electromagnetic

15 Articles

Scavenging Ambient Electromagnetic Energy

July 11, 2011 by 65 Comments

energy_harvesting_from_radio_waves

At this very moment, unseen radio waves are bouncing off almost everything that surrounds you. Emitted by everything from radio and TV stations to cell phone networks and satellites, these waves are full of unharnessed energy. That is, until now. Researchers at the Georgia Tech School of Electrical and Computer Engineering have been working diligently to harness this unused energy, and recently unveiled their new antenna technology at the IEEE Antennas and Propagation Symposium.

The team, led by professor [Manos Tentzeris] has been working to develop ultra-wideband antennas to tap into the energy all around us. Using printers filled with a specially-formulated ink compound, they have been able to print these antennas on paper and polymer substrates. The antennas can harness energy stored in radio frequencies ranging from 100 MHz all the way up to 60 GHz, depending on the printing medium.

The team can currently power temperature sensors using television signals, and is preparing a demo in which they will power a microcontroller simply by holding it up in the air. The technology is still in its infancy, but the list of applications is almost endless. We doubt you’ll be powering your TV with this technology any time soon, but it definitely holds promise for things such as wireless sensor mesh networks and the like.

[Thanks, morganism]

Building An Electromagnetic Pendulum Clock

June 6, 2011 by 9 Comments

electromagnetic_pendulum_clock

[Stephen Hobley] has been experimenting with an electromagnetic pendulum in order to build himself a clock. Through the course of his experiments, he has learned quite a bit about how pendulums function as well as the best way to keep one moving without the need for chains and weights, which are typically associated with these sorts of clocks.

His first experiments involved driving a simple pendulum with a pulse motor. He discovered that the easiest way to keep the pendulum moving was to use a coil to detect when the it reached the equilibrium point, pushing it along by sending a small pulse to that same coil. He noticed that he could keep the pendulum moving at a pretty good tick if he triggered the magnetic coil every third pass, so he implemented an Arduino to keep count of passes and apply the appropriate force when needed.

He has been making pretty decent headway since his first experiments and now has nearly all of the clock works assembled. Crafted out of wood, he uses a 15-tooth primary drive ratchet, which powers two 60-tooth gears responsible for keeping track of seconds, as well as a pair of larger gears that track the minutes and hours.

It’s looking good so far, we can’t wait to see it when finished.

Stick around to see a quick video demonstration of the clock with all of its gearing in action.

Continue reading “Building An Electromagnetic Pendulum Clock” →

Build Your Own Magnetic Levitator

August 31, 2010 by 34 Comments

Here’s a great magnetic levitator build. [Scott Harden] dug up the link after seeing that awesome rotating globe this morning. This version hangs objects below an electromagnet but it has a sensor system to provide a constant distance between magnet and object even if the payloads are a different weight. This is done with a couple of infrared sensors. One acts as a reference detector, always viewing an IR LED in order to get a baseline measurement. That measurement is compared to a second detector mounted slightly lower. The circuit adjusts the electromagnetic field, making sure the object is always breaking the lower beam but never interrupting the reference beam. No microcontroller needed, this is handled with a couple of OpAmps. See it in action after the break.

Continue reading “Build Your Own Magnetic Levitator” →

Terminate RFID Tags

December 22, 2009 by 49 Comments

This gun hunts only RFID tags.[mnt], who brought us laser gesture control, built this RFID Zapper but included so much more. Any good weapon has to sound mean, a feat he’s accomplished by incorporating an MP3 player into the rifle. The coil that zaps the RFID tag is powered by a photo-flash unit, but for visual feedback he’s got a second unit that flashes light to signal the demise of your German passport (see the video after the break).

It’s hard to believe we haven’t covered RFID Zappers yet. The concept came out of the Chaos Communication Congress a few years back. This method works by sending a very strong electromagnetic field through the RFID tag that causes it to burn out. There’s a wiki post on RFID Zappers but Firefox threw a certificate warning when we loaded it up; read at your own risk.

Continue reading “Terminate RFID Tags” →

Table For Electronic Dreams

May 29, 2009 by 7 Comments

table

The table for electronic dreams is an interactive table that is sensitive to electric activity.  Though it looks similar to the table built by EMSL, this one lights up based on electromagnetic fields. You can get the schematics and such from the instructable, but there is also a video located at the bottom of the project’s home page. It would be really cool if the effect could be localized more.

TEMPEST: A Signal Problem

January 25, 2009 by 12 Comments

TEMPEST is the covername used by the NSA and other agencies to talk about emissions from computing machinery that can divulge what the equipment is processing. We’ve covered a few projects in the past that specifically intercept EM radiation. TEMPEST for Eliza can transmit via AM using a CRT monitor, and just last Fall a group showed how to monitor USB keyboards remotely. Through the Freedom of Information Act, an interesting article from 1972 has been released. TEMPEST: A Signal Problem (PDF link dead, try Internet Archive version) covers the early history of how this phenomenon was discovered. Uncovered by Bell Labs in WWII, it affected a piece of encryption gear they were supplying to the military. The plaintext could be read over that air and also by monitoring spikes on the powerlines. Their new, heavily shielded and line filtered version of the device was rejected by the military who simply told commanders to monitor a 100 feet around their post to prevent eavesdropping. It’s an interesting read and also covers acoustic monitoring. This is just the US history of TEMPEST though, but from the anecdotes it sounds like their enemies were not just keeping pace but were also better informed.

[via Schneier]

24kJ Capacitor Bank

September 20, 2008 by 42 Comments

The Leyden jar capacitor posted the other day fails to compare to what [FastMHz], one of the members over at the 4HV.org forums, has been busy building, a 24kj capacitor discharge bank. This capacitor bank will be configured for 4500v @ 2400uF and can be charged up slowly using microwave oven transformers. It can then release all its stored energy in under a millisecond through a triggered spark gap. This allows for some pretty big sparks as seen in this video, we are not sure about the laughing in the video maybe the power has gone to his head? Continue reading “24kJ Capacitor Bank” →