Own an electric toothbrush? Then youalready have wireless electricity athome. Toothbrush chargers useinductive coupling to provide power withoutelectrical contacts. When current from themains runs through a coil of wire in the chargerunit, it produces a fluctuating magnetic fieldwhich induces a current in a second coil embedded inside the toothbrush. Thisprinciple also underlies charging mats whichpower up phones and cameras at close range.
The catch, however, is that inductive coupling is only effective over a very short range - indeed, stray by just a few millimeters and the magnetic field tails off rapidly. One solution is to throw resonance into the mix. Resonance is the phenomenon which enables an opera singer to shatter a wineglass with their voice alone. For this to happen, the frequency of the singer's voice has to match the glass's innate resonant frequency - the rate at which the glass naturally vibrates.
To apply this idea to wireless electricity, scientists fine-tune two coils to resonate to the same frequency of magnetic field. This makes transmission across a few metres possible as the second coil amplifies the energy of the first. The low-frequency magnetic fields used don't interact with people or pets, making this tech safe to use in a domestic environment.
If you want to beam power over much greater distances though, converting energy into electromagnetic radiation (for example, light or microwaves) is the way to go. Laser-transmitted power has already been used to power unmanned aircraft. First, electricity is converted into a high-powered infrared laser beam; a photovoltaic cell at the other end then turns this back into electrical current. Microwave-transmitted power follows much the same idea, converting energy into microwaves then back into current with the aid of a rectifying antenna, or rectenna. Although this is more efficient than laser beams it does require much bulkier equipment.
B) How bursting bubbles turn sound into light?
Sonoluminescence occurs when a tiny bubble focuses energy from sound waves and releases it as light. Producing this effect is surprisingly straightforward: just pour some water into a flask, press some speakers up close and turn the volume up. The changes in pressure as intense sound waves pump through the water are violent enough to break it up, leaving minuscule bubbles of water vapour and gas. Continuing to fire sound waves at one of these bubbles causes it to expand to ten times its original size before suddenly being crushed. The abrupt collapse focuses the sound energy, compressing the gas inside the bubble. This produces temperatures hotter than the Sun's surface, culminating in an incredibly short flash of blue and ultraviolet light. Physicists first observed sonoluminescence quite by accident in the 1930s, but it wasn't until 1989 that they were able to study the phenomenon more closely by immobilising a single bubble in water. Even today, it's very difficult to measure what is going on inside the bubbles, meaning that, as yet, not everyone agrees on where the light comes from. One suggestion is that the high temperature causes noble gases like argon and xenon to incandesce, turning heat into light like red-hot coals. Another idea is that the water molecules themselves are being torn apart and giving off energy as they recombine. Or gas inside the bubble may become a glowing plasma as the extreme heat pulls its atoms apart. While they are fascinating in their own right, some have suggested sonoluminescent bursts of light could also be used for medical imaging, or to trigger certain chemical reactions very precisely. There are a number of scientists who even believe we could harness the intense energy from sonoluminescence to kick-start nuclear fusion reactions.
(from "How it Works?")