This is a project I've been working on for about 6 months now next to my regular studies. It is a levitating light bulb. This project came to life when i saw Jeff Lieberman's implementation of it a few months before starting. I was fascinated and started research on building my own, reading many academic papers and spending long nights reading up on pretty much every project which included wireless power transfer or magnetic leviation. What I found is that there are many many existing projects of both, but only a few have combined both these technologies. Once you have both working it's really just a matter of overlaying them. The high frequency magnetic field generated from the wireless power transfer circuit does not effect the leviation aspect of the build.
Of course I had many failed attempts and have a small box full of wasted components and boards I've soldered. Stable leviation is not easy. Instead of boring you with the failed attempts, instead I'll tell you what worked. For the levitation system I ended up slightly modifying an existing circuit built by Eric Taylor. My configuration is slightly different and am using a 3 pin linear hall effect sensor from RS components to act as the feedback mechanism. I opted for a 1.325mV/g sensor (the smallest sesnsitivity i could find), as the magnetic flux it was sensing was maxing out the reading on others. If you are looking to build one, this circuit is simple and works with only slight modification depending on the input sensor you have. The drive coil I'm using is 300 metres (1kg) of 20awg wire. It draws about 0.2 - 0.25A when stable at 12V. It doesn't seem to heat up over time, unless the light is not levitating, in which maximum (0.8A) current is driven through the coil.
Efficient wireless power transfer was the more painful part of this project. I started off with 555 oscillators used by a few people, but the power transfer is not strong enough and the waveform was horrendous. For my final design I must give credit to an old but very simply design by Marko. I have modified his circuit slightly to better limit the heat generated by this circuit. It runs at pretty much exactly 1Mhz pulling 0.5A at 12V. Although this consumes around 6 watts, after running it for a half an hour, the small heatsinks are merely warm. After having built an oscillator, the next part was to build the wireless power receive circuit, which is a simple LC circuit tuned at exactly 1Mhz. After spending a few nights with my scope and components, i managed to tune it fairly well. It is actually amazing how small changes in the geomertry of the coil (changing the inductance and resonant frequency) effect the coupling of the resonant coils so largely. It is therefore fairly time consuming but rewarding to tune this part accurately.
I have already begun building a new levitator, which is designed to have greater strength and a better control system. It is using a 3.5kg copper drive coil (@24v) wound on a better core. Did i mention the one in this video is using a regular bolt from the hardware store? The control system I am building from scratch, which I am hoping to incorporate some fancy features such as computer controlled height control and light dimming, through the use of a microntroller. Again, as i did with this one, it is designed for 24/7 operation with only a small cooling fan.