Forces and torques on rods in an ultrasonic standing wave

In this paper we observe and simulate the effect of ultrasonic standing waves on elongated objects, including interactions between multiple objects. Alignment of 25-40 micrometer long and 10 micrometer diameter glass rods has been observed in water when standing waves were excited by a PZT actuator at 2.1 MHz. COMSOL has been used to simulate the acoustic fields for one or more rods in water. The stress tensor was determined from the acoustic field, and then the force and torque on the rods was calculated using well-established expressions. The results give insight into the formation of aggregations of objects.