Implementation and Analysis of Noncontact Acoustic Tweezers Using Quasi-Standing Waves

Noncontact tweezers using acoustic levitation technology are useful for microhandling processes as they have fewer restrictions with materials or particle shapes. This has significant value in the development of composite materials and biotech industries where the contamination is an issue, such as the production of advanced microbiochips for health diagnostics. This involves the mixing of multiple components in a stable suspension of drops without a container. In this paper, a quasi-standing wave field generated by crossing two ultrasonic waves from piezoelectric transducers is adopted to develop acoustic tweezers. Compared with general single-axis acoustic levitation, the proposed acoustic tweezers can levitate small particles at pressure nodes without the need for a reflector and has the capability of 2-D movement. Additionally, a theoretical model of the proposed acoustic tweezers is derived such that the pressure distribution of the tweezers can be calculated from the operating conditions to determine the trapped position. With a 10^° inclination and frequency of 27.6 kHz, a 400 Pa levitated pressure can be generated to float polystyrene spheres with a density of 16.37 kg/m³, and a 2 mm × 3 mm movement of the trapped position is demonstrated by adjusting the relative orientation and the relative distance of the two transducers, respectively. The simulation and experimental results demonstrate the effectiveness of the proposed acoustic tweezers´ model to predict particle trapping.