reflectors which focuses solar radiation onto a tower-mounted solar absorber, and the systems described in the specifications of US patents Nos 4,148,301, 4,387,574 and 4,572,160). SUBSTITUTE SHEET It is recognised that such arrays of reflectors - and equipments using a single reflector - have drawbacks. For example, in the case of solar water heaters, there is the obstruction of incident radiation by the tubular heat absorbing element, which is positioned at the focus of a parabolic mirror. However, the generally held opinion is that such drawbacks cannot be overcome, and thus the design of the equipment should aim to minimise their effect. Lenses have also been used to direct solar energy (see, for example, the specifications of US patents Nos 3,986,021 and 3,991,741) It is also known that an array of internally reflective channels can function, in a limited way, in a manner similar to a lens. Michael F Lund, in his paper entitled "Animal Eyes with Mirror Optics", which was published in Scientific American, Volume 239, pages 88 to 99, 1978 describes how a hemispherical array of internally reflective channels is used to focus light on receptors in the eyes of macruran crustaceans (such as lobsters, crayfish and prawns) - a discovery first made by Klaus Vogt and reported in 1975. The only utilisation of this discovery known to the present inventor is the use of arrays of internally reflective micro-capillaries to focus and collimate x-ray and neutron beams. Such multi-channel arrays are described in the specifications of International patent applications Nos PCT/AU87/00262 (WIPO Publication No WO 88/01428) and PCT/AU91/00530 (WIPO Publication No WO 92/09088). The former of these specifications discloses only the use of cylindrical channels and flat SUBSTITUTE SHEET plate geometries (including a curved array of flat plates) for focusing x-ray and neutron beams. The latter describes the use of capillary channels with internal reflecting surfaces which have rectangular (preferably square) cross-sections and various orientations. Disclosure of the Present Invention It is an objective of the present invention to provide improved energy-directing devices which utilise arrays of optically reflecting elements (in some instances in the form of arrays of internally reflecting channels) for general application to the focusing, direction or collimation of energy which propagates as transverse waves (for example, electromagnetic radiation or surface waves) or as longitudinal waves (for example, acoustic waves) in a wide spectral range. In the electromagnetic spectrum, the spectral range extends from the vacuum ultra-violet to radio frequencies, including ultraviolet, visible, infra-red and microwave radiation. According to the present invention, there is provided an energy directing device for energy which has a wave-like propagation mode, said device comprising an array of reflecting elements, said array having a surface of curvature (as hereinafter explained), all of the elements of the array being positioned with their reflective surfaces substantially orthogonal to the surface of curvature. In most applications of the present invention, the array will be a curved array, with the surface of curvature of SUBSTITUTE SHEET the array parallel to the envelope of corresponding points of the elements of the array. However, the array may be a flat array (or have any other required shape) with the orientation of the reflective surfaces of the array defining its "surface of curvature". If the device of the present invention is to be used to focus radiating energy to a point, it is preferable that the reflecting elements of the array are internally reflecting channels which have a rectangular cross-sectional shape (a square is a special case of a rectangle). The channels may contain a medium having a refractive index which is greater than 1.0. For a better understanding of the present invention, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is a ray diagram showing how a collimated beam of radiation (for example, light from a distant source) can be brought to a focus by a circularly-curved convex array of flat mirrors. Figure 2 is a ray diagram showing how a collimated beam of radiation is spread from a virtual focus by a circularly-curved concave array of flat mirrors. Figure 3 illustrates a flat array which has a surface of curvature (as this expression is used in this specification) which are equivalent to that of the arrays illustrated in Figures 1 and 2. SUBSTITUTE SHEET Figure 4 shows an arcuate array of planar mirrors, in which the envelope of corresponding points on elements of the array is not the surface of curvature of the array. Figure 5 is a schematic diagram of an arcuate two-dimensional array of square-section channels having reflecting internal surfaces, which illustrates the geometric principles upon which the present invention is based. Figure 6 is a schematic sectional view of a solar collector, which utilises a cylindrical array of elements, constructed in accordance with the present invention. Figure 7 is a cross-sectional view of a practical form of a solar water heater of the type indicated in Figure 5. Figures 8 and 9 are schematic illustrations of variations to the solar collector of Figure 5, which may be incorporated into the solar water heater of Figure 6. Figures 10 and 11 are schematic illustrations of skylights which incorporate the present invention. Figure 12 illustrates how the present invention may be used as a light concentrator for a desk or work bench. Figure 13 is a schematic diagram showing the use of the present invention to concentrate and direct heat radiation. SUBSTITUTE SHEET Figures 14 and 15 illustrate the use of the present invention as a beam splitter. Figure 16 is a schematic plan view of a hydrophone assembly