Anyone seen the Prestige? For the few of you that say yes, you might recall Hugh Jackman’s meeting with Tesla in a ghostly looking town where they planted lighbulbs on the ground and shared electricity for free. Believe it or not, totally true.
Many of you have probably watched as a kid the popular experiment where someone holds a lightbulb in the hand and steps close to a sparkling Tesla coil to have it instantly alight, no wires attached. The first person to play that trick was, obviously, Nicola Tesla himself.
Tesla’s ultimate goal to this respect was free distribution of electric energy on the air. Just imagine that your mobile phone goes dry of juice and you just need to hold it on thin air to load it back. Cool, right? Of course, this free-for-all way of thinking did not sit well when he moved from Croatia to US, so we still need to plug our equipment and pay accordingly to our electricity provider. However, he has fairly successful in proving it was possible.
The key idea to energy wireless transmission was electrical resonance, which is nicely explained here. The basics are fairly simple: if you put together an inductor and a capacitor (LC circuit), the magnetic field in the inductor generates electric currents that charge the capacitor, whereas the discharge of the capacitor produces electric currents that generate a magnetic field in the inductor and … you get the drill. This works like your conventional pendulus: in absence of other forces, it could go on forever (in practice, though, what we get is actually LRC circuits, where the R(esistor) stands for the unavoidable electrical losses in the circuit). Resonance happens when capacitors and inductors get along optimally, i.e. their transfer function is close to 1, meaning they give their maximum to each other. This is similar to pushing a kid in a swing: if you push in the right moment, speed and height increase significantly (and the kid will complain way less).
A Tesla coil is a circuit like the one below. The left part of the circuit, including the high voltage transformer, is simply meant to charge the high voltage capacitor on the right until the voltage on both sides of the spark gap is enough to ionize air -turning it into a neat conductor- and close the right circuit, that charges the secondary coil and produces the expected current (resonator 1). At the same time, the Torus on top of the secondary coil behaves like a capacitor with respect to the ground and, hence, becomes resonator 2 with the coil as well. Now that we have two resonators at the same frequency, and resonator 1 gives the required push to resonator 2 in the right time, like in the swing example, increasing its juice until breakout happens. The process is fully explained here in detail and it is obviously the basis for the Tesla Guns in Warehouse 13.
Electrical resonance for wireless power transmission works pretty well, but only in close distances, because transmission of power through air obviously results in a significant loss of energy. In order to solve losses in the air, Tesla decided to send energy through the ground instead. This was a long shot because we all know that, in fact, the ground is were currents go to die and all, but he figured out that if he charged the ground enough (which is quite a lot), it would magically become a conductor. A conductor connected with virtually everything, too. At this point, since they wouldn’t let him test his stuff on New York City (with some criteria, in fact), Tesla moved to Colorado Spring, where the local power company even provided juice for him at no cost. At least, until he burnt down the installations, that is. He built there a Frankenstein-like lab, toppled with a 180-foot metal tower, his “magnifying transformer”. And here is where he planted light bulbs on the ground within 100 feet of the tower and lit them wirelessly.
However, Tesla wanted to go world wide, so he decided to pump 10.000.000 volts into the earth surface to see if he could make them reach the other side of the planet and come back. To prevent losses, he sent power as a series of pulses reinforcing each other, like waves in the sea. Plus bounced back energy added to the peaks too! All in all, the experiment resulted in an amazing 130 feet long arc of lightning, along with thunders and all, plus the destruction of Colorado Springs power generator.
Needless to say, that marked the end of Tesla’s experiments with wireless power transmission. With the american grid, at least. However, Power Cast has recently announced its line of products to wirelessly load low power electronic devices (MICROWATTS to LOW MILLIWATTS). Without the arc of lightning, we expect 🙂