Note: Descriptions are shown in the official language in which they were submitted.
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ADAPTIVE MODIFICATION OF SURFACE PROPERTIES TO ALTER
THE PERCEPTION OF ITS UNDERLYING STRUCTURE
Specification
Field
Adaptively modifying properties of a viewed surface to
change the perception of its underlying structure.
Backqround
Many of the definitive characteristics of a structure are
perceived by a viewer or investigative system by properties of
its surface. While the surface characteristics may be entirely
different from characteristics of the underlying structure, still
they at least suggest to the observer significant information
about the structure itself.
For example, a coat of paint on the chassis of a vehicle,
says somethirig about the shape and color of the coat' of paint on
the vehicle, but it says nothing about the metal -skin on which it
is laid, except for its outer shape and color assuming that the
paint is a uniform layer. Similarly it says nothing about an
engine or anything else inside of it or inside an overlaying or
shrouding skin. Thus, the characteristics of a surface which is
directly viewed by the observer convey all of the information
available to the observer. Changing these characteristics can
change the observer's perception of the structure itself..
For example, in visible light, color patterns in a coat of
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paint.may be of considerable interest. National emblems,
cautionary displays, distracting or misleading images, and colors
that do or do not contrast with the background are.examples.
Some colors may be intended to be glaringly obvious, while others
are preferred to fade into the background. The art of color
camouflage exemplifies one field of presenting a colored surface
that is hopefully hidden in plain sight.
The above relates to reactions to visible light which light
is emitted by, or which is reflected from the surface. This is
only one example of means to perceive a structure. Other means
which are pertinent to this invention are responses to
frequencies outside of the visible spectrum, for example infrared
and radar frequencies. For these, observation devices vary from
reception of frequencies emitted or which are reflected by the
surface itself, namely its infrared emission, or received (or
modified) reflection of radar frequencies originated by the
observing device which are reflected by the surface.
It is an object of this invention adaptively to change
significant properties of the surface of a structure, by altering
the emissive properties of the surface itself, or by altering its
reflective properties. In both of these circumstances an
observing device or person will be convinced to perceive
pertinent properties that are not necessarily those of the
underlying structure.
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Reduced to absurdity, a structure may be camouflaged by
repainting it, or by painting over indicia, for example. But
then this arrangement remains until a next coat of paint is
applied. Desert vehicles are painted once. If they are sent to
the Arctic, they may be painted another color. But when they are
in one place, their perceived color pattern is established and
does not change.
In contrast, this invention proposes to alter surface
properties literally on demand, between at least two different
conditions. In this specification, the "perceived surface" is
the interface with the atmosphere which is sensed by an observer.
Its properties are determined by its immediate substrate. For
example, the perceived surface of a coat of paint possesses
properties determined by its substrate paint. A coating that
does not alter the characteristics being observed is not regarded
as the perceived surface for purposes of this invention.
This invention utilizes the effect of temperature of the
perceived surface to alter the observed characteristics. For
adaptive purposes, if temperature is the sensed property, the
alternating property is.the temperature itself. if color or some
other reflected observable property is to be sensed, then a
temperature-responsive substance is used for the exposed surface,
with a substrate whose temperature can be changed. Of course,
the surface may itself be the boundary of a substrate of the same
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material; for example a coat of paint. Thermochromic films or
layers for change of colors, and embedded radar absorbing
particles whose size changes with temperature to vary reflection
or adsorption of radar frequencies are examples.
The change of temperature is achieved by the use of the
well-known Peltier effect, in which a lower temperature is
created on one side of a semi-conducting array or layer, and an
elevated temperature on the opposite side. This essentially is
the transfer of caloric heat to or from the first surface,
(usually the exposed surface) to an underlying substrate or
structure. The temperature of the exposed surface can thereby be
changed, either increased or decreased, by current applied to the
device, and the direction of the effect. To increase the effect,
one merely increases the current density. Thus, by the mere
exertion of an electrical current, the temperature, and with it
the perception of a surface, can adaptively be adjusted and
changed. Such devices are frequently used as "thermoelectric
coolers" (TEC).
With the change in*temperature of the exposed surface, its
visible or emission properties can be changed, resulting in
confusion of the observer.
Brief Description
This invention utilizes the Peltier effect to control the
temperature of a perceived surface. The controlled temperature
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is determined by the intensity and direction of the electrical
current applied to the Peltier device.
According to this invention the Peltier device is applied as
a surface on or spaced from an underlying structure or substrate
that is shielded from direct observation by the Peltier device
itself.
The device itself may be the directly observed surface or it
may carry on it or have applied to it a cover such as paint which
will share the controlled temperature. This cover may itself
have thermochromic properties that are specifically visually
observed, or radar-frequency reflective or absorptive properties
that are specifically reflected or absorbed, the reflection being
:the observed property.
The perceived surface need not itself be a contiguous part
!of the underlying structure. For example it might be
:,sufficiently spaced from the underlying structure (such as a jet
engine tail pipe), that its own surface temperature is riot unduly
associated with the tailpipe temperature, but it is seen by the
observer (for example by a heat-seeking missile) as the structure
itself. Of course it must be suitably spaced from, or suitably
insulated from, such hot gases or surfaces that might melt or
otherwise hamper the Peltier device.