utilising the present invention. F i gure 17 shows an array combination that is equivalent to a Keplerian telescope. Figure 18 shows an array combination that is equivalent to a Galilean telescope. Detailed Description of Illustrated Embodiments A lt h ough, as noted above, both lenses and reflectors have been used to direct solar energy in a desired manner, the present inventor has found no disclosure of the use o f mult i -channel "lenses" formed by arrays o f re l ecting elements in any application other than to x-radiation an d neutron beams. Possibly, this results from a failure to appreciate that an array of reflecting elements, with each element having its reflective surface orthogonal to the surface of curvature of the array, has a general application to the direction (including focusing) o f wave-like energy, and is not restricted to the specialise d area of x-radiation and neutron beams. This is, in the present inventor's opinion, a surprising situation for, in some applications, a multi-channel lens will have distinct a d vantages over conventional lenses and parabolic reflectors. Thus it is appropriate to provide an explanation of the optical features of the present invention before describing some of its useful embodiments. SUBSTITUTE SHEET Figures 1 and 2 illustrate, in two dimensions, the way in which curved arrays of double-sided planar reflecting elements, with their planar surfaces at right angles to the curvature of the envelope of corresponding points (such as the outer edges) of the reflecting elements of the array, act in the manner of a lens, in the focusing of radiant energy. Figure 1 shows a convex array 10 of seven spaced apart flat mirrors 12. The outer edges of the mirrors 12 of the convex array 10 have an envelope 19, which has a centre of curvature 16. Since the flat mirrors 12 have their reflecting surfaces at right angles to the envelope 19, the envelope 19 is also a "surface of curvature" of the array 10. For convenience, the spaces 13 between the mirrors 12 will be called "channels". Figure 1 shows how the array 10 of mirrors 12 is able to bring parallel incident rays of light 14 from a distant source, such as the sun, to a common focus 15 located behind (that is, on the concave side of) the array 10. Since the outer edges of the mirrors lie on the envelope 19, which is an arc of a circle of radius R, and centre 16, and the planes of the mirrors 12 are orthogonal to that arcuate surface, the array 10 acts like a convex refractive lens with the focus 15 located a distance %R behind the array. If the position of the distant source of radiation changes, so that the incident radiation is represented by the dotted lines 17, the angle at which the incident radiation meets the array changes (by moving off-axis upwards), and the focal point of the radiation falling on the "lens" created by the mirrors 12 will change to position 18 on a 'focal circle' of radius R. SUBSTITUTE SHEET In a similar way, it will be apparent from Figure 2 that an axial collimated beam of radiation 14a is spread by a concave array 10a of flat mirrors 12, the corresponding edges of which have an envelope (which is also the surface of curvature) 19, as if the reflected rays were diverging from a virtual focus 15a located a distance R in front of the array of mirrors 12. In this respect, the concave array acts like a simple concave spherical lens. Figure 3 shows a flat array 10b of flat mirrors 12. The mirrors are positioned in the array with their reflective surfaces at right angles to the dashed curve 39, which is the arc of a circle of centre 35 and radius R. It should be readily apparent that the flat array 10c of Figure 3 is the equivalent of the array 10 of Figure 1 in respect of radiation incident upon the array from the right of the array 10c, and is equivalent to the array 10b of Figure 2 with regard to radiation incident upon the array from the left of array 10c. The dashed curve 39 is the surface of curvature (as this term is used in this specification) of the array 10c, and the point 35 corresponds to points 15 and 15a in Figures 1 and 2, respectively. Figure 4 illustrates a curved array lOd of flat mirrors 12 which has a surface of curvature 39 that is not the same as the envelope 36 of the outer edges of the mirrors of the array. From an inspection of Figures 1, 2 and 4 it will be appreciated that, if the array 10, 10a or lOd is of cylindrical form, the channels 13 will be longitudinal SUBSTITUTE SHEET slots extending along the array in an axial direction relative to the surface of curvature of the array. These slots may be sub-divided to form shorter slots. When sub-dividing the longitudinal slots, it is preferred that the sub-division is used to produce cell-like channels having a rectangular, preferably square, cross-section, with each wall of the channels constituted by a reflective surface. If corresponding points on the reflective elements of the array 10 or 10a have a spherical or part spherical envelope, the channels could, in principle, form "great circle" slots, but in practice they will normally be cell-like channels, with reflective walls, as illustrated in Figure 5. Figure 5 depicts an array 30 of "cells", the inner edges of which have an envelope which is a portion of the surface of a sphere of radius R. The "cells" are identical and define channels 32 of square cross-section. All four internal walls of each channel 32 are reflective for multiple reflections. To explain the operation of the array illustrated in Figure 5, cartesian coordinates (X, Y and Z) have been imposed upon the array 30. The centre of the envelope of the inner edges of the cells of the array (which, in this case, is also the surface of curvature of the array) is at C, and the intended focus of radiation from a distant source which lies on the Z