Optics Question 844
Question: A possible means for making an airplane invisible to radar is to coat the plane with an anti-reflective polymer. Radar waves have a wavelength of 3.00 cm and the index of refraction of the polymer is n=1.50. How thick would you make the coating?
Options:
A) 1.50cm
B) 3.00cm
C) 0.50cm
D) None of these
Show Answer
Answer:
Correct Answer: C
Solution:
[c] Treating the anti-reflectance coating like a camera-lens coating, one can obtain for its thickness t:
Condition (1) is the condition for the destructive interference for the normally incident and reflected electromagnetic wave.
The minimum thickness of the coat refers to m= 0.
This gives for the thickness:
This anti-reflectance coating could be easily countered by changing the wavelength of the radar to L50 cm now creating maximum reflection.
