# EM waves amplitude's effecting penetration?

## Main Question or Discussion Point

If you held frequency constant, and changed the amplitude of EM waves coming from a source, then would the distance into a material the EM waves would penetrate change?

Related Classical Physics News on Phys.org
Anybody out there?

Generally, yes but the extent to which it happens or is possible depends largely on the material considered. For a conductor, check out the concept of skin depth.

Born2bwire
Gold Member
Yes by virtue of the fact that the amplitude is larger and so it will take a correspondingly large distance to drop the penetrating fields down to a given amplitude. In general the physics does not change since we generally work with linear materials so the amplitude of the incident wave does not affect the material properties. So a wave with an electric field of 1 V/m will experience the same decay profile as one of 100 V/m.

Not a simple question to answer.

There is a long thread here somwhere...try microwave oven...and if nothing interesting turns up, try that in wikipedia....

A microwave oven, or simply a microwave, is a kitchen appliance that heats food by dielectric heating. This is accomplished by using microwave radiation to heat polarized molecules within the food.

This excitation is fairly uniform,
leading to food being more evenly heated throughout (except in dense objects) than generally occurs in other cooking techniques.
http://en.wikipedia.org/wiki/Microwave_oven

I don't see why it should change the penetration. You just use:

$$\tilde E (z) \;=\; E_0 e^{-\alpha z} e^{-j\beta z}$$

For conductors, they just defined the skin depth and that does not affect by amplitude.

What am I missing?

A projectile of 1 gram(think amplitude) and a velocity of 1,000 fps(think frequency) will have a lower penetration capacity as oppossed to a 2 gram projectile at 1,000 fps velocity.
But even that depends on the material being hit.

Even still, this is much different than dealing with EM waves.
A shiny mirror might reflect a laser beam of 1/2 watt versus 1 watt equally effective without ANY penetration difference.
Yet, a 100 watt laser might just burn a hole through that same mirror.