Why can't metal mesh be used to make planes stealthy?

  • Level: Undergrad 
  • Thread starter Thread starter likephysics
  • Start date Start date
  • Tags Tags
    Radiation
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
8 replies · 2K views
likephysics
Messages
638
Reaction score
4
A solid metal body reflects radio waves. But a metal mesh like the one in a microwave oven cancels it and does not let it go out(except for a tiny amount). So why can't the same mesh be used on planes to make them stealthy?
 
Physics news on Phys.org

Discussion

the mesh in a microwave oven is what's called a 'Faraday Cage' and prevents electric fields originating INSIDE them from reaching outside them and shields their inside from electric fields OUTSIDE. Putting such a mesh over a fighter would simply reduce the ability of the pilot to pick up radio signals inside their cockpit and the outside from detecting radio signals originating from within the cockpit. Neither would prevent the incoming radar from bouncing off the fuselage of the plane and giving away its position
 
I thought the mesh in the microwave prevented the microwaves bcoz of destructive interference. The same principle could be applied to radars, so they won't be reflected.
 
likephysics said:
I thought the mesh in the microwave prevented the microwaves bcoz of destructive interference. The same principle could be applied to radars, so they won't be reflected.

The incident radiation induces currents on the surface of the mesh/conductor. These currents produce their own secondary electromagnetic waves. These waves will destructively interfere with the incident waves on the transmitted side of the mesh/conductor, but not on the incident side. The mesh is supposed to behave just like a continuous sheet of metal conductor. The only reason why it is a mesh is so that you can see through into the microwave to watch your burrito rotate.
 
likephysics said:
A solid metal body reflects radio waves. But a metal mesh like the one in a microwave oven cancels it and does not let it go out(except for a tiny amount). So why can't the same mesh be used on planes to make them stealthy?

There is no difference between a sold metal surface and a mesh, as long as the hole size in the mesh is notably less than the wavelength. Both the mesh and solid metal reflect the microwaves in the same way. Yes, the mesh could just as well be used on a stealth vehicle, but it would cause a lot of aerodynamic drag because of all the turbulence it would produce.
 
fleem said:
... Both the mesh and solid metal reflect the microwaves ...

Yes, exactly.

If the mesh absorbed rather than reflected, microwaves would waste energy in heating the mesh as well as water. But it does not work that way, the microwaves are reflected by the mesh so they stay inside the microwave.
 
can someone explain how mesh hole and wavelength are related?
 
Essentially a Faraday Cage should be solid but if there are holes that are significantly smaller than the wavelength of the em you're trying to contain it doesn't matter. The wavelength of microwaves is on the order of 10's of centimeters, the wavelength of visible light is on the order of nanometers (billionths of a meter). You'll notice your microwave oven has a mesh with holes that are maybe 2mm diameter. Thus these holes have little to no effect on its shielding potential for microwaves but allows visible light to go through