Abstract
The acoustic radiation force can drive small dispersed particles into a pre-defined pattern. This process has promising applications in advanced manufacturing, but how quickly the pattern can be formed depends on the absolute magnitude of the acoustic radiation force, which is challenging to measure. Additionally, the acoustic radiation force may change as the pattern forms, further complicating the process. This work presents two experimental methods to measure the absolute magnitude of the acoustic radiation force on polystyrene microspheres in a water-glycerol mixture, which allows us to study the impact of the formed pattern on the acoustic radiation force. The first method uses particle tracking to create a 2D map of the acoustic radiation force during the pattern formation process, while particles are dispersed. The second method rotates the device so that the acoustic radiation force can be measured through balance with gravity after the particle pattern has formed. By comparing the acoustic radiation force before and after the pattern formation, we can determine the impact of the particle agglomerations on the acoustic radiation force. We apply these two measurement methods to a multi-wavelength planar standing wave device. Our results show that agglomerating the dilute, dispersed polystyrene microspheres into dense bands does not significantly alter the acoustic radiation force on the microspheres. Additionally, the 2D force map showed spatial variations in the acoustic radiation force that were not visually apparent in the final pattern but may have implications for the quality of parts made using acoustic radiation force.
