Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to radiant energy
reflecting devices, and in particular concerns a
radiant energy reflecting member which can be used
to form a solar energy barrier or screen having a
plurality-of reflecting members which are disposed in
such a manner as to prevent the penetration of un~wanted
energy by reflection into a shaded space. The invention
has particular, but not exclusive, application to solar
- energy screens which are constructed as louvred screens,
latticed screens or folded or gathered screens. The
term "louvred screens" will generally be understood to
include venetian blinds, louvred storm windows, and
louvred doors and shutters.
Other areas of application of the present invention
include gr.illes to allow the passage o fluid media, but
not radiant energy, for example, ventilation grilles for
equipment and for buildings.
The reflecting member of the present invention
utilises certain aspects of one form of "retro-reflection"
of energy. Retro-reflectors are reflecting bodies which
reflect incident radiation back in the direction from which
it is incident. They generally take one of three basic
forms, namely (a) two or three planar reflectors at right
angles to each other, (b) a lens with a mirror in its focal
plane, and (c) a concave mirror with a - ~
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smaller mirror at or near its focus. Each of these basic
forms may be eith r a first-surface reflector ~in which
reflection occurs on the front face of the reflector) or
a second-surface reflector tin which the incident radiation
penetrates a transparent material~ the front surface of
which constitutes the first face, and reflection occurs at
the second or rear face of the transparent material).
The present invention has a number of similarities to these
types of retroreflector surfaces, but the distinction
between such surfaces and the present invention will
become apparent as the description proceeds.
In more detail, the property of retro-reflection
is exhibited where two reflectors are placed at right
angles to each other. An incident energy ray in any plane
which is reflected from one reflector to the other will be
reflected in a parallel (but displaced) plane. Furthermore,
if three reflectors are placed at right angles to each
other (so as to form the internal corner of a cube), an
incident energy ray which is reflected sequentially from
each of the three reflectors, will be reflected in a
parallel (but displaced) path. Such reflectors are known
variously as retro-reflectors, retro-directive mirrors~
and cube-corner reflectors. This principle is further
described, for example, in the l'Encyclopedia of Science
and Technology" published by the McGraw-Hill Book Company,
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Inc., in 1960 under the headiny "Mirror Optics'l.
The closest prior art ~o the present invention
is believed to be the venetian blind assembly
illustrated in U.S. pa~ent specification No. 2l103,788
(to Mohrfeld)~ That specification discloses a slat for
venetian blinds and the like in which one surface of the slat
has a plurality of longitudinally extending, adjoining,
narrow, highly reflecting surfaces disposed at an angle
of approximately 45~ to the plane of the slat and at
angles of approximately 90 to each other. Such a surface
comprises a two-plane, first-surface retro-reflector as
discusse`d above, and such a surface does operate to reduce
the amount of solar energy penetrating into a space shaded
b~ the venetian blind. However, blinds constructed in
accordance with Mr. Mohrfeld's design suffer from a disad-
vantage; they permit inward re-reflection of incident
energy (as will be shown later).
Re-reflection of incident energy into the shaded
space is also a problem with the highly reflective sur-
faces disclosed in Australian patent speci~ication
No. 203,859.
It is a prime ob~ective of the present invention
to provide a radiant energy reflecting member which can
be used in venetian blinds and the like and which are
effective to reduce the transferrence of radiant energy
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into the shaded space by re-reflection.
According to the present invention, there is provided
a radiant energy reflecting member comprising ~a) an elongate
body; and (b) a p-lurality of reflecting elements formed in or
attached to said body, said elements being located adjacent
to each other, each element providing retro-reflection of all
incident energy from one particular direction, said elements
being arranged so that said particular direction varies
progressively with the transverse position of the elements
on said body.
Preferably the elements each comprise a pair of
elongate reflecting surfaces inclined relative to each other.
Also, the elongate body is preferably a lamellar body.
In another aspect of the present invention, there is
provided a radiant energy screen assembly comprising a
plurality of radiant energy reflecting members of the present
invention, having lamellar bodies, arranged in a louvre
configuration. This aspect of the present invention is
especially useful for the construction of light- and
heat-screen assemblies such as blind assemblies, particularly
venetian blind assemblies, for the exterior windows of
buildings.
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The present invention, as will be seen, also
encompasses radiant energy reflecting members of the ~ype
defined above, in which a layer of transparent material
is located on top of the reflecting surfaces of the
reflecting elements.
The radiant energy reflecting members of the present
invention may be formed in any suitable manner, including
rolling, casting or stamping the desired reflective
surface configuration into a body, such as venetian blind
strip material, and subsequently (if necessary) applying a
coating of a reflective material. Other methods o-f
forming the radiant energy reflecting members will be
described later.
