Art Unwin wrote:
On Mar 21, 9:15 am, joe wrote:
Art Unwin wrote:
If on places a am/fm radio inside a box made of thin aluminum foil the
radio will be able to hear am broadcast band but not the fm band.
(Experiment by Harvard in Boston)
What did the Harvard experiment in Boston describe as the cause for
this? Some vague reference to an experiment somewhere does not show
anything. Provide a proper link if you want anyone to take the reference
seriously.

Intuition tells me that when using a perforated plate the lower the
frequency then the smaller the perforations in the shield to create a
blocking effect.
I believe this conflicts with your particle concepts. Why should hole
size have any effect on spinning particles of different frequencies?

You position also is in conflict with general understanding. If you are
correct, what hole size blocks very high frequencies. You concept would
result in a simple wire frame enclosure.

This would, I believe, opposes the progression of
skin depth with respect to frequency.
The books state for a mesh shield the perforations should be less
than 1/10 of a WL which on the surface opposes the results obtained by
the box experiment!
You may be ignoring the differences in the antennas. AM may have used a
ferrite loop, while FM may have been a whip. (We don't know because you
provide no details.)

Could one antenna be responding the magnetic component of the signal
more than the other? (We don't know because you provide no details.)

Is the difference involved with calculations
changes for sheets that are thinner than skin depth such as circuit
board traces or something else?
Type of materials, type of antenna, relative dimension may all play a
factor. You need to determine all of the effects that enter into the
situation and not focus on one or two.

Where has my intuition gone wrong in opposing the books?
Probably because you don't pay attention to the details and are relying
upon an understanding of the topic that is not correct.

Thanks for your response.
The article only gave me the given facts for the experiment and
nothing more.

If it is this article,
http://www.fas.harvard.edu/~scidemos...SkinDepth.html
Then more was given.

It was an experiment in skin depth.
AM was significantly attenuated, too.
It specified the frequencies used and the associated skin depth.
The radio is also specified.

Using an extremely cheap radio as a measurement tool is not sound
technically.



Yes my concepts on radiation are in opposition to the
norm so I am using the facts presented as a way of destructing or
confirming my perceptions.



When I read up on Faraday shields the concept of "particles"
predominates as opposed to "waves" without exception and I am trying
to make some sense of these differences when considering propagation.

Perhaps it is a problem with how you do searches. On this page
http://en.wikipedia.org/wiki/Faraday_cage
There is no mention of particles as the means of transport to the
shield. Electrons are mentioned as they are part of the cage and respond
to applied fields.

With respect to receive of the radio. Since the foil is flat and
without perforation it should be sensitive to everything thrown at it.

But the experiment in question is about skin depth which does vary with
frequency.

Unless, of course, you are talking about some other Harvard article, but
we only have to guess, because you still don't identify it.

How do you expect us to know what you are really talking about?