Nearfield forces generated using tunable liquid lenses

In previous work, we introduced 4- and 6-channel liquid-tunable acoustic lenses, demonstrating their ability to generate ultrasonic beams exhibiting limited diffraction with adjustable focal zones and depths of field. The target phasing was based on that of the fraxicon, a quasi-planar stepped lens, and the beams formed by the liquid lenses had comparable structures. This current study investigates the forces generated in the near field of beams formed using these tunable lenses. The forces are calculated using the Gor’kov potential applied to measured ultrasonic pressure fields. We compare results with those produced by fraxicon, which has demonstrated the capacity to facilitate the extraction, trapping and manipulation of droplets. A variety of phase profiles for the liquid lenses are used to investigate the presence of field structures similar to the trapping zones generated with the fraxicon. The tunable liquid lens has the potential to be adapted to a variety of targets and systems, providing flexibility not afforded by fixed-phase quasi-planar lenses.