axis is at S. Thus the Z axis is also the optical axis of the array. A channel 32a located at (x,y) will be considered. An incident ray 34 passing through this channel and emerging as reflected ray 34a is directed SUBSTITUTE SHEET to focus S. Since this is true for all values of (x,y), all light incident from a remote source on the Z axis will be focused to a spot at S. Note that, in this drawing, the exemplary ray 34 experiences two reflections within the channel 32a; one reflection is from the "vertical" surface of the reflectors, the second reflection is from the "horizontal" reflecting surface. For a more comprehensive analysis of the geometric optics of a spherical curved array of channels having reflecting walls, in which both the axis of each channel and the plane of each wall is normal to the envelope of the inner edges of the cells of the array, reference should be made (i) to the paper by H N Chapman and A V Rode entitled "Geometric Optics of Arrays of Reflective Surfaces", which is shortly to be published in Applied Optics; (ii) to the aforementioned WIPO publication No WO 92/09088; and (iii) to the paper by H N Chapman, K A Nugent and 5 W Wilkins entitled "X-Ray focusing using Square-channel Capillary Arrays", which appeared in Review of Scientific Instruments, Volume 62, pages 1542 to 1561, 1991. The application of the present invention to solar collectors will now be described with reference to Figures 6 and 7, both of which are sectional elevations of dome-like cylindrical arrays of channels, designed to focus solar radiation onto tubes having radiation absorbing outer surfaces. Figure 6 is provided to illustrate the principle of this application of the present invention. In this drawing, an SUBSTITUTE SHEET array 50 of flat double-sided reflectors 52 surrounds an elongate array of tubes 56 which contain water. The envelope 59 of the outer edges of the array 50 is a cylinder of circular cross-section. The surfaces of the tubes 56 are located approximately at the half-radius of the envelope of the array 50. The sun's ecliptic is indicated by arc 58 and a light beam 60 is drawn for the sun near its zenith at 62. Another light beam 64 is drawn for a position (66) of the sun low in the sky. It will be seen that, whatever the position of the sun, a significant proportion of the component rays of each beam that is incident upon the array 50 will be brought to a line focus on a surface of a tube 56, determined by the angle of the sun. The beam 60 of solar radiation from the sun at its zenith position 62 is divided (for the purpose of illustration) into groups of rays according to the manner in which they are reflected (or not reflected) by the mirrors 52 of the cylindrical array. The central rays 66 (shown dashed) are essentially parallel to the reflective surfaces of the mirrors. These central rays pass through the channels or slots formed by the mirrors without deflection, to strike a tube 56 at or close to the desired focus 70 for the beam 60. The rays 68 (shown as solid lines) are reflected only once in a channel formed by the mirrors before striking a tube 56. These rays are also directed to the region of the desired focus 70 for the beam 60. The outer rays 72 of the beam 60 are reflected twice within a channel formed by the mirrors and are not focused at 70. As shown in Figure 6, some of these rays 72 may fail to strike a tube 56. SUBSTITUTE SHEET However, some of these outer rays 72 (see illustrated ray 74) will be reflected three times within a channel and such rays will be directed to the region of focus 70. Simple geometry dictates that exactly the same situation will apply for the solar beam 64, which is focused onto a different tube 56 when the sun is at the position 66, nearer to the horizon. Figure 7 is a transverse cross-section of one prctical realisation of a solar water heater of the general type shown in Figure 6. This heater is designed to be mounted on the pitched roof of a house. In the southern hemisphere, the roof preferably faces north. In the northern hemisphere, the roof preferably faces south. In each case, the cylindrical axis of the heater should be oriented in a generally north-south direction. The heater consists of cylindrical hot-water tank 80 encased in an insulating plastic-foam moulding 82 that also forms the base portion 85 of the heater assembly. A series of substantially parallel water tubes 86, mounted in close proximity to each other, are arranged concentrically above the tank 80. The tubes 86 are insulated from the tank 80. One end of each tube 86 is provided with a heat-sensitive valve (not shown) which opens to permit heated water to flow from the tube into the tank 80 via a tank inlet at the uppermost end of the tank 80. Cold (or cool) water leaves the tank 80 through an outlet 88 in the lower-most end of the tank 80. This arrangement allows the tubes 86 and the tank 80 to form a thermal siphon which continuously SUBSTITUTE SHEET circulates water when one or more of the tubes 86 is heated by radiation incident upon the dome-like array of reflectors 90. However, the precise construction of the water-circulating arrangement of the solar water heater is not an essential feature of the present invention. Any suitable water-circulating arrangement may be used. Many such arrangements (some including heat exchangers, pumps and/or hot-water extractors) are known in this art. The array 90 may be formed from long reflective strips, glued together to form an elongate, dome-like shell of uniform circular cross-section, subtending an angle of about 270°. In this form of construction, the shell 90 may be made by packing the reflective strips on a cylindrical mould or support, clamping them in position, applying a suitable cement to the strips, then removing the clamps when the cement has cured. However, an