U.S. patent number 3,788,729 [Application Number 05/248,479] was granted by the patent office on 1974-01-29 for thermal convection flow light valve.
This patent grant is currently assigned to Research Frontiers, Inc.. Invention is credited to Matthew Forline, Francis C. Lowell, Paul Rosenberg, Robert L. Saxe.
United States Patent |
3,788,729 |
Lowell , et al. |
January 29, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
THERMAL CONVECTION FLOW LIGHT VALVE
Abstract
A light valve includes a cell containing a fluid capable of
being acted upon by an electric or magnetic field, or both, to
change the transmission of light through the fluid, and means for
applying such a field thereto. Specifically described is a fluid
suspension of minute particles acted upon by an electric field. An
external or internal conduit connects opposite edge portions of the
cell and heat is applied to the fluid in the cell or conduit to
produce a thermal convection flow of the fluid through the cell and
conduit.
Inventors: |
Lowell; Francis C. (Roslyn,
NY), Forline; Matthew (Ozone Park, NY), Rosenberg;
Paul (Larchmont, NY), Saxe; Robert L. (New York,
NY) |
Assignee: |
Research Frontiers, Inc.
(Plainview, NY)
|
Family
ID: |
22939324 |
Appl.
No.: |
05/248,479 |
Filed: |
April 28, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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129873 |
Mar 31, 1971 |
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Current U.S.
Class: |
359/296 |
Current CPC
Class: |
G02F
1/172 (20130101) |
Current International
Class: |
G02F
1/01 (20060101); G02F 1/17 (20060101); G02f
001/36 () |
Field of
Search: |
;350/147,150,16R,267 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wibert; Ronald L.
Assistant Examiner: McGraw; V. P.
Attorney, Agent or Firm: Feldman; Stephen E.
Parent Case Text
This is a continuation of application Ser. No. 129,873, filed Mar.
31, 1971, and now abandoned.
Claims
We claim:
1. A light valve including a cell for containing a fluid capable of
being acted upon by an electric or magnetic field, or both, to
change the transmission of light through the fluid, said cell
having spaced wall sections, and means for applying a respective
electric or magnetic field, or both, to the fluid between said
spaced wall sections to change the light transmission thereof, in
which the improvement comprises conduit means for connecting
substantially opposite edge portions of said cell, at least one of
said conduit means and cell having a portion thereof extending in a
direction having a substantial vertical component, and means for
producing a thermal gradient in the fluid in said portion having a
substantial vertical component to produce a flow of the fluid
through said cell.
2. A light valve including a cell containing a fluid suspension of
minute particles dispersed therein capable of being acted upon by
an electric field to change the transmission of light through the
suspension, said cell having wall sections spaced apart a distance
which is small compared to the lateral dimensions of the sections
to confine the fluid suspension therebetween to a layer, and area
electrodes on opposite sides of said layer for producing an
electric field through the layer to change the light transmission
thereof, in which the improvement comprises conduit means for
connecting substantially opposite edge portions of said cell, at
least one of said conduit means and cell having a portion thereof
extending in a direction having a substantial vertical component,
and means for producing a thermal gradient in the fluid suspension
in said portion having a substantial vertical component to produce
a flow of the fluid suspension in said layer.
3. A light valve according to claim 2 in which the spacings of the
walls of said cell at said opposite edge portions connected by said
conduit means are substantially greater than the spacing of the
wall sections in the region of said layer, thereby forming channels
at opposite edges of said layer.
4. A light valve according to claim 3 in which a portion of said
conduit means extends in a direction having a substantial vertical
component, said means for producing a thermal gradient in the fluid
suspension including heating means operatively associated with said
portion of the conduit means for heating the fluid suspension
therein.
5. A light valve according to claim 3 in which said cell extends in
a direction having a substantial vertical component and said
channels are at upper and lower edges of said layer, and including
heating means for heating a region of said cell extending laterally
of the cell near the bottom thereof to produce said temperature
gradient.
6. A light valve according to claim 3 in which said cell extends in
a direction having a substantial vertical component and said
channels are at upper and lower edges of said layer, and including
means for subjecting at least a portion of the fluid suspension in
said layer and at least a portion of said conduit means to
different ambient temperatures to thereby produce said temperature
gradient.
