Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROMAGNETIC RADIATION COLLECTOR
BACKGROUND OF THE INVENTION
Field of the Invention
[00011 The present invention relates generally to electromagnetic
radiation collection.
Related Art
[00021 The collection and concentration of electromagnetic (EM)
radiation is well known. Radio waves are typically collected and concentrated
using parabolic dishes. Solar radiation is collected and concentrated using
parabolic mirrors or lenses. The former devices suffer from requiring a
relatively
high height-to-collection area ratio and the latter being expensive, heavy and
fragile. Both these types of device also suffer from the requirement to track
the
source in order to function properly.
BRIEF SUMMARY OF THE INVENTION
[00031 The invention seeks to overcome at least some of the
deficiencies in the prior art by providing an EM radiation collection and
concentration device which can cover a large area, have a low profile, have no
requirement to track the source and be constructed so as to be relatively
light and
inexpensive.
[00041 There is a pressing need to be able to generate energy from
renewable energy sources. Solar energy is one such resource which has
potential
to be exploited. Conventional devices for collecting radiant energy to
generate
energy in a useful form suffer from a high capital cost and/or the inability
to
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generate nign enougn temperatures to be useiul for many applications. 1 ne
invention seeks to overcome these deficiencies in the prior art by providing a
radiant energy concentration device that can gather energy from a relatively
large
area and concentrate it onto a small target area. The device is relatively
inexpensive to produce, can be light in construction and has the potential to
generate high target temperatures or, in the case of conversion to electricity
by
photovoltaic cells, require only a small area of cells, thus saving cost.
[0005] The invention is directed to a device that can cover relatively
large collections areas at relatively low cost, does not necessarily require
materials
'_u ofi:articuiar refractive index, can be made of light construction and can
concentrate the radiation onto a single target area.
[0006] The invention is capable of being less massive and having a
lower profile than prior art concentration devices. It is also capable of
having high
concentration factors. It is suitable in any application where it is desired
to collect
and concentrate EM radiation, with particular utility in the collection and
concentration of solar radiation. In the case of solar radiation, a device in
accordance with the invention can be used in conjunction with photovoltaic
cells
or to heat a fluid to harness the solar energy for a desired purpose. In the
case of
radio frequency radiation, the subject device could be used to collect, focus
and
tune the radiation.
[0007] An example of the device has an assembly of channeling areas
that are used to collect and concentrate the incident EM radiation. Also
disclosed
are methods for manufacturing the subject devices.
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[0008] Particular embodiments of the invention provide an
electromagnetic radiation collector having a concentration chamber for
collecting
and concentrating electromagnetic radiation and directing it to a target, the
concentration chamber having at least one inlet opening, the inlet opening
having
a cross-sectional area. The collector also has a channeling area having an
entry
end for receiving the electromagnetic radiation, the entry end having a cross-
sectional area, an exit end adjacent to the inlet opening of the concentration
chamber, and at least one reflective wall between the entry end and the exit
end.
The cross-sectional area of the inlet opening is smaller than the cross-
sectional
area of the entry end of the channeling area.
[0009] Other embodiments of the invention provide a method of
collecting electromagnetic radiation. The method includes channeling
electromagnetic radiation in a channeling area, the channeling area having an
entry
end for receiving the electromagnetic radiation, an exit end, and at least one
reflective wall between the entry end and the exit end, the entry end having a
cross-sectional area; collecting and concentrating the electromagnetic
radiation in
a concentration chamber, the concentration chamber having at least one inlet
opening adjacent the exit end of the channeling area, the inlet opening having
a
cross-sectional area; and directing the collected and concentrated
electromagnetic'
radiation to a target. The cross-sectional area of the inlet opening is
smaller than
the cross-sectional area of the entry end of the channeling area.
