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Homework Help: Can a radar detect a plastic object?

  1. Jun 27, 2005 #1
    can a radar detect a plastic object? could the uhf and microwave signals be reflected by the target if it's made of plastic material? please give justifications :smile:

  2. jcsd
  3. Jun 27, 2005 #2
    Sure it can, radar doesn't act like a metal detector. If a surface can reflect light, radar can sure spot it. When you look at the plastic top on a bottle of soda or water you couldn't see it if it didnt reflect light. Just about anything that is opaque can be seen by radar, unless it is stealth. The way stealth aircraft work is that their covered in RAM or radar absorbant material. This is kind of like a clear paint whose media has a very high index of refraction. When light enters this "clear" layer of paint it becomes trapped inside and dissipates into thermal energy.
  4. Jun 27, 2005 #3


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    Try this site about Ground Penetrating Radar http://www.cpeo.org/techtree/ttdescript/gpr.htm

    See also - http://www.soe.ucsc.edu/~milanfar/GPR2002SPIE.pdf [Broken] (pdf file).

    One application of GPR is the detection of plastic encased land-mines.

    Stealth technology involves object geometry as well as radar absorbent material. Metals reflect radar, so the Stealth aircraft are largely non-metal composites. In additions, the sharp edges and faceted surfaces reflect the radar signal in other directions rather than back to the source/detector.
    Last edited by a moderator: May 2, 2017
  5. Jun 27, 2005 #4
    Do you think the skin depth plays any role? :smile: skin depth of an insulator is infinite...

    however, if we go to molecular level, it depends on the frequency of vibration of the atoms;if that's more than the signal freq then it's detected else the signal gets absorbed....don't you think so? remember its a uhf/microwave signal.
  6. Jun 27, 2005 #5


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    The paint is important in a stealth aircraft, but even more important is the form.
    When any electromagnetic wave hits a surface, it is partially refracted and partially reflected. The reflected wave forms with the normal to the surface an angle that is equal to the incidence angle.
    If a radar emission hits a plane surface it will only be reflected to the receiving antenna if the surface is orthogonal to the direction of the wave. But if there is another surface forming a dihedral angle, the new reflection can be directed to the antenna.
    An ordinary fighter has several dihedral angles: The wings to the body, the extra fuel tanks, bombs or missile to the wings etc.
    A stealth plane is constructed so that it presents no dihedral angles, so the incident energy will be mostly scattered. The paint of course helps by absorbing part of that energy.
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