RSSMicrowaved CD
Nice gallery of a microwaved CD - so you don't have to... You can see the current vaporizing the aluminum in the CD as well as the arcs of microwaves, from what I understand the patches of aluminum become antenna-like.
Update: Bill writes:
The fractures first grow via a fascinating effect called "electromigration." Once the aluminum layer has been spontaneously sliced into separate sections, high voltage appears across the fractures, and arcs start leaping across.Try this: put one or more glasses of water in the microwave. It slows down the whole "zapping" process.
The arcing is not quite a "radio antenna" effect. An empty microwave oven contains an extreme e-field because of resonant rise. Any two conductive objects will be at two different voltages with respect to ground. The voltages can be pretty high (many kilovolts.) If two sharp-edged conductors such as the foil segments in a CD are very close together, the high voltage between them will cause arcing. It's purely a voltage effect rather than the electric/magnetic effect present in a radio antenna. (An unloaded microwave oven is very much like a Tesla coil.)
But the aluminum layer gets sliced up before all this high-volt stuff happens. Why? It's because there are large currents induced in the aluminum foil by the radio waves. The current isn't nearly enough to hurt the foil. But if tiny defects exist in the foil, such as microscopic regions of insulator, these defects cause the "lines of current" to become compressed near the defect. It's sort of like a lightning bolt, but rather than lines of e-field being attracted to the sharp tip of a plasma streamer, instead lines of charge-flow are pushed away by the sharp tip of a growing fracture in the aluminum. The lines are squeezed and the current density increases. If the tip of a fracture was infinitely sharp, the current density in the metal in front of the fracture would be infinitely high. A microscopic region of aluminum "goes away," and the fracture gets longer. New fractures grow from the sides of old ones.
It's like "inside out lightning bolts," since the fractures are a network of insulators growing in a conductive environment, and the growth is caused by currents rather than voltage which concentrates at the tips of the growing fractures.
Posted by Phillip Torrone |
May 17, 2008 12:00 AM
Arts, Electronics |
Permalink
| Comments (4)
| Email This |
| Digg this!
Recent Entries
- Best of CRAFT
- Not so lazy Sunday... Weekend Project - Ultimate LED fan sign
- Making Austin Weird: LED Bling
- Brush knuckles
- Found object robot sculptures
- Blob Mentality
- Got 10 hours? Make a paper swan
- Make it or break it
- Maker Faire Austin: Oct. 18th and 19th, 2008, Austin, TX (2 weeks away!)
- Halloween science grossology
Comments
Oldest comments listed first.
| Posted by: bill beaty on May 17, 2008 at 8:57 PM |
The fractures first grow via a fascinating effect called "electromigration." Once the aluminum layer has been spontaneously sliced into separate sections, high voltage appears across the fractures, and arcs start leaping across.
Try this: put one or more glasses of water in the microwave. It slows down the whole "zapping" process.
The arcing is not quite a "radio antenna" effect. An empty microwave oven contains an extreme e-field because of resonant rise. Any two conductive objects will be at two different voltages with respect to ground. The voltages can be pretty high (many kilovolts.) If two sharp-edged conductors such as the foil segments in a CD are very close together, the high voltage between them will cause arcing. It's purely a voltage effect rather than the electric/magnetic effect present in a radio antenna. (An unloaded microwave oven is very much like a Tesla coil.)
But the aluminum layer gets sliced up before all this high-volt stuff happens. Why? It's because there are large currents induced in the aluminum foil by the radio waves. The current isn't nearly enough to hurt the foil. But if tiny defects exist in the foil, such as microscopic regions of insulator, these defects cause the "lines of current" to become compressed near the defect. It's sort of like a lightning bolt, but rather than lines of e-field being attracted to the sharp tip of a plasma streamer, instead lines of charge-flow are pushed away by the sharp tip of a growing fracture in the aluminum. The lines are squeezed and the current density increases. If the tip of a fracture was infinitely sharp, the current density in the metal in front of the fracture would be infinitely high. A microscopic region of aluminum "goes away," and the fracture gets longer. New fractures grow from the sides of old ones.
It's like "inside out lightning bolts," since the fractures are a network of insulators growing in a conductive environment, and the growth is caused by currents rather than voltage which concentrates at the tips of the growing fractures.
| Posted by: Dave on May 23, 2008 at 9:40 AM |
CD in microwave at 600 FPS
http://www.youtube.com/watch?v=JEeeBaGMPl4
Leave a comment
Subscribe to MAKE Magazine!
Subscribe today, save 42% and get web access to MAKE free. MAKE Digital Edition is available only to subscribers.
$34.95 / 1 year
(4 Quarterly Issues)
Features and more @ MAKE!
Add MAKE to iGoogle - GoogleGoogle.
Add MAKE to your RSS reader - Real simple.
Add MAKE on Twitter.
Add MAKE on FriendFeed & the MAKE room.
Why advertise on MAKE?
Read what folks are saying about us!
Click here to advertise on MAKE!
Phillip Torrone
Senior Editor
Tel: 707-827-7311
Gareth Branwyn
Robot Maker
Kip Kay
Video Maker
Jonah Brucker-Cohen
Artist / Researcher
Natalie Zee Drieu
Senior Editor
CRAFT
Becky Stern
Culture jammer
Collin Cunningham
Sound Maker
Marc de Vinck
CNC Maker
Current Podcast
Weekend Project: Ultimate LED Fan Sign
Here is the ultimate sports fan item, a portable Flashing LED Sign.To download Ultimate Fan Sign MP4 click here or subscribe in iTunes....
More...