[00010] Still other embodiments of the invention provide an
electromagnetic radiation collector that has a tapering element having an
entry end
for receiving electromagnetic radiation, the entry end having a central axis
along a
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first direction, and a cross-sectional area perpendicular to the first
direction; an
exit end having a central axis along a second direction, and a cross-sectional
area
perpendicular to the second direction; and a wall connecting the entry end to
the
exit end, the wall being capable of channeling the electromagnetic radiation
received by the entry end to the exit end. The cross-sectional area of the
entry end
is larger than the cross-sectional area of the exit end, and the second
direction is
not parallel to the first direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[00011] The foregoing and other features and advantages of the
invention will be apparent from the following, more particular description of
preferred embodiments of the invention, as illustrated in the accompanying
drawings wherein like reference numbers generally indicate identical,
functionally
similar, and/or structurally similar elements.
[00012] Figure 1 shows an example of a first embodiment of the
invention;
[00013] Figure 2 shows an example of a second embodiment of the
invention;
[00014 j Figure 3 shows a:, example of a third embodiment of the
invention;
[00015] Figure 4 shows a cross-sectional view of fourth embodiment of
the invention;
[00016] Figure 5 shows a cross-sectional view of fifth embodiment of
the invention;
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[00017] Figure 6 shows a sixth embodiment of the invention; and
[00018] Figure 7 shows a seventh embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[00019] An exemplary embodiment of the invention is shown in the
5 drawings and described herein.
[00020] An example of a device in accordance with the invention has an
assembly of channeling areas wherein the EM radiation can be internally
reflected
within the channeling areas. The channeling areas are constructed such that at
least some of the EM radiation that enters a broad end of the channeling areas
will
be steered within the channeling areas to exit a narrow end of the channeling
areas
at a direction different to that which it entered. The broad ends of the
channeling
areas are assembled to form a surface that is herein termed the collection
surface.
EM radiation falls on the collection surface and enters the broad ends of the
channeling areas. The EM radiation is reflected from the walls of the
channeling
areas so as to be directed to exit from the narrow end of the channeling
areas.
This is achieved by ensuring that at each reflection point the angle of
incidence of
the EM radiation to the reflecting surface is less than 90 . A method for
ensuring
that this is the case for a wide arc-ofangles of the EM radiation incident on
tl:t
collection surface is to shape the channeling areas such that they are much
longer
than they are broad at their broad end. This provides, in some embodiments, a
small angle of taper of the walls of the channeling area thus fulfilling the
reflection angle requirements for a broader range of incident EM radiation
angles.
The ratio of length of the channeling area to the breadth of its broad end
should
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desirably be between 2 and 1000, more preferably between 5 and 100, and most
preferably between 10 and 50. Figure 1 shows an example of a single channeling
area and a typical path 20 that EM radiation might take within the area.
[00021] The channeling areas can be made of solid material that is
capable of transmitting the EM radiation that is to be collected and
concentrated
and with walls that reflect the EM radiation back into the channeling area. In
another embodiment of the invention, the channeling areas are formed as
cavities,
where the walls of the cavities are capable of reflecting the EM radiation
back into
the cavity.
[i:+0022] In one embodiment of the invention, the narrow ends of an
assembly of channeling areas are gathered together into an area that is
smaller than
the area of the broad ends of assembled channeling areas. In such an example,
the
EM radiation collected over the broad ends area is concentrated into the
narrow
ends area. An example of this embodiment is shown in Figure 2.
[00023] In a particular embodiment of the invention, the narrow ends of
the channeling areas open into a concentration chamber which serves to further
concentrate the radiation exiting from the narrow ends of the channeling
areas.
The narrow ends of the channeling areas open onto one face of the
concentration
chamber wherein the faces of the concentration chamber are capable of
reflecting
the EM radiation. At least one, and preferably only one, of the faces of the
concentration chamber is transmissive to or absorptive of the EM radiation
with
all other faces being reflective of the EM radiation. The face of the
concentration
chamber that is transmissive or absorptive, termed herein the exit port, is
the port
though which the concentrated EM radiation can exit the device or be absorbed
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and utilized in the desired manner. In one embodiment, a target that utilizes
the..
