Optical camouflage uses retro-reflective materials and a system of cameras, computers, projectors and mirrors to render objects invisible. It works by capturing the scene behind an object, processing the image, and projecting it onto the retro-reflective material covering the object so that viewers see through to the background scene. Current prototypes can only achieve invisibility within the visible light spectrum and over a narrow range of viewpoints. Metamaterials that can manipulate electromagnetic waves are being developed to improve optical camouflage and potentially allow true invisibility. Potential applications include medical, aviation, automotive and home uses. However, limitations remain around the wavelengths and movement that can be cloaked.

1. Op tical
Camouflage
By:
Abhinav Sagar
1DS05EE002

2. Is Harry Potter’s cloak really that
magical?

3. Could James Bond have an
invisible car?

4. Outline
 Introduction
 Emerging Technological Innovation
 Key Challenges
 Markets & Application
 Future
 Conclusion

5. begin?
BEFORE NOW
Tokyo ~ Professor Tachi Professor Tachi came up with
from the University of Tokyo retro-reflective material which
said that he had first had the causes the coat to act as a
idea of developing something screen and gives a transparent
to make objects invisible in - or invisible - effect. Similarly,
1977. But the image was flat Duke University is using
and unrealistic. microwave beam deflection,
making it appear almost as if
nothing were there at all.

6. WHAT IS OPTICAL
CAMOUFLAGE?
• Optical camouflage is a hypothetical type of active camouflage
currently only in a very primitive stage of development. The idea is
relatively straightforward: to create the illusion of invisibility by
covering an object with something that projects the scene directly
behind that object .
• Optical camouflage is a kind of active camouflage which
completely envelopes the wearer. It displays an image of the scene
on the side opposite the viewer on it, so that the viewer can "see
through" the wearer, rendering the wearer invisible.
• Although optical is a term that technically refers to all forms of light,
most proposed forms of optical camouflage would only provide
invisibility in the visible portion of the spectrum. Prototype examples
and proposed designs of optical camouflage devices range back to
the late eighties at least, and the concept began to appear in fiction
in the late nineties.

7. OPERATION

8. HOW DOES IT WORK?
Creating complete optical camouflage across the
visible light spectrum would require a coating or suit
covered in tiny cameras and projectors, programmed to
gather visual data from a multitude of different angles
and project the gathered images outwards in an equally
large number of different directions to give the illusion of
invisibility from all angles. For a surface subject to
bending like a flexible suit, a massive amount of
computing power and embedded sensors would be
necessary to continuously project the correct images in
all directions. This would almost certainly require
sophisticated nanotechnology, as our computers,
projectors, and cameras are not yet miniaturized
enough to meet these conditions.

9. INVISIBILITY CLOAK
• The cloak that enables optical camouflage to work is made from a
special material known as retro-reflective material .
• A retro-reflective material is covered with thousands and thousands
of small beads. When light strikes one of these beads, the light rays
bounce back exactly in the same direction from which they came.

10. • To understand why this is unique, look at how light reflects off of other
types of surfaces. A rough surface creates a diffused reflection because
the incident (incoming) light rays get scattered in many different
directions. A perfectly smooth surface, like that of a mirror, creates what
is known as a specular reflection -- a reflection in which incident light rays
and reflected light rays form the exact same angle with the mirror surface.
In retro-reflection, the glass beads act like prisms, bending the light rays
by a process known as refraction. This causes the reflected light rays to
travel back along the same path as the incident light rays. The result: An
observer situated at the light source receives more of the reflected light
and therefore sees a brighter reflection

11. WHAT DO WE NEED FOR AN
INVISIBILITY CLOAK?
• Optical camouflage doesn't work by way of magic. It works by
taking advantage of something called augmented-reality technology
• Augmented-reality systems add computer-generated information to
a user's sensory perceptions
• Most augmented-reality systems require that users look through a
special viewing apparatus to see a real-world scene enhanced with
synthesized graphics. They also require a powerful computer.
Optical camouflage requires these things, as well, but it also
requires several other components
• Here's everything needed to make a person appear invisible:
• A garment made from retro-reflective material
• A video camera
• A computer
• A projector
• A special, half-silvered mirror called a combiner

