Contact charging with levitated particles: toward fast and spatially sensitive charge detection using acoustic levitation

When two insulating materials are brought into contact, an exchange of charge can occur. To study this phenomenon, we use acoustic levitation to levitate a spherical particle over a plate. Contacts are done by briefly switching off the acoustic field and letting the sphere bounce on the plate once. The particle’s charge is then obtained by tracking the sphere with a camera as it reacts to an external electric field. While this setup has proven to work very well, it does come with some significant limitations. These include the fact that the camera tracking is very data-heavy, rendering the observation of a large number of bounces to reach saturation charge unrealistic. Additionally, we monitor neither the charge distribution nor the transfer process itself.

To overcome these limitations, an event vision system (EVS) is replacing the optical camera. EVS cameras record only changes in intensity, making them ideal for efficient position tracking. This will allow us to significantly speed up the analysis process and eventually observe the charge saturation process.

To obtain information about the charge distribution on the surface of the sphere, a capacitive system with a fast (>1MHz) amplifier is used. This lets us resolve the charge exchange on a timescale of microseconds as well as measure signs of e.g. dipole moments on the sphere.