EM radiation is placed at the exit port. The narrow ends of the channeling
areas .
opening into the concentration chamber are configured such that the EM
radiation
exiting the narrow ends of the channeling areas is directed toward the exit
port,
either directly or via one or more reflections from the reflective faces of
the
concentration chamber. An example of such a.configuration is given in Figure
3,
which shows a schematic cross-section of a portion of the device. In Figure 3,
the
device 100 has channeling areas 120 having broad ends 130 and narrow ends 140.
A concentration chamber 200 has entry ports 210 and an exit port 220. Also
shown in Figure 3 is an indicative path 22 that a beam of EM radiation r_:igct
iaicr..
through the device. In an alternative embodiment, the concentration chamber
200
may have an additional exit port 230 at its other end such that any EM
radiation
which is reflected toward that end of the concentration chamber could also be
utilized. This could add somewhat to the cost of the device but could serve to
increase its efficiency.
[00024] In order that the EM radiation entering the concentration
chamber is directed toward the exit port, while also providing a device with a
low
profile, it is desirable to steer the EM radiation within the channeling areas
such
that the direction normal to the plane of the narrow end of the channeling
areas
different from the direction normal to the collection surface. One way to
achieve
this is to curve the channeling areas as shown, for example, in Figure 3. In a
particular embodiment, the angle of curvature of the channeling areas is
approximately equal along their length to enhance the manufacturability of the
device, however this is not necessary for the device to function.
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[00025] In some embodiments of the invention, the channeling areas are
tapered in only one dimension, that is they take the form of tapered slots. In
other
embodiments, the channeling areas are tapered in two dimensions so that they
take
the form of tapered rods, where the rods can be of any cross-sectional shape
that is
suitable for packing together at high density. Examples of such shapes are
circles,
squares, rectangles, triangles and other multi-sided polygons.
[00026] When the channeling areas take the form of tapered rods, to aid
in accommodating the curvature or the rods,.maintain a high packing density
for
the broad ends of the channeling areas and enhance the strength of an assembly
of
the channeling areas, the channeling areas can be assz~r.:bieci. suc;i tiiat
eaõ"r.
channeling area is staggered relative to its neighbors. In a particular
embodiment
of this aspect of the invention, rows of channeling areas are assembled such
that
the channeling areas in each row are offset from the row in front such that
the
narrow end of each channeling area is between the narrow ends of the
neighboring
channeling areas in the rows immediately in front of and behind the subject
row.
By assembling the channeling areas in this way it is possible for the narrow
end of
each channeling area to curve into the space between the neighboring
channeling
areas in the row in front of it. This allows the channeling areas to be curved
while
maintaining high packing density of the broad ends of the channeling areas.
1000271 It is desirable to maintain a high packing density of the broad
ends of the channeling areas at the collecting surface so that the highest
fraction of
the EM radiation incident on the collecting surface enters a channeling area
and is
not reflected back.
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[00028] In one embodiment of the invention, the channeling areas are.
circular in cross-section and the broad ends are assembled in a packing
arrangement as is shown in Figure 4, where a top view of the assembled rows of
the broad ends of the circular channeling areas are shown offset from one
another.
Triangles are superimposed on the view to show the relationship of the centers
of
the circular ends. This arrangement increases packing density and allows space
for the channeling areas to be curved as disclosed above. With this
arrangement, a
.maximum fraction of 7c/243 (approx. 90%) of the incident radiation is
collected.
In a particular embodiment of this aspect of the invention, channeling areas
with a
square or rectangular cross-secti:in are used. A top view of this arrangement
is
shown in Figure 5. With this shape of channeling area, the broad ends of the
channeling areas can be packed such that close to 100% of the incident
radiation
enters the channeling areas and is thus collected. Note that in the embodiment
shown in Figure 5 it is possible, but not necessary, for the channeling areas
to be
of rectangular cross-section down their full length. For example, the
channeling
areas may be square or rectangular at the collecting surface but then
transition to a
circular area as we move down the channeling area toward its tip.