alternative (and preferred) way of constructing the array 90 is by an injection moulding technique, followed by a metallising of the surfaces of the moulded shell. Whichever construction technique is used, the outside of the array 90 may be provided with a non-reflective coating 70 which is adapted to maximise penetration of solar radiation into the array. The inside surface of the array 90 may be provided with a selective coating 71 which transmits the in-coming solar radiation but reflects energy radiated (at much longer wavelengths) from the tubes 86. In this way, the array 90 and its coatings 70 and 71 form a shell which acts in the manner of a greenhouse (glasshouse). The finished shell is then fitted into place SUBSTITUTE SHEET on the moulding 82 (as indicated) and suitable insulating end closures (not shown) are fitted. A particular advantage of the use of a shell, comprising an array of relecting elements with at least one coating applied to its surface, is that convective losses from the tubes 86 to the atmosphere are limited and the water in the tubes or pipes 86 is prevented from freezing during frosty nights. Another advantage of this type of solar heater construction is that the cylindrical focal region of the array of reflectors is located behind the array, and not in front of the reflector (as in the case of a solar heater which uses a conventional parabolic mirror). This feature avoids the significant thermal losses that occur, in many water heaters having parabolic mirror collectors, when delivering water heated by the collected solar energy to a storage tank at the earth's surface. Those thermal losses have been estimated to be up to 40 per cent of the energy collected by the parabolic reflector. A further beneficial feature of the wide collection angle of the arrays 50 and 90 of the heaters shown in Figures 6 and 7 is that these arrays permit the collection, and utilisation for heating, of radiation which is not received directly from the source (the sun). In particular, the arrays will collect diffused radiation, which is present on cloudy days, and solar radiation that is scattered from almost any direction. The construction variations shown in the schematic drawings of Figures 8 and 9 utilise this feature. SUBSTITUTE SHEET The solar water heater illustrated in Figure 8 has a flat surface 73 positioned on each side of the elongate array 90. The surface 73 is preferably a highly polished surface (a mirror). However, beneficial results are also achieved when this surface 73 is a scattering surface - for example, a surface of aluminium foil, which reflects in a diffusive manner due to its micro-roughness. It will be apparent from the rays drawn in Figure 8 that a significant proportion of the radiation reflected by the polished surface (or scattered by the micro-roughness of the scattering surface) 93 will be collected by the array 90 and used to heat water (in some cases to produce steam) in the tubes connected to the absorber. In the water heater featured in Figure 9, the array of reflectors and the array of heat-absorbing tubes with its associated water storage tank are raised slightly by an insulating plinth 76, and an inclined reflecting surface (or a scattering surface) 77 is positioned on each side of the water heater, to further improve the collection of solar radiation. The operational benefits, with regard to off-axis incident radiation, of the heater illustrated in Figure 9 are similar to those of the heater depicted in Figure 8. A further variation in the construction of water heaters of the type illustrated in Figures 6 to 9 of the accompanying drawings involves the inclusion of a medium having a refractive index, n, which is greater than 1.0, in the region between the inner surface of the array 90 and the water-containing tubes 86. The inclusion of such a medium SUBSTITUTE SHEET may improve the efficiency of the collection of t h e solar radiation, because the radius of the array of tubes 86 will b e reduced, and there will be a higher concentration of solar energy on a tube of the array. Care has to be taken, however, to ensure that the concentration of energy benefits are not cancelled by the absorbtion of energy by the medium. When a high concentration of solar energy is required (for example, in the generation of steam using solar energy ) , the array of tubes 86 will be replaced with a single tube an d this tube will be moved ("tracked") to ensure t h at it is always in a position where radiation from the sun is focused. If the aray 90 should be a parabolic array and not a spherical array, it would be necessary to track t h e array for maximum heating of the tube throughout the d ay. It will be appreciated that although the descriptions o f F igures 6 to 9 have referred to an elongate water heater, hav i ng a cylindrical array 90, a cylindrical array o f tu b es or pipes 86 and a cylindrical water storage tan k 80, t h e solar collector may comprise a remote water tan k , a spherical array 90 and a spherical array of tubes or pipes 86. If this is the case, the reflective or scattering surface 73 may be used, but it will be a disc-shaped surface surrounding the array, and the surface 77 wil l be frusto-conical in shape. An advantage of the use of a substantially spherical array 90 and a generally spherical pipe or tube configuration is that, for optimal collection of solar radiation, it is not SUBSTITUTE SHEET necessary to mount the heater on an inclined surface and use a mechanical arrangement to track the sun. In solar energy applications of the present invention, when the array of reflectors is a spherical array (in the form of a dome) of internally reflective channels, and the incident radiation is to be sharply focused onto a spherical surface at the half-radius of the array, the cross-section of