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Re: [Phys-l] evanescent microwaves?

Bill!

Yes, I found it in my microwave file -- it's rather complete and more detailed than I've done. For the evanescent, I use a bare point contact diode (IN23B) with twisted pair leads to PD meter. I think the twisted pair acts as a cap. in addition to the connection. I mounted it on a wooden stand which is on a translation stage to obtain +/- ~ resolution (detail IIRC. I'm too lazy to search in the black hole garage for it) It results ina reasonable*** exp. fit. I copy my note extract to a Swiss demo expert I coincidentally sent last nite, "proving" again that life is an example of the Poisson interval distribution.

*** mealy mouthed non-physics statement

----------------------------
Anonymous:


First off - I by accident discovered a different tap-l archive than I had been using to reply individually. It opened 2001-10-12 the day of the kerfufel.

So I read all the "cleyet" posts -- then scanning further and found your worry about your transmitter.

Do you still worry?

I'll interleave:
Date: Mon, 15 Oct 2001 20:25:18 +0200

Author: Urs Lauterburg

Subject: Re: 3cm wave equipment.

Post:

Alistair,

1 What type of wax is suitable.

We have a two large prisms of white paraffin wax, kind of like the wax the
white candles are made of. We made a wooden mold which was filled by
pouring the hot wax layer by layer.
---------------------

RAFT had a barrel of candle ends (like cloth bolt ends inch or two w/ wicks. I melted it scooped up the wicks and poured three + pair prisms kept one and gave the others at the workshops I gave on microwave optics.

resource area for teachers - Google Search


http://www.google.com/search?client=safari&rls=en&q=resource+area+for+teachers&ie=UTF-8&oe=UTF-8
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2 Hints on making the molds.

We treated the inside of the mold with silicone oil, but it might not even
have been necessary because the wax is pretty oily too.


-------------------------------

As I used plywood w/o a release agent, some sticking. But except for a special use <1/10 wave length roughness is unseen by E-M radiation

--------------------------------
3 Expansion/contraction problems with the wax during making.

The paraffin wax contracts a bit upon cooling but pouring it layer by
layer, the effect will not affect the final shape too much.
------------------------------

Curiously I did complete pour ~ four litters? -- however I didn't until skimmed over

-----------------------------
4 Can they be made smaller without introducing problems?.

I would make the forms as large as possible. Our prism is about 50cm tall
and with 3cm wavelengths this is a pretty small prism, quite hard to see,
thinking it to be proportional to the length of light waves.
-----------------------

I have trouble carrying one of mine!

------------------------
5 Other....

Actually our 3cm klystron is quite old and sometimes I worry a bit about
its sustained performance. I would actually like to continue experimenting
with 3cm microwaves as opposed to the more common millimeter microwaves
used for experimenting. So what do you people know about 3cm microwave gear
manufacturers?

------------------------------------------

On the surplus specialty market and bc's supplies I have at least a dozen new in boxes 723/2k25 klystrons -- also a few xtra horn transmitters and receivers (1N23B xtals)



Where is it possible to still buy this stuff and what would
be the best device, offering a good price/performance ratio? My klystron
generator is self made, allowing to modulate a 1kHz sine wave or an
external audio signal on to the microwaves.

We also do diffraction experiments on aluminium slit apertures. One can
detect distinct maxima and minimas but due to a relatively large variations
of the signal amplitude at a fixed location of he detector these the
patterns can be pretty noisy. Also there is always the effect of having a
minima in the center position when we use a grid and assume it is due to
the near field (Fresnel diffraction). So is the noise mostly due to
disturbing reflections happening all over or is it possible to extract
microwave modulated signals with proper equipment?


Noise?


Thanks for any insight to 3cm microwave technology

Kind and completely apolitical regards to all of you

X

---------------------------------

I've been meaning to put on my site pictures of my demos and even the making of the prisms. I have also pics of making artificial waveguide lenses, etc.


If interested that will prompt me to raise its priority.

Finally, on this subject: It is essential that one face each of two prisms be rather flat so they may be contacted. Then FTIR may be shown. (I think I have pics. of this when I demo'ed it at the Naval Postgrad. School in nearby Monterey.)

[forget to add: I used a large thick Al plate on a hot plate to face the prism -- one face each only of the two prisms.]

I then separated the prisms successively using metal shims to measure the separation. The decrease in intensity fitted the 1/ hyperbolic sin^2 theoretical eq.

One of my favoured demos is a 1/4 wave plate made from wood. It's become rather poor perhaps from water absorption. Wooden and plastic straws and stir stix are more stable.

My goal is someday to show anomalous dispersion using an artificial dielectric made from angled wires. My source used 10cm and I have an HP generator from RAFT, but it may not work (not time to try it out!)


Finally!

............


On 2012, Feb 22, , at 13:41, Bernard Cleyet wrote:


On 2012, Feb 22, , at 12:31, Bill Wehrbein wrote:

Have any of you performed the experiment (e.g., Albiol et al, Amer. J. Phys, Feb 1993) exploring evanescent waves produced by the typical introductory lab microwave set ? Any tips or suggestions for updating and improvement? Thanks!
Bill Wehrbein, Nebraska Wesleyan University
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l



Yes, many times. I'll read the AJP article and reply. (may have already, as I've searched several times this subject.).


bc thinks restoring N, so the evanescent wave becomes a transmitted one is more interesting, and considers himself an expert on microwave optics.