In principle, wireless power transmission is easy to do and it involves beamed microwave electromagnetic radiation to a device that converts this to electricty.
Nasa demonstrated a large scale version of this in 1975:
However, this is inherently unhealthy if actually deployed in the real world. Indeed, had a human stepped into the microwave beam in this test, they would have been essentially melted.
However, on a much smaller, scale, a recent development in magnetically coupled resonance transmission, dubbed WiTricity, shows promise.
This works as follows:
Two resonant objects of the same resonant frequency tend to exchange energy efficientl.
A child on a swing is a good example of this. A swing is a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy.
Another example involves acoustic resonances: Imagine a room with 100 identical wine glasses, each filled with wine up to a different level, so they all have different resonant frequencies. If an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses.
In any system of coupled resonators there often exists a so-called "strongly coupled" regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient.
For magnetically coupled resonators a system of two electromagnetic resonators coupled mostly through their magnetic fields and this coupling is preserved even when the distance between them was several times larger than the sizes of the resonant objects. This way, efficient power transfer was enabled.
In principle, for low wattage applications, one could imagine a situation like this:
This is essentially transferring "electricity" via magnetic induction using this concept of resonance to increase efficiency.
This idea has been physically plausible/possible for some time now. But only recently is there strong demand for charging several handheld devices per household.
However, this kind of wireless power transmission scheme may have a real, eventual application, in the form of E-paper:
