Separation Of Small Solid Particles Based On Ultrasonic Rotary Driving

Separation of micro particles has potential applications in bioengineering, chemistry,micro-electromechanical system, and other areas. Conventional methods of micro particles separationinclude filtration, dielectrophoresis, magnetic separation, optical tweezers and ultrasonic separation,etc. filtration is likely to block membrane and has relatively high expenses, dielectrophoresis andmagnetic separation require charged particles and magnetic particles respectively, and opticaltweezers can only deal with single particle. All the above limits can be avoided in ultrasonicseparation.This article is based on the previous research of professor Hu. Theultrasonic actuator with analuminum plate can separate mixed micro particles. The aluminum plate is mechanically driven bysandwich-shaped ultrasonic transducer operating in the thickness mode vibration. Two piezoelectricrings are pressed against each other between two square aluminum plates by a bolt structure. To excitethe thickness mode vibration in the transducer, the two piezoelectric rings are aligned with oppositepoling directions and driven by an AC voltage near the thickness resonance. In the experiment, wemeasured the vibration mode of the working areas of the aluminum plate by Laser DopplerVibrometer. The separation of mixed micro particles which include shrimp eggs, glass balls and saltparticles was observed under the high speed camera of Keyence VHX-1000E.From the measurement of vibration mode of the working areas, a traveling wave is existed on thepart of the aluminum plate. It well explains the rotation movement of the particles on thesubstrate.Thehighest separation efficiency is appeared at resonant frequency, for the mixture of saltand shrimp eggs, a large proportion of salt could be sweep away. Similar results were obtained for themixture of glass balls and shrimp eggs. Mostly glass balls could be separated from shrimp eggs.Different results were observed for the salt and glass balls, all of the particles would get out in thesame condition.Themain innovation point is the novel transducer which without mechanical rotation axis. It canseparate small particles quickly in air.