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[Phys-L] Re: Microwave experiments



I recommend the appendix J in Strong's "Concepts of Classical Optics" as
the best answer for microwave optics demonstration questions. Any
physical optics text should answer your questions also (except, likely,
wave guide ones), as the only diff. is scale.

Hint: Do mirrors absorb? [Maybe that's a bit subtle. Metallic
absorption and reflection are related.]

Specifically:


The E field causes the quasi free electrons in the tines to oscillate.
What would happen in a superconductor?

Try this xpt.: Cross polarize the xmittr and recvr and insert the comb
at 45 deg. Explain (simply) using composition of vectors.

Note, a previous thread dealt w/ the counterintuitive reason for
polarizer absorption, and misleading textbook explanations.

One may also use the comb (and a plane reflector) to produce an
elliptically polarized wave also.

bc, thinks he's a microwave demo. xpert. and suspects he has the same
CENCO apparatus as does KPHOX.

p.s. I xpct to give a microwave workshop at the next NCNAAPT meeting
'06 April 21. Including Miraldi's spot, optical activity (artificial
and natural), artificial and natural lenses, etc. i.e. demos. beyond
Cenco and Pasco.


SSHS KPHOX wrote:

I seek to be educated about an aparatus I was using today.

I have a microvave emitter that emits at 10 GHz. I receive the waves with
a diode which, since I can modulate the wave with an audible frequency,
will let me hear when I have a good signal or not. Rotating the diode
makes it clear (to me) that the emission is polarized (say vertically)
since the diode must have some vertical component to its orientation to
receive a signal.

One piece of apparatus that came with the kit 30 years ago, is a "comb"
whose tines are 10 cm long, 2 mm in diameter and spaced 9 mm apart. When
the tines are parallel to the diode (vertical) the signal disappears. Not
so when the tines are horizontal. My understanding has been that the E
component of the em radiation causes the energy to be absorbed in the
tines. Is that a reasonable explanation?

Then today for some reason I turned the "comb" so while still vertically
oriented I rotated it so that its plane made a 45 degree angle with the
direction of propagation. There was a strong reflection from the "comb"
and I think I might have noticed a variation of intensity as I moved the
diode receiver ( which is placed in a box like funnel) across the
reflected beam. I am not sure I understand either the reflection or the
variation of intensity. I hope I have described the event well enough that
one of you can help me.

Thanks in advance.

Ken Fox




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