12. WHAT DO WE NEED FOR AN
INVISIBILITY CLOAK?
• Optical camouflage doesn't work by way of magic. It works by
taking advantage of something called augmented-reality technology
• Augmented-reality systems add computer-generated information to
a user's sensory perceptions
• Most augmented-reality systems require that users look through a
special viewing apparatus to see a real-world scene enhanced with
synthesized graphics. They also require a powerful computer.
Optical camouflage requires these things, as well, but it also
requires several other components
• Here's everything needed to make a person appear invisible:
• A garment made from retro-reflective material
• A video camera
• A computer
• A projector
• A special, half-silvered mirror called a combiner

13. The Complete System

14. Once a person puts on the cloak made with the retro-reflective material ,
here's the sequence of events:
• A digital video camera captures the scene behind the person wearing the
cloak.
• The computer processes the captured image and makes the calculations
necessary to adjust the still image or video so it will look realistic when it is
projected.
• The projector receives the enhanced image from the computer and shines
the image through a pinhole-sized opening onto the combiner.
• The silvered half of the mirror, which is completely reflective, bounces the
projected image toward the person wearing the cloak.
• The cloak acts like a movie screen, reflecting light directly back to the
source, which in this case is the mirror.
• Light rays bouncing off of the cloak pass through the transparent part of the
mirror and fall on the user's eyes. Remember that the light rays bouncing off
of the cloak contain the image of the scene that exists behind the person
wearing the cloak.
• The person wearing the cloak appears invisible because the background
scene is being displayed onto the retro-reflective material. At the same time,
light rays from the rest of the world are allowed reach the user's eye, making
it seem as if an invisible person exists in an otherwise normal-looking world.

15. Difference Between
Invisibility Cloaks
Tokyo Method: Duke Method:
1. Uses camera to capture 1. Rely on product called
picture “metamaterial”
2. Processes it to a 2. The metamaterial will
computer influence the
electromagnetic waves
around it creating a
3. Projected onto the “warped effect.”
reflective cloak
3. This creates the invisible
effect

16. Metamaterial?
 Meta in Greek means “beyond”…
 Therefore the term “metamaterial” means to
create something that doesn't exist in nature.
 Metamaterials,(MTMs) are a class of
artificially engineered composite materials
having extraordinary electromagnetic
properties .

17. A metamaterial
possesses…
 negative permittivity (ε < 0)
 and/or negative permeability (μ < 0)
 negative refractive index (n < 0)

18. n = ± εµ OR n=± ( −ε ) ( −µ )
ABSORPTION
+ε, -μ +ε, +μ POSITIVE
REFRACTION
NEGATIVE -ε, -μ -ε, +μ
ABSORPTION
REFRACTION!!

19. Where are we today?(1)
 Recent developments by Professor John
Pendry have shown that…
certain configurations of metal yield unique
responses to electric and magnetic fields.
 This is the first time a substance with clean
negative permeability has been found.

20. Where are we today?(2)
 Pendry's initial idea was that metallic wires
aligned along propagation direction could
provide a metamaterial with negative
permittivity (ε<0).
 Pendry demonstrated that an open ring
with its axis along the propagation direction
could provide a negative permeability(μ<0).

21. Where are w e today?(3)
This ‘C shaped’ ring is known as a
split-ring resonator.

22. SRR s
 SRRs are pairs of concentric annular rings
with splits in them at opposite ends.
 They are made of nonmagnetic metal like
copper and have small gap between them.
 These tiny ring structures are assembled in a
giant crystalline-like lattice.

23. How do metamaterials work?(1)
 The design of SRR
components looks back to
the first principles of
electronics--simple R-C-L
circuits.
 The electromagnetic waves
passing through arrays of
tiny resistors,capacitors,
inductors and other
dielectric materials
positioned in free space.

24. How do metamaterials work? (2)
 The SRR acts as the "magnetic atom”.
 The ring and wire units act as atomic
dipoles…
 the wire acts as a ferroelectric atom
 the ring acts as an inductor L
 the open section acts as a capacitor
C
 the ring as a whole therefore acts as a
LC circuit.