-To further understand the present invention, this
description will now contlnue with reference to the
accompanying drawings, in which : -
Figure 1 illustrates a portion of a known form of
.radiant energy reflector device, namely the venetian
blind slat construction chosen by Mohrfeld for the screen
illustrated.and-described in his U.S. patent specification
No. 2,103,788;
Figure 2 illustrates the retro-reflective property
of the surface of the embodiment of Figure 1, and its
failure to be retro-reflective :in general;
Figures 3 and 4 illustrate possihle re-reflection
paths for incident radiant energy in louvred screen
devices which incorporate slats having the structure of
~igure l;
Figures 5 and 6 are cross-sectional representations
of alternative embodiments of radiant energy reflecting
members constructed in accordance with the present
invention;
Figures 7 and 8 illustrat~ a radiant energy reflec-
ting member, constructed in accordance with the present
invention, in the form of a second surface reflector;
Figures 9 and 10 illustrate a retro-reflective
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surface utilising a cube-corner reflector; and
Fi~ures 11 to 14 illustrate further slat
constructions, utilising lensjfocal plane mirror retro-
reflectors and concave mirror/secondary mirror retro-
reflectors, which the present inventor has designed.
Referring firstly to Figure 1, there is shown a
two-plane first-surface retro-reflective device which
consists o~ a longitudinally corrugated aluminium reflector
having reflective surfaces A and B disposed substantially at
righ~ angles to each other. Referring to Figure 2, which
is a cross-section through two reflective surfaces of the
device of Figure 1, it will be seen that, in general, when
a beam of energy is incident upon.the reflective surface,
a portion of the beam, typified by the illustrated beam
15 path 6-8, it will be reflected from the surface A to the
surface B along the path 8-9 and, on re-reflection from the
surface B, will emerge from the reflactor alon~ path 9-10
in a parallel plane. It will al.so be apparent from Figure
2 that another portion of the beam of energy incident upon
the reflective surface, typified by beam paths 4-1 and 5-7,
will be reflected once only to be scattered in direction
1-11 and 7-12. Thus it can be seen from this Figure that in
general, only a portion of an incident beam of ener~y is
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truly retro-reflected~ unless the incident beam strikes
at one particular angle, which is illustrated by rays
P-1-3-S and Q-7-9-R. Because the rays P-1-3-S and Q-7-9-R
are totally retro-reflected rays 7 and incident beams from
all o~her direction are only partially retro-reflected, I
have termed the direction from which beams P, Q, R and S
are incident the "major axis" of the reflector ~those
familiar with reflecting surfaces will recognise that, in
the case of the slat of Figure 1, the "major axis" is a
pencil beam, having cross-sectional dimensions which
correspond to the peripheral shape of the slat, and whose
direction is at right angles to the slat).
Thus, the "major axis" of a reElecting element is,
at any point on that element, the direction from which
every beam of electro-magnetic energy having a wavelength
in the visible, near infra-red and near ultra-violet
regions of the s~ectrum, will be -fully retro-reflected.
Figures 3 and ~ illustrate a venetian blind constructed
of slats having the shape illustrated in Figure 1, positioned
between imaging inner and outer surfaces, 17 and 18,
res~ectively. From these Figures it can be seen how
undesirable re-reflection o~ incident energy can occur.
Figure 3 illustrates a case in which slats C and D are
oriented so that a ray entering along path 15 is deflected
~rom one slat to the next and into the shaded space
along path 16. Similarly, referring to Figure 4, it
can be seen that such undesirable re-reflection into the
shaded space may take place when a high elevation beam 15
strikes the outer end of the reflector surface.D. It can
be seen rrom these diagrams that, in practice, inward
re-reflections from a low sun angle ~Figure 3) occur as a
result of a beam such as beam 4-l-ll in Figure 2.
I have found that such single reflections from
louvred screens having this type of slat construction can -
be reduced if the reflecting facets on the edge of the
screen slats on the shaded side of the screen are reduced
from the profile 1-2-3 of Yigure 2 to, for example, profile
7-2-3 of Figure 2, and the reflec:ting facets on the other
edge of the screen slats are simultaneously reduced from
profile 1-2-3 of Figure 2 to, Eor example, profile 1-2 9
of Figure 2. That is, reflection of energy into the shaded
space will be reduced if the slats which constitute the
reflecting members of a louvred screen are shaped so that
the "major axes" of the reflecting members vary pxogressively
across the width of the screen. Clearly a similar result
is obtained if a reflecting structure which is not a
corrugated lamellar body, but nevertheless has a varying
: "major axis", is used for the slats.
