# Microwave Reflectors

1. Oct 10, 2005

### sid_galt

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

2. Oct 10, 2005

### Danger

Yes, hence the existence of parabolic antennae.

3. Oct 10, 2005

### waht

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

4. Oct 10, 2005

### sid_galt

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

5. Oct 13, 2005

### Staff: Mentor

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.

6. Oct 13, 2005

### Danger

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

7. Oct 13, 2005

### Staff: Mentor

:rofl:

Well both actually. :rofl: 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.

8. Dec 7, 2011

### 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?

9. Dec 7, 2011

### AntonRUS

*On the other side, not under the microwaves

10. Dec 7, 2011

### 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.

11. Dec 7, 2011

### yungman

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 $W=I^2R$.