7. A light valve according to claim 3 in which said cell extends in
a direction having a substantial vertical component, said channels
are at upper and lower edges of said layer, and said conduit means
is a conduit of heat-transmitting material positioned exteriorly of
said cell and connecting said channels, and means for subjecting at
least a portion of said cell and at least a portion of said conduit
to different ambient temperatures to thereby produce said
temperature gradient.
8. A light valve according to claim 3 in which said cell extends in
a direction having a substantial vertical component and said
channels are at upper and lower edges of said layer, said conduit
means comprising a barrier wall between the walls of said cell on
one side of the region of said layer, said barrier wall being
spaced from the corresponding side of the cell and spaced from the
top and bottom of the cell to form a conduit between said upper and
lower channels of the cell, the spacing of the walls of the cell
between said barrier wall and the corresponding side of the cell
being substantially greater than the spacing of the wall sections
in the region of said layer.
9. A light valve according to claim 8 in which said means for
producing a temperature gradient comprises electric heating means
for heating the fluid suspension in said conduit.
10. A light valve according to claim 8 in which said means for
producing a temperature gradient comprises electric heating means
extending laterally of said cell below said area electrodes.
11. A light valve according to claim 10 in which said electric
heating means comprises an electrical resistive coating on the
inner surface of at least one of the walls of the cell below the
area electrode on the respective wall and insulated therefrom.
12. A light valve according to claim 3 in which said cell extends
in a direction having a substantial vertical component and said
channels are at upper and lower edges of said layer, said conduit
means comprising a pair of barrier walls between the walls of said
cell on respectively opposite sides of the region of said layer,
said barrier walls being spaced from the respective sides of the
cell and spaced from the top and bottom of the cell to form a pair
of conduits between said upper and lower channels of the cell, the
spacing of the walls of the cell between said barrier walls and the
respective sides of the cell being substantially greater than the
spacing of the wall sections in the region of said layer.
13. A light valve according to claim 12 in which said means for
producing a temperature gradient comprises electric heating means
for heating the fluid suspension in each of said conduits.
14. A light valve according to claim 3 in which said cell and at
least a portion of said conduit means are at different vertical
levels with a portion of the conduit means extending in a direction
having a substantial vertical component, and said channels are at
horizontally separated edges of said layer.
15. A light valve according to claim 14 in which said means for
producing a thermal gradient includes heating means operatively
associated with said portion of the conduit having a substantial
vertical component.
16. A light valve according to claim 14 in which said cell is at a
lower vertical level than a portion of said conduit means, and said
means for producing a thermal gradient includes heating means
operatively associated with one of said channels for heating the
fluid suspension therein.
17. A light valve according to claim 16 in which said heating means
comprises an electrical heating element in said one channel, and
including a barrier wall in said one channel positioned between
said heating element and the adjacent edge of said layer and spaced
from the adjacent edge of the layer, one end of said barrier wall
being spaced from the adjacent edge of the cell to allow flow of
the fluid suspension thereby.
18. A light valve according to claim 15 in which said cell is
disposed generally horizontally and said flow of the fluid
suspension in said layer is in a generally horizontal
direction.
19. A light valve including a cell for containing a fluid capable
of being acted upon by an electric or magnetic field, or both, to
change the transmission of light through the fluid, said cell
having spaced wall sections and means for applying a respective
electric or magnetic field, or both, to the fluid between said
spaced wall sections to change the light transmission thereof, in
which the improvement comprises means for producing a thermal
gradient in the fluid to produce a flow of the fluid through said
cell when said fluid is being acted upon by said electric or
magnetic field or both.
20. The light valve of claim 19 wherein the fluid is a fluid
suspension.
21. A light valve including a cell for containing a fluid capable
of being acted upon by an electric or magnetic field, or both, to
change the transmission of light through the fluid, said cell
having spaced wall sections and means for applying a respective
electric or magnetic field, or both, to the fluid between said
spaced wall sections to change the light transmission thereof, in
which the improvement comprises means for producing a thermal
gradient in the fluid to produce a flow of the fluid through said
cell in a defined path to prevent significant agglomeration in the
fluid.
