Non-contact acoustic trapping in circular cross-section glass capillaries: a numerical study

Ultrasonic particle manipulation has many applications in microfluidic systems. Such manipulation is achievable by establishing an ultrasonic standing wave in fluid filled micromachined chambers. In this work, the focus is on analyzing the trapping potential of water filled capillary tubes actuated ultrasonically. The curved walls necessitate the use of a finite element modeling approach. Multiple arrangements of the piezoelectric transducers were studied along with the effects of changing the capillary and piezoelectric transducer thicknesses. Additionally, different modes of driving the piezoelectric transducers were investigated. It was found that positioning four piezoelectric transducers equally spaced around the capillary tube provided the best force potential field for trapping polystyrene spheres in the center of the capillary.