Defense Intelligence Reference Document Invisibilty Cloaking Theory And Experiments

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direction from the propagation. The clearest and most advanced form of this concept is
the complementary media invisibility cloak. 3 Here, an optical antiobject is placed beside
the object one wishes to make disappear. The antiobject should be made of a
negatively refractive material that exactly compensates the optical appearance of the
object. An image is contained in the deformations of light-wave fronts caused by the
imaged object. If these deformations are reversed, the image disappears, and the
object becomes transparent-that is, invisible. The optical antiobject must be tailored to
the object and placed precisely at the correct distance-that is, the distance where it is
made to cancel the image of the object. The more complex the object is, the more
complex the antiobject must be for reversing all the scatterings of light. Such cloaking
at the distance cannot be instantaneous, as the light scattered by both object and
antiobject must settle to a stationary state where it becomes synchronized. A stationary
light field has only one color. So, in practice, these forms of transparency will work only
for small objects and for small parts of the spectrum and not for large objects in many
colors.
a) b)
(
-L 0 L -L 0 L
c) d)
Figure 5. Complementary Media Invisibility Cloak: (a) The slab of empty space x with O < x <Lis optically
canceled by a slab of negat1ve-1ndex material in -L < x < 0. (b) The same cancellation effect works with an obJect
in O < x < L if the negative-index slab contains an antiobject. (c) A spherical shell b < r < c is optically canceled by
a negative-index shell a < r < b. If the corer< a is optically equivalent to a sphere of radius c, then this device is
invisible. (d) The same as (c), but with an object in the canceled shell b < r < c. The object 1s cloaked: both it and
the cloaking sphere are invisible.
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