22. The light valve of claim 21 wherein the fluid is a fluid
suspension.
23. The method of preventing significant agglomeration in a fluid
suspension in a light valve wherein the light valve includes a cell
for containing the fluid suspension which is capable of being acted
upon by an electric or magnetic field, or both, to change the
transmission of light through the fluid suspension comprising the
steps of producing a thermal gradient in the fluid suspension when
said fluid suspenson is being acted upon by the electric or
magnetic field or both and causing a flow of the fluid suspension
through the cell by means of the thermal gradient.
24. The method of preventing significant agglomeration in a fluid
suspension in a light valve wherein the light valve includes a cell
for containing the fluid suspension which is capable of bring acted
upon by an electric or magnetic field, or both, to change the
transmission of light through the fluid suspension comprising the
steps of producing a thermal gradient in the fluid suspension and
causing a flow of the fluid suspension through the cell in a
defined path by means of the thermal gradient.
Description
BACKGROUND OF THE INVENTION
This invention relates to light valves of the type including a cell
containing a fluid capable of being acted upon by an electric or
magnetic field, or both, to change the transmission of light
through fluid.
The invention is particularly applicable to light valves utilizing
a fluid suspension of minute particles dispersed therein. Light
valves of this type have been known for many years. Fluid
suspensions of herapathite in a suitable liquid have commonly been
preferred, although other types of particles have been suggested.
In general, the shape of the particles is such that in one relative
arrangement they intercept more light than in another relative
arrangement. Particles which are needle-shaped, rod-shaped,
lath-shaped or in the form of thin flakes have been suggested. The
particles may variously be light absorbing or light reflecting,
polarizing, birefringent, metallic or non-metallic, etc. In
addition to herapathite, many other materials have been suggested
such as graphite, mica, garnet red, aluminum, periodides of
alkaloid sulphate salts, etc. Preferably dichroic, birefringent or
polarizing crystals are employed.
Very finely-divided or minute particles are employed, and are
suspended in a liquid in which the particles are not soluble, and
which is of suitable viscosity. In order to help stabilize the
suspension when in the non-actuated state, a protective colloid
should preferably be used to prevent agglomeration or settling.
A fluid suspension which has been used with success uses generally
needle-shaped particles of herapathite, isopentyl acetate as the
liquid suspending medium, and nitrocellulose as a protective
colloid. Plasticizing agents such as dibutyl phthalate have also
been used in the suspension to increase the viscosity.
Both electric and magnetic fields have been suggested for aligning
the particles, although electric fields are more common. To apply
an electric field, conductive area electrodes are provided on a
pair of oppositely disposed walls of the cell, and an electric
potential applied thereto. The electrodes may be thin transparent
conductive coatings on the inner sides of the front and rear walls
of the cell, thereby forming an ohmic type cell wherein the
electrodes are in contact with the fluid suspension. It has also
been suggested to cover the electrodes with a thin layer of
transparent material such as glass in order to protect the
electrodes. Such thin layers of glass form dielectric layers
between the electrodes and the fluid suspension, and the cells may
be termed capacitive cells. Direct, alternating and pulsed voltages
have been applied to the electrodes in order to align the particles
in the fluid suspension. When the voltage is removed, the particles
return to a disoriented random condition due to Brownian
movement.
Commonly the front and rear walls of the cell are transparent, for
example, panels of glass or plastic. With no applied field, and
random orientation of the particles, the cell has a low
transmission to light and accordingly is in its closed condition.
When a field is applied, the particles become aligned and the cell
is in its open or light transmitting condition. Instead of making
the rear wall transparent, it may be made reflective. In such case
light is absorbed when the cell is unenergized and is reflected
when the cell is energized. These principal actions may be modified
by employing light reflecting rather than light absorbing
particles. It is also possible to select types of particles and
applied fields such that application of a field closes the cell and
removal of the field opens the cell.
In such cells a serious problem is the agglomeration of the
particles. While protective colloids are helpful in reducing or
avoiding agglomeration in the stored or inactive condition, when
the cell is in use the tendency to agglomerate increases. Depending
on the particular suspension employed, and the voltage and
frequency used, agglomeration may become noticeable in a matter of
seconds, minutes or hours of use. Once agglomeration has occurred,
it tends to remain more or less permanently even though the
exciting voltage is removed.