the channels must be rectangular (preferably square). To form a spherical surface of squares is not always an easy task. The present inventor has found that an array having an essentially spherical surface may be formed in sections, with each section consisting of a sub-array of channels having (i) a rectangular cross-section and (ii) reflecting walls. The array sections may be formed into an icosahedral, dodecahedral or globe-like array structure, or a structure which is a non-regular polyhedron - such as mixture of pentagons and hexagons, and triangles of different shapes. Each of such structures is a reasonable approximation to a sphere. As will be shown later in this specification, there are applications of the present invention in which a sharp focusing of the incident solar energy is not of paramount importance. In those applications of the invention, it is sometimes disadvantageous for the array to have reflective channels of rectangular cross-section. One example of the use of the present invention without the need for sharp focusing of incident radiation is in the SUBSTITUTE SHEET generation of electrical power using solar radiation which is incident upon an array of photo-voltaic cells. In this application of the present invention, the general arrangement illustrated in Figures 6 to 9 can be used, with the replacement of the tubes 86 and the water tank 80 by an array of photo-voltaic cells. The present invention may also be used in the construction of a skylight for a building. Skylights are being used in increasing numbers to provide natural illumination in rooms that normally do not receive any direct sunlight (or that receive too little direct sunlight) . Two examples of skylights which include the present invention are shown in the schematic sectional diagrams of Figures 10 and 11. Both of these skylights are designed for use with a light well that projects through the roof of a building. Light wells usually comprise tubular structures having highly reflective internal walls, which facilitate the transmission of light through straight or curved pathways within a building, to a translucent or semi-opaque plate (such as a frosted glass panel) which is mounted in the ceiling - or sometimes in the wall - of a room in the building. To increase the effectiveness of the collection of light from the sun, the dome-like array 101 of reflective channels is preferably ellipsoidal in shape and directs incident radiation towards the light well 102. Preferably, the light well has a substantially circular cross-section, in which case the dimensions of the ellipsoidal array 101 SUBSTITUTE SHEET should be such that the focal point of the array is approximately at the internal wall of the light tube most remote from the light source. Thus, on a bright day, at low elevations of the sun, the light from the sun is focused at a spot or zone on the reflective wall of the light well, just inside the top of the light well. This focal spot or zone moves from one side of the light well to the other side of the light well during the course of one day. As shown in Figure 10, the light from the sun is reflected by the wall of the light well 102 to fall on a translucent plate 103, mounted in the ceiling 104 of a room. The translucent plate 103 thus provides a source of additional (diffused) light for the room. The ellipsoidal array shown in Figure 10 is a truncated or annular array. This form of array may be used when it is perceived that when the sun has an elevation which exceeds a predetermined value, ample illumination, via the light well 102 and plate 103, is provided without the need to focus the sun's rays into the light well 102. A full height ellipsoidal array is featured in the light well arrangement of Figure 11. Another optional feature of the arrangement illustrated in Figure 10 is the inwardly curved top end 105 of the wall of the light well 102. If, as shown in Figure 10, the focal spot or zone is on this inwardly curved part of the wall of the light well, a light ray which is reflected into the light well will penetrate further into the light well SUBSTITUTE SHEET before it is reflected a second time by the wall of the light well than a light ray which does not fall on this inwardly curved region. In general, a light beam reflected from the end region 105 of the light well will experience fewer reflections at the wall of the light well before striking the translucent plate 103. Figure 11 illustrates how an array 110 of reflecting channel elements may be used to direct sunlight into a light well 112 which is divided into two light ducts 114 and 116, each of which terminates in a respective translucent plate 113. The light well 112 is also provided with an inwardly projected top end region 115. Although the reflecting channels of the arrays 101 and 110 of the skylights illustrated in Figures 10 and 11 have rectangular cross-sections (to focus incident light on to the end regions 105 and 115, respectively, of the light wells), it is not essential for that incident sunlight to be focused to a spot or zone. Thus it is not essential for the channels of the arrays 101 and 110 to be rectangular in cross-section. In fact, any convenient cross-sectional shape may be used for the internally reflecting channels. In addition, it is not essential for the array of reflecting channels to be an ellipsoidal array. It will be appreciated that the arrays 101 and 110 will be provided with an optically transparent protective cover, which will be connected (directly or indirectly) in a weather-tight manner to the roof on which the skylight is mounted. SUBSTITUTE SHEET A n optional conical reflector or scattering plate, surrounding the array 101 or 110 in the manner shown for the solar collector of Figure 9, may be used to increase the effective collection area of the