Brief Description of the Drawings
Fig. 1 is a fragmentary cross-section of a Peltier device
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installed according to this invention;
Fig. 2 is a plan view showing a plurality of devices
according to Fig. 1 installed as a group;
Figs. 3 and 4 are fragmentary conceptual views showing two
observed conditions;
Fig. 5 is a schematic side view, partly in cross section,
showing a use for this invention;
Fig. 6 is a view similar to Fig. 5 showing another use for
this invention;
Fig. 7 is an axial cross-section of another embodiment of
this invention;
Fig. 8 is a cross-section taken at line 8-8 in Fig. 7; and
Fig. 9 is a circuit drawing for the control of this
invention.
.Detailed Description
As an example of the intended effect of this invention Figs.
3 and 4 show two different colorations on a surface 21. Surface
21 includes a patterned area 22 and a background area 23. At
normal temperatures, for example atmospheric temperature between
perhaps 70-110 degrees, the surface color, of areas 22 and 23
will be the same. A visual observer will perceive the entire
surface as a single-colored continuum. The outline 24 of
patterned area 22 is shown schematically. It is not a visible
line.
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.When this invention is utilized and the patterned area 22 is
thermochromic, this area became visible in some color different
from the background area 23. A cross thereby became visible,
while the color of background area 23 remained unchanged.
This is an example of a visible camouflage. It is equally
possible for the cross to be visible at atmospheric temperature,
but to disappear when heated or chilled to change the temperature
of the viewed surface. Persons skilled in camouflage will
readily recognize the advantages this will provide. Entire
vehicles can change color or color patterns to agree with their
surroundings, for example.
The purpose of Figs. 3 and 4 is to illustrate the use of
this invention to modify the perception of a surface locally, or
over broad surfaces. It is also useful as a shield to conceal or
confuse something inside it.
.For example, Fig. 5 schematically shows a jet engine tail
pipe 30 which is notoriously hot, and is an identifiable target
for heat seeking missiles. The missiles seek the infra-red
source, namely the hot tail pipe. Fig. 5 also shows a shield 31
according to this invention with a perceived surface 32 equipped
with this invention as will be described.
Of course this shield cannot be directly applied to the hot
tail pipe. Instead it will be spaced from it by a spacing 33
which insulates it from heat damage.. If desired, insulation
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material (not shown) can be placed between them, instead of
merely an air gap.
The mode of employing this invention is schematically shown
in Fig. 2. This illustrates a region 45 in which a group of
Peltier devices 46, 47, 48, 49 are planted or applied, These are
shown to be rectangular although they could instead have any
desired contour. Also they are illustrated'as planar bodies,
although they can be curved or otherwise configured.
While they are shown spaced apart, generally they will be
quite close to one another. All will have circuit connections
connecting to a control yet to be described. It will be observed
that these devices may be separately controlled, individually or
in groups, to provide for various surface appearances. For
example, some areas may need to be colder than others, especially
when a coating might have more than one pertinent color which can
be selected by a respective temperature.
Fig. 1 is a fragmentary cross-section of a Peltier device 60
(sometimes herein referred to as a thermoelectric cooler - TEC).
It is installed on the surface 61 of a substrate 62 whose
perception is to be changed. A layer 63 of electrical insulation
is placed on surface 61.
A thermoelectric semiconductor 65 is placed between two
electrical conduGtors 66,67, which are arranged as not to contact
each other, because they become heat sinks as well as the supply
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of electrical current to the thermoelectric semiconductor.
A layer 70 of electrical insulation overlays this
arrangement. The material whose temperature is to be controlled
may be a layer 72 of thermochromic paint whose color is to be
controlled. Alternatively, an interim thermally conductive layer
(not shown) of material protective of the Peltier device may be
placed between the paint and the insulation.
A thin protective layer 73 may be laid on the paint or other
responsive surface if desired.
Fig. 5 is directed to presenting a different emitted
property such as color or temperature as viewed by a viewing
device 80 through a lens 81 or'collector.
Fig. 6 is directed to presenting a different reflective
property such as a changed frequency or absorbed frequency. A
thermally responsive layer 85 is applied to a TEC layer 86, it
receives energy from a source 87 such as a radar transmitter, and
reflects energy to a receiver 88. The properties of the received
beam 89 and the reflected beam 90 are different, having been
modified by the thermally-responsive layer. The composition of
thermally responsive layer 85 will be described in more detail
below.
The TEC may be formed in shapes other than flat. They may
be curved to conform to the shape of a substrate, or even, as
shown in-Figs. 7 and 8 be made in the form of circular rods,
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wires, or as flexible threads or strings which can be woven into
fabrics.
A typical example is shown in Fig. 7, showing a wire having
a central conductor 91, a surrounding thermoelectric
semiconductor 92, an electrical insulator 93, and a surrounding
thermochromic layer 94. The conductor acts as a heat sink. The
outer layer of the thermoelectric semiconductor can change the
temperature of the thermochromic layer.
