Measuring charge loss in acoustically-levitated, airborne materials

Electrically charged particles suspended in gas exist in numerous planetary environments. Salient examples include volcanic plumes, airborne Saharian sand, dust devils on Mars, and the dune fields of Titan. Yet the microphysical processes that lead to electrification are not understood, such as the lifetime of charge on electrified particles or the processes that lead to their electrostatic neutrality. Our laboratory measurements aim to answer these questions through acoustic levitation to ensure that charge is not lost through physical contact. Two hemispherical transducers produce an acoustic standing wave that lofts particles of millimetric scale. An ionizer then charges these particles, and the remaining charge is measured over days or weeks by moving the particle through a Faraday cup. Previous measurements were limited to low-density, porous particles. Now, we have constructed an acoustic levitation device capable of suspending dense materials such as copper. Additionally, in environments of varying humidity and pressure, we investigate the mechanisms leading to airborne particle charge loss, and it’s relation to the material hydrophobicity.