[00029] Devices in accordance with the invention are useful in
applications where EM radiation concentration devices have been used in the
prior
art, in particular solar radiation and radio frequency radiation. Examples of
such
uses particularly relevant to the collection and concentration of solar
radiation are
to heat fluid circulating through a tube or pipe, to generate electricity
directly
using photovoltaic cells or to produce hydrogen from water. Note that the
invention has particular utility in the application of producing electricity
using
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photovoltaic cells as it allows the light to be collected from an extended
area using
the relatively inexpensive device of the invention and concentrate it on to a
relatively small area of the relatively expensive photovoltaic cells. This
potentially allows electricity to be generated at lower capital cost. Also,
this
5 device addresses deficiencies in the conventional art when attempting to use
a
concentrator with photovoltaic cells. Apart from expense and weight, the
conventional devices suffer from relatively low concentration factors of
typically
less than 10 and the problem of the photovoltaic cells overheating and
becoming
less efficient. The invention can have high concentration factors. For
example, for
10 a panel according to the en;bodi;,i.znt shown in Figure 3 that is two
meters long
with an exit port nonnal to the axis of its length, running the full width of
the
panel and 2 mm high, the calculated concentration factor is 1000. Also, for an
embodiment as shown in Figure 3, the photovoltaic cells would be placed
adjacent
to and facing the exit port, such that the back of the panel of photovoltaic
cells is
in free space rather than against a surface such as a roof as would usually be
the
case in the conventional art. In this configuration, the back of the panel of
photovoltaic cells is thus easily accessible to cooling means such as finned
heat-
sinks, pads onto which water could be dripped and evaporated by ambient air
currents, or other cooling devices.
[00030) A low profile collector and concentrator is most desirable in
applications for radio frequency (RF) radiation. In these applications, the
device
could be used to focus the RF radiation onto an RF receiver. Also, by careful
choice of the dimensions of the channeling areas, the subject device could be
used
to tune the collected RF radiation to a frequency that can be received more
easily
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by a receiver. For example, the device can be used to tune the RF radiation to
a,
higher frequency, which requires a smaller and more easily implemented
receiver.
[00031] The subject devices can be made by any suitable method. The
channeling areas can be solid elements transmissive of light and made from
materials such as polymers or glass. For these solid elements, the walls of
the
elements can be coated with a reflective material or the refractive index of
the
material can be such that in most cases the incident angle of the EM to be
reflected
to the wall of the element exceeds the critical angle so that total internal
reflection
occurs. This embodiment has potential advantages in ease of fabrication but
can
also tend to be heavy. This embodiment could be constructed. by raunu;~cturing
many elements and assembling them into arraysas disclosed above. The broad
ends can be clamped or otherwise held together and, in the case of the
embodiment shown in Figure 3, the narrow ends can be set so that that they are
mounted in and penetrate a plate that forms the upper surface of the
concentration
chamber.
[00032] A particular embodiment is one where the channeling areas are
cavities formed in a monolithic block made of metal or polymer material. This
may be somewhat harder to fabricate but will be lighter. A method of
manufacturing this embodiment is to form an assembly of curved elements, for
example tapered elements, from a malleable material such as copper or nickel.
The assembly can be one of individual elements or of rows of elements formed
into combs where each tapered element is a "tooth" of the comb. Each comb
forms a row or portion of a row of the elements and the "teeth" of the combs
of
successive rows in the assembly are staggered to give the arrangements shown
in
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Figures 4 or 5. Before being assembled into an array, the elements can be
straight.
or already curved. If the elements are straight, a bar can be passed over the
assembly of the narrow ends of the elements as a convenient method of
introducing the desired curvature. The assembled elements can be held in their
assembly by being clamped into a frame or other similar device. The curved
assembled elements, in conjunction with side walls and, if applicable, a top
and/or
base, can then be used as a mold for the final monolithic shape. The shape
with
the desired assembly of cavities can be molded by any applicable method. It
may_
be cast by pouring polymer into the mold and letting it set or by injection
molding
techniques. In this process it is desirao:? t~~ ~al c:,at i,ie ~,).oid v~; i a
suitable
release agent to facilitate removal of the mold elements from the cast shape.