Fig. 9 shows a useful example of control circuit to vary the
temperature of a group of thermoelectric cells 100,101,102.
These cells are connected in parallel, the direction of heat flow
and thereby the temperature of the surface being observed.
With reference to the drawings, the following is a
description of the operation of the circuit.
Turning on power switch Sl energizes the timer consisting
of a 555IC operating as a monostable "one shot" The time in
seconds is set by RI and CI. RI is adjustable from the left side
of box, Clockwise (CW) turning of adjustment increases the time.
Time can be set between approximately 0.5 seconds to 10 seconds.
Selecting $3 from OFF to HOT or COLD sets the painted surface
temperature choice. The timer is triggered by momentarily
pushing S2 operating K1 supplying power to the TECs through K1
contacts, which open at the end of the set time. S3 can be
switched in the opposite direction and a new cycle initiated if
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desired. Frequency of cycles is limited by the heatsink
capacity, Turning S3 and Sl to OFF removes all power. The
battery can be recharged externally through J1 mounted on the
right side of box. The battery is a 12V battery.
Conventional Peltier device materials can be used, but in
many situations they would be excessively rigid or thick. An
alternative construction is proposed by the invention herein,
namely structures formed by thin film manufacturing techniques.
Such film structures can enhance flexibility, efficiency,
temperature ranges, and quick response times.
Conventional thermoelectric devices normally utilize
materials such a bismuth telluride with "p" and "n" type
semiconductor junctions. Silicon and dopants are included in the
basic materials to provide or enhance the semiconductor
-properties. In addition, conventional technology utilizes
brittle ceramic insulating elements and requires inherently
thick, rigid construction.
A preferred embodiment for the present invention in thin
film planar or fiber form would be to utilize doped silicon
carbide as the semiconductor material. Dopants such as bismuth
telluride, gallium arsenide, or gallium compounds enhance the "p"
and "n" characteristics. Silicon carbide is a majority carrier
(also called a wide bandgap semiconductor) which is noted for low
leakage current and relatively high temperature stability. Thus
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high current densities can be supported (compared to silicon).
The thin film silicon carbide Peltier effect layer can best
be fabricated by plasma arc deposition essentially the same as
that described in Snaper U.S. Patent No. 5,254,235 which is made
a part hereot by reference for its disclosure of this technique.
The apparatus and method-outlined therein would be identical.
Only the deposition materials would differ. Other suitable
fabrication methods would include chemical vapor disposition,
sputtering, and vacuum deposition.
Compared to silicon or gross bismuth telluride, silicon
carbide offers up to four times better thermal conductivity,
higher blocking voltage range, and predictable area specific
di.fferential resistance. Due to these characteristics, silicon
carbide thermoelectric junctions can be made thinner without
voltage breakdown limitations (compared to silicon) and can also
be effectively paralleled. Silicon carbide also has a practical
switching frequency of up to 500KHz which is desirable should
rapid response be desired for some applications.
Radar masking can also be accomplished by the incorporation
of radar absorbing particles or dipol_es added to the
thermochromic paint layer or to the active film. For example
very small fibers or particles of materials such as carbon,
carbon nonotubes, or conductive metals such as copper or silver
in which the particle length-is sized to act as a dipole absorber
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for the general frequency utilized in radar detection or ranging.
These materials by a process ot absorption, adsorption, multiple
internal reflection tend to disperse radar impingement and reduce
the amount of direct reflection back to the radar source thus
shielding the target from detection to a great extent.
Another unique feature possible is that by controlling the
temperature of the thermochromic film containing the radar
shielding particles, the particles can be made to expand or
contract by controlling the over all film temperature. This
minute expansion, and/or contraction with temperature change can
effectively lengthen or shorten the dipole particles and thus can
be "tuned" for a specific impinging signal. The size change of
the temperature controlled particles in most case need only be
very minute, perhaps on the order of nanometers, to achieve this
effect.
Thermochromic materials are widely used and well-known. For
example they are frequently used on oral thermometers. These
materials may be incorporated in a paint layer, or they
themselves used as a paint layer. The specific product used will
be selected for its color at specific temperatures.
As a single example, Tomn Industries, Inc., North Hollywood,
California USA 91436 product # MC-8 is colored black at about
below 100 C, and colored clear at about above 100 C.
Various of these products can be mixed to achieve effects at
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different temperatures.
This invention is adaptable to respond to commands from its
own proprietors, or to incoming signals, and is responsive and
adaptive over a wide spectrum range. This frequency range
extends from infrared through color to very high frequencies.
For example, if 'the user is concerned about the IR emission
he may change it by program or switching systems actuated by him.
Alternatively, sensing an incoming heat seeking missile can cause
a response in the system to change the temperature of the
surface.
Similar arrangements are useful for color control and color
change.
As to radar frequencies, the system can be arranged so that
the perceived surface reflects or absorbs as desired. it
requires only small dimensional changes in the surface contents
to make a surprisingly large difference in radar reflection or
absorption.
Such a broad range of adaptability is unknown at the present
time.
This invention is not to be limited by the embodiments shown
in the drawings and described in the description, which are given
by way of example and not of limitation, but only in accordance
with the scope of the appended claims.
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