EMF shielding

Quote:

The magnetic field you speak of has to be generated at first. Due to the
Maxwell equations, a electromagnetic wave will be generated. So you might
think the wave isn't able to enter the shielding. That's against
measurements.

The problem you stand of is: you have to understand the maxwell equations
without really knowing them.

But there's a solution, and from this point on, I start to think instead
of knowing. But I think I have a good basis to start from. If you don't
want to read everything, read at least the last paragraph.

At first, any material, even conductors like copper, aren't refractive
("shielding") at every wavelength. It's true for visible light and
nerarby wavelengths. When you have a blue glass only the blue part of the
visible light can pass through it. In general, if your wavelength is
_short_ enough, it can pass through copper - like gamma rays, for
instance.

Second, you can treat the static magnetic field as an electromagnetic
wave with an infinite wavelength (so it doesn't change at all). The
shielding of electromagnetic waves is due to the shielding of the
electric part of the waves (electrons are moved around, so that they
generate a wave wich extinguishes the incoming wave). Because the
wavelength is infinite, the electric component doesn't appear and so this
shielding can't take place. The magnetic field enters the sphere.

Third, in other conductors, wich are ferromagnetic (copper isn't), a
slowly varying magnetic field (a homogenous field is varying infinite
slow) causes the dipole momentums (formally speaking: spins) in the
material to strengthen it. You can see this, if you stick a magnet on the
fridge: if it wouldn't strengthen the field, the magnet would fall down.
This gives a problem with the shielding you speak of, but the effect
almost disappears if you change the magnetic field too fast (like in
microwaves or in visible light)

Last, the field really enters the sphere (you might speak of "tunneling",
but you really don't need quantum mechanics to understand it classicaly).
You can calculate this analytically with hard mathematics or you just use
the more simplified equations for refraction:

--> there is no 100% shielding in no material. <--
You want an example? Think of mirrors you can see through out of one
side. If you are on the other side and go really close to the mirror, you
can also thee the person watching you.

Greetings,

Thomas

On Tue, 30 Oct 2007 14:33:59 +0000 you wrote Efthimios:

Your opinion to the following will be appreciated

Lets imagine a sphere made of a conductor (copper) placed within a
static magnetic field. The field will penetrate the within the shier.
Next we place inside the sphere a coil producing a variable
electromagnetic field. The electromagnetic field can not escape out side
the shier due to shielding effect of the cooper sphere.

The question is: Taking in consideration the shielding effect created by
the variable electromagnetic field within the shier, can the static
magnetic field penetrate within the shier?- Hide quoted text -

- Show quoted text -