With the number of inquiries we are getting about wireless power technologies, we though it would be helpful to explain some of the principals involved. Much of the early work was done by Nikola Tesla somewhat after 1890. While he contributed a great deal to the handling of AC power, and did some limited experiments with Near Field wireless power, his concepts on world wide distribution of wireless power were flawed, and ultimately he lost the investment backing. There is a great deal of myth surrounding what Tesla was doing, and some people think his theories were suppressed due to commercial interests. The reality is that he didn’t fully understand the physics, resulting in a rather large error in trying to build his “Tower of Power” to distribute power over a large area.
The oldest form of these wireless power systems are referred to as Near Field. The coupling for the power transfer is either inductive or capacities.
Inductive coupling has been seen in things like Power Mat, and a system used by Starbucks a little while back. The two coils transfer energy magnetically when they are in close proximity. In practice this means the mobile device is usually laying on the transmitting coil. The current drawn by the transmitting coil will vary depending on what is placed in it’s field.
The Tesla coil generated high voltages which allowed for capacitive coupling of power. This really has not been used in commercial systems due to a tendency to generate electrical arcs that would be destructive to most modern electronics.
This can get longer distances that the Near Field effects, but is still not without it’s drawbacks. Energy loss being one of them. Inefficiencies in focusing the Radio Frequency energy results in energy sent other places in the room. Diffraction of the signal path also disperses the energy. Using higher frequencies, such as microwave can help in directing it, but if the focus is tight enough then some kind of tracking is necessary. Energy will also either be absorbed or reflected by other objects it may hit. Battery trickle charging systems have been demonstrated since 2015, and this has fueled the idea that everything could be wireless. While it is possible to feed higher amounts of power, there is the problem that other things and people in the room will also absorb the power. This is not a huge deal for battery chargers, but it would be for devices such as microwave ovens and washing machines. The RF would be at dangerous levels in order to accomplish that.
This is the new thing, but not as new as people believe. This is still based on the physics of the other wireless power system, both good and bad points. The closest relative is the RF far field system. One thing that can’t be forgotten is that energy is neither created nor destroyed. This is the first law of thermodynamics. So these devices are not able to gather more energy than was delivered to them. There is some indication that they may be aiming the RF field towards the device being charged, but that is unverified, and it is unlikely to be very tight, so there will be power loss as well as RF exposure to humans. One of the things it looks like they have created is a smaller antenna.
In all of the wireless power systems, they will work more efficiently if they are tuned to the frequency of the power. Again, something that Tesla noted, and was working on. In the case of antennas, the wave length is important.
One of the properties that has been demonstrated on NanoCrystals, is that the wave propagation speed is slower. This will shorten the wavelength, and thus allow for a smaller, reasonable efficient antenna. This allows for a package size reduction, but still does not mean it can intercept energy that was directed somewhere else in the room. The smaller size means that less of the energy will intersect the antenna, and thus not be collected.
While this technology may be interesting as a battery charger, it is really only going to be a trickle charge, taking hours to complete. The concept of delivering high amounts of power over long distances to portable devices is not practical. There is a theory about microwave power transmission, but for safety it has to be spread over a wide area, and collected the same so that the power concentration is not too high in any one area. It is interesting that in the excitement of having a wireless battery charger, that the concern over the RF exposure has been forgotten in favor of a device radiating far more power than the cell phone itself.