Can materials efficiently reflect microwaves and radio waves?

[sid_galt]

Do materials exist which can efficiently reflect microwaves, radio waves and other long wavelength electromagnetic waves?

 

[Danger]

Yes, hence the existence of parabolic antennae.

 

[waht]

Any metal will reflect radio and microwaves, but a highy polished metal like silver or gold would refelct microwaves better.

 

[sid_galt]

But wouldn't the microwaves heat the metals up by inducing currents?

 

[Astronuc]

As far as I know, the energy density in the microwaves or radar are very low, and so therefore are the currents.

I recently put a bag of aluminized plastic in a microwave oven at home (it contained some frozen food) - pretty exciting to watch. But I don't recommend doing that, because one can damage the microwave oven or could cause a fire. Certainly there was enough energy to cause the plastic to burn slightly since the microwaves could not penetrate the metal - and the microwaves did heat the bag, but not the contents.

 

[Danger]

So, Astro... was this an experiment, or were you just too hungry to waste time unwrapping it?

 

[Astronuc]

So, Astro... was this an experiment, or were you just too hungry to waste time unwrapping it?

Well both actually. I was a bit impatient, but on the other hand, I was curious. I had to shut off the microwave quickly because of the electrical discharges - looked pretty cool though (like an aurora), but I could have easily toasted the electronics.

If one has an old microwave, it would be an intesting experiment, but don't do this to a good piece of equipment.

I can imagine my wife would have toasted me if I had destroyed our microwave oven.

 

[AntonRUS]

Can cold water circulating in close proximity of the polished metal be used to cool down the reflector surface and to avoid melting/overheating?

 

[AntonRUS]

*On the other side, not under the microwaves

 

[yungman]

Any good conductor like metal surface is a good reflector of RF MW. The reason is because RF MW have a very very shallow penetration and mostly reflected back out.

Long wave don't reflect as good with metal and the penetration depth is much deeper. I don't know slow frequency as much, I can just say things in 100MHz reflect well on metal.

 

[yungman]

But wouldn't the microwaves heat the metals up by inducing currents?

Not necessary, even though surface current formed by magnetic boundary condition, by if the surface resistance is low, not much power dissipated on the metal. It is just $W=I^2R$.