Such agglomeration considerably impairs the usefulness of the light
valve since it creates inhomogeneities in the suspension and hence
changes the light transmission from point to point. Also it reduces
the ratio of optical density between the closed state and the open
state. Further, the density in the closed state may decrease.
The possible setting of particles out of the fluid suspension has
previously been recognized. In this connection it has been
suggested to furnish a constantly renewed supply of particles to
the suspension, or to stir up and redistribute settled particles,
or to cause a slight current or flow of particles within the
container so as to assure a constant suspension. While such
expedients may help to avoid settling, agglomeration may still
occur during use. Also, the turbulence involved may appreciably
affect the performance of the cell.
In copending application Ser. No. 25,542, filed Apr. 1, 1970 by
Matthew Forlini for "Light Valves with High Frequency Excitation,"
the use of frequencies higher than heretofore proposed is
described, in order to avoid agglomeration of the particles in the
suspension. While effective, the use of high frequencies involves
considerable power consumption in the high frequency power source,
and the power source may be quite expensive.
In copending application Ser. No. 174,494 filed Aug. 24, 1971 and
now U.S. Pat. No. 3,708,219 by Matthew Forlini et al. for "Light
Valve with Flowing Fluid Suspension" a circulating system is
described for producing a flow of fluid suspension through the cell
during operation thereof to reduce or avoid agglomeration of the
particles. Various means are described for producing a smooth
generally laminar flow of the fluid suspension in the active region
of the cell. Mechanical pumps are particularly described. While
effective, the pumps may be relatively costly, bulky, heavy and
somewhat noisy, and may produce undesirable mechanical vibrations
in the cell. Also substantial power may be required to drive the
pump.
The present invention is directed to producing a flow of the fluid
suspension by less expensive, less bulky and lighter means which is
completely free of vibration and noise and requires a relatively
small amount of power for operation.
SUMMARY OF THE INVENTION
In accordance with the present invention, thermal convection flow
of the fluid or fluid suspension through the cell is produced. To
this end, fluid conduit means connects substantially opposite edge
portions of the cell and the conduit means and cell are arranged so
that the conduit means or cell, or both, have a portion thereof
extending in a vertical direction, or in a direction having a
substantial vertical component sufficient to yield the desired
thermal convection flow. Means are provided for producing thermal
gradient in the fluid in the portion having a substantial vertical
component to produce a thermal convection flow of the fluid through
the cell.
Preferably the spacings of the walls of the cell at the opposite
edge portions connected by the conduit means are substantially
greater than the spacing of the wall sections in the active region
of the cell so as to form channels promoting a smooth generally
laminar flow in the active region.
In certain embodiments of the invention both the cell and the
conduit means extend vertically, or in a direction having a
substantial vertical component, and the conduit means connects
channels at the upper and lower edges of the active cell region. A
differential temperature is produced between at least a portion of
the fluid suspension in the cell and at least a portion of the
fluid suspension in the conduit means, thereby producing a thermal
gradient in the vertical direction which causes a thermal
convection flow of the fluid suspension through the cell. The
conduit means may be one or more conduits positioned exteriorly of
the cell, or may be built integrally with the cell structure so as
to extend upwardly on one or both sides of the active cell region
and separated therefrom by barrier walls. The differential
temperature may be produced by applying heat to the conduit means.
Or, heat may be applied to a laterally extending region of the
cell, preferably below the active region thereof.
In other embodiments of the invention, the cell, conduit means and
heating are arranged so that fluid flow in the active area of the
cell is generally horizontal, although still produced by thermal
convection. This is advantageous in the case of long narrow
vertical cell panels where the long dimension is horizontal, and
also permits the cell panels to be oriented in a horizontal
plane.
Broadly, in these other embodiments the cell and at least a portion
of the conduit means are located at different vertical levels, and
heat is applied at a suitable region to produce a thermal
convection flow. As specifically illustrated, the channels
connected by the conduit means are at opposite
horizontally-separated edges of the active cell region, and heat is
applied to an upwardly-extending portion of the conduit means, or
in a channel connected to such an upwardly-extending portion.
