Electric sparks are used for welding, powering electronics, killing germs or for igniting the fuel in some car engines. Despite their usefulness, they are hard to control in open space, they split into chaotic branches that tend to go towards the closest metallic objects.

A recent study uncovers a way of transporting electricity through air by ultrasonic waves. The level of control of the electric sparks allows to guide the spark around obstacles, or to make it hit specific spots, even into non-conductive materials.

"We observed this phenomenon more than one year ago, then it took us months to control it, and even longer to find an explanation," says Dr. Asier Marzo from the Public University of Navarre, lead researcher of the work.

This guidance occurs because the sparks heat up the air, which expands and lowers its density. The hot air is then guided by ultrasonic waves into regions where the sound intensity is higher and the next sparks then follow these regions of lighter air because of its lower breakdown voltage.

"Precise control of sparks allows their utilization in a wide variety of applications, such as atmospheric sciences, biological procedures and selective powering of circuits," comments Prof. Ari Salmi from the University of Helsinki.

Previously, sparks could only be guided with laser induced discharges colloquially called Electrolasers which required the use of dangerous lasers, as well as precise timing between the laser and the electric discharge. The developed method uses ultrasound rather than lasers, and it is safe to the eyes and skin. The equipment is compact, affordable and can be operated continuously.

"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," says Josu Irisarri, first author of the publication from the Public University of Navarre.

The study was carried out in collaboration between researchers from the Public University of Navarre (UPNA), the University of Helsinki and the University of Waterloo and it has been published in the esteemed Science Advances journal.