Ultrasonic collection of small particles by a tapered metal strip

A pi-shaped ultrasonic actuator can collect small particles by its two sharp edges. However, the collection of particles is weak in air and not very stable in water. In this paper, a refinement to the pi-shaped ultrasonic actuator is made for a more efficient collection of small particles in air and water. In the refined structure, an ultrasonic actuator with a metal strip is used to collect small particles. The metal strip is mechanically driven by one corner of a rectangular, sandwich-shaped ultrasonic transducer operating in the thickness mode vibration. The metal strip is tapered along its length and has a strong vibration at its tip. Small particles in air and water can be attracted to the radiation surface near the end of the metal strip. The dependence of the number of collected particles on driving frequency and voltage is investigated for shrimp eggs, mint seeds, and grass seeds. For a given driving voltage and particle type, the number of collected particles reaches a maximum value at some driving frequency. Increasing driving voltage increases this maximum number to some extent; but too large a driving voltage decreases it. The maximum number also depends on the weight per particle. It increases as the weight per particle decreases for the particles with close densities. Furthermore, the relationship between the number of collected particles and vibration amplitude at the end of the metal strip is investigated for shrimp eggs, mint seeds, and grass seeds. The number is approximately linearly proportional to the vibration amplitude when the vibration amplitude is not too large. In addition to the application in which the length of the metal strip is parallel to gravitation, the actuator also can be used with its length perpendicular to gravitation. However, the latter has a weaker capability of collecting small particles. It is also found that the actuator has a stronger capability to collect particles in water than in air.