An ultrasound trap experiment has made it possible to study with precision how electric charge is transferred when two surfaces collide, a phenomenon known as triboelectric charging. The results show that the charge accumulated in each collision follows a predictable pattern, contrary to the idea that this process is essentially random and impossible to control.

Triboelectric charging — the charge generated by rubbing or separating materials — is an everyday phenomenon, yet it remains poorly understood at a fundamental level. Predicting how much charge is transferred in a given contact has historically been an open problem, limiting applications ranging from triboelectric generators to dust management in industrial processes and in space.

The team used an acoustic trap based on ultrasound to trap and make particles collide in a controlled way, measuring the resulting charge collision by collision. This setup allows the impact conditions to be varied systematically and the transferred charge to be recorded, something difficult to achieve with conventional contact methods.

The authors note that understanding and predicting contact electrification could improve the design of devices that harness or avoid static charge build-up. The work also opens the door to more accurate models of the behaviour of charged grains and dust, from industrial processes to the dynamics of the surfaces of airless asteroids and moons.