25. How do metamaterials work? (3)
 When the electromagnetic field passes through the
ring, an induced current is created and the
generated field is perpendicular to the magnetic
field of the light.
• The magnetic resonance results in a
negative permeability and index of
refraction.

26. So now what…?
Now, in an SRR structure, we have sub-micron
shapes of a metal, which acts an electrical conductor.
 When this sees the oscillating electric field due to an
incident light wave, the free electrons in the metal wiggle around
in a collective oscillation called a plasmon mode.
 These plasmons generate both electric and magnetic
fields,whose behavior depends very sensitively on the size and
shape of the object in which the electrons are sloshing around in.

27. This is what…
􀁺 Due to its negative refractive index
􀁺 the net effect is of a wave propagating in the
reverse direction of the light and energy flow.
 􀁺 These tiny structures within the rings divert
the incoming waves around the object
preventing both reflection and absorption.
 􀁺 Meeting up on the other side as if nothing
were there.

28. Types of Refraction
NORMAL: METAMATERIAL:
POSITIVE NEGATIVE
TRANSPARENT
MATERIAL
VIRTUAL IMAGE REAL IMAGE

29. We can use metamaterials as an
invisibility cloak
LIGHT
SOURCE
LIGHT
RAYS
OBJECT
METAMATERIAL

30. Does the object need to be
inside the cloak?
CLOAKING LIMIT
LETS LOOK AT
THE RADIATION
OBJECT
BACKGROUND FIELD
“NORMAL”
UN-DISTURBED
MATERIAL
METAMATERIAL
METAMATERIAL
COATED CYLINDER

31. What does an invisibility cloak
look like?

32. T he Market
Skillfully mixing the real
world and the artificial
world to make your life and
work convenient
• Four markets
Medical Aviation Automotive Home Improvement

33. Medical
 Buyers: Hospitals
 Users: patients and doctors
 Function:
 Improve psychological well being of patients
 Improve the efficiency and precision of surgical procedures
 Market: 7000 hospitals nationwide

34. Application #1: Medical
•Patient-centered design
rooms
•Improve the psychological
well-being of people in
closed environments

35. Application #1: Medical
 Surgery
 Doctors could use the
“invisibility” to see through
their hands and tools to
make the underlying tissue
more “visible.”

36. Aviation & Automotive
 Buyers: Car and airplane manufacturers
 Users: pilots and car drivers
 Function:
 More visibility when automating vehicles and airplanes
 Increase in safety
 Luxury feature
 Market: privately owned cars
7 million manufactured cars
2 airplane manufacturers

37. Application #2:
Aviation
 Pilots could use optical
camouflage to make cockpit
floors transparent
 They can see through the
cockpit floors to the runway
and landing gear.

38. Application #3: Automotive
 Cars
 A transparent rear hatch or tailgate would
make it easy to know when to stop.

39. Home Improvement
 Buyers: Home owners and construction companies
 Users: Home owners
 Function:
 Improve interior designing
 Allow spacious looking rooms
 Increase in security
 Luxury feature
 Market: 73.8 million homeowners in the United States

40. Improvement
 More fanciful
application:
Transparent ceiling to
provide a view of the
outside
 Transparent door
replaces peep hole

41. Other Applications:
 Solar panels coated with metamaterials would
be much more efficient than those coated with
conventional black paint, which reflects 5
percent or more of incoming light.
 Telescopes lined with metamaterials would sop
up random flecks of incident light, providing a
blacker background to detect faint stars.
 In military,invisibility phenomena could be used
to hide tanks, bunkers, submarines or make the
warships invisible to radars.

42. Limitations for
Metamaterials
 The invisibility effect would work only for a
specific range of wavelengths. It operates only
over a narrow range of frequencies .
 The cloak could be made to cover a volume of
any shape, but you can't flap your cloak. Moving
the material around would spoil the effect.

43. CONCLUSION
• Now all of us have had a small tour of the
interesting world of optical camouflage.
• A lot of interesting thing have been done and
already we have seen that anyone can be
almost invisible with this technology.
• But the future promises us a lot more.
• Research work is going on and soon we will
have even more astonishing results.