Figures.5 and 6 illustrate alternative embodiments
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incorporating such new reflecting members. Figure 5
illustrates a corrugated retro-reflective construction
in which the included angles between reflecting elements
remain unaltered at approximately 90, but the element
widths are varied so that the energy reflecting member has
a curved profile. The reflective sturcture shown in
Figure 6 is also corrugated but the reflective surfaces
are constructed so that the upper included angle between
the reflective elements is 90 only at the mid-width point
10 of the lamellar structure. In this embodiment, alternate
reflective facets no longer lie in parallel planes.
Figures 7 and 8 illustrate a further embodiment of
the present invention r in which each reflecting element is
a two-plane second-surface reflector. This structure may
15 conveniently be formed by extruding a transparent venetian
blind slat with the corrugations on the underside, configured
in accordance with the principles illustrated in Figures 5
and 6, then coating the underside of the slat with a reflec-
tive film. Figure 8 is a cross-section thorugh such a
20 reflecting element and illustrates that a ray incident along
path 6-1, strikes the surface of the transparent material
at point 1, and is refracted along path 1-2. It is then
reflected along path 2-8 to point 8 on the surface, where it is
totally internally reflected. It then strikes the reflecting
25 surface at 4 and leaves the structure along path 5-7 at a
different angle to the ray emerging along path 1-11 of Figure
2, but
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nevertheless at an angle which would be effective to
prevent energy penetrating a louvred screen having .
slats made ln this fashion by re-reflection, as shown in
Figures 3 and 4. Thus, by utilising this form of
reflecting member, the undesirable reflections illustrated
in Figures 3 and ~ may be further reduced or eliminated.
Turning now to Figures 9 and 10, there is shown a
known form of three-plane, first-surface (Figure 9) and
second-surface (Figure 10) reflector structure, namely an
array of "cube-corner" reflectors, which may.be
embodied in a curved venetian blind slat to form a
radiant.energy reflecting member of the present invention.
When compared with similar two-plane reflectors, the reflec-
ting structures of these Figures exhibit the further advantage
that reflected incident energy is reflected in a parallel
line, and not a parallel plane. Once again, this form of
reflecting surface may be overlaid with a transparent
medium, thus utilising the principles discussed above in
relation to the embodiment of Figures 7 and 8.
It is also possible for energy reflecting members
of the present invention to ~e constituted by a curved
lens/focal plane mirror construction. As with two-plane
and three-plane reflecting structures, these can provide
retro-reflectivity in two dimensions (for example, in the
form of an extruded transparent curved sheet with lens-
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profile surfaces, mounted over a mirror-surfaced base
member) or in three dimensions (for example, in the form
of an array of glass spherical beads, suspended over a
curved reflective surface). Figure 11 illustrates one
such configuration in which elements 21 are transparent
rods or spheres set in a matrix 22 of lesser refractive
index, above a reflective base member 23. They may be - -
first-surface reflective, (therefore with the reflector
separate from the lens) or more commonly second-surface
reflective, with the reflector attached to the rear of the
lens system (for example, as shown in Figure 11). The
advantage of such a reflecting structure is that non
retro-reflection of the type illustrated in Figures 2 and
8 does not occur.
Figure 12 illustrates a modified form of the venetian
blind slat of Figure 11. The slat of Figure 12 has an
outer surface 51 comprising a matrix of glass bead lens
element located in the surface of a transparent medium,
above a reflecting surface 52.
The last form of energy reflecting member illustrated
in the drawings is a curved lamellar body constructed as a
concave mirror/secondary mirror retro~reflector (~or example,
a "cats-eye" retro-reflector). In Figure 13, a concave
mirror 31-32, which may be circular or parabolic in cross-
section, has a small mirror 33 near its focus~ A typical
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ray path 34-32 is retro-reflected through 180~ to
emergy along ray path 31-35. As with other retro-reflec-
tor types, these embodiments may be two-directional with
longitudinally extending mirrors of constant cross-section,
or they may be three dimensional, with primary mirrors
formed of sphere segments, thus providing total retro-
reflectivity rather than planar retro-reflectivity. In
addition, reflection may be either first or second surface
reflection, although the preferred form for the present
application would be as second surface reflectors. Figure
14 is a cross-secticn through a venetian blind slat, in
which 41 is the transparent body of the slat, elements 42
are a series of concave reflectors formed on the rear of
the slat, and elements 43 are small secondary reflectors
formed on the transparent face of the slat.
Finally, it should be noted that since the energy
reflecting members of the present invention are effective
to reduce the transmission of energy by re-reflection when
incorporated into louvred screens, it is possible to make
the inward facing surfaces o~ such screens highly reflec-
tive, hence lowering their emissivity.
While the present invention has been described
herein with reference to preferred embodiments, it wi.ll be
generally understood by persons skilled in the art
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that various changes may be made and equivalents
substituted for ~lements thereof without
departing from the true spirit and scope of the
present invention. -
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