Electricity is chaotic, and we normally need to constrain it to wires and circuits to make use of it. Scientists in Europe and Canada have now managed to guide sparks through thin air and even around obstacles using ultrasound waves.
In open air, electricity tends to branch out in seemingly random directions – just picture a lightning bolt. These paths are guided by subtle differences in air density and charge, and attraction to metal objects. Accounting for all those factors makes it hard to precisely control.
In a new study, scientists at the University of Helsinki, Public University of Navarre and the University of Waterloo have demonstrated a way to guide electric sparks through the air. The method allows sparks to be directed so precisely that they can bend around obstacles, and hit specific spots on a material even if it isn’t conductive.
“We observed this phenomenon more than one year ago, then it took us months to control it, and even longer to find an explanation,” said Asier Marzo, lead researcher on the study.
The trick is to use ultrasound. Sound waves of these frequencies create air pressure that can be strong enough to levitate light objects. In this case, they aren’t directly pushing the electricity itself but shaping its path.
When a spark ignites, it heats up the air around it. This warmer air expands, which reduces its density. Since electricity prefers to travel through lower density air, the spark moves in that direction. The ultrasound pulses move this hotter, lower-density air around, which in turn guides the electricity with surprising precision.
The team tested the technique using two 360-degree rings of ultrasound emitters surrounding the point where a spark is generated through a Tesla coil. When the ultrasound is switched on, the plasma spark transforms from a tree-like shape of random branches into a single line. This line can then be aimed in different directions by either physically tilting the ring of emitters, or adjusting the strength of different emitters within the ring.
The researchers were able to steer the plasma to hit specific electrodes and avoid others, which could make for controlled switching in wireless circuits. It could also allow it to strike materials that electricity normally wouldn’t “choose” to. Other applications the team suggests include etching patterns into colonies of bacteria, and even devices that generate haptic feedback by delivering low-power plasma bolts to the skin.
“I am excited about the possibility of using very faint sparks for creating controlled tactile stimuli in the hand, perhaps creating the first contactless Braille system,” said Josu Irisarri, first author of the study.
The research was published in the journal Science Advances. Check out the ultrasound-guided electricity in action in the video below.
Source: University of Helsinki