Electric heating coils, resistive coatings, heating wires or
ribbons, etc. may be employed, energized with A-C or D-C from a
suitable power source. Other sources of heat (or cold) may also be
employed, if desired, as will be mentioned hereinafter. Control of
the heating is desirable in order to permit obtaining the maximum
rate of flow without an excessive temperature rise which might
degrade the suspension.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a light valve using an external
conduit with an electric heater associated therewith;
FIG. 2 is a face view of the arrangement of FIG. 1, with portions
broken away;
FIG. 3 is a cross-section taken along the line 3--3 of FIG. 2;
FIG. 4 is a face view of another embodiment of the invention, with
portions broken away, using an internal conduit with a heating
strip along the bottom of the cell;
FIG. 5 is a cross-section taken along the line 5--5 of FIG. 4;
FIG. 6 shows another embodiment of the invention, with portions
broken away, using internal conduits with heating means located
therein;
FIG. 7 is a horizontal cross-section taken along line 7--7 of FIG.
6;
FIG. 8 shows an alternative structure to that shown in FIG. 7;
FIG. 9 illustrates a light valve with external conduit mounted in
the wall of a building;
FIG. 10 is a cross-section taken along the line 10--10 of FIG.
9;
FIG. 11 illustrates an embodiment of the invention in which fluid
flow in the cell is horizontal rather than vertical, and FIG. 12 is
a cross-sectional along the line 12--12 of FIG. 11; and
FIGS. 13-17 illustrate several different conduit and cell
arrangements for horizontal fluid flow.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Referring to FIGS. 1-3, a light valve generally indicated as 10 is
formed of two sheets 11 and 12 of transparent material such as
glass, plastic, etc. Transparent conductive coatings 13 and 14 are
formed on the inner surfaces of sheets 11 and 12 to form parallel
area electrodes in the desired active area of the valve. As shown,
the electrodes are in contact with the fluid suspension, thereby
forming an ohmic type cell. If desired they could be covered with a
thin layer of transparent material such as glass to form a
capacitive type cell.
In the region between coatings 13 and 14, the front and rear walls
are spaced apart a distance which is small compared to the lateral
dimensions of the wall sections so as to confine the fluid
suspension therebetween to a layer. Spacings of the order of 10 to
25 mils are advantageously employed, although spacings outside this
range may be used if desired.
The spacings between the front and rear walls at the upper and
lower portions of the cell are substantially greater than the
spacing of the wall sections in the region of the layer, as shown
at 15 and 16 in FIG. 3, and may be of the order of one-half inch,
for example. These relative dimensions are impractical to show in
the drawings. The transparent sheets are separated by thin spacers
on each side of the cell, one of which is shown at 17 in FIG. 1,
and by thicker spacers at the top and bottom, shown at 18 and 19.
The spacers may be of sealing material or cemented to the
transparent sheets, etc. to produce a completely sealed fluid-tight
enclosure for the fluid suspension. The upper and lower regions 15
and 16 of the cell are connected by a conduit 21. Spacers and
sealing materials are desirably inert to the suspension. For
example, spacers such as glass, or a plastic such as polyethylene,
polypropylene or epoxy-filled fiberglass, may be employed.
The entire cell and conduit are filled with a suitable fluid
suspension of minute particles dispersed therein capable of
orientation by an electric field applied between area electrodes 13
and 14. To avoid confusion, the fluid suspension is not
specifically shown in the drawings, but arrows indicate the thermal
convection flow thereof as will be described below.
Heating means are provided for heating the fluid suspension in the
conduit 21 and here takes the form of an electric heating coil 22
enclosed in the heating insulating casing 23. Advantageously the
turns of the coil are closely spaced to avoid local hot and cool
sections. The heating coil may be energized in any suitable manner,
either with A-C or D-C, as desired. In FIG. 1, a plug 24 is adapted
to be connected to the power mains and a switch 25 and variable
resistor 26 are inserted in series with the coil to control the
energization thereof.