skylight. Such a conical reflector will be particularly beneficial on cloudy days, when the natural light is from a partially diffuse source. Another use of the present invention without the need for sharp focusing of incident radiation is as a light concentrator for a desk or work region. One example of this application of the present invention is shown in F igure 12, in which an array 120 of internally reflecting channe l s 120, each having a non-rectangular cross-section, is mounted at one end of a flexible support 121. The other end of the flexible support 121 is connected to a heavy base 122 or is securely mounted on a desk, work-bench, s h elf, wall or any other convenient structure. Preferably, the array 120 is an array of reflective channels having a circular cross-section, so that the array focuses incident light radiation with a lower concentration ratio than that which is achieved with channels of rectangular cross- section. The incident light from a range of directions is projected by the elements of the array 120 towards a zone or bright region 123 on the desk, work bench or the like. The zone or bright region 123 has an area which is smaller than the area of the array 120. The flexible support 121 enables the array 120 to be moved to a position in which it concentrates light from a window or an array of fluorescent lights (or any other source of lighting) onto the bright region 123. SUBSTITUTE SHEET The above embodiments of the present invention have all illustrated the use of the invention in solar radiation applications. However, as noted in the introductory part of this specification, the present invention may be used with other forms of energy which is propagated in a wave¬ like manner. Figure 13 illustrates the use of the present invention as both a concentrator and director of infra-red (heat) radiation. A focusing array 130 of internally reflecting channels is positioned in front of an infra-red radiator 129. The heat radiation from the radiator 129 is focused to a zone 131 and is excluded from the zone 132. This arrangement may be used in any situation where it is desired to concentrate infra-red radiation, and/or where it is required to exclude heat from a particular region. One example of a situation in which heat is to be excluded from a particular region is a kitchen, in which heat from a stove is preferable excluded from a region of the kitchen in which food is prepared. The present invention may be used in a similar manner with microwave radiation. For example, directive arrays may be used in diathermy, where it is highly desirable to ensure that an operator of the diathermy equipment is protected from unwanted reflected radiation, or in a microwave oven to concentrate microwave energy in a particular region. Figures 14 and 15 illustrate the use of the present invention as a beam splitter for vacuum ultra-violet radiation. A flat array 140 of parallel elongate reflectors is positioned so that, when viewed from the SUBSTITUTE SHEET direction of an incident beam of collimated radiation 141, the array appears as a series of spaced-apart, parallel, elongate reflectors. The array 140 is thus an array in accordance with the present invention, with a surface of curvature (as this term is used in this specification) ( i) having a radius of curvature which is infinite, and (ii) which is inclined at an angle γ (which must be less than 45°) relative to the axis of the array. Thus when the incident collimated beam 141, having an intensity I 0 , reaches the array 140, part of the beam passes directly through the array and the remainder of the beam, whic h impinges upon the reflectors, is reflected by an angle 2γ. If the area of the array is A, the projected area o f t h e reflectors in A(R), and the reflectivity of the reflectors is R(γ), then the directly transmitted part of the incident beam has an intensity I-. given by the relationship and the b eam which is deflected by an angle 2γ has an intensity I 2 given by the relationship Two flat arrays of parallel elongate reflects, arranged as shown in Figure 15, will act as a beam splitter which > SUBSTITUTE SHEET produces two beams, each deflected by an angle 2γ, from a collimated beam of radiation. Although described above as a beam splitter for radiation in the vacuum ultra-violet region, it will be apparent that the arrangements illustrated in Figures 14 and 15 can be used with visible wavelength radiation, infra-red radiation (compare with Figure 13), and soft x-rays - but it should be noted that when used with soft x-rays, the incident angle of the beam 141 must be less than the critical angle for total internal reflection, or equal to the Bragg angle for monochromatic radiation when the reflectors are made of crystals. A particular advantage of the use of the present invention with equipment for processing radiation of differing wavelengths is that, prior to the use of the equipment, the required alignment of the components can be established with precision using optical techniques. It will be apparent, from Figures 13, 14 and 15, that a parallel array of elongate reflectors can be used for one- dimensional focusing (line focusing) of radiation. Two such parallel arrays, crossed at right angles, will create the equivalent of square channels with two-dimensional focusing. Thus a two-dimensional focusing array can be constructed from two arrays of parallel reflector strips. This use of two crossed arrays not only provides a convenient method of manufacturing a two-dimensional focusing array; it also enables the surfaces of the reflectors to be polished and tested before manufacturing SUBSTITUTE SHEET t h e array, and permits the surfaces to be coated (optionally with multiple layers) to improve the reflectivity of the surfaces or to make the surfaces selectively reflective at