After
the cast shape is set the mold elements can be removed. This can most easily
be
achieved by first removing the cast shape from the mold side walls, top and/or
base then unclamping the assembly of elements and removing them separately or
in groups as is most convenient and practical. Note that in most cases the
elements will need to be straightened somewhat to be withdrawn from the
cavities
so it is desirable that the material from which the tapered elements are made
be
malleable so that in can undergo the straightening process without breaking or
distorting the shape of the cavity from which it is being withdrawn. This
process
results in a cast shape that contains an assembly of densely packed curved,
light
guiding cavities, wherein the broad ends of the cavities all open onto one
face of
the shape and the narrow ends of the cavities all open on to a different face
of the
shape.
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[00033] If the shape is not cast trom an intrinsically reflective material
such as metal or metal filled polymer, then the external faces of the shape
and/or
the walls of the cavities can to be coated with a reflective layer. For
polymer
material this is most easily achieved with an electroless metal deposition
process
such as electroless chrome or nickel deposition. A further transparent coating
could be applied over the reflective coating if desired to protect the
reflective
coating. The molded and coated shape can then be assembled into a collector
and
concentration device by mounting the shape in a box with a reflective internal
base
surface when the face of the shape into which the narrow ends open is spaced
apart from the re;lec~.:ve bas:, of the ~ox. base of the box and the lower
face
of the shape then form the top and base of the concentration chamber, where at
the
end of the box to which the narrow ends of the cavities are directed is the
opening
or transmissive.portion which serves as the exit port. A sheet of transmissive
material such as glass or clear polymer sheet can be placed over the assembled
array of broad ends of the cavities that forms the collecting surface in order
to
facilitate cleaning and prevent dust, dirt or water from entering the
cavities.
[00034] An alternative method for collecting the EM radiation to inject
it into the concentration chamber is to use a series of mirrors that focus the
light
into a series of spots or slots in the top of the concentration chamber. In
the case
of a slot, the optimal mirror shape is parabolic in the plane of the slot and
normal
to it. In the case of spots, the mirror is optimally a parabolic dish. The
slots or
spots are arranged to be at the focal line or point of the mirror such that EM
radiation reflected off the mirror is substantially concentrated into the
openings in
the top of the concentration chamber. To allow for different angles of EM
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radiation incident on the mirrors, the mirrors can be rotated about their
focal line
or point such that the focus of the light remains co-incident with the
openings in
the concentration chamber. A control mechanism can perform the rotation
whereby a signal, which could be the output from the EM radiation target or
from
a separate sensor, is monitored and the rotation of the mirrors performed so
as to
maximize the amount of EM radiation impacting the target.
[00035] In another aspect of the invention, the concentration chamber
can be designed so that the lower face of the concentration chamber slopes
from
the non-target end of the concentration chamber to the target end, with the
slope.
i1?i:-ng s'ach tha'c the tai get end nas a larger height than the non-target
end. This
assists in minimizing the number of reflections that are required in the
concentration chamber before the EM radiation impinges on the target.
[00036] In another aspect, the openings in the top of the concentration
chamber can be designed such that on the edge of the opening furthest from the
target a flap is attached that hangs down into the concentration.chamber. This
flap
helps to deflect the EM radiation entering the concentration chamber to
shallower
angles such that it is more likely to impinge on the target with a reduced
number
of reflections in the concentration chamber and helps to prevent light that
has
entered the concentration chamber from being lost through the other openings
in
the top of the concentration chamber. The openings in the top of the
concentration
chamber can be gaps in a solid element or alternatively they can be areas of
an
integral solid element that are transparent to the EM radiation, with other
areas of
the element being reflective of the EM radiation. For example, the top of the
concentration chamber can be a glass or polymer sheet which is selectively
coated
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with a reflective coating in areas other than those forming the openings to
the
concentration chamber. In this embodiment, the flaps could still be flaps of
material protruding into the concentration chamber or they could be formed as
the
back surface of a bulge in the top of the concentration chamber where the back
5 surface of the bulge is coated orotherwise made reflective, and the front
surface
(that closer to the target end of the concentration chamber) is transmissive
of the
EM radiation.
