Crystals glued to the outside and inside of a metal wall act as an invisible channel. One, receiving current, starts to tremble, and these vibrations, like ripples on water, spread out in all directions through the metal. The inner crystal catches this tremor and generates electricity again.
They studied two types of tremor: compression (like a point impact on water) and inflation (like a push on an inflated ball). Which is better depends on the dimensions. For a quick assessment, scientists suggested looking at ripples at different frequencies — much like pebbles of different sizes create different circles on a pond. This instantly shows whether the pair is suitable for high-power charging.
Surprisingly, hundreds of watts can be sent through such "vibrational ripples" — enough for serious equipment. This solves the problem of power supply in sealed containers, from chemical reactors to satellites. And although gravitational waves are also all-pervasive, our method is simple and tangible, like the circles from a fallen apple.
The simplest piezoelectric material is sugar: if you crush a sugar cube in the dark, you can see faint sparks.