particular wavelengths. T h e arrays o f the present invention can also be used as acoustic l enses for ultrasound (ultrasonic radiation) purposes, particularly in ultrasound medical diagnosis equipment. One particular use of the present invention in the field of acoustics is in hydrophones. In an underwater environment, it is impractical to scan a parabolic mirror or a dish array to monitor sounds from all directions. It has been necessary, therefore, to use the inherent directionality and sensitivity of hydrophones suspended from a group of spaced-apart buoys to listen for the sounds made by, for example, a school of fish or a submarine. Using telemetric d ata f rom the hydrophones, the type, direction of movement, speed and depth of the sound-emitting source can be computed. Figure 16 is a schematic plan view, from above, of a hydrophone assembly which includes the present invention. A cylindrical array 160 of reflectors (compare Figure 6 ) surrounds an annular array of hydrophones 161. The hydrophones have their signal outputs connected to a data processing and/or transmitting unit 162. An incident beam 163 o f acoustic energy from a distant sound source is f ocuse d onto a hydrophone of the array 161. The incident radiation causes a signal to be transmitted by the SUBSTITUTE SHEET hydrophone to the unit 162 which, in turn, transmits data indicating information about the received energy beam 163. In a similar manner, reception - and, by the principle of reciprocity, transmission - of radiofrequency beams, without the need for large, moving antennas, can be effected using suitable arrays of reflectors around, or partly surrounding, arrays of radiofrequency receivers and/or transmitters. Thus it will be seen that the present invention, in one or more forms, can be used in a wide range of technologies for the focusing, directing or dispersing of energy which is propagated in a wave-like manner, provided the dimensions of the reflector arrays are chosen to suit the wavelength of the radiation being processed. When the invention comprises an array of reflecting channels, the ratio of the length of the channel to the width of the channel determines the size of a focused spot or zone, and should be optimised for the particular application of the invention. The optimal value of this ratio varies according to the wavelength of the radiation. It should be apparent to persons of skill in this art that arrays of the present invention may be used in combination, for a wide variety of purposes. To illustrate this point, Figure 17 shows how two arrays of the present invention can be positioned to act in a manner equivalent to a Keplerian telescope or collimator, and Figure 18 shows the use of two arrays in a manner equivalent to a Galilean telescope or collimator. These and other "complicated" lens structures are particularly useful in the construction of optical instrumentation for use with ultra-violet radiation. Until SUBSTITUTE SHEET the present invention, optical instrumentation for ultra¬ violet radiation has not been readily available. It is also possible to use different aspects of the present invention at the same time. For example, in solar energy applications, the focusing of incident radiation by an array may be used to produce hot water or steam, while diffuse light incident on the array may be used to generate electricity from photo-voltaic cells. Finally, it is emphasised that the arrays of the present invention can have any required form. Arrays having a hyperbolic "surface of curvature" will be used for imaging purposes, and arrays having a parabolic "surface of curvature" will be used for high concentration of incident, collimated radiation. SUBSTITUTE SHEET

Claims: Claims An energy directing device for use with energy which has a wave-like propagation mode, said device comprising an array of reflecting elements, said array having a surface of curvature (as hereinbefore described), the elements of the array being positioned with their reflecting surfaces substantially orthogonal to the surface of curvature. An energy directing device as defined in claim 1, in which each element of the array is an elongate planar reflector. An energy directing device as defined in claim 2, in which the elongate planar reflectors are positioned to define an array with a surface of curvature which is an arc of a cylinder of circular cross-section, whereby said device acts to direct incident collimated energy to a line focus at the half radius of curvature of the surface of the array. An energy directing device as defined in claim 2, in which the elongate planar reflectors are positioned to form a planar array, said reflectors being positioned in the array with their reflective surfaces inclined at an acute angle less than 45° relative to the normal to the plane of the array, said reflectors being spaced apart so that their projection onto the plane of the array is an array of spaced apart strips, whereby a collimated beam of radiation incident normal to the array is partially transmitted through the SUBSTITUTE SHEET array and is partially reflected by an angle which is twice said acute angle. 5. An energy directing device as defined in claim 3, in which said array is a planar array, and said surface of curvature is created by mounting each planar reflector with its plane at an angle relative to the normal to the array. 6. An energy directing device as defined in claim 1, in which each element of said array is a channel, the internal surface or surfaces of the channel being a reflecting surface or reflecting surfaces. 7. An energy directing device as defined in claim 6, in which each channel of the array has a rectangular cross-section. 8. An energy directing device as defined in claim 7, in which each channel of the array has a square cross- section. 9. An energy directing device as defined in claim 7 or claim 8, said array being a planar array, said device being formed by the superposition of two arrays as defined in claim 5, with the elongate direction of the reflecting elements of one of said two arrays being at right angles to the elongate direction of the reflecting elements of the other of said two arrays. 10. A n energy directing device as defined in claim 7 or claim 8, in which the envelope of corresponding points on the reflecting elements of the array is part of a SUBSTITUTE SHEET 6 - 30 - surface having a shape which is selected from the group consisting of a sphere, an ellipsoid, a paraboloid and a hyperboloid. 11. A n energy d irecting device as defined in claim 3, sai d array o f re f lecting elements being constructed as a d ome over an array of tubes adapted to contain water, sai d tu b es b eing positioned substantially at the half- radius of curvature of the array of reflecting elements, said tubes forming part of a solar heater for the production of hot water or steam. 12. A n energy d irecting device as defined in claim 3, said array of reflecting elements being constructed as a d ome over a tu b e adapted to contain water, the surface o f said tu b e being positioned substantially at the h a lf -ra d ius of curvature of the array of reflecting elements, said tube forming part of a solar heater for t h e production of hot water or steam. 13. A energy directing device as defined in claim 12, including tracking means to adjust the position of said tube to maintain maximum transfer of incident radiation to said tube. 14. A n energy directing device as defined in claim 10, said envelope being part of a sphere, said array being constructe d as a dome over an array of tubes forming part of a solar heater for the production of hot water, the surface of said array of tubes being at su b stantially the half-radius of curvature of the array of reflecting elements. SUBSTITUTE SHEET 15. An energy deflecting device as defined in claim 11, claim 12 or claim 13, including a pair of reflecting or scattering surfaces positioned adjacent to the array, one on each side of said array of reflecting elements, to reflect or scatter radiation towards said array of reflecting elements. 16. A n energy deflecting array as defined in claim 15, in which said surfaces are inclined relative to the plane of the edge of said array of reflecting elements. 17. An energy directing device as defined in claim 14, including a disc-like reflecting or scattering surface adjacent to the edge of said array of reflecting e l ements, to reflect or scatter radiation towards said array of reflecting elements. 18. An energy directing device as defined in claim 17, in whic h said reflecting or scattering surface is frusto- conical in shape. 19. An energy directing device as defined in any one of claims 11 to 18, including a coating which is transparent to incident radiation, said coating being positioned over said array of reflecting elements. 20. A n energy directing device as defined in claim 19, including a second coating, said second coating being transparent to electromagnetic radiation in the visi bl e and near-visible region but opaque to infra¬ red radiation, said second coating being applied over the inner surface of the array of reflecting elements. SUBSTITUTE SHEET 21. An energy directing device as defined in claim 3 or claim 6, constructed as a dome over an array of photo ¬ voltaic cells. 22. An energy directing device as defined in claim 10, constructed as a dome adapted to fit over a light well, to direct radiation incidental on said array of reflecting surfaces into said light well. 23. An energy directing device as defined in claim 22, in which said envelope is part of an ellipsoid, said light well comprises a cylindrical tube of circular cross-section having a highly reflecting inner wall, and said array of reflecting elements is adapted to focus incident light to a spot or zone at the end of the inner wall adjacent to said array of reflecting elemen s. 24. An energy directing device as defined in claim 23, in which said end of the inner wall is curved inwards. 25. An energy directing device as defined in claim 1, in which each reflecting element is a cylindrical channel having an inner surface which is a reflecting surface, said channel having a non-rectangular cross-section, said array of reflecting elements being constructed as an extensive array which is mounted at the end of a flexible support, to form an adjustable array for concentrating light onto a work space. 26. An energy directing device as defined in claim 2, in which the elongate planar reflectors form an annular array adapted to focus collimated radiation incident SUBSTITUTE SHEET upon the array from any direction onto a zone or .spot on a cylindrical surface at the half-radius of said annular array, a plurality of hydrophones being positioned at said cylindrical surface at the half- radius, each of said hydrophones having an output which is connected to a signal processing and/or transmitting unit. 27. An energy deflecting and concentrating device for microwave radiation, infra-red radiation, or ultrasound radiation comprising a device as defined in any one of claims 1, 2, 3, 5, 6, 7, 8, 9 and 10. 28. An instrument including a plurality of energy directing devices as defined in any one of claims 1 to 9 and 10. 29. An energy directing device as defined in claim 1, substantially as hereinbefore described with reference to the accompanying drawings. SUBSTITUTE SHEET

Inventors: RODE ANDREI VLADIMIROVICH, RODE, ANDREI, VLADIMIROVICH
Applicants: RODE ANDREI VLADIMIROVICH, UNIV AUSTRALIAN, THE AUSTRALIAN NATIONAL UNIVERSITY
Application year: 1993
Main classification: G02B17
IPC codes: E04B9, E04D13, F21S11, F21V7, F24J2, G02B17, G10K11, H01L31