When heat is applied by coil 22, the heating of the fluid
suspension causes a thermal convection flow of the fluid suspension
as indicated by the arrows in FIGS. 2 and 3. As the fluid
suspension is heated by coil 22, it expands and its specific
gravity decreases. Accordingly, the heated suspension rises in
conduit 21, thereby forcing the suspension above it upward and into
the channel 15 at the top of the cell and drawing the suspension
from the channel 16 at the bottom of the cell into the lower
portion of the conduit 21. This causes a downwardly flow of the
suspension in the thin layer between electrodes 13,14. The
suspension gradually cools as it circulates until it again reaches
the heating region of coil 22, so that a differential temperature
is maintained between the suspension in the heating zone of the
conduit and that in the cell. Thus a continuous thermal convection
flow is produced.
By making the upper and lower regions 15 and 16 of substantially
greater spacing than that between electrodes 13,14, the resistance
to fluid flow in 15 and 16 can be made much less than that between
the electrodes. Thus the flow in the layer between the electrodes
is smooth and substantially laminar, rather than turbulent, so that
the flow does not interfere with proper operation of the light
valve.
The area electrodes 13 and 14 are energized in any desired manner
from a source generally indicated as 27, in order to vary the light
transmission of the cell.
Inasmuch as the fluid suspension in regions 15,16 is not in the
active region of light control, these regions may be made opaque by
suitable coatings, framing, etc.
The heating coil 22 is shown approximately at the middle of conduit
21, which is considered preferable. However it can be positioned
higher or lower if desired. By adjusting resistor 26, the heating
can be controlled to yield a suitable convection flow without
raising the temperature of the fluid suspension to a degree which
will degrade the suspension. The conduit 21 is advantageously of
metal having good heat conductivity to promote more efficient and
rapid thermal convection flow, although other materials could be
used if desired. For example, if heating means is provided inside
the conduit, it may be advantageous to form the conduit of heat
insulating material.
Referring to FIGS. 4 and 5, an internal conduit 31 is formed on one
side of the cell by a barrier wall 32 of heat-insulating material.
The barrier wall is sealed to the front and rear walls of the cell
and is spaced from the corresponding side 33 of the cell. It is
also spaced from the top and bottom of the cell to form a closed
path for the circulation of the fluid suspension. The spacing of
the walls at the upper and lower portions 15 and 16 of the cell is
greater than that between the area electrodes, as in the previous
embodiment, and the spacing at conduit 31 is also greater so as to
reduce resistance to fluid flow therein.
In this embodiment the heating of the fluid suspension is along the
bottom of the cell, rather than in the conduit. To this end
laterally-extending electrical resistive coatings 34 and 35 are
formed on the inner surfaces of the cell walls and spaced from the
area electrodes 13 and 14 as indicated at 36 and 37 so as to be
insulated therefrom. The resistive coatings 34,35 are supplied with
heating current from a suitable source 39 under the control of
switch 25 and rheostat 26. If desired, a resistive coating on only
one cell wall could be employed. These resistive coatings need not
be transparent, since they are below the active region of light
transmission control.
Inasmuch as heat is applied below the active cell region in this
embodiment, the fluid suspension will rise by thermal convection as
indicated by arrows 41, and will return downward through conduit
31, as indicated by arrows 42. The suspension will gradually cool
as it circulates until it again reaches the heating zone.
Instead of using a resistive coating on the inner walls of the
cell, electrical strip heaters may be employed. If necessary, the
heating coating or elements may be covered with a thin layer of
insulating material such as a thin layer of glass so as to insulate
the heating element from the fluid suspension and the electrodes
13, 14. Alternatively, a heating wire or wires may be embedded in
the glass sheet or sheets, or wrapped around the bottom of the
cell.
The embodiment of FIG. 4 with an internal conduit 31 is more
compact than that of FIG. 1 and hence advantageous for many
applications. If desired, however, an external conduit may be used
as in FIG. 1, thereby promoting more rapid cooling of the
suspension outside the heating region 34, 35.
It is possible that in some instances coatings 34, 35 could be made
conductive and the power source connected between them to heat the
lower region of the suspension by current flow therethrough. This
is not preferred at the present time since the suspensions commonly
employed are of high resistance even in thin layers and sufficient
heating would be difficult to obtain.