[00037] Figure 6 is a cross-section schematic which depicts these
aspects. In this example, a device 300 has focusing mirrors 310, slots or
spots 320
l0 onto which the EM radiation is focused, flaps 340 on the back edge oi a.'~
spots 320, a target 350 for the EM radiation and a sloped lower face 360 of
the
concentration chamber 330 that helps to direct the EM radiation toward the
target
350. In order to allow for different incident angles of EM radiation onto the
mirrors 310, the mirrors 310 can be made to rotate around their focal points
or
15 focal lines. Alternatively, the whole device can be rotated such that the
EM
radiation presents a constant incident angle to the min-ors 310 or a
combination of
rotation of the whole device with rotation of the individual mirrors 310.
[00038] A potential limitation of the embodiment shown in Figure 6 is
that the rotation of the parabolic mirrors in an counter-clockwise direction
(as
drawn in Figure 6) can be limited if the bottom of the mirrors collide with
the top
of the concentration chamber. The effect of this limitation is that the range
of
angles of light incident on the parabolic mirrors can be limited.
Specifically, in
some configurations light at some angle greater than normal to the plane of
the
mirror tops cannot be focused onto the entry points to the concentration
chamber
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as it cannot be made to intersect with the concave parabolic surface of a
mirror.
To overcome, or at least ameliorate this limitation, the back surface of the
mirror
structures can be formed so as to reflect light incident at angles past the
normal
onto the concave surface of the parabolic mirror behind it at the correct
angle such
that the light is then focused onto an entry point to the concentration
chamber. In
this aspect, the back surface is preferably a flat mirror, at least over the
portion
upon which light incident at the past normal angles to be focused impinges.
That.
is, the required portion of the back reflective surface of the mirror
structure is at a
constant angle relative to the incident light angle. The mirror structures can
be
rotated in a clockwise direction (as drawn in Figure 5; iO ensure chat iight
ai
different incident angles past the normal are focused onto an entry point to
the
concentration chamber, once they have been reflected from the concave
parabolic
surface of the preceding mirror structure. In an alternate embodiment, to
ameliorate this limitation the parabolic mirrors can be placed closer
together, thus
decreasing somewhat the cross-section of the entry area for each channel. This
allows the base of the parabolic mirrors to be raised, so as to increase the
gap
between the base of the parabolic mirror and the top of the concentration
chamber,
while still ensuring that all EM radiation that enters the channelling area
through
the entry area impinges on the concave surface of the parabolic mirror. The
increased gap between the base of the parabolic mirrors and the top of the
concentration chamber allows the mirrors to be rotated further in a counter-
clockwise direction (as drawn in Figures 5 and 6) such that a larger range of
angles
of radiation incident on the entry to the channelling area can be directed
toward
the exit of the channelling area.
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[00039] Figure 7 is a cross-section schematic which shows such a
variation of the example shown in Figure 6. In this variation, focusing mirror
310
that have a back side adjacent to a slot or spot 320, have a rear reflecting
surface
370 that reflects EM radiation (an example of which is depicted by light ray
400)
onto one of the focusing mirrors 310. Reflecting surfaces 370 can increase the
amount of EM radiation that eventually gets directed into slots or spots 320.
Similarly, the upper outside surfaces of concentration chamber 330 can be
shaped
to reflect EM radiation onto reflecting surfaces 370 and/or focusing mirrors
310 in
order to capture even more EM radiation.
[00040] The invention is noc iimited to ihe auuve-described exemplary
embodiments. It will be apparent, based on this disclosure, to one of ordinary
skill
in the art that many changes and modifications can be made to the invention
without departing from the spirit and scope thereof.
