Friday
Nov122010
Seeing Where the Microwaves Are
Friday, November 12, 2010 at 02:46PM Microwaves are invisible, so you can't see them inside microwave oven, but their presence can be detected with neon lamps. The changing electromagnetic field from the microwaves will make charged particles move, and so the electrons in the metal legs will move creating current. This current makes the lamps glow. I drilled a grid in a piece of 1/4 inch acrylic and slipped the lamps in. I bought the lamps here, but Tom Senior found a better price here. As the platter turns, the lamps light up showing where the microwaves are the strongest.
My grid is based on another group's work.
Reader Comments (16)
so, what's the wiring like? are they wired in series (chain, net/web or...), or do you pigtail them (connecting cathode to anode of the same bulb)?
Wiring? Did you not have any comprehension of the entire experiment? Please review and then wish you had not posted.
I leave the two wires separate and straight out like they came in the packet.
Awesome job, Zeke, this is really clever! If you remove the turn table, does the light pattern remain constant? Or do the microwaves shift a bit with time?
This is really neat. Thanks for sharing. Can you build one of these to detect ambient EMFs? Like Wifi and cell phone microwaves?
Salty Water in your food doesn't absorb microwaves because it's conducting. Perfectly distilled water will heat as well. Microwaves heat water molecules by spinning them about their axis, giving them rotational kinect energy. The angled shaped of the water molecule means that it has a slight separation of charge about its axis. This allows an em field of the right frequency to spin the molecules up, when they interact with other molecules this rotational kinect energy is converted Into translational kinetic energy and the water is heated.
This is covered in first year physics.
@Mike Yeah, it does come across like I'm saying that only electrically conducting thing absorb* microwaves. Of course, that isn't true, any polar molecule that can move around will get energy. However, it seems like salty water does absorb microwaves better than distilled water, even when the quantity of salt is quite is only 0.5 parts per thousand.
Still many websites and texts seem to suggest that microwaves are only absorbed by polar materials and reflected by all metals. This is not the case and that is what I was trying to get at.
*"absorb" isn't probably the best term anyway, but I'm not sure what would be better.
@JF Probably can't detect WiFi or cellphones this way. The energy in the microwave oven is on the order of 800 W while the energy, even when right on the top of WiFi or cellphone antennas is much, much lower. Now the cellphone tower antennas are much higher energy, but it falls off very fast.
@db If I remove the turntable and leave the array still, the pattern doesn't change. I should post some pictures of that.
This is very clever. I like the lights a lot. I remember when Monzy dot com (from google) did this by creating a 3 dimensional cube out of tooth picks and marshmallows. :) @JF yeah he's right, microwaves can be even 1100W where as WiFi on a SOHO Router is probably .5W if that. Some wifi stations using high gain panel antenna's on the roofs of buildings which connect long range can be up to 1000W and being in front of them during operation is much like being in a microwave! On the other hand there is a small experiment you can do using a netbook which involves putting the netbook into the microwave after setting up a file share on it and attaching it to a BSS or iBSS then start sending it data from another machine. (don't turn the microwave on of course, heh) You will see that 2.4GHz passes directly through the microwave! I think the reason that the 802.11 frequency passes through the door of the microwave and not the harmful high power waves from the oven itself is the amplitude. A much higher amplitude, or taller wave, cannot pass through the tiny gates of the grid in the microwaves door until they have dissipated enough to resemble the energy of waves of 802.11 And I think since the waves are a product of planks constant and frequency that they are a much lower frequency by the time they leave through the microwave door as well.
@Zeke you're right about the salts they dope the water and allow the conductivity of electricity to be higher.
:)
These neon bulbs of yours -- they look like LEDs but I'm sure you're being quite accurate -- so instead, I'm guessing you're using the trusty NE-2s which I used to play around with, back in the (pre-LED) day. But I'm confused because the light emitted by an NE-2 is an obvious orange (just like a beer or pizza neon sign) whereas in your video they look red. My own spectrographic analysis of the light from a neon tube (known in the sign trade as Clear Red) is they emit three discreet wavelengths, a red, an orange and a yellow, all of about the same intensity, so maybe the predominate red is some artifact of your video camera.
Fascinating video -- thanks!
> If I remove the turntable and leave the array still, the pattern doesn't change
That surprises me too, because the turntable isn't (or didn't used to be) required. My understanding was the microwaves were beamed at the fan which then caused them to shift through ninety degrees, back and forth, and that oscillation caused the food molecules to realign, back and forth, the friction between them heating up the whole.
@Zeke: Our prof explained to us that a salty water will heat faster because the inpurities allow for a more easy transition from rotational to translational kinetic energy.
You can see this effect when you heat a mug of water in the microwave for awhile but it does not boil. Then you add a spoonful of instant coffee and the water that seemed not hot enough to boil flashes into steam. This can actually be violent and dangerous.
Anyway, that was only afirst year class, perhaps there are other factors like conductivity involved, but I've never come across it before.
I forgot to say, though, great experiment and demonstration.
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My understanding was that the microwaves in a microwave oven were tuned to the vibrational (rather than rotational ) frequency of water - not the -H streches but the angular oscilations about the oxygen atom.
Nice experiment and lots of fun.
Can you use little LEDs or it has to be neon bulbs?
Microwaves can be harmful if you let it burn constantly.
The increase of temperature might cause them to explode.