The light transmission of the valve is controlled by source 27, as
in the previous embodiment. The connections from source 27 to the
area electrodes 13 and 14 are shown conventionally as wire leads
28, 29. In practice, conductive coatings may be formed on the inner
surfaces of the front and rear sheets and brought out to the edge
of the cell, so as not to interfere with fluid flow in conduit 31.
Regions 15, 16 and those of coatings 34, 35 and conduit 31 may be
made opaque if desired, since they are outside the region of light
control.
Referring to FIGS. 6 and 7, internal conduits 51 and 52 are
provided on each side of the cell by barrier walls 53 and 54, and
heating wires 55 and 56 are mounted vertically therein by
insulating plugs 57. The heating wires are energized in any
suitable manner as indicated by power source 58. Suitable current
control may be employed as described in connection with previous
embodiments. The fluid suspension will rise by convection in both
conduits 51 and 52, and flow downwards between the area
electrodes.
In this embodiment, instead of sealing the glass walls together
around their peripheries, a U-shaped metal frame 61 is employed,
e.g., of stainless steel. As indicated in FIG. 7, the barrier walls
53, 54 establish the desired separation of the glass walls between
area electrodes 13 and 14. The metal frame 61 is then sealed to the
exterior surfaces of the walls by a suitable adhesive. Insulated
coatings extending vertically on the walls of conduits 51, 52 could
be used in place of resistance wires 55, 56, if desired.
FIG. 8 shows an alternative arrangement in which one glass wall
extends beyond the other and an L-shaped metal frame 62 is employed
which is sealed to the glass walls.
A metal frame of the type shown in FIGS. 6-8 could also be employed
in the previous embodiments if desired, and in general would
promote cooling of the suspension outside the heating region.
FIGS. 9 and 10 show an arrangement of the type of FIGS. 1-3, but
with the heating coil 22 and insulating casing 23 omitted, mounted
as a window in the wall of a building so that a differential
temperature between cell and conduit is established without
requiring a specific heat source. Here the cell is mounted in an
opening in the wall 65 with the conduit 21' extending inside the
building. As specifically shown, the conduit 21' is connected at
the top and bottom edges of the cell rather than at the top and
bottom of a side edge, but still serves to connect channels 15 and
16. Connection to the side edge as in FIGS. 1-3 would be possible
provided the adjacent room wall 65 is cut away so that the conduit
21' is still exposed to the inside temperature.
When the outside temperature is lower than the inside, the fluid
suspension in conduit 21' will be at a higher temperature than that
in the cell, and thermal convection flow will occur as desired in
connection with FIGS. 1-3. When the outside temperature is higher,
thermal convection flow will be in the opposite direction. If
necessary, additional thermal insulation can be placed between
conduit 21' and wall 65.
It is possible, of course, for the outside and inside temperatures
to be the same. However, a temperature differential may still be
present due to the difference in radiation impinging on the cell
and conduit, from sunlight for example, and wind may disturb the
thermal equilibrium. Although the temperature differential in FIG.
9 is less positive than in the other embodiments, and convection
flow may sometimes be less strong, the embodiment has the
advantages of simplicity and lower cost and requires no source of
electric power.
The embodiments of FIGS. 4 and 6 could also be used in the wall
arrangement of FIG. 9, and the specific heating means eliminated.
In such case the internal conduits can be mounted in the wall so as
to be insulated on the outside but exposed on the inside to room
temperature.
It is possible also to arrange the conduits so as to be exposed to
the outside temperature, since the cell walls will be thermally
exposed to both outside and inside temperatures and hence the fluid
suspension in the active cell region will be at an intermediate
temperature.
In the preceding embodiments the cells are assumed to extend in a
vertical direction, or at least in a direction having a substantial
vertical component, and the flow of the fluid suspension in the
active cell region is generally upward or downward. In subsequent
embodiments, fluid flow in the cell is generally horizontal.
FIGS. 11 and 12 show the cell 10 disposed in a vertical plane, with
channels 71 and 72 located at the side edges of the active cell
region between area electrodes 13 and 14 so that the channels are
horizontally separated. The cell construction is otherwise like
that shown in FIGS. 1-3 and need not be described in detail.
Energization of the electrodes is omitted for simplicity. Conduit
70 has a horizontal portion 73 and vertical portions 74, 75
connecting channels 71 and 72. A heat source is arranged to heat
the fluid suspension in one of the vertical portions 74, 75 here
shown as an electrical heating coil 76. The coil would normally be
heat insulated as illustrated in FIG. 2, but is shown only
diagrammatically for simplicity of illustration.
With heat applied, the fluid suspension rises in conduit section 74
and flows through the conduit, as shown by arrow 77, to channel 72
and thence through the active cell region between electrodes 13,14
to channel 71 and back to conduit section 74. Since the layer
between area electrodes 13, 14 is very thin compared to the
corresponding dimensions of channels 72 and 71, the fluid flow
across the cell is generally laminar.
In subsequent embodiments the active cell region between area
electrodes 13, 14 is indicated by dash lines, and channels 71, 72
are denoted CH.
FIG. 13 is similar to FIG. 11 except that the cell 10 is located at
a higher vertical level than the conduit 70, and channels CH are
tapered to join with the conduit. The tapered configuration could
be used in FIG. 11, or the ends of the conduit could be connected
to the bottom of channels CH in FIG. 11.
In both the arrangements of FIGS. 11 and 13, the cell 10 could be
disposed in a horizontal plane with conduit 70 above or below the
cell, suitable bends being introduced in the conduit so that the
portion thereof at which heat is applied extends vertically, or in
a direction having a substantial vertical component. Fluid flow
will still be in the direction indicated by the arrows.
FIG. 14 is similar to FIG. 11, but here a resistance heating
element 78 is positioned in the outlet channel 71' to heat the
fluid suspension. Advantageously a barrier wall 79 is positioned in
channel 71' between the heating element 78 and the adjacent edge 81
of the thin layer of fluid suspension between the area electrodes,
so as to avoid local circulation currents near edge 81. Barrier
wall 79 extends from the upper toward the lower edge of the cell
and is spaced from the lower edge to allow flow of the fluid
suspension thereby as indicated by arrow 82.
FIG. 15 is similar to FIG. 11, except that the conduit is connected
to the outlet channel at the bottom thereof, rather than the
top.
FIG. 16 shows the conduit connected to lateral edges of the
channels CH, the connection to the inlet channel being near the
bottom thereof and the connection to the outlet channel being near
the top thereof.
FIG. 17 is similar to FIG. 13, but here cell 10 is disposed in a
horizontal plane, or generally horizontally, thereby enabling it to
be used in the roof of a vehicle, as a skylight, in a greenhouse,
etc. where light control is desired. The conduit sections 74", 75"
are bent laterally so that the connecting portion (not shown) will
not block the beam of light through the cell.
The specific embodiments show rectangular cells which are likely to
satisfy a wide variety of applications. However the cell shape may
be different if desired, such as round, square, tapered, etc. Also,
cells could be arranged in series or parallel with a single
recirculating conduit and heat source. In the series arrangement
one cell would form part of the conduit means for the other
cell.
The specific heat sources in the embodiments of FIGS. 1-8 are
electrical in nature and are generally convenient to use. However,
radiant heat sources designed to concentrate heat in the desired
regions could be employed if desired, or other suitable means for
applying heat to the proper regions. Also, instead of using a
source of heat to produce a temperature difference, it would be
possible to use a cooling or refrigerating source, although such
sources are commonly more expensive and bulky at the present
time.
Although the light valves described are commonly used with visible
light sources, with suitable suspensions it may be possible to
control the passage of other types of electromagnetic radiation
such as infrared and ultraviolet light. Also, instead of using
continuous area electrodes within the active region of the cell,
the electrodes may be formed in patterns so as to exhibit a desired
display. Further, instead of allowing light to pass through the
cell from front to rear, the rear surface may be made reflective so
as to provide a mirror of variable reflectivity. It will be
understood that the term "light valve" applies to these various
types of applications.
The invention has been described in connection with a number of
embodiments thereof, and certain variations have been mentioned. It
will be understood that other modifications are possible within the
spirit and scope